Design and Analysis of 

"' Microalgal Open Pond 

Systems for the Purpose of 

Producing Fuels 

A Subcontract Report 

J. C. Welssmen 

R1 P. Goebel 

Microbial Products, tnc. 

Fairfield, California 
SERI/STR-231-2840 

UC Category: 61c 

DIE87001 164 

*Design and Analysis of 

Microalgal Open Pond 

Systems for the Purpose of 

Producing Fuels 

A Subcontract Report 

J. C. Weissman 

R. P. Goebel 

Microbial Products, Inc. 

Fa~irfield. California 

April 1987 

Prepared under Subcontract No. XK-3-03153-1 

Solar Energy Research Institute 

A Division of Midwest Research Institute 

161 7 Cole Boulevard 

Golden, Colorado 80401 

Prepared for the 

U.S. Department of Energy 

Contract No. DE-AC02-83CH10093 
NOTICE 

This report was prepared as an account of work sponsored by the United States Government. Neither the 

United States nor the United States Department of Energy, nor any of their employees, nor any of their 

contractors, subcontractors, or their employees, makes any warranty, expressed or implied, or assumes any 

legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, 

product or process disclosed, or represents that its use would not infringe privately owned rights. 

Printed in the United States of America 

Available from: 

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5285 Port Royal Roacl 

Springfield, VA 22161 

Price: Microfiche A01 

Printed Copy A1 1 

Codes are used for pricing all publications. The code is determined by the number of pages in the publ~cation. 

lnformation pertaining to the pricing codes can be found in the current issue of the following publications, 

which are generally available in most libraries: Energy Research Abstracts, (ERA): Government Reports 

Announcements and Index (GRA and I); Scient!fic and Technical Abstract Reports (STAR): and publ~catlon. 

NTIS-PR-360 available from NTlS at the above address. 
PREFACE 

The Solar Fuels Research Division of the Solar Energy Research Institute 

manages a program of research and development on the production of 

microalgae and their conversion to liquid fuels (e.g., gasoline and diesel) for 

the U.S. Department of Energy, Biofuels and Municipal Waste Technology 

Division. As part of the effort, three subcontracts were awarded in 1983 to 

design and provide cost estimates for the construction of a microalgae 

facility on a scale suitable for commercialization. 

This report is the final report submitted by Microbial Products, Inc. for the 

project entitled "Design and Analysis of Microalgal Pond Systems for the 

Purpose of Producing Fuels." This work was supported through SERI subcontract No. XK-3-03 153-1 as part of the Aquatic Species Program. 

Aquatic Species Program Coordinator 

Approved for 

SOLAR ENERGY RESEARCH INSTITUTE 

Solar Fuels Research Division 
SUMHflRY AND CONCLUSIONS 

OBJECTIVES 

The purpose of this report is to present a detailed analvrrs and desiqn of a 

two acre experimental mrcroalgal production facility that can be used to test 

the technical and economic potential of a commercial size facilitv (1000 

acres). The design is based on extensive assessment of biological and 

technical requirements and important considerations such as resource use and 

availabilitv and the rmpact of design assumptions on final product cost. 

Design feasibilitv and cost estimates are based on actual data obtained from 

standard cost estimatrnq procedures, consultant input, and vendor quotes. 

The proposed facility can be used to test the following important assumptions 

and concerns about microalaal biomass production. 

1. Performance of a lowest cost design. 

2. Efficiencv of nutrient utilrzation, particulariv carbon. 

3. Achievement of hiqh lipid productivitv. 

4. Reliability of a cost effective bioaass harvestinq method. 

5. Longterm maintanence of biological and engineering standards 

of performance in a svstem with a high level of internal recycle. 

DESCRIPTION OF THE EXPERIMENT 

The site chosen for the experimental svstem is in Brawlev, in California's 

Imperial Vallev, on a one thousand acre farm which borders the Salton Sea. 

The climate is favorable for microalqal cultivation, with virtually a vear 

round growing season. It is representative of the warmer, drrer regions of the 

4merican Southwest. Ample land is available for both the experimental system 

and for potential scale up. Virtually anv water resource can be simulated by 

varvinq the mixture of the two water resources available: water from the 

Salton Sea, which is as saline as ocean water, and grondwater from an existing 

well which produces 1700 gallons per minute. Flexible lease agreements can be 

neqotiated with the land owners for use of the site and facilities. 

The proposed experimental svstem IS sized to allow validation of the 

commercial srze facility with a minimum of extrapolation. The choice of two 

one acre qrowth ponds is based on an optimization of this validation 

requirement and cost of the experimentation. Three smaller qrowth ponds, of 

50m2 each, are included for testing scaled down subsvstem options. These 

can be constructed and operated at lower cost than the one acre versions, and 

used to determine which options show the most promise and thus should be 

tested at the larger scale. The 50m2 ponds will also be used in qrowth and 

harvesting studies. The harvesting subsystems for the one acre ponds are 

designed to directly emulate the full size subsystems so that translation of 

successful results concerning this important aspect, to the commercial scale, 

is assured. 
The experimental svstem also includes a covered, anaerobic lagoon to be used 

for determining the extent to whlch nutrients can be recovered and recycled 

back to the growth ponds, This is essential to validate the economic 

predictions of the full scale design, 

INNOVATIVE CONCEPTS, DESIGNS, AND TESTS 

The designs and systems presented in this report include many concepts and 

experiments which are innovative. The design and operation of a low cost 

system is innovative in and of itself, The successful achievement of process 

and procuctivity goals in such a svstem would be an important advance In the 

state of microalgal technology and in its prospects +or application. The cost 

effectiveness is realized by minimizing capital costs of the system and 

achieving efficient use of inputs. Extensive engineering analysis of 

carbonation, mixinq, and harvesting subsystems has elucidated both the lowest 

cost, most efficient options and the essential parameters needed to construct, 

test, and evaluate these subsystems, The use of growth ponds sealed with clay 

and lined with crushed rock results in canstructian cost savings of 50% 

relative to ponds lined with synthetic membranes, In addition a low cost but 

efficient design allows improvements in technology, like productivity 

enhancement, to have the fullest iwpact on final product cost reductions. 

In addition to the innovations in construction, the operational efficiency of 

the design is novel in being both higher and more jeasible than that attained 

by any previous system concept of comparable scale. This efficiency is not 

achieved by fanciful optimism, but rather by concerted effort to ascertain 

what can be done and how to do it effectively, The recycle fraction of 

nutrients such as carbon, nitrogen, phosphorus, and water, must be hiqh, 

realizable, and not achieved simply by substituting extreme capital and 

operating cost increases in one area for cost savings in another. The water 

chemistry analysis has led to operational specifications which minimize water 

use and virtually ellainate losses of. carbon dioxida to the atmosphere, The 

carbon dioxide injection system is designed for 957. efficiency, but is still 

low cost. The construction af a large scale, covered anaerobic lagoan, to 

convert and recycle carbon, nitrogen, and phosphorus has not been attempted at 

the scale analyzed here. Yet, this recycle of non-product biomass is 

essential for achievinq economic affordability. 

The low cost bimass harvesting concept presented in this report is a majar 

innovation, adapting the advances in other disciplines far application in 

microalgal systems. The concept is to tailor. high molecular weight poi ymers 

for flocculation and coaqulation of alqal biomass, inducing characteristics 

which. ailon collection of the biomass in sedimentation ponds, . These ponds are 

designed for inexpensive construction and operation, Successful achievement 

of performance goals will represent another major breakthrough in alqal 

production technology. 
Attainment ot the lipid productivity assumed in this report. 30 om/m21d 

average with 50% as lipid, in the system as outlined, would aqain represent a 

major advance. hlqal strains with high lipid accumlatina capability wlll be 

used in the experimental system to test productivity goals. The manaoement 

strateales developed and the environmental conditions existinq in the ponds 

will be evaluated for effect on productivitv. Understanding the inhibition of 

productivit~ by high levels of dissolved oxygen, and developlnq means to 

alleviate it, is a possible route to achieving enhanced productivity. 

CONCLUSIONS OF ECONOMIC ANALYSIS 

The system described, with desiqns for efficient use of inputs included, is 

analyzed in the report in terms of the costs of the alqal biomass produced and 

the unextracted lipid "oils" it contains. At the 1000 acre scale, the 

production cost of the biomass is 3205lmt. The lipid only price is S62/bbl. 

The sensitivity analysis presented shows that both the recycle of nutrients 

that do not leave in the lipid product stream, and the low capital cost of the 

system are essential for attaining further product cost reductions. The 

impact of higher productivity is only significant under these conditions, 

Increased productivity must not be accompanied by a decrease in the efficiency 

of use of inputs, significant increases in system construction costs, nor bv 

reduction in lipid content of the biomass. When svstem performance is 

maintained, a 50% increase in biomass productivity results in a 20% decrease 

in final product cost. If carbon is not recycled and system costs increase in 

proportion to the increase in productivity, then the cost reduction is well 

under 10%. Use of a system which is more than twice as expensive to construct 

as the one presented in this report renders the economics of fuel production 

untenable. Production costs are most sensitive to the price and recycle 

effiency of C02, the content of lipid in the biomass, and the combination of 

the cost of capital and the cost of svstem construction. However, the system 

must be desiqned and constructed so that each component which contributes to 

the final cost is minimized, in order for the concept to approach 

affordability and for further innovations to have any impact. 

RELATIONSHIP OF THE PROPOSED EXPERIMENT TO PROBLEMS IN FUEL PRODUCTION FROM 

MICROALGAE 

8nv estimate of the cost of producing lipids from alqal biomass is dependent 

on the assumptions used to generate the inputs to the economic model. It is 

necessary to determine which are most important and thus deserving of 

attention, and which are reasonably valid. Four questions must be answered in 

order to evaluate the overall feasibility of the concept: can inexpensive 

C02 be found and can it be used efficiently, does a larqe enouoh water 

resource exist which can make up for the losses incurred, con strains be found 

which form lipids at high rates of production and which will dominate the pond 

flora, and can methods be devised for harvestinq the biomass inexpensively. 
The resource evaluation questions cannot, for the most part, be answered at 

the present time, However, it is clear that the efficiency of utilization of 

the resources will be part oi the determnination of how larqe the resource 

base must be, In the case at water, the production system must be operated 

with a high recycle ratio. This has yet to be tested tor an extended period 

of time or on a meanlnqtul scale at the recycle level needed here. This is 

proposed in the experiment. In the care of COZ. the system must be designed 

to recvcle as much of the non-lipid carbon as possible, the inleetian systems 

must be 90+X efficient, and the management of the pond operations must such 

that vrrtually no outgassing occurs. In the engineerinq analyses qiven in the 

report, several means are presented to do all of these. In the experimental 

plan, efficiency of CU2 use is plven the hiqhest priorlty, including the 

testing o+ an anearobic lagoon +or nutrient recycle. 

The harvesting of the algal suspension 1s a problem that will reourre 

continuous attention in terms of applvinq new developments in polvmer 

chemistry to a changeable pond environment. A repertoire oi polymers must be 

available for use when a contaminant arlseg which has-different flocculatinq 

characteristics from the desired strain. 

'The discovery of productive, lipid +arming strains, wh~ch are highly 

competitive as well, is a basic requirement. However, productive accumulation 

of carbohydrates or protein has been looked for and found. There is no reason 

to believe lipid cannot be prolifically produced as well. The sensitivity 

analvsis indicates that hiqh lipid content, 40-50X of the biomass is 

necessary, but that overall lipid productivity need not be higher than 25 

t/acre/yr. Before increases in productivity have too much effect, the 

operating costs of the svstem must be reasonably low. Once these costs have 

been lowered, the capital costs become more important, While on the surface 

it may appear that increased productivity is a panacea, closer examination 

reveals that this is so only under one condition: lowest C02 requirement 

and cost, combined with low capital cost which is not increased significantly 

in order to attain the higher productivity. The system designed, and to be 

tested during the proposed experiment, is a low cost system, operating 

efficiently in terns of C02, and limited in terms of productivity onlv by 

the availability of productive aiqal strains. 

The last requirement, that the strain be dominant, may depend on how unusual 

lipid accumulation by algae turns out to be. Enough stralns which are known 

to store lipids must be identified, so that once a universal harvesting method 

is developed (as the polymer flocculation method potentiallv is), one could be 

relatively sure that nitrogen depletion will lead to the desired product 

despite the identity of the particular strain. This needs to be demonstrated, 

vii 

TABLE OF CONTENTS (CaNT.1 

SECTION 5.0 

SECTION 6.0 

SECTION 7.0 

SECTION 8.0 

Paqe 

Mixing System Specification ............ 33 

Analysis of Harvesting Systems ........... 34 

Introduction .................... 34 

Capital Costr of Primary Harvesting Devices . . , , 34 

Pretreatment Options ................ 35 

Lnalysis Overview and Implications for System Design 37 

Water Chemistry .................. 37 

Carbonation .................... 38 

Nutrient Recycle .................. 39 

Nutrient Losses .................. 41 

nixing System ................... 41 

Mixing Velocity and Oepth ............. 42 

PondLininq .................... 43 

Harvesting System ................. 44 

Productivity Enhancement and Species Control .... 44 

Effluent Disposal ................. 45 

Pond Construction ................. 46 

Pond Size and Geometry ............... 46 

Pond and System Configuration ........... 40 

Pond Design Alternatives and Costs ......... 53 

Harvesting System Design .............. 64 

Micrastraining ................... b4 
TABLE OF CONTENTS (CONT.) 

SECTION 9.0 

9.1 

9.2 

9.3 

9 -. 4 

9.5 

9.6 

SECTION 10.0 

SECTION 11.0 

Paqe 

Belt Filtration .................. 68 

Settling ...................... 71 

System Wide Costs ................. 79 

Water Supply and Distribution ........... 79 

Carbon Dioxide Supply and Distribution ....... 84 

Nutrients ..................... 84 

Blowdown Disposal System .............. 85 

Buildings ..................... 85 

Roads and Drainage ................. 86 

Electrical Supply and Distribution ......... 86 

Machinery ..................... 87 

OtherCosts. ................... 87 

Large Scale System Operations and Operating Costs . 88 

Operations Overview ................ 88 

Operational Costs of a 1000 hcre System ...... 91 

Economic Analysis of a 1000 Acre Production System . 95 

Base Case ..................... 95 

Sensitivity of Base Case to Productivity Chanqes . . 95 

Sensitivity of the Base Case to Carbon Recycle ... 98 

Recycle Case: Productivity Sensitivity ...... 100 

Recycle Case: Sensitivity to C02 Price ...... 100 

Recycle Case: Sensitivity to Lipid Content .... 105 
TABLE OF CONTENTS (CONT. ) 

Page 

11.7 Recycle Case: Sensitivity to Depreciable 

Capital Investment ............... 105 

11.8 Recycle Case: Sensitivity to Cost of Capital ... 108 

11.9 Recycle Case: Sensitivity to Polymer Dose .... 108 

11.10 Canslusions. ................... 108 

SECTION 12.0 Experimental Systen Design and Construction Costs . 112 

12.1 Site Description ................. 112 

12.2 Experimental Systea Description and Justification . 155 

12.3 Rlternative Sites ................. 116 

12.4 Experimental System Design ............ 117 

SECTION 13.0 Experimental System Operation and Costs ...... 132 

13.1 Introduction ................... 132 

13.2 System Construction ................ 132 

13.3 Experimental Plan ................. 133 

13.4 Operations Summary and Experimental Priorities . . 138 

13.5 Experimental Schedule ............... 139 

13.6 Budget Description ................ 139 

0UDGEfm.r.. ...r......m....m.m~..rr.. 1143 

REFERENCES ............................ 144 

APPENDIX I Carbon Dioxide Transfer ............... 145 

APPENDIX II Gaslift Pumps for Combined Pumping and Gas 

Contacting in Algal Production Systems ....... 154 

APPENDIX I11 Pond System Design: Background Information ..... 176 

APPENDIX IV Harvesting System Design: Background Information . . 183 

APPENDIX V Design of Anaerobic Lagoon ,.............. 185 

APPENDIX VI Sensitivity finalysis: Cost Summary Tables ..... 194 

xi 
LIST OF TABLES 

Table 

2- 1 

3- 1 

3-2 

3-3 

3 . 4

3-5 

4- 1 

4-2 

4-3 

6- 1 

6-2 

7- 1 

7-2 

7-3 

8- 1 

8-2 

8-3 

8-4 

8-5 

8-6 

9-1 

9-2 

Paqe 

Chemistry of Water Resources ................. 6 

Covered Carbonator . % Areal Coverage ............ 14 

Effect of Assumed Transfer Rate on Sump Depth ........ 17 

Sump With Gas Recycle .................... 18 

Average Hold-up and Lift in 1.5 m Deep Carbonation Sumps ... 20 

Average Hold-up and Lift in Counter . Current Sumps ..... 21 

Effect of Sump Depth on Air Lift Efficiency ......... 30 

Gas Lift Efficiency as a Function of Liquid Velocitv ..... 30 

Lift and Efficiency of a Draft Tube Air Lift System ..... 31 

Nutrient Partitioning in an Anaerobic Lagoon ......... 40 

Recvcle of Nutrients ..................... 40 

Pond Design Calculations . Single Pond ............ 49 

Pond Design Calculations . Pond System ............ 50 

Growth Pond Cost Sumnary . 192 Hectare System ........ 63 

Microstrainer Design Assumptions ............... 65 

Capital Costs of Microstrainer Harvesting Option ....... 69 

Capital Costs of Belt Filtering Harvesting Option ...... 70 

Settlinq Pond System Flow Rates ............... 75 

Capital Cost of Settling Pond Harvesting Option ....... 77 

Estimated Operating Costs of Harvesting Options ....... 78 

192 Hectare System Capital Cost Summary ........... 80 

192 Hectare System . Electrical and Maintanence Cost Summary . 81 

xii 
LIST OF TABLES (CONT.1 

Table 

9-3 

9-4 

9-5 

10-1 

10-2 

10-3 

11-1 

11-2 

11-3 

11-4 

11-5 

11-6 

11-7 

11-8 

11-9 

11-10 

11-11 

12-1 

12-2 

f 2-3 

12-4 

Page 

Capital Cost o-f Water Supply System .............. 82 

Capital Cost of Carbon Dioxide Distribution System ...... 85 

Capital Cost of Buildings .................. 86 

Base Case Desiun Parameters ................. 91 

Total Operating Costs . Base Case .............. 93 

Labor Required +or I000 Acre System ............. 94 

Base Case Economic Analysis ................. 96 

Economic Model Input Parameters ............... 97 

Base Case: Sensitivity to Fradurtivity ........... 98 

Economic Analysis: Base Case + Recycle ........... 99 

Recycle Case: Productivity Sensitivity ........... 101 

Recycle Case: Sensitivity to C02 Price ........... 104 

Recycle Case: Sensitivity to Lipid Content ......... 106 

Recycle Case: Sensitivity to DCI .............. 107 

Recycle Case: Sensitivity to Cost of Capital ........ I09 

Recycle Case: Sensitivity to Cost of Capital at 2x DCI ... 110 

Recycle Case: Sensitivity to Polymer Dose ......... 111 

Climatic Conditions at the Proposed Experimental Site .... 112 

Chemical Composition of Experimental Site Water Resources . . 115 

0.4 Hcctarc Pond Design Calculations ............ 120 

0.8 Hectare System Calculations ............... 121 

0.8 Hectare System Pond Costs ................ 123 

xiii 
LIST OF TABLES (CONT.) 

Table 

12-6 

12-7 

12-8 

12-9 

12-10 

13- 1 

13-2 

13-3 

13-4 

50 m2 Ponds Cost Breakdown ................. 

Exuerimental Svstem Settling Pond Cost ........... 

Experimental System Water Storage Pond ........... Experimental System Buildings Cost ............. 

Experimental System Cost Summarv .............. 

Experimental System . Pond Equipment Cost .......... 

Laboratory ......................... 

Operating Haterials and Supplies .............. 

DirectLabor.. ...................... 

Paae 

124 

126 

128 

129 

131 

139 

141 

142 

142 

xiv 
LIST OF FIGURES 

Figure Paqe 

2-1 Carbonate Chemistry of Seawater ................ 7 

2-2 Carbonate Chemistry of C~nditioned Type 11 Water 

. 125 Blowdown Ratio ...................... 8 

Carbonate Chemistry of Conditioned Type 11 Water 

. 25 Blowdown Ratio ...................... 9 

Effect of fond Size on Wall Lenqths ............. 47 

Effect of Pond Sizeon Pond Costs .............. 47 

Pond System Layout ...................... 51 

Single Pond Layout ...................... 52 

Wall Construction Alternatives ................ 55 

Paddle Wheel Design (Typical) ................ 61 

Microstrainer-based Harvesting Schematic ........... b7 

Settling Pond System Layout ................. 72 

Harvesting Pond Details ................... 74 

Settlinq Pond Flush System and Secondary Thickening ..... 76 

Water Distribution System .................. 83 

Recycle Case: Sensitivity to Productivity ......... 102 

Location of ~xperimental System ............... 113 

Experiemental Site ..................... 114 

Experimental Site . Plan View ................ li8 

Experimental Site . Section View .............. 119 

Experimental System Zettling Pond .............. 125 

Experimental Schedule .................... 140 
SECTION 1.0 

INTRODUCTION 

1.1 OBJECTIVES 

The objective of this report, as described in the stataent of work, is to 

develop a cost e+fective design for a microalgae culture facility, that 

meets specified location, resource, and product requirements. The 

conceptual design and operating options presented are based on field and 

laboratory experiments, conducted by Nicrobial Products, Inc., engineering 

cost analysis, and assessment of the work in the literature. 

In developing the design and analysis, the major decision in choosing 

among identified alternatives has been potential cost effectiveness and 

economic efficiency, This approach is based on the fact that the ultimate 

success of microalgae-based fuels will be determined by aarket economics. 

1,2 STATE OF THE ART 

An evaluation of the state of the art of algal biomass production can be 

based on information from actual producing plants and from extrapolations 

of results oC experimental iaciiities, In the +orner, the costs of 

constructing the system approach 100x 103/acre, the resource base is 

well-defined but limited and relatively expensive, and the final cost a+ 

the biomass is $2-S/dry lb; The costs derived from extrapolation vary 

extensively and are generally based on unrealistic assumptions used. For 

this reason, only the results of Wei3sman and Ooebel C13, Benemann et a1 

121, and Laws f31 will be used in the following discussion, These 

investigations are, in any case, among the most recent and thus the latest 

in the state of the art. 

The three major technical and economic concerns of algal biomass 

production are: the cost and availability of the two malor resources 

NOZ and water), the costs of constructinp and maintaining the syater, 

and the design and coats of the biomass harvesting and procerring 

syetems. At present none of these concerns has been resolved for a 

process which must produce the biomass at a coot of S,OS/lb as must be 

accomplished for fuel precurser biomass. 

Despite the effort that has been put into identifying the water resources 

available for large scale algal biomass production, no suitable resource 

has yet been identified. The rPasonB for this are 1) data on groundwaters 
are sparse, non-random, and difficult to compile and 2) the selection 

criteria have not been fully applied so that the resource data have not been 

properly evaluated. It is not possible to conduct a corprehensive 

investigation of water resource availability. Rather it seems more useful to 

state the criteria which any water resource must meet in order to be suitable 

for use in a low cost alqal biomass production system. In discussing the 

water availability, it is important to consider the interdependencies among 

the water, land and C02 resources required for algal production systems. 

In existing production facilities, system sizes vary fraa 1-20 acres and the 

amount of water required is small, Thus water from wells with special 

characteristics or inexpensive irrigation waters, already available for 

agriculture are used. When unique growth media are required, as in the high 

bicarbonate medium for Sejrgljng production, recycling of the growth medium 

is necessary, further lowering the water demand. For fuel ' production f ram 

nicroalgae, the scale increases 50-5000 fold, changing the resource question 

entirely. Now the agricultural water, which is not too costly per se, is not 

utilizable because the competition from conventional agriculture makes the 

land too expensive. This leaves only three water resources left for 

consideration: seawater, groundwater that is too saline for agriculture, and 

agricultural drainage water, 

In the U.S., coastal property with access to seawater is extremely 

expensive. However, since so much work ha8 been done in seawater, and since 

this is really the only unlimited water resource, we will consider the 

consequences of using it. One thing that must be kept in mind when 

considering the use of seawater is that much more water must be used since 

the initial salinity is already high. One really cannot consider even a 

50-100% increase in the salinity, due to evaporation, for two reasons. 

First, salinity restricts the number of species that will tolerate the medium 

and there are already very many species screening criteria. Second, the 

growth rate and productivity of algae on waters with increasing salinity, 

above seawater, decreases rapidly even for species which tolerate the higher 

salinity 141. 

Saline groundwater is the prime candidate for alqal biomass production, 

because it may be the only resource available in large enough quantities at 

low enough cost, where land is inexpensive. The groundwater resources 

identified to date 153, are most likely useable, after conditioning, as will 

be shown below. However, the size of the resource base is only speculative 

at present. Nonetheless use of saline groundwater will be a basic assumption 

in this report and serves as an example of a theme to be repeated throughout 

the report; the assumptions used will often be speculative, but it will be 

shown that the alternatives are much too costly to be seriously considered. 

The major effort will be to demonstrate that the speculative assumptions are 

the only economic a1 ternative. 
Agricultural drainage waters are becoming a larger and larger resource as 

irrigation waters are made more available in the semi-deserts of the U.S. 

southwest. These drainage waters ate becoming recognized as a major waste 

disposal problem. hlthough use of these waters poses same of the same 

problems a3 the use of irrigation water (available where land is 

relatively expensive) the credits for evaporating some of this water say 

outweigh the expenses. The following analysis nill thus cover the use of 

seawater and several types of saline groundwaters, delineating the 

consequences that the characteristics have an the design of law cast algal 

biomass systems. 

The major resource necessary for fuel precurscr production from microalgae 

is carbon dioxide. Even at l4O/ton, C02 is likely to comprise over 502 

of the operating costs. Itr requirement is proportional to biomass 

production so that increasing the output of a system, per acre, doas 

little to alleviate the cost burden of CQ2. C02 is available in 

moderate to large quantities from three resources: nello, re+inary 

cracking processes, and power plant aff gases, The legistits of siting a 

pond system close to both water and C02 resources poses one of the most 

difficult problems. Ye nill not delve into this area except to say that 

at least in tha future enough CO2 is available for largo system uss even 

if power plants mufit be bui'lt to supply it. The design conliderations 

will emphasize efficient use of Cop, assumed to be available at various 

specified costs. fllgal biomass production systeas in operation today use 

comnercirl GO2 produced at refineries and truckpd or traincd to the pond 

site. Co~ts of this range from $50-100/ton. This is the C02 resource 

that will be specified for the experimental system devetloped. 

State of the art systems are emall and very e~pensive per unit area to 

construct. Although the recovery of the cost of construction can be 

spread over many years, none of the existing systems could make a profit 

if the product value were not greater than about flO/dry lb, High 

construction casts and the large scale of the systems required to produce 

energy combine to discourage private investment. Thus the designs 

spec~fied in this report were devised to keep capital costs of 

construction as law as posjiblc while still achieving production goals, 

For example, pond lining with plastic aeabranes was considered too 

expensive to buy and install initially, as well as being a potential 

maintenance problem, 4 crushed rock lining, on the other hand, is much 

less expensive, Thh theme of our approach is repeated; intensive algal 

production has not been atterpted in large ponds, sealed with clay and 

lined with crushed rock, but we feel that in order for the praces9 to 

approach affordability, this option must be specified. 
Perhaps the foremost technical problem in low-cost algal biomass production 

has been recovering the cells from suspension. Besides simple sedimentation, 

there is no method yet developed that is inexpensive. All straining, 

filtering, and chemical flocculation methods presently being analyzed are too 

expensive. Induced bioflocculation, possibly aided by small doses of 

chemical flocculant, followed by sedimentation or flotation are potentially 

effective means of harvesting which would not be too costly. Both 

conventional and the proposed means will be analyzed in the body of the 

report. 

1.3 ORGANIZATION OF THE REPORT 

The report contains thirteen sections including this introduction. In 

sections 2.0 - 5.0 the analyses which serve as the basis for design criteria 

are presented. The chemistry of the water resource ir the subject of Section 

2.0. The water used and the blowdown ratio assumed determines the carbon 

storage capacity and pH arange of operation. This determines the transit 

time between carbonation stations, which is needed as an input to determining 

the pond size.. The design criteria for two different types of carbonators 

is the subject of Section 3.0. In Section 4.0 two methods for mixing are 

analyzed: paddlewheels and gas-lift pumps. The results are stated in terme 

of efficiency and power requirements to obtain channel mixing velocities of 

20 cm/s. Harvesting systems is the subject of Section 5.0. The methods 

analyzed include flocculation, with and without small chemical doses, 

folloned by either a two-step sedimentation system, air/DO flotation using a 

foam collection device, microstraining, or belt filtration. Section 6.0 

summarizes the analyses of preceding sections, provides an overview of other 

iaportant considerations not previously presented, and discusses the 

implications of the analytic results on the design and operation of a large 

scale algal production system. In Sections 7.0-9.0, the design of a large 

scale ponding system is presented along with the construction .costs. The 

cost of operating such is presented in Section 10.0. The sensitivity of the 

economics of algal biomass production to changes in the initial assumptions 

and design is the subject of Section 11.0. Finally, the experimental system 

which is to be used to validate the operation of the proposed system, is 

presented in Sections 12.0 and 13.0. 
SECTION 2.0 

WATER RESOURCES 

2.1 CHARACTERISTICS OF WATER RESOURCES 

The chemical composition of the water resource has several primary 

consequences for both the design and operation of the system. Pond size 

and/or the number of carbonation stations per pond is determined by the 

carbon storage capacity of the water, Since it ,is least expensive to 

restrict the "power" corridor to one end of the channels, one carbonation 

station per pond is optimal unless this criterion restricts pond size to legs 

than about 10 acres. In that case, pond construction will be more expensive 

because more carbonation stations will be needed per pond, requiring a more 

extensive C02 and electrical distribution system. The water chemistry nil1 

also e~ert a sclectlon criterion on the algal species. Thus the species must 

be screened for performance on the anticipated water resource. .The water 

available may also require some conditioning prior to use. For algal systems 

this is likely to be the case when the water hardness (Ca in particular) and 

carbonate exceed the solubility product at the projected pH range. The 

situation is more acute when the calcium concentration exceeds the 

alkalinity. In both cases same nater softening ill be required. The 

conditioning is achieved at lowest cost by the addition of sodium carbonate, 

followed by settlinq. If removal of magnesium is also required, then both 

lime and sodium carbonate need to be added, 

In Table 2-1, several nater resources are shown along with the correspanding 

carbon chemistry and nater conditioning rsquirements. 4150 shown are the 

outgassing consequences, the precipitation of calciua carbonate, and the 

levels of dir~olved COZ. Figurer 2-1,2,3 show the pH dependency of there 

 factor^ and thus the data upon which the specified pH range of operation was 

chosen. This range is liflited on the acid side by loss of C02 due to 

outgarsing and on the baaic side to 1) low C02 concentration and 2) calcium 

carbonate precipitation. The latter ia critical in waterr in which there is 

a lot of calcium which could precipitate cau~ing r turbidity problem and 

especially critical where the alkalinity is low, a9 in seawater. Here 

calcium carbonate precipitation results in a major loss of buffering and 

carbon storage capacity. When the calciua concentration is low (1-4mH) and 

the alkalinity moderately high (12-40sH), precipitation is not a problem. 

The figures were constructed assuming infinite solubility of calcium 

carbonate. At finite solubility (indicated in the figures) the figures are 

still accurate when carbonate alkalinity is much greater than calcium 

concentration, On the other hand, seawater chemistry changes considerably as 

calcium carbonate precipitates. 
Table 2-1. Chemistry of Water Resources 

............................................................................. Seawater Salton Sea Type I L Low TDS Type 11 L Exp't. ............................................................................. 

BDR .95 .95 ,125 .25 .I25 .I27 

Ca removed - 600 500 0-40 125 1100 

P Pm 

Na2C03 - 1500 1250 0- 100 0 2750 

added, ppro 

Ca, mtl 10.3 10.3 .5 1-4 1-4 1-4 

pH range 6.5-8.0 6.5-8.0 8-8.5 7.5-8.5 8.0-8.5 8.0-8.5 

8-9 7.5-9.0 8-9 8.0-9.0 

7.3-9.5 

C out, 

gm/m2/d 

C storage 

timc,hrs 

Pond depth = 20 co, prod. =49m/n2/ hr=. 03mfl C/hr , ~~s0~ 04mihr for 

outgassing 



Six water respurcss are characterized in Table 2-1. The first two represent 

high TDS waters which cannot bear much concentration due to evaporation 

without severely limiting the number of species which will prow 

productively. Thus seawater is a resource that requires substantial 

blowdown. The Salton Sea water can be used at the proposed experimental site 

in southern California to simulate seawater as a once through resource, after 

conditioning to remove more than half of the calcium. (Salton Sea water has 

2.5 tines as much calcium as regular seawater). For seawater the upper limit 

on pH is rather strictly set by calcium carbonate precipitation because the 

alkalinity is so low, as discussed above. The lower limit is set, by C02 

outgassing, at pH about 6.5. Due to the low alkalinity, only about one hours 

worth of carbon can be stored in the water. If pond depth were halved only a 

half hours worth of carbon could be stored. 

The saline groundwaters examined by SERI were evaluated for their usefulness 

in open ponds systems. Generally speaking, the major water resource cited, 

the Type I Low is unsuitable for this application. It has too much calcium, 

requiring S2400lacrelyr for conditioning in chemical cost alone. Although 

the Type I moderate has a more favorable ratio of alkalinity to calcium, it 

ends up requiring more sodium carbonate because it must be blown down more. 

The low waters can bear an eight fold concentration whereas the moderate can 

bear only a twofold concentration. The Type I high has a favorable 

alkalinity to calcium ratio meaning that the calcium can be removed by 

equilibration with air in a settling pond to allow precipitation of calcium 

carbonate, followed by sedimentation. However the water is so high in TDS 

that it cannot be concentrated further and thus too much of it would be 

required. Not only does it become very expensive to pump so much water, but 

there is no evidence that enough of this resource exists. So for the 

purposes of analysis the Type I waters are unsuitable. If similar water, but 

lower in calcium were found it could be utilizable. At 50 tons/acre/yr algal 

productivity, and a blondown ratio of ,125, the chemical cost of calcium 

removal is about a half cent per kg dry we. of biomass per 100 ppm calcium. 

A similar analysis reveals that the Type I1 water of TDS 4ppt can be used 

despite its high calcium. The much higher alkalinity results in 

precipitation of most of the calcium as calcium carbonate upon equilibration 

with the air. The low Type I1 water can be concentrated many fold in terms 

of TDS. It is not clear whether high TDS or high alkalinity would first 

limit the extent to which this water type could be concentrated. Whether 

magnesium would precipitate as the water concentrates is an issue that must 

be addressed by experimentation. If not there would be no water conditioning 

costs beyond a settling pond and possibly some fiocculant to remove calcium 

carbonate precipitates. If aagnesius needed to be removed, lime would be 

used. A complete water conditioning analysis would be needed. However, 

preliminary analysis indicates that about 6-8 mM lime would reduce the 

magnesium content 60%, the alkalinity 70%, leave little residual calcium, and 

increase the pH to about 9-9.5. This would cost about one cent per kg 

biomass. The uncertainty in the water conditioning status results in an 

uncertainty in the alkalinity of the treated water. Starting with an excess 

of alkalinity over calcium of 10 mM, an eight fold concentration by 

evaporation in the ponds would lead to a "steady state" alkalinity of 80mM. 

This would require a pH of close to 9 to avoid considerable outgassing, It 

might be difficult to find organisms which grow well at such a high alkalinty 

and pH (although the C02 concentration would still be quite high). 
2.2. LARGE SCALE DESIGN WATER 

The water source selected for the large scale systea design is Type 11 saline 

groundwater with an initial TDS of 4 ppt, Since removal of calcium, some 

magnesium, and concommitant alkalinity is likely, the design includes a water 

holding pond to be used to sediment precipitates. After conditioning and 

evaporative concentration with a ,125 blowdown ratio the steady state 

salinity is 32 ppt with an alkalinity of 32-b0 mM. It is areumed that 

caiciua and magnesium have been lowered to levels nhich do not cause 

precipitate problems. 0f course, it is also assumed that an adequate 

resource base exists +or this type water, 

Given this water resource, with an alkalinity of greater or equal to 32 mfl, 

the upper limit of pH is dictated by the growth response of the algae to 

C02 concentration. If the organism grows well at or below air levels of 

C02 then the pH could go up to 9 or higher. If it requires higher COq 

then a pH of 8.5 is more suitable, The low limit is set by outgassing, which 

increases steeply below pH 8 due to the high alkalinity as shown in Figure 

2-3. But, also due to the high alkalinity, large amounts of carbon can be 

stored with a small change in pH. With just one carbonation station per 

pond, a pond o+ 40 acres could be operated, For a smaller pond, the pH range 

could be narrowed, further lowering the outgassing loss (by increasing the 

low pH limit) or increasing the minirum CQ2 concentration (by decreasing 

the high pH limit), 

2.3. EXPERIMENTAL SYSTEM WATER RESOURCES AND GROWTH MEDIA 

The proposed experimental site is located in Brawley, California in the 

Imperial Valley. The site borders the southwest side of the Salton Sea. 

Water from the sea is available by pipeline or by drilling a shallow well, 

An existing 1700 gpm well provides brackish (2.5 ppt) groundwater. As 

discussed above, saline groundwaters can be expected to contain high levels 

o+ alkalinity after concentration, On the other hand naters that are 

originally highly saline, like seawater, contain little alkalinity. The 

water resources available on the proposed site can be mixed in various 

proportions, after conditioning, to obtain waters that are representative of 

both high and low alkalinity resources. The primary experimental alkallnity 

nil1 be 24meq/l. In some cases, however it will be convenient to operate at 

lower alkalinities. The basic formula for the experi.nenta1 water resource 

for the demonstration system is a mixture of Salton Sea water (after reaoval 

of all of the Ca) and well nater in a ratio 04 about 19: 1- achieving a TDS of 

4 ppt and an alkalinity of about 3 neq/l. After evaporation, the TDS is 32 

ppt and the alkalinity is 24 meq/l. Any starting TDS is achievable by using 

a different ratio of Salton Sea water to well water. This allows variation 

of the concentration of major ions (although not independently) and blow donn 

ratio. Since only the Salton Sea nater needs conditioning, the cost per acre 

per year is about $300. The conditioning can be achieved by addition of line 

and soda ash if both calcium removal and magnesium remaval is required. If 

only calcium is to be removed, soda ash alone is added. .The practical 

methods of nater conditioning that would be used at the large scale will be 

tested in small scale holding ponds. 
SECTION 3.0 

ANALYSIS OF CARBONATION SYSTEMS 

3.1 INTRODUCTION 

In the last section, the carbon storage capacity of several waters was 

analyzed. This, along with the constraints of minimizing dissolved C02 

level at the lowest pH and maximizing it at the highest pH defined both the 

pH range of operation and the transit time allowed between carbonation 

stations. This transit time was based on the summertime daily demand 

averaged over 12 hours, which is equal to the production of 4 qm/m2/hr of 

algal biomass. When demand is lower, the pH range can be narrowed and/or the 

carbon inflow rate diminished. In this section the means with which thls 

maximal rate is supplied from the gas stream to the pond liquid is analyzed. 

The basic chemical engineering of gas-liquid transfer is presented in two 

appendicesi A1 and AII. The results for two different types of carbonators, 

a bubble cover and an in-pond sump, are discussed below. Along with the 

parameters relevant to each manner of transfer, the consequences on the 

mixing requirements of the ponds are analyzed. 

3.2 COVERED AREA CARBONATORS--BUBBLE COVERS 

By covering a small percentage of the pond area with a membrane-covered 

structure submerged at its edges, gas transfer can occur passively through 

the pond surface under the cover. The cover serves to trap a gas volume with 

a high concentration of C02. The flow of gas under the cover can be 

turbulent or laminar, depending on the placement of the injection sites. 

Laminar flow allows somewhat higher stripping efficiencies since the gas bled 

off will contain the lowest C02 concentration. A gas bleed is necessary 

since desorption of oxygen and nitrogen will occur under the cover. If the 

percent coverage is low the bleed rate needed is even a lower percentage of 

the inflow rate, so it has little effect on the carbon transfer efficiency. 

The percent coverage of the pond depends on the transfer rate of GO2 under 

the cover. As detailed in Appendix AI, this depends on the hydaulics under 

the cover, i.e., the rate of turnover of an element of water surface. 

Several techniques can be used to increase this surface renewal rate. 

Anything which increases the hydraulic slope under the cover, like increasing 

the flow velocity by lowering the depth, increases the renewal rate. 

However, since the area of coverage is not negligible, the effect of this 

increased mixing on the overall power and head loss must be considered. 

Alternatively, the roughness coefficient under the cover can be increased. 

The reans proposed for doing this is to increase the roughness of the 

underside of the cover and place the cover partially in contact with the 

water. This "rippled" cover design can be effected by using a corrugated 

material for the cover. In this manner the average surface element lifetime 

for a 20 cm deep pond mixed at 20 cr/s, could be decreased from 50 s to less 
than 4 s (corrugation spacing of 5 cm). This, too, will increase the head 

loss and mixing power required but only about 5-IOX, much less so than if the 

same low turnover time were achieved by lowering the depth to 10 cm and 

increasing the velocity to 40 cm/s under the cover. As shown below this 

latter design increases the overall mixing head and power required by 50%. 

The results of the analysis are shown in Table 3-1, Three basic cases are 

detailed: a pond 30 cm deep mixed at 15 crn/s, a pond 20 cm deep ~ixed at 20 

cm/s, and a shallow pond only 10 cm deep mixed fast at 30 cm/s. Several 

simplifying assumptians were made in constructing the table; the major ones 

being that temperature is con~tant at 30° C, that tho water can atore the 

carbon transferred, and that the dilution by O2 outgassing is negligible. 

It can be seen from the results that a low concentration C02 gas phase 

(like flue gas) would require much to high a percent coverage in all cases. 

In order for the coverage to be less than 5X, a turnaver tine o+ less than 10 

s is required, which is theoretically equivalent to a mass transfer 

coefficient of .04-,05 m/hr. The coefficients used in the construction of 

Table 3-1 were obtained from empirical correlation of stream flow data (see 

Appendix AI). The coefficients measured by Weissman and Goebel El3 in high 

rate ponds 20 cm deep mixed at 20 cn/s were higher by a factor of 3.4 than 

those calculated using the correlation, If the higher, reasured values are 

used then each of the values for Z coverage in Table 3-1 could be reduced by 

multiplying by ,3, The percent coverage for eases 2% and 3 then become BX 

and 4% respectively. If in addition, tho rippled cover is ured instead of 

the smooth one, then the covered area for case Za is reduced 9rom 0% to 2%. 

In case 3, this reduction is only from 4% to 2% since the turnover time was 

initially shorter. 

The assumption here is that a covered area carbonator is feasible if the 

percent coverage is low [about 2%). This may be achievable with a smooth 

cover in shallow, fast mixed ponds, in 20 cm deep ponds if the area under the 

cover is made shallow, or in these moderately deep, iasd~rately mixed ponds i9 

a rippled cover is used. The effects on mixing head and power can be 

expected to be significant when a portion af the pond-i!3 made shallow, hut 

mall when the roughness and wetted perimeter are increased by a rippled 

cover. 

3.3 IN-POND CARBONATION SUMPS 

In alternative nay of transferring CU2 to the pond water is to inject the 

gas at or near the botto~ of a sump which spans all or part of the channel. 

As in the case of the covered carbonator, theoretical results must be taken 

as only approximate since the actual process invalved is complex. In all of 

these gas transfer problems, the real answer is only obtained from the 

operation of pilots. Nonetheless, the theoretical treatments do give a senee 

of what is possible and economically feasible. The cheaical engineering 

treataent of sump carbonation is detailed in Appendix IP. The major results 

of that analysis and the major uncertainties involved w~,ll be summarized 

first, 
Table 5-1. Covered Carbonator - % fireal Coverage 

.............................................................................. 

Case 1 a lb 2 a 2b 2 c 3 a 3b 

Depth 30 10 2 0 10 20 10 10 

C m 

Vel. 15 4 5 2 0 4 0 2 0 30 3 0 

cm/ s 

K L ,013 ,070 ,022 ,061 ,085 ,047 .085 

m/hr 

c in900 2200 640 1900 2463 1400 2465 

% area 44 8 2 6 10 6.7 12 6.7 

head 100 170 300 450 --- 1700 --- 

X la 

power 100 170 400 600 - - - 3500 --- 

X la 

Carbon supply (C in) and carbon demand 1C req.) are in aaoles/m2/hr 

Assumes pure C02 equilibrates to 29mH and back pressure is negligible. 

For flue gas 115% C02) multiply coverage by 6.7. 

The depths and velocities listed are those under the cover. Case a) of each 

group gives the depth and velocity for the pond since no changes occur under 

the cover in these instances. 

Cases 2c and 3b refer to the rippled cover, which determines KLm 

KL = (diffusion coefficient/turnover tine)li2 

The values in the table are based on an empirical correlationgiven in the 

literature. hctual values have been measured to be over three times faster, 

see text. 
Gas transfer is qualitatively different in sumps. Under bubble covers the 

hydraulics of the flow under the cover determines the mix.ing that is needed 

to disrupt the thin film which effects transfer and mixes the dissolved gas 

with the bulk liquid. In sumps it is the movement of the bubble swarm 

relative to the flowing liquid which "renews" the transfer surface. Thus the 

behavior of bubble swarms determines transfer rates. This behavior is quite 

complicated and the models used thus only appoximate the actual process. 

The inajor uncertainties in the modeling are the bubble size distributlan, the 

consequent average rise velocity relative to the water, and thus the average 

rate of gas-liquid transfer. In the treatment in Qppendix IT, an average 

bubble rise velocity, relative to the water, of 30 cm/s was assumed. It was 

further assumed that the mass transfer rate distribution 1s very narrow. 

These assumptions have empirical justification, in that it has been found 

that after about .5-1.0 meter of rise the bubbles coalesce to a minimum 

equilibrium size with these characteristics, However it has been noted C6,71 

and measured Cl,b,73 that in shallow sumps the transfer rates exceed, by a 

large factor, those predicted on the basis of this equilibrium, 

Consequently, we will analyze the sensitivity to assumed transfer rate. 

Given a transfer rate, one can estimate the average bubble diameter and then 

the rate of rise, With this information, the basic parameters of sump 

transfer can be calculated. These parameters are the depth oi the sunp 

required to strip a specified percentage of C02 and the gas hold-up which 

determines (for a given sump depth) the head gained by the water column in 

co-current flow or the head opposing the water flow in counter-current flow, 

One more case of interest is when the sump does not contain a baffle to 

direct the water flow, In this case of "lateral" ffon the gas has little 

effect (except causing some extra turbulence) on water Read, 

The average hold-up,e, is given by the folloninq formula far ca-currant flow! 

Qg is the gas flow rate, QL is the water flow rate, Vg is the average 

rlse velocity of the bubble. relative to the water, VL is the water 

velocity, and Cp, is the average pressure correction factor for the 

compression of the gas at subsurface depths. hppendix Table AII-1 gives 

values for this correction factor as a function of depth. For pure C02 a 

further correction factor is required since the volu~c of gas decreases with 

time as gas is absorbed. This factor is the log mean of the flow rate at the 

entrance to the sunp and at the exit. There is also a pressure factor to 

account for the fact that most of the gas volume is at the loner depthe. 

This is somewhat arbitrarily assigned the value of ~,~,/p2~3, but is only 

of the order of 10% for shallon sumps, For counter-current flow the term 

inside the parentheses in the denominator becomes VB/VL - 1 where - - 

VB>VL and both are considered absolute (positive) values. The hold-up is 

related to the lift or head by: 
where ho is the level of outflow above the sump sparger, hi is the 

distance between the inflow liquid level and the sparger level, g is the 

acceleration of gravity, and K is a friction factor for losses upon entry, 

transit through, and exiting the sump. These losses are small at low liquid 

velocities. 

As discussed in Appendix 11, the stripping rate of oxyqen has been found to 

be .7Xls or, at a bubble rise velocity of 30cmIr in still water, .7X/foot. 

The transfer for C02 is related to that of oxyqen by the ratio of the 

diffusion coefficients to the two-thirds power times the ratio of the 

solubilities. At 20° C this ratio is about 18, yielding a stripping rate 

for C02 of 12.5%/$. Table 3-2 shows the sump depth required for stripping 

95tof the infloning gas fro@ the bubbles given several different stripping 

rates per second. This stripping rate has to be considered an unknown 

parameter since measured values have been found to depend on sump depth, some 

have been found to be much greater, and the bubble size is known to depend on 

sparger type and flow rate as wellC6,71. For low flow rates, spargers which 

produce fine bubbles (and hence are more expensive) can be used. These will 

likely provide transfer'rates higher than those calculated based on the 

oxygenation experiences, since it ray take a considerable fraction of the 

sump height for an equilibrium bubble size to be reached. As flow rate 

increases, due either to the use of recycle or in the flue gas utilization 

case, not only does initial bubble size increase in a device specific manner, 

but the type of device may need to be changed to one which can handle the 

higher flow rates at moderate cost. Ususally this aeans that the device 

produces larger bubbles to begin with. To add to the uncertainty, the 

salinity of the medium affects the equilibriuri bubble size and the rate of 

attainment of equilibrium due to the inhibitory action of charged species on 

bubble coalescence. Significant enhancement of transfer rates has been seen 

at TDS as low as 5 ppt 183. 

The lowest rate shown in Table 3-2 corresponds to the rate found for 

oxygenation (adjusted for COZ), the next lowest is considered the minimum 

value that would exist in a shallow sump when purified C02 is used, and the 

last is a value which is similar to that found by Weisraan and Goebel f13 in 

a water column of 20 cm. The table shows the sump depths for co-current, 

counter-current, and lateral (no baffle to direct water flow) flow. In 

addition, the bubble size and bubble rise velocities calculated from the 

analysis of Aiba et alC71 which would yield the given stripping rate, are 

shown. These values must be taken as highly approximate, but do aid in 

choosing sparger type. As bubbles get above .2-.25 cr, they change from 

being rigid spheres to having deformable walls. One consequence of this is 

that the rate of gas transfer from the bubbles becomes somewhat insensitive 

to bubble size because the volume to surface area ratio decreases with 

deformation. At even moderate gas flow rates, the turbulence prevents the 

bubble size from getting very much larger than .5-1 cm. In tho end, only 

experimentation will yield reliable results and design specifications. 
The cost of construction of a sump depends on sump depth. Not only does the 

naterial requirement increase with depth, but in addition, deep ~mps require 

more expensive construction methods. For this reason, the sump depth is to be 

kept below 1.5 m or so. Costs o+ construction in this range of depth are 

relatively low. 

A method that can be used to keep the sump shallow is to cover it with a 

membrane, capture the gas, and recycle it via a blower back down to the 

sparger. Given a suap depth of 1.5 meters, the recycle ratio required to 

achieve 90-952 (using pure C02) or 80% (using flue pas) overall stripping 

of carbon is shown in Table 3-3 for several different conditians, 4 louer 

reroval efficiency is used for flue gas because the back pressure from 

dissolved COq becomes significant a5 carbon is stripped from the dilute 

gas. Since the depth of the sumps cannot be predicted precisely, recycle 

adds flexibility to the ways in which a given sump depth tan be made 

adequate. 

Table 3-2. Effect of Assumed Transfer Rate on Sump Depth 

--~~-l---l-I-,~~*-L"L*-------I-I-I-,IIII----------.----"---"-~---~---m-~------ 

Transfer Rate,% Remaval/s 13 25 50 

Bubble Dialeter , crl >.2 .125 .08 

Rise ~clocit~,cr/s~ 30 15 9 

Distance Traveledh, cm 

Co-current 

Lateral 

Counter-current 

Time Required, 95X Overall 

Removal, s 

Suap Depth, 95% Overall 

Removal, m 

CP-current 

Lateral 

Counter-current 

Liquid velocity = 20cmls 

171 and Stoke's Law 
Table 3-3. Sump With Gas Recycle 

.............................................................................. Transfer Rate Over a1 1 REEYE~E-Rp!! 

X Removal/s Removal ,X Inflow .............................................................................. 

Pure GO2 

Lateral 

Later a1 13 

Sump Depth = 1.5 meter 

Liquid velocity =. 20 ce/s 
Table 3-4 gives the average hold-up as a function of C02 demand for 

co-current flow in a sump of depth 1.5 m. This gives a range of head lift to 

be expected during carbonation. The assumed stripping rate may be too high 

for flue gas relative to pure C02 since the gas flow rates, and 

consequently the hold-up are so high, The lift for the flue gas case in 

which inflow of gas is provided 24 hours a day is just sufficient to mix the 

8 hectare pond. However, the CD2 injection efficiency is quite low. 

Table 3-5 gives results for counter-current flow. Here the water velocity 

can be lowered by widening the sump beyond the value of the pond depth to 

prevent wash-through of the average bubble, and to reduce the head opposing 

the channel flow. As can be seen from the table, the opposing head is 

already significant when pure CU2 is used and prohibitive when flue gas is 

used. To a good approximation, the hold-up is inversely proportional to sump 

width. An equation is given in the Table 3-5 relating hold-up to transfer 

rate, sump volume, and gas flow far the case in which the liquid velocity is 

equal to the average bubble rise velocity but opposed to it. In this case 

hold-up depends on the steady state ratio of gas to liquid volumes. It can 

be decreased by deepening the sump. 

The values of hold-up and head shown in Tables 3-4 and 3-5 were calculated 

for an eight hectare pond, which was the size chosen for the large scale 

design. If a pand size of four hectares was chosen, halving the flow o+ 

GO2 into the sump, no adjustment is required in hold-up and head if the 

length to width ratio is changed so that channel width is also halved (thus 

halving the liquid flowrate), By maintaining the same length to width ratio 

of 20, the liquid flowrate only decreases by a factor of 1.4, Thus the ratio 

of gas to liquid flowrates in the sump decreases by a factor of 1.4, 

decreasing hold-up and head by the same factor at low flowrate ratios, and 

somewhat less at high ratios. Head attained with gas lift puaps is discussed 

more fully in Section 4.0. 
Table 3-4. Average Hold-up and Lift in 1.5 m Deep Carbonation Sumps 

............................................................................ Co-current, transfer rate = ~~XIS, VB a 15cn/s .............................................................................. 

C02 req. ,gm/m2/hr 8.6 8.6 4.3 4.3 

Gas Composition, Z C02 100 15 100 15 

No Recycle, Overall Removal = 71% 

Input Gas Flowrate, l/s 167 1129 8 3 56 1 

Gas flowrate/Liq.flowrate ,056 .65 ,028 .32 

Head, cm 4.4 39 2.2 2 2 

With Recycle 

Overall Removal, % 9 5 80 95 8 0 

Input Gas Flowrate, 11s 116 925 58 462 

Gas flonrate/Liq.flowrate .06 1.04 .03 .52 

Head, cm 4.4 54 2.2 33 

C02 req. = (1.2) 11.8) x algal productivity (either 4 or 2 gm/m2/hr, 

includes 20% for increased C content of high lipid producing algae. 

Pond area = 8 hectare 

Input gas flowrate at 1 atm, 30° C. 

Liquid flowrate through sump = 1725 l/s (43.1 RI wide channel, 20cm deep, V = 

2Ocu1/s, sump spans channel, sump width equals pond depth) 

For pure C02 cases, gas flowrate (for ratio) ir log mean of gas flow rate 

at sump bottom and sump top, pressure corrected. 

See Table 3-3 for recycle ratios. 
Table 3-5, Average Hold-up and Lift in Counter-Current Sumps 

. . -. . . - - - - - - - - - - - - - - - - - - - - - - -- . . . .. . . .. . 

Counter-current, transfer rate = ISXIs, Vg = 30cm/s -1--1----1-----111--------1----a----------------a---------------------m-=----- 

CD2 req. ,gm/a2/hr 8.b 8.6 4.3 4.3 

Gas Composition, X C02 100 15 100 15 

No Recycle, Overall Removal 862, Sump Depth 1.5 rn 

Input Gas Flourate, l/s 128 060 64 430 

Gas~lowrate/Liq.flowrate .03 .SO ,015 .25 

Hold-up, % 5.3 48 2.7 32 

Head, cm 0.0 72 4.1 48 

With Recycle, Sump Depth = 1.0 m 

Overall Removal, X 95 85 95 85 

Recycle Ratio ,31 .17 .31 .17 

Input Gas Flowrate, l/s 116 870 50 435 

Hold-up, X 

Head, cn 

Counter-current, VB = VL 

10---1--------11-----.I----r-----o-----------1-----------------------------0--- 

Pure C02: 

Holdup = Input gas flowrate/trrnafer rate/cunp depthlsump Xgec, area 

Flue gasr hold-up gets very large -- as unabsorbed gas builds up, until 

channeling occers, 

For conditions see Table 3-4. 
3.4 RECYCLE OF NON-LIPID CARBON FROM EXTRACTION RESIDUES 

Since carbon is one of the most expensive inputs to the system, and since 

only part of the carbon is extracted in lipid products, recycle of the carbon 

remaining in the unextracted residues must be considered. An effective 

method of processing the residues is to anaerobically digest them, A covered 

lagoon is specified in the large scale design for this. With 60% of the 

algal biomass as lipid and 90% of this extracted, the residues contain 46% of 

the algal carbon. 65% of this will degrade in the lagoon to methane and 

C02 in a ratio of 614. The other 35% will be split between the two liquid 

compartments of the lagoon; the sludge and the lagoon water. Both the 

gaseous comeponents and the lagoon water (effluent) can be recovered. The 

digester gas is combusted to operate an engine generator, The resultant flue 

gas is about 14% C02, and contains 31X of the original algal carbon. 

Hixing this with the pure C02 input, in a ratio (by volume at STP) of 7:1, 

yields a gas containing 35% COZ. If this is then injected into the ponds 

with a 90-95% efficiency, and the dissolved carbon in the digester effluent 

is recycled back to the ponds, the result is a decrease in overall CQ2 

input from 2.4 kg/kg algae to 1.6 kg/kg (see Table 6-31. 

The 35% C02 gas phase can be introduced into the ponds just as any other 

gas phase. Now, however, an overall stripping efficiency of 90% is assumed 

as opposed to 95% with pure C02 since backpressure reduces the driving 

force near the top of a sump. Again, the transfer rate is not certain. With 

90X overall removal, the sump would have to be 5.3 ITI deep if the transfer 

rate is 13X/s and 1.3 m deep if the rate is 25X/s, for lateral flow of the 

pond relative to the bubbles. If the gas is injected co-currently, more head 

can be gained than in the pure C02 case due to the larger gar voluae. For 

the two transfer rates, the sump depths required are 7-9 a and 2.3-3 r 

respectively. The lifts obtained are 28-53 ca amd 19-27 ca respectively. 

Thus the lift gained by co-current injection of a mixture of pure and 

recycled digester flue gas matches the mixing requirements of the system when 

moderate transfer rates are assumed. 

The recycle of non-lipid carbon has perhaps the greatest potential for 

reducing the cost of the lipids produced of any single factor. This will be 

more fully discussed in several ensuing chapters. 

3,s OXYGEN DESORPTION 

The desorption of oxygen, and nitrogen to a lesser extent, affects the 

efficiency of C02 transfer in both sumps and under covers. The ratio of 

oxygen mass transfer to C02 transfer depends approximately on the ratio of 

driving forces, since diffusion coefficients are similar. fissuring no C02 

back pressure, which is very nearly true in the pure CD2 case even with 95% 

absorption, and a dissolved oxygen concentration that is 500Y. of saturation, 

the dilution of C02 by O2 under a covered area carbonator is only about 
10%. That is, at steady state the gas phase under the cover would be over 

90% C02 and the bleed rate wauld be about iOX. If C02 moved by plug flow 

across the uripple" covered channel, then at the end the transfer rate nould 

be slowed somewhat by oxygen dilution, but the gas bled o+f would have a 

higher oxygen concentration. Similarly, in sumps the C02 transfer rate 

would decrease near the top of the sump nhere the dilution of the gas phase 

nith oxygen is greatest. This dilution would not affect transfer 

significantly in the pure C02 case, because ample driving force of CD2 

would remain until very near the top of the sump. Since flue gas is already 

dilute in C02, further dilution would also not be significant except at the 

tail end of transfer. It should be noted, however, that the back pressure of 

dislolved C02 may be significant when carbonating moderately alkaline 

waters to near neutral pH when flue gag is used, with or without further 

dilution by oxygen, 

Potentially more serious' is the desarption of supersaturated oxygen in a 

sump due to nucleated bubble formation, Using the mass transfer coefficient 

for outgassing through the surface of a 20 em deep pond mixed at 20 cmh and 

the supersaturatian level of 500% found by Weissman and Ooebel t13 about 402 

of the oxygen produced outgassed due to mass transfer through the sur#ace of 

the pond. Since these conditions existed for prolonged perlode of time, 60% 

can be estimated to have desorbed due to nucleated bubble formation. I+ 

oxygen loss in a ouap, for example, reduced steady state levels to 200% 

supersaturation, the mass transfer 1055 through the p~nd surface would be 

only 25X of the oxygen produced, At the lower DO nucleated bubble farmation 

would be substantially reduced, implying that about 50X of the oxygen 

produced would need to be removed in the sump to maintain such a low DO. The 

rest of the oxygen desorbs, due to nucleated bubble formation, through the 

pond surjace, The rate of desarption through the surface by bubble formation 

(as distinguished from mass transfer) calculatad +ro@ the above condition 

(500X) is ,007 mH/s. In order for the DO to be dropped from 500% to 200% by 

sparqing air in a sump with gas residence time of 4 s, the desorptisn rate 

would have to be 25 tiaes as great. At this point no data exists concerning 

the desorption of supersaturated oxygen due to catbbnation or aeration. 

However if such a reduction was attained it would dilute the gas volume of 

pure C02 by 30-BOX, depending on the ratio of input gas flow rate to the 

flow rate of pond liquid through the carbonator. This would have impact on 

sump design, i.e., sump depth required for a given tranafer efficiency, 

especially in sumps with recycle. The desorption of supersaterated oxygen 

and the impact on sump design will be tested in the proposed experimental 

system. Of course, if very e+ficient removal of oxygen were attainable, a 

separate sump just for this purpose would be con3tructed ahead sf the 

carbonation sump. In the case of flue gas carbonation, the dilution is 

5-lo%, which wauld further aggravate the backpressure problem far transfer 

near the top 25% of the sump. 
The desoprtion in sumps by sparged gas will be used to determine the 

practicality of using aeration as a means of preventing the build-up of 

oxygen to inhibitory levels, i.e., to determine how many sumps would be 

required to maintain the DO within specified limits. 

3.6 CHEMICAL ENHANCEMENT OF CARBON DIOXIDE TRANSFER 

A detailed discussion of the chemical reactions of C02 with other dissolved 

species, and the effect of this on transfer coefficients, is given in 

Appendix I. Even at the highest alkalinities and pH imagined for algal 

ponds, the enhancement due the reaction of C02 and hydroxyl ions is 

negligible. The pH independent, first order reaction of C02 and water to 

form bicarbonate is fast enough to enhance transfer rates that have not 

already been enhanced hydraulically by increased surface renewal. The tno 

processes are competitive, so that the chemical enhancement is still very 

small in sumps, where surface renewal rates are on the order of 100-150 per 

second. The covered area systems were designed so that surface renewal rates 

were as high as possible to increase transfer rates. The renewal rates 

discussed above were on the order of .25/s for 2% coverage and .016/s for 

13% coverage. Chemical enhancement due to a first order reaction goes as the 

square root of 1 + k/s where k is the reaction rate constant and s is the 

surface renewal rate. k is equal to about .02/5. Thus physical transfer 

rates would have to be small, meaning high areal coverage, for chemical 

enhancement to have much effect. It say be of interest that several 

catalysts which have significant effect on the first order rate constant may 

be present in an algal system. These include carbonic anhydrase which is 

often secreted by algae and phosphate which is a media component. 

Enhancement due to these can be tested by comparing transfer in media not 

including these species to that in aedia which does contain them. 

3.7 LhRGE SCALE SYSTEM CARBONATOR DESIGN 

The Base Case design specification of the carbonation system for the large 

scale system will be taken as a 1.5 m deep sump for the introduction of pure 

C02. Pure C02 mixed with anaerobie digester flue gas serves as a case 

with significant cost reduction possibilities. The use of unpurified power 

plant flue gas would most likely require deeper sumps. In addition, unless 

the power plant is actually within about 1 km from the pond system, the 

transport of dilute C02 becomes too expensive 121, Thus even if power 

plant derived gas is used to serve multiple large pond systems 193, it may 

well have to be purified for transport. 

The shallow depth of the sump is still considered adequate due to the 

flexibility provided by gas recycle. The introduction of the C02 will be 

controlled by pH on an on/off basis. Due to the lag time for return of the 

water to the carbonation station, 2.5 hours for an eight hectare pond, the 

low limit pH set point must allow for storage of enough C02 to meet the 

maximum demand for two transit times. At lower demand the upper pH reached 

in the pond nil1 not be as great as when the demand is high. Thus the flow 
rate of C02 must be able to meet the expected averaga hourly demand, ~hich 

ray change over long time periods (seasons). An alternative nay of 

controlling C02 input is to control the flow rate of gas so that a 

specified amount of carbon is stored. This could be accomplished with a 

microcomputer controller, programmed to calculate or determine from a table, 

carbon storage as a function of pH change. One would want to use such a 

system in situations where the alkalinity is low, requiring many carbonation 

stations per unit area. Such a scheme would preclude installing more 

stations than needed to meet the maximum hourly demand, i.e., only enough 

carbon is needed for one as opposed to two transit times. 

3.8 EXPERIMENTAL SYSTEM DESIGNS hND TESTS 

The experimental system is designed to allow determination of the carbonation 

parameters and design specifications needed to remove most of the uncertainty 

that now exists, In addition, several of the alternative types at 

carbonation systems described above will be constructed and tested. Yet the 

primary method is still considered to be shallow rumps with pure C02. 

Tests will include mea~urement of overall transfer ed+icieney, in both 

uninoculated medium and algal suspensions, as a function of aparger type, gas 

flow rate, gas to liquid flowrate rat.io, sump depth, and pond DO. DO removal 

will also be aeasured. Covered carbonators with smooth and rippled surfaces 

will be tested for transfer ef+iciency as a function af covered area,. 

hydraulic slope under the cover, and bleed rate. If necessary gas recycle 

will be tested in sumps as well. 
SECTION 4.0 

ANALYSIS OF MIXING SYSTEM 

4.1 OPEN CHQNNEL FLOW 

Some form of mixing is required to maintain cells in suspension, to prevent 

thermal stratification, and to disperse nutrients. The most widely used 

formula for open channel flow is the Manning's formula: 

where: V = velocity, meters/sec 

Rh = hydraulic radius, meters (= depth for wide channels) 

S = hydraulic slope = head loss/unit length 

n = Manning's roughness, sec meters'0a3 

For a given velocity and channel length, the equation can be rearranged to 

solve for the head loss: 

where: h~ = head loss, meters 

L = channel length, meters 

Typical values of n are 0.010 for very smooth surfaces, 0.014 for unfinished 

concrete, 0.017-0.025 for srooth earth (canals and ditches), 0.029 for 

gravel. A value of 0.018 was used in the head loss calculations for the 

large scale ponds, These ponds will be lined with graded crushed rock, 

rolled to a smooth finish. The mixing power requirement is given by: 

where: P = power, watts 

A = pond area, meters2 

e = overall mining system efficiency 

Note that the power varies as the cube of the mixing speed, and actually 

increases slightly at lower depths. The efficiency term includes both the 

hydraulic efficiency of the pumping device and that of the drive. Overall 

efficiencies can be a high as 70% for large centrifugal pumps, whereas 30-40% 

is more typical for paddle wheels or airlift pumps. 
4.2 PADDLE WHEELS 

Paddle wheels have emerged as a preferred method for mixing high-rate ponds 

for the following reasons: (1) They are well matched to the pumping 

requirements of high-rate ponds in that they are high volume, low head 

devices (i.e, high specific speed); (2) Their gentle mixing action minimizes 

damage to colonial or flocculated algae, which inproves harvestability; 

(3) They are mechanically aimpie, requiring a minimun of maintanence; (4) 

Their drive train can easily be designed to accamodate a wide range of speeds 

(high turn-down ratio) without drastic changes in efficiency; (5) They do not 

require an intake sump, but simply a shallow depressien for maximum 

e+ficiency, Some of the disadvantages are: (1) The paddle wheel itsel+ must 

be custom designed; (2) They are large relative to other types of mixers, 

especially at higher heads; (3) They are fairly expensive, though not 

particularly so for a low shear type pump, (4) For practical purposes, the 

maximum head is limited to 0.5 meters. This would only be a constraint in 

very large 020 hectares) ponds. or at high 030 cm/sec) velocities in 

moderate sized ponds, 

The two primary conpetitors for pond mixing are air lift pumps and Arckemedes 

screw pumps, The air lift pump has a lower initial cogt, but is generally 

considered to be a low efficiency device, Actual e9ficiencies appear to be 

very design specific, although theoretical efficiencies (see Section 4,s) are 

comparable to paddle wheels. In practice, the potential ebficiency of paddle 

wheels are probably greater. about IOX of the losses in paddle wheel systems 

can be attributed to the variable speed unit, which may not be necessary in 

thslong run. Air lift pumps probably produce higher shear forcer than 

paddle wheels, which could interfere with aut~floccualtion. The hrchemedes 

screw pump has been successfu~ly used far high rate pond mixing, but has a 

higher first cast and requires an intake sump. At high heads. 00.5 meter), 

the screw pump may be more economical than paddle wheels, 

Although paddle wheels are chosen in the large scale system design, the 

experimental system will include one 50 mZ pond nixed with an air lift. 

This will allow studies of combined mixing and carbonation as outlined in the 

next section. The optimization of mixing systems, although of interest, is 

not as critical a technical issue as harvesting or apeeies control, 

The actual design of the paffle wheels is covered in Section 7.3. 
4.3 GAS LIFT MIXING 

Gas lift mixing is an alternative to paddlewheel mixing which doesn't require 

large. custom fabricated mechanical parts. It is an interesting option in 

systems for which carbon is supplied via an in-pond sump due to the potential 

for combining the carbonation and mixing systems. In this section, gas lift 

is analyzed in its own right, but is also related to the carbon demand of the 

svstem. When flue gas is used for carbonation the lift mav be derivable from 

the carbonation alone for part of the time, but most likelv an air supply 

system would need to be available to substitute for the flue gas when carbon 

demand is low and during the nighttine. When pure C02 is used, 

supplementary air would alwavs be required. 

The basic relations needed to analyze gas lift mixing are derived in Appendix 

1 Two of them are used in the following discussion and are thus 

reproduced, The efficiencv of the gas lift is given by, for adiabatic 

compression of air: 

Cpe is an averaqe correction factor for compression of air with depth 

g is the acceleration of gravity, 980 cm/s/s 

ho is the depth of the sump in em 

VL is the liquid velocitv in the sump in cmls 

VB is the averaqe rise of the gas bubbles relative to the liquid in cm/s 

H is the lift in cm 

~~~~~12 is the total friction loss for liquid entering, traversing and 

leaving the sump 

Em, is the compressor motor efficiency 

Ed is the dynamic efficiency which covers losses due to the irreversible 

nature of the real compressor and is taken equal to .7 

)( i 5 the theoretical adiabatic work of compression of the gas~cm3 

K = Cp/Cv = 1.4 for air 

nTR =(1,210x10'~ mol OK) (8.31~107 erg/sol OK) = 1.012~10~ for 1 

cm3 gas entering the compressor at 1 atm at any temperature. 
The lift is equal to the aas hold-up times the sump deoth minus fluid flow 

For shallow sumps, (10 meter or so, Table 4-1 shows that the efficiencv 

doesn't change with sump death for constant ratio o+ qas and li~uid 

velocities. For moderate liquid velocities, ail terms in equation 4-1 are 

nearlv equal to unity except for the efficiency factors and the velocitv 

ratio term, Thus the efficiency is q~verned by the velocitv ratlo. Table 4-2 

shows the overall efficiencv as a function of liquld velocitv. Gas bubble 

rise velocity was taken as 30 cm/s which is consistent for a situation where 

the flow rate of gas is not expected to be verv low, The efficiencv is only 

25% at the design liquid velocitv oi 20 cmis. Increasing this to 40 cm/s, bv 

narrowing the sump to baffle distance to 10 cm, increases efficiencv to 

34%. Further increases in efficiency require even hiqher liquid velocities 

(relative to gas bubble rise rate, which could be attained by directina pond 

channel flow into a shallow sump leadinq inta a set of draft tube entrances. 

The liquid velocitv increases linearly with the ratio sf channel cross 

sectional area to total draft tube cross sectional area, If this option is 

chosen then the efficiency can be much hiqher, Usually, however, large 

veioclties are used for svotems with very large li+t, because the velocitv 

head, which is significant at high velocity, is easily lost upon exit +ram 

the draft tube. 

The lift is determined by the ratio of gas and liquid +low rates through the 

sump as well as the ratio of the velocities. The two dependencies on 

velocitv ratio act toqether in that detreasinq the ratio of qas to liquid 

velocities, increases both the efficiency and the lift, Table 4-3 gives the 

efficiency in terms of liquid velocity and lift for a system with three draft 

tubes. The fluid losses are significant when the liquid velocity exceeds 100 

rm/s. 
Table 4-1. Effect of Sump Depth on Air Lift Efficiency 

1 ,954 

1.5 ,934 

3.0 ,966 

5.0 ,816 

0.0 ,740 

10.0 ,699 

SO. 0 ,365 

100.0 .24S 

Table 4-2. Gas Lift Efficiency as a Function of Liquid Velocity .............................................................................. 

* All other efficiency factors a~sumed equal to .9x.7. .95 for shallow 

sumps. Velocity head losses neglected. 
Table 4-3. Lift and Efficiency of a Draft Tube hir Lift System 

Area ratio 2.5 5 i 0 25 

Pipe D, cm 120 85 bO 38 

Lift, C(A 20 20 20 20 

Tube rise length, cm 130 120 100 95 

Efficiency. X 38-36 45-36 43-24 26-6 

For three draft tubes 

Ratio of gas to liquid flourate = .3 

Ed€,, .7x.9 = m63 

This assuaes a flared entrance, one regrented 9a0 bend, smooth pipe, and a 

total draft tuba length of about 200 em. 

The range in lasts and in efficiency corresponds to OX or 100% lass of the 

velocity head, 
The combination of gas lift nixing and carbonation requires matching the 

mixing system performance to the constraints set by the carbonation. As 

shonn above, the air lift efficiency increases with increases in liquid 

velocity. However, the injection efficiency of C02 increases only with gas 

bubble rise time which decreases as liquid velocity increases unless the 

height of rise is made greater. As an example consider narrow, long draft 

tubes into which the channel flow has been directed. he liquid flow rate 

increases in proportion to the area contraction ratio. This increase leads 

to a shortening of the time a gas bubble stays in contact with the liquid and 

thus a decrease in the overall transfer efficiency, unless the tube length is 

appropriatley lengthened. The degree of difficulty encountered in trying to 

optimize a combined gas lift and carbonation system, depends on the distance 

which must be bridged between the initial configurations and requirements of 

each. With pure C02 the lift attainable was much lower than required to 

mix the pond while with flue the lift was much greater than necessary. When 

carbon is recycled from digester flue gases mixed with pure C02, a good 

match is achieved between transfer and mixing needs during times of maximal 

carbon demand. 

When purified C02 is used as the gas for mixing, the total flow rate of gas 

is restricted to that required to carbonate the pond. It was concluded in. 

Section 3.0 that even for an 0 hectare pond with 43m wide channels, the gas 

flow rate would be low enough to attain a transfer rate of 25%/s and a gas to 

liquid flowrate ratio of about .02 for sumps without recycle and ,056 for 

shallower sumps with recycle. The former sumps were 4.2 m deep the latter 

only 1.5 m deep. The lift provided by these configurations was only 4 em. 

Only by increasing the pond size draaatically (and also increasing the carbon 

storage capacity of the medium) can the lift attainable be increased faster 

than the lift required. That is, if the pond area is increased X fold, 

maintaining the same length to width ratio, the ratio of gas flow to liquid 

flow increases by xli2, This increases the lift. The lift is also 

increased by increasing the liquid velocity, accomplished by adjusting the 

baffle placement. Hany workable configurations are possible. For example, a 

40 hectare hectare pond could be mixed at 20 cm/s by pure C02 sparged into 

a 5.5 r deep sump, when C02 demand is highest. At other times, air would 

be needed to dilute the C02. Since the efficiency of such a setup would be 

35-40% and air would be required about 75% of the time, the overall power 

requirement would be about the same as with a paddlewheel mixing system. For 

smaller pond sizes the mismatch between lift needed and pure C02 required 

for carbonation is too great. If long draft tubes are used, the rise time of 

the bubbles still needs to be 12 s for 95% stripping efficiency. The tubes 

would need to be 20 m deep (long) and have an area of one tenth of the 

channel cross section to provide a lift of 20ca. 
With flue gas, as with dilution of the C02 by air, the lift increases due 

to the increased flow. It can be assumed that the increase in gas flow rate 

would lead to an increase in average bubble size and hence an increase in.the 

depth needed to rtrip COp efficiently. For flue gas, at a maximal average 

carbon demand of 0 gn/m2/hr, the lift attainable in a 6.2 a deep sump (00% 

injection efficiency) is over 74 em. The gas flow could be lowered by 

carbonating 18-24 hours a day into a medium containing sufficient alkalinity 

to minimize pH fluctuations in the upward direction during the day and 

downward during the night. This lowers the lift to 39 em, about twice that 

needed, The most promising possibility for combined precesses would be to 

supply the carbon as flue gas over 24 hours during the high productivity 

months but only over 12 hours when productivity is lower, During these times 

air would substitute for the Clue gas at night, when mixing speeds could be 

lower, reducing the power input. Since the cost o+ transporting the flue gag 

to the site includes the cast of pressurization sufficient for injection the 

overall power casts would be low. In order to reduce the lift enough, the 

baffling would need to be arranged to lower the liquid velocity in the sump 

to, say, 10 cm/s. Then, an eight hectare pond could be mixed at 20 cm/s by 

flue gas in a 5 m deep sump when demand for CU2 is (averaged aver 24 hours) 

2 qa/n2/hr. The airlift efficiency would be low, about 15-20% and the deep 

sump required would be a substantial capital cost and in increased 

maintenance cost, but nu additional cost would be incurred for mixing p6wer. 

Of course the power plant needs to be very close to the pond system to 

transport it unpurified. 

Given the uncertainties in the parameters +or both carbonation and gas lift 

taken alone, design and cost estimation of a combined system must await the 

results of the experiments proposed. A configuration which allows economic 

use of C02 for gar lift nay be possible, but it aust be kept in mind that 

carbon is the most expensive input into an algal biomas~ p~oductian ry~tem, 

Any systen for combining air lift and carbonation rust use the C02 with the 

highest efficiency, essentially as high an efficiency as carbanation alone 

~ould achieve. 

4.4 HIXING SYSTEH SPECIFICATION 

For the 1000 acre system, both paddlewheel and airlift mixing. systems were 

designed. The former requires twice the capital to construct as the latter, 

but there is more experiencs on nhich tu base its efficiency, AB discussed 

in Section i1.0, the impact of this eost difference on production costs is 

small, The airlift system is comprised of three draft tubes, each 2 m long, 

as described in Table 4-3, The calculated efficiency for this configuration 

was the same as for the paddlewheel system, about 40%. However, confirmation 

of this estimate, from the experimantal system, is necessary. 

No specific design is specified for a combined gas lift mixing- carbonation 

system. The gas transfer parameters are not known well eneugh to formulate a 

meaningful design at this time. Again, the impact of capital cost savings is 

minimal , 
SECTION 5.0 

ANALYSIS OF HARVESTING SYSTEMS 

5.1 INTRODUCTION 

Harvestinq algal biomass from dilute suspension (.uS-.lX) is ususallv a two 

step process: a primary concentration step which reduces the volume o+ water 

20-50 fold and a secondary step, usuallv centrifuoation, which further reduces 

the volume 5-10 fold. The capital and operatinq costs ot industrial 

centrifuges are so high that it precludes their use without the in~tial 

concentratinq step. In special circumstances, as in the harvestina of 

Selr~i~!g with screens, only one step 1s necessarv, This is due to the hlqh 

value of the algal biomass in this case, as well as to the larae size o+ the 

filaments and the manner in whlch they pack on screens whlch allows hiqh flow 

rates ot water. An inclined screen or vibrarinq screen 19 used. Generally, 

however, a harvesting process must be able to concentrate varled types of 

cells, especially when the harvester effluents are to be returned to the 

qrowth ponds. Any organisms which the harvesting process fa115 to remove from 

the recycle stream, will be qiven a potentially significant competitave 

advantaqe in the growth pond Clll. Only in rare circumstances as the growth 

medium so selective for a chosen oraanism that this advantage will not result 

in dominance of an unwanted species, Thus, the harvesting process must not 

onlv remove the desired organism, but also any potential contaminants. 

Four prlmary harvesting methods were examined: microstraining, belt 

filtering, flotation with float collection, and sedimentation in two stages. 

Each of these methods discriminates on a size and/or density basis in 

performing the biomass separation. The strainer and +liter are, of course, 

slze discriminators, with performance characteristics that improve as the 

algal particle size increases. However, the filter is also more efficient +or 

oraganisms which form a mat, thus decreasing the effective pore size. 

Sedimentation and flotation devices collect biomass on the basis of both size 

and density. Since the operation of each of these devices becomes tenuous for 

small cells ((6-8 microns), and since the harvester must, in a strict sense be 

universal in its removal capabilltiy, some universally effective method is 

required to transform all cells into a form which can be removed by the chosen 

collection device. As will be shown, the maJor cost of a harvestinq system 

lies in this trans+ormation process. 

5.2 CAPITAL COSTS OF PRIMARY HARVESTING DEVICES 

The four types of primary harvestinq devices vary considerably in their 

installed capital costs. Conventional dissolved qas flotation units cost 

about .25 million dollars per million pallons per day ot suspension. The 

costs of microstrainers, belt filters, and settling ponds, on the same basis 

are ,09, .12, and .05 million dollars. Nevertheless, it no pretreatment of 

the cells were required to 1) make each devlce work effici,ently. and 2) make 
each work un~versally, the ca01ta1 cost differences would not tran5late to 

large dl+f erences in annualized pr~ductlon cost. The most expensive device, 

the dissolved oas flotation unit, would add 50% to the capital costs o+ the 

system, but these only contribute LO-25% of the annual production, The 

important point is that none of the collectors functions either well or, more 

importantly, universailv on ~ts own. H rouqh calculation shows that I+ 

conditioner is added to the suspension prior to primary harvestinq, +or eacn 

cent ot cond~tioner added per kg of b~omass harvested, the production cost 

increases by about 10%. The concius~on is that while cost di#terences do 

exist amonq various prlmarv harvesting devlces, the impact a+ these 

di+terences is small compared to the potentla1 Impact of the co%t ot 

pretreating the biomass so that an; or a11 of the devices are, in fact, 

useable, 

5.3 PRETREATMENT OPTIONS 

There is ample experience wrth chemical flocculation o+ suspended solids to 

imprave the separation characteristics. T.he thrust o+ recent work with 

chemical #locculants is to manu#acture new chemicals, or devise new 

combinations of known chemicals, which reduce the dose and cost of the 

+iocculation step, rhis subject will not be reviewed here, except to say that 

work on the use o+ flocculants ie advancing due to the recently acquired 

capabi iity of manufacturing very high molecular weiqht pslymers, If enough 

fl~cculant is added, the deslred characteristics can be induced. At present, 

the use ot standard chemicals, like iron chloride, would require about ,75-iwfl 

per gm biomass, or about 4-6 cents per kq biomass. Thus an alternative to 

conventional flocculants is required. 

One alternative 1s to condition the algae without addino flocculants. 

Nitrogen deprivation is generally recognized to enhance the sedimenting 

characteristics of alqae, although data in the literature is not applicable to 

the situation here. Sedimentation rates were generally not measured and the 

algae were usually starved for prolonged periods of times, well past anv 

active growth. H report, by one of the.authors, an the ,other hand presents 

data supportinq the hypothesis that normally non-settling, unicellular, 

flagellated organisms (hfiaiigLlar can be made to settle at rates hiqh enough 

for collection in settlinq ponds, by short term nitrogen deprivation L4I. 

This process was found to work with ail but the smallest orqanisms (2-5 

micron) and even with an ~~~~h~~~~~,~er containing 60% lipid. But the 

question of universality of the process still poses a proslea, 

Anuther alternative is to utilize the supersaturated oxygen to tloat the cells 

to the surface of the pond, to a foam collector. The advantage o+ tnis over 

sedimentation lies in the fast rate 04 rise due to the digsolved gas coming 

out of solution, However, the universal~ty of this approach is, agaln, open 

to question. 
Preliminarv experiments have been pertormed, at Mirrobiai Products, Inca, 

usinq hioh Charge denstiy, high molecular weiqht polymers to flocculate a test 

orqanlsm in saline medium, A ChiorqlLg-gp, was used to demonstrate that even 

small cells (3-5u1 can be clarified bv simple sedimentation when first 

pretreated with the polvmer. The media used to qrow the alqa, to a densitv of 

500 pom oraanic dry weight, contained 32 opt TDS, mostly as NaCl, hlkalinitv 

was 30 mH, pH was 8.45, and hardness was 5mM. The cells were nltroqen 

su+ficient. The dose ot polymer necessarv to etfect complete claritication 

wlth an adequate sedimentation rate oi the flocs 050 cmlhr) was lppm polvmer 

Per 5uU ppm biomass. this is the basis tor the desian assumption used in this 

report. The experiments were ot a verv preliminarv nature, and not 

necessarilv ootimized, However. nor have they Peen validated on a laroe 

scale. havinq Peen pertormed In jar tests with 250 mi ot suspension. The 

universalltv ot the approacn has also not been demonstrated, but the tvpe ot 

oroanism Used provided a strinqent test. It 1s the oplnion of the authors 

that such an aporoacn is hiqhlv promisino, but use on a larqe scale must be 

accompanied by continual monitorinq ot the eSiectiveness ot the tlocculation 

as oond conditions chanpe, Ihe type and mlxtures ot podvmer used mav nave to 

be chanqed on an onaoinq basis to avoid selecting tor organisms whleh elude 

entrapment by a particular +locculant. 

The primarv method of harvestina the biomass produced in the larqe scale and 

experimental systems is specified as pretreatment wlth polymer followed bv 

sedimentation in a deep pond. lhe nitroqen depleted condition of the biomass 

should, in the experience of the authors, promote flocculation and 

sedimentation. The slurry trom this pond is then further concentrated in 

thickeninp tanks ot much reduced volume. 

fhe budqet +or the proposed experiment has Sundr specifieallv for tastlnq and 

monitorinq polymer induced harvesting. 
SECTION B.0 

SUMHARY OF ANALYSIS AND IMPLICATIONS FOR SYSTEM DESIGN 

b.1 WATER CHEMISTRY 

The characteristics which are desirable in a water resource are low hardness, 

an excess of alkalinity over hardness, and low TDS (but still too salty 9er 

conventional agriculture), Any hardness which cannot be removed by the 

already present alkalinity (by equilibration with the atmosphere) casts f.005 

per kg algae produced per 100 ppm hardness to be removed. Lower TDS results 

in lo~er net water usage, although the difference becomes less as the 

blowdown ratio (= recipricol 04 salts concentration faetor) decreases. 

Considering a TDS of 40 ppt as the practical upper limit for productive 

cultivation, a seawater system uses 4.5 times as much water as a system with 

an input water TDS of 4 ppt, for the same rate of evaperation. 

The water chemistry determines the carbonation system specifications and the 

pH range of operations. The lower limit of pH is determined by outgassing of 

C02. Since C02 is the single most co~tly input to the system, outgassing 

must be minimized. With low to moderate mixing velaeities 113-20cm/s) and 

proper specification of the low pH limit, overall loss of carbon due to 

outgassing can be kept to less than 5% of the carbon incorporated into 

bioflass. The upper limit of pH, for properly conditioned waters, is 

determined by the physiological response of the algae to dissolved Cap 

concentration. This is unknown, but a safe level (one that shauld not lead 

to substantial loss of productivity) is 3-b times air saturation or 30-6QuM. 

The carbon storage capacity of the medium depends on the alkalinity and the 

pH range of operation. It determines the number of carbonation stations 

required for a pond of specified size, depth, and liquid velocity, or 

alternatively, the mrximua pond sire serviceable with one C02 tati ion. the 

details of interaction between alkalinity, pH, and C02 concentration are 

discussed in Section 2,O. 

All of these considerations combine to determine water resource requirements 

and pH of operation. The combination used for the 1000 acre design are the 

following: water resource is Type IJ at 4 ppt TDS with excess alkalinity 04 

4 meq/l, nu water conditioning chemical costs, and gight fold evaporative 

concentration resulting in a aedium with TDS = 32 ppt, alkalinity of 32 

meq/l, and a pH range for operation not to exceed 0.0-9.0. Water usage 

calculates to (assuming an average evaporation rate of .01m/n2/day) 11.5 

liters /n2/dry or 16.5 x a3/400 ha/yr. When this water is abtained 

from wells of 50 II pumping depth, the electrical energy cost O,Ob5/KW-hr) is 

$220,000 or Slblacre-ft. 

In tho operation of the experimental system, the large scale water 

spee'ification will be simulated by a mixture of the two types of waters that 

are plen-tif'ul on the proposed site: 5X Salton Sea water, preconditioned by 
addinq sodium carbonate at a cost of $300 per acre per year or $450/acre-ft 

used and 95% well water available at 1700 qpm. The cesposition of these 

water resources is tabulated in Section 10.0. 

6.2 CARBONATION 

The C02 required to produce algal biomass with SOX lipid is 2.2kg/kg 

biomass. Even at the lowest extrapolated cost of C02 E91, the cost of this 

input comprises over 50% of the annual production cost. Thus the most 

important aspect of the design is the efficient use of carbon. In this 

subsection, the methods of transferrinq C02 into the ponds are summarized. 

Recycle of carbon in particular, and all nutrients in general, is discussed 

in subsection 6.3 below. 

Tno typms of carbonators ~mrm analyzed8 covered aria carbonators and 

carbonation sumps, The former type may be feasible when pure C02 is used, 

the latter is feasible for both pure C02 and flue gases. The practical 

efficiency approaches 93% for stripping a pure C02 lnput gas and 80% for a 

flue gas input. 

Gas-liquid mass transfer was analyzed from first prineiples and evaluated in 

light of the large body of biochemical engineering data that has been 

accumulated. Nonetheless, a great uncertainty remains in the trans9er rate 

that is to be expected in large scale algal systems. In the sump carbonation 

problem, the transfer rates were shown to depend on the average rate of rise 

of bubble swarms, which depends on the distribution of bubble sizes. This is 

determined by sparger orifice, gas flow rate, and bubble coalescence factors 

(salinity, surfactants, turbulence). The rate of removal par unit length of 

sump depth can be much faster than would be expected if the bubble swarms 

travel through a considerable per cent of the sump depth before the 

equilibrium size distribution is attained and/or if the equilibrium bubble 

size is small due to anti-coalescence factors. Although the empirical data 

from C02 transfer into algal ponds is sparse, and based en small systems, 

it has been found generally that transfer is +aster than an equilibrium 

analysis would predict in the absence of some of the accelerating factors. 

The covered area carbonator was analyzed in terms of surface renewal theories 

of gas-liquid transfer with parameters determined using empirical 

correlations developed for stream and channel aeration. Again, however, 

experiments on transfer through the surface of algal ponds, yielded rates 

significantly falter than were predicted. Thus with either carbonation 

method, the design specificatione cannot be fixed with great precision until 

rvasults from carefully designed experiments are obtained. At present the 

following options are specified for the 1000 acre system. 
1 "Ripple" covered area carbonator covering 2% of the pond area for pure 

C02, 90-952 efficiency. 

2. 1.5 m deep carbonation sump for pure C02, 95X efficiency. 

3. 2-3 m deep sump for flue gas, with carbonator gas recycle flow of 

100-200%, BOX efficiency. 

4. 2-3 r deep sump far the mixture of pure C02 with digester flue gas, no 

recycle, 90% efficiency. 

0pt.ion 2 is used in the Base Case economic analysis, but option 4 has the 

mst potential +or reducing lipid production costs. 

The experimental system will be used to determine the carbonation 

parameters. Both covered and sump carbonators will be tested, In addition, 

the effect of oxygen desorption, during carbonation, on the efficiency of 

C02 input will be determined. These test3 will also serve as the baair for 

the decision as to whether is ts feasible to remove dissolved oxygen from 

solution, and thereby relieve its potentially inhibitory affect on 

photosynthesis. - 

6.3 NUTRIENT RECYCLE 

Since carbon is such a significant input into the systcn, recycle a# the 

carbon left in the residue from the lipid extraction process was considered, 

It was concluded that anaerobic digestion of these residues in a covered 

lagoon would allow recycling of 34% of the algal carbon, reducing carbon 

~nput from 2.2kg/kg algal biomass produced tc 1.45kg/kg. This recycled 

carbon is considered available at no cast, in terms of operations, due to the 

electrical energy derived fron the inethane gas produced which is used to 

pressurize thr recovered C02 for in~ection into the pondB. The capital 

cart of the digmrtor-generator rystea is included in the economie evaluation 

of thie option, The flue gas obtained from the coabustion of the digester 

gases is 14% COZ. Wnen colbined in the required volurctric proportion with 

purified Cap, the rerultrnt mixture is 35% C02. This will be more 

expensive than purr CO2 to inject into the ponds but leer axp~nsive than 

flue gas. The extra expense comes as a capital cost of constructing deeper 

carbonation sumps, and possibly use of recycle. Since operating costs, 

especially the cost of carbon, will be shown to dominate annual costs, these 

increased capital expenditures have little impact on production costs. The 

30% savingr in C02 input ha5 significant impact. 

In addition to carbon, much of the nitrogen and phosphorus remaining in the 

extract residues can be recycled. The potential for recycle is even greater 

than for carbon, Table 6-1 summarizes the elemental balance for C, N, and P 

in the anaerobic digestion process. The partition of the ,elements in the 

liquid portions of the digester can only be roughly estiaated at the present 

time, but it is evident that the potential exists for these eleaents to be 

recovered to a significant extent. 
Table 6-1. Nutrient Partitioning in an Anaerobic Lagoon 

.............................................................................. 

Digester Compartment X of Total C X of Total M Y. of Total P .............................................................................. 

Gas Phase 6 5 0 0 

Liquid Effluent 18 7 5 5 0 

Sludge 

In constructing Table 6-1, it is assured that 65% of the carbon entering the 

digester is gasified (39% to methane,26% to C02), that the nitrogen is 

predominantly solubolized to ammonium, and that the phosphorus partitions 

evenly between the liquid and sludge fractions. The gas and liquid effluent 

fractions are recyclable. Table 6-2 gives the recycled nutrients as a per 

cent'of the total, using the assumptions that the algae is 60% carbon, lipid 

is 70% carbon, soluble nutrients are recycled with 100% efficiency and the 

gaseous carbon is utilized with 90% efficiency due to losses upon injection 

into the pond. 

Table 6-2. Recycle of Nutrients 

.............................................................................. 

Nutrient Kg Recovered/Kg alg. Kg Lost/Kg alg. Net Input Kg/kg 

Carbon (.25~.18)+(.25~.65~.9)r.19 (.25~.17+.35)/.9=.44 .44 

Nitrogen ,04x, 750.03 .04x.25=.01 . 0i 

Phosphorus .005x.S0=.0025 ,005~. 5Q=. 0025 ,0025 

Recycle thus lowers the nutrient demand, per kg algal biomass produced, to 

1.6 kg for carbon (from 2.4 kg), to .01 kg for nitrogen (from .04 kg), and to 

,0025 kg for phosphurus (from ,005 kg). 

A covered lagoon digester and engine generator is specified for the 1000 acre 

system. If budget constraints allow, a test lagoon will be constructed for 

the experimental system, but without combustion of diqestor gas, as engine 

generators are disproportionately expensive at such a small scale. The 

recycle of N and P will be determined and the use of digester flue gas can be 

simulated by diluting pure C02 with air. 
6.4 NUTRIENT LOSSES 

[he loss o+ nutrients trom the svstem is a potentiallv signrficant problem 

unless care is taken in the desicn and operation a+ the svstem to prevent sucn 

losses. Ihe loss of carbon, primarily as CU2 to the atmosphere, has been 

discussed extensively in Sections daU and 3.0, In the base Lase design, to be 

specitled In detail in Section 10.0, the pond depth is 20 cm and the mixinq 

velacitv is 20 cmrs. Shallower depth and higher mixino velocitv both act to 

aqgravste outgassing, which becomes about 2.5 times qreater if depth is 

halved and mixinq velocitv increased to 50 cmfs. In addition, carbon storaqe 

in the medium, on an areal basis, decreases with decreases 1.n depth. For 

media ot the same alkalinity and the same ranqe of drssolved COZ 

concentration, the shallower, taster mixed pond must be ouerated in a narrower 

pH range to achieve the same etficiencv ot use ot carbon. I'his means that 

mare carbonation stations are required per unit area ot orowth pond. 

Ammanla IS another volatile species when present in unionized torm. in fresh 

water, the pK o+ the ammonium-ammonia acid-base ovstem is 9.5, l4ctivitv 

coe+ficients decrease as Ionic of the medium iuncreases. In the mixed acrditv 

constant convention (protons expre5sed in activity, other saecleg expressed in 

concentratlonj the pK for the ~onization of ammonium increases. In the 

approximation that the activitv coefflclent +or ammonium is the same as for 

bicarbonate, the pK in a medium with the ionic strength of seawater is 9.85. 

I+ all of the nitraoen demand of the algae is introduced a5 ammonia at the 

beglnnnlnq o+ each batch cycle [a worst case scenario) then the concentration 

of total ammonia-nitrooen would be about 2.5mM. fit pH 8.5 and 9,0, the 

traction of this total that is present a5 ammonra is, respectively "04 and 

.12. With a mass transfer coefficiet of ,06 m/hr tor transter throuqh the 

suriace, the lass o+ ammonia is, at the two pH's, ,03nM/L/hr and .09mfl/L/hr. 

This 1s low com~ared tu the rate of nltroqen uptake by algae, However. i+ 

aqain the pond depth is halved and the mixinq velocity is increased to 30 

cm/s, the rate of outaassinp is five times a!! high (the volumetric rate of 

uptake by algae is also twice as qreat), SO the outgassing losses oi carbon 

at low pH combined with the outgassinq losses of ammonia at high pH act to 

squeeze the pH of operati~n down, and more severlv so with shallower, faster 

rnlxed pond designs. In the Base Case, nitrogen losses were specified at 30%. 

which should be amply conservative even when the autgassinq during carbonation 

and airli+t is included, 

6.3 NIXING SYSTEM 

three options were analyzed +or mixinq the ponds: paddlewheels, airli+t, and 

combined carbonation and mixing in sumps. The overall efficiency of the three 

methods are, respectivelv 40%,40%, and 20%. The lower efficiency of the 

combined system is due to the need to optimize for efficient transhr a+ 

C02. However, the net power consumed in this option is only 35% hiqher than 

the other two because the C02 cost includes power for compression, and air 

use i's on1 y supplementary, The paddlewheel system is twice-as capital 

intensive as the airlift svstem, The combined carbonation-mixlng svstetn costs 
almost as much as the paddlwwheei svstem because the sump used must be deee to 

insure efticient carbon utilization. 

The decision on which svstem, paddlewheels or airlift, is best suited for mlxinq 

algal arowth ponds, must await the results ot experiments in which an optimal 

desion for each has been tested. rhey are not actually beina compared on an 

equal basis in this report. The practical eftlciencv of the paddlewneel system 

is much better known, i.e., the dvnamic losses are more easilv factored into the 

analysis. Thus the 40% efficiency is most likely achievabl@. The alrlitt 

svstem, on the other hand, was evaluated from first prlnclples, wlth an ac-hgc 

tactor inserted tor dynamic losses. No airlift has been deslaned, to the 

authors' knowledqe, which both +its the appl~cation here and is scalable to 

laroe systems, The engineering experience with airlifts 1s based on much hioher 

lifts used in conjunction with difficult to handle materials or in air iift 

fermenters. The efficiency achievable in a pondln~ aplllcation is vet to be 

determined. 

Based on the literature, consultant input, and previous experience, a 

paddlewheel system thouaht to be structurallv sound and e9flcient has been 

desiqned. Several confiqurations o+ airlift, and combined qasltft-carbonators, 

are presented in Section 4.0. These confiqurations are merely plausible at tnis 

point. since the behavior ot bubble swarms in relativelv shallow sumps in saline 

water which may contain surfactants, needs to be empiricallv determined. Thus 

the proposed experimental system has been desiqned for the measurement oi tne 

relevant parameters. 

A novel type of mixinq system, applicable to very large systems, has been 

analyzed based on the design specifications of a hydraulic consultant. The fan 

pump has potentially verv high efficiency when pushang larqe flows, at low 

velocity aoainst relatively low head (a meter or more). Ulthouqh this 

alternative has not been included in the 1000 acre deslqn, nor the exparlmental 

system, it does open up the po~sibilitv of operatinq much laraer ponds than has 

been considered practical up to now. 

6.6 MIXING VELOCITY AND DEPTH 

The mixinq velocity and depth specified for the 1000 acre design are 20 cm/s and 

20 cm. These are considered sufticient to serve the respective purposes of 

keeping algal solids suspended and providing carbon storage in the medium. 

Although there is same evidence for enhanced produetivitv at increased mixing 

velocity and lower depth when devices are installed an the ponds to induce 

orqanized mixinq regimes t31, the evidence is not conclusive. This 

specification increases capital costs. stemminq from menufacturinq the airfoils 

used to establish the organized mlxing and trom the increase In both maxinq 

system costs (due to the hiqher rtixinq velocity) and carbonation station 

requirements (due to the lower areal carbon storage capacitv). In addition, the 

operating costs increase due to the increased power input for mlxsng, which 
~ncreases as the velocity to the 2.5-3 power and depth to the neqative li3 

power. CU2 utlllzation effic~encv also can be expected to decrease as the 

mass transter coef f iclent for outqasslng increases WI th mixina veloci tv 

increments and depth decrements (the surface turnover rate ~ncreases), Ihe 

potential ~mpractlcality of tnstallina airfolls at reasonable cost makes 

baslno the entire system design on thls tenuous. 

ihe experimental svstem is also designed for 20 cm depth and 20 cm/s mixinq 

velocity, although the system will be constructed with the flexibility to 

varv both, 

6.7 POND LINING 

Yome form of pond 11ninq 1s required to ellm~nate loss of water due to 

percolat~on, In the larqe scale dasiqn, the lin~nq specified 1s crushed rock 

over a clay sealer. fhls combination 1s ~nexpensive when the materials are 

not too distant +orn tha site, The major quest~ons to be investiaated during 

the proposed experiment a r e t h e deqrec of seahng that 1s achievable wlth 

thl~ linln~ and the etfect on mixinq power input and C02 outgasred. Both 

are expected to be somewhat qreater than with a plaetlc liner aue to tne 

increased roughness of the pond bottom. Slnce the rock is qraded and rolled, 

the anticipated rouqhness coefilcient is ,018 compared to verv smoothly 

applied plastic lining of roughness ,012. 

Plastic liners were considered but not chosen as a primarv design 

speci+ication due to initial cost, installation difficultv, maintenance 

pr~blems, and questions as to whether linings would perform as well as 

expected. The least expensive plastic lining would cost between $1.3-2.0 per 

m2 installed. However. these liners would need to be constantly under 

water to avoid photodearadation. In addition, the verv small thickness (10 

mil) predisposes such a lininq to developing small hales which leak. Rodents 

may also wreak havoc bv chewino through the liner. The high quality plastic 

hners cost $5.5 per n2. Althouqh performance goals would be much easier 

to achieve with expensive liners, problems with rodent damage could be 

serious. The hiqh capital cost of these liners, $23 million per 1000 acres, 

makes the economics of their use narqinal. It doubles the depreciable 

capital investment, but DCI only contributes 10-20% to the annualized 

production costs. If a plastic liner were required, +ew experts recommend 

the cheaper liner over the expensive one. 

High quality plastic llners are specified for all ponds In the proposed 

experimental svstem except +or the larqest ponds. In one a+ these .4 hectare 

ponds, clay sealer w~th a crushed rock overburden will be tested, The other 

will be plastic lined (hvpalon), Thus the performance of both options will 

be evaluated. 
6.8 HARVESTING SYSTEM 

Primarv harvestinq was evaluated in terms of devices for concentratinq the 

aloal biomass and in terms of the reliabilitv and universalitv ot each method. 

flicrostraininq and air plus DO flotation proved to be more expensive than 

usina a belt filter, which was analvzed as more expensive than simple 

sedimentation. It was noted, however, that the differences in costs, both 

capital and operatinq, would not translate into a larqe difference in the 

overall cost of producing algal bioaass(see Section 11.0). The most important 

conclusion is that none of the devices, in and of themselves, could be 

expected to be very reliable in the longterm. Each discriminates on the basis 

of size and/or densitv, which would eventually lead to a situation where 

organisms that eluded the primary collection would be given a competitive 

advantage in the qrowth ponds. 

It is necessarv to develop a means ot pretreating the biomass, with 

flocculants, so that all biomass 1s collected bv whatever device is used. 

Recent work with verv high molecular weight, highly charged polymers appears 

to be a promising method of accomplishing this. W given polvmer flocculates a 

wide variety of organisms from a given medium. In addition, a repetoire BC 

similar polvmer can be tailored, on site, to deal with chanqes In pond flora 

or simply changes In conditions that result in different flocculant needs. 

The conclusron IS that harvestina microalqae appears feasible but will require 

constant monitoring. Fhere does not appear to be one sinqle answer, in terms 

of chemical additrves, unless pond conditions are extremely constant. 

Final concentration of the biomass is accomplished bv centrifuoation. The 

cost of this step does depend on the device used in the primary concentration. 

Flows from microstrainers are expected to be five times those from settlinq 

ponds and flotation collectors. A belt filter concentrates, or is expected to 

concentrate somewhat more than the other methods. 

6.9 PRODUCTIVITY ENHANCEMENT AND SPECIES CONTROL 

Dissolved oxvgen accumulates to hiqh concentration in moderate to larqe ponds 

durino active growth of algae. Recent experiments C11 as well as a wealth of 

laboratory and limnological data implicate oxyqen as an inhibitor of 

photosvnthesis. The desorption of oxyqen is a problem which is not amenable 

to analytic solution in all but hiqhlv specified cases. It is a 

non-equilibrium, nucleation process which is specific to both the chemical and 

hydraulic characteristics of each particular situation. Thus the feaoibality 

of intentionally restricting DO levels to within prescribed limit2 will be 

tested empirically in the proposed experitnent. The results will be evaluated 

so as to suggest large scale approaches. It will also be necessary to measure 

biomass productivitv as a function of DO in order to determine the need for DO 

removal and the cost effectiveness of lowering it to a given level. 
finother posslbie productivitv enhancement method ~nvolves creatlnq conditions 

of orpanrzed mixins in the ponds, Several means ot accampllshina this were 

analyzed, includinq contaurtng the pond bottom to include +low obstacles, 

iavina rows of obstacles on the bottom, and usma arrtmls. None were 

determined to be attractive ln terms of ef+ectiveness of promoting the deslred 

fl~w patterns and/or in terms of cost. Until evidence to the contrary 1s 

firmly established, the assumption used in this report 1s that productivity is 

determined by climate, medium, and especially strain cultivated, Certainly 

the a+fect of recvcling the medium on lonqterm productivitv wlll be manltored 

in the experiment. 

Lonqterm species control is related to productivity. Strains used must be 

highly productive and competitive as well. Up to now, except in extreme 

conditions of medium composition (which results in low product~vitv) natural 

strains have dominated all outdoor pondinq systems. One advantage of 

producing carbohydrates instead of lipids is that all of these dominant 

organisms observed to date, accumulate the tarmer under nitroqen limntinq 

conditions. /4 comprehensive survey ot strains which accumulate lipid and are 

highly competitive as well is, however, just underway. 

6.10 EFFLUENT DISPOSAL 

Of the many technical, resource, and logistic obstacles which must be overeome 

for the proposed process to be success+ul, one has net received enough 

attention. Ihe blow down water represents a signi+icant disposal problem. 

With the specified blowdown ratio of 1/8 of the inflow, or 1/7 of the 

evaporative losses, the volume of water per hectare per year is over 5000 

m3. The mass of salts (predominantly NaCI) is over 150 Mt, or about 1.5 lit 

salt per Ht dry biomass. This water mass can be evaporated in ponds with an 

area o+ A4 hectare per hectare of qrowth ponds. These ponds need not be 

lined, since the precipitates will quickly seal them, Even sa they must be 

dredqed, +orminq salt "mountains" in short order. Either this salt must be 

stored as such indefinitely, or it must be transported to a d~spasal site, 

i.e., the nearest gulf or ocean. Thus an operating cost should be included 

for the transport of this material. The onlv wav to reduce the amount of salt 

produced, from open system5, is to utilize less saline water resources and/or 

to decrease the blowdown ratio. Assuminq that seepage and percolation losses 

are not persistent, the lower limit on blow down is set by the secondary 

concentration. If 10-20% solids is the flnal concentration be+orc processing, 

and ,005--1% solids are in the pond effluent the minimum blow down is 2% of 

evaporation, Unless fresh water is used, this mintmum is unrealistic. For 

practical purposes, if a water resaurce containinq 2 ppt TDS is used and the 

blowdown ratio is .04, then the volume of water and mass of salt coming out sf 

the system per hectare per year become 1600 e3 and 80 Mt or .75 Ht/Nt 

biomass. These are st111 large numbers. fi cost of $.0067 per kq of salt is 

assumed for the large scale system to transport the salts to a disposal slte, 

The orqanic matter that is not either a product stream or recycled back ta the 

growth ponds, must be dredged from the bottom of the anaerobic laaoon 

periodically. This sludge can be dried and disposed of on site. 
SECTION 7.0 

POND CONSTRUCTION 

This section examines the basis for choosing a particular pond design, and 

Presents specific details relating to its construction. Section 7.1 

discusses the various factors which influence growth pond size and geometry. 

Section 7.2 specifies the particular configuration chosen, and lists the 

design parameters of importance to pond construction. Section 7.3 presents 

the specific design options and their costs for each major element of pond 

construction. The high-rate pond concept, consisting of open, shallow 

channels in which the culture circulates, is used as the basis of pond design 

in this report. This chioce is based on both experience (of the authors and 

others), and on an analysis of alternative designs within the context of 

fuels production, where the cost constraints are extreme. It should be noted 

that within the basic high-rate pond franework, there is still ample room for 

innovation and cost optimization, as the analysis in this section will show. 

7.1 POND SIZE AND GEOMETRY 

The basic geometric parameters in high-rate pond design are pond size, number 

of channels, and length to width (L/W) ratio. The latter is defined in this 

report as the lenth of the center divider wall (i.e, the length of a single 

channel without bends) divided by the single channel width. In general, a 

single loop (two channels) is preferred from a hydraulic standpoint. If the 

pond is large enough, this configuration can take full advantage of a paddle 

wheel mixer (123. The choice of pond size and shape is driven by economic 

factors and the effect on other system elements, such as mixing and 

carbonation. A simple geometric optimization indicates that a large pond 

with a low L/W ratio gives the most pond area for the least wall length, as 

illustrated in Figure 7-1, for the case of twelve ponds in r side-by-side 

(shared walls) configuration. Since the walls are a significant cost item, 

and since other pond elements also show economies of scale, ponds need to be 

made as large as practical. The choice of L/W ratio must take into account 

the trade-off between minimizing wall length and other factors which affect 

costs. At low L/W ratios, the channel width increases, as does the cost of 

those elements related to channel width, such as aixing stations, 

carbonation sumps, etc. Once a tentative size and L/W ratio is chosen, the 

head loss (which depends also on velocity and roughness) can be calculated by 

Manning's formula, and evaluated relative to the proposed nixing system. The 

channel length may then need to be adjusted to fully utilize the capabilities 

of the mixing system. 

Figure 7-2 shows the cost of the growth ponds as a funtion of pond size for 

the range of 2-10 hectares. For each point, the number of ponds is adjusted 

to maintain r total system area of about 200 hectares, so the economies of 

scale indicated in the figure are a result of geometric factors rather than 
declining unit costs. (One exception is for laser grading, which has a 

slight scale economy built into unit cost function, since the cost depends 

somewhat on the channel width). The figure shows a marked increase in cost 

below 4 hectares, with diminshing returns above 10 hectares, Both the cost 

figures and shape of the cost curve are unique to the specific design 

presented in this section, and may not apply to other designs. A further 

point with regard to Figure 7-2 is that it includes only the cost of pond 

construction, mixing, and carbonation, and does not include harvesting, water 

or carbon supply, engineering, etc. 

An alternative to the conventional " r a c e t r a c k H c o n f i g u r a t i o n described above 

was suggested by Dr. James Harder of the U.C. Berkeley, as a method of 

generating circular flow patterns (secondary flowo), for cycling the culture 

in and out of the light with a minimum af head loss. fi low auund with 

sloping sides would be canstructed using conventional earthnoving equipment. 

The channel would then be built in a spiral pattern on the mound. This would 

produce a continuously sloped bottoe, as required +or shallan, mixed ponds. 

(Each channel would be later be graded flat acrorr its width if nscersrry). 

The inner and outer channels would be joined by an inverted siphon, with the 

mixing head provided by an large diameter, low speed axial flow pump ("fan 

pumpn), custom designed for the head requirements af the pond, The spiral 

con!iguration ray have distinct advantages in the construction of very large 

ponds 020 hectares), although the secondary flows are rinimal at large radii 

of curvature. It replaces the abrupt channel bends with a continuous gradual 

bend, eliminating the need for flow deflectors, and providing a more uniform 

mixing regime, Since it^ ohape is more compact than a long narrow pond, it 

nay better eonforn to a given terrain and reduce the initial rough grading 

costs. (However, the fine grading will likely be more difficult than with 

straight channels). Although the spiral configuration was not employed in 

the baseline design, it does deserve consideration, especially in the context 

of very large ponds. 

7.2 POND AND SYSTEM CONFIOURATIDN 

For the large-scale system a pond size of 8 hectares (19.8 acres), with a L/W 

ratio of 20/t was chosen. Key design parameters are listed in Table 7.1 for 

the individual pond, and in Table 7.2 for the 192 hectare pond system, 

eonuioting of 24 ponds as shown in Figure 7-3, Figure 7-4 shows r plan view 

of a single pond. The time required to complete one loop around the pond at 

20 ca/sec is about 2.6 hours. A single carbonation station wilt satisfy the 

carbon storage requirements, given the assumptions about water chemistry 

outlined in Section 2. Referring back to Figure -7-3, the 8 hectare pond 

takes full advantage of the economies of scale, without puahing the sire into 

a region of dimiehing returns, some of which are not readily quantifiable 

le.g. loss of operational flewibility, problear of solids deposition, etcl. 

Table 7-1 Pond Design Calculations - Single Pond 

DESCRIPTION 

Pond Area 

# of Channels 

t/W Ratio 

Depth 

Channel Velocity 

Manninas 'n' 

Paddle Eff. 

Drive Eff. 

PW Width/Chan Width 

Evaporative Rate (max 

Blowdown Rate (maxl 

Detention Time 

Wall Ht. (above grade) 

Wall Ht. (below grade) 

Sump Depth 

DESCRIPTION 

Channel Width 

Paddle Width 

Centerwall Length 

Single Channel Length 

Total Channel Length 

Total Wall Height 

Slope 

Total Head Lass 

Total Efficiency 

Hydraul i c Power 

Total Power 

Total Unit Power 

Velocity at Paddle 

Pond Volume 

Evap. Flowrate 

(alternate units) 

Blowdonn Flowrate 

(alternate units) 

Harvest Flowrate 

laltsrnate units) 

NAME 

---- 

AREA 

#CHAN 

L/W 

DEPTH 

VEL 

MANN I NG 

PW. EFf 

DR. EFF 

PAD/CHAN 

EVAP 

BLOWDOWN 

DET.TIME 

WALL.HT. CI 

WALL, HT* 0 

SUMP.DEPTH 

NAME 

---- 

CHPIN. WID 

PAD,WID 

CW. LEN 

CHAN, LEN 

TOT.CHAN.LEN 

TOT, WALL. HT 

SLOPE 

HEAD. LOSS 

TOT. EFF 

HYD. PWR 

TOT. PWR 

TOT.UNIT.PWR 

VEL. PPID 

VOLUME 

Q. EVAP 

VALUE 

0.0 hectare5 

2 - 

20 - 

20 em 

20 cm/sec 

0.010 sec/mA0.33 

0.6 - 

0.7 - 

0.75 - 

1.50 cm/day 

0.21 cm/day 

4.00 days 

40 cm 

10 cm 

1.5 meters 

S.I. UNITS 

43.06 meters 

32.30 meters 

861.25 meters 

928.89 meters 

1857.78 meters 

0250 meters 

1.107 x 10"-4 

20.98 cm 

42% 

3477 watts 

8278 watts 

0.10 watts/sq m 

26.7 cm/sec 

16000 cu meters 

1200 cu miday 

833 liters/min 

168 cu m/day 

117 litershin 

4000 cu m/day 

2770 li ters/min 

ENGLISH UNITS 

141.3 feet 

106.0 feet 

2825.6 feet 

3047.5 feet 

6095.0 feet 

1.107 x 10"-4 

8.26 inches 

42% 

4.66 hp 

11.10 hp 

0.10 w/sq m 

Ob87 +thee 

565035 cu ft 

42378 cu ft/day 

220 gpm 

5933 cu ft/day 

31 gPm 

i41259 cu ft/day 

734 gprn 
Table 7-2 Pond Design Calculations - Pond Svstem 

Uses input from table above, as well as the following: 

* INPUTS* 

DESCRIPTION NAME 

------------ ---- 

# of Adjacent Ponds #CIDJ.PONDS 

Sets of Adj. Ponds #SETS 

VALUE 

*OUTPUTS* All outputs refer to the entire pond system 

DESCRIPTION -.- NAME 

----------- ---- 

Total # of Ponds #PONDS 

Total Pond System Area S.AREA 

(alternate units) 

Center Wall Length S. CW. LEN 

Tot.Straight Wall Length S.STR.W.LEM 

Curved #all Length S.CUR. #. LEN 

Total Wall Length S.TOT.W.LEN 

Total Wall Area S.TOT. W.AREA 

System Pond Volume S. VOLUME 

Evap. Flowrate S.Q.EVAP 

(alternate units) 

Blowdown Flowrate S.Q.BLOWDOWN 

(alternate units) 

Harvest Flowrate S.Q.HARVEST 

(alternate units) 

S. I. UNITS 

---------- 

2 4 

192 hectares 

1920000 sq meters 

20670 meters 

43062 meters 

6494 meters 

49556 meters 

48695 5q meters 

384000 cu meters 

28800 cu mlday 

19999 literslmin 

4032 cu m/day 

2800 liters/min 

96000 cu mlday 

66662 liters/min 

ENGLISH UNITS 

------------- 

474.4 acres 

20666304 sq ft 

67814 feet 

141279 feet 

21304 feet 

162583 feet 

524149 sq ft 

13560845 cu ft 

1016928 cu ftldav 

5284 gpm 

142370 cu ftlday 

740 gpm 

3389760 cu ftlday 

17612 gpm 
Table 7-3 Growth Pond Cost Summary - 192 Hectare System 

INSTALLED COST FUR 192 HECTARE SYSTEM -------1--------------.-----1------ 

24 PONDS 8 HECTARES EACH 

DESCRIPTION QUAN UNITS UNIT $ TOT $ $/HECTARE 1----1--1---. --.I- ----- --...- ----. ---=---me 

GROWTH PONDS 

Earthworks 

Rough Grading 474.4 acre 500 $237,21b $1,236 

Lazar Level 1 ing 474.4 acre I, 000 474,432 2,471 

Finish Grading* 474.4 acre 2,500 1,1861080 6,178 

Sump Excavation 19293 cu yd 2.5 48,232 251 

Walls & Structural 

Straight Wallr 231761 sq ft 4.0 927,044 

Curved walls 34949 rq ft 3.0 174,744 

Flow Deflectors 10485 sq ft 5.0 32,424 

Sump bottom 1956 cu yd 100 195,635 

Sump ends 104 cu yd 200 20,729 

Rails 8 Piers 13359 ft 12.0 162,713 

Solids Removers 61,000 

Mixing System 

Paddle Wheels 24 8 PW 35,790 858,960 4,474 

P.M. Structural 24 # ponds 1,500 36,000 108 

P.W. Depression 331 cu yd 150 49,377 238 

Carbonation System 24 # Ponds 14,640 351,360 1,830 

Instruaentation 

GROWTH PONDS TOTAL 

24 t Ponds 4,000 96,000 500 

-.---- ----- 

* Includes crushed rock liner 


7.3 POND DESIGN ALTERNATIVES AND COSTS 

This section presents the actual designs of the various growth pond elements, 

along with an estimate of their costs. In some cases, a brief analysis is 

included, and alternative designs are explored. Sections 7.3.1 through 7.3.8 

treat earthworks, walls and dividers, sumps, solids rrroval, carbonation, and 

mixing respectively. In section 7.3.9 a summary of costs, based on the chosen 

a1ternative.s is presented. Harvesting is treated in Section 8. 

-As a preparation for laser levelling, the pond grade is established rouqhly 

with conventional earthmoving equipment. The amount of rough grading will 

vary from almost nil on flat terrain to major quantities of cut and fill #here 

the terrain is rough or sloping, requiring terracing to establish the pond 

grade. Compaction of fills is essential to prevent settlement and can be a 

significant cost. Presence of rocks, roots, and other material can add 

appreciably to rough grading costs. Dikes or drains to control surface 

drainage may also be required. Earthworks for access reads, storage 

reservoirs, etc., is not included. For favorable terrain, rough grading costs 

can vary from 0 to 94000lhectare. A value of S1200lhectare is used in the 

cost estimate, 

Laser levelling is needed to achieve the tolerances required fur shallow pond 

operation, and to establish the very flat channel slopes to meet hydraulic 

requirements. It has become a widely used technique in agriculture, where the 

cost can be as low as $900/hectare for large fields. For pond construction, 

the cost will be greater, since the slope must be set separately for each 

channel, and tolerances will be quite rigorous. A value of t2500/hectare is 

used in the cost estimate. 

The cost constraints of fuel production may prohibit the use of synthetic pond 

liners, nhich alone would cost $38,000-50,00Q/hectare depending on the quality 

of liner used. In the cost estimate, it is assumed that the ponds will be 

built on tight soil, which is sufficiently impermeable to control seepage. 

Seepage rates generally decline with time as a result of clogging by organic 

matter and inorganic precipitates. In sore cases, a clay liner (15-30 cin) 
say be necessary. Often, the clay is available on-site, as in the case of . 

the experimental facility described in Section 12. If not, finished grading 

costs could be substantially higher, if long haul distances were involved, 

However, even a doubling or tripling of finished grading costs would have a 

minor affect on overall pond construction costs. Finish grading is usually 

required on clay soils due to loss of grade from construction activites such 

as trenching, etc. The soil will be overlain with a minimum thickness 

blanket (3-9 crn) of crushed rock or other coarse granular material to control 

suspension of fines, The particle site distribution and degree of compaction 

of this rock overburden will determine the channel roughness. Transport 

costs for imported granular material can be appreciable if local material is 

unavailable. The total cost for finish grading and crushed rock liner will 

likely cost between $4000-B,OOO/hectare, A design value of JbZOOlhsctare ig 

used in the cost estimate, 

A variety of wall construction techniques are conceivable, ranging from 

earthen berms to slipfurm concrete. This section will examine five options, 

cite their pros and cons, and give coot estimates for each. Four of these 

options are illustrated in Figure 7-5. In general, walls need to be about 

0.4 meters high, except in areas where wave action nould require more 

freeboard (e.9. downstream of paddle wheels), or where water accumulates 

under quiescent conditions. Very large ponds would probably require higher 

walls since larger wind induced waves could occur. In general, the center 

wall which divides the two channels can be of identical construetion as the 

exterior walls. In small ponds with low head losses it may be possible to 

uee a less expensive method for the dividers (e,g. membrane dividers). 

Earth berms must be constructed of compacted fill by over-building, trimmed 

to give 8maoth ride slopes, and then protected againat erosion. A minimum 

top width before trimming is about 2 meters, for conventional compaction 

equipment. Slape protection material would have to be several times the 

thickness of the bottom blanket, because of more difficult construction and 

greater erosion potential, Even so, there is likely to be high maintanence 

costs associatad with slope protection, Extra protection, e.g. gunnite, will 

be required where wave action tends to concentrate. Weed growth on the top 

and sides of earth berms is also a potentially costly maitanence problea. 

More land is required as compared to narrow walls. Although it may he 

possible to construct berms far a5 little ae $lbllinear meter with special 

equipnent, the Otfl disadvantages weigh heavily against earth berms. Earth 

berms say be appropriate for those walls which form the perimeter of the pond 

system, since an access road will be needed around the perimeter, and 

drainage considetotions may require it to be elevated. 

A novel technique, used by Dodd in Singapore, employs corrugated 

asbestos-cement roofing sheets embedded in a shallow concrete-filled trench. 

The lheets are cut and drilled o#f-site, then installed with the corrugations 

running vertically, Adjacent pieces are caulked and bolted together, formlng 

a free standing, waterproof wall which can expand and contract with changes 

in temperature, Haterial costs are about $9/m@ter, with total installed 

costs estimated at about $24,50/meter. 0&H costs are likely to ae quite low. 

The membrane wall consists of a Hypalon membrane supported on a +ramwork of 

2'92" redwood posts spaced 1,2 meters (4 feet) an center. The posts are set 

in 15 cm (6 inch) diameter holes fitlad with concrete #or anchoring and 

stability. The top of the membrane is anchored between two railings again 

made of 2x2 redwood. The bottom of the membrane is anchored in a 30 cm (12 

inch1 deep trench backfilled with earth which also prevents seepage under the 

wall. This estimated cost of this method is $18.07/meter ($S.Sl/ft, see 

Appendix 111). Although this makes it one o+ the lowest cost options, it is 

also the least durable, so that O&M costs would probably offwi?t initial cost 

savings, However, experimental ponds are often membrane-lined, so this 

method, or some variation, would be appropriate, The experimental ponds at 

Vacaville, CA used golid wood walls and a membrane liner. 

The concrete block wall consists of a poured concrete footing 15 cm x 

30 cm (6" n 12") with 2 courses of 4nxB'tnibH blocks get on top, The block 

cells would be filled with pea gravel concrete and a single t4 reinforcing 

bar set in the top block to give the wall adequate longitudinal 8trength. 

The dooting would be set below grade for stability and te prevent seepage 

under the wall. Thm estimated cart o+ this option is $23,35/m M7.12/6t). 

The poured concrete divider wall is set on a 15 cm x 30 cn footing, is 

10 cs (4') thick and 40 cm (16") high. Custom made seuruable forms are 

proposed that are free-standing to reduce installation and relocation labor. 

One 14 reinforcing bar would be set along the upper part of the wall to hold 

the wall together and minimize cracking, Cracking would be contralled by 

joints every 6.1 meters (20 ft) and sealed with silicon to tniniaize seepage 

through cracks in the contra1 joints. The cost of this option is about 

217,50/meter ($S,34/ft). Given the large quantity of walls to be constructed 

for the large scale system, it should be possible to employ slip-farming 

techniques at about the same cost, The key concern with eoncrlete walls is 
seepage. Shrinkage cracks will definitely occur, but there was a lack of 

agreement among consultants as to their effect. One 9elt that the control 

joints plus the tendency for craeks to clog would mitigate the problem, while 

another felt that the need to wake control joints waterproof would greatly 

increase the cost of concrete con6truction. The author's experience with 

experimental (1000 m2) high rate ponds tends to support the former, but the 

problem is certain to be more pronounced in large ponds. Although most 

seepage will be contained within the pond system by virtue of the 

side-by-side layout, excessive seepage would result in short circuiting 

within the pond. If sempage is not a serious problem, then the concrete 

walls are the preferred method of construction, possibly in combination with 

corrugated walls for the curved portions. Such a coabination was used in the 

cost estimate. The difference in cost between the two alternatives 024.JO/a 

for the corrugated vs $17.50/m for the concrete) is not enough to have a 

major impact on the system capital cost. 

The curved flow deflectors aid in minimizing the extent ob eddy formation and 

the associated stagnant zone downstream of the bend. Again, these can 

normally be built in the same manner as the straight walls, although some of 

the wall options outlined above are more easily adapted to curves (e.g. 

corrugated walls). The situation is improved if the brtfler and end walls 

are placed eccentrically, and the channel width decreased through the bend, 

as shonn in Figure 7-5. The acceleration of flow is sufficient to reduce 

eddy formation and eliminate most of the solids deposition. The channel 

constriction technique is also used at the other end of the pond, which 

allows access to the paddle wheel t121. An alternative to curved deflectors 

are turning vanes, also shown in Figure 7-5. Turning vanes are widely used 

in analogous fluid systems, (e.g. air ducts), although Dainippon Ink & 

Chemical, Inc. apparently holds an application patent for their use in algae 

production ponds. If closely spaced, (i.e. at intervals equal to the pond 

depth), the vanes are quite efficient, and virtually eliminate problems of 

eddy formation and solids deposition. They also allo~ the ends of the pond 

to be square, which sirplifies construction. The quantity of raterial 

required for both curved deflectors and vanes is about the same, but the 

latter require more elabarate support and would be more expensive to 

install. Curved deflectors were used in the design, priced at $25/reter 

($273/hectare). Vanes would cost about twice this amount. 

Sump8 are neceseary in order to provide a deepened area for CO2 additions 

so that high aboorbtion is acheived, and to provide a collection point for 

draining the pond. The sump may also provide an area of retduced veloeity 

where inert solids and settleable organic matter can accunulate and be 

removed. The analysir of C02 absorption presented in Section 3.0 concluded 
that for an for an 8 hectare pond, a sump depth of about 1.3 meters will 

result in 95% absorption of Cog, if the diffusers produce bubbles about I 

me in diameter, This depth is also suf+icient to prevent vortexlng and air 

entrainment in the drain pipe, The sump cross-section is shown in Figure 

7-4. In order to facilitate drainage, insure uniform carbonation, and 

expedite excavation, a single suap is constructed across the entire width of 

the channel. The transition into the sump is gradual to ininiaite turbulence 

and avoid the need for concrete formwork, The length (in the direction of 

flon) is related to the issue of solids removal, as discussed in the 

following section. In the baseline design, the length is kept ta a minimum 

(1 meter). The distribution pipe far C02 is located at the downstream end 

of the sump, so as not to interfere with any solids deposition that nay 

occur. Cog sbmorption actually takes plrcr in the dcnnstream transition 

section. The harvesting/drain piping originate from small "sub-sumps" 

located in the bottoin of the sump, so that a submergence of 1.9 meters is 

maintained. 

The accumulation of both inert and organic solids, which by virtue af their 

density or tendancy to agglomerate into flocs and settle, is inevitable after 

a period of pond operation. This material tends to settle in "dead spotsH 

We. stagnant areas) within the pond, and will eventually lead to 

operational problems. Since a sump is to be included for the reasons 

outlined above, the question arises whether it could also serve as a 

sedimentation basin for removal of settleable solids. If, for instance, the 

sump were made 5 meters long (bottom length), the detention time of fluid 

passing through the suap would be about 300 setands. A geometric analysis 

indicrtrr that only very rapidly settling particles (Vp/30 crlmin) will be 

removed completely, with the remainder being removed in proportion to their 

settling rate divided by 30 cm/min. Since most of the solids settle at rates 

well below this, the efficiency of the sump for solids removal is likely to 

be quite low, Although the efficiency could be improved by increasing the 

length of the sump (Vp varies as f/L), the marginal increase in performance 

would not justify the expense, The problem is that bath low velocities and 

long detention times are necessary, Thus it may be necessary to design 

stagnant zones, similar to those created by an unbo9fled turn, in which 

solids can accumulate and be removed, but in such a way so as not to disrupt 

the mixing regime over a large area of the pond. It may be possible to do 

this in a portion of the carbonation sump, or perhaps in a smaller sump riqht 

after the bend before the paddle wheel. The whole issue of solids 

accumulation needs to be assessed at the pilot scale, since most of the 

current information comes from observations of waste treatment ponds, which 

are subjected to high organic loadings, and in which a large accumulation of 

solids would be expected. 4 method for removing solids from the main sump, 

which user a suction device mounted on a travelling bridge, has been 

developed 1121, and is described in Appendix III. For an 8 hectare pond, 

this method would cost about $1300/hectare, most of which is for the piers 
and rails on which the bridqe travels, Regardless of whether the sump will 

accumulate sufficient solids to justify the expense of the travelling bridge, 

the $1300/hectare has been included in the cost estimate, since it will allow 

access to the sump for servicing the carbonation system and effluent drain 

valves. Also described in Appendix I11 is a mechanical method for dredging 

the pond channels, which is estimated to cost 8310/hretare. The final 

decision on the best approach to solids removal must await pilot scale 

studies which will define the severity of the problem and the effectiveness 

of the variuos alternatives. 

The analysis in Section 3 concluded that a single carbonation station per 

pond would be sufficient to maintain an adequate level of dissolved carbon in 

the culture. The carbonation system is designed to supply the peak demand of 

7.2 gm ~0~/m~lhr, which corresponds to about 4800 liters/min (170 cfmi at 

the assumed delivery temperature of 27OC (80°F). 4 100 mm (4")- 

distribution pipe spans the channel on the downstream side of the sump, with 

spargers spaced along its length, The effect of sump depth and bubble sine 

on C02 transfer efficiency was also described in Section 3. The analysis 

concluded that very fine bubbles (1 mm) were necessary +or lateral flow 

carbonation in shallow sumps, and that the sump depth increased rapidly for 

larger bubbles. While it is a fairly simple matter to generate bubbles of 

2-3 mm diameter with porous diffusers, to produce 1 ms bubbles the flowrate 

per diffuser must be quite low (bubble sine is more sensitive to flowrate 

than to pore size). The aanufacturers contacted could provide only cautious 

estimates of flowrates for this application, so that the actual type and 

number of diffusers will have to be determined by pilot scale testa. For 

purposes of cost estimation, a relatively conservative approach was taken, 

based on information supplied by Cardox Co., a manufacturer of porous tube 

diffusers. The total cost of $10,800 ($2350/heetare) includes the pH 

controller, control valve, C02 flowmeter, and associated piping. Since 

experience has shown that the rates of C02 absorption are often better than 

those predicted by the methods of Section 3, significant cost reductions are 

possible in this category. 

For an 8 hectare pond mixed at 20 cwlaec, the Manning's formula predicts a 

head loss of 21 cm (8.3'1, for an assumed roughness factor of n=0.018. The 

corresponding hydraulic power is 3480 watts (4.67 hp). Paddle wheels are 

chosen for mixing, for reasons outlined in section 4-2. The constriction in 

channel width (see Section 7-3-51 allows the paddle wheel to be 25% smaller 

than the channel width, and allows access to the drive. Even so, the width 

is 32.3 meters (106 ft), so the paddle wheel is broken into three sections, 

separated by flexible couplings that allow some vertical and angular 

aisallignment. Design of the paddle wheels is based on a stress and 
deflection analysis of the paddles, the drive tube, and of each paddle wheel 

section. Although the low rotatianal speed means that torques are very high, 

it is the deflection of the paddle wheel under its own weight (and that of 

attached growth, which can be significant) that governs design of the 

tube. The design is similar to the small paddle wheels used in the 

Vacaville, CA experimental ponds shown in Figure 7-6, with some notable 

changes. Many of these changes are based on improvements made by Dodd in the 

course of designing several "generations" of paddle wheels. The number of 

blades is increased from six to eight, and adjacent sections are offset by 

22A0, both of which reduce pulsations on the drive train and in the flow 

of the water, R solid baffle between sections also blacks flow across the 

channel. A small clearance between the paddle tip and the shallow (5cm) 

curved depression below it makes the paddle wheel in effect a large positive 

displacement pump, with a minimum of backflow, The drive shaft is a steel 

pipe with solid stainless steel stub shafts at the bearings. The drive 

consists of a 15 hp electric motor, a variable speed unit, an in-line speed 

reducer, and a two-stage chain and sprocket reduction. The +inal driven 

sprocket is inboard o+ the bearing, so that the stub shaft merely supports 

the paddle wheel weight, and does not transmit the drive torque. The variaus 

components (and their cost) are fisted in appendix 111. The drive tube and 

hubs are epoxy coated steel, while the spokes and paddles are fiberglass, +or 

corrosion resistance. In order to have the necessary rigidity in bending, 

the paddles must either be supported with a structural member li+ flat), or 

be formed into r structural shape themselves. The large quantity of paddles 

required for the large scale system allows the use of custam designed shapes, 

at very little cost over that of flat sheets. Thus a curved shape paddle was 

designed that has sufficient rigidity to span the 2.43 meters (8 ft) between 

hubs without structural backing, The paddle is 0.64 cm thick, 57 cm high, 

and has a 61 cm radius of curvature. (The paddle height must accomodate the 

nominal depth, lift, depression, and wave action generated by the paddle 

wheel itself). The curved shape also sheds water efficiently as it leaves 

the water, With each pair of ponds laid out as a mirror image, the two 

drives are close together, minimizing wiring casts. 

The paddle wheels are a major cost component of the growth pond systea, each 

one costing about $37,500, including structural supports, concrete 

depression, and installation, This is almost 20% of the growth pond cost. 

Instrumentation to measure temperature and dissolved oxygen will be provided 

for each pond, and this information, along with pH, CO2 flowrate, and 

make-up water flowrate will be transflitted to a microcomputer-based data 

acquisition unit which records the data and prepares summary reports. Given 

the relatively low price of such systems, one will be installed at each 

harvesting station, (i.e. for each eight growth ponds), eliminating the long 

data transmission lines that would be necessary in a totally centralized 

system. Allowing $2000/pond for the measuring and transm,ittinq equipment, 

and $16,000 per harvesting station for the data acquisition syetem (installed 

costs), the overall cost is $96,000, or SSOWhectare. i4 system of this type 

could Later be expanded to automate harvesting aperatians, an option not 

provided for in the cost estimates. 

A summary of costs for the 24 eight hectare ponds is given in Table 7-3, The 

table was developed on a spreadsheet, so that the sensitivity to changes in 

design or costs could be examined with relative ease. The quantity of 

material in each category is an equation based on the Pond Design 

Calculations, samples of which were listed in Tables 7-1 & 7-2. In mo5t 

cases the unit coats were fixed, although in some cases (e.g. carbonation, 

mi~ing), they were represented by an equation, or reference to a look-up 

table. For this reason, the range of the program is liaited to ponds of 

about 2-10 hectares, althouqh the quantities coluan is accurate over a much 

wider range, The mixing system costs were generated a separate program, - 
SECTION 8.0 

HARVESTING SYSTEM DESIGN 

This section presents three alternative designs for harvesting, inluding (1) 

Microstraining; (2) Belt Filtration; (3) Settling. (Air/DO floatation, 

mentioned in Sections S.and 12, is not analyzed in this section). In each of 

the three cases, further concentration is acheived through centrifugation, in 

order to bring the solids content of the slurry up to 10% VS. However, the 

costs of centrifugation vary widely according to the level of concentration 

achieved in the primary harvesting step. The harvesting operations are based 

on the analysis of Section 6, which concluded that an induction phase would be 

necessary to achievm high lipid levels in the cells, This in turn implies 

batch, as opposed to continuous, harvesting. The harvest flowrates are based 

on a four day (system average) detention time,although the growth/induction 

cycle will most likely be longer, especially in the winter months. 

8.1 NICROSTRAININQ 

Hicrostrainers are an attractive harvesting method because of their mechanical 

simplicity and availability in large unit sizes. The recent availability of 

very fine resh polyester screens has revived interest in their use for 

microalgae harvesting. Fabrics as fine as one micron ( n o m i n a l ) h a v e been 

successfully employed for algae removal from lagoon effluents. However, 

attempts to harvest saall unicellular algae with the one micron fabric have 

yeilded disappointing results, in spite of the fact that the cells were larger 

than one micron in size 1131. (The lack of success in straining small algae 

with the one micron weave can be attributed to the fact that the actual 

openings in this fabric are rectangular, nith dimensions of approximately one 

by six microns). Subsequent studies concluded that it would be necessary to 

flocculate the cells prior to microstraining. Current research is aimed at 

determining the types and amounts of flocculant necessary for various 

species. The use of flocculants in harvesting can have a significant impact 

on operating costs, depending on the dose required. Under certain conditions, 

it may be possible to use microstrainers without adding flocculants, as in the 

case of large unicellular (e.g. Platymonas) or colonial algae, or with 

culturing techniques that induce uautoflocculation,n 

The design assumptions for the microstrainer based harvesting system are 

listed in Table 8-1, and are discussed below. The critical deeign parameters 

are hydraulic loading (flonrate/net effective submerged area), solide removal 

efficiency ((influent TSS-effluent TSS)/influent TSS), and concentration ratio 

(concentrate TSS/influent TSS). Although accurate prediction of these 

parameters requires pilot scale tests nith the particular species, some 

reasonable estimates can be made from existing information. The hydraulic 

loading determines the size and number of microstrainers required, and so has 
TABLE 8-1. Microstrainer-Based Harvesting Svstem 

Design Parameters 

Single growth pond volume 

System pond volume 

Detention ~ind 

System harvest flow 

(alternate units) 

Microstrainer influent density 

Microstrainer hydraulic loading 

Net effective submerged areahnit 

Flow per unit 

Number of units required 

Concentration Ratio 

Centrifuge influent density 

Flowrate to centrifuge 

Centrifuge design loading 

# of units required 

Concentration ratia 

Centrifuge effluent density 

4 days 

3.7 m dia X 4.9 m long 

22.6 n2 

7345 litershin 

10: 1 

7500 mg/l 

6700 litershin 

15000-3800 liters/min 

2 

13: 1 

100 g/l (10% Total solids) 

he text 

224 hr/dsy basis . 

3~nvirex Model 
a strong impact on capital costs. Its value depends primarily upon the 

influent solids concentration, the size of the screening media, and the 

characteristic size of the algae. The "one micron" screen imposes too severe 

a penalty on hydraulic loading to be a practical alternative. Since this 

analysis presupposes large, colonial, or dlocculated algae, the required mesh 

size will fall in the range of six to twenty microns. The hydraulic loading 

is assumed to be 329 lpr/m2 (8 gpm/ft2), a reasonable value for the mesh 

range specified. The importance of solids removal efficiency depends on the 

mode of operation, ranging from critical for "once-through" systems (e.g. 

seawater), to moderate for recycle systems, wherein unharvested cells are 

returned to the ponds in the harvest return stream. On the other hand, the 

microstrainer must produce a significant increase in solids density to 

justify its relatively high cost. For lagoon effluent polishing, a 

concentration ratio of 6:l is typical. However, these systems are operated 

to produce the lowest possible effluent density, not to concentrate algae. 

When optimized for the latter, a tenfold concentration should be attainable. 

This corresponds to a tenfold reduction in flow to the secondary harvester. 

Since centrifuge capacity is largly flowrate dependent, the concentration 

ratio is of major importance. 

In order to reduce large diameter piping runs, the primary harvestinq is 

decentralized into three harvesting stations, each containing three 

microstrainers, and each serving eight growth ponds. An alternative would be 

to use slightly smaller microstrainers (increasing the number to twelve) and 

buildinq six stations, each serving four ponds. This would further reduce 

piping runs, but the savings would be offset by higher microstrainer and 

facilities costs. This trade-off is not considered in the cost analysis. A 

schematic of the harvesting system is shown in Figure 8-1. 4n entire pond 

volume is harvested on the fifth day of the growth/induction eycle, so thsl 

system average detention time is actually five rather than four days, and 

harvesting could be spread aver 1.2 days per pond. However, a one day per 

pond timetable is more practical and allows some flexibility in OIH. 

An unfortunate consequence of batch harvesting is the need to store the 

clarified effluent until harvesting 6s completed. In a continuous process, 

it is returned immediately to the pond, but in a batch process this would 

dilute the culture along an exponential curve. Since the microstrainers are 

likely to be limited by solids, rather than hydraulic loadings, it may be 

possible to return the effluent, while gradually increasing the harvest 

flowrate to compensate, Obviously there are practical limits to this, as 

flowrates would have to increase indefinitely in order to harvest all of the 

cells, so in fact some algae would always go unharvested. With careful 

controls, the correct aaount of seed algae could be left in the pond for the 

next batch. However, given the uncertainties involved, it is prudent to 

include storage ponds in the design, which hold the clarified effluent until 

harvesting is complete. If located entirely above grade, tho effluents can 

be returned to the growth pond by gravity. If harvesting begins after dark 

on the fourth day and is finished 24 hrs later, the entire night is available 

to drain the effluents from the storage pond back into th,e growth pond. 

The concentrated harvest stream frow all microstrainers is pumped to a 

centralized secondary harvesting facility. The total flowrate to this 

facility, assuming 24 hr/day operation, is 6670 l/nin (1760 gpa). Three 

large horizontal solid bowl decanter centrifuges, constructed with corrosion 

resistant materials, are required. These are rated at 1510-3960 lpr 

(400-1000 gpm) each, depending on feed characteristics, flocculant dosage, 

and degree of concentration required. Although the use of disk nozzle 

centrifuges might reduce capital costs, the savings would most likely be 

offset by higher operating costs E121. The centrifuges concentrate the 

solids by a factor of 10-13, producing the required 10% slurry. The solids 

are discharged continuously by neans of an internal screw conveyor. The 

clarified effluent from the centrifuges is returned to the ponds via the 

makeup water network, eliminating the need for separate return piping. 

Capital costs for the microstrainer-centrifuge harvesting option are shown in 

Table 8-2, The total harvesting cost is t21,800/hectare. If the centrifuges 

could be operated at 3700 lpm (very close to their maximum rated capacity), 

then only two units are required, and the total harvesting costs are reduced 

to $18,70O/hectare. Estimated annual operating costs are shown in Table 8-6, 

for an assumed flocculant cost of $.Ol/kg dry algae. The sensitivity of 

operating costs to flocculant dose is discussed in Section 11. Although one 

would intuitively expect a trade-off between the quantity ob flocculant used 

and the microstrainer design parameters (which would effect capital costs), 

there is not sufficient data at this time to evaluate this trade-off, other 

than to say that certain species simply cannot be harvested without 

flocculants. 

8.2 BELT FILTRATION 

A vaccuun belt filter for algae harvesting, developed by Dodd in 1972, used a 

fine mesh stainless steel screen with a paper precoat. The concept was later 

refined, with the sreen and precoat being replaced by a polyester fabric 

similar to those used in microstrainers. A pilot scale unit operated in 

Singapore was very successful in harvesting Hicractinium and other large 

species, somewhat less so with small algae such as Chlorella. In general, 

the floccuant dose should be less than in the case of ricrostrainers, since 

the algae eat aids in filtration. Although the belt filter has a relatively 

high capital cost, it can concentrate solids much more effectively than a 

microstrainer, by a factor of about 70a1 as opposed to 10:l. Since the 

product is more concentrated, flow to the secondary harvester is reduced 

substantially, resulting in lower secondary harvesting cost and reduced 

energy consumption. For the entire 192 hectare system, the secondary 

harvester flow is about 950 lpa (250 gpm). The layout of a belt filter 

systea would be very similar to the aicrostrainer system shown in Figure 

8-1. The capital cost of the belt filter option is shown in Table 8-3, based 

on estimates supplied by Dodd. (The belt filter was assured to cost SOX mora 

than'a aicrostrainer of equal capacity). Storage ponds are again necessary. 
TABLE 8-2. MICROSTRAINER BASED HARVESTING OPTION 

CAPITAL COSTS 

PRIMARY HARVESTING 

9 Microstrainers (3.7 m dia x 4.9 rn) 

stainless steel construction, includes 

motor & contrals @ $160,000 ea. $1,440,000 

3 Housings, with concrete pit & sumps 

@ $50,000 150,000 

3 Pumps stations, including all valves & Piping 300,000 

6 Storage ponds 300,000 

TOTAL 

TOTAL /hec tare 

SECONDARY HARVESTING 

2 Sharples PM95000 centrifuges, complete with 

motor 6 control @ $650,000 

1 Housing & concrete pad (4000 ft) 

1 Pumps & piping 

TOTAL 

~~~A~/hectare 

TOTAL WVESTfNG 

TOTAL /HECTARE 
TABLE 8-3. BELT FILTER BASED HARVESTING OPTION 

CAPITAL COSTS 

PRIMARY HARVESTING 

Belt Filters (1.5 x Microstrainer Costs) 

3 Housing, with concrete pad & sumps 

6 Effluent Storage Ponds 

3 Pump Stations, including a-1 harvest/return 

piping, valves, etc. 

Total 

SECONDARY HARVESTING 

2 Sharples PM60000 Centrifuges @ $275,000 

1 Housing + concrete pad (2000 ft2) 

1 ~ump/piping system 

Total 

Totallhectare 

TOTAL HARVESTING 

TOTAL /HECTARE 
The centrifuge cost is based on two units, each smaller than those used with 

the micrastrainers, The choice of two smaller, rather than a single larger 

unit reflects the O&H realities of the need for more than a single 

centrifuge. Since the solids concentration going into the centrifuge is so 

much higher than in the case of the eicrostrainers, a Bore conmervativo 

design flowrate was used. The overall coot is $17,8OO/hectare. Harvesting 

cost is not nearly as sensitive to centrifuge flowrates as in the cases of 

microstrainers, Operating cost estimates for the belt filter option are 

shown in Table 8-6. Note the significant reduction in energy cost associated 

with this option. 

A comparison o# Tables 8-2 and 8-3 shows that the two option8 presented thus 

far have capital costs very nearly the same, if the favorable assumption 

regarding centrifuge flowrate is made for the ~icrostrainer option. 

Operating costs for the belt filter option are gignificantly less. However, 

any comparison should be made with some caution, since large microstrainers 

are commercially available and their costs are known, whereas the belt filter 

represents a new technology, for which casts are necessarily more uncertain, 

8.3 SETTLING 

The use of settling for nicroalgae harvesting is baaed en the observation 

that nitrogen-starved cultures will settle at rates of 30 cm/hr or greater 

without adding flocculants. (The addition of small amounts a9 polymer can 

increase this rate and produce a more compact concentrate). The same 

phenomenon has been observed in non-nitrogen etarved cultures, but in a less 

consistant, and more species and media dependent fashion. 

A settling rate of 30 cm/hr is still relatively low, and requires long 

detention times in the settling device, whether it be batch or continuous, 

The latter would not apply in this case, given that the gronth/induetion 

process is inherently batch. The major engineering problem in a large scale 

batch settling process ia to devise on effective, inexpensive solids removal 

scheme. The major drawback of batch settling is the large piping systems 

that are needed to transfer the fluids in relatively short per~odg oC time, 

so that more time is available for quescient settling. This is partially 

overcome by the use of shared settling pond^ and pump stations, whish service 

a number 04 ponds in sucesaion. Other questions raised in connection with 

large scale settling ponds include the eifcct of wind nixing on settling 

rates and the possible degredation of the lipid fraction during the pr~cess, 

The wind mixlng problem can be mitigated through the use of berms. 

Degredation is not likely to be a problem in the time period (approximately 

24 hours) involved in the proposed design. 

The layout of the settling pond system is shown in Figure 8.2. A two stage 

process is proposed, consisting o+ a large (0,5 hectare) settling pond, which 

concentrates the algae by a factor of 20, follu~ed by a second gravity 

thic-krning stage, which concentrate5 by an additional tactor of 2.5, for an 

overall concentration factor of 50. The choice 04 a two stage process is 

based on experience in operating the 40,000 liter batch settling pond in 

Vacaville, CA. This approach greatly reduces the need for precise 

discrimination between the concentrated bottoa fraction and the less 

concentrated layer that farm above it, albiet at a greater cost. The 

large settling pond is sired to hold one pond volume (16,000 meter3) in 

a 3 meter depth, The working volume is all below grade, so the ponds can 

be drained by gravity. It is a conventional eloped-sidewall basin, with 

211 sideslopea. The dimensions are shown in Figure 8.3, along with other 

relevent details. The pond is lined uith ~~~alonl or CPE~, The pond 

bottoin slopes towards a central alley on a 2% grade. Both supernatant and 

concentrate piping go to an external pumping station that is shared by two 

settling ponds. The following sumsarizes the harvest sequence1 (1) The 

contents of the growth pond are drained to the settling pond. The drain 

lines are sized to complete this in four hours, (2) The contents settle 

for a period of eight hours. (3) The supernatant is decanted off over a 

period of ten hours, and is returned to the growth pond (see Figure 0-3 

far draw-off details). Since liquid is removed from the top of the pond, 

settling continuos in the loner layers, When tho liquid level reaches the 

break in the slope, decanting is complete, Approximately 5% of the 

contents remain in the aettling pond, (4) The remaining concentrate is 

pumped to the secondary thickener. At various intervals, the concentrate 

stream tor stored secondary supernatant) is diverted into the flushing 

system, washing dawn solids that have have settled on the bottom of the 

pond into the collection alley, which Ieada to the concentrate sump. The 

concentrate removal process takes about two hours. The settling pond is 

now available for the next growth pond. (5) The concentrate reaains in 

the thickener for abaut eight hours. The secondary supernatant is 

returned to the gro~th ponds, while the secondary concentrate is pumped to 

a centralized facility for centrifugation to 10Z solids, as in the other 

harvesting schemes. 

The sequence as described above is based on a four day cycle time, which 

is the shortest conceivable period +or growth and induction. Actual cycle 

times will probably be five days or longer, depending on the time of the 

year, so that settling and decanting times way actually be longer than 

described above, The flowrates of the various fractions are listed in 

Table 0-4, for the four day cycle. Additianal harvesting details are 

given below, 

The pump station is a wet pit design, and is divided into two sections for 

supernatant and concentrate, Three vertical mixed flow pumps, each sized 

at 50% of the required flowrate, are provided. The pump station operate8 

A synthetic rubber liner manufactured by DuPont 

Chhrinatcd polyethylene liner 

almost continu~usly when the cycle time is four days. Two screw pumps are 

used to pump the primary concentrate into the secondary thickener. (LOW 

shear solids handling pumps are required for handling all concentrate 

fractions). The flush system is very similar to those used in dairies for 

manure collection, and is designed to provide flushing velocities o+ about 

1 meters/sec (3 ft/sec), which should be sufficient to resuspend and 

transport solids accumuiated on the bottom of the pond. The channels are 

divided by 0.10 meter (4 inch) concrete curbs which are either poured 

directly on the liner or precast and set in place. In the figure, the 

concentrate itsel+ is diverted into the flush network, consisting of a 

distribution pipe which sequentially feeds the flush water into 16 

channels, 0 on either side Q+ a concrete collection alley (see details in 

Figure 8-4). It may be necessary to divert some a+ the initial 

concentrate (which will have the least amount of solids) into a small 

storage pond, and use this liquid for flushing, ar build two smaller 

secondary thickeners and flush with recyled secondary supernatant. Since 

good distribution of the flush water over the width of the channel is 

essential, optimization of the geometry may also be necessary, tine. a 

larger number of channels, or a change in pond geometry to longer, narrow 

channels). None of these options would have a major impact on cost5, 

These and other issues, such as the optimal duration and frequency of 

flushing, must be resolved in pilot studles, 

After settling in the secondary thickener for about 8 hour%, the secondary 

supernatant is decanted in the same fashion as behre, and pumped into the 

return flon network. Secondary c~ncentrate is pumped to the central 

facility for centrifugatian. The average flawrate is 402 greater than in 

Table 0-4 Settling Pond System Flowrates 

SINBLE POND: 

Volume Time Flouratr 

Fraction m3 gat lons hrs. 1 P~R gPfi ---L--LII--LI--LII----------------------------------------------------- 

Pond Volume 16,000 4.23110bf 4 66700 17612 

lo Supernatant 15,200 4.02(106) 10 25300 6690 

to Concentrate 800 2.11 (lo5) 1.2* 11 400 3000 

2O Supernatant 400 1.27110~) 2 4000 1057 

2O Concentrate 320 8.45(104) 2 2670 905 

SYSTEM (centrifuge flowrate); 

2O Concentrate 320 a3/4 days x 24 ponds 1330 352 

* Total removal time is longer because of recyle to flush system. 

the case of the belt filter, but a factor af five less than in the case of 

microstrainers. Capital costs for the settling option are shown in Table 

0-5. At 511,26O/hectare, cost of this option is substantially 1994 than for 

either microstrainers ar belt filters. Estimated operating costs are shown 

in Table 8-6" 

Table 8.5 Settling Pond Harvesting Option 

Capital Costs 

PRIHARY HRRVESTINO (2 stage) 

Each harvesting station consists of 2 settling panda (below grade), one 

pump station, and 1 secondary thickener. Each station server 8 growth ponds. 

Station System 

------.. ------ 

Excavation & shaping: 25,000 yd3 @ $2.50/~d~ u 2 5125,000 1375,000 

Liners: 71650 itZ $0.60/ft2 x 2 = 

Piping, valves, sumps, pumps (see Table AIV-1) 

Secondary thickening (see Table AIV-2) 

Primary Harvesting Subtotal 

Primary Harvesting Subtotal/hectare 

SECONDARY HRRVESTING: 

2 Sharples Pfl75000 centrifuges @$330,000 

Housing & concrete pad 

Pumps & piping 

Secondary Harvesting Subtotal 

Secondary Harvesting Subtotal/hectare 

TOTAL HARVESTING 
Table 8-6 Estimated Operating Costs of Harvest Options 

MICROSTRAINER BELT FILTER SETTLING PONDS 

------------- ----------- -------------- 

ELECTRICAL 

Primary, kwh/yr 174,000 348,000 343,000 

Secondary, kwh/yr 2,578,000 967,000 1,096,000 

--------- ------- --------- 

Total, kwh/yr 2,732,000 1,315,000 1,439,000 

Total, $/yr $178,900 $85,500 $93,500 

FLOCCULANTS $216,000 $216,000 $216,000 

MBINTANENCE 

TOTAL 

Notes: 

Costs are for 192 hectare system 

Electrical cost based on b,5c/kwh 

Flocculant cost based on l.Oc/kg dry algae 

Maintanence cost B 3% of capital cost includes materials and outside 

labor only, not operating labor. 
Section 9 

SYSTEM-WIDE COSTS 

System-wide costs include the water, carbon, nutrient, power, and blowdown 

systems, as well as roads and buildings. In the case of carbon and power, the 

e~phaeis is on the distribution rather than on the source, since SERI has has 

examined the resource issues in far greater.depth than would be posgible in 

this report. hn exception is the issue of nutrient recycle within the system, 

which is examined in Section 6, Table 9-1 lists the system wide costs, and 

also summarizes the total cost for the 192 hectare system. Table 9-2 Iists 

the electrical and maintanence costs for the system, Both tables are based en 

the use of settling ponds +or harvesting, Total operating casts arc presented 

in Section 10. 

9 WATER SUPPLY AND DISTRlBUTION 

The capacity of the water supply system is based on a maximum evaporative rate 

of 1.5 cm/day and blowdown rate of 0.2 cm/day. Ha~inuw, rather than the 

average rates must be used because such rates are likely to persist for a 

period of months during the summer, Additional nater is required for initial 

filling of ponds, but this is assumed to take place during the nun-suamer 

months, when excess capacity is available, The required volumes and f1owrates 

were listed in Table 7-2, On a continuous basis, the conbined flowrate is 

22,700 lpa (6000 gpn). Both the supply and distribution system will be sited 

an this basig, although puaping costs are based on yearly averages of 15,200 

Ipm 14000 gpm), which reflects both reduced evaparation and some contribution 

from rainfall, The authors believe that the SERI eetirates for water 

consumption were too low, while estimates for the cost/unit delivered werB 

high. This analysis assumes a separate well field for each 192 hectare 

module, which differs from the approach taken in the SERI resource studies, 

The well field is assumed to be off-site, to avoid 0&H interference and 

possible subsidence problems, Eight 30 em (12") wells, each rated at 2840 lpm 

(750 gpa), are set in a grid pattern with a spacing of 1600 aeters (0.5 

rile). The wells are assumed to be 122 meters 1400 ft) deep, with a static 

lift of 46 meters (150 ft). A water storage reservoir (16,000 m3) is 

included as part of the supply systea. if necessary, water conditioning 

facilities would be located at the reservoir (see Section 2). 

A cost estimate of the water supply system is presented in Table 9-3, The 

coat of wells is based on information supplied by well drillers in the Salton 

Sea area, The cost of the piping network is based on the assumption that 

inexpensive '1100 ft headn PVC is used. While heavier, more enpensive pipe is 

always used in municipal nater systems, the 100 ft head pipe is widely used in 

law pressure agricultural applications, especially when large diameters are 

required. All large diameter pipes specified throughout this report are of 

this'type, The unit costs in all cases include9 installation, which runs 
Table 9-1 192 Hectare Svstem Capital Cost Summary 

Base Case: 112 mt algaelhalyr 

TOTAL $ $/HECTARE 

GROWTH PONDS ------- --------- 

Earthworks* $1,945,960 S 10,135 

Walls & Structural 1,594,290 8,304 

Mix i nq Svstem 944,537 4,919 

Carbonation Syster 351,360 1.830 

Instrumentation not included elsewhere 96,000 509 

HARVESTING - Settling Pond Option 

Primary** 1,436,000 7,479 

Secondary (centrifuqation) 760,000 3,958 

SYSTEM-WIDE COSTS 

Water Supply 

Water Distribution 

C02 Distribution # 

Nutrient Supply System f 

Blondonn Disposal System* 

Buildrnqs (harv. blds. not included) 

Roads & drainage* 

Electrical Drstributron (3% of above) 

Electrical Supply 

Machinery 

ENGINEERING (10% of above)* . 899,656 4,686 

CONTINGENCY (15% of above), 1,484,433 7,731 

LAND COSTS 01250/hectare)+ 

TOTAL CAPITAL COST 

DEPRECIABLE PORTION $6,415,601 $33,415 

NON DEPRECIABLE PORTION $5,445,049 $28,360 

Notes: 

* non-depreciable item 

*+ patrially non-depr, ($375,000) 

112 utt/ha/yr = 30 g/m2/day 

.Land area 2 x qrowth pond area 
Table 9-2 Electrical & flaintanence Operatinq Cost Summary - 192 Hectare Svstem 

GROWTH PONDS 

Earthworks 

Walls & Structural 

nixing System 

Carbonation System 

Electrical* Hal nt anence* 

kwh/yr S/yr XcfCap S/yr -ww--- -1111- 1-111--- --m" 

HARVESTING - Settlina Pond Optlon 

Pr i rnary 543000 22,295 

Secondary (centrifugationi 1096000 71,240 

SYSTEM-WIDE COSTS 

Water Supply 1555000 101,075 

Water Distribution 121000 7,865 

C02 Distrtbution 

Nutrient Supply Syatem 104000 6 760 

01 owdown Di spoeal System 

Buildings (harv. blds, not 200000 13,000 

Roads & drainage 

Electrical Distributton 

Electrical Supply 

Machrnery 

TOTAL 

HECTARE 

* Rssumes electricity costs So.065 / kw-hr 

*# Maintanence materials only 
about $10-26lmeter ($3-8/ft), depending on size, 

The water distribution system includes eveything beyond the storage reservoir 

and water conditioning system. Three vertical propeller pumps feed into a 

piping network that supplies makeup water to the growth ponds. The system 

schematic is shown in Figure 9-1, along with pipe sizes, flawrates, and 

pressure losses. The flows are for evaporative makeup only, the blowdown 

make-up is added when the pond is refilled after harvesting. In a system 

using settling ponds, the central corridor is fairly wide, (about 110 meters), 

so it is more practical two use tno distribution mains which run down either 

side of the central corridor. A puap station is located at the storage 

reservoir. Pressure requirements are assured to equal the dynamic (mainly 

pipe friction) losses, since some static head is available at the reservoir. 

The water distribution system could conceivably operate by gravity flow, but 

this assumption was not made. 

Table 9-3 Water Supply System Cost 

Pipe Total Installed Total 

Size Di stance Cost Cost 

inches meters feet $/f t t ..................................................................... 

10' dia. 4024 13200 $6.00 $73,200 

15" dia. 005 2640 9.00 23,760 

20" dia. 805 2640 15.00 36,600 

24H dia. 500 1640 2 1.00 34,440 

------ 

TOTAL PIPING $177,000 

VALVES & FITTINGS 30 000 

DRILLING t CASINGS 8 x 400 ft B %50/ft 160,000 

PUMPS, Submersible S.S. 8 x $10,000 

Electrical equipment 

Instal lation 

HYDROLOGICAL STUDIES & TESTING 

* STORAGE RESERVOIR 

9.2 C02 SUPPLY AND DISTRIBUTION 

The source of C02 for microalgae production has been examined in some 

detail C93. It was concluded that C02 could be acquired from existing or 

proposed power plants and the competition fron enhance oil recover (EOR) 

would not pose a serious problem. The cost of CD2 derived in this fashion 

depended on a number of assumptions regarding scale, location, ownership of 

the power plant, etc., and ranged from $0.07 - $0.21/m3. This report does 

not attempt to refine the SERf estimates. Instead, the C02 cost is treated 

as a variable, and subjected to a sensitivity analysis in Section 11. 

The design of the distribution system depends upon the pressure at which 

C02 is delivered to the site, assuming that about 2.5 psi is required at 

the pond to satisfy the static head and sparger losses (1.5, 1 psi 

respectively). If this pressure is high 050 psi), then the distribution 

network can consist of very small (6" and less) pipe sizes. For medium 

pressures (e.g. 10 psi), pipe sizes would range fron 8" to 3". For very low 

pressures (3.5 psi, or a 1 psi drop through the distribution system), sizes 

would range from 12" to 4". The latter might apply to a system which 

recovered unpurified flue gas at atmospheric pressure. In such a case, a 

trade-off exist6 between compressing to medium pressure (lower capital cost, 

higher operating costs) versus low pressure (higher capital cost, lower 

operating cost). A high pressure distribution system is not practical, since 

the compressors required are very expensive compared to the high voluae 

turboblowers that would be used for low or medium pressures. The low ve. 

redium pressure trade-off war not evaluated, because the impact on overall 

costs is very small. The medium pressure case was used to size the C02 

distribution network. The cost of C02 is assured to include delivery at 10 

p%i, except in the nutrient recycle scenario, where coapresaion costs for the 

anaerobic lagoon flue gas are included (see Sections B t 91). 

Since the supply costs are included in the delivered unit CD2 cost, and the 

flow metering and control systems were included under growth pond carbonation 

(Section 7.3.61, the costs shown in Table 9-1 consist solely of tho piping 

network, which is itemized in Table 9-4. Except for the pipe sines, the 

network is identical to that of the makeup water distribution system, and 

therefore is not shown. 

9.3 NUTRIENTS 

The types of nutrient required and their source is discussed in Section 10. 

Liquid ammonia is used for nitrogen requirements. A11 other nutrients are 

purchased as salts. Since all of the nutrients ate added at the beginning of 

the batch, with the possible exception of soae additional ammonia during the 

first two days, the facilities can be located at the harvesting stations, 

with nutrients being added into the return flow network. If necessary, an 

ammonia tank can be located at each set of ponds for supplemental nitrogen. 

In general, a batch growth cycle greatly simplifies the process of nutrient 
additions. 

Since the cost of adding nutrients (other than COZ) is minor, r detailed 

design was not performed. An estimate of $40,000 per harvesting station plus 

$2500 per set of ponds, for a total of $150,000 na5 included in Table 9-1. 

TLBLE 9-4 C02 DISTRIBUTION NETWORK CAPITAL COSTS 

Pipe Tot a1 Inet a1 led total 

Size Distance Cost Cost 

inches meters feet $1 f t $ 

-,1-------11-----1---------------CL-I.*.r)--w--------w-------"--"-"---------9- 

8 134E1 4420 5,OO $22,i00 

b 603 2240 4.00 8 960 

4 372 1220 3m50 4,270 

3kh 40) 366 1200 3.50 4,200 

--C*-- 

PIPE TOTAL 39,500 

VALVES, FITTINOS, nlsc. 

TOTAL 

9.4 BLOWDOWN DISPOSAL SYSTEM 

The issue of blowdonn was discussed in Section 2. A blowdown rate equivalent 

to 14% of the evaporative rate is specified. For an average evaporation of 1 

cdday, the blowdown f loaratr is 2700m3/day (95,000 ft3/day). The 

blondown is taken from the centrifuge effluent stream, and pumped to 

evaporation ponds, where it is concentrated back to solid form. Ultimate 

disposal is by trucking the aalt to a suitable landfill. The evaporation 

ponds cover 27 hectares (14% of the growth pond area), and consigt of 

shallow, unlined oerthen ponds. These ponds cast about $110,000 to 

construct, with another $50,000 budgeted for puaps, piping and misc., for a 

total of 5160,000. A cost of Iclkg algae (0.67clkg salt) is included in the 

operating cost for ultimate salt disposal, 

Buildings include an office, lab, shop, and storage sheds for nutrients and 

machinery. The coat of buildings for harvesting machinery was included in 

the harvesting cost estimates. The offices, lab, and culture rooms can be 

large permanent trailers. The shop has a concrete floor and utilities. Tho 

sheds have concrete f1oors, are open on one aide, and have a minimum of 
utilities. A rough estimate of the building costs is given in Table 9-5. 

Table 9-5 Building Costs 

Offices (trailers): 1000 ft2 C $30/ft2 130,000 

Lab, culturerooas (trailers): 1000ft2~$30/ft2 $30,000 

Shop: 2200 ft2 Q f1s/ft2 33,000 

Sheds; 2000 ft2 Q $8.5/ft2 

TOThL 

9.6 ROADS AND DRAINAGE 

Roads and drainage are difficult to estimate in the absence of a specific 

site. If the perimeter walls of the pond syster are earth berms, then the 

cost of upgrading them to roads (unpaved) is minor, since large amounts of 

crushed rock is already being imported for p~nd lining, Drainag~ would 

involve construction of diversion channels (if necessary), placing of 

culverts, etc, and would be integrated into gron pond @arthworks. A figure 

of $100,000 is assigned to roads and drainage. 

9.7 ELECTRICAL SUPPLY AND DISTRIBUTION 

Electrical distribution includes the cost of all on-site power distribution 

and wiring, exclusive of the utility service, substation, and motor starters 

and controller-s Ith, latter were included in the individual cost estimates). 

Power distribution systems are normally estimated in terms of total facility 

cost, taking both complexity and scale into account. Given the size and 

relative simplicity of tho syster, a factor of 3% is used. Considering that 

so much of the facilities cost ia for earthworks and pond walls, which have 

no electrical power requirements, this estimate is quite reasonable. 

In order to arrive at a figure for electrical supply, it was arbitrarily 

assumed that S miles of transmission lines would be required. fl recent 

estiaate for from the Imperial Irrigation District af $3/ft (essentially 

independent of load) was used +or transrission line cooto (980,000) a fin 

additional 143,000 (again IID estimate) was allocated for the substation cost 

(1000 kVA), for a total of $113,000 for electrical supply, 
9.0 H4CH I NERY 

A budget of 980,000 is included for vehicles and machinery. Typical 

requirements would be two pick-up trucks, one flatbed truck, a 

bachhoe-loader, and misc. shop machinery, 

9.9 OTHER COSTS SHOWN IN T4BLE 9-1 

The remaining costs shown in Table 9-1 (engineering, contingency, land), are 

taken from the SERl econoaic rodel. The land cogt is based on a total land 

requirement of two times the growth pond area. Actual land requirements are 

quite sensitivh to the well spacing, which is difficult to estimate, 

However, the contribution of land cost to total cost is minor, so that an 

error will have very little efhct, especially on an annualized basis. 
SECTION 10.0 

LARGE SCALE SYSTEM OPERATIONS AND OPERATING COSTS 

10.1 OPERATIONS OVERVIEW 

The operations described below form the Base Case that serves as the 

reference for cost sensitity analyses in Section 11.0. Deviations from this 

case are so labeled. 

The basic operation of the conceptual large scale system consists of batch 

growth followed by batch accumulation of lipids (to 50% of the ash free dry 

weight) induced by nitrogen limitation. Both processes are invisioned to 

take place in the same pond. Recent results of Laws 131 indicate that high 

productivity of nitrogen sufficient biomass is attainable in batch culture. 

The biomass productivity after nitrogen depletion from the medium, in batch 

operation, ha6 been shown t1,103 to be nearly equal to that of nitrogen 

sufficient batch growth when carbohydrate is accumulated. For lipid 

accumulation, a higher heating value must be ascribed to the biomass so that, 

on a dry weight basis some decrease in biomass productivity must be 

expected. There is little or no evidence that algae have a high enough lipid 

content during active growth. Since nitrogen sufficient batch growth appears 

to be productive, and lipid accumulation aust be done in batch, there is no 

real reason to operate any of the system continuously. Cells would 

accumulate storage products under nitrogen depleted continuous dilution, but 

much of the biomass harvested would not be induced, or only partially so. 

The average productivity of the system is postulated to be 30 gm/m2/day 

averaged over a 360 day year. This is equal ta a photosynthetic efficiency 

of 7.5% of visible light. Productivity is expected to be lower during the 

late fall, winter, and early spring and higher at other times. The density 

of cultures reflects this, being lower during cooler, less sunny times of the 

year. Since productivity is not a linear function of temperature and 

insolation, batch density would be lower when productivity is lower, even 

though detention times are longer. At times of high productivity, nitrogen 

sufficient batch growth would last from 1.5 to 2 days followed by a 2-3 day 

induction period. At times of law to moderate productivity, these perlods 

would be, on average, 2-3 days and 3-4 days. The density achieved when 

nitrogen first becomes depleted from the medium are, for the two eases 

respectively, 400-500 ppm and 250-300 ppm. This would increase under 

induction conditions by a factor of about two to 800-1000 ppm and 500-600 ppm 
for the two average cases, Thus, at the time of harvest the density of the 

cultures would range between 500 and 1000 ppm with a lipid cuntent of about 

SOX and a nitrogen content of about 4X, with 20-25 X protein 15-207. 

carbohydrate and a balance of iOX other chemicals. 

The induced biomasa is to be harvested either by a two-stage settling process 

or by flotation followed by foam collection. Either process would be 

followed by centrifuging material concentrated by a factor of 50. The 

primary harvesting processes are not expected to be 100% efficient. This is 

not a problem since an inoculum must be left for start of the succeeding 

batch. A harvesting efficiency of 90% is postulated for the Base Case. The 

centrifugation of the 205% slurry increases the density to 10-20X ash free 

solids, 

Since substantial performance is being expected of the primary harvesting 

process, it may become necessary to use chemical flocculants to aid 

clarification rate and efficiency. The dose of chemical is postulated to be 

low (<t.OZ/kg biomass). In the Base Case, the cost of polymer addition is 

set at $.Ol/kg harvested biomass, 

The organism required t~ function in this system must possess several 

important characteristics. It rust be competitive, pr~ductive, induce lipid 

prolifically, not be subject to inhibition by light, oxygen or fluctuations 

in temperature, and it must be able to recover from depigmentation quiekly 

and become highly productive soon after nitrogen is replenished in the 

medium, Each of these characteristics has been observed in at lea~t sore 

organism, but not all in any one organism, However, a concerted effort to 

find such an organism has just recently begun at SERI. Probably the most 

severe criterion of those listed is the ability to store large amounts of 

lipid quickly. A recently isolated chrysophyte, called ChryggmEI, is 

tentatively chosen as a test organism, It aecululates l i p i d s p r o l i f i c a l l y 

(personal communication, 0. Barclay of SERI), has a broad salinity tolerance, 

but must be tested far its tolerance to high temperature. The P1giyin"gn2,g2- 

grown in Hawaii, although not a lipid producer, will be used as a 

productivity standard, since it is, as of now, the nost productive organium 

grown in intensive, outdoor culture. 
Carbon is to be supplied as purified COZY introduced into the ponds via 

sumps 1.5 m deep. The source of carbon, at a 400 hectare scale must either 

be commercial or, in the best of circumstances a C02 well near the site. 

Power plant carbon containing gases are not a feasible source at this 

relatively small scale. The algal biomass, after extraction of the lipid 

component, will be anaerobically decomposed in a covered lagoon from which 

the liberated gases are recovered. The methane energy is to be converted to 

heat and electricty with tho C02 remaining recycled for the growth of more 

algal biomass. 34% of the carbon needed for new growth can be provided in 

this manner, reducing the demand of new carbon to algae ratio from 1:1.7 to 

1:2.4. The recycle of nutrients from the anaerobic digester is not included 

in the Base Case. 

The water resource specified for use im tMs system is similar to the Type I1 

nater described by SERI. This water has a TDS of 4 ppt, an alkalinty of 

13-15 req/l and a Ca concentration of 10 mH. The water needs to be 

conditioned by equilibration, in holding ponds, with the atmosphere to induce 

precipitation of the calcium as calcium carbonate. The precipitate will be 

removed by alum or lrme flocculation, if necessary, and sedimentation. The 

resulting water is low in calcium (1 rH is the practical lower limit) and 

still contains about 4 req/l alkalinity. fin eiqht-fold average concentration 

of solutes is achieved when an average amount of water is blonndown which 

equals 1/7 of the average evaporation. Since the system is to be operated in 

batch, the salinity will fluctuate soaewhat, but this is a secondary effect. 

Thus the pond mediu~ will avaraqe 32 ppt TDS. 

The approximately 1.5 mt of salts produced per mt of algal biomass will be 

transported to a large body of salt water, or other disposal site, at a eost 

of .67 cents per kg. The sludge from the lagoon will be dried in sludge 

drying beds and plowed in on site. 
10.2 OPERIITIONAL COSTS OF A 1000 4CRE SYSTEH 

The parameters of the Base Case deslqn uf the lrr~e scale system are 

summar~ted in Table 10-1. This design is uaed in Section 11.0 as the 

reterence case tor cost sensitivitv analysis, 

Table 10-1. Base Case Oesiqn Parameters 

Parameter Spec1 f ication --------o-----I------------------m-----------------------------------o------------- 

Pond slze, hectares 

Ponds/ modul e 

Module size, hectares 

Number 04 modules 

land required/lU00 acres 

growth ponds, acres 

Evaporation rate, 

n/ d/yr 

Blow 'down ratio 

Water requirement, 

m3/ yr 

Avcraqe well depth, m 

Pond depth, m 

Pond volume, n3 

System volume. a3 

TDS of water resource, 

PP~ 

Operating TDS, ppt 

Salt disposal mt/yr 

Erowinq season, days 

Daily praduct~vity, 

qm/m2/d 

Total production, mt/yr 

Lipid content, X 

Pond channel velocity, 

cnrls 

Carbon source 

Nitrogen source 

Phosphorus source 

20 

Purified C02 

fimrnon I a 

Superphosphate 
The operatinq costs of the Base Case desiqn are 5u~mariZed in Table 10-2. fill 

costs are given on a per hectare per vear basis, a per module (192 ha) per 

Year basis, and on a total cost per 1000 acre per year. For the chemical 

inputs, the unit requirement and the unit cost are qiven as well. Power unit 

cost is taken at 6.5 cents per kilwatt hour. Disposal of salts contained in 

the blowdown (evaporated and transported to a disposal site) is taken as .67 

Cents per kg salt produced. The breakdown of the maintanance and labor costs 

are given in Table 9-2 and 10-3 respectivelv. 

The carbon source is purified C02, at a low cost of $35/mt. This value is 

varied in the sensitivity analysis presented later. 2.2 kq C02 is required 

to produce a kq of alqal biomass at 50% lipid. Losses are assumed to be less 

than 5%. Nitroqen, at $250/mt is derived from ammonia, and used with a 75% 

efficiency to cover losses. The phosphorus, at t900lmt as derived from 

superphosphate. Iron is added as ferrous sulfate and costs t500/mt Fe. 411 

other nutrients are assumed to be present in the water resource, or as a trace 

contaminant of the above nutrients. Even with the low price of C02 assumed, 

this one input alone dominates the production price of the alqal biomass. 

A high molecular weight polymer is included to flocculate the alqal biomass 

prior to primary concentration in a settling pond. It is assumed that I ppm 

of polvmer is required for each 500 ppm biomass. The cost of the polvmer is 

$5.00/ kg. 

The only operating cost associated with the water resource is the cost of 

pumping from a 50 m deep well and transport to the holdino ponds. Water 

conditioning is presumed to occur durinq the eiqht day holdinq time, and is 

due to the precipitation of calcium carbonate by the alkallnity in the water 

upon equilibration with the atmosphere. Power costs are included for mixing, 

harvesting (dominated by centrifuge power), nutrient supply pumping, and 

building utilities. 

The maintenance operating costs are for materials only, as detailed in Table 

9-2 of Section 9.0. The labor for maintenance is included in the personnel 

breakdown listed in Table 10-3 Estimates are based on five shifts per week, 

360 days per operation, and rough judqement of people needed en hand. 

For this base case, the total, non-annualized operating costs are $6.2 million 

for the 45,450 mt of algal biomass produced. fit 50% lipid and a conversion of 

7.14 bbl lipid per mt lipid, the "lipid oil" produced equals 140,000 bbl/yr, 

The capital cost summary was given in Section 9.0. Together with the 

operatinq cost summary Table 10-2, the total annualized production cost will 

be calculated in the next section using the SERL economic model. 
Table 10-2 Total Operating Costs - Base Case 

QUPIN UNIT I.L- YEARLY COST, Thousands --- 

RED ' D COST 192 ha tOOO ac 

kg/ kq $/mt S/ha/yr 

NUTRIENTS t 1) ----- ---- ------- 

C02 2.2 35 $8.65 

N, as NH3 0.053 250 1.47 

P, as Superphosphate 0.005 900 0.51 

Fe, as FeS04 0.005 500 0.28 

------ 

Total $10.91 

FLOCCULANT 

POWER 

Mixing 

1 Harvesting 

2 Harvesting 

Water Supply 

Nutrient Supply 

Bui ldings 

Total 

SALT DISPOSAL 

MAINTANENCE (matl's) 

LABOR 

TOTAL 

(1) kg/kg kg required / kg algae produced 

(21 See Table 9-2 

(3) See Table 10-3 

* 192 ha basis 
[able 10-3. Labor Required for 1000 Acre Svstem 

............................................................................... 

litle No. Hrs/Yr $/Hr $/Yr ............................................................................... 

Pl ant Hanaqer 1 2080 2 5 52000 

Shift Supervisors 4 2080 17 141,440 

Pond Operators 10 2080 10 166,400 

Centrifuoe Operators 5 2080 12 124.800 

Laboratorv Hanaqer 1 2080 17 35 ,'360 

Laboratory rechnicians 2 2080 10 41.600 

TOTAL 561,600 
SECTION 11.0 

ECONOMIC ANALYSIS OF A 1000 ACRE ALGAL PRODUCTION SYSTEH 

11.1 BkSE CASE 

fhe capital cost of the Base Case desiqn was presented in Table 9-1, the 

operatinq costs in Table 10-2. hppendix Vi contalns these tables aqazn as 

well as the capltal and operating costs for all of the sensitivltv analyses, 

In the Base Case the biomass productivity is 45.5 x lu3 at/vr at a lipid 

content a+ SOX. This 1s well in excess of any currently achievable lipid 

product~vity. The biomass production value has been achieved, on a year round 

basis C33, but under conditions af nutrient su+ficiencv and at IS-20% lipid 

content. The price of CU2 used in the Base Case is S35/mt whlch is about as 

much a5 a verv large scale user would be charged for commercial LO2 if 

transportation d~stance were less than 200 miles. The installed system cost 

is $76,600 per hectare using a low cost system design and favorable 

assumptions concerning the suitability of land and other resources needed +or 

system construction. The total capital cost of construction is $25 million 

dollars, Thus the Base Case must be considered verv optimistic in terms of 

lipid productivitv, nutrient costs, and attainment o# capital cort goals. In 

this section. the sensitivity of the production cost of algal bromass and 

lipid ail (unextracted), to these assumptions will be analyzed to determine 

where the future work must be concentrated. 

Table 11-1 shows the input and output data of the Base Case using the SERI 

economic model. The parameters of this model are given in Table 11-2, II 

quick glance at the economic figurer reveals that even at f35/mt. GO2 costs 

dominate the Base Case econamics. Half of the annuallzed product~on casts 

come from this. Unless the prlce, or quantity of C02 is reduced, the 

economics a+ producinq Low value products from algae cannot improve 

siqnificantly, In addition, Increases in productivity have relatively tittle 

effect on final costs when CU2 is so dominant a factor. Thus only some 

initial sensitivity is presented with the Base Case as the re+erence level. 

The cost of the carbon input rs significantly reduced by the addition of an 

anaerobic laqoon, in which extraction resldues containinq about half of the 

algal carbon, are degraded to volatile carbon gases which are recycled to the 

qrowth ponds. The design of an efficient, law cost recvcling system, is an 

important feature o+ the large scale design and experzrnental system tests. 

11.2 SENSITIVITY OF BhSE CASE TO PRODUCTIVITY CHANGES 

Table 11-3 shows the effect of varying the system biomass productivity on the 

annualized production costs. Capital costs of sore items, like centrifuges, 

were increased using a scale factor of ,7. However, no increases in capital 

costs were assumed necessary to achieve the two and three.fold increases in 

productivity analyzed. The major increases came in operating costs, 

particularly in proportional increases in the CO2 required. Ooublinq the 
Table 11-1 Base Case Economic Analysis 

INPUTS BASE CASE ............................................. 

Depreciable capital investment $13,940,000 

Non-Deprec capital investment 11,060,000 

Annual operating costs 6,180,000 

Annual maintenance costs 510,000 

System algal yield mt/vr 45450 

System Lipid yield bbls/yr 150000 

Carbohydrate yield mt/yr 910Q 

Protein yield mt/yr 9100 

CALCULATED VALUES 

----------------- 

Cost of capital 0.0475 

Cap Recov Factor (book life) 0.0692 

Cap Recov Factor (depr life) 0.0943 

Fixed Charge Rate 0.0951 

PV of Capital Investment $17,349,560 

PV of NonDsprsc Invaatmrnt 13,765,150 

PV of Operating costs 123,965,000 

PV of Maintenance costs 10,930,980 

TOTAL PV OF FACILITY $166,010,700 

Annualized Cost Algae Plant $11,934,510 

LIPID only price $/bbl 79.56 

ALGAE prico $/mt 262.59 

Lipid price by weight $/mt 304.6r8 

Lipid price by value S/mt 284.56 

Protein price by weight $/mt 304.68 

Protein price by value $/mt 327.07 

Carbohyd price by weight $/mt 304.68 

Carbohyd price by value $/mt 327.87 

Annual i zed Capi tal Cost DCI $1,650,002 

Annualized Capital Cost NCDI 952,285 

Annualized Operating cost OPP 8,976 007 

Annualized Mainten. Cost HNT 756,215 

Annualized Cost Total A AP 11,934,508 

Annualized Capital Cost DCI 13.8% 

Annualized Capital Cost NCDI 9, 0% 

Annualized Operating cost OPP 71.9% 

Annualized Mainten. Cost NNT 6.3% 

Annualized Cost Total AAP 100. 0% 
Table 11-2 Economic Model Input Parameters 

FINRNCIAL PARAllETERS 

Base year for constant dollars 

Year for investment outlay 

Year for cost information 

Year first commercial oper 

System oper life (baok life) 

fax life for depreciation 

annual other taxes fn of CI 

Annual ins premium fn of GI 

Effective income tax rate 

Investment tax credit 

Debt:tctal capitalization 

Common Stk:tot capitalization 

Prefer Stk:tot capitalization 

Ann rate return on debt 

hnn rate return common stk 

Ann rate return prefer stk 

Rate of general inflation 

Escalation capital costs 

Escalation operating costs 

Escalation maintenance costs 

Cost capital [optional) 

Cap Recovery Factor (optional) 

Fixed Charge Rate (optional) 

Lipid credit $/st 

Protein credit $/nt 

Carbohydrate credit t/mt 
productivity only decreases unit production costs by 207.. '[ripling 

productivity only leads to a further decrease of less than 5%. or 23% 

reduction from the Base Case. Thus productivity enhancement will only be 

meaningful if the amount or cost of C02 is decreased. The cost was already 

assumed to be quite low. The recvcling of carbon will be seen to dramaticailv 

affect the sensitivity of production costs to productivity increases. 

Table 11-3. Base Case: Sensitivity to Productivity ............................................................................... 

Cost BASE 2XPROD. 3XPROD. ............................................................................... 

LIPID onlv price.S.bb1 

ALGAE price b/mt 

Lipid price by weight t/mt 304.68 244.28 235.60 

Lipid prlce by value f/mt 284.56 228.15 220.04 

Protein price by weight $/at 304.68 244.28 235.60 

Protein price by value $/at 327.87 262.88 253.53 

CHO price by weight $/mt 304.68 244.28 235.60 

CHO price by value %/st 327.87 262.08 253.53 

DCI, X total 

NDCI, X total 

OPP, % total 

HNT, Xtotal 

AAP, % 

11.3 SENSITIVITY OF THE BASE CASE TO CARBON RECYCLE 

The low cost anaerobic diqester is a major proposed innovation in that 

recovery of the input nutrients for return to the algal growth ponds has not 

been attempted on large scale. The efficiency of the recovery and reuse of 

nutrients from biomass degraded in a low cost, covered lagoon is a factor that 

must be empirically determined in the proposed experimental system. The 

lagoon not only allowr recycle of carbon (33%) but also up to 75% of the 

nitrogen and SOX of the phosphorus. In addition, the methane produced is 

combusted to produce electrical power, at about 25-302 efficiency. This 

electricity can be used on site, for mixing power, etc. In some of the cases 

analyzed, the electrical output of the digestion system exceeds the needs of 

the system. In these cases, the surplus value of the power produced, 

calculated at 6.5 cents/Kw.hr, is added as a negative number to operating 

costs. 

The recycle of carbon reduces the demand of new input carbon, per kg algal 

biomass, from 2.2kq to 1.6 kg. Table 11-4 shows the effect of the savings in 

C02 quantities on the annualized production costs of biomass and lipid. The 

capltal costs of the Base Case were modified to include the costs of the 

covered lagoon and engine generator. tlaintanance costs increased, but 

operating costs decreased due to the lower quantity of C02 used and the 

power generated. Since all of the unextracted biomass goes into the lagoon 
Table 11-4 Economic Analysis: Base Case + Recycle 

INPUTS BASE CASE RECYCLE -------------------IIIIII---L-""---L*-..)"~"~---I------""-"- 

Depreciable capital investment $13,940,000 $17,620,000 

Non-Deprec capital investment 11,060,OQO f1,430,000 

hnnual operating cost6 6,100,000 3,640,000 

Annual maintenance costs 510,000 800,000 

System algal yield mt/vr 45450 45430 

Syetem Lipid yield bbls/yr 150000 150000 

Carbohydrate yreld mt/yr 9100 

Protein yield mt/yr 9100 

CALCULATED VALUES 

----------------- 

Cost of capital 0.0475 0.0475 

Cap hecov Factor (book life) 0.0692 O.Ob92 

Cap Recov Factor (depr life) Q.0947 0.0947 

Fixed Charge Rate 0.0951 8.0951 

PV of Capital Investment $17,349,560 $21,?29,b50 

PV of NonDeprac Investment 13,763,150 14,225,640 

PV of Operating costs 123,965,000 73,014,990 

PV of Maintenance costs 10,930,980 17,14hf630 

TOTAL PV OF FACILITY $166,0iQ,700 $125,316,900 

Annualized Cost Algae Plant $11,934,510 $9,307,186 

LIPID only price Wbbl 79.56 62.05 

ALGAE price $/mt 262.59 204.70 

Lipid price by weight S/mt 304.68 443.82 

Lipid price by value S/mt 284.56 221.91 

Protein price by weight $/mt 304.60 443.82 

Protein price by value %/mt 327 . 87 

Carbohyd price by weight $/mt 304.68 443.82 

Carbohvd price by value $/mt 327.87 

Annual ized Capital Cost DCI $1,650,002 $2,085,584 

Annualized Capital Cast NCDI 952,285 984,142 

Annualized Operating cost OPP 8,5769007 5,051,241 

Annualized Maintan. Cost HNT 756,215 1,186,219 

Annualized Cost Total ARP 11,934,508 9,307,186 

Annualized Capital Cost DCI 13.0% 22.4% 

Annualized Capital Coet NCDI 8.0X 10.6% 

Annualized Operating cost OPP 71,9Y, . 54.3% 

Annualized Mainten. Cost HNT 6.3% l2.7X 

Annualized Cost Total AAP 100, OX 100,OX 
for digestion, there are no carbohydrate or protein by products. hlthouqh net 

included in the model, the lagoon sludoe is a potential fertii~zer product. 

The production cost of biomass drops 22% compared to the base case, from 

0263/mt to 6205/mt. The lipid onlv price drops from $79.b/bbl to Sb2lbbl. 

This is as much a decrease, relative to the Base Case, as triplinq the 

productivitv provided. More importantlv, it will be shown below that now 

productivity increases have much more impact on final cost than thev d~d 

without carbon recycle. This is due to the decrease, in terms of per cent of 

total annualized cost, of operating relative to capital outlavs. In the Base 

Case operating costs contributed over 70% of the total, capital onlv 22%. 

With nutrient recycle and power generation, operating drops to 54% of the 

total and capital rises to one third. 

11.4 RECYCLE CASE: PRODUCTIVITY SENSITIVITY 

The results of variations in assumed biomass productivitv, with 50% lipid, on 

the annualized production costs, are presented in Table 11-5. The 1.0 x 

productivitv case re+ers to the nutrient recvcle case discussed above. 

Doubling productivity now reduces production cast 30%, whereas without recycle 

the reduction was 20%. Biomass production cost is S144/mt, lipid prlce is 

544/bbl. If productivity is only increased by 50%, a 20% savings is still 

achieved in production costs. When processing of the biomass 1s included, 

i.e,, extraction and conversion to useable fuel, the impact 09 productlvitv 

increases is likelv to be reduced. The production costs are sensitive to 

reductions in productivitv, with a 30% reduction leading to almost a 30% 

increase in cost. Thus, a productivity of 30 gm/m2/dav on average wlth a 

50% lipid content, appears to be a high but economically reasonable goal. 

Decreases in productivity have substantial impact, but increases above 1.5 

fold begin to have diminishing returns as well as being unrealistic. This is 

shown in Fiqure 11-1 as a decrease in the slope of the graph of lipid prlee 

versus productivity. 

11.5 RECYCLE CASE: SENSITIVITY TO C02 PRICE 

Althouqh the price of C02 used in all of the preceding analvses is not 

inconsistent with commercial C02 cost under favorable circumstances, the 

quantities needed for verv large scale svstems, and the remote siting 04 these 

svstems, may preclude the use of commercial C02. In this case, the b35/mt 

price is a low one, as purification of C02 from power plant stack qases is 

more expensive than from refinery off gases. TO demonstrate the s@nsitlvity 

of the design to variation of the assumed price of C02, two cases were 

analyzed: free C02 and $70/mt COZ. The results are shown in Tahle 11-6. 

Doubiing the cost of carbon increases annualized production costs about 40X. 

#hen C02 is free (an exceptional case onlv applicable to small svstems 

located near an existing well) the costs are reduc@d 40%. Thus again, the 

Base Case assumption on carbon price appears to be an econom~callv reasonable 

one that must be achieved. The addition of nutrient recvcle to this cost is 

one of the most necessarv features to successfully develdp. Carbon is too 

costly, in general, to allow half of it to escape from the system without 

beinq incorporated into product. 
Table 11-5 Recycle Case: Productivity Sensitivity 

INPUTS R, 0.5xP R, 0.67xP R, 1.0~~ ...................................................................... 

Depreciable capital investment $14,370,000 $15,290,000 217,620,000 

Non-Deprec capital investment i0.820,000 11,030,000 11,430,000 

Annual operating costs 2,650,000 2,990,000 3,640,000 

Annual maintenance costs bC10,OOO 690,000 000,000 

System algal yield mt/yr 22725 303 15 45450 

Svatam Lipid yield bbls/yr 73000 100000 150000 

Carbohydrate yield mt/yr 

Protein yield mt/yr 

CALCULATED VALUES 

Cost af capital 

Cap Recov Factor (book life) 

Cap Reccv Factor (depr life) 

Fixed Charge Rate 

PV of Capital investment. 

PV of NonDeprec Investment 

PV of Operating cost3 

PV of Maintenance casts 

TOTAL PV OF FACILITY 

Annualized Cost Algae Plant 

LIPID only price Wbbl 

ALGAE price $/mt 

Lipid price by weight $/mt 

Lipid price by value $/at 

Protein price by weight S/mt 

Protein price by value S/mt 

Carbohyd price by weight S/mt 

Carb~hyd price by value S/mt 

Annual ized Capital Cost DCI 51,724,572 $1,809,794 $2,085,584 

Annualized Capital Cost NCDI 931,621 949,702 984,142 

Annualized Operating cost QPP 3,477,414 4,149,233 5,051,241 

Annualized Mainten. Cost HNT 978,631 1,023,114 1,106,219 

Annualized Cost Total A AP 7,312,237 7,931,843 9,307,186 

Annual ited Capital Cost DCI 23.6% 22.81): 22.4% 

4nnualized Capital Cost NCDI 12.7X 12.0% 10.6% 

hnnualized Operating cost OPP 50.3% 52,3'/. 54.3X 

Annualized Mainten, Cost MNT 13.4X 12.7% 12.7X 

Annualized Cost Total RPlP 10O.OY. 100.03: 100.0% 
Table 11-5 Recycle Case: Productivitv Sensitivity (continued) 

INPUTS R, 1.5xP R, 2xP ------------------,--------------------------------------------- 

Depreciable capita,l investment $19,640,000 $21,900,000 

Non-Deprec capital investment 12,000,000 12,550,000 

Annual operating costs 4,630,000 5,620,000 

Annual maintenance1 costs 1,000,000 1,120,000 

System algal yield mt/yr 68 175 90900 

System Lipid yield bbls/yr 225000 300000 

Carbohydrate yield mt/yr 

Protein yield mtfyr 

CALCULATED VALUES 

----------------- 

Cost of capital 

Cap Recov Factor (book life) 

Cap Recov Factor (depr life) 

Fixed Charge Rate 

PV of Capital Inve!stment 

PV of NonDeprec In~vestment 

PV of Operating costs 

PV of Maintenance coots 

TOTAL PV OF FACILITY 

Annualized Cost Algae Plant 

LIPID only price d:/bbl 

ALGAE price %/at 

L i p i d p r i c e by weight $/mt 

Lipid price by value $/at 

Protein price by weight $/mt 

Protein price by value $/mt 

Carbohyd price by weight $/et 

Carbohyd price by value $/nt 

Annualized Capital Cost DCI 

Annualized Capital Cost NCDI 

Annualized Operat i ng cost OPP 

Annualized Hainten. Cost HNT 

Annual i zed Cost Total A AP 

Annualized Capital Cost DCI 

bnnual ized Capital Cost NCDI 

Annualized Operating cost OPP 

Annualized Hainten. Cost MNT 

Annualized Cost Total A AP 

Table 11-6 Recycle Case: Sensitivity to C02 Price 

INPUTS R, Free R, $33/mt R, $70/mt ...................................................................... 

Depreciable capital investment $17,300,000 $17,620,000 $17,300,000 

Nan-Deprec capital investment 11,420,000 11,430,000 11,420,000 

Annual operating costs 1,100,000 3,640,000 6,180,000 

Annual maintenance costs 800,000 800,000 800,000 

System algal yield mt/yr 45450 45450 45450 

System Lipid yield bbls/yr 150000 150000 150000 

Carbohydrate yield mt/yr 

Protein yield mt/yr 

CALCULATED VALUES 

----------------- 

Cost of capital 0.0473 0.0475 0.0475 

Cap Recov Factor (book life) 0.0692 0.OQ92 0.0692 

Cap Recov Factor (depr life) 0.0947 0.0947 0.0947 

Fixed Charge Rate 0.0951 0,0931 0.0951 

PV of Capital Investment $21,531,380 $21,929,650 $21,531,380 

PV of NonDeprec Investment 14,213,200 14,229,840 14,213,200 

PV of Operating costs 22,064,970 73,014,990 123,965,000 

PV of Maintenance costs 17,146,630 17,146,830 f79146,630 

TOTAL PV OF FACILITY $74,956,100 $126,316,900 $176,856,200 

Annualized Cost Algae Plant $5,743,601 $9,307,186 912,793,210 

LIPID only price $/bbl 30.29 62.05 05.29 

ALGAE price $/mt 126.37 204.78 281.48 

Lipid price by weight $/mt 273.89 443.02 610.06 

Lipid price by value S/mt 136.95 221.91 305.03 

Protein price by weight $/st 273.09 443,82 610.06 

Protein price by value $/mt 

Carbohyd price by weight $/at 273.89 443.82 610.06 

Carbohyd price by value $/mt 

Annualized Capital Cost 

Annual i zed Capital Cost 

Annualized Operating cost 

Annualized Hainten. Cost 

Annualized Cost Total 

Annualized Capital Cost 

Annualized Capital Cost 

Annualized Operating cost 

Annualized tlainten. Cost 

Annualized Cost Total 

DC I 

NCD I 

OPP 

HNT 

A AP 

DC I 

HCD I 

OPP 

MNT 

AAP 
, 11.6 RECYCLE CASE: SENSITIVITY TO LIPID CONTENT 

Lipid content of the biomass produced (at 30 gn/m2/d) was varied from 2OX to 

50% (the Base Case value) to determine the effect on lipid price. 4s shown in 

Table 11-7, reduced lipid dramatically increases lipid price, Thus the Base 

Case assumption o# 50% lipid content needs to be achieved when lipid ail is 

the desired product. Recycle of carbon was assumed in this analysis and had 

the effect of causing a decrease in biomass production cost as lipid content 

was decreased. This analysis could be adapted to the case of methane fuel 

production if the non-lipid fraction is assumed accessible to deqradation and 

if the amount of carbon recycle is corrected for removal of carbon as the 

methane product. No such analysis was done in detail as lipld production is 

the primarv goal. The svstem would have to produce biomaes at 975/mt to 

provide methane at $S/flBTU. The svstem designed is effectve In producing 

methane gas if the covered lagoon digester performs as well as assumed, This 

will be studied in the proposed experimental svstem. 

1.7 RECYCLE CASE: SENSITlVITY TO DEPRECIABLE CAPITAL INVESTMENT 

The capital investment does not appear to significantly affect the annualized 

production costs until it qets large. Three variations in DCI were analyzed 

for their impact. The first, 1.5 times the DCI e+ the recvcle case would 

apply if the primarv harvesting device were much more expensive than the 

proposed sedimentation system. kn example of a device that would +all into 

this range of DCI increase is an enqineered dissolved gas flotation reactor, 

costing about $12 million per 1000 acre system. The second change in DCX, ta 

twice the baseline level, corresponds to lining the ponds with a hiqh quality 

synthetic material costing @SS. OO/mZ, or about $22 mill ion dollars per 1000 

acres of qrowth pond area. This type of liner would be used if ponds lined 

with less expensive earthen materials proved to lose too much water. The five 

fold increase in DCI would correspond ta lininq and covering a pond svstem. 

This is very costly and as yet there is no evidence that, en a large $talc, 

this concept is at all workable, As shown in Table 11-0, the SOX increase in 

DCI leads to a 15%' increase in product cost which implies that it is 

affordable if it is necessary far gaod performance of the harvesting system. 

The 100% increase in DCI, for a liner, increases cost of lipid product by 

SOX. This is affordable only if the increase is offset bv same other savings 

or by productivity increases. Thus use of a finer is marginal, The 400% 

increase, for a covered system, results in 2.25 fold increase in production 

costs, which is bv all means toa much even if the covered system somehow mad@ 

all other performance goals achievable. It must be kept in mind that 

synthet~c materials used for lininq and covering will likely inflate with 

crude oil prices, so that hoping for dramatic oil price increases to make such 

systems affordable is not warranted. 
Table 11-7 Recycle Case: Sensitivity to Lipid Content 

INPUTS R,20% Lipid ............................................. 

Depreciable capital investment $19,120,000 

Non-Deprec capital investment ' 11,850,000 

Annual operating costs 1,910,000 

Annual aaintenancs costs 1,000,000 

System algal yield mt/yr 45450 

System Lipid yield bbls/yr 60000 

Carbohydrate yield mtlyr 

Protein yield mt/yr 

R,30% Lipid R,4O% Lipid ,------rr_------------------- 

$18,370,000 $17,910,000 

11,710,000 11,570,000 

2,440,000 3,040,000 

940,000 880,000 

45450 45450 

90000 120000 

CALCULATED VALUES 

----------------- 

Cost of capital 0.0499 0.0475 0.0473 

Cap Recov Factor (book libel 0.0692 0.0692 0.0692 

Cap Recov Factor (depr life) 0.0947 0.0947 0.0949 

Fixed Charge Rate or095 1 0.0951 Q.0931 

PV of Capital Investment $23,796,330 $22,863,090 $22,290,580 

PV of NonDeprec Investment 14,748,370 14,574,130 14,399,996 

PV of Operating costs 38,312,810 48,944,110 60,979,550 

PV of Maintenance costs 21,433,290 20,147,290 18,861,300 

TOTAL PV OF FACILITY $98,291,010 $106,528,600 $118,551,300 

Annualized Cost Algae Plant $7,416,723 $7,962,412 $8,639,566 

LIPID only price $/bbl 123.61 88.47 72.00 

ALBAE price $/mt 163.18 175.19 190.09 

Lipid price by weight $/at 884.18 632.82 514.98 

Lipid price by value S/mt 442.10 316.42 257.50 

Protein price by weight $/mt 884.18 632.82 514.38 

Protein price by value $/mt 

Carbohyd price by neight $/wt 884.18 632.82 514.98 

Carbohyd price by value $/at 

Annualized Capital Cost DCI 12,263,131 tZ9174,3S8 $2,119,910 

Annual ized Capital Cost NCDI 1,020,305. 1,008,251 996,197 

Annualized Operating cost OPP 2,650,514 3,385,996 4,218,618 

Annualized Hainten. Cost PINT 1,402,774 1,393,807 1,304,841 

Annualized Cost Total A AP 7,416,723 7,962,412 8p639,566 

Annual i zed Capital Cost DCI 30.5X 27.3% 24.5% 

Annualized Capital Cost NCDI L3.8X 12.7% 11.52 

Annualized Operating cost OPP 35.7% 42.5% 48.8% 

Annualized Hainten. Cost HNT 20. OX 67.5% 15.1% 

Annualized Cost Total A AP 100. 01 fOO.0X 100. 0% 
Table 11-0 Recycle Case: Sensitivity to DCI 

INPUTS R, 1 .SxDCI: R,2xDCI R,5xDCI - - 

Depreciable capital investment $26,430,000 

Non-Deprec capital investment 11,430,000 

Annual operating costs 3,640,000 

Annual maintenance costs 1,060,000 

System algal yield mt/yr 45450 

Svstem Lipid yield bbla/yr 150000 

Carbohydrate yield mtlyr 

Protein yield mt/yr 

CALCULATED VALUES -----------n----- 

Cost of capital 0.0475 

Cap Recov Factor (book life) 0.0692 

Cap Recuv Factor (depr life) 0,0947 

Fixed Charge Rate 0.0951 

PV of Capital Investment $32,894,470 

PV of NonDeprec Investment 14,225,640 

PV of Operating costs 73,014,990 

PV of Maintenance costs 22,719,290 

TOTAL PV OF FACILITY $142,854,400 

Annualized Cost Algae Plant $10,735,500 

LIPID only price Wbbl 71.37 

ALGAE price $/mt 236.20 

Lipid price by weight S/mt 511,94 

Lipid price by value Wmt 255.97 

Protein price by weight S/mt 511.94 

Protein price by value Wmt 

Carbohyd price by weight $/mt 511.94 

Carbohyd price by value $/mt 

Annualized Capital Cost 

Annualized Capital Cost 

Annualized Operating cost 

Annualized Hainten. Cost 

Annualized Cost Total 

Annualized Capital Cost 

Annualized Cap.i tal Cost 

Annualized Operating cost 

finnuatized Mainten. Cost 

Annualized Cost Total 

DCI 

NCD I 

OPP 

MNT 

A AP 

DC I 

NCDI 

OPP 

MNT 

AAP 
11.8 RECYCLE CASE: SENSITIVITY TO COST OF CAPITAL 

All of the modellnq done so +ar rs based on assumptions which lead to a cost 

ot capital of about 5Z. While this mav be reasonable mn some clrcumstances, 

manv orlvate investors wlll want to see a greater return for rlsklnq capltal 

or tor investina In a capital intensive business. Uslno the recvcle case. 

three cost ot ca~ltal factors were used to test sensitivitv to tnls parameter, 

each with the oriqinal DCI and with the 100% Increased DCI. The results are 

q!ven In Tables 11-9 and 11-10. 

A5 expected, the cost of capital has qreat impact on final product costs and 

thls impact Increases as capital costs increase. The contribution of 

annualized capital cost to total annuallzed cost increases from 33% at the 

lowest rate and lowest level of capital requirement to 60% at the highest of 

each. This means that, except at the most favorable borrowinq rate, the 

capltal intensltv 04 a svstem 1s an important factor. Verv expensive svstems 

must be justified in terms of verv great increases in productivitv, However 

productivitv has an upper limit which is less two than times the base Case 

value, i.e., it is doubtful that a lipid accumulating alga could ever be 

expected to be 15% efficient in converting solar energv. For these reasons, 

the design criteria used in this report, lowest cost with highest effect, 

appears to be justified. 

11.9 RECYCLE CASE: SENSlTIVITY TO POLYMER DOSE 

Harvesting is one of the steps in the overall process that must be hiqhlv 

reliable. In the basic design of the system, it was assumed that a high 

molecular weight polymer would have to be added to the algal suspension to aid 

in flocculating the biomass prior to primary concentration. The dose of 

polymer used, 1 ppm per 500 ppm of biomass, is a low one. The results of the 

sensitivity analvsis shown in Table 11-11 indicate that this dose could be 

doubled without increasing product cost more than 7X, and even a five fold 

higher polymer dose would only lead to a 20% increase. A low dose, 1-3 ppm/ 

ppm, is becoming state of the art due to the capability of tailorinq polvmers 

to specific applications. 

11.10 CONCLUSIONS 

The sensitivity analyses performed confirm that the optimistic assumptions 

used in setting the larqe scale system performance standards are necessary to 

produce fuel products from algae economically. The analyses also indicate 

that a low cost, carbon efficient system has the best opportunity of ackievlng 

these standards. Productivity increases, which appear necessary despite the 

high lipid productivity assumed here, will have the most impact on final 

product cost when achieved within the framework of the system specified here, 

The questions of resource availability were not, a+ course, solved by these 

analyses. However, the system designed is very efficient, in its utilization 

o+ resources. 
fable 11-9 Recycle Case: Sensitivity to Cost of Capital (k) 

INPUTS R, kz.047 R, k=.07 R, k=.iO 

--- ----------1-1-1-------I----........II-I-I------------~-------~----------~ 

Depreciable capital investment $17,620,000 $17,629,000 517,620,900 

Non-Deprec capital investment 11,430,000 11,430,000 11,430,000 

Annual operating costs 3, b40,000 3,640,000 3,640,000 

Annual maintenance costs 800,000 800,000 800,000 

System algal yield mt/yr 45450 45450 45450 

System L-ipid yield bbls/yr 150000 150000 150000 

Carbohydrate yield mtlyr 

Protein yield mt/yr 

CALCULATED VALUES 

---------....------ 

Cost of capital 0.0475 0.0700 0. 1000 

Cap Recov Fartor._ l book 1 i f el 0,0692 0.0858 0,1102 

Cap Recov Factor (depr life) 0,0947 0,1098 0.1315 

Fixed Charge Rate 0.0951 0,1202 0.1581 

PV of Capital Investnent $21,929,650 $23,373,740 $25,395,390 

PV of NonDeprec Investment 14,22!5,440 13,162,420 16,473,860 

PV of Operating cczts 73,014,990 57,974,420 44,343,790 

PV of Maintenance casts 17,146,630 13,572,460 10,342,760 

TOTAL PV OF FACILITY $1261316q900 t11010839000 $96q5569090 

hnnualized Coat Algae Plant $9,307,186 $10,250,610 $11,853,790 

LIPID only price $/bbl 62.05 68.34 79.03 

ALGAE price C/mt 204.70 225.54 260.81 

Lipid price by weight S/mt 443.82 488.81 5b5.26 

Lipid price by value $/mt 221.91 244.41 282.63 

Protein price by weight $/st 443.82 488.81 565.26 

Protein price by value $/mt 

Carbohyd price by weight t/mt 443.82 488,81 563,26 

Carbohyd price by value $/wt 

Annual i zed 

Annualized 

Annual ired 

Annual i z ed 

CInnualized 

Annualized 

Annual i zed 

Annual i zed 

hnnual i z sd 

Annual i zed 

Capital Cost DCI 

Capital Cost NCDI 

Operating cost OPP 

Mainten. Cost MNT 

C~st Total CI AP 

Capital Cost DCI 

Capital Cost NCDI 

Operating cost OPP 

Hainten, Cost MNT 

Cost Total AAP 
Table 11-10 Recycle Case: Sensitivity to Cost of Capital at 2x DCI 

INPUTS 

2x DCI 2x DCI 2x DCI 

R, k1.047 R, kz.07 R, k=. 10 

Depreciable capital investment $35,240,000 $35,240,000 $35,240,000 

Non-Deprec capital investment 11,430,000 11,430,000 11,430,000 

Annual operating costs 3,640,000 3,640,000 3,640,000 

Annual maintenance costs 1,320,000 1,320,000 1,320,000 

System algal yield mt/yr 45450 45450 45450 

System Lipid yield bbls/yr 150000 150000 150000 

Carbohydrate yield at/yr 

Protein yield mt/yr 

CALCULATED VALUES 

----------------- 

Coet of capital 0.0475 0.0700 0.1000 

Cap Recov Factor (book life) 0 , 0692 0.0858 0.1102 

Cap Recov Factor (depr life) 0.0947 0.1098 0.1315 

Fixed Charge Rate 0.0951 0.1202 O.lS81 

PV of Capital Investment $43,859,290 $46,747,480 $50,790,780 

PV of NonDeprec Investment . 14,223,640 15,162,420 16,473,860 

PV of Operating costs 73,014,990 57,974,420 44,343,990 

PV of Maintenance costs 28,291,940 22,394,550 17,065,560 

-TOTAL PV OF FACILITY $159,391,900 $142,278,900 $128,674,200 

Annualized Cost Algae Plant $12,163,810 $13,817,670 $16,608,590 

LIPID only price $/bbl , 81.09 92.12 110.72 

ALGAE price S/mt 267.63 304.02 365.43 

Lipid price by weight $/at 580.05 658.91 792.00 

Lipid price by value $/mt 290.03 329.46 396.00 

Protein price by weight t/mt 580.05 658.91 792.00 

Protein price by value $/mt 

Carbohyd price by weight $/at 580.05 658.91 792.00 

Carbohyd price by value S/mt 

Annualized Capital Cost 

Annualized Capital Cost 

Annualized Operating cost 

Annualized Hainten. Cost 

Annualized Cost Total 

hnnualized Capital Cost 

Annualized Capital Cost 

Annualized Operating cost 

Annualized Hainten. Cost 

Annualized Cost Total 

DC L 

NCD I 

OPP 

MNT 

AAP 

DCI 

NCDI 

OPP 

HNT 

A AP 
Table 11-11 Recycle Case: Sensitivity to Polymer Dose 

INPUTS R, IX Polyn R, 2xPoly. R, 5xP01~. --------------------------------------

Oepreciable capital investment $17,620,000 $17,620,000 $17,620,000 

Non-Deprec capital investment 11,430,000 11,4301000 11,430,000 

Annual operating costs 3,640,000 4,094,000 5,456,000 

Annual maintenance costs 800,000 820 000 820,000 

System algal yield mtlyr 45450 45450 45450 

Svstem Lipid yield bbls/yr 150000 150000 150000 

Carbohydrate yield mt/yr 

Protein yield mt/yr 

CALCULATED VALUES -----------I----- 

Cost of capital 0.0475 0.0475 0.0475 

Cap Recov Factor (book life) 0,04172 0.0692 0,0692 

Cap Recov Factor (depr life) 0.0947 0.0947 0.0949 

Fixed Charge Rate 0,0931 8,0951 0.0931 

PV of Capital Investment $21,929,690 $21,929,650 $21,929,650 

PV of NonDeprec Investment 14,225,640 14,225,640 14,223,640 

PV of Operating costs 73,014,990 82,121,800 109,442,200 

PV of Maintenance costs 17,146,630 17,575,300 17,575,300 

TOTAL PV OF FflCILITY $126,316,900 $135,852,400 9163,172,800 

Annualized Cost Algae Plant $9,307,186 $9,764,858 $11,856,910 

LIPID only price S/bbl 62.05 66.45 99.65 

ALBAE price t/mt 204.78 219.29 2BB. 88 

Lipid price by might $/mt 443.82 475. 28 565,41 

Lipid price by value $/mt 221.91 237.64 282,71 

Protein price by weight $/at 443.82 475.20 565.41 

Protein price by value S/mt 

Carbohyd price by weight $/mt 443.82 475,20 565.41 

Carbohyd price by value $/mt 

Annual i zed Capital Cost DCI 

Annualized Capital Cast NCDI 

Annualized Operating cost OPP 

Qnnual ized Hainten. Cost HNT 

Annual ized Cost Total AAP 

Annualized Capital Cost DCI 

Annualized Capital Cost NCDI 

Annualized Operating cost OPP 

Annualized Mainten. Cost MNT 

Annual ized Cost Total UAP 
SECTION 12.0 

EXPERIMENTAL SYSTEM DESIGN AND CONSTRUCTION COSTS 

12.1 SITE DESCRIPTION 

The site chosen for the experimental svstem is in Brawlev. California in the 

Imperial Valley on a two thousand acre asparagus farm. Over one thousand 

acres of land are at present not cultivated. The location of the pond svstem 

is on land that borders the southwest side of the Salton Sea, makino that 

water resource available bv pipeline or shallow well. The land is 

substantially flat. with sandy and clay soils and sparse vegetation. Fiqures 

12-1 and 2 show the qeneral location of the site and the specific location of 

the pond construction area, 

The climate in the Imperial Valley is representative o+ the warmer. drier 

areas of the fimerican Southwest. Ihe annual rainfall averaoes 7cm. tne net 

pan l4 evaporation averaqes 240cm, and the mean insolation is 480 Lanalevs/dav 

total, Table 12-1 summarizes the mean monthlv and yearly climatic data. 

Table 12-1. Climatic Conditions at the Proposed Experimental Site .............................................................................. 

Month Rain.cintl41 Evap. ,cmCl41Lanq/Cl51 Max T Min T Av T ,°C1151 ............................................................................... 

Januarv 

February 

March 

Apr i 1 

May 

June 

Jul Y 

Auqust 

September 

October 

November 

December 

Total 7.3 244.4 Av 485 Av 22.5 

Althouqh the pond location is adjacent to a developed farm, it is essentiallv 

undeveloped. The benefits from the farm will be made available to the 

experimental system through a rental agreement. These shall include: access 

to water from the 1700 qpm well. access to power lines, lease of land 

required, option for expansion of land requirement, and use of office space. 

The agreed rent is $2000 per month. 


[he characteristics of the well water and of Salton Sea water are qiven in 

Table 12-2. Both waters are known to support the growth of photosvnthetic 

orqanlsms. The hiqh calcium level in the Salton Sea water necessitates some 

form of water conditioninq. After conditioninq, this water can be mixed with 

the well water to obtain a resource with almost any salinity. The two 

starting salinities of interest are 4 and 8 ppt, allowing experimental 

blowdown ratios of ,125 and .25 respectively, to attain a aedium salinity af 

32 ppt. The mixture ratios required to yield the two salinities are, well. 

water to Salton Sea water, 19 to 1 and 4 to 1. In addition, the Saltion Sea 

water can be used to approximate ocean water, 

rable 12-2, Chemical Composition of E~perimental Site Water Resources 

Salton Seal163 Groundwater 

------------------------------------------------------------------------------ 

12.2 EXPERIMENTAL SYSTEH DESCRIPTION 4ND JUSTIFICATION 

Aside from laboratory and other support systems, the experimental svstem 

consists of six 1.5 n2 ponds, three 50 m2 ponds, two 4000 a2 ponds (one 

acre each) and, if budget allows, one 4 hectare pond (10 acres), The qoai of 

the experimental system is to demonstrate, on a scale that can be extrapolated 

with a large degree of confidence to a full scale system, the desiqns and 

operational performance goals of the full scale system. The 4 hectare pond is 

the minimum site that is still close enouqh to full module size to ailow a 

direct transfer of results to a larger svstem. In that sense it is the optimal 

choice for this project. It is, however, costly, Thus the experimental 

system, without the 4 hectare pand, has been designed to test all of the full 

scale system parameters. fi greater degree of extrapolation is needed, of 

course, to transfer the results. Especially in the cases of mixing and 

carbonation, the larger pond is desirable. However, the .4 hectare ponds can 

be operated to simulate, in head loss and carbon storage time, the larger 

ponds. A11 o+ the final engineering results must be obtained from the .4 or 4 

hectare ponds. 
It is not the qoal of this experiment to encompass the aetivities of the other 

work carried on in the ASP. Species screening in general, bnoloq~cal 

adaptation studies, and development of resource analyses are all functions 

that are bevond the scope of th~s experiment. However, whenever an outdoor 

system is operated there is an abundance of laboratorv culture work and small 

scale test work that must accompany the demonstration experiments. Each site 

has its own environmental input parameters which must be studied. Each 

organism obtained from a screening program responds differently to these 

specific site inputs. The 1.5 a2 and 50 m2 ponds specif led are for use in 

these support studies. A large number of the former are included because they 

are easy to operate and manipulate, and also inexpensive. Beinq outdoors they 

are more realistic a test svstem that lab cultures. The 50 mL ponds bridge 

the qop botween the small ponds and the real demonstration ponds. Thev do this 

literally by providing an intermediate volume for inocuium build-up. In 

addition, less expensive mock-ups 04 engineerinq designs can be tested in 

these ponds, yielding results which serve in the evaluatian of the overall 

feasibility of a desiqn and thus input into the decision whether to go ahead 

and test at the larger scale. Two of the 50m2 ponds are +or testing basic 

desiqn parameters, two being the minimum number required far controlled, 

simultaneous experimentation. The third is t~ be used to vary subsvstea 

designs, e.q., airlift vs. paddlewheel mixing. More detail 15 given in 

Section 13 on the use of each of the pond systems. 

12.3 ALTERNATIVE SITES 

Two back up sites have been identified for the proposed experiment. Neither 

is as optimal, overall, as the primary site in Brauley! Ca., but each has 

epecific advantagas. One of the sites is also located in the laperla1 Valley, 

at Salton Citv. Lt borders the Salton Sea as well, Tkr advantages of this 

site are that it has more presently constructed laboratory and shop space and, 

most importantly, an inexpensive source of C02 from a well. The 

disadvantages are that the supplv of low TDS, water is signi-ficantly more 

expensive and that the enpansion potential is limited to under 0 hectares. 

Microbial Products, Inc, has an in-formal option to use this site. The seeond 

back up site is located in the area of Roswell, New Hexiso. No specific site 

has been selected, however conversations with personnel at the New Hexico 

Solar Enerqy Institute indicate that many sites are available. The Institute 

and other state agencies, as well as private eoncerns arc potentially 

interested in co-funding an algae based experimental and/or demonstration 

svstea. This is one of the primary advantages of this site. Water, of 

varyinq salinity is plentiful, laboratory and culture facilities are available 

for lease, and C02 pipelines are nearby. Thus this site would appear to be 

the least expensive at which to construct a -facility. However, the climate is 

not as warm, especially in late fall and early spring, os the Imperial V~lley 

o+ California. This could limit the length of the growing season. hlthouqh 

this may be a realistic condition for much of the Southwest, an experimental 

facility produces data more cost-effectivelv when the growing season is long. 

Ln any case, the de~iqn of the proposed svstem could be easily adapted to 

either of the alternative sites. 
12.4 EXPERIflENTAL SYSTEM DESIGN 

Since a primary goal of the experimental system is to validate the design 

concept8 of the large scale system, it5 design uill closely parallel that of 

the ponds and harvesting systems presented in Sections 0 & 9. Obviously, 

only a limited number of the more promising and important design options 

outlined in those chapters will be constructed, and the operation of the 

experimental system will focus on resolving the most important technical 

issues. 

The proposed experimental sits was described in the previous section. A nore 

detailed view of the actual pond site is shown in Figure 12-3. The large 

ponds (3 t 10 acres) shown are for reference only, and are not included in 

the baseline enperimental proposal. The proposed two 0.4 hectare ponds would 

be located in the lower middle portion of the site, as indicated on the 

figure. A section view of the site is shown in Figure 12-4, with approximate 

elevations above the Salton Sea. 

In the sub-sections which follow, each element of the experimental system is 

described, along nith its cost, starting with the two 0.4 hectare growth 

ponds. In most cases, the unit costs are significantly higher than in the 

192 hectare system, reflecting the 240-fold difference in total system size. 

Design parameters for the single pond and the two pond system are listed in 

Tables 12-3 L 12-4. 

Rough grading costs were estimated conservatively pending a more detailed 

gurvey of the pond rite. A local earthworks contractor quoted a price of 

$.~5/~d~ for cutting and filling. An allowanca was also made for possible 

diversion of the shallow gulley shown on the bottom of Figure 12-3, as well 

as for initial site clearing. fi total of $5000 was budgeted for this 

category. This should also cover the additional area required for the site 

building3 and the settling pond. Lazar levelling will cost about $3000 

total. The 52000 finish grading cost is actually lesr than in the large 

scale design because the liner costs (one membrane lined, one crushed rock) 

are 1 i sted separately. $900 is budgeted for sump excavation. 

The cracking/saepage issue discussed in Section 7.3.3. will be examined by 

building the divider wall and a portion of the outside wall in the unlined 

pond out of poured concrete. The outside wall, which has the full 20 cm of 

head across, it is wore likely to indicate a prablem, if any exists. If so, 

reaeilies,are available (e.q. covering the ingide of the !all nith a me~lbrane) 


Table 12-3 0.4 Hectare Pond Desiqn Calculations 

DESCRIPTION 

------------ 

Pond Area 

# of Channels 

L/W Ratio 

Depth 

Channel Velocity 

Mannings 'n' 

Paddle Eff. 

Drive Eff. 

PW WidthIChan Width 

Evaporative Rate (max) 

Blowdown Rate (ma%) 

Detention Time 

Wall Ht. (above grade) 

Wall Ht. (below grade) 

Sump Depth 

DESCRIPTION 

----------- 

Channel Width 

Paddle Width 

Centerwall Length 

Single Channel Length 

Total Channel Length 

Total Wall Height 

Slope 

Total Head Loss 

Total Efficiency 

Hydraulic Power 

Total Power 

Total Unit Power 

Velocity at Paddle 

Pond Volume 

Evap. Flowrate 

(alternate units) 

Blowdown Flowrate 

(alternate units) 

Harvest Flowrate 

(alternate units) 

NAME 

---- 

AREA 

#CHBN 

L/W 

DEPTH 

VEL 

MANNING 

PW. EFF 

DR. EFF 

PADICHAN 

EV AP 

BLOWDDWN 

DET.TIME 

MALL. HP. A 

WALL.HT.B 

SUMP.DEPTH 

NAME 

---- 

CHAN.WID 

PAD. WID 

CW.LEN 

CHAN. LEN 

Tt3T.CHAN.LEN 

T0T.WALL.HT 

SLOPE 

HEAD. LOSS 

TOT, EFF 

HY D. PWR 

TOT. PWR 

TOT.UNIT.PWR 

VEL. PAD 

VOLUME 

13. EVAP 

VALUE 

----- 

0.4 hectares 

2 - 

20 - 

20 rm 

30 cm/sec 

0.018 sec/mA0.33 

0.6 - 

0.7 - 

0.75 - 

1.50 cmlday 

0.21 cnrlday 

4.00 days 

40 cm 

10 em 

1.5 meters 

S.I. UNITS 

---------- 

9.69 meters 

7.26 meters 

193.71 meters 

208.92 waters 

417.84 meters 

0.50 meters 

2.492 x loh-4 

11.33 cm 

42% 

594 watts 

1413 watts 

0.35 watts/sq m 

40.0 cmlrec 

809.4 cu meters 

60.7 cu @/day 

42.2 litets/min 

8.5 cu @/day 

5.9 literslmin 

202.4 cu mlday 

14Q.5 lit@rs/min 

ENGLISH UNITS 

------------- 

31.78 feet 

23.83 feet 

635.52 feet 

685.43 fret 

1370.86 feet 

2.472 x loA-4 

4.44 inches 

42% 

0.796 hp 

1.894 hp 

0.35 wattslsq m 

1.31 ftlsec 

28584 cu ft 

2144 cu ftlday 

1i.a gpm 

300 cu ftlday 

1.6 gpm 

7146 cu ftlday 

37.1 gpm 
Table 12-4 0.8 Hectare Pond System Desiqn Calculations 

(uses input from above, as well as the following) 

DESCRIPTION NAME VALUE 

----------.- .-- --.-- 

# of Adjacent Ponds #CIDJ.PONDS 2 

Sets of Adj. Ponds #SETS 1 

*OUTPUTS* All outputs refer to the entire pond system 

DESCRIPTION 

--LI"II"I"" 

Total # of Ponds #PONDS 

Total Pond System Area S. AREA 

(alternate units) 

Center Wall tenqth S. CW. LEN 

T~t.Straight Wall Length S.STRmW.LEN 

Curved Wall Length S. CUR. W. LEN 

Total Wall Length S,TOT.W,LEN 

Total Wall Area S. TOT. W.ARER 

System Pond Volume S. VOLUME 

Evap. Fl owrate 8.0. EVBP 

(alternate units) 

Blowdown Flowrate S, Q, BLOWDOWN 

(alternate units) 

Harvest Flowrate 5, Q, HARVEST 

(alternate units) 

S.I. UNITS ENGLISH UNITS ----ow---- ---.-------ohectares 

sq meters 

meters 

meters 

meters 

meters 

sq meters 

cu meters 

cu m/day 

liters/min 

cu m/day 

liters/min 

cu m/day 

liters/min 

2.000027 acres 

87121.38 sq ft 

1271 feet 

3178 feet 

399 feet 

3577 feet 

50ha sq ft 

57167 cu ft 

4288 cu ft/day 

22.3 gpm 

600 cu ft/day 

3.1 gpm 

14292 cu .ft/day 

74.2 gpm 
to keep the pond operational. The issue is moot for the membrane lined pond 

since the meabrane will extend up to the top of the wall. The curved walls 

will be built using Dodd's corrugated panel technique, Tho issue of existing 

patents on the flow deflector vanes will be examined, and if favorably 

resolved, vanes will be installed at one end oi the ponds. The total cost of 

wells and flow deflectors is $25,100. 

The sumps are identical to those described for the large scale system in 

section 7.3.4. Rails and piers will be installed installed 1%3400), and 

$5000 is budgeted for solids removal equipment, which will not be built until 

the severity of the problem is evaluated. 

Paddle wheels will be built, incorporating the features discussed in Section 

7.3.6. The paddle wheel design specifications and costs are included in 

Appendix 111. Since these are experimental ponds, the design is based on a 

maximum velocity of 30 cw/sec. The cost is $24,400 for the two mixing 

systems. 

Carbonation efficiency is a key technical issue to be studied in the 

experimental system. The 0.4 hectare ponds, with their full-scale sized 

sumps, will provide data which can be extrapolated to larger ponds with 

confidence. The cost of tho two carbonation systems is $7000, which includes 

the pH controller and aocociated,inatrumentation. 

One of the ponds will be lined with a good quality membrane liner (Hypalon or 

CPE), while the other uill be lined with a 0.3 meter (1 ft) clay base topped 

with a thin layer of crushed rock, rolled to a smooth finish. The clay is 

necessary because of the sandy soil at the pond site, and is available 

on-site for the cost of hauling. The crushed rock liner is an important cost 

saving feature of the large scale system which needs to be evaluated. The 

relatively long channels will allow accurate head loss nea~ureeents to be 

aade, from which roughness coefficients can be determined. 

A summary of the construction costs for the two 0.4 hectare experimental 

ponds is presented in Table 12-5. 
Table 12-5 0.8 Hectare Experimental System Pond Costs 

INSThLLED COST FOR 0.8 HECTARE SYSTEM -*"~C111wI---"1---"3LLL~--1-w---*-1--wI----I2 PONDS 0.4 HECTARES EACH 

OESCRIPTION QUAN UNITS UNIT $ TOT $ 

--I---------- L--- I---- ---I-- ww--- 

GROWTH PONDS 

Earthworks 

Rough Grading* 2.0 acre $2,500 $5,000 

Lazar Level 1 lna 2.0 acre 1,500 3,000 

Finish Grading 2.0 acre i ,000 2,000 

Sump Excavation 362 cu yd 2.5 904 

Walls & Structural 

Straight Walls 5213 sq ft 4.0 20,851 

Curved walls b55 sq +t 5.0 3,275 

Flow Deflectors 197 sq ft 5.0 903 

Sump bottom 3h.7 cu vd 150 5,500 

Sump ends 8.6 cu yd 250 29159 

Rails & Piers 254 ft 13.5 3,431 

Solids Remover 5,000 

Mix~nq System 

Paddle Wheels 2 # PW 10,700 21,400 

Pa#, Structural 2 # ponds 900 1,800 

P.M. Depression 6 cu yd 200 1,239 

Carbonation System 2 # Ponds 3,500 7,000 

Lining (membrane) 

Channel s 43730 sq ft 0,55 24,051 

Ends 6865 sq ft 0.60 4,119 

Lining 

Clay 1874 cu yd 0,75 1,405 

Cruehed Rock 319 cu yd 7.00 2 867 --I--- 

GROWTH PONDS TOTf4L 

* Includes drainage diversion % site clearing 
Three 50 m2 experimental growth ponds will be constructed for biological 

and small scale engineering studies. TWO of these will be mixed with paddle 

wheels, one with an air lift. All three ponds will be lined. The cost 

breakdown for these pond6 is shown in Table 12-6. 

Table 12-6 SO e2 Pond Costs 

Site Peparation (levelling, etc): 

Walls: 430 ft @ Selft 

Sumps: 3 x $500 

Hixing Systems (2 P.M., 1 air lift); 

Carbonation: 3 x $2000 

Submersible Pumps: 2 x $300 

Drains, piping: 3 x $800 

Hisc.: 

TOTAL, 3 Ponds 

In order to validate the settling pond concept, a settling pond sized for the 

volume of a 0.4 hectare qrowth pond will be constructed. Rather than 

building a scaled down version of the large settling ponds of Section 8, the 

experimental settling pond will be an almost full scale version of one of the 

channels in the larger pond. The depth, width, and length will be 

approximately 80X of full size, An identical 2% bottom slope will be used. 

This pond will allow meaningful evaluation of settling characteristics and 

proposed concentrate collection system of the large pond. The side walls 

will be made as steep as possible (possibly lined with gunnite instead of a 

membrane) in order tu reduce "edge effects.' Two 20,000 liter tanks, with 

sloped bottoms, will be used for secondary settling, flush storage, and Cor 

primary settling tests with the 50 r2 ponds. Figure 12-5 shows the 

proposed settling pond system, while Table 12-7 lists its cost. 

Table 12-7 Experimental System Settling Pond Cost 

Excavation & shaping: 1000 yd3 @ $4.00/yd 

Lininqr SO60 ft2 4? $0.65/ft 

Pumps & accesories: 

Supernatant, contrifugal 500 gpr 

Concentrate, solids handling 100 gpm 

Supernatant decanter (fabricated) 

Flush storage/secondary settling tanks 2 x 20,000 liters 

A11 piping & valves 

Instrumentation t misc.: 

TOTAL 

A total of $30,000 has been budgeted for the development of an alternative 

harvesting method, which would be either belt filtration or air/DO 

floatation. The belt filter was discussed in Section 8. Although a pilot 

scale unit would probably cost more than $30,000, there a possibility of 

purchasing the unit built by Dodd in Singapore. The other alternative is to 

develop a air/DO floatation separator, which operates in much the same 

fashion as a dissolved air floatation, but uses fine bubble spargers in 

conjunction with the release of dissolve oxygen to float the algae to the 

surface. LOW doses of polymer are used to enhance coagulation. A budjet of 

$30,000 should be sufficient to develop a reasonable sized experimental unit. 

Cnnirif use 

An additional $30,000 is budgeted for the purchase of pilot scale centrifuge, 

since centrifugation is likely to follow any primary harvesting process. A 

small horizontal solid bowl unit can be purchased for this amount, from whrch 

the necessary scale-up data data can be compiled. Alternatively, a larger 

unit, many of which are available on the used equipment market, could be 

purchased. 
12.4.4 System-wide Costs 

An covered anaerobic lagoon will be constructed to test the feasibility of 

nutrient recycling, and to stabilize algal solids before disposal. The 

lagoon will significantly reduce the quantity of solids to be dried and 

disposed of. although there are no plans for utilization of the methane 

produced (since suitable engine-generators ate quite expensive), the lagoon's 

performance will be monitored. A rough estimate of $20,000 was provided by 

the consultant who designed the anaerobic lagoon system for the large scale 

system, +or a lag~on sized to handle the thickened ef+luent from the 0.4 

hectare p~nds. 

An existing well at the proposed site has ample capacity to provide 

groundwater to the pond system. The cost of piping this water from the well 

to the pond site was estimated at $23,508, fin additional 510,000 is budgeted 

to construct a shallow well near the Salton Sea as a source o+ highly saline 

uater. With there two sources, a wide range of salinitjes can bo formulated, 

A lined water storage pond will be constructed as part a# the water supply 

sygtem. The pond will also serve as a settling pond for water treatment, 

The design and dimensions of the water storage pond is shown in Table 12-8. 

flost of the piping for the experimental system is contained within a small 

area at the head of the growth ponds, $1500 is budgeted for water 

distribution to the experimental ponds and settling pond. The C02 will 

come from a rented storage tank. The carbonation system itself is included 

in the pond cost (Table 12-51, Most nutrients are added in salt form 

directly into the pends, or in some cases, are dissolved in a small mix tank 

and pumped. Nitrogen will be added as aqua-ammonia #rom a storage tank 

(these are normally rented). A total of 83500 is budgeted for mlx tanks, 

piping and valves associated with C02 distribution and nutrient additions. 

The offices, lab, and culture rooms will be located in ranted trailers, with 

the exception of a small 'lab annex", which contains balances and ather 
Table 12-8 Experimental System Water Storage Pond 

STORAGE POND DESIGN - Volume of Truncated Prism 

Slope= 2.0 (RunIRise) 

Depth= 8 ft (Do not include freeboard) 

Vol ume 

L 1 L2 R A 1 A 2 Am (CU ft) (gallons) - - - - -- -- - - - - ------- --------- 

90 5 8 16 8100 3344 547b 4449 1 332790 

STORAGE POND DIMENSIONS - Including freeboard 

From table abover Additional design parameters: - 

Slope= 2 (run/rise) Desired freeboard 1 ft 

Depth= 8 ft Addl. liner beyond 

L1 = 90 ft top of berm I 2 ft 

Computations; 

Length at top of berm I 

Length of bottom a 

Area of bottom (I 

Area of bottom liner a 

Side panel height, to waterline = 

Side panel height, to top of berm = 

Side panel height, total a 

Side panel area (based on total) m 

Area of all four side panels I 

Total liner area = 

SINGLE LINER 

------..----- 

9 4 ft 

58 ft 

3364 sq ft 

3364 sq ft 

16 ft 

18 ft 

20 ft 

1520 sqft 

6080 sq ft 

9444 sq ft 

COST: 

Excavation & berms: 862 cu yd B $31~~ yd = 

Liners . 9444 sq ft @$,bOlsq ft = 

Hisc. a 

TOTAL 
instruments that must be on more solid ground. Additional buildings include 

a shop and centrifugelchemical storage shed at the pond site. The cost of 

buildings is shown in Table 12-9. 

Table 12-9 Experimental System Buildings Cost 

Lab annex: concrete flaor, air conditioned, 350 ft2 @ 130/ft2 $10,500 

shop: concrete floor, 1000ft2 e $15/it2 LS,OOO 

Centrifuge shed, concrete floor, one side open, 500 ft2 @ $0/ft2 4,000 

----.ITOTAL $29,500 

A small amount ($25001 is budgeted to extend an existing dirt road to the 

proposed pond site. 

--------------- Instrumentation 

This category covers the cast of instrumentation not already included in 

other categories, (e.g. solar monitor, pond temperature and level sensors, 

power measuring equipment, etc) and for a microcomputer-based data aquisitian 

system. Ultimately, the system could be used to automate various pond 

operations, as most of the package data aquisition systems have digital 

output lines that can be used to open valves, turn an pumps, etc, 4 total of 

$15,000 is budgeted for this category. 

The cost of electrical distribution and wiring is normally estimated a5 a 

percentage of total capital costs. Fur a relatively small project such as 

the proposed experimental system, 5% is typical. 

A total o+ $15,000 is budgeted for machinery, to cover the cost of a pick-up 

truck, shop tools and equipment. 
The engineering budget, 5% of capital costs, or about $20,000 is to cover the 

cost of any outside engineering (e.g, surveying, drafting, soils analysis) 

required for the construction of the ponds. Most of the engineering will be 

done in-house, and is included in the operating cost budget in the folloning 

section. 

A 10% contingency is included to cover unforseen costs and unusual 

circumstances. 

A summary of all construction costs for the proposed experimental faeility is 

given in Table 12-10 The two 0.4 hectare growth ponds account for about 25% 

of the total, the small ponds about 72, the harvesting systems about 202, 

system-wide costs about 33X, engineering 52, and contingency lo%, 
Table 12-10 Experimental Facility Construction Cost Summary 

6ROWTH PONDS: 2 x 1 acre 

Earthworks* 

Walls & Structural 

Mixing System 

Carbonation System 

Lining (1 membrane, 1 crushed rock) -. 

GROWTH PONDS - 3 x 50 sq meter 

- 6 x 1.5 sq metar 

HARVESTING 

Settling Pond System 

Air/DO Floatation 

Centrifuge 

SY STEfl-W.IDE COSTS 

flnaerobic Lagoon System 

Water Supply (groundwater 1 

Water Supply (Salton Sea water) 

Hater Storage Pond 

Water Distribution 

C02 & Nutrient Supply 

Buildings 

Roads 

Instrumentation not included elsewhere 

Electrical Distribution (5X o+ above) 

Hachinery 

ENGINEERING (5% of above) 

COMTINGENCY (10% of above) 

TOTAL $ 

--I---- 

$10,904 

41,199 

24,439 

7,000 

32,443 

TOTAL COST 
EXPERIMENTAL SYSTEM OPERATION AND COSTS 

13.1 INTRODUCTION 

The work plan and work schedule are presented below for the construction and 

operation of the experimental system. The plan is broken down into 

individual tasks, each describing an essential aspect of construction or 

operation. The schedule follows, with each task assigned a time span for 

completion. The cost of labor, equipment, supplies, and overhead is then 

delineated. The final budget, including construction and operating costs, 

follows this section 

13.2 SYSTEM CONSTRUCTION 

The design, and any changes made during the review process, aust undergo a 

final review for insertion of detail and finalization of the .construction 

schedule. This work would actually be done primarily before a contract start 

date and continue during the first month. 

Concurrent with Task 1, during the first month of the project, construetion 

contractors will be sought and interviewed. After the solicitation of bids 

and negotiations, a final construction schedulg ill be drawn up and any 

variation from the initial budget reviewed. 

Continqent on the weather, the construction of the entire proposed system 

would take four months. The acquisition of trailors far office space, the 

c~nstruction of storage and utility buildings, and earthworks will be done 

during the first of these four months. After laying water and power lines, 

the system itself will be constructed. 
During the eighteen month contract period, the laboratory will be set up 

primarily in trailors. Acquisition of trailors and installation of 

laboratory equipment will begin once the site utilities ara in place and the 

earthwork completed. Same of the laboratory equipment will have to be haused 

in a small pre-fabricated building on a concrete slab for stability, As soon 

as possible thereafter, a laboratory technician will be hired to initiate the 

algal culture collection and prepare for growth of inoculum. The 1.5 r2 

ponds will be operational at this the. 

13.3 EXPERIMENTAL PLAN 

The water resource is an important parameter of the ov~rall system, Since it 

is yet of rather undefined composition, the experimental system must be 

flexible enough to test a nide variety ob water resources. Thc two water 

resources available at the proposed site provide thi% flexibility #hen 

combined nith water conditiening, The Salton Sea provides the sodaurn 

chloride needed to achieve any conceivahly useful TDSp It can be diluted 

with the well water to achieve any intermediate salinity allowing the systm 

to be operated at almost any blow down ratio. The calcium concentration is 

very high in the Salton Sea, so that some water softening is required, The 

magnesium level is aleo high, Conditioning will be done with soda ash far 

calcium removal, and nith lime and soda ash for removal of both, Input 

stream splitting will allow adjustment of both to different degrees. Still, 

the waters composed in this manner ray only approximate specified water 

resource characteristics. It should be noted that these specifications are 

only averages so that precise duplication is not realistic, Hewever, the 

small ponds,. 1.5 m2, and laboratory cultures can be used to formulate and 

test any given water c~spasition, hs of now, the water resources o+ interest 

are Type EI concentrated eight fold and seawater. The followinq e~periaents 

will be performed regarding water chemistry and algal gronth on the~e 

waters. 

A. Water Conditioning 

1. Cost oi conditioning va aaount removed and e+ficiensy 

2. Precipitate removal by settlng 

3, Precipitate formation, after initial conditioning, upon additional 

concentration 
Be Water Chemistry 

1. Identification of species precipitating and remaining ion 

composition, by outside analytic laboratory 

2. Approximate determination of inorganic carbon reaction equilibrium 

constants by inflection points in titrations. Determination of carbon 

storage capacity as a function of pH change. 

C. Controlled Tests of Alqal Growth on Waters Used 

1. Bottle tests in laboratory, with Type I1 water as control for the 

growth of the lipid containin strains like ChrysoIF1 and Cheatoceros 

2. Growth tests in 1.5 m 9 ponds with Type I1 water as control for 

Chryso/F1 (or other promising lipid producer) and seawater as control for 

growth of Platymonas. 

D, Media Recycle 

1. Preliminary media recycle experiments will be conducted in the 1.3 

sad 50 m2 ponds to determine the minimum blow down ratio that is feasible. 

These experiments will be done for one month at a time, which is short in 

terms of what must be actually practiced in a real system, but long enough 

assess feasibility. 

2. All experiments in ponds'of .4 hectare site will be performed with 

media recycling. This is necessary for minimizing the operational cost of 

there experiments and crucial for assessment of the utiliization of saline 

groundwaters in any practical system which is to be operated in the arid 

areas of the U.S. Southwest. Productivity and species dominance as a 

function of the duration of cultivation on recycled medium are the main 

factors to be analyzed. 

Although in-pond sumps were specified for carbonation in the large scale 

design, both sumps and covered area carbenators will be tested in the 

experimental system. Sumps, however, will be provided in the larger 

experimental ponds, being the primary method. Covers will be added later if 

the results from 50 m2 ponds are positive, The carbonation tests will be 

extensive and will be done prior to inoculation in both freshwater and 

media. The specific tests follow. 

A. Sump Carbonation 

1, Stripping rate per unit depth of sump 

a. versus sump liquid depth 

b. versus the ratio af gas flowrate to liquid flowrate 

c. versus sparger type (initial bubble size) and gas flowrate 
2. Overall transfer efficiency in 1.5 m deep sunp 

a. versus sparger type 

b. for co-current, lateral, and counter-currant flow 

3. Performance of gas recycle, if necessary 

8. Covered area carbonator 

1. Overall transfer efficiency for given area of cover 

2. Effect of water velocity under cover 

3. Efficiency of ripple cover 

C. Effect of algae and supersaturated oxygen on transfer e+ficicncy 

1. Measure C02 transfer and O2 out 

2. Determine if algae excretion products enhance transfer 

Dissolved oxygen can be measured using an Orion DO prabe and cheeked with the 

Winkler method. Carbon uptake can be measured by calculating the change in 

total inorganic earbon from pH change and the carbon equilibrium equatisns, 

Although many paddlewheel syeteas arc now used 58r mixing algal cultures, 

there is little data on the actual efficiency obtained in large pond^. Less 

data is available concerning airli+t mixing systems for law Raad, low 

velocity systems. Thus it will be important to determine jut how #elf these 

different options perform. Since the prinary system to be installed in the 

experimental ponds is the paddlewheel, airli+t mixing will be testad 

initially by sparging air into the earbonatiun sumps adapted for the purpose 

by installation of a baffle. Pteasurements will include head less and various 

power nu~berg as a function of aatar velocity. In addition, C02 outgassing 

will be measured as a. function 09 ini~ing speed. If the pareneters det~rmined 

for airlift mixing are favorable a draft tube system for airlift will be 2 designed and installed in a 50 m pond for testing, Scale-up to ,4 ha will 

depend on the evaluation of rasults and budget constraints, 

The parameters detarmined from the carbonation tests and the airlift mixing 

tests will be used to evaluate and design a combined gaslift and carbonation 

system, The calcuiati~ns nil1 be performed +or- a 41ue gas 5ystem thigh gas 

flow rates), a diluted CD2 gas phase (3SX Cog, at three times the flaw 

rate of a pure C02 ryste.1, and for pure tD2 flow gas flaw case). 

Studies on the rowth and productivity of the algae will be perf~rmed in the 

1.5 m2 and 50 n S ponds. Ths best conditions will be scaled up to the .4 

ha pands for validation of the full scale design. Both indoor bottle 

cultures and the 1.5 a2 cultures provide a convenient nesns to test quickly 

a moderate number of factors and values. Initial work indoors usually 

indicates whether a factor is important or not, encept fur those that depend 
on high light intensity. For these the outdoor small ponds work well. Thus 

media optimization studies can be performed indoors, while pH and DO work is 

best done outdoors. Since the mixing regime in a small pond does not 

simulate that in a larger one, the initial results obtained at the small 

scale need to be tested, in the short and long term, at the 50 m2 and .4 

size. Factors to be tested for affect on productivity include pH, DO, 

alkalinity, temperature, batch detention time, continuous vs batch operation, 

and nitrogen depleted productivity and storage product accumulation. Routine 

measurements include pH, temperature, DO, insolation, GO2 input and biomass 

density, Chemical composition is measured as required to determine lipid 

productivity. Since correlation of productivity with various parameters is 

often a useful evaluative tool, much data needs to be taken and stored in an 

organized manner. A computer automated data acquisition system will be 

installed for this. In addition, with this in place, the status of 

productivity in a pond can be determined approximately on-line, without 

having to wait for cell density measurements, by monitoring the CO2 input 

and the pH, When corrected for injection and outgassing losece, C02 input 

is proportional to productivity. 

Tno harvesting methods nill be tested in the operation of the experimental 

system: flotation followed by foam collection and slow primary settling in 

large settling ponds followed by secondary settling in small tanks. Both 

aethods will be followed by centrifugation to provide a final product a% 

10%-20% volatile solids. The biomass to be separated will be nitrogen 

starved and flocculated with small doses of high aolecular weight polymers. 

Polymer flocculation is an inportant feature of the harvesting process. On 

site polymer flocculation tests will be conducted with the aid o+ 

consultants. The hypothesis being tested is that polymers can be tailored to 

the specific needs, i.e., chemical medium and algal type, while still 

maintaining enough versatility to function as a univerally effective 

flocculant. The collection method, sedrmentation or flotation, will be 

evaluated in terms of flocculant type and dose required to achieve efficient 

and reliabe separation and concentratran. The dose of flocculant must not 

exceed the equivalent of s.02 per kg dry biomass, and preferably half that. 

For gas flotation studies, some testing nill be done right in the ponds. The 

density of biomass leaving the flotation station will be used to calcualte 

the harvesting efficiency. This will be measured as a function of pond DO, 

biomass density (since several passes through the harvester will be made, 

each with lower incoming biomass density), GO2 ~nput, duration of nrtrogen 

depleted growth, and flocculant dose. 

Unharvested biomass will re-enter the nitrogen sufficient growth phase. Thus 

it will be necessary to test strains for the ability to quickly absorb newly 

introduced nitrogen and enter an active growth stage. 
The sedimentation tests will be performed in two phases: cell settling and 

sedimented slurry removal. The settling rates of the biomass will be 

measured as detailed previously I11 in indoor tests, with and without 

+locculant, When the velocity for most of the biomass exceeds 30 cm/hr, the 

pond will be fed flocculant and pumped into the settling basin. 

Sedimentation time will be determined on the basis of equivalency to settling 

3 m in 10-15 hrs. After decanting the supernatent, the slurry recovery 

system nill be tested for efficiency and rate af slurry removal. Then the 

rate of thickening in tanks will be determined. 

Centrifugation tests are important at thls point ta determine the throughput 

and hence the size and number of centrifuges needed at the large scale. 

Centrifuge vendors are available to test the characteristics of the biomass 

slurry and consult on centrifuge selection and operation. 

Once the harvesting parameters have been deterained with bi~mass from 50 n2 

ponds, the process will need to be validated using the large growth and 

settling ponds. The latter have been designed to emulate directly the solids 

removal system specified for the full scale design. The experimental 

settling pond is a "slice" of the full scale settling pond, having the same 

characteristic dimension for solids flushing. 

13 . 3.6 Qiqcatlqn-ef -B~~~~~I!-I~_~~-C!!Y~LE~,~C~~~!!-!!~-!!!~~~E~-RE~YEL~~~-I~!!~- 

- --------- Task 10 

A 9111111, covered lagoon will be constructed t~ digest, anaerobiaclly, the 

biomass harvested from the large ponds. These tests will be somewhat 

artificial in that the "pretreatment" due to lipid extraction will be absent, 

The results will still be extremely valuable in acertaining how the biomass 

components, that do degrade, partition in the lagoon. This information is 

necessary to validate the assumption upon which the extensive recycling of 

carbon, nitrogen, and phosphorus was based. The lagoon has been sized to 

accept the total biomass harvest of a one acre pend, The tests will provide 

the data necessary for evaluating the system's capability of producing a 

methane fuel product. 

A significant capital cost savings incorporated into the large scale design 

is the use of clay sealer and crushed rock overburden far pond lining. One 

of the ,4 ha ponds, and the 4 ha pond iS constructed, will be lined in this 

manner. The liner must be evaluated, over the longterm, bur water lass and 

buildup of deleterious organic solids. This must be done in a large pond in 

which the hydraulics are similar to a full scale pond. The other .4 ha pond 

nill be lined with a high qpality plastic liner and serve a control, as well 

as a test of the endurance of such a liner under field conditions. 411 o# 

the 50 n2 ponds will be similarly lined. 
13.4 OPERATIONS SUMMARY AND EXPERIMENTAL PRIORITIES 

The proposed system consists of six 1.5 m2 ponds, three 502 ponds, and 

two .4 hectare ponds. A 4 hectare pond would yield results directly 

transferrable to large systems, but it is not cost effective research at this 

time. The 1.5 a2 ponds are to used for initial screening of promising 

algal species under outdoor conditions of temperature and irradiance. Media 

and growth parameters will be determined in these small ponds, The 50 m2 

ponds will be used to test the various subsystem designs (carbonators, mixinq 

systems, air flotation, sedimentation systems) at a scale which will indicate 

feasiblilty at lowest experimental cost. These ponds will also be used for 

growth studies and to provide inoculum for the .4 ha ponds. The latter will 

serve as the primary testing facilitiy for validati~n of the large scale 

design over lonqterm operation. As far as validation of the large scale 

dasiqn, the highest priority experiments are those which determine the 

utilization efficiency of C02, including mass transfer coefficients and 

lo~ses throughout the system; those which test cost effectiveness of methods 

for primary concentration of the algal suspension, including polymer 

flocculation tests and evaluation of collection device performance and cost 

(settling ponds, flotation devices); use of an inexpensive anaerobic lagoon 

for recycling nutrients (especially carbon) that would not be removed in the 

product stream, including the partitioning of these nutrients in recoverable 

fractions of the lagoon; evaluation of the pond lining alternatives, most 

importantly the water losses when plastic liners are not used and the 

endurance of each of the liners! and the effect of longterr media recycling 

on system performance. 

The biomass and lipid productivity goals will be evaulated, but attainment of 

these goals is substantially dependent upon provision of strains pre-screened 

for the ability to produce lipid. A preliminary choice of strains include 

the high lipid producing Chryso/Fl, a productive and potentially high lipid 

producing strain of Chaetoceros, and the Hawaiian Platyaonas for use as a 

biomass productivity standard. The possibility of removing 

photosynthetically produced oxygen from the pond medium will be examined--no 

determinationn is possible prior to experimentation--and the effects of such 

removal on productivity will be studied. 

Two important growth characteristics of the organisms will be scrutinized 

during this experiment. First is the ability to recover quickly from 

nitrogen starvation after addition ~f new nitrogen into the medium, This 

involves resistance to photo-oxidation and photo-bleaching in already 

depigaented cells. Second is the ability to maintain high productivity in a 

medium that has undergone extensive recycling. This usually means that the 

organism must not excrete organics into the medium in significant quantity. 
13.5 EXPERIHENThL SCHEDULE 

Figure 13-1 lists the eleven tasks described above and shows the anticiapted 

schedule of completion. Many o+ the tasks are oS an onqoing nature, with 

periodic evaluation. Task 12, data evaiuatlon and reportinq, is indicated on 

the +igure. 

13.b BUDGET DESCRIPTION 

t'he comolete budqet IS qiven at the conclusion ot thls section, The eiements 

of the budget are described in Tables 13-f,2,3, and 4. Table 13-1 gives the 

cast ct pond equipment, Fhese items were included in the total pond 

construction costs given in Section 9.0. The costs listed in lable 13-2, are 

tor laboratory equipment. Iwa cast columns are included in this table. fhe 

trrst gives the cost at acquiring new equipment as specifled, Those rtems 

whrch are owned by Hicrobial Products, Inc. or are qavernment owned but, at 

present available for use bv Microbial Products, Inc, will be made availabie 

for use on this project, Thus the second'colunn lists the cost of equipment 

which must be purchased for this project. The supplies and materials (other 

than those used in constructing the pond system) are detailed in Table 13-3, 

The costs shown are based on vendor quotes or on previous experience, fit the 

enperimental scale, nutrient costg are high because quantities are relativeiv 

small, The breakdown of direct labor costs is given in Table 13-4. The tlme 

alotments are in equivalent full months of work, not by scheduled work time. 

The budget forfn that follows at the end of this section gives the total 

project cost for the eighteen month effort, including overhead and fee. 

Table 13-1, Experimental System - Pond Equipment ~~1--~~11~1o~~~1o~"~I.r~oLLLLLICICIC~~

Item cost, r I~~~"I"III~III~~""~~~L~oooI)~~

Motors, speed reducers +or 1 acre ponds 4800 

pH controllers, 2 2000 

Flowmeters, 5 1450 

Motors, cantrollers, small ponds 1500 

Pumps, 5 8 100 

Ccntrltuqe, harvest 30000 

&ir/DO, harvest (partial) est. 5000 

Computer, interfaces I5000 

Total 
--------------------------------.----------------------------------------------- 

I'ask 1 2 3 4 5 6 7 d 9 10 11 12 13 14 15 16 17 18 

--------------------------------.----------------------------------------------- 

1. Desi qn Hevi ew X 

3.Svstem Construct. X X X X 

4.Lab. Set up X X 

5.Water Res. Exp't. 

Water Cond. XXX 

Water Chem. XXXX 

Growth tests XXXXXX 

Media recvcle XXXXXX X ;IX XXX X X 

6.Carbonation Tests 

Sump 

Covered area 

Media Effects 

X X X X X 

X X 

X X X X X 

7.Hixing lests 

50m2 ponds X X 

1 acre ponds X X XX 

--------------------------------,----------------------------------------------- 

1 2 3 4 5 6.7 8 9 1011 1213 1415 1617 18 --------------------------------,----------------------------------------------- 

8.Growth Studies XXXXXXXX X X X X X X X X 

9. Harvesting rests 

Jar tests XXXXXXXX X X X XXX X X 

50m2 XX X X X 

1 acre X X XX XXX X X 

16.Diqestion-Recycle XX X X X X X X X X 

11.Liner Inspection 1 X X 

12.Reporting 

Design review X 

Budget review X 

Construct.progress X 

Construct.fina1 X 

Semi-annual rsport X 

Final Report 

Figure 13-1. Experimental Schedule 
Fable 13-2. Laboratory Equipment 

Item l4vailabilitv ficqui 5i tion Coat ,$ Budgeted Cost ,$ 

-----------------L-----*---"I)eee-e-e-33.c--------------------~------------------ 

Air conditioninq 

Culture room 

Bui ldinos 

Culturinq equip, 

Llqht banks 

Gas mlxers 

Shaker 

fnoc. hood 

Air compressor 

Tables 

Laboratorv equip. 

Fume hood 

Centr~fuqe 

l4utoci ave, used 

Steam qenerator 

pH meters, 2 

Uven, dtvinq 

Furnace, mu+fle 

Bai ance 

Microscope 

Uven, vacuum 

Cell disrupter 

Spect~~photometer 

Furniture 

Total 

Purchase required 

Owned by Nicrob~al Products 

Government equipment 
Table 13-3. Operating Materials and Supplies 

................................................................................ 

Item Basis, $ Total Cost, t --------------------------------u----------------------------------------------- 

Culturing supplies 

Lab. analysis 

Water analysis, 

outside lab. 

Polymer consultant 

Pond Chemicals 

co2 

C02 vessel rent 

Ammoni a 

Phosphate 

Iron 

Sodium carbonate 

Pond utilities 

500 Monthly, 16 mo. 

500 Monthly, 16 moo 

200-500/sample, 10-20 samples 

Quote 

05/ton, 200 tons/yr,quote 

30 ton capacity, 750/mo.,auote 

500/ton, 20 tons/yr, list pr. 

2000/ton, 20 tons/yr list pr. 

4500/ton, 20 tons/yr list pr. 

300/ton, 20 ton/vr list pr. 

500/mo., 18 mo. 

Total 99500 

'Table 13-4. Direct Labor 

Eighteen Month Project --------------------------------*----------------------------------------------- 

Title Equiv. Months $/mo. Total, $ 

--------------------------------.----------------------------------------------- 

Research Scientist 7 3750 26250 

Research Engineer 1 8 3750 30000 

Engineer 3 3750 11250 

Lab. Tech.1 18 1667 30000 

Lab. Tech.2 6 1667 10000 

Pond Operator 12 2083 25000 

Total 132500 
BUDGET 

............................................................................... 

CATEGORY COSTS, $ 

............................................................................... 

Materials and Supplies 

Pond construction (Table 12-9 minus $67. 850 for equipment 

included below ............. 375. 253 

Operating (Table 13-31 .................... 99. 500 

Special Equipment 

Pond Equipment (Table 13-11 ................. 67. 050 

Laboratory (Table 13-21 ................... 6. 000 

Direct Labor (Table 13-41 .................... 132. 500 

Total Direct Cost ........................ 681. 103 

Indirect Cost (1.318 x Direct Labor) .............. 174. 635 

Total Direct plus Indirect .................... 855. 738 

Fee (7% of total direct plus indirect) .............. 59. 901 

TOTAL Project Cost 
REFERENCES 

1. Weissman, J.C. and R.P. Goebel, "Production of Liquid Fuels and 

Chemicals By Microalgae," Eigal-Rgegot, SERI #XK-3-030135-1, 1985. 

2. Benemann,J.R., R.P. Goebel, J.C. Weissman, and D.C. Augenstein, 

"Microalgae as a Source of Liquid Fuels,' Eigpl-Rgegrt, DOE 

DEACOS 81 ER 30014, 1982. 

3. Laws, E.A., "Research and Development of Shallow Algal Mass Culture 

Systems for the Production of Oils," Subcpq~~a~t-Rpgg~i, SERI 

#XK-3-03136 Oct. 1984. 

4. Weissman, J.C. and J.R. Benemann, "Microalgae Production of Glycerol 

and Related Chemicals on Saline Waters," [Fggl-Rppgot, NSF, 

PFR-8008748, 1981. 

5. Barclay, B., Personal Communication of results of SERI Water Resource 

Project, 1985 

6. Moo-Young, H., and H.W. Blanch, "Design of Biochemical Reactors: Mass 

Transfer Criteria for Simple and Complex Systems," 

7. Aiba, S., A.E. Humphrey, and N.F. Millis, Bipghggjcpl-Egqi~g?rin_g, 

2nd ed., Academic Press, New York, 1973. 

8. Zlokarnik, M., "Sorption Characteristics for Gas-Liquid Contacting in 

Mixing Vessels," figy,Blpche!,Engyl, 8, T.K. Ghose, ed., 

9. Hill, A,, D. Feinberg, R. Mclntosh, B. Neenan, and K. Tepry, tlF~els 

form Hicroalgae: Technology Status, Potential, and Research Issues," 

Qysfi-Rgppot, SERI, 4625.20, Dec. 1984. 

10. Weissman, J.C. and J.R. Benemann, "Polysaccharide Production By 

llicroalgae," Eiqal-Rgppot, NSF, PFR-7917646, April 1980. 

11. Weissman, J.C. and J.R. Benelmann, "Biomass Recycling and Species 

Competition in Continuous Cultures," 13ipieghqp3,-jipegql, 21, 1978. 

12. Dodd, J. Personal Communication. 

13. Shelef, G., et al, "Hicroalgae Harvesting and Proc@ssing: A Literature 

Review," hbspntyact-fipepyt, SERI, #XK-3-03031-01, August,1984. 

14. Imperial Irrigation District, fiqnggl-~ggi~gr-Su~!g~y 1914182, Records 

of the Watermaster, 1982. 

15. Clinntg,fi~lg~-pf-thg-~~S~, U.S. Dept. Commerce, 1979. 

16. Imperial Irrigation District, Laboratory Certificate, Nov. 7, 1983 
~PPENDIX I 

CARBON DIOXIDE TRANSFER 

4.1 INTRODUCTION 

Transferring carbon to algae ponds is a major design pr~blem. Unlike typical 

fermentations, which may have volumetric production rates of 15 g 

biomass/L-hr in deep, weil-stirred tanks, algae ponds have 200-1000 times 

lawer peak volumetric production rates in shallow, open ponds. Thus, large 

volumes of water rust be transported to carbonation sites where C02 is 

injected. In the plug-flow regime of high rate ponds, enough Cup must be 

injected, and subsequently stored in the water to meet the carbon demand of 

the algae, as well as any CO2 larser due to outgassing as the water travels 

between carbonation stations. Storage capacity is a function 04 depth, 

alkalinity and pH change. The alkalinity can be supplied by the water 

source, and concentrated by water evaporation from the pond, to a level 

determined by the blow-down ratio. The allowable pH changes are determined 

by biological tolerance of the desired @icroalgae population and water 

resource charactcristics. flany inexpensive water sources cantain hardness 

which tends to precipitate, The extent of precipitation depends en pH and 

alkalinity, i.e., carbonate concentration. Thus, the variables ef water 

chemistry, blowdawn rate, depth, pH changes, and C storage potential are all 

interrelated. C02 lasses due to outgassing depend on pH, alkalinity and 

carbonator spaclng, as well as mixing speed. 

2 PHYSICAL ABSORPTION OF C02 

Gas-liquid mass transfer is a subject which has received much attention in 

the chemical and biochemical engineering literature. Theories and 

experi.mental carrel ations are wel l devel aped. However, they give on1 y 

approximate and/or relative estimates of transier rates. In the final 

analysis, rates must be empirically derived from prototypes and pilots. This 

is especiallv true of open channel carbonation, where irregular surface 

deformations occur due to turbulence, wind and bubbles. These disturbances 

may well have signi+icant effect on gas transfer in ponds, The following 

analysis quantifies same o+ the more pertinent aspects 09 algal pond 

carbonation and evaluates, relatively, the sensitivitses to depth and mixing 

intensity, 

The theories of gas-liquid tpansfer into agitated liquids all involve some 

simplified manner of incorporating the hydrodynamics into the basic 

diffusional models. The rationale is that at some scale, close to the 

gas-liquid interface, turbulent eddy diffueian is damped ta the extent that 

rolecuiar diffusion is responsible for transfer. In the thin film model fl, 

21 film thickness parameter, d, incorporates (in a mostly unspecified manner) 

all of the hydrodynamics, yielding a transfer rate equal .to (Did) (C*-Ca), 

ahere D is the molecular diffusion coefficient of the solute gas in cn2/r, 
C* is the molar concentration of solute gas that would be in equilibrium with 

the partial pressure of solute in the gas phase, in mmoles/cm3 and Co is 

the molar concentration of solute gas in the bulk liquid. The mass transfer 

coefficient, kL is equal to D/d . k~ is defined from the empiricallv 

observed relationship VdColdt = kLa (C*-Co). Here dCo/dt is the transfer 

rate, mmoles/cm3.sec, V is the volume in cm3, a is the interfacial area 

in cm2, KL is in cm/sec. Ihe intensity of turbulence determines the film 

thickness, but the latter is difficult to infer theoretically and hard to 

measure. 

In other models, the liquid turbulence is viewed as causing replacement of 

small interfacial surface areas with liquid from the uniformly mixed bulk, 

The type of distribution of surface ages assumed determines the quantitative 

prediction of these models. Hiqbee's surface renewal model assumes all 

elements of area have a uniform lifetime C31. A convenient model, and the 

one used below, is Danckwert's renewal model t41 in which the probability of 

any element of surface being replaced is proportional to the age of the 

surface element, Then the surface renewal is a Poisson process, havlng manv 

calculational conveniences. 

In this approximation, gas side resistance to diffusion is considered 

negligible, so that at the gas liquid interface equilibrium does exist 

between the bulk gas partial pressure of solute and the concentration of 

solute in the liquid at this interface. The relationship between gas side 

partial pressure and liquid side concentration is given by Henry's solubility 

law, with Henry's constant appropriately decreased for elevated temperatures 

and ionic strenqth and composition of the liquid. Especially for anything 

but small gas phase partial pressures of C02, where diffusion of solute 

molecules to the interface actually limit transfer, the equilibrium 

relationship is valid. 

Once an element has been "renewed," transfer is assumed to go as in an 

infinitely deep, stagnant liquid. All transfer properties are determined as 

averages over the entire interfacial area, using the Poisson distribution as 

the weighting function. Purely physical transfer (without chemical reaction) 

goes as iDS)1/2(~w-~o), where S is the rate of surface renewal, or 11s is 

the average age of any surface element after formation. Several other 

models are available, however, there is little empirieal evidence for any one 

in particular. In most circumstances, all models give similar quantitative 

predictions and, in addition, relative prediction as to the effect of 

chemical reactions on gas absorption. As alluded to above, in many 

instances, the model chosen for use depends on ealeulational ease in the 

specific case. 

The renewal rate, S, embodies all of the effects 09 turbulence on gas-liquid 

transfer. It is not possible to measure, directly, this idealized parameter, 

but its value can be inferred from experiments. Flow of water in flumes, 
streams, and sewers is closelv related to that in open channels, The 

empirical formula developed for kL as a function of slope, velocity and 

depth from sewer data (5) has been found to correlate (6) with numerous sets 

o+ data taken for flumes, streams and open channels. hs indicated in Table 

AI-1, Danckwcrt .s model, in which k~ = (0~1~~~. was used to calculate S , 

from k~ based on purely physical absorption. Although the oripinal 

correlations were made. for aeration, S is independent of the diffusion 

process and can thus be determined. The procedure is to tl) choose a channel 

roughness coefficient and use Manning's formula to determine slope from given 

depth and velocity values, (2) insert the depth, velocity, and slope values 

into the Parkhurst-Pomeroy (5) correlation to determine k~, and 3) use 

Danckwert's model to determine S from kL and DO2. Table Q1-2 shows 

values of kL (for oxygen, for C02 multiply by (1.91/2.28)) an.d renewal 

rate calculated according to this procedure with n = .02S0 

TfiBLE AI-1. MASS TRANSFER COEFFICIENTS FOR FLOWING WATER 

Basis: S1 = (1.491-~(d)-~/~(n~)~ 

Wherer Sl = elope 

d = depth, ft. 

V = linear flow velocity, 9t/sec. 

g = gravitational acceleration, 32.2 ft/sec2 

kL = transfer coefficient, cmlsec measured at 20°C 

Do = diffusivity of oxyqeo = 2.28 x 20'~ cm2/sec at 20O~ 

S . average rate of surf ace renewal, sec-l 

The purpose of this procedure is to get approximate values of carbonation 

coefficients using data +ram aeration experiments and develop a means of, in 

theory, determining the effect of chemical reaction on carbonation relative. 

to purely physical absorption, The first objective could be met without 

calculating renewal rates, The results would again depend on the particular 

model chosen since k Dm where m is 1 or 03, or a value in between. 

Since relative molecular diffusivities are not substantia,lly difhrent, 
model discrimination is not possible based on experimental determination of rn 

(7). However, this also means that, for an approximate analysis, the result 

is substantiallv independent of the model basis. The second objective is 

conveniently attained using the renewal rate when the chemical reaction is 

first-order or considered pseudo-first order. 

A1.3 CHEMICAL ENHANCEMENT OF C02 ABSORPTION 

The concentration gradient of a gaseous solute diffusing into a liquid can be 

steeper if the solute reacts with components of the liquid phase. The 

magnitude of this effect depends on the physical absorption time constant, 

the reaction rate constants, and the concentrations of reactants. hbsorption 

of C02 into alkaline waters may be accelerated by one of two major 

uncatalvzed reaction paths, the hydration of' C02 and subsequent acid-base 

reaction to form bicarbonate ion and the direct reaction of C02 with the 

hydroxyl ion to form bicarbonate. The rate of the former reaction is faster 

at pH values below 8, while the second dominates above pH 10. Between 8 and 

10 both can be important. Several investigators (7) have calculated the 

magnitude of the enhancement of C02 absorption rates caused by these 

chenlcal reactions. Banckuert's renewal model is particularly convenient 

when the reaction is first order or pseudo-first order. Although the 

reaction of C02 and OH ion is, in general, second order, under some 

circumstances the OH ion concentration mav be considered constant during that 

time interval between renewal of a surface element, when stagnant diffusion 

conditions are assumed to prevail. Thus if the rate of surface renewal is 

high enough, relative to the influx of C02 and subsequent depletion of OH 

in the surface layer, so that OH is not significantly depleted, the 

pseudo-first order conditions prevail. 

When the renewal time is long, the absorption rate of LO2 is high and/or 

the concentration of OH is low the reaction proceeds quickly, depleting the 

OH concentration just below the interface. When these conditions prevail, 

the rate of absorption is nearly the same as if the reaction were 

instantaneous. The instantaneous reaction gives the maximal enhancement for 

the qiven conditions. The enhancement factors are pH dependent because the 

concentration of reactant, OH, depends on pH. The alkalinity affects OH 

concentration by buffering pH changes upon absorption of C02. Thus, 

although the reaction rate is governed by the diffusion of C02 down from 

the interface and diffusion of dissolved OH from the bulk liquid, in certain 

pH ranges the diffusion of many more molecules of C02 (from the saturated 

interface) is needed than of OH from the bulk, due to the buffer action. For 

example, at pH 9, over 100 molecules of C02 must diffuse downward for each 

molecule of OH actually depleted from the reaction zone. 
ThBLE AI-2. C02 MASS TRANSFER COEFFICIENTS AS A FUNCTION 

OF POND HYDRAULICS 

Velocity 

Depth ft/s (cm/s) Slope kL cm/sec S, sec-I t , sec 

-----1----------1-------------------------.-------"-"-.-------"--.1----------- 

-a164 +t ,16 ( 5) 8.2 x lom5 2.5 x loe4 2.7 x loa3 370 

* For C02 at 20°C this overestimates k~ by IOX. However, since 

diffusion coefficients are significantly greater at higher temperatures more 

accurate estimation is not called for. 
The hvdration reaction, on the other hand, differs in that it is not pH 

dependent at the surface (below the surface it is, which limits the reverse 

reaction), and it is first order in C02. Thus, enhancement due to this 

reaction is essentiallv the same at all pH values between 7 and 11. Table 

AI-3 qives the forward and reverse reaction rates, and Table 41-4 the 

concentrations of reactant, at the surface and in the bulk at pH 7.5 and 

10.3. All rate constants are for 20°C and infinite dilution, giving lower 

limits to enhancement. Reverse reactions are negligible. 

TABLE AI-3. CHEHICAL ENHANCEMENT FACTORS (9) AND REACTION 

RhTE CONSTANTS .............................................................................. 

Enhancement of First Order Reactions: (1 + ~IS) lI2 

Enhancement of Instantaneous Second 

Order Reaction: 1 + D~~(oH)~I~D~~~~co~) * 

k 1 fast 

Reaction%: H20 + GO2 - H~CO~-H+ + HC03- v 

k 2 

7 

k - 1st order reaction rate constant or pseudo first order constant 

B - Bulk liquid concentration 

* - Saturated surface concentration 

Z - Effective stoichiometric coefficients 

Constants: kl 0.02 5ec-l 

- k2 = 20 sec-l 

k3 = 104 L mole -1 sec-1 

All 20°C, infinite dilution 
Considering the second order reactian of C02 and OH at pH 10.3, the 

parameters whlch determine whlch regime is approptiatae (pseudo-first order 

or instantaneous,, are (1) the rate of C02 absorption, (2) the ratio of OH 

to dissolved C02 at the surface, and (3) the ratio 04 the time any element 

ot +hid remains at the surface (the turnover time = inverse af the renewal 

rate) to the maximal rate of the pseudo-first order reaction, kS(OH). With 

1 atm C02-in the gas phase, the physlcal absorption rate is .01 x 

nmules/cm2/sec., or after 200 sec. of quiescence of an element of fluid .1 

cr deep. 20 mmales C02/L is absorbed. This amount of absorption overwhelms 

the buffet, causing a drop In OH concentrations. Thus, the pseudo-first 

order approximation does not apply. Similar calculations for other pH ranges 

Table Ai-4) confirm this over the entire pH range of interest. 

The effective stoichionetry of the reaction is pH dependent, as shown in 

[able QI-4. This stoichiometry, along with the bulk concentration af QH and 

the saturated level of C02 determines the maximal enhancement of an 

instantaneous reaction regime. Even though the stoiehiometry can become 

quite high, the concurrently falling OH con cent ratio^ keeps the maximal 

enhancement from going above 1*0S. Even this is not achieved due to the 

tinite reaction rate constant of lo4 L/male-sec. Thus the direct reaction 

of Cop and OH does not serve to enhance the reaction when the turnover time 

is on the order of 200 sec. 

Even when the turnover time is only 6 sec., there is no appreciabIe chemical 

enhancement. Mound pH 9.5 the reaction is close to first order because the 

anount of Cog absorbed during hart contact time can be buffered by the 

solution, keeping the PH concentration relatively constant. However, this 

concentration is low, keeping the reaction rate low relative to the rate of 

physical absorption. Increases in absorption rates under these conditions is 

due almost entirely to the hydrodynamic enhancement discussed previously. 

The other reaction path, the hydration of dissolved GOZ, is a first order 

reaction which can never be considered instantaneous. Rccordinq to any of 

the models the enhancement factor is 2-3. Again if hydrualic conditions are 

chosen to incrase the renewal rate, and hence the physical absorption rate, 

then chemical enhancement is reduced. For example, with a 6 sec vs. a 200 

sec turnover time, physical absorption rates increase 6-fold, but chemical 

enhancement decreases by almost the same factor, qivinq overall only a 12% 

increase in absorption rates, This is a consequence of the low value of the 

reaction rate constant, 0.02 sec-l. The enhancement varies as 

(1 + k/9) so at higher values of S, the reaction conpeter poorly with 

turnover in absorbing Cog. 

Since even with 30 meq/L ~f alkalinity the buffer capacity is not great 

enough to enhance the absorption rates, the net effect of chemical reactions 

is the same f~r the low pH, low alkalinity case. Here again, due to the 

first order reaction of CQ2 and water, rates are enhanced-2-3 fold at a 

slow-turnover rate (corresponding to a 1 foot deep pond mixed at 0.5 fpr) and 

about 12X at high turnover rates (a pond depth of 1/3 #t: and linear velocity 

of 1.5 fps under the cover). 

Chemical enhancement can therefore be expected to lower areal carbonator 

coverage bv 50967% when that coverage was initially calculated to be hrgh. 

If measures are taken to increase physical absorption rates under a cover, 

then the 80% reduction in coverage thereby gained will not be much more 

affected by chemical reactions, In sumps chemical enhancement is also not 

effective under pond conditions, unless the reactions are catalyzed. 

REFERENCES 

1. Whitman, W.G.,-Cheg-an~-~pt,-5ggL, 29, 147, 1923. 

2, O'Conner, O.J. and W.E. Dobbins, "The Hechanism of Reaeration In 

Natural Streams," JL-s~~~ti,E~grrl-~~~ZZ4SC,E,J~~ SAC 1-30, 1956. 

4. Danckwerts, P.V., 'The Significance of Liquid Film Coefficients in 

Gas Absorption," in Indl_~~qgq,-&g,, !3, 1460, 1951. 

5. Parkhurst, J.D. and RID. Pomeroy, "Oxygen Absorption in Streams," 

JL,j~~jtL-E~gggl,Piv_IIfl~GZ, zg, sgr, 101-124, 1972. 

6. Wilson, G.Y. and N. HacCleod, "h Critical Appraisal of Empirical 

Equations and flodels for the Prediction of the Coefficient of 

Reaeration of Deoxygenated Water," b$gc,Re~~~ 8, 341-366 1974. 

7. Danckwerts, P.V., @g,-L~gy~u-qg~gfjgn& McGraw Hill , New Yark, 1970. 
APPENDIX A11 

by D. C. Augenstein 

GASLIFT PUMPS FOR COMBINED PUMPING AND 

GAS CONTACTING IN ALGAL PRODUCTION SYSTEMS 

AII.1 INTRODUCTION 

Gaslift pumps have been proposed to fulfill the simultaneous needs for 

pumping and gas transfer in microalgal growth systems. This treatment 

examines, first, the factors governing pumping efficiency, then factors 

governing the gas transfer function. Gas transfer requirements dictate the 

most important design parameters. Likely performance of a gaslift meeting 

both pumping and gas transfer requirements is then examined. 

Prior to presenting detail, some important conclusions can be summarlzed 

here. With a configuration guaranteeing adequate (>80%) fractional transfer 

of C02 from stack gas, energy available to pump liquid meets or exceeds 

pumping needs anticipated for high rate pond systems with channel velocities 

in the 15-30 cm/sec range. A good match between pumping capacity and system 

needs seems possible with several plausible combinations of other 

parameters. When C02 containinq stack gas is sparged to supply C02 

needs, it seems that energy requirements will be high but probably tolerable 

function - 5 to 25% - of system output. However, when transfer of pure C02 

is considered, a gaslift configuration guaranteeing adequate (>90%) 

fractional C02 transfer seems unable to meet pumping needs. Energy demand 

for pure C02 sparqing would be less than 3% of system output. 

Representative pumping eificiencies are in the range of 20-50% and optimum 

sump depths range between 5-20 meters. It appears that if power plant stack 

gas is to be considered bar C02 source, more energy efficient transfer 

methods through qaslifts might be considered. Major remaining uncertainties 

affecting this treatment concern the channel roughness, n, which will 

acatuallv be encountered, and the absorption coefficient, Kg, for CO2 in 

the pond liquid. Other details are presented in the report, which follows. 

AI1.2 GENERAL DESCRIPTION OF AIRLIFT CONTACTOR/PUMP 

The schematic of an airlift system of the type envisioned for application in 

an algal growth system is shown in Figure 411-1. In the figure, a ductinq 

system (A) brings liquid to the base of the unit. There, at the base 04 the 

vertical draft tube (0) gas is introduced through a sparger to create a 

dispersion of gas in liquid. Because of the lower effective density of the 

gas/liquid dispersion relative to the liquid, it rises through the vertical 

Section B as shown and is discharged at an elevated head (the pumping head) 

relative to the inlet. Necessary gas-liquid contacting (to be discussed 

later) is also accomplished in the vertical section 0. In practice, in.an 

algal growth system with wide channels, the gaslift configuration would be 

one in which the necessary number of airlift units, side by side, span the 

channel, or a unit with cross section of Figure AII-1 (rectangular) spanning 

the channel, or even, just one draft tube, Analyses to follow are general to 

all these possible configurations. The advantage claimed for airlift use - 

relative to independently pumping at one location in the system and sparging 

gas in at another - is that it provides both pumping and gas contacting 

functions in one unit operation. 

A11.3 GENERAL BACKGROUND 

Recent chemical abstracts (1980-83) contained no relevent references on 

gaslift use solely for pumping liquids. Further communications with Dr. R. 

T. Hatch (who has extensively researched and published on airlift fermenters) 

resulted in the finding that the only recent use of gaslifts known to him has 

been in handling of liquid radioactive wastes in nuclear fuel processing 

plants, and in collecting ("vacuuming") manganese nodules from the sea 

floor. In essence, gaslift pumping has been used recently only when either 

its high reliability (due to no moving parts) and/or its ability to handle, 

unattended and remotely, very abrasive slurries such as manganese nodules at 

great depths is required. It seems - although no rigorous analysis is done 

here - that alternative pumping methods are in most cases reliable enough and 

more efficient and economical than the combined cost of the compressor/draft 

tube required for the gaslift approach. It is worth commenting, however, 

that before the development of improved materials and pumps, airlifts were 

used extensively in applications such as primary sewage, oilwell, and coal 

mine (acid water) pumping. References to these applications date to the 

early 1900's C2,31. For reasons stated, and also because optimizing gas 

transfer (treated later) gives operating conditions outside the range for 

existing correlations t4,51 it will be necessary later to treat airlift 

pumping based on first principles. 

411.4 GENERAL ASPECTS OF PAST INVESTIGATIONS: PUMPING AND CONTACTING 

Because of extensive pilot and commercial application of airlift fermenters, 

numerous articles are available discussing aspects of their operation - for 

example references 6-12. Pumping efficiency in airlift fermenters - which 

determine cycle time around the flow loop consisting of the annulus and draft 

tube in such fermenters - is almost always adequate and hence pumping has not 

been a concern. It is, however, addressed in reference 8. A major topic for 

analysis in the cited references 6-13 has been the ability of the unit to 

transfer oxygen efficiently. This transfer capacity relates directly to the 

ability of the unit to transfer C02, which is the concern with algal growth 

systems. Central to both gas transfer and pumping is the behavior of the 

gas-liquid dispersion in the updraft section, and, in particular, the 

behavior of the bubble swarm generated within the upflow section. As bubble 

behavior is critical in both these respects, this topic is addressed first. 
1.5 BEHAVIOR OF BUBBLE SW4RMS IN GAS-LIQUID DISPERSIONS 

A number of correlations have been developed to describe the behavior sf 

swarms of bubbles which result from sparging 09 gas into liquid. The 

treatment to follow uses some simplifying assumptions which are valid for 

aqueous systems with low surfactant levels. Such low surfactant conditions 

are expected to exist in most algal growth systems, 

Sparging of gas into liquid results in swarms of individual gas bubbles which 

rise away from the sparger. The size distribution u+ the bubbles leaving the 

sparger may initially be a strong function of the sparging method, However, 

as bubbles of differing site rise through the fluid at differing velocities, 

coalescence of the smaller bubbles occurs; on the other hand, bubbles above a 

certain critical diameter, about 0.5 cm in water, will be broken up by fluid 

forces. The net result of this coalescence of smaller bubbles and breakup of 

larger ones is that a steady-state bubble size distribution is attained once 

gas has risen a certain distance above the sparger. Coalescence (and hence 

the height above the sparger at which equilibrium size distribution is 

attained) depends strangly on fluid properties, but for fluids similar to 

water, at gas holdups e>.01, equilibrium would appear to be attained bv the 

time gas had risen above 1 meter C131. This can be intuitively understood by 

considering velocities of bubbles of various sizes. (for bubble diameter 

DB ( 0.2 cm, the Stoke's range, the bubble velocity VB IIB2) and the 

fact that a larger bubble sweeps out a cylindrical locus exceeding its own 

diameter (DE), Within that cylinder it will catch up and coalesce with a 

smaller, slower bubble above it. 

The outcome of an example calculation can illustrate the coalescence 

process, Consider an initial case of two bubbles with a diameter ratio of 2 

(DO,l = 0.2 cm and DO,t = 0.1 cm, both in Stokes law range) and an 

initial vertical separation 09 15 cm, with the smaller bubble above the 

larger, (This circumstance will exist en the average in the case where e = 

0.01). The larger bubble will catch up and coalesce with the smaller bubble 

after only a 25 em rise. (Note though that higher levels of surfactants and 

electrolytes can hinder the coatescence process, and the analysis is done 

only for fluids with properties near water, for example low TDS algal growth 

systems.) Power dissipation can affect the equilibrium bubble size, but for 

power dissipations expected in airlift operation this affect has.been shawn 

(albeit in other types of fermentations systems) to be negligible L663. Gas 

holdup, e, may vary with pressure but any effect on bubble diameter from this 

is also expected to be negligible, both as pressure effects are negligible 

and as the coalescence dispersion process tends to maintain the 

characteristic size distribution. 

Rise velocities of bubbles have been established as a function of bubble 

diameter C151. Bubbles may be classified into two categories, "rigid sphere" 

up to D0 0.2 cn which rise according to Stokes' law, at velocities up to 30 

cm/s-for D0 = 0.2 cm, and larger bubbles whose gasiliquid interface is 

fluid and which - over a wide range of sizes, D0 0.25 to 2.0'cm - rise at 

about 25-32 cm/sec ti51. At an equilibrium bubble size distribution 

discussed nost gas, 93+X, is in bubbles with Dg N.25 cm and a very 

important consequence of this is that the averaqe rise velocity of gas 
through liquid, at least at gas holdups up to E = 0.25, is about 28-32 

cmlsec. An average bubble rise velocity of 30 cm/sec relative to the liquid 

will be assumed for analysis to follow. finother assumption is that cross 

section of flowing liquid in the gaslift - hence the average liquid velocity 

- is constant. This assumption is to some extent artificial but introduces 

little error and simulifies the mathematics. 

Given a net rise velocity of 30 cmlsec of gas relative to liquid, a constant 

liquid velocity VL and a flow rate ratio of gas to liquid of Qqc/QL 

(where Qgc is the gas flow corrected for pressure, temperature and moisture 

effects - these corrections are treated later), the following relations hold: 

where AL and AgC are the flowinq cross section of liquid and gas, 

respectively. Gas holdup, e, which can alternatively be defined as the void 

fraction of gas in the gas-liquid dispersion, is given by 

and, making the necessary substitutions, average holdup can be derived in 

terms of Qg/QLr and VL as 

where Qg is the gas flow, at STP, into the sparqer and the term Cpe is a 

pressure correction factor. Expression (4) will be referred to later. 

A11.6 CORRECTION FOR PRESSURE 

As noted, pressure must be compensated for in determining. gas holdup. If gas 

flow through the liquid is expressed at 1 atmosphere, then the ratio of 

actual gas volume and volumetric flow to these values at one atmosphere can 
be easilv computed as a function of aressure and liauid head. An average 

correction factor, termed Cpe here, can also be computed for the gas stream 

between the soarger and surface in the draft tube sectian. This factor, Cpe, 

can be expressed either in terms of pressure or alternatively in terms of 

hi and do (refer to Fiqure 1911-1). This correction has been compiled 

qraphically with results shown in Table 411-1, Another assumption is that 

water vapor and temperature corrections ((5% total) can be neglected. No 

corrections are in fact necessary if both 1) the temperature of the qaslift 

fluid equals compressor inlet temperature, and if 2) inlet air to the 

compressor has the same weight ratio of water to gas as the saturated gas 

rising through the draft tube. 

411.7 PUMPING BY GASLIFT PUMPS 

Refering to Figure AII-1 it is evident that a flow equation can be developed: 

where 

hi = inlet liquid surface elevation above sparger 

ho outlet (and hi - hi = pumping head) 

p~ f liquid density 

g = 980 cm/su2 

e holdup (= eoCp,) 

KC = contraction coefficient of liquid on entering gaslift inlet 

duct 

Kg = Frictional loss coefficient of liquid in inlet duct-draft tube 

turn 

KE = exit coefficient 

f = frictian factor (dimensionless) 

L = length of fluid flow path in gaslift (inlet conduit and draft 

tube) 

D = hydraulic diameter (= 21 width for long rectangular crmss 

section) 

VL = Fluid velocity in airlift (assumed equal to channel velocitv) 

It is convenient to define the overall friction coefficient, as KF = (KL + 

KB + KC + 4fLID). Then equation 5 becomes 
TABLE AII-1. Computed Values of CpE vs. Depth* 

Depth, cm C~~ 

100 .96 

200 .92 

300 .89 

400 .86 

500 ,823 

600 .803 

700 ,775 

800 ,752 

1000 ,712 

1200 ,676 

1400 ,645 

1600 ,619 

*Gas volume correction factor for depth and pressure. See Text. 
It 1s evident that with values for CpE available equation b can be used for 

various predictive purposes. Discussion of the use oi equation 6 will come 

later after it is demonstrated how gas transjer and pumping requirements fix 

some of the independent variables, 

Before going on, it is interesting to consider likely magnitudes of 

frictional loss terms within the gaslift due to fluid flow, if gaslifts are 

applied to algal growth systems channel flow. Velocities proposed for 

high-rate pond systems range from 10-30 cm/sec C173. The fluid head 

increment at an airlift pumping station is likelly to be in the order of 30 

to 100 cm, or even more, to provide economical pumping station spacing C171. 

It is interesting to note that a 30 cm pumping head is equivalent to 65 

velocitv heads (= pv2/2). It can be readilv calculated that if fluid flow 

in the gaslift is 30 cm/sec, and that if (for one "bad case" example) jluid 

is both drawn from and existing into stagnant liquid, in which case by 

Reference 20 KC = 0.43 and KL = 1.0 - that the frictional entrance and 

exit losses are anlv about 2,4% of the work expended to pumpinq liquid 

through the pumping head. The balance of expected frictional losses, from a 

(possible) 180° bend between gaslift inlet duct and draft tube, and the 

total frictional loss from channel flow at LID = 20, will total less than 3% 

of the pumping work. Thus for this example total frictional losses in the 

airlift pump are small, abcut 9%. Because VL and Vch can be equal, and a 

bend configuration can be chosen to minimize frictional loss, frictional 

losses due to fluid flow should in fact be in the range of 1% of the pumping 

work expended for cases of interest. 

While frictional losses are minor, relative to useful work done in pumping, 

other inefficiencies exist. Dne of these, which is major, can be understood 

intuitively as due to the 30 cm/sec slip velocity of qas relative to liquid 

discussed earlier, This and other factors relating to efficiency are 

di scussed next . 

A11.8 EFFICIENCY CALCULATIONS 

The work done by an element of gas on the liquid can be stated as (force 

exerted by gas on liquid) X (distance moved by liquid during time farce is 

exerted). Note that the distance is gpt the total moved by the gas element, 

as the forcexdistance product of the 30 cm/sec gas movement through the 

liquid i.5 lost, i.e., dissipated as heat. (Also note here that the following 

analysis is in C.G.S. units. and based on 1 cn3 gas or viewed by the 

compressor.) 

The average force exertad bv 1 cn3 gas on the liquid ir gCpp A4 , with 

Cpe as calculated earlilerr for the time the gas is in the liquid. If gas 

rises from the sparger to the surface, the time qas is in contact with the 

liquid is h,/(V' +'30). Thus the work done by the 1 cm3 gas element on 

the liquid, wg~ during the rise of the gas element, is 
qaslift temperature Tgl is different from compressor inlet temperature 

, the term Tql/TC compensates for this. The term Ap is assumed to 

1 qm/cm3 and so is omitted in 7. Other terms were defined earlier. 

For low head compression, which is the case for algal growth systems, single 

staqe isentropic compression will be applied, and the expression for the work 

done to pump 1 cm3 gas, Ugc, is given by 

where 

n = mols gas in 1 cmJ at compressor inlet temperature 

TC = gas temperature entering compressor, OK 

k = Cp/CV of gas, = 1.4 for air 

PI = compressor inlet pressure, "I atm (or loh dyne/cm2) 

PZ = compressor outlet pressure 

X = polytropic compression factor, 3.5 (dimensionless) 

In CGS units, R = 8.31 X la7 erg/mall0K. For 1 cm3 gas entering the 

compressor at one atmosphere the product nTC is constant (whatever the 

temperature) at 1.218 X k10'~ a01 OK, and with this value (8) becomes, in 

ergs expended to pump 1 em3 (compressor inlet conditions) 

Isent 

porti 

is in 

r opic 

on of 

teres 

compression is less efficient than isothermal compression since a 

the isentropic compression work appears as unusable heat, but it 

ting that efficiency of isentropic compression is still high 

relative to isothermal at pressures likely to be needed. For example, at a 

compression ratio of 2/1 (or ca 10M depth for hi), isentropic compression 

is 91% as efficient as isothermal. 
The work done bv an element of gas on the liquid has been given previously as 

equation (71, Given equation (6) and if it is assumed for the moment that 

channel and gaslift flow velocities are equal then this energy expenditure 

divides between pumping head and fluid frictional losses in the ratio 

The expression far efficiency, Eg/p, defined as the ratio of pumping work 

accomplished to gas compression work requirement then becomes 

The remaining factor to be considered is the motor/compressor efficiency 

by which I1 i5 multiplied to give E,, the overall cxpr~rsion for 

efficiency: 

It is of interest to note that overall puaping efficiency E, should range 

by equation (12) between about 25% and 50%. One set of typical operating 

conditions (based on 80% COg transfer need, computations presented later) 

might consist of a fluid gaslift and channel flow velocity of 15 ce/sec, 

dra$t tube height = 5.4 meters, and a pumping head of 14.5 cm. Efficiency 

under these circumstances at Em, = 0.8 would be about 29.52. If COp 

transfer efficiency rises to 95X, and fluid flow velocity is increased to 30 

cmfsec, the pump head needed will increase to 1.lb m . With other parameters 

kept the same, the draft tube height must increase to 13.5 aeters and overall 

efficiency would increase somewhat, to 40.8%. Higher efficiencies are 

obtainable with higher channel and gaslift flow velocities; however, such 

higher velocities can result in energy consumption which is a large fraction, 

easily around SOX, of total expected system output (see later discussion) and 

in addition, there is no evidence that such flow velocities are required. 

Such velocities might in f?ct be deleterious in terns of suspending solids in 

the types af unlined channel systems which are likely to be affordable. 
The pumping needs of a channel growth system could be met with any suitable 

combination of gaslliquid flow ratios f(= Qg/QL), and gaslift draft tube 

height and area. However, configurations must also be able to meet CO2 

transfer needs. Because of the importance of gas (C02) transfer and design 

constraints posed by gas transfer, this topic is addressed next. 

A11.9 GAS TRANSFER FROM BUBBLE SWARMS TO LIQUID 

Oxygen transfer is an important unit operation in fermentation and waste 

treatment. It has been established that the overall transfer coefficient, 

KL, is in one range for small rigid sphere bubbles DBL (2 mm, and in 

another range - about twice as high, for larger bubbles DB >2 mm. A number 

of correlations (for example as discussed in 21) have evolved for these 

bubbles of various size ranges, This would seem on the surface to implv a 

difficult analytical situation. However, even with this disparity of 

transfer coefficient with bubble size it fortunately transpires that the 

coalescence and redispersion of bubbles in a rising swarm leads to a steady 

state size distribution a short distance above the sparger as discussed 

earlier (and as intuition would suggest). In this steady state the ratio of 

KLaT the combined mass transfer coefficient (whose units can be h,-I or 

nmol/L.hr.atm) to volume of the rising gas, is constant. Also, gas pressure 

(hence solubility) and area terms cancel. A very important implication of 

this is that the fractional approach to liquid equilibrium activity of a 

given gas component in the gas phase is constant per unit time. (It has been 

established that power dissipation in the liquid does not affect KL.) If 

thermodvnamic activity of gas dissolved in the liquid phase stays constant 

relative to gas phase acativity, then the fraction of gas phase component 

which is lost from the gas is constant per unit time. Thus, 

where 

Pg = activity of species in gas phase, atm 

PL = activity of species in liquid phase, atm 

Kg transfer coefficient based on gas activity 

more specifically the transfer coefficient can be expressed as 

Atmospheres gas lost/unit tire 

K, =-------------------------------- . Ataosphere gas driving force 
The constant fracti~nal stripping o+ ~f oxygen per unit height has been 

established in particular for reference 8 (Hatch) and in reference 13 in the 

deep tank work of Schmidt and Redmond, 

For oxvqen, the fractional absorption per unit time from the gas phase is 

.0065 - .0075 seto1 at 20°C (0. 13). A value of 0.007 will be used in 

this analysis. However, the critical problem for algal growth systems is not 

oxygen transfer, but CU2 transfer. Though no literature was found 

directllv applicable to Cog transfer in the situation envisioned for the 

algal growth system, a well established mas5 transfer correlation may be used 

to compare the Kg for C02 transfer from that of 02 t7, 131. 

Specifically, at a qiven gas phase partial pressure the liquid oide mass 

transfer coefficient per unit area, which controls KL, is proportional to 

D~~*~~ (where D = gas diffusivity in liquid). Kq is in turn 

proportional to K times salubilitv. Thus 

and Kg for C02 can be computed to be about 0.125 sec'l (though a 

cautionary note is that smaller bubble size with surfactant present could 

give a much higher Kg). With this Kg, a swarm of gas bubbles rising through 

qas-free liquid would lose about 13X of their remaining CB2 each second. 

(In deriving CQ2 transfer data from U2 data, note here that it has been 

established that there is negligible chemical acceleration of CO2 uptake - 

see Ref. 17). 

A11,lO COMPUTATION OF TIME AND HEIGHT NEEDED FOR TRhNSFER 

The limiting case will sometimes exist where back pressure of C02 is 

negligible. This wlll be true in particular when the system is operated at 

low CQ2 and high alkalinity to prevent CO2 escape to the atmosphere 

E171. In this case computation of the required contact time is 

straightforward from equation (13) and Kg = 0.125 sec-l. Required contact 

tines for BOX and 95% absorption of C02, for both 15 ca/sec and 30 cn/sec 

draft tube velocities in each case, are shown in Table 411-2. These values 

of draft tube height and +low velocity are those which were used earlier to 

compute representive efficiencies. 

In the majority of cases CO2 transfer will take place where backpressure is 

not zero. The partial pressure of C02 (PL in equation 13) is needed and 

can be derived as a function of any ~f several interrelated paramet.ers. One 

convenient derivation is a5 a function of pH (or ti+ conce'ntration) and 

alkalinity, A. Here, alkalinity is defined as nilliequiialents per liter 

excess of cations over all anions other than carbonate species. It is also 
assumed as a simplifving measure in this analysis that no buffers other than 

carbonate are present. The simplification can also be made for pH values of 

interest (5-11) that H' and OH' are negligible relative to carbonate 

species. Data in the analysis to follow is from reference 18 and 19. The 

term C C02 is used to define the sum of C02 and H2C03 in solution. 

A = meq/L alkalinitv = HC03' + 2C03 = 

(H') (C03= given that --------------- - = 4.4 X 10-l1 Refs. 18, 19 

HC03- 

and 

Also, given that 

(H') (HC03-1 /CCO2 = 4m31 

p -------- -------------- 

and Cc02 

4.3~10'~ H+ + 8.8~10'~~ 
letting K1 4.31 X loe7 and K2 = 4.4 X 10-11, 

total carbon in solution, TC, is given by 

As solubility of COT is 29 mmol/L .atm (20°C) the term PI for use in 

equation (13) would-be 1129.1 atr X C C02 or 0.034 CCU2 kt 200. 

Other temperatures can be treated in the sane way using the C02 solubility 

+or those temperatures, 

All.11 COMPUTATION OF REQUIRED RESIDENCE TIME IN DRAFT TUBE 

The entire proacedure for computinq transfer time (or height) is complex and 

only the briefest possible description will be given here, Given equation 

I? and 20 a graph can be constructed showing total carbonate species Ii.e. 

nmol/L C in liquid) and PC02 as a function of pH. It is assumed here that 

gas and liquid flows are known, and that the starting compositions of both 

the gas and liquid phases (at the sparger in the draft tube) are known. Thus 

a point can be drawn above the inlet liquid composition/pH point showing 

pC02 of the inlet gas and liquid. Gas and liquid flows will be concurrent 

where the gaslift is used for pumping as well as C02 transfer; thus the sun 

of gas and liquid fluxes upward is constant. Specifically, 

where Bg and QL are flow rates of gas (S.T.P.) and liquid, The material 

balance of equation 21 can be used to construct a PC02 for the gas phase 

corresponding to each PC02 of the liquid phase. The time needed for 

transfer can then be computed through the following iteration: 

1) Starting with initial PCO2 of gas and liquid elements, choose a 

PCO2 increment for each (nepative for gas, positive for liquid) by 

equation 21 small enough that use of averages for PL and Pg gives 

acceptable error, Then the average driving force for transfer is 

(PC02gI + PCO2qF) - (PCO2I.I + PCO2LF) = PC02 average. The 

subscripts g, L, I, and F are gas, liquid, initial, final 

respectively, 
2) Compute time necessarv for transfer as 

3) Repeat procedure for the next chosen increment of gas and liquid 

PC02. 

The procedure is continued until the final desired P~02 gas 

and liquid are attained. The height needed for transfer is easilv derived 

from this time and the gas velocity (VL + 30). 

There certainlv exists a rigorous analytical solution for the height 

calculation, but it is almost certainly too messy to be useful. The 

preceding computation should, however, be easv to accom~lish with an 

appropriate computer program. 

411.12 COMBINED PUMPING AND GAS TRANSFER 

To this point in the analysis expressions have been developed for gas flow 

required for the pumping function, and for the draft tube height needed for 

C02 transfer. Regarding which independent variables are to be fixed, two 

sets of circumstances are of interest: one situation is where the draft tube 

height is sufficient only to accomplish needed C02 transfer, with the 

balance of pumping - if needed - accomplished by other means. The other 

situation is where transfer requirements are met and gas does all of the 

pumping work as well. 

In a typical channel flow system, depth and flow velocity will be fixed on 

the basis of various criteria such as 1) sufficiency to mix algae, 2) 

avoidance off erosion and sediment transport in unlined pond sysstems, 3) 

spacing of gas transfer and mixing stations, and other factors (more 

discussion is presented in reference 17). Choice of depth and channel flow 

velocity dictate pumping energy requirements and grade, or liquid surface 

slope in the direction of flow. Grade in turn determines pumping head (= 

grade X length of flow path). Carbon dioxide addition must be sufficient to 

meet the needs of photosynthesis by the algae. The assumption here is that 

algal productivity will average 75 metric tons/hectare yr., with a maximum 

productivity of 20 gm/m2.dav and that 2 qms of C02 must be transferred to 

the system per gram of algae which is grown C171. It is assumed thaat C02 

loss from the liquid surface - or in alternate terms, back diffusion to the 

atmosphere - is minimal so that the C02-containing gas stream can be 

introduced into the system, and mixing can be carried out, 24 hr/day. This 

is an operating characteristic important for system economics. For purposes 

of illustration and analysis, model systems will be assured with 

characateristics shown in Table AII-2. 
TABLE AII-2 

SYSTEM CHARAACTERISTICS USED FOR ILLUSTRATIONS (See Text) 

A, Stack gas use 

I. Channel flow velocity = 15 cm/sec 

Channel Depth = 30 cm 

Pumping head = 7.2 cm (From Manning equation, n = .02, pumpinq 

station = 3240 m, 6 hr circulation time) 

Algal Pr~ductivitv = 20 grlm2.dav 

Cog requirement = 40 gn/n2.dav 

80% abgorption of C02 from qas stream 

Required Q9/QL = 0.155 (Qg expressed at 25OC. 1 atm, 15% 

Cop) 

Required hL for 80% absorption = 5.4 M 

11. 4s above, except 

Channel Flow Velucity = 30 ca/sec 

Pumping station spacing = 6480 meters 

Pumping head = 58 cm (6 hr circulation time) 

Qg/OL = 0.139 (Qg at 25OC 1 at., gas has ISX CO2 by 

volume) 

Required hL for 90X absorption = 13.4 meters 

0. Pure C02 use 

With pure C02 (other assumptions abave hold): 

See text for further discussion of pure C02 case. 
A11.13 COMPARISON OF GASLIFT PUMPING ChPACITY WITH CHANNEL GRQWTH SYSTEM 

NEEDS 

The choices for C02 content of the suarged gas, in combination with desired 

fractional C02 stripping and desired fluid flow velocity in the qaslift 

draft tube fix the gaslift draft tube height. (Calculated heights for the 

examples are shown in Table AII-2.) Values chosen for these parameters also 

fix the qas holdup in the system, and power input which is directly 

proportional to gas holdup. Holdup needed to provide a given pumping head, 

from equation 6, can be compared to the actual holdup from chosen parameters 

by equation 4. If holdup by equation 4) is less than needed from equation 4) 

then auxilliary oumping power must be provided. 

Holdups calculated by equation 4 for case A1 and AII are 0.0406 and 0.045 

respectively. If the pumping head needs for the two systems are 7.2 and 58 

cm, respectively, then pumping power availability is a factor of above three 

times need for case 01, but is in almost perfect balance (holdup computed at 

1.04 times need) for the assumptions of case AII. As there are uncertainties 

(discussed under "uncertainties" later) this must be considered a perfect 

match within computationai precision. 

For the pure C02 transfer case, it is necessary to take into account the 

volumetric change as C02 is absorbed during bubble rise. The situation is 

complicated by back diffusion of oxygen into the bubbles. Tho assumption 

made here is that the C02 volume of the rising gas decreases exponentially 

with height (as would occur with the constant bubble size distribution 

discussed earlier) but that back diffusion of oxygen ie eoual to 25% of the 

C02 which diffuses out. For the 80% C02 absorption case, this leads to a 

final gas volume of 40% of the initial, and for the 75% absorption case, a 

volume which is 29% of the initial. The average gas flow (STP) used in 

computinq holdup is considered to be the log mean of inlet and outlet, times 

a pressure correction factor, P1/P2, for a depth of 2/3 of hL (3.6 M 

for case BI, 9fl for 011) to account for the fact that the majority 04 gas is 

at lower than mean depth. (This correction factor is ta be distinguished 

from the term CpE used earlier). With these assumption, the holdups for 

cases 01 and BII are 0.0035 and 0.00304. These values are only 15% and 5% of 

need, respectivelly, for 15 and 30 cm/sec channel flow velocities, 50 that an 

auxilliary pumping process would be needed where pure C02 is used to supply 

carbon needs. 

The above calculations are only illustrations, but it is evident that when 

CQ2 is supplied by stock gas with plausible requirements for mixing 

velocity and fractional stripping, that gaslift punpinq capacity can be 

capable of meeting total system needs. It is worth noting that a value of 

0.02. was used for the Manning equation roughness, n (See 22 for discussion). 

A value of n = 0.01 could equally well be encountered with a smooth channel 

bottom, which would mean for even channel flow velocities of 30 cm/sec that 

pumping power of the stack gas transfer system could be well in excess of 

needs. At n = 0.01, power availability' for the pure ~O~,'cas@ could supply 

a large function, or possibly all pumping needs, if channel 
velocities of 5-10 cm/sec could be tolerated. Uncertainties which attend the 

estimates are discussed later, but a good match between gaslift pumping power 

and needs seems possible with reasonable assumptions. 

A further important consideration is that the system must also be energy 

efficient, which is to say that the Cop transfer/pumpinp functions should 

not consume a large function of system energy output. Not energetics are 

examined next . 

A11.14 NET ENERGETICS; GASLIFT ENERGY CONSUMPTION AS 4 FRACTION OF TOTAL 

GROWTH SYSTEM OUTPUT 

In addition to choices made earlier, twa additional parameters must be 

assumed in order to calculate energy demand of the gaslift system as a 

function of system output. These are f) the gross system energy output per 

unit area per day, and 2) the thermal to mechanical conversion efficiency 

which is obtained when converting the qroaa energy output, in the form of 

dilute algae, to mechanical energy. The working assumption here for 1) is 

that the 20 gm/m2 day of algae have a gross heating value of 5000 cal/gn (= 

9000 BTU/lb) so that system gross energy output is 100 ~cal/in*.dav. A 

second assumption, without specifying mechanism, is that this gross energy 

can be converted to mechanical energy at a thermal - to mechanical conversion 

fatio, or ef+iciency, of 30X. Available mechanical energy, from which energy 

for grslift operation must come, is with this assumption 1.26 X lo2 

erg/n2.day. Using equation (8) and a value of EnL = 0.8, the fraction of 

total system energy requirement for sample case AI of Table 2 is 7.9% and for 

AH, pumping through 13.4 M, it is t5.2X. These are fairly major, but not 

intolerable, levels of energy cunsumption. For cases BI and BII, where C02 

is pumped tghrough the same heads, with other assumption as presented 

earlier, consumptions are 1.2% and 2.2% of total system output. Carbon 

dioxide from some sources (e.g. geological reservoirs) may be pressurized. 

No energy at all would be required to sparqe this C02 if it is available on 

site at more than about 2 atmospheres. 

A11.15 UNCERTAINTIES 

U number of uncertainties exist in the preceding calculations regarding 

efficiency of gas transfer and net energy consumption by the gaslift. Han~ 

of these have already been mentioned, but it is worthwhile to review the 

possible sources of error and-uncertainty here. Some sources of error and 

their magnitude are discussed below. 

A value of 0.125 sec-l for Kq was derived based on the premise that gas 

bubbles in algal systems will behave as air bubbles do in'steady-state dilute 

aqueous systems. There is major uncertainty in the assumption, but r 
range cannot be given to the uncertainty at this time. Experimental values 

for Kg are being observed at 2-5 times the 0.125 sec-i assumed here C221. 

This may indicate high fractional C02 stripping from small bubbles near the 

sparger before coalescence/dispersion establishes a steady state, or else, 

prevention of coalescence (hence maintenance of smaller C02 bubbles and 

higher Kg) by surfactants in algal growth systems. Experimentation will be 

required to give some answers in this area. This topic is quite important as 

both energy consumption (but also available pumping capacity) are inversely 

proportional to Kg. 

Values for n, the channel wall and bottom roughness, cauld easily vary by a 

factor of 3, which could change power requirements by an equal factor. 

Establishment of the value for n (if not 0.02 as assumed) will require 

considerably more analysis and is beyond the scope of this treatment. 

In computing energy consumption by the compressor, and buoyancy effect of 

sparged gas, account must be taken of temperature differences between the 

compressor inlet and in the rising column of bubbles in the draft tube. 

Corrections should also be made for variations in water vapor content between 

the two points. However, these corrections are small with minimum total 

error at less than 5%. 

The calculation of pumping work done on the liquid by rising gas bubbles was 

predicated on liquid "plug flaw," i.e. that all liquid elements in the draft 

tube had the same velocity. Obviouely, they do not, and there will be an 

efficiency loss relative to that calculated earlier if fluid has a velocity 

distribution characteristic of turbulent flow 1213 even when gas bubbles are 

uniformly distributed over this area. This error in pumping efficiency 

calculating has been worked out C23; detail not shown1 and is, surprisingly, 

less than 2%. This error is small because the turbulent flow velocity 

profile is rather flat, though it does vary. If gas "channels," or is 

unequally distributed in the cross section, or travels in fluid elements 

having much greater than average velocity, then pumping efficiency losses 

could be large. It is not possible to state what the efficiencv decrement 

might be, but in any event this situation can be avoided by sparging so as to 

introduce gas uniformly over the draft tube cross section. 

Power input and efficiency were computed earlier for stack gas (15% C02) 

sparglnq on the basis of unchanging gas volume. However, the actual stream 

flow-could actually change by as much as 15%. This 15% seems to be the 

likelv maximum error from this source. Back diffusion o+ 02, and the fact 

that some C02 remains with the gas stream during its rise, will probably 
keep this error to 10X or less, with stack gas. For pure Cog suarqing, the 

gas absorption correction is obviously major, but Cop pumping is not a 

major energetic drain (if any energetic drain at all) and pure CQ2 sparging 

does not appear to supply enough pumping power in most likely cases, to meet 

system needs. Thus modeling gaslift pumping by pure C02 streams does not 

seem to be a pressing need. 

There are likely to be other sources of error which have not been 

considered. However, it seems that the surface roughness and CD2 

absorption Kg uncertainties are dominant. Thus in summary, the conclusion 

must remain that a gaslift system capable of transferring stock gas should be 

capable of providing enough or more than enough pumpinq capacity to meet the 

needs of a high rate pond system with channel flow velocities of 15-30 

cm/sec. Energy consumption for this approach should be a high (525%) but 

tolerable function of system output. 
REFERENCES 

Hatch, R.T., Chemical Engineering Department, University of Maryland. 

Personal Communication, August 1984, 

Parch, Proceedings of the Institute of Mechanical Engineers, 1917 cf 

Ref. 4 below. 

Ivens, Trans. A.S.M.E. 1909 CF Ref. 4. 

Mark's Mechanical Engineers Handbook p. 1874 Fourth Edition (1941). 

Perry's Handbook of Chemical Engineering pp. 5-39, 5-40, and 6-13. 

Fifth Edition, 1973. 

Dussap, C.J. and J.B. Gross. Energy Consumption and Interfacial Mass 

Transfer in' an Airlift Fermenter. Chemical Engineering Journal 

(France) 25 151-162 (In English). 

Moo-Young, M. and Blanch, Ha#. Design of Biochemical Reactors: Mass 

Transfer Criteria for Simple and Complex Systems. Advances in 

Biochemical Engineering. 

Hatch, R.T., Ph.D. Thesis, M. I.T., 1973. 

Lippert, J., Adler, I., Meyer, H.O., Lubbert, A. and K. Sckurgerl. 

Characterization of the Two-Phase Systems in Airlift Tower-Loop Readers 

During the Cultivation 0f.E. Coli. Biotech. Bioeng. 25(2) p. 437-50 

4 1983). 

Merchuk, J.C., Stern, Y. and R.I. Mateles. Distributed Parameter Model 

of an Airlift Fermenter, Biotech. Bioeng. 22 pp. 1189-1261 (1980). 

Moresi, M. Optimal Design of Airlift Fermenters. Biotech. Bio~ng. 23 

p. 2537-2560 (1981). 

Schmid;t, F.L. alnd D.T. Redmon. Oxygen Transfer Efficiency in Deep 

Tanks. Journal Water Pollution Control Federation 47(11) 2586-2590 

(1975) 1 

Augenstein, D.C. Oxygen Transfer in Fermenters at High Power Inputs. 

M.S. Thesis. M.I.T. (1967). 

Far example, in "Airlift Fermentation; A Bibliography to the BRL 

Airlift Fermenter, available from Bethesda Research Laboratories, 

Gartnersburg, Md. (1983). 

RIII-1 TRAVELLING SOLIDS REMOVER FOR POND SUMPS 

(By Joseph C. Dodd, Consulting Engineer) 

Continuous rails are provided so that a single solids remover say service a 

number of pond sumps where the ponds are arranged to allow this. The rails 

are supported on piers and pond nalls, nith spacing to allow use of light 

rolled berms such as 6" or 8" WF or B sections (span 15-20 ft.). Steel 

sections at about 15#/ft nith a high quality protecive coating is preferred, 

although fiberglass sections are available but more expensive. The pier 

spacing must be coordinated with the walkway support requirements, which may 

be more critical if timber is used (2" x 10" stringers with 15' span 

previously used). tlinimum pier thickness is 4" for rebar cover. 

The travelling solids remover is fabricated from 6' Cs, rolling on 6" steel 

nheels with rubber treads (to protect coatings). Two wheels are driven by a 

hand crank to move the collector at the speed which just picks up the blanket 

of solids. A sight glass on the suction hose ray be used to estimate the 

rate of travel. The collector is a stainless steel pipe ara with perforated 

tee pipe having rollers to maintain the desired bottom clearance. The arm 1s 

pivoted up to clear the walls when transferring to another pond. It may also 

be moved along the solids remover rail to sweep several strips along the 

bottom to remove as much settled solids as possible. The solids are pumped 

by a self-priming pump (e.g, progressing cavity). 

Power supply to the pump and solids discharge hose are draped between a fixed 

nast at the center of the sump and a mast on the solids remover. Quick 

connect couplings allow transfer from one pond to the next. The discharge of 

solids is conveyed in a pipe supported along the walkway or rail, either to 

disposal, or to a settling tank(s) for thickening and return of supernatant 

to the pond. The latter method reduces salt loss and disposal requirements 

but adds to facilities cost and operational complexity. 

Cnef 12 or-l92,He~t~ce~14Z9~s?c_reL-S~ste~ 

For saline systems, frequency of cleaning is less than with wastewater 

systems, so two removers can probably handle 12 ponds, or a total of 4 

removers for the 192 hectare systen. A 2" or 3" pump should be used, 

operated at a reduced speed (say 500 - 800 rpr) due to abrasive nature of 

solids. Settling tanks (if used) should be designed for 50 gpa overflow rate 

of 3000 gpd/ft2. Need 24 ft2 or approx. b ft. diameter, nith hopper 

bottom. 
Rough estimating costs: 

Rails @ 612/ft. includlnp coatings, specials, 

anchor bolts, installation, 

Pter concrete (assume 10 per pond) 

0.5' X 1.5' x 4.5' . 33.8/27 = 1.25 yd3/pond 

1.25 x 24 pondr B $200/~d~ $6.000 

Solids remover (ea). 

Complete except far pump, elec. & piping 10,000 

Pump, elec, & piping (to fixed raet) 5 , 000 

------ 

Total $15,000 

hssume piping & electrical on pond structure is included in other estimates 

(7. of project costs). 

Total for 475 acre module: 

Rails (4 rails x 3400' = 13,600 8 $12/ft,) 

Piers 

Solids removers 4 x lSaOOO 

Total without tanks 

With tanks, add 4 @ $5,000 

Appendix AIII-2 

SLUDGE RECMOVAL FROM SHALLOW GROWTH PONDS 

(by Lloyd Bracewell, Consulting Engineer) 

Shallow high rate algal growth ponds with mixing low velocities will eventually 

experience some settling out of organic and inorganic materials to form a 

sludge layer over the pond bottom. Since the growth ponds have only about 20 

cm of depth, any significant layer of sludge would interfere in the pond's 

operation. It is therefore necessary to provide for the removal of sludges 

from the bottom of the growth ponds once the depth reaches about 15 percent 

of the water depth or 3 cm. The proposed method of construction of the growth 

ponds and their layout create severe constrints on the methods that can be 

used cost-effectively for sludge removal. In particular, access is limited 

to the ends and the pond bottoms will be of earthen construction. 

A form of hydraulic removal of sludge would therefore be most appropriate 

if required on a frequent basis. If the pond mixing velocity is increased 

several-fold then the sludge would be resuspended in the water column and the 

water could be withdrawn for settling in another basin with adequate detention 

time for solids removal. This approach would require sizing the mixer drive 

motors much larger than necessary for normal mixing purposes. One possible 

solution to keep the installed size of the motors to a minimum would be to 

design the mixing systm to include a power take-off so as to accommodate the 

installation-of a supplemental driver only when sludge removal was needed* 

The sludge removal approach proposed whenever thorough pond cleaning is required, 

such as annually, is to decant the pond water, install a boom and sludge 

pump arrangement, operated by a winch and by a combination of dragging and 

pumping, move the sludge to small smps at each end of each pond. The boom 

would be the width of the pond and dragged by several cables connected to 

winches installed on mounts for that purpose when needed to remove sludge. 

Small sludge pumps would be mounted on the boom with 100 ft discharge pipes 

suspended along the pulling cables to keep excessive amounts of sludge from 

accumulating in front of the boom as it is dragged along the pond bottom 

toward a sludge sump. This reduces the load on the cables and boom as the sludge 

is gradually moved to the end of the pond. The sludge collected in the end 

slumps would be pumped to a storage pond for later disposal. The boom would be 

constructed of 12 by 12 inch wooden beams 20 feet long and hinged at each connecting joint for the width of the pond. A pulling cable would be attached 

at each of the connecting joints and attached to individual winches. A 

3 horsepower sludge pump would be mounted on each section of the boom with its 

suction manifold set along the front of that section of the boom to pump 

sludge as it acculates in front of the boom. The pump discharge hose would 

be extended along the pulling cable approximately 100 feet to keep the pumped 

sludge ahead of the boom as it travels the length of the pond. The sludge as 

it was pumped would tend to flow, albeit slowly, toward the end of the pond 

since the dragging would be done in the direction of the pond gradient. 

The estimated cost for a sludge removal system of this type is about $60,000. 

A single system would be shared among all the ponds. 
Appendix AIII-3 

DIVIDER WALL COST ESTIMATES# 

METHOD ----- MATERIALS ------ -------- LABOR -------- 

QTY UNIT TOTAL HOURS HOURLY TOTAL SUBTOTAL 

PER FT COST RATE 

1. HYPALON MEMBRANE 

POSTS 0.250 $1.65 $0.41 0.025 $35.00 $0.88 $1.29 

CONCRETE 0.004 $5 1.50 $0.19 0.004 $16.35 $0.06 $6.25 

MEMBRANE 2.000 $0.50 $1.00 0.100 $16.35 $1.64 $2.64 

RAILINGS 1.000 $1.00 $1.00 0.020 $16.35 $0.33 $1.33 

TRENCHING 0.019 $1.00 $0.02 $0.02 

------ 

TOTAL $5.51 

2. CONCRETE BLOCK 

BLOCKS 1.780 $0.66 $1.17 0.130 $16.35 $2.12 $3.30 

MORTAR 0. 080 $2. 60 $0. 21 $0.21 

GROUT 0.244 $2.25 $0.55 0.067 $16.35 61.09 $1.64 

STEEL 1.000 $0.23 $0.23 0.008 $16.35 $0. 13 $0.36 

FOOTINGEXC0.019 $1.00 $0.02 $0.02 

CONCRETE 0.0 19 $50.00 $0.93 0.04 1 $16.35 $0.67 $1.60 

----- 

TOTAL $7.12 

3. POURED CONCRETE 

CONCRETE 0.035 $51.50 $1,80' 0.061 $14.40 $0.88 $2.68 

STEEL 1.OClQ $0.23 $0.23 0.008 $16.35 $0.13 $6.36 

FORMWORK 2.670 $0.10 $0.27 0.116 $17.35 $2.01 $2.28 

FOOTINGEXC0.019 $1.00 $0.02 $0.02 

------ 

TOTAL $5.34 

PIPE 1.000 $6.77 $4.41 0.012 $94.00 $1.13 $5.54 

FOOT I NG 0.025 $50.00 $1.23 0.055 $16.35 $0.90 $2.13 

----- 

TOTAL $7.67 

S S~lppl i ed by Lloyd Eracewell, consul ti ng engineer 

St Not described in text 
Appendix AIII-5 

Large Scale System Paddle Wheel Costs 

DESCRIPTION 

Drive Tube 

Hubs 

Fl anqes 

Spokes t f -gl ass) 

Paddles I ' 1 

Fasteners 

Drive motor 

notar Starter 

Hot or lase 

Var. Speed Unit 

Speed Reducer 

5R Base 

SR Sprocket 

Jackshaf t 

JS 0earinqs 

JS Spr. t1 

JS Spr, t2 

PY Solid Shrfto 

PW Drive Spr a 

Dr. Chain #I 

Dr. Chain I2 

Chain Guard9 

PU Beilrinqs 

PU Coupling 

Torque liriter 

Hisc, 

-- -LC---"L..II-I------........ 

PADDLE WHEEL COST BREAKDOWN 8 

-- ..-.."1-1-...1.-..-.--....- 

8.0 Hectare lasis 

0-0 I------ flATERIhLS-------------- 

RUAN UNITS UNIT $ COST 

---- ----- ------ ---- 

46% lb 0.55 2,361 

498 lb 0.55 274 

869 lb 1.00 863 

431 ft 2'73 1,103 

1473 sq f t b.00 0,836 

353 

1 900 900 

1 450 450 

1 

I 2,700 2 q 700 

1 1,400 1 T400 

------- 

TOTAL 24 799 

IHSTbLLATION (not incl structural 1 

COST 

1,280 

411 

0 

59 2 

incl. 

TOTAL 

COST 

----- 

3,841 

685 

869 

1,777 

8,836 

333 

900 

450 

277 

2,700 

1 400 

27 5 

25 

648 

200 

75 

SO 

1,344 

100 

25 

50 

200 

1,500 

1,700 

350 

COHNEff T 

------- 

16' 150 psi steel 

Fi berqlas 2~2~0.25 

Fiberglas 0.30' thk 

15 hp, Severe Duty 

NERA size 2, type 4 

Base oniv, not struc, 

Boi er 15ACY, 29: 1 

Cyclo 1870 

Bdse only, nat structral lupport 

3.38' dir S,S,, 24'lonp, n/ keyways 

3,s' dir S,S,, 12' long, one keyway 

Rol ler bearing, split housing 

Fa1 k 120T t l~t) a lOOT(2nd) 

TOTbL IHSTALLED COST 
Appendix AIII-6 

Experimental System Paddle Wheel Costs 

DESCRIPTION 

------------ 

Drive Tube 

Hubs 

Flanges 

Spokes (f -qlass) 

Paddles ( ' 

Fasteners 

Drive rotor 

notor Starter 

Hot or Base 

Var, Speed Unit 

Speed Reducer 

SR Base 

SR Sprocket 

Jackshaf t 

35 Bearings 

JS Spr, #I 

JS Spr, 12 

PW Solid Shafts 

PW Drive Spr . Dr. Chain #I 

Dr. Chain I2 

Chain Guards 

PW Bearings 

PW Coupling 

Torque Liri ter 

Misc. 

------------------------- 

+ PhDDLE YHEEL C0iT BREAKDOWN + ........................... 0.4 Hectare Basis 

---------- MATERIALS---- 

PUAN UNITS UNIT $ 

---- ---- ------ 

819 lb 0,bO 

139 lb 0.60 

195 lb 1.00 

140 ft 3.00 

331 sq ft 6.00 

-me------ FAB. 

COST COST 

---- ---- 

492 246 

84 125 

195 0 

420 210 

1,987 incl. 

79 

350 

200 

TOTAL 

COST 

----- 

737 

209 

195 

630 

1,987 

79 

350 

200 

47 

750 

700 

275 

25 

196 

100 

50 

25 

140 

7s 

2s 

30 

200 

300 

0 

300 

250 

--- --- 

TOTAL 6,826 7,897 

INSTPilLATIOl (not incl rtructural) 2,764 

TOTAL IN8TUED COST 

(unit prices have bem ad justed for quantity) 

COHHENT 

------- 

8' sch 40 steel 

Fi berglas 2~2~0.25 

Fiberqlac 0.23' thk 

2 hp, Severe Duty 

EflA sire 0, type 4 

Base only, net struc. 

Bei er ZACY, 29: 1 

Cyclo 1870 

Base only, not structral support 

1.63' dia S.S., 24"lonj, w/ keyways 

1.75' dir S.i., 12' long, one keyway 

Roller bearing, split housing 
TABLE 6-1V-1 SETTLING POND HARVEST OPTION 

1st Staqe Pumps and Piping Costs 

For one harvesting station serving 8 growth ponds (64 hectares). 

Includes 2 settling ponds, one pump station + piping. 

Does not include secondary thickening (see A-fV-2). 

PIPE: A11 pipe is "fQO ft. head" PVC, includes installation 

Pond drain lines 

22" dia X 2300 ft @ $20/ft $46,000 

Effluent return lines 

22" dia X 1100 ft 4 $ZO/ft = 22,000 

Settling pond supernatant drain system 

16" dia X 200 ft @ 512/ft = 2,400 

-- 

VALVES: All valves are low head type with epoxy coated cast iron 

bodies, stainless steel structurals, installed 

Pond Drain (2 per pond) 

16 X 22' canal gate @ 91200 = 19,200 

Effluent Return 

8 X 22" canal gate @ 51200 9,600 

4 X 18" adapt-to-line gates @ 51500 = 6,000 

Check valves at pumps 3 @ $600 = 1,800 

Air release valves 10 @ $250 = 2,500 

PUMPS: Primary supernatant, includes 

motor, starter and installation 

3 X 12" vertical mixed flow pumps I $9,000 = 27,000 

SUMP, with pump support 7,000 

FITTINGS and MISC. 

TOTAL COST/HARVESTINO STATION 

TOTAL COST/HECTARE 
TABLE A-IV-2. SETTLING POND HARVESTING OPTION 

Secondary Thickening Cost Breakdown 

EXCAVATION: 1200 yd3 I $3.00/yd3 

CONCRETE (or gunnite) TANK 

Structural 36 yd3 $300/yd3 

Slab bottom 38 yd3 @ $100/yd3 

CONCRETE ALLEY in SETTLING POND 

PIPING & VALVES (installed) 

Settling pond concentrate lines 

22" dia. X 00 ft $18/ft 

Concentrate valve at sump (2) 

Flush system piping 

18' dia X 1200' @ $14/ft 

Flush system valves 

32 X 15" mud valves with h.ydraulic actuators 

Thickener influent/effluent piping 

Supernatant decanter and return piping 

Concentrate piping to central processing 

6" dia X 1000' (ave) @ $4.00/ft 

Flush diverter valves 

PUflPS (installed on slab) . 

2O supernatant, 2 centrifugals, 500 gpa each 

Z0 concentrate, 2 solids handling, 300 gpn each 

lo concentrate, 2 screw pumps, 1500'gpa each 

FLUSH SYSTEII CONTROLS 

Sequencer and solenoids, hydraulic lines 

HISC. 

TOTAL COST/HARVEST STATION 
MPENDIX V 

CS COVERED LAGOON BIOGAS SYSTEM 

FOR ALGAE PROCESSING WASTES 

Jeff Chandler 

Jeff Chandler + Associates 

1114 21st Street 

Sacramento, California 

(916) 456-0126 

The covered lagoon biogas system approach has been Cound wel lsuited for a variety of liquid wastes. For over 13 years laqoone 

have been covered far ador control or potable water protection. 

Biaqas produced by these first facilities was often viewed as a 

process byproduct requiring flaring. However in April o+ 1982, 

the first covered lagoon system designed specifically far 

biogas collection and utilization was placed into operation at a 

hog farm in Cal if ornia (Chandler et a1 . 1983)- For the past 

three years this system has demonstrated itself as being 

efficient, law cost and easy ta maintain system. Recently a 

similar system has been applied to distillery wastes. Thus the 

covered lagoan approach appears amendable to a large variety of 

agr-i cc11 tural and industri a1 l i quid wastes. 

Covered lagoons are typicaLly large unheated basins using 

floating rubber-like membrane covers. They have been iound to be 

very efficient at converting wastes to biogas at temperatures as 

low as 36:) degrees fahuenheit. Covered lagoons are sttitable for 

ambient temperature waste streams in mild climate regions at the 

U.S.. Since algae production facilities must also be located in 

warm regions, it appears that converting algae processing wastes 

to biogas using the covered lagoon approach holds promise. 

In this repart a covered lagoon biogas system for processing 

~a~astes from a 1000 acre algae production facility is examined. 

'l"t-\i s dcsi. qn uses the mast current in-fcrmation and e:-:peri ence 

trom other waste streams. This is a preliminary analysis and 

fctrther worl:: 1s necessary to verify the feasibility of the 

proposed desi gn. 

DESIGN PARAMETERS 

The proposed 1OOO acre facility is expected to produce 24,Y90 

tons-of processing waste volatile solids (VS) annually. The 

waste stream as-produced is 13 to 20 percent total sol ids ITS! of 

which 83 percent are VS. It has been assumed that 5,124 tons of 

VS are produced each month during a 6 month summer per-iod (1.5 

times! annual monthly averaqe) and 1,041 tans of VS are produced 
load during the summer months while ?nly une unit will be 

@per-ational during the wint.er. Each unit will be equipped with a 

act.towla.tic trackins device which wi 11 match gen-set ocltput to 

bioqas availability. These units are intended to be operated 

under lean burn conditions iair;fuel = -iO/l) inorder that air 

emission standards can be rnet without catalytic converters. Each 

unit will have its own heat rejection system. Both gen-set and 

heat rejection system will be trailer mounted by the system 

designer and delivered to the site as a turnkey system. All 

three gen-sets will feed power- to a single substation. 

DESIGN COS'T' 

Table 5 pr-esents the estimated installed cost of the covered 

lagoon system. The preparation and storage basin intended to 

have near-vertical gunite walls inorder to minimize the use of 

poured-i n-pl ace concrete. The covered 1 agoons rvere assumed not 

to need a bottom liner. Standard 45 mil 5 ply Hvpalon is 

specified for th~ fl.oatinq c@vers. 'The total installed cost for 

the co.k,cred 1 agoon system i ncl udi nq 15 percent- contingency and 2(.! 

percent enqineeirinq .fee is .614,C!OC!. 

Table b shows. tt-te turnl::e\,?' =.yst~.rn costs for the Z; MW gen-set 

system. 'lhese costs were quoted by a colnmercial system 

+&br.icat.or. wi tt.) previous e:.:perience packaging megawatt-size qenset: systems. 'f'he total t.urnl::ey cost i~. $8,20r:),<i)00',, 

DESlGN ECONOMICS 

Fable 7 presents a economic surlimary for the 3 MW covered lagoon 

bioqas e,ystem. The total capital cc~st has been estimated at 

.f3,814,(3OC!. Gross e1ect.r-icitv revenue has been estimated to 

exceed 81,00i?,(:)00 annuallv. Net electricity revenue is e:.:pected 

tln c:.:ceed $745,0i:)C) and rrst..!l t in less than a 5 year pavbacl::. 

It should be again noted that the system described was sired to 

accornodate t:.he ma:.: j. ml-tm' sunirner processi nq waste production 1 eve1 . This to sotne de~r-ee has ad\:,erselv a.ff@ct.ed system economics 

Gei:a~.tse of the drastic se3.cc1nal vari atlori in proces~inq wac.te 

prc:lcl~-rctian. Fr~r example., the '3 MW system hag a very low 

inc5tal led cost. ot :f 1 ,2?ii.il::!r.j. lt rA$a.ate prodc!ction could of been 

ma]. ntiai ned at scrmtrrer cortdi t i on 1 e.*el s year- r-crund, the svstem 

wn!-rlcl p~scibly pay tor itc~lt 1.n less than 3 %,!ears. 

l'hic simple analysic accni~nts oniy for t.he electricitv derived 

revent..!c pr-c~dr.~.ced by the cystem. i)b..v:iously the e,\;r;tem 

accompl i shes some wastc tr-eatment and di sposal benef i t . It was 

?.scucr~cd that tt-tc tnarl:et ,./ali.te of soli d5 removed trom the lagoon= 

a.nd dried only equal their- handling costs. Furthermore no credit 

t~ac bc~ri +:alien tor- the geri-set. t- ecovcrabl e wa5t.e heat. 'Thus the 

' deccri bed Co\cered laqoon bioqac svst.em cov.ld bc beneficial in 

sever-al ways to t.1.1~ li)(X) acre al.sae productiori f aci 1 i tv. 
each month dt.{ring the 6 month winter period 0'').9 times annual 

monthly averagei. This results in a three-fold seasonal 

variation in waste stream production. It was assumed .for this 

design that conv;rsion and treatment of a1 1 of the processing 

wastes year round is desirable thus lagoons and engine generators 

(qen-sets) were sired to accomadate summer production l eve1 s. 

Table 1 .presents important design parameters for sizing the 

covered lagoons. It has been assumed that the processing waste 

stream will require dilution to 7 percent TS primarily due to 

it's high salt content, A t~iqh loading rate 0.f 70 ltts/l00(:) cu ft 

- day was assumed. This loading rate has been employed with 

distillery wastes with low pH (4 or below). This is considered 

satisfactory given the long resultins hvdraulic retention time 

(HWT'? of 50 days and the near nuetral pH oS thr waste stream. In 

total , over 23 mi l l ion gal 1013s of covrred 1 agoon vol umr i s 

required. 

Table 2 presents the estimated methane and biogas yield from 

algae prac~ssing wastes., It has been assumed that algae 

processing will produce a readi lv degradable waste stream. k 

volztti le sol ids destruction ef.+iciency of 65 percent has been 

as~umed. The high methane and bioqas yields shown are assumed to 

be achievable year round. Any reduction in biogas prcsdcrction due 

to decreased winter lagoan temperatures should mare than be 

compensated by very long winter HRT's of over 150 days. 

'Table 3 shows the estimated summer and winter average daily - 

biaqas and electricity production. Over 1.6 milli-on standard 

ct~bic feet (SCF) of biogas will be produced during summer month.; 

whila only r:).5 million SCF is wpected durinq winter months. 

Summer- and winter electricity production capacities are 297-(3 and 

990 IzW respectivcl y. 

Table 4 presents a annual energy production summary +or the 

covered lagoon systcm. almost 373 million SCF of biagas 

equivalent to 2.2 million therms of natural gas will be praduc~d 

anncrally. A total o.f 15.9 million kwh is expected to be prodttce. 

t3ecoverable waste heat f rorn the qen-sets can ranqe f.ran~ brJ,5(:)t:) to 

103 , 1 r:)O mrrrtiT!J annual l y . 

Ficjcrr~! 1 present.; a bloci:: diaqram of the 3 MW rapacity covered 

lagoon biogas system. 'The systern c=anr=,ists of a I lC),!:)OC) gal Ion 

waste preparation and storage basin where the as-recieved 

processing waste is diluted to 7 percent TS. The diluted waste 

is then pumped to thr-ee B million gallon capacity lagaans 

operated in parallel. Each lagoon has appro,:imatel.y 50,00C) sq tb 

of. :Liquid scrrface area. Liquid lagoon effluent is to be r-etcrrned 

ta the alqae production ponds as a nutrient suppiement while 

solids will periodically be pumped from the bot.tom of each lagoon 

arrd under-ga further 1 i quid sol ids separation in sand dryi ng beds. 

Assuminq less than 12 percent of inflow TS will reach the bottom 

and using a standard loading rate uf 22 lb/sq f.t-yr (U.S.E.P.A., 

1974?, 8 acres uf sand drying beds have been specified. 

The biogas produced will be r-emovsd from the lagoons by suction 

blo~.~-r and ~"tsed to dir-ectly tc.trl 3 - 1 MW turbocharged gen-set.;. 

It. is anticipated t.hat all three units will be operated near- full 
TABLE 1 

COVERED LAGOON SYSTEM DESIGN F'AHAMETERS 

BASED ON SUMMER PRODUCTION LEVELS 

Daily TS Production: 

Daily US Production: 

Influent TS Content: 

Daily Flow: 

Loading Hate: 

Total Lagoon Volume Required: 

Hydraulic Retention Time: 

251,000 lb 

2t:)a,250 ib 

7% 

432,000 gal 

70 lb vs/l(:)t:)i) cu ft-day 

C.T ~.-,.9 million gal 

52 days 

TABLE 2 

ALGAE PORCESSING WAS'TE METHANE ANE BIOGAS YIELD 

VS Destruction: 

COD/VS (1) : 

Methane Content (1) : 

Metilane Yield: 

Eiogas Yield: 

652 

1.25 

60% 

4.83 SCF'ilb VS added 

8.04 SLFfl b VS added 

1. Adapted from: Jewel1 and Schraa. 1981 
SCIMMEF;: CANU Ill I N'I Eb: 4AVF:AGE. DA I LY E( I OGAS 

ANij ELEC'TF: I C I 'I"''/ PHODUC'T I ON 

Winter 

------ 

--. E1ec. Prod. (C::Llh.!'ht-3 (1:': ../ f. , 2 5 (1) A T -7 .-v , ;j z, [I) 

Ave. Capacity (P:W./'hr): 97!:1 Q g (:! 

1: 23.5 SCF/kWh average conversion efficiency assurncd 

1: 334 da-;+~s/yr production 

L: "F'at-a1 Ull! t;'rodtrct.ior-I .7 .:, : $.+s, 5 5 .l+<:,ic-l(l~ 7 t.1 1.:: b.1t.j 

dl, : f2~. ci t.l.iTit3 5 bkf\;:Q? l.j f'!..) ,I' I:: bll-\ 
'TABLE 5 

EST' IMA'1 ED COVERED LAGOON SYSTEM INSTALLED COST 

I. Preparation S( Storage Pit 

I. 11(:),0(:)(:! qal Gunite Basin (3 $(:).3'.;5iqal: 38 , 5(:!0 

-. Pump System: 17 , ~QI.! 

3. Plumbing 8< Controls: 2 5 , (1) (1) i:) 

4. Misc. 1 2 , c:! i:) I:! 

------- 

Scl.btota1 : =i 3 , I:) C) 

5. Contingency i 15%) : 

'Total Fi: 

11. Covered Lagoons 

1. 3 - =- ,..l!-),<-)c;ri:! sq +t covers @ $2.35/c,q 

2. E;.:ca.,-~at ion 85,875 yds @ $2. 25jyd: 

3. Compaction 21,s(;)(:! yds @ $3.(;)(:)/yd: 

4. Lagoon Solids Plumbing: 

5. Solids Drying 8 ac @ 621,750iac: 

6. Gas 'rake-of f s and Seals: 

7. Gas Handling ZC, Scrcrbbinq: 

8. Misc.: 

4. Contingency (15%! : 

Total tc: 

'Total C?r+B: 

111. E17~gi1-1eerinq <2<:!X!: 

I'otal Inst-all ed i.oct :: 

st: 7 c -',a c - - .-t d- , .J (-) t-) 

193 2(:,rI) 

6 3 , 9 (I! r:) 77 

-8 .L , 4(:)!:) 

174 , Oi!i:! 

2 1 , [:!t:!!:l 

1 5 (3 , (I! (I! 1;) 

9{:! , t::!<:it:j 

--------- 

1 , <I! :? 7 , i.) !I I:! 
13 Mbtl GEN-SE'I' TCfRNk::EY SYSTEM CDS'T'S 

3 -- 1 MW Turbocharqed Gen-sets 

trai lcr-mounted: 

3 - Heat Rejection Systems: 225 , 1:33!:) 

i - Substation: 175, tjol:,, 

1 - Utilitv Wetering Package: 

'l otal : 

1 : C'jssumec Lamb i r'tcd I-.roduct i on P,: L'apac i t y Ca 3.C'- (:~65/' k14t-1 

2: C3 & P( Estimated @ $t).c)18.iC:Wh 

2: i4scurncc I@,!:.'. Il'L tat::cri and subtracted from installed cost 

2. C:hand:L~~~- d. i',. ? 5. 3. Her-me=, I.::. D. Smith "A Low Cost 75i::N 

t?o\ietr-ed Lagoon Hi ogas System" Faper presented at ENEF:G"< FROPI 

fillZlMfiSS AtJ1.j WhS-IES '911, La!::@ Buana '$istea, F.lor.ida Jan~tary ,?f 148:: 

2. 1 i . : Schraa "Microalqac Separation, Ccsr~centra.tiori, 

(2nd Convpr-(==,iar.l 1~t :I=uel Mitt1 Ari Cinacrubic E:.:parrded Bed F;:eactclr" 

[JSpaE Final fieport #,~i3-9-l2--b:.-l-.3 Jul yi; 14131 
Table AVI-la Capital Cost Summary - Base Case 

Basis: 112 mt algae/ho/yr 

1000 acres 

TOTAL $ $/HECTARE 

GROWTH PONDS ------- --------- 

Earthworks* $4,102,083 $21,365 

Walls & Structural 3,360,763 17,504 

Nixing System 1,991,083 10,370 

Carbonation System 740,667 3,858 

Instrumentation not included elsewhere 202,368 1,054 

HARVESTING - Settling Pond Option 

Primary** 3,027,088 15,766 

Secondary (centrifugation) 1,602,080 8,344 

SYSTEM-WIDE COSTS 

Water Supply 

Water Distribution 

C02 Distribution 

Nutrient Supply System 

Blondonn Disposar System* 

Buildings (harv. bldr. not included) 

Roads b drainage* 

Electrical Distribution (3% of above) 

Electrical Supply 

Machinery 

ENGINEERING (10% of above)* 1,896,475 9,877 

CONTINGENCY ( 15X of above) * 3,129,104 16,298 

LAND COSTS ($1250/hectareI* 

TOTAL CAPITAL COST 

DEPRECIABLE PORTION $13,939,587 $72,602 

NON DEPRECIABLE PORTION $11,062,662 $57,618 

Notesr 

* non-depreciable item ** partially non-depr, ($373,000) 

112 rt/ha/yr = 30 g/m2/day 

Land area = 2 x growth pond area 
Table AVI-lb Operating Costs - Base Case 

Basi s: 112.3 mt algae/ha/yr 

(30 gm/sq m/day) 

UNIT YEARLY COST, Thousands 

COST 

kg/kg 

NUTRIENTS (1) ----- 

4202 2.2 

N, as NH3 0.053 

P, as Superphosphate 0.005 

Fe, as FeSO4 0,005 

Total 

FLOCCULCINT 

POWER 

Mixing 

1 Harvesting 

2 Harvesting 

Water Suppl y 

Nutrient Supply 

Bui 1 dings 

SALT DISPOSfiL 

MAINTANENCE (matlrs) 

TOTAL 

(1) kg/kg = kg required / kg algae produced 
Table AVI-2a Capital Cost Summary - Base Case + Nutrient Recycle 

Basis: 112 mt algae/ha/yr 

1000 acres 

TOTAL S 

GROWTH PONDS ------- 

Earthworks (1) $4,102,083 

Walls k Structural 3,360,763 

Mixing System 1,991,083 

Carbonation System 740,667 

Instrumentation not included elsewhere 202,368 

HARVESTING - Settling Pond Option 

Primary (2) 3,027,088 

Secondary (centrifugation) 1,602 , 080 

ANAEROBIC LAGOON SYSTEM 

Depreciable Capital 

Non-depreciable Capital 

SYSTEM-WIDE COSTS 

Water Supply 

Water Distribution 

C02 Distribution 

Nutrient Supply System 

Blowdown Disposal System (1) 

Buildings (harv. blds, not included) 

Roads b drainage (1) 

Electrical Distribution (3% of above) 

Electrical Supply 

Machinery 

ENGINEERING (10% of above) (1) 2,016,985 

CONTINGENCY (15% of above) (1) 3,328,023 

LAND COSTS ($12!50/hectare) (1) 1,011,840 

ELECTRICAL GENERATOR (3) 

TOTAL CAPITAL COST 

DEPRECIABLE PORTION 

NON DEPRECIABLE PORTION $11,427,334 $39,517 

('1) non-depreciable i tern 

(2) patrially non-depr, ($373,000) 

(3) firs bid for turnkey eystea - enqr. & contingency not required 

112 mt/ha/yr = 30 g/mZ/day 

Land area = 2 x growth pond area 

Table AVI-3a Capital Cost Summary - 0.5 x Prod. + Recycle 

Basis: 56.2 mt algae/ha/yr 

1000 acres 

TOTAL $ $/HECTARE 

GROWTH PONDS ------- --------- 

Earthworks (1) $4,102,003 $21,365 

Walls & Structural 3,360,763 17,504 

Mixing System 1,991,083 10,370 

Carbonation System 457,073 2,381 

Instrumentation not included elsewhere 202,360 1,054 

HARVESTINO - Settling Pond Option 

Primary (2) 3,027,008 15,766 

Secondary (centrifugation) 988,660 5,149 

ANAEROBIC LAGOON SYSTEM 

Depreciable Capital 

Non-depreciable Capital 

SYSTEM-WIDE COSTS 

Water Supply 1,391,200 

Water Distribution 398,412 

CO2 Distribution 65,043 

Nutrient Supply System 316,200 

Blowdown Disposal System (1) 337,200 

Buildings (harv, blds, not included) 23 1,880 

Roads & drainage (1) 210,000 

Electrical Distribution (3% of above) 529,950 

Electrical Supply 230,204 

Machinery 168,640 

ENGINEERING (10% of above) (1) 1,860,101 9,680 

CONTINGENCY (15% of above) (1) 3,069,299 15,986 

LAND COSTS ($1250/hectare) (1 1,011,040 5,270 

ELECTRICAL GENERATOR (3) 

TOTAL CAPITAL COST 

DEPRECIABLE PORTION $14,566,771 $75,869 

NON DEPRECIABLE PORTION $10,820,503 $56,357 

(1) non-depreciable item 

(2) patrially non-depr. ($375,000) 

(3) firm bid for turnkey system - engr, & contingency not required 

112 mtlhalyr = 30 g/m2/day 

Land area = 2 x growth pond area 
Table AVI-3b Operating Costs - .SxProd. + Recycle 

Basis: 

UNIT YEARLY COST, Thousands 

COST 

1000 ac 

$/mt $/ha/yr 8/yr 

QUAN 

REQ' D 

kg / kg 

NUTRIENTS (1) ----- 

C02 1.6 

N, as NH3 0.013 

P, as Superphosphate 0,0025 

Fe, as FeSO4 0.005 

Total 

POWER 

Mixing 

1 Harvesting 

2 Harvesting 

Water Supply 

Nutrient Supply 

Bui 1 dings 

Total 

Elect. Produced 

SALT DISPOSAL 

MAINTANENCE (matl's) 

LABOR 

TOTAL 

(1) kg/kg = kg required / kg algae produced 

199 
Table AVI-4a Capital Cost Summary - 0.67 x Prod. + Recycle 

Basi s: 75 mt algae/ha/yr 

1000 acres 

TOTAL $ $/HECTARE 

GROWTH PONDS ------- --------- 

Earthworks (1) $4,102,083 $21,365 

Walls & Structural 3,360,763 17,504 

Mixing System 1,991,083 10,370 

Carbonation System 560,646 2,920 

Instrumentation not included al~ewhere 202,368 1,054 

HARVESTING - Settling Pond Option 

Primary (2) 3,027,088 15,766 

Secondary (centrifugation) 1,212,690 6,316 

ANAEROBIC LAGOON SYSTEM 

Depreciable Capital 527,558 2,748 

Non-depreciable Capital 256,342 1,335 

SYSTEH-WIDE COSTS 

Water Supply 1,391,280 

Water Distribution 398,412 

C02 Distribution 79,782 

Nutrient Supply System 316,200 

Blondown Di spoeal System (1 337,280 

Buildings (harv. blds, not included) 231,880 

Roads & drainage (1) 210,800 

Electrical Distribution (3% of above) 546,188 

Electrical Supply 238,204 

Machinery 168,640 

ENGINEERING (10% of above) (1) 1,915,929 9,979 

CONTINGENCY (15% of above) (1) 3,161,283 16,465 

LAND COSTS ($125O/hectare) (1) 1,011,040 5,270 

ELECTRICAL GENERATOR (3) 

TOTAL CAPITAL COST 

DEPRECIABLE PORTION $15,293,753 $79,655 

NON DEPRECIABLE PORTION $11,033,277 $57,465 

(1) non-depreciable item 

(2) patrially non-depr, ($375,000) 

(3) firm bid for turnkey system - engr. & contingency not required 

112 mt/ha/yr 30 g/m2/day 

Land area = 2 x growth pond area 
Table AVI-4b Operating Casts - .&7xProd. + Recycle 

Basi s: 75 rnt algae/ha/yr 

(20 gm/sq m/day) 

kg/kg 

NUTRIENTS ( 1 > ----- 

C02 1.6 

N, as NH3 0.013 

P, as Superphosphate 0.0025 

Fe, as FeS04 0.005 

Total 

UNIT 

COST 

YEARLY COST, Thausands 

FLOCCULANT 0,002 5000 $0.75 303 

POWER 

Mixing 

1 Harvesting 

2 Harvesting 

Water Supply 

Nutrient Supply 

Bui 1 dings 

Total 

Elect. Produced 

SALT DISPOSAL 

MAINTANENCE (matl's) 

LABOR 

TOTAL 

(1) kg/kg = kg required / kg algae produced 

201 
Table AVI-5a Capital Cost Summary - 1.5 x Prod. + Recycle 

Basis: 168 mt algae/ha/yr 

1000 acres 

TOTAL $/HECTARE 

GROWTH PONDS ------- --------- 

Earthworks (1) $4,102,083 $21,365 

Walls 81 Structural 3,360,763 17,504 

Hi xi ng System 1,991,083 10,370 

Carbonation System 985,590 5,133 

Instrumentation not included elsewhere 202,360 1,054 

HARVESTING - Settling Pond Option 

Primary (2) 3,027,088 15,766 

Secondary (centrifugation) 2,131,873 11,104 

ANAEROBIC LAGOON SYSTEM 

Depreciable Capital 

Non-depreciable Capital 

SYSTEM-#IDE COSTS 

Water Supply 

Water Distribution 

C02 Distribution 

Nutrient Supply System 

Bl owdown Disposal System ( 1) 

Buildings (harv. blds. not included) 

Roads & drainage (1) 

Electrical Distribution (3% of above) 

Electrical Supply 

Machinery 

ENGINEERING 110% of above) (1) 2,160,627 11,253 

CONTINGENCY (15% of above) (1) 3,565,034 18,560 

LAND COSTS ($1250/hectare) (1) 1,011,040 5,270 

ELECTRICAL GENERATOR (3) 

TOTAL CAPITAL COST 

DEPRECIABLE PORTION $19,644,484 $102,315 

NON DEPRECIABLE PORTION $11,999,204 $b2,496 

(1) ,non-depreciable item 

(-2) patrially non-depr. ($375,000) 

(3) firm bid for turnkey system - enpr. & contingency not required 

112 mt/ha/yr 1 30 g/m2/day 

Land area = 2 x growth pond area 
Table AVI-Sb Operating Casts - 1.SxProd. + Recycle 

Basis: 168.4 mt a1 gae/ha/yr 

(45 gm/sq m/day) 

UNIT 

COST 

YEARLY COST, Thousands 

kg/kg 

NUTRIENTS (1) ----- 

C02 1.b 

N, as NH3 0.013 

P, as Superphosphate 0.0025 

Fe, as FeS04 0.005 

Total 

FLOCCULANT 0. Qb2 5000 $1.68 680 

POWER 

Mixing 

i Harvesting 

2 Harvesting 

Water Supply 

Nutrient Supply 

Bui 1 dings 

Total 

Elect, Produced 

SALT DISPOSAL 

MAINTANENCE (matl's) 

LABOR 

(1) kg/kg = kg required / kg algae produced 
Table AVI-6a Capital Cost Summary - 2.0 x Prod. + Recycle 

Basis: 225 at algae/ha/yr 

1000 acres 

TOTAL $ $/HECTARE 

GROWTH PONDS ------- --------- 

Earthworks (1) $4,102,083 $21,365 

Walls & Structural 3,360,763 17,904 

Mixing System 1,991,083 10,370 

Carbonation System 1,205,472 6,279 

Instrumentation not included elsewhere 202,368 1,054 

HARVESTING - Settling Pond Option 

Primary (2) 3,027,088 15,766 

Sacondary (centrifugation) 2,607,465 13,581 

ANAEROBIC LAGOON SYSTEM 

Depreciable Capital 

Non-depreciable Capital 

SYSTEM-WIDE COSTS 

Water Supply 

Water Distribution 

C02 Distribution 

Nutrient Supply System 

Bl owdown Disposal System ( 1) 

Buildings (harv. blds. not included) 

Roads & drainage (1) 

Electrical Distribution (3% of above) 

Electrical Supply 

Machinery 

ENGINEERING (10% of above) (1) 2 , 295 , 737 11,957 

CONTINGENCY (19% of above) (1) 3,787,967 19,729 

LAND COSTS ($1250/hectare) (1) 1,011,840 5,270 

ELECTRICAL BENERATOR (3) 

TOTAL CAPITAL COST 

DEPRECIABLE PORTION $21,904,291 $114,085 

NON DEPRECIABLE PORTION $12,548,620 $65,357 

(1) non-depreciable item 

(2) pattially non-depr, ($375,000) 

(3) firm bid for turnkey system - engr. & contingency not required 

112 mtlhalyr = 30 g/m2/day 

Land area 2 x growth pond area 
Table AVI-6b Operating Costs - 2xProd. + Recycle 

Basi s: 224.6 mt a1 gae/ha/yr 

(60 gm/sq m/day) 

WAN 

REQ' D 

UNIT 

COST 

YEARLY COST, Thousands 

kg/kg 

NUTRIENTS ( 1 ) ----- 

COZ 1.6 

N, as NH3 0.013 

P, as Superphosphate 0.0025 

Fe, as FeS04 0,005 

Total 

FLOCCULANT 0.002 SO00 $2.25 907 

POWER 

Mixing 

1 Harvesting 

2 Harvesting 

Water Suppl y 

Nutrient Supply 

Bui 1 dings 

Total 

Elect. Produced 

SALT DISPOSAL 

MAINTANENCE (matl's) 

LABOR 

(1) kg/kg = kg required / kg algae produced 

205 
Table AVI-7a Capital Cost Summary - Free C02 + Recycle 

Basis; 112 st algae/ha/yr 

1000 acres 

TOTAL $ 

GROWTH PONDS ------- 

Earthworks (1) $4,102,083 

Walls & Structural 3,360,763 

Mixing System 1,991,083 

Carbonation System 742,055 

Instrumentation not included elsewhere 202 , 368 

HARVESTING - Settling Pond Option 

Primary (2) 3,027,088 

Secondary (centrifugation) 1,605,083 

ANAEROBIC LAGOON SYSTEM 

Depreciable Capital 

Non-depreciable Capital 

SYSTEH-WIDE COSTS 

Water Supply 1,391,280 

Water Distribution 398,412 

C02 Distribution 105,598 

Nutrient Supply System 316,200 

Bl owdown Disposal System ( 1) 337,280 

Buildings (harv, blds. not included) 231,880 

Roads & drainage (1) 210,800 

Electrical Distribution (3% of above) 575,759 

Electrical Supply 238,204 

Machinery 168,640 

ENGINEERING (10% of above) (1) 2,017,458 

CONTINGENCY (15% of above) (1) 3,328,805 

LAND COSTS ($1250/hectare) (1) 1,011,840 

ELECTRICAL GENERATOR (3) 

TOTAL CAPITAL COST $28,732,600 $149,649 

DEPRECIABLE PORTION $17,304,093 $90,125 

NON DEPRECIABLE PORTION $11,428,586 $59,524 

Cl) non-depreciable iter 

(2) patrially non-depr. ($375,000) 

(3) firm bid for turnkey system - enqr. b contingency not required 

112 nt/ha/yr = 30 glm2lday 

Land area = 2 x growth pond area 
Table AVI-7C Operating Costs - Free C02 + Recycle 

Basis: 112.5 mt algae/ha/yr 

(30 grn/sq m/day) 

QUAN UNIT YEARLY COST, Thousands 

REQ' D COST 

lOOCI at 

kg/kg $/mt $/ha/yr $/yr 

NUTRIENTS ( 1 ) dm--- ---- ------- ------- 

COT! 1.6 0 $0.00 $0 

N, as NH3 0.013 250 0.37 151 

P, as Superphosphate 0.0025 900 0.25 102 

Fe, as FeS04 0.005 500 0.28 113 

------ --------- 

Total $0.91 $366 

FLOCCULANT 

POWER 

Mixing 

1 Harvesting 

2 Harvesting 

Water Supply 

Nutrient Supply 

Bui 1 dings 

Total 

Elect. Produced 

SALT DISPOSAL 

MAINTANENCE (matl's) 

LABOR 

TOTAL 

c/ kwh em--- 

6.5 

6.5 

6.5 

6.5 

tr. 5 

6.5 

(1) kg/kq = kg required / kg algae produced 
Table AVI+b Operating Costs - $70/mt C02 + Recycle 

Basis: 112.3 mt a1 gae/ha/yr 

(30 gm/sq m/day) 

WAN 

REQ'D - 

kg/kg 

NUTRIENTS ( 1 ----- 

C02 1.6 

N, as NH3 0.013 

P, as Superphosphate 0.0025 

Fe, as FeS04 0.005 

Total 

UNIT YEARLY COST, Thousands 

COST 

1000 ac 

$/mt $/ha/yr $/yr 

---- ------- ------- 

70 $12.58 65,08 1 

250 0.37 15 1 

900 0.25 102 

500 0.28 113 

------ --------- 

$13.48 65,448 

FLOCCULCINT 0.002 5000 $1.12 454 

10 kwh/yr 

POWER --------- 

Mixing 4.34 

1 Harvesting 0.72 

2 Harvesting 2.31 

Water Supply 3.53 

Nutrient Supply 0.22 

Bui 1 dings 0.42 

----- 

Total 11.55 

El ec t . Produced -15.87 6.5 

----- 

-4.32 

kg/kg c/kg 

SALT DISPOSAL ----- ---- 

1.5 0.67 

MAINTANENCE (matl's) 

LABOR 

1 OTAL 

(1) kg/kg = kg required / kg algae produced 

208 
Table AVI- 9a Capitai Cost Summary - 20X Lipid Content + Recycle 

Basis: 112 mt algae/ha/yr 

1000 acres 

TOTPlL $ 

GROWTH PONDS __-I__- 

Earthworks (1) $4,1029083 

Walls & Structural 3,360,763 

Hi x i ng System 1,991,083 

Carbonation System 742,055 

Instrumentation not included elsewhere 202,360 

HARVESTING - Settling Pond Option 

Primary (2) 3,027,088 

Secondary (centrifugation) 1,605,083 

4NAEROBIC LAGOON SYSTEM 

Depreciable Capital 

Nan-depreciable Capital 

SYSTEM-WIDE COSTS 

Water Supply 

Water Distribution 

C02 Distribution 

Nutrient Supply System 

01 andown Di spusal System (1 

Buildings (harv, blds. not included) 

Roads & drainage (1) 

Electrical Distribution (3X of above) 

Electrical Supply 

Machinery 

ENGINEERING (10X o+ above) (1) 2,089,764 

CONTINGENCY 115% of above) (1) 3,448,110 

LAND COSTS ($1250/hectare) (11 1,011,840 

ELECTRICAL GENERhTOR (3) 

TOTAL CAPITAL COST - 

DEPRECIABLE PORTION 519,117,593 

NON DEPRECIABLE PORTION $11,049,757 

(.I) non-depreciable item 

(2) patrially non-depr. ($375,000) 

13) firm bid for turnkey rystea - engr. & contingency n0.t required 

112 mt/ha/yr 3 30 g/m2/day 

Land area 1 2 x grawth pond area 
Table AVI-9b Operating Costs - 20X Lipid Content + Recycle 

Basis: 

QU AN 

REQ' D 

NUTR IENTS ( 1 1 ----- 

C02 0.9 

N, as NH3 0.013 

P, as Superphosphate 0.0025 

Fe, as FeS04 0.005 

UNIT YEARLY COST, 

COST 

Total 

Thousands 

FLOCCULANT 0.002 5000 $1.12 454 

POWER 

Mixing 

1 Harvesting 

2 Harvesting 

Water Supply 

Nutrient Supply 

Bui 1 dings 

Total 

Elect. Produced 

SALT DISPOSAL 

MAINTANENCE (matl's) 

LABOR 

TOTAL 

(1) kg/kg = kg required / kg algae produced 

210 
Table IVI-101 Capital Cost Summary - 30% Lipid Content + Recycle 

Basi s: 112 wt algae/ha/yr 

1000 acres 

TOTAL $ S/HECTPIRE 

GROWTH PONDS -I.(ll--= -----...--- 

Earthworks (1) $4,102,083 $21,365 

Walls & Structural 3 , 360,763 17,504 

Mixing System 1,991,083 10,370 

Carbonation System 742,055 3,869 

Instrumentation not included elsewhere 202,368 1,054 

HARVESTING - Settling Pond Option 

Primary (2) 3,027,088 15,766 

Secondary (centrifugation) 1,605,083 8,360 

ANAEROBIC LAGOON SYSTEM 

Depreciable Capital 

Non-depreciable Capital 

SYSTEM-WIDE COSTS 

Water Supply 

Water Distribution 

C02 Di str i but i on 

Nutrient Supply System 

01 owdawn Disposal System ( 1) 

Buildings (harv. blds, not included) 

Roads & drainage (1) 

Electrical Distribution (3% of above) 

Electrical Supply 

Machinery 

ENGINEERING (10% of above) (1) 

CONTINGENCY (13% of above) (1) 3,408,342 17,752 

LAND COSTS ($1250/hectare) (1) 1,011,840 5,270 

ELECTRICAL GENERATOR (3) 

TOTAL CAPITAL COST 

DEPRECIABLE PORTION 

NON DEPRECIABLE PORTION $11,709,367 $60,906 

(-1 non-depreciable i tern 

(2) patrially non-depr. ($373,000) 

(3) firm bid for turnkey sygtem - engr. & contingency not required 

112 mt/ha/yr = 30 glm2lday 

Land area = 2 x growth pond area 
Table AVI-lob Operating Costs - 30% Lipid Content + Recycle 

Basis: 112.3 mt algae/ha/yr 

(30 gm/sq m/day) 

QUClN 

REQ' D 

kg/kg 

NUTRIENTS (1) ----- 

C02 1.1 

N, as NH3 0.013 

P, as Superphosphate 0.0025 

Fe, as FeS04 0.005 

Total 

UNIT YEARLY COST, 

COST 

Thousands 

FLOCCULANT 0.002 5000 81.12 454 

POWER 

Mixing 

1 Harvesting 

2 Harvesting 

Water Supply 

Nutrient Supply 

Bui 1 dings 

Total 

~l ect . Produced 

SALT DISPOSAL 

MA INTANENCE (mat 1 ' s 2.32 939 

LABOR 

TOTAL 

(1) kg/kg = kg required / kg algae produced 
Table AVI-lla Capital Cost Summary - 40% Lipid Content + Recycle 

Basis: 112 mt algae/ha/yr 

1000 acres 

TOTAL O 

GROWTH PONDS I--..)--- 

Earthworks (1) $4,102,083 

Walls & Structural 3 , 360 , 763 

Mixing System 1,991,003 

Carbonation System 742,055 

Instrumentation not included elsewhere 202,368 

HARVESTING - Settling Pond Option 

Primary (2) 3,027,088 

Secondary (centrifugation) 1,605,085 

ANAEROBIC LAGOON SYSTEM 

Depreciable Capital 944,800 

Non-depreciable Capital 459,120 

SYSTEM-WIDE COSTS 

Water Supply 

Water Distribution 

C02 Distribution 

Nutrient Supply System 

Bl owdown Disposal System (1 1 

Buildings (harv. blds. not included) 

R~ads & drainage (1) 

Electrical Distribution (3% of above) 

Electrical Supply 

Machinery 

ENGINEERING (10% of above) (1) 2,041,560 

CONTINGENCY (15% of above) (1) 3,368,573 

L4ND COSTS ($1250/hectare) (11 1 101 1,840 

ELECTRICAL GENERATOR (3) 

TOThL CAPITAL COST 

DEPREClbBLE PORTION 

$1 HECTARE --..l--.---- 

NON DEPRECIABLE PORTION $11,560,977 $60,253 

. (1) non-depreciable item 

(2) patrially non-depr. ($375,0001 

13) firm bid for turnkey system - enqr, & contingency. not required 

112 mt/ha/yr = 30 g/m2/day 

Land' area = 2 x growth pond area 
Table AVI-1lb Operating Costs - 40% Lipid Content + Recycle 

Basis: 

kg/kg 

NUTRIENTS ( 1 ----- 

C02 1-35 

N, as NH3 0.013 

P, as Superphosphate 0.0025 

Fe, as FeS04 0.005 

Total 

FLOCCULANT 

POWER 

Mixing 

1 Harvesting 

2 Harvesting 

Water Supply 

Nutrient Supply 

Bui 1 dings 

Total 

El ect . Produced 

SALT DISPOSAL 

MAINTANENCE (mat 1 ' s) 

LABOR 

TOTAL 

UNIT 

COST 

$/mt 

---- 

35 

250 

900 

500 

YEARLY COST, Thousands 

(1) kg/kg = kg required / kg algae produced 

214 
Design and Analysis of Microalgal Open Pond Systems October 1985 

for the Purpose of Producing Fuels 

I 

1 7. Author(s) 1 8. Performing Organization Rept. No. ] 

Document Control 

Page 

Microbial Products, Inc. 

Fairfield, Calif 

1. SERl Reporr No. 2. NTlS Accession No. 

SERI/STR-231-2840 

J. C. Weissman, R. P. Goebel 

9. Perform~ng Organization Name and Address 

4513.10 , I 

11. Contract (C) or Grant (G) No. 

3. Recipient's Accession No. 

4. Title and Subtitle 

10. Project/Task/Work Unit No. 

5. Publica!ion Date 

' Technical Monitor: R. McIntosh 

' 16. Abstract (Limit: 200 words) The designs and systems developed include many innovative concepts and experiments, including the design and operation of a low-cost system. 

12. Sponsorin Crganization Name and Address 

Solar clergy Research Inst~tute 

cost-effectiveness i s real ized by minimizf ng capital costs of the system and 

achieving efficient use of inputs. Extensive engineering analysis of carbonation, 

mixing, and harvesting subsystems has elucidated both the lowest cost, most efficient options and the essential parameters needed to construct, test, and evaluate 

these subsystems. The use of growth ponds sealed with clay and 1 ined with crushed 

rock results in construction cost savings of 50% over ponds lined with synthetic 

membranes. In addition a low-cost but efficient design allows improvments in 

technology to have maximum impact on final product cost reductions. In addition to 

the innovations in low-cost construction, the operational efficiency of the design 

is both higher and more feasible than that attained by any previous system concept 

of comparable scale. The water chemistry analysis has led to operational specifications that minimize water use and virtually eliminate losses of carbon dioxide to 

the atmosphere. The carbon dioxide injection system is designed for 95% efficiency 

but is still low in cost. The construction of a large-scale, covered anaerobic 

lagoon to recycle carbon, nitrogen, and phosphorus has not been attempted at the 

scale analyzed here. Yet efficient recycling is essential for achieving economic 

13. Type of Report 8, Period Covered 

17. Docurent Analysis af f ordabi 1 i ty . a. Descriptors 

Biomass ; Carbon Dioxide ; Cultivation ; Cultivation Techniques ; Ponds ; 

Productivity ; Unicellular Algae 

b. Identifiers/Open-Ended Terms 

c. UC Categories 

61 c 

A Division of Midwest Research Institute Technical Report 

18. Availability Statement 

National Technical Information Service 

U.S. Department of Commerce 

7617 Cole Boulevard 

Go1 den, Col orado 80401 -3393 

19. No. of Pages 

232 

20. Price 

All 

J 

14. 

Form No. 0069 (3-25-82) 

15. Supplementary Notes