October 1989 

Design and Operation 

of an Outdoor 

Microalgae Test 

Facility 

Final Subcontract Report 

J. C. Weissman 

D. M. Tillet 

R. P. Goebel 

Prepared under Subcontract No. XK-7-06113-1 
SERllSTR-232-3569 

UC Category: 2sI 

DE89009493 

Design and Operation of an 

Outdoor Microalgae Test 

Facility 

Final Subcontract Report 

J. C. Weissman 

D. M. Tillett 

R. P. Goebel 

October 1989 

SERl Technical Monitor: W. Bollrneier 

Prepared under Subcontract No. XK-7-06113-1 

Solar Energy Research lnstitute 

A Division of Midwest Research Institute 

161 7 Cole Boulevard 

Golden, Colorado 80401-3393 

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 an agency of the United States government. Neither the United States government nor any 

agency thereof, nor any of their employees, makes any warranty, express 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. 

Reference herein to any specific commercial product, process, or service by trade name. trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors 

expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. 

Printed in the United States of America 

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Price: Microfiche A01 

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Cdes are used for pricing all publications. The code is determined by the number of pages in the publication. Information 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): Govemment Reparts Announcements and Index (GRA and I); Scientific and Technical Abstract Reports {STAR); and publication NTIS-PR-360 available from NTlS 

at the above address. 
PREFACE 

The Solar Fuels Research Division of the Solar Energy Research Institute 

(SERI) mana es the Aquatics Species Program for the U.S. Department of 

Energy (DOE 5 Biofuels and Municipal Waste Technology Division under DOE 

Contract No. XK-7-06 1 13-1. A major emphasis of this program is to develop the technology for mass culture of microalgae in large outdoor ponds for 

conversion of the microalgae to liquid fuels, such as diesel. 

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

completion of Contract No. XK-7-06113-1. 
ACKNOWLEDGMENTS 

This work was supported in part by the New Mexico Research and Development Institute 

with a grant administered through the city of Roswell, N. Mex. We thank Dr. Larry 

Icerman, director of the Institute; John Capps, the Roswell assistant city manager; and 

Charles Sparnon, the Roswell utilities manager, for their efforts. 

The authors would like to acknowledge the contributions of Ronald S. Sturdevant in both 

the fabrication of the experimental systems and their operation. In addition, we thank 

Gary Beatty, Eddy Trujillo, and Ken Irvin for their aid and support. 
SUMMARY 

Objective 

The objective of this project is to establish and operate a facility in the American 

Southwest to test the concept of producing microalgal biomass as a feedstock for the 

production of liquid fuels. The site chosen for this project was an existing water 

research station in the city of Roswell in southeastern New Mexico. The climate and 

water resources are representative of those in the Southwest. Fulfillment of this objective includes testing specific designs, modes of operation, and strains of microalgae; proposing and evaluating modifications to technological concepts; and assessing the progress 

in meeting cost objectives set for the Aquatic Species Program (ASP). 

The objectives during the first year were to evaluate outdoor produc Ion performance of 

prescreened species of microalgae in six small-scale reactors (3 m 5 ) and to begin the 

development of a larger-scale facility. The objectives durin+ the second year were to 

continue evaluating biomass and lipid productivity in the 3-m system, to finish installation of two 0.1-ha raceways, to perform an engineering analysis of the system, and to 

begin long-term production of algal biomass. 

Discussion 

2 In the 3-m ponds, 15 strains of microalgae were tested for productivity potential. Six of 

the strains grew well enough to evaluate. The small ponds were operated for almost 

1 1 months, allowing annual productivity to be estimated. Based on this year's growth, 2 that average is at least 16 g ash free dry weight (AFDM)/m /d of algal biomass. 

Improvement during several critical months, during which insolation is high but tempera- 2 tures are variably cool, could easily bring this average above 20 g AFDM/m /d. To significantly improve productivities above that will require an understanding of why short1 2 term productiv'ties exceed 50 g AFDM/m /d during the summer when averages are only 

30 g AFDM/m Id, and selection of organisms that perform better at temperatures 

between 5" and 10°C. 

The growth response to lowered pCOZ was also studied. When productivity of Cog 2 replete cultures (285 ~rn C02) averaged about 20 g AFDM/m Id, lowering pC02 to 

20 prn at a pH of 8.3 only lowered productivity 15%. That the decrease was small is 

significant, since loss of inorganic carbon (via outgassing) is almost negligible at this C02 

concentration. Through continued study, we will determine whether the reduction is so 

2 modest when productivity is at a higher level (e.g., 35 g AFDM/m Id). 

After the two 0.1-ha raceways were completed, the system was evaluated in terms of 

effectiveness of mixing; energy losses in fluid motion along channels, through bends and 

sumps; efficiency of the paddle wheel as a mixing device; and efficiency of the carbonation sumps in getting C02 absorbed into the water. We found that uneven grading of the 

pond bottoms limited the shallowness of the ponds to more than 15 cm, and probably to 

20 cm. At lower depths, in-pond sedimentation of biomass was a significant problem. In 

general, velocity profiles were as expected: fairly uniform across the channel, decreasing 

quickly within a few centimeters of the pond bottom, and highly nonuniform around 
bends, sumps, and at the paddle wheel intake. The large velocity head created at this 

intake lowered the mixer efficiency at high mixing rates. Mixing power required to 

overcome friction was close to that estimated previously. Adjustments to these 

estimates were, however, required to account for losses in bends and sumps. The smooth, 

plastic-lined channels had a Manning's roughness of 0.0100, while the clay-lined, rockcovered channels had a roughness of 0.01 73. 

The countercurrent operation of the carbonation sumps allowed a C02 injection efficiency of above 80%, even without gas recycle. To achieve the 90+% desired, recycle of 

the gas that escapes above the sump will be required. The overall efficiency for utilization of C02 was 60%. At pH 7.5 to 7.8, 25% of the C02 absorbed in the carbonation 

sumps was lost to the atmosphere by outgassing through the pond surface. Operating at 

pH 8 to 8.3 should reduce this to less than 10%. 

Operation of the two 0.1-ha raceways began in August 1988. Productivities in the lined 2 pond were 80% of those in the 3-m fiberglass ponds while those of the unlined pond were 

only 60%. In-pond sedimentation of biomass appears to have been the major difference 2 

among the three types of ponds, being negligible in the 3-m ponds and worst in the 

unlined pond. Operating at greater depth and placing additional flow deflectors will be 

used to alleviate this problem. C02 outgassing was greater from the unlined pond, due to 

the faster rate of renewal of surface resulting from greater bottom roughness. Power 

consumption was also greater, especially when compared to the effectiveness of the 

mixing in keeping cells suspended. Finally, water loss was somewhat greater, primarily 

due to leaks. These leaks should be correctable, Percolation was minimal, after an initial 

month of operation during which time the pores sealed. 

Conclusions 

Several strains of microalgae have been found to grow well in the outdoor environment of 

southeastern ew Mexico. Productivities in small test ponds were as Pigh as r 50 g AFDM/m /d during the best summer days, and averaged over 16 g AFDM/m /d over 

the entire year. Several strains have b en found that tolerate freezing conditions during 4 the winter. Initial scaleup to 1000 m was initiated. The significant scaleup problem 

encountered involved the effectiveness of the mixing system in keeping cells suspended. 

Strategies to improve the mixing have been developed and will be tested during the next 

subcontract period. Efficiency of the utilization of mixing power, water, and C02 were 

all found to be good, although improvements will still be necessary. 
Page 

1. 0 Introduction ........................................................ H 

1.1 ProjectGoals .......0.......................................~.. I 

1.2 Project Site ................................................... 1 

1.3 GoalsfortheCurrentYear ...................................... 3 

2.0 Completion of Large-Scale System .................................... 5 

2.1 Introduction ................................................... 5 

2.2 Pipelines ...................................................... 5 

2.3 Earthworks .................................................... 5 

2.4 Mixing System ................................................. 7 

2.5 Nutrient System ............................................... 7 

2.6 Dilution System ................................................ 8 

2.7 Carbonationsystem ............................................ 8 

3.0 Large-Scale System Engineering Analysis ............................... 9 

3.1 Introduction ................................................... 9 

3.2 Grading and Pond Depth ......................................... 9 

3.3 Visual Observations of Flow ..................................... 9 

3.4 Velocity Profiles ............................................... 13 

3.5 Head Losses ................................................... 14 

3.6 Roughness Coefficients ......................................... 21 

3.7 Mixing Power .................................................. 22 

3.8 Carbonation ................................................. 24 

4.0 Operation of the Large-Scale System .................................. 31 

5.0 Operation of the Small-Scale System ................................... 34 

5.1 Experimental Plan .............................................. 34 

5.2 Materiais and Methods .......................................... 34 

5.3 Results .................................................... 35 

6.0 Conclusions and Future Work ......................................... 55 

7.0 References ...................................................... 56 

vii 
LIST OF FIGURES 

Page 

Location of Roswell, N. Mex. ......................................... 

Large-scale system pond layout ................... .... ................ 

Depth profiles along channel bottoms for average pond depths 

of 13.7 cm in North (lined) pond and 13.5 cm in South 

(unlined) pond. ...................................................... Depth profiles along channel bottoms for North (lined) pond 

(average depth of 13.7 cm) at five locations across channel ............... Depth profiles along channel bottoms for South (unlined) pond 

(average depth of 13.5 cm) at five locations across channel ............... 

Velocity-depth profiles in North (lined) pond at paddle 

wheel rotation settings of 0.3 (2.7 rpm) and 0.5 (4.4 rpm) ................. 

Velocity-depth profiles in North (lined) pond at paddle wheel 

rotation settings of 0.7 (6.1 rpm) and 0.9 (7.8 rpm) ....................... 

Velocity-depth profiles in South (unlined) pond at paddle wheel 

rotation settings of 0.3 (2.7 rpm) and 0.5 (4.4 rpm) ....................... 

Velocity-depth profiles in South (unlined) pond at paddle wheel 

rotation settings of 0.7 (6.1 rpm) and 0.9 (7.8 rpm) ....................... Profiles of depth-averaged velocity across the return channel 

(1.4-m upstream from sump) in each 0.1-ha raceway ................... .. Mixing power as a function of average water velocity in 

0.1-haraceways ..................................................... Daily total insolation at the Roswell Test Facility, N. Mex. ............... 

Maximum and minimum air temperatures at the Roswell 

Test Facility, N. Mex. ............................................... Maximum and minimum temperatures in unheated ponds .................. 

Productivity of Amphora sp. RTF ...................................... 

Harvested productivity of T. suecica and CyclotelZa sp. RTF .............. 

Harvested productivity of C. rnuelleri CHAET9 and 

C.muelleriCHAET63...... .......................................... Harvested productivity of M. minutum MONOR2. ........................ Productivity of nitrogen-depleted induction batches of 

C. rnuelleri CHAET63.. .............................................. 

viii 
LIST OF FIGURES (Conciuded) 

Page 

5-9 Productivity of nitrogen-depleted induction batches of 

C. muelleri CHAET9. ................................................ 50 

5-10 Productivity of nitrogen-depleted induction batches of 

M.minutum MONOR2 ............................................... 51 

5-1 1 Productivity of nitrogen-depleted induction batches of 

Cyclotella sp. RTF.. ................................................. 52 

5-1 2 Productivity of nitrogen-depleted induction natches of 

T. suecica TETRAI. ................................................. 53 

5-13 Productivity of nitrogen-depleted induction batches of 

Amphorasp.RTF ................................................... 54 
LIST OF TABLES 

Page 

Mineral Composition of Water Resources at RTF 

and40% Seawater .................................................. 

Facility Development Plan .......................................... 

Mixing System Design Criteria ....................................... 

0.1-ha Pond Depths and Deviations ................................... 

Average Depths. Velocities. and Flow Rates 1.4-m Upstream from 

Sumps in 0.1-ha Raceways ........................................... 

Average Velocities in 0.1-ha Raceways ................................ 

Total Head Loss (CM) for Each Section of O.l.ha Raceways .............. 

Manning's Roughness Coefficients for O.l.ha Raceways .................. 

Mixing Power Requirements for O.l.ha Raceways ....................... 

pH. Partial Pressure of C02 (pCOZ). and TIC Relationship for RTF Water26 

Summary of Carbonation Tests in Sump ............................... 

Summary of Carbonation Tests in 600-L Tank .......................... 

Summary of Outgassing Results ...................................... 

Large-scale System Productivity ..................................... 

Average Daily Water Loss from Large-scale Ponds ...................... 

Carbon Utilization Efficiency in Lined Pond ........................... 2 Monthly Productivity Results from 3-rn Algal Cultures ................. 2 Productivity of Algal Strains Cultivated in 3 rn ..................... .. 2 Effects of Heating on Algal Productivity in 3-m Ponds ................. 

Effects of pC02 on Productivity ..................................... 

Effects of Dirution Rate on Productivity .............................. 

Productivities of Nutrient-suf f icient and -deficient 

AlgalCultures ..................................................... 
1.0 INTRODUCTION 

1.1 Project Goals 

The overall objectives of this project are to develop and to operate a test facility in the 

American Southwest to evaluate microalgal productivities and to examine the problems 

and potential of scaling up and operating large microalgal production systems. This 

project includes testing specific designs, modes of operation, and strains of microalgae; 

proposing and evaluating modifications to technological concepts; and assessing the progress in meeting cost objectives of the Aquatic Species Program (ASP). 

The objective during the first year of the project (March 9, 1987, to March 11, 1988) was 

to evaluate the outdoor production performance of prescreened microalgae species in six 

small-scale reactors (3 m2) and to begin the development of a larger-scale facility 

(Weissman et al., 1988a). 

1.2 Proiect Site 

The project is located at an established water research facility in the city of Roswell in 

the southeastern part of New Mexico (Figure 1-1). The site is representative of those 

that may be available for construction of an actual production plant. It is characterized 

by high insolation, low precipitation, flat land, and an abundant supply of highly saline 

groundwater. Much of the infrastructure required for this type of project was already in 

place: triple-lined evaporation ponds for disposal of pond effluents, land at very affordable rental rates, and laboratory and office space. In addition, a chemical analysis laboratory exists, much of which is common space for the tenants of the facility. 

Two abundant water re urces are available at the New Mexico site: city water (at Y $326/acre-it or $0.26/m ) and saline groundwater (800 gpm at a pumping cost of about 3 $75/acre-ft or $0.012/m ). The mineral composition of each is given in Table 1-1. The 

groundwater has a salinity similar to 40% seawater, differing primarily in that it contains 

about one-third as much magnesium and twice as much calcium. Growth on this water 

would be representative of growth on high-calcium, low-alkalinity waters similar to 

seawater and Type I groundwaters (Barclay et al., 1987). It is believed that this water 

resource is typical of most saline aquifers in the Southwest. 

The Roswell Test Facility (RTF) has flat, usable land around the main laboratories. A 

small part of this area is currently used to operate our six small-scale experimental 

ponds. One mile east of this location are 36 ha of triple-lined evaporation ponds 

arranged as a set of three 12-ha units. The large-scale system was constructed within 

one-half of one of these ponds, leaving room for expansion in the future. Another 12-ha 

evaporation unit is used for evaporative disposal of the growth pond effluents. This preexisting disposal system at the RTF is one of the major attractions of the facility. Construction of an evaporation system of the requisite size, from two to five times the 

growth pond area, would have been a major cost item. 

At the beginning of the project, a plan was developed for establishing the test facilities 

during the first several years. The plan was based on total funds of about $300,000 for 

fabrications. The schedule of development and the corresponding costs ar iven in 

4 4g Tabi 1-2. The facility now includes a small-scale system comprising six 3-rn ponds, a 

50-m inoculum pond, two 0.1-ha growth ponds (one lined with earthen materials, one 

with a membrane), and the infrastructural development required (power, storage sheds, 

water lines, etc.). A large, 0.5-ha pond and a harvesting system based on flocculationflotation have not yet been built. 

Table 1-1. Mineral composition of Water Resources at 

RTF and 40% Seawater 

40% 

City Water Saw Seawater 

Sodium 

Potassium 

Calcium 

Magnesium 

Chloride 

Sulfate 

Bicarbonate 

Silicon 

TDS 

pH 

Values are mg/L. 

RTF water analysis courtesy of G. Beatty, RTF chemist. 

1.3 Goals for the Current Year 

During the second year (March 12, 1988, to March 11, 1989) the object9es of the project 

were to continue evaluating biomass and lipid productivity in the 3-rn pond system, to 

finish installation of the two 0.1-ha raceways, to evaluate the large system in terms of 

hydraulics and carbonation, and to begin year-round operation of the large system. Each 

of these tasks is discussed in a separate section of this report. 
Table 1-2. Facility Development Plan 

1 st Year: 2 Small-scale system (six 3-rn ponds) 

Large-scale system 

Water to site 

Power to site 

One 0.1-ha growth pond (membrane-lined) 

One 0.1 -ha growth pond (earth-lined) 

Power distribution network 

Engineering 

TOTAL: 

2nd Year: 

Inoculum pond - 50 m 

2 

Chemical storage shed 

Power distribution network 

Engineering 

TOTAL: 

Subsequent Years: 

One 0.5-ha growth pond (eart h-lined) 

Electrical distribution network 

Harvesting system (for all large ponds) 

Engineering 

TOTAL: 

-- 

Note: Does not include labor by project personnel. 
2.0 COMPLETION OF LARGE-SCALE SYSTEM 

Much of this section was described in the last annual report (Weissman et al., 1988a). It 

is repeated here for the convenience of the reader and extended to describe any changes 

made during completion of the system. 

2.1 Introduction 

The layout of the large-scale systey is shown in Figure 2-1. The system consists of two 

0.1-ha growth ponds and one 50-rn pond, along with the nece sary mixing, dilution, and 3 nutrient systems. The growth ponds have a capacity of 150 m at the nominal operating 

depth of 0.1 5 m. The North pond (the lined pond) is lined with a plastic membrane, and 

the South pond (the unlined pond) is lined with crushed rock over clay. The channel 

length-to-width (L/W) ratio of 1 1 was chosen as a compromise between scaleup considerations (larger ponds would typically have a higher L/W ratio) and the desire to have reasonably wide channels for studying bend hydraulics and mixing systems. The final choice 

in fact approximates that of a projected 4.0-ha pond, which would be somewhat constrained in length by the site. 

2.2 Pipelines 

The source of dilution water for the large-scale system is the deep well at the RTF, the 

same water used in the small-scale system. A 15.2-crn (6-in.) line (Class 125 PVC) was 

installed between the test facility and thp pond site, a distance of approximately 1280 m. 

This line has a capacity of about 120 m /h (2000 L/min), sufficient to operate both the 

two 0.1-ha ponds and a future 0.5-ha pond. The two 0.1-ha ponds are operating solely on 

artesian preJsure. A 7.6-cm (3-in.) freshwater line was also installed, with a capacity of 

about 36 rn /h (600 L/min), to allow blending of the two water types and to have fresh 

water at the site. As shown in Figure A-2, the pipelines tee intf a main "utility corridor," which runs along the ends of the 0.1-ha growth and 50-m inoculum ponds and 

then over to evaporation pond /#2, which will take waste from the system. The utility 

corridor contains all supply, harvest, and drain piping, as well as electrical and C02 lines. 

Piping at the south end of the utility corridor was terminated to allow expansion to addit ional ponds. 

2.3 Earthworks 

This phase of the construction involved removing the existing vegetation, placing and 

compacting fill, and grading the fill material to the required slope. Placing, compacting, 

and grading the fill material was difficult because of soft spots at various locations on 

the pad. A test hole revealed groundwater at about 1 m below the level of the final 

grade. As will be discussed in Section 3, the limited ability to grade has had some consequences for pond hydraulics. Work may be required, during the next subcontract 

period, to make the grade more uniform. 

On this scale, we determined that a continuous slope in the direction of flow (corresponding to the head losses at the nominal flow velocity) was impractical, since the 

total head loss, even at 30 cm/s, was only about 4 cm. To do so would have required four 

changes in slope over the width of the pad, adding substantially to the cost, and probably 

could not have been done with sufficient accuracy given the difficulties encountered. 

Instead, the entire pad was graded to drain toward the west at a slope of 0.0006, corresponding to about 4.5 cm over the length of the pond. This approach makes it easier to 

drain ponds, although it causes the culture depth to vary (in this case, 210% from 

nominal) as it moves around the pond. This, in turn, makes analysis of the hydraulics 

more complicated, since conditions of uniform flow can prevail only in the return 

channel. 

2.4 Mixing System 

Design criteria for the mixing system are listed in Table 2-1. The choice of 42 cm/s as 

the maximum mixing velocity was somewhat arbitrary, since this speed was about twice 

the normal mixing speed. The cost of designing for even greater speeds is high, given the 

cubic relationship between mixing speed and input power. (The details of the paddle 

wheel mixing system were given previously in Weissman et al. [1988a].) The paddle wheel 

and drive systems were installed during this project year. 

The paddle wheel is driven directly by a speed reducer, which is belt-driven by a motor/ 

variable speed unit. A 1.1 2-kW (1.5-hp) motor is face mounted to the variable speed unit 

(Beier Variator NZAXCY), which permits a 3:l variation at the turn of a handle. Lower 

speeds are possible by changing the pitch diameter of the variable pitch pulley mounted 

on the output shaft. A V-belt couples this unit with the input of the two-stage cycloidal 

speed reducer (Cyclo 443 16511 1, 210: 1 ratio). The speed reducer input pulley incorporates 

an adjustable torque limiter (American Autogard 409) that disengages upon overload. 

The output shaft drives the paddle wheel through a jaw coupling (Browning JS7Q). A 

direct drive between speed reducer and paddle wheel was chosen. In larger ponds, the 

two would typically be coupied with sprockets and chain, designed to reduce the speed by 

an additional 3: 1 or 4:1, allowing a smaller and less expensive speed reducer to be used. 

As will be discussed in Section 3, this choice of drive had a distinct disadvantage: the 

power consumption of the reduction system and the inefficiency of a large motor operated at low rpm coupled to produce a large, no-load power. This made the overall efficiency of the drive system very low. For research purposes, however, the flexibility 

gained outweighs this reduced efficiency. 

2.5 Nutrient System 

The nutrient system was installed during the fall of 1988. Nutrients are mixed in concentrated solutions and fed into the dilution lines. The following nutrients and their 

respective mixing tank sizes are used: silica (as sodium metasilicate pentahydrate), 

Table 2-1. Mixing System Design Criteria 

pp - - - - -- - - - - 

Parameter Nominal Maximum Units -- - - - - 

Width at channel 

Width at paddle wheel 

Paddle wheel efficiency 

Drive efficiency 

Manning roughness 

Velocity in channel 

Velocity at paddle wheel 

Head loss 

Hydraulic power 

Total power 

Paddle wheel speed 

Paddle wheel torque 
1000 L; urea, 375 L; phosphate (as potassium phosphate dibasic), to be added to urea 

tank; iron (as ferrous sulfate slurry), 200 L; and sulfuric acid, to neutralize the sodium 

metasilicate, 190 L drum. Nutrient solutions will be mixed with deionized water to prevent formation of precipitates. Deionized water is produced by a small reverse-osmosis 

unit (Kiss international, Statesman I, 2000-L/d capacity) located on-site. The mixing 

tanks are e uipped with mixers appropriate to the size of the tank (e.g., 113 hp for the 

1000-L tank \ . Chemical feed pumps (e.g., Blue-White Industries) will feed the concentrated solutions into the dilution lines where they pass under the control box. An electrical interlock permits the pumps to operate only when dilutions are taking place. 

2.6 Dilution System 

3 The dilution system was designed to accommodate a peak dilution flow rate of 8.56 m /h 

(143 LJmin) per pond. Influent lines branch off the main saltwater line. They are 

metered with a paddle-type flow sensor (Signet MK 515-PO, with MK 575 indicator/ 

totalizer), receive concentrated nutrients, and pass through throttling and automatic 

shutoff valves before discharging into the growth ponds. The piping was laid out so that 

fresh water could easily be tied into the dilution system if required. Effluents are 

pumped (Little Giant 8-CBA) through a throttling valve, are metered with a magnetic 

flowmeter (Signet MK565A, with MK575 indicator/totalizer), and then are passed into 

two harvest lines that run to the waste pond. The harvest lines can also be used for 

inter-pond transfer or for filling either growth pond from the inoculum pond. Influent 

and effluent flow rates will be matched manually with the diaphragm throttling valves, 

allowing for the average evaporation. A level sensor in the pond will shut off the 

influent flow as necessary to compensate for mismatched flows or rainy days. During the 

fall of 1988 and winter of 1989, the large-scale system was operated manually in a batch 

mode. 

2.7 Carbonation System 

The internal sumps were constructed to allow carbonation by counterflow injection of 

CO . The 0.91-rn deep x 0.62-m wide sumps have vertical walls and span the full width 

of $he channel opposite the mixing station. A vertical baffle placed in the sump 

obstructs the flow, forcing it down one side, around the bottom, then up and out the 

other side. A 6.5-cm radius was formed into all corners to reduce flow losses. C02 is 

sparged into the downflowing stream using porous polyethylene diffusers. By matchlng 

the downflow velocity with the average bubble rise velocity, long contact times are 

achieved, resulting in high C02 absorption efficiencies. The downf low velocity is controlled by both mixing speed and the relative position of the movable divider baffle. The 

bubble rise velocity (actually the velocity distribution) is a function of bubble size, which 

depends on sparger design, C02 flow rate, salinity, and other factors. Counterflow carbonation creates hydraulic losses as a result of turbulence induced by the changes in flow 

direction and the "lift" associated with the rising COZ. The latter effect is negligible 

because ty volumetric ratio of water/COZ is high (at 20 cm/s no inal mixing velocity 

7 P 

oy and 3 /m /h algae roductivity, flow rate of water (Qw) = 0.28 m Is, flow rate of C02 

(QCOZ = 0.00076 m 1s). However, it is likely that higher sparging rates will be tested to 

simulate conditions in larger ponds. Losses due to turbulence are difficult to estimate 

but are unlikely to exceed two velocity heads (1.3 cm). 

The CO is added on demand via a solenoid activated by the pH controller (Cole-Parmer 

~5654-36). Instantaneous and integrated C02 flow is measured by positive displacement 

flowmeters and mass flow controllers. 
3.8 LARGE-SCALE SYSTEM ENGINEERING ANALYSIS 

3.1 Introduction 

The large-scale system wy designed as a research vehicle intermediate in scale between 

the small fiberglass (3-m ) raceways and a larger 0.5-ha demonstration raceway. Biological and engineering scaleup problems are uncovered, and solutions elucidated, using 

these 0.1-ha raceways. To begin this process, an engineering analysis was performed on 

the system. The goals were to evaluate performance of construction techniques, 

hydraulic operation, and carbonation systems in terms of design expectations and future 

scaleup. 

3.2 Grading and Pond Depth 

The grade was designed with a 0.0006 slope from east to west, resulting in a 4.5-cm 

depth differential from one end of each channel to the other. This design was implemented for ease of construction (of this relatively small system) and as an aid in draining 

and cleaning the ponds. The 180" bends were banked and were more shallow towards the 

walls. This design was used to minimize cross-channel secondary flows. 

Depth profiles for the two 0.1-ha raceways are shown in Figures 3-1 through 3-3. Generally, the design intent would have been accomplished, except that the soil structure at 

the site was poor. Earth compacting was extremely limited; the spongy clay soils did not 

fully compact. Instead, certain areas compacted and sank subsequent to the grading 

efforts. The salient result is evident in the figures: the depth profile undulates. This 

has had two deleterious consequences. First, the ponds are not easy to drain and clean. 

Second, the contractions and expansions of flow, due to the depth changes, complicate 

the hydraulics in the ponds and lead to an increased problem of in-pond deposition of 

particulates. A decision will be made later whether to correct the problem in the lined 

pond by using sand to even the grade. 

Table 3-1 gives the deviations in channel depths for average depths of 13.5 and 13.7 cm. 

The depth of operation during 1988 was about 14 cm. Greater depths were used 

beginning in the spring of 1989 to reduce the magnitude of depth changes along the 

lengths of the channels. 

3.3 Visual Observations of Flow 

The raceways were first operated without flow deflectors around the 180" bends. As 

expected, the flow was characterized by large eddies formed just after the bends and 

continuing far into each channel. The most serious problem, however, was that the flow 

was not straight entering the paddle wheel: water depth varied across the channel just 

upstream of the mixer. This condition led to flow across the paddle wheel blades, and to 

cross flows just after the mixer. In addition, the flow was characterized by separate 

concentric "tracks" traveling at various speeds around the pond. The track closest to the 

center wall moved the fastest, and the head differential across the mixer (upstream to 

downstream) formed a gradient that was greatest next to the center wall. The installation of two flow deflectors at each bend greatly straightened and evened the flow. This, 

in turn, reduced the areas of stagnation in each channel. It also caused the stream to 

flow into and off of the paddle wheel more evenly. With a straight flow at the head of 

each channel, fewer dead zones and cross flows occurred. In general, velocities were 

more uniform. 



Table 3-1. 0,l-ha Pond Depths and Deviations 

(All depths in cm) 

North Pond South Pond 

NC* SC** Overall NC* SC* * Overall 

Average depth 13.6 13.8 13.7 13.6 13.3 13.5 

Standarddeviation 2.1 1.8 -- 1.9 2.0 -- 

*NC = north channel 

* *SC = south channel 

n > 100 for each channel 

Variations in velocities were visually apparent in the ponds because of the variations in 

water depth. These may be alleviated somewhat by operating at greater depth. As mentioned earlier, we may need to improve the evenness of the grade. This will be possible 

if the settling of the ponds stabilizes. 

3.4 Velocity Profiles 

Velocity profiles in open channel flow have been fit to various curves, but a simple 

logarithmic relationship is often satisfactory (Daugherty and Franzini, 1977). The data 

from the velocity-depth profiles were fit to the relationship: A + B log(y/d), where A and 

B are constants, d is the depth, and y is the distance from the bottom to the measuring 

point. This fit breaks down at y = 0 (the velocity profile near the bottom changes shape 

as it approaches zero at the pond bottom) and usually again at y = d (the surface velocity 

may even be lower than beneath the surface). For the measurements taken here, the 

functional form given here was adequate. Virtually all of the correlation coefficients 

were higher than 0.95 and most were higher than 0.98. It has the advantage of allowing 

easy calculation of the depth-averaged velocity from the fitted curve. The average 

velocity is equal to B - A, or the velocity at y/d 0.368. This fit also allows for an easy 

estimate of the corrections to the kinetic energy of the flow. If the velocity were uniform with depth, the kinetic energy could be represented by a single velocity head 

term. For non-uniform velocities, this term is multiplied by a correction factor, which 

was calculated from the log curve and determined to be 1.05. 

Velocity profiles were taken 1.4 m upstream from the sump in each pond at six rneasurement stations in each channel: 0.60, 1.83, 3.05, 4.27, 5.49, and 6.10 m from the center 

wall. Thus the width of a given channel was divided into seven sections, each bounded by 

two measurement stations. After the average velocity was calculated at each of the stations (from the depth profiles), the section averages were calculated by averaging the 

two (depth-averaged) velocities that bounded each section. Then each section was 

assigned a weight, determined by the section length divided by the channel width. The 

average velocity of the channel was calculated as a weighted average of the section 

averages. Using the average depth and average velocity, an average flow rate was calculated for each section. These, in turn, were used to determine an overall average flow 

rate. Given the average depth of any reach of channel and the average flow rate, the 

velocity of flow in that reach could now be estimated. These calculations were done for 

several paddle wheel rotation speeds, and used in relationships between head loss and 

velocity (or flow rate). 
The velocity profiles obtained at four paddle wheel rotation speeds are shown in 

Figures 3-4 through 3-8. Average values of velocity 1.4 m upstream from the sump (in 

the return flow channel), average depths, and flow rates for the North (lined) and South 

(unlined) raceways are given in Table 3-2. Overall average velocities for both ponds, 

based on flow rate and average pond depth, are shown in Table 3-3. 

The mixing system was designed to allow variation in mixing velocity from 15 to 

40 cm/s. The to speed could not be reached because of mixer inefficiency at the high 

lifts engendered P see Section 3.5). 

3.5 Head Losses 

Depth of flow was measured across the channel at six locations in each pond at a series 

of paddle wheel rotation speeds. Using the still water level as a datum, the potential 

energy of the water was estimated at each measuring station from the difference 

between the measured depth of the moving water and that of the still water. If flow 

were steady and uniform, these measurements would be enough to determine total head 

losses, since flow velocities would be equal (that is kinetic energy associated with the 

flow would be constant). We know, however, from the depth profile, that even under 

steady flow conditions attained, the flow was not uniform. In one channel of each pond, 

the slope of the pond bottom was adverse (increasing in the direction of flow); there were 

depth constrictions and expansions, and there were nonuniformities associated with bends 

and the lift stations. Thus, some estimate had to be made of the velocity head at each 

location to approximate total head. Once this estimate was completed, differences in 

total head between locations could be estimated. 

Measurements taken before and after the paddle wheel were used to indicate total losses 

in mixing the pond. When multiplied by water density and flow rate, these Losses gave an . 

estimate of hydraulic power requirements for mixing. Measurements taken before and 

after each bend were used to estimate bend losses. Measurements were also taken 

before and after the carbonation sumps (to determine their contribution to losses) and at 

the beginning and end of the channels in each pond (to isolate the "open channel flow" 

losses). Estimates of the head loss for each pond section are given in Table 3-4. 

Each of these measurements contained a considerable level of approximation. An error 

of 0.05-0.1 crn was associated with each depth measurement at the lower mixin speeds, 

and an error of twice this at the higher speeds (despite the use of stilling wells. Since 

two subtractions were needed to obtain a head difference, the minimum measurement 

error for potential head loss was 0.1 to 0.2 cm. The errors in estimating velocity head 

were composed of the individual velocity measurement errors (about 10% of the mean at 

low velocity and 3% at high velocity), the errors in determining average velocity over 

pond depth and channel width (about lo%), the propagation errors in the translation of 

velocity from the velocity-measuring station to the head-measuring station (using the 

equation of continuity for flow rate), the underestimate of the correction to kinetic head 

deriving from highly nonuniform velocity distributions (especially near bends, sumps, and 

around the paddle wheel), and the propagation errors in subtracting to get velocity head 

differences. At low mixing speeds, the velocity head differences were insignificant 

compared to the potential head differences. Thus, errors in measuring depths, and error 

propagation led to about a 0.2-cm limit to precision. At high mixing speeds, the velocity 

head differences were 5% to 30% of the potential head differences. Thus, both sources 

of error were important in the overall observed error of 20% of the mean. The accuracy 

of the measurements was also limited. Accuracy errors were introduced when averaging 

the head differences across the channel. Four discrete measuring poirlts wcre used. 

Velocity was only measured in the direction along the chanrlt.1. A l t l~ot~gli t tt. f low was 





Table 3-2. Average Depths, Velocities, and Flow Rates 1.4-m 

Upstream from Sumps in 0-1-ha Raceways 

North Pond South Pond 

Padd le Whee 1 

Rotat ion d V Q d V Q 

(rpm) (cm) (cm/s> (L/s) (cm) (cmls) (L/s) 

Note: Average pond depths were 13.7 and 13.5 cm for North and South 

ponds, respectively, when measurements were taken. 

Table 3-3. Average Velocities in 0.1-ha Raceways (cmls) 

- - - 

Paddle Wheel Rotation Speed (rpm) 

- -- 

North pond 16.7 24.4 27.6 30.8 33.0 39.5 

South pond 15.8 17.1 21.3 22.1 23.0 25.0 

*Velocity determined from interpolated flow rate. 

Note: Velocities were calculated from measured flow rate and average 

depth of 13.7 crn for North pond and 13.5 cm for South pond. 

predominantly in this direction, large eddies, cross flows, and vertical flows all contributed to the kinetic energy of the flow, but were not included in the measurements. 

At the higher mixing speeds, the effects of wave action were averaged when head and 

velocity were estimated. Their contribution to the energy of flow may have been greater 

than the average used. 

From the nonlinearity in the curve of velocity versus paddle wheel rotation speed 

(Table 3-3), the mixer in the unlined (South) pond appears to have become more inefficient at higher rpm. The frictional losses were so great during circulation around the 

pond at high flow rate that the draw down to the paddle wheel intake became very 

great. Thus the amount of water lifted by each blade of the paddle wheel was suboptimal. In addition, the paddle wheel was not able to convert the increased water 

velocity on the intake side into potential energy on the output side. Thus the large 

velocity head, due to the draw down, was dissipated. These problems may be alleviated 

by operating the ponds at greater depth. As mentioned earlier, this will be done to 

minimize depth variation (as a fraction of average depth) at all mixing velocities. The 

paddle wheel intake could also be designed differently; but we do not anticipate that the 

ponds will be operated at high paddle wheel rotation speeds. 
Table 3-4. Total Head Loss (cm) for Each Section of 0.1-ha Raceways 

Paddle Wheel Rotation Speed (rprn) 

North pond 

First channel 

Second channel 

First bend 

Second bend 

Carbonation sump 

Total 

South pond 

First channel 

Second channel 

First bend 

Secondbend 

Carbonation sump 

Total 

Note: Numbers in ( ) are percentage of total head loss. 

3.6 Roughness Coefficients 

For design purposes, open channel flow is characterized by the Manning equation and the 

Manning's roughness coefficient. Although these devices are most useful for ideal 

channels (uniform flow), they are still guides in the estimation of head loss of large 

channel reaches. To derive estimates of Manning's n, we used the data from the first 
channel (outgoing flow from the paddle wheel) and second channel (return flow). In the 

return channels, the average grade was at Least in the direction of flow. However, 

because of the depth variations, flow was probably never uniform. The roughness coefficients calculated are given in Table 3-5. Both the 0.010 value for the North (lined) pond 

and the 0.0 173 for the South (unlined) pond are within the range expected. 

3.7 Mixing Power 

From the measurements of total head loss around the ponds and the flow rates, the power 

dissipated by the fluid motion was calculated. This is called the hydraulic power. A 

theoretical hydraulic power was calculated from Manning's equation, assuming that the 

only losses were due to the bottom roughness. The ratio gives an indication of how much 

of the actual hydraulic power was dissipated in bends, the sumps, and deviation from 

uniform flow in ideal channels. This ratio was 41% for each of the ponds. The actual 

power delivered to the paddle wheel shaft (the net shaft power) was estimated for the 

Table 3-5. Manning's Roughness Coefficients for 0.1 -ha Raceways 

Paddle Wheel Rotation Speed (rpm) 

North pond (lined) 

3 Flow rate (m /s) 

First channel 

Avg. depth (cm) 

Head loss (cm) 

Manning's n 

Second channel 

Avg. depth (cm) 

Head loss (cm) 

Mannings n 

South pond (unlined) 

Flow rate (m3/s) 

First channel 

Avg. depth (cm) 

Head loss (cm) 

Manning's n 

Second channel 

Avg. depth (cm) 

Head loss (cm) 

Manning's n 
North (lined) pond. This was done, at each paddle wheel rotation speed, by taking the 

difference between the wattage input to the mixing drive system (motor, speed reducers, 

shaft) with water in the pond (load power) and without water in the pond (no-load 

power). The hydraulic power divided by this net shaft power is an estimate of the paddle 

wheel efficiency. As alluded to above, the mixer efficiency decreased with increasing 

mixing speed, from 76% to 40%. At the two highest mixing speeds, the kinetic energy of 

the water entering the paddle wheel lowered the total hydraulic head loss 30% and 50%, 

respectively. The inability of the mixer to conserve this kinetic energy resulted in the 

lower efficiency. Table 3-6 summarizes the power measurements taken. 

A paddle wheel efficiency greater than 100% was calculated for the lowest mixing 

speed. The errors associated with the measured power were large at low mixing speeds. 

Since the system was designed to produce velocities ranging from 15 to 40 crnls, large 

motors and speed reduction units were used. However, these were not very efficient at 

low mixing speed. A large amount of power was dissipated even under no-load conditions. The net shaft power is the difference between a loaded and non-loaded power measurement. At all mixing speeds both of these numbers were large (500-1500 W), but at 

low mixing speeds, the difference was small (less than 20 W). The propagated error of 

subtraction was 15 W, so the errors in estimates of net shaft power were large. Another 

error, stemming from the influence of wind on the power measurements (especially 

no-load measurements), is difficult to estimate. The standard deviation of replicate 

wattmeter readings taken one right after the other was about 0.5%. However, the 

standard deviation of sets of replicates, taken at various temporal separations was 

greater, about 3%. in addition to these precision errors, there was an accuracy error in 

the method. The no-load wattage is an estimate of the power dissipation in the drive 

train under load conditions, as opposed to the power delivered to the paddle wheel 

shaft. This power is not independent of load, so that use of the no-load measurement 

probably resulted in an underestimate of the drive train power and thus an underestimate 

of the paddle wheel efficiency. Figure 3-9 summarizes the results of the power rneasurements as plots against average pond velocity. 

Table 3-6. Mixing Power Requirements for 0.1-ha Raceways (given in W) 

Paddle Wheel Rotation Speed (rpm) 

North pond (lined) 

3 Flow rate (m 1s) 

Head loss (cm) 

Net shaft power 

Hydraulic power 

Paddle wheel efficiency 

(%I 

Theoretical power 

South pond (unlined) 

3 Flow rate (m /s) 

Head loss (cm) 

Hydraulic power 

Theoretical power 
AVERAGE MIXING VELOCITY, CM/S 

Figure 3-9. Mixing power as a function of average water velocity in 0.1-ha 

raceways 

Total hydraulic power consumption: North (lined) pond, boxes; 

South (unlined) pond, diamonds. Power consumption due only to 

channel roughness: North pond, pluses; South pond, triangles. 

3.8 Carbonation 

3.8.1 Introduction 

Carbon dioxide is the single most costly input to the algal biomass fuels process (Neenan 

et al., 1986). The delivery and utilization of carbon in algae ponds are significant to the 

design and operation. Unlike other algal nutrients (e.g., nitrogen and phosphorus) which 

have a high solubility in water (relative to their content in algae) and can be added 

intermittently, carbon dioxide has a low solubility in water and must be continually 

replenished in an actively growing culture. One factor that aids the storage of C02 is 

the carbonate buffer; however, the Roswell Saw and seawater (alkalinities of 3.4 and 

2.7 mmol, respectively) can only store enough C02 to produce approximately 1 g/m for 

a pH rise from 7.0 to 7.5. In summary, the amount of storage a given water type will 

have is dependent upon its alkalinity, carbonate equilibria, and, of course, its pH. 

The CO is injected into the ponds near the bottom of the sumps. The sumps contain a 

baffle t 8 at prevents the lateral flow of water. Instead, the flow is directed down to the 

sump bottom, under the baffle, up behind the baffle and out. (The predicted operation of 

sumps is discussed in detail in Weissman and Goebel [1987].) The efficiency depends primarily on the contact time and area between the gas and liquid phases, and is affected by 

the buffering capacity of the liquid. The contact area is determined primarily by the 
bubble size distribution of the gas. The contact time is determined by these factors 

along with the water velocity (direction and magnitude) which determine the rise velocity of bubbles relative to the water. Minimization of capital expenditures requires that 

the number of sumps be reduced as well as their depth. Thus, a rather large mass of gas 

must flow into a relatively few sumps, be efficiently absorbed, and be stored in the liquid 

buffer while still maintaining both the pH and C02 within the range optimal for algal 

growth. 

Unfortunately the C02 which is injected and stored in the water's carbonate buffer can 

also be lost to the surrounding atmosphere as the water tries to equilibrate with air 

levels of C02. The raceways' ponds are shallow reactors with an enormously large surface-area-to-volume ratio, which is essential since the limiting input--the sunlight-- 

enters only through exposed surface area. As a consequence, C02 can easily escape from 

the liquid to the atmosphere, where the concentration is low. The two factors that 

affect outgassing the most are the concentration in the liquid and the resistance to 

movement through the gas-liquid interface. Both are unfavorably affected as pond depth 

is decreased. The mass transfer resistance also decreases as the mixing energy input to 

the pond increases, since this increases the rate at which the pond surface is renewed 

with C02-rich water from beneath the surface. Thus, a major undertaking of this project 

has been to optimize the often conflicting goals of increasing algal productivity (sufficient mixing and pC02) and decreasing the opportunity for C02 loss. 

The sumps in the large-scale system were designed to be of moderate depth (about 1 m), 

to be operated either co- or countercurrently, and to be capable of being retrofitted with 

a cover for catching gas and recycling it. During this subcontract period, operation was 

restricted to the nonrecycle, countercurrent mode to assess the injection efficiency. 

3.8.2 Materials and Methods 

All of the pH measurements were made with a Model 601 Orion Ionalyzer. Alkalinity was 

determined on 50-mL samples with either 0.05 or 0.01 N HCI and titrating to pH 4.20. A 

minimum of three titrations were performed per sample. 

Total inorganic carbon (TIC) was measured using an Ocean Instruments Total Organic 

Carbon analyzer (Model 520). This instrument works by acidifying a sample with 5% 

H3P04, which converts all inorganic forms of carbon to C02. The sample is then purged 

with a gas stream of N2 and passed through a nondispersive infrared detector. Integrated 

signal response is compared against a standard for conversion to mg/L total carbon. The 

instrument was blanked with N purged deionized-distilled water, and the carbon 

standard was a 100 mg/L (on a to ? a1 carbon basis) solution of Na2C0 . Reproducibility 

of the standard was within I%, and the average percent deviation 04 all runs was less 

than 0.5%. 

Samples were withdrawn automatically every three minutes from a 2-L, wide mouth 

Erlenmeyer flask that served as an equilibrium vessel. The flask was mixed with a magnetic stir bar and sparged with a COZ/NZ gas mixture introduced through a coarse-fritted 

cylinder near the bottom of the vessel. The gas mixture was adjusted using N2 (2 slpm) 

and C02 (50 sccm) flow controllers (Model FC-260, Tylan Corp.). The amounts of each 

gas were adjusted electronically. The gas flow was passed through a humidifier before 

entering the equilibrium vessel. Equilibrium was defined by no change in pH (.01 unit) for 

a period of 10 min. 
sea 

The dissociation constants for the carbonate system were determined by regressing the 

pH-TIC data using the equilibrium equations as given in Table 4.2 of Stumm and Morgan 

(1980). The best fit was determined by a trial and error procedure until we obtained a 

minimum in the sum of squares. The pH-TIC data set included some previous measurements not reported in Table 3-7. These measurements had to be corrected for a difference in alkalinity, which was done by calculating dTIC/dAlk at each pH value. 

Injection efficiencies were measured in the carbonation sump of one of the 0.1-ha ponds 

and in a 600-L polyethylene tank. These experiments were performed by measuring the 

increase in total carbon in the liquid after sparging a known amount of carbon as CO 

into the vessel. Liquid phase inorganic carbon was determined by measuring the pH an 3 

calculating TIC using the carbonate dissociation constants determined for the RTF Saw 

groundwater. The pH measurements were taken before and after carbonation, with the 

'?afterw measurements collected following a period of hand mixing. The amount of CO 

injected was measured by a Sierra Instruments Mass Flow Controller (0-75 slpm) whic I? 

also totalized the flow. The C02 was introduced through a 2.5-cm-diameter, porous, 

polyethylene diffuser located in the bottom of the tank and approximately 0.25 m from 

the bottom of the carbonation sump. Two 0.3-m-long diffusers were mounted at the end 

of five main feedlines distributed across the width of the sump. Thus a total of 3.1 m of 

diffuser pipe was used in the carbonation sump. In the tank, only one header was used; 

therefore, only 0.6 m of diffuser was used, which was located approximately 0.05 m from 

the tank bottom. 

Rates of outgassing were determined by measuring the change in pH per unit time in 

clean, noninoculated, 0.1-ha ponds. For each condition of mixing speed and depth, the pH 

was allowed to rise at least 0.5 pH unit--typically in the range of 7.0 to 7.1. At each 

value of pH, total carbon and dissolved CO were calcuiated. The outgassing coefficient 

was then determined by linear regression 05 the average C02 driving force with the rate 

of change in total carbon. 

Table 3-7. pH, Partial Pressure of C02 (pC02), 

and TIC Relationship for RTF Water 

- 

PH PCOZ C02 TIC SD 

(%> (mmol) (mmol) (mmol) 

*Measured at 23°C. 

Note: -log(kH) = 1.435 at 20°C. 
3.8.3 Carbonate Equilibria 

Calculations of the mass transfer coefficient for outgassing and the injection efficiency 

in the in-pond sumps both require knowledge of the carbonate equilibria. The Saw at 

Roswell is significantly different from either fresh water or seawater; therefore, we 

could not rely on published values of the dissociation constants for these waters. Instead, 

we directly measured the relationship between total carbon and pH. 

Table 3-7 shows the relation between total inorganic carbon, pH, and pC02. Solution pH 

was varied by equilibrating with different concentrations of C02 in the gas phase. Each 

TIC value represents the average of five measurements. This set of measurements was 

done at 20°C. The water had an alkalinity of 3.30 + 0.02 mmol. The accuracy error 

involved in estimating the carbonate alkalinity was probably several tenths of a mmol/L 

because of the uncertainty in the true endpoint for the titration and also because of the 

small amounts of other titratable bases. 

The measurements shown in Table 3-7 (excluding the point at pH = 5.1) were combined 

with a previous data set and the best fit equilibrium constants were determined. The 

point at pH = 5.1 was not included in the fit because of uncertainties in the temperature 

correction and the disproportionate weighting of such a large TIC value. The curvefitting yielded pKl = 6.05 and pK2* = 9.37. The standard error of the fit was calculated 

as 0.326 mmol. Sensitivity of the fit to changes in pK1 or pK2 were determined by 

calculating the amount of change in either value to produce a standard error of 

0.115 mmol from the best fit case. This gave an error in pK1 of about 0.01 and in pK2 of 

about 0.2. However, changes in the estimated value of the carbonate alkalinity resulted 

in large changes in the best fit values of the equilibrium constants. Assuming the true 

alkalinity was 0.3 mmol higher led to a value for pK1 that was 0.13 units lower and a 

value for pK2 that was 0.49 units lower. 

Since the regressed values of the equilibrium constants were so sensitive to small errors 

in estimates of carbonate alkalinity, the data were analyzed with a different method. 

This method was based on calculating, for each data point, the ratio of dissolved CO to 

total carbon. From this, the first equilibrium constant could be calculated when is 

below 7.5. In this pH range, influence of the second dissociation on this ratio was insignificant. From four data points, pK1 was valued at 6.20 with a standard deviation of 

0.01. If data points above pH 8.5 were available, then the second constant was determined with small error. Without these points, pK2 could only be estimated to have been 

between 9.0 and 9.5, which was insignificant because all carbonation work was performed 

at low pH. 

The accuracy of this method depends on the accuracy of the estimate of the Henry's Law 

constant. The KH* is sensitive to temperature and ionic strength but not sensitive to the 

ionic distribution of the water type (Loewenthal and Marais, 1984). Using the ionic 

strength of 0.264 M Sa W (calculated from the measured composition) and an empirical 

relationship for the ratio of the activity of C02 in pure water to that in the test water 

(natural logarithm of the activity ratio = 0.22 x ionic strength), a Henry's Law constant 

at 20 C02 of 0.0367 (pKH = 1.435) was calculated. When KH was calculated from the 

*pK 1 = -log (first ionization constant for dissociation of carbonic acid) 

pK2 -log (second ionization constant for dissociation of bicarbonate to carbonate) 

*KH = Henry's Law Constant for the concentration of a solute in a solution at a given 

partial pressure. 
comparison of the gas partial pressure of C02 (as given in Table 3-7) and the dissolved 

C02 predicted by the regressed equilibrium constants, pKH was greater than 1.50, which 

is greater than that of seawater. This discrepancy could easily be attributed to errors in 

the equilibrium constants as estimated by regression. In the future, these will be 

reestimated on the basis of Gran titrations. 

3.8.4 Injection Efficiency 

The experiments were designed to test the sensitivity of the injection efficiency (IE) to 

variations in height above diffuser and gas flow rate. Results are shown in Tables 3-8 

and 3-9 for the sump and tank tests, respectively. The data for the sumps were used to 

yield three estimates of IE: one based on the regressed values for the equilibrium 

constants, one based on the actual TIC measurements (points for which the IE test endpoints corresponded closely to pH-TIC measurements as given in Table 3-7), and one 

based on the pK1 as determined from the Henry's Law constant. IE averaged 76% by the 

first method, 90% by the second, and 100% by the third. Visual observation of the 

bubbles breaking the surface during the tests indicated a very high IE. Clearly, the first 

method underestimated the IE, while the third method overestimated it. Given the magnitude of the errors involved, the true IE was most likely in the range of 80%-90%. 

A more important result of the experiments is that despite variation in gas flow rate and 

liquid height, little change in IE occurred. Although there is uncertainty about the 

absolute value of the calculated injection efficiencies, these results are significant in 

that they corroborate a high IE value. So much gas was absorbed that the bubbles 

became minuscule. This would results in very little bubble "slip" relative to the liquid. A 

lack of dependence on the gas flow rate indicates that the hydrodynamic condition is only 

slightly altered by changes in the gas flow rate. 

3.8.5 Outgassing 

The outgassing coefficient was determined at two mixing speeds for the lined North pond 

(see Table 3-10). Measuring outgassing rates in the South (unlined) pond was difficult 

because of a small amount of photosynthetic uptake of CO during the experiments (from 

sediment activity); therefore, these rates are not reported ere. i 

Each of the reported values represents two measurements. The uncertainty in individual 

measurements ranged between 1596-3096 of the regressed value of KL (the coefficient of 

mass transfer for outgassing COZ). Because determination of the outgassing coefficient 

involves the derivative of the collected data, a small error (or noise) in the pH 

measurement can result in a large error in the rate of change in total carbon and 

therefore increase the uncertainty in KL. In some cases discrepancies in pH 

measurements were the result of the discrete nature of the measurement process (versus 

continuous). A source of systematic error results from the uncertainty concerning the 

carbonate equilibria. The error is introduced because of possible deviations between the 

calculated TIC, and the true TIC, or more specifically errors in the slope, dTIC/dt, over 

the region of pH change. Fortunately over the range of pH values where dTIC/dt is 

calculated, there is negligible difference between measured rates of change and those 

determined by the equilibrium expressions. 
Table 3-8. Summary of Carbonation Tests in Sump 

Run Depth Width Volume Qco2 dTICg* Efficiency (%) 

(m) (m) (m3) (slpm) (mol) I 2 3 

*dTICg is amount of C02 injected, calculated as flow rate x duration of injection. 

Method I--based on nonlinear regression to determine pK 1, pK2. 

Method 2--based on measured TIC at pH before and after injection. 

Method 3-based on Raoult's Law to determine pK1. 

Table 3-9. Summary of Carbonation Tests in 600-L Tank 

Run Depth Volume Qco dTICg Efficiency 

/# (m) (m3) (slpmf (moll (96) 

-- 

*Hand-mixed during sparging. 

Note: All values calculated by method 1, except for value in ( ), 

which was calculated from method 2. 

3.8.6 Conclusions 

The 80%-90% inject ion efficiency measured for the large-scale carbonation system needs 

improvement. The data indicate that increasing the height of the water column in the 

carbonation sump is ineffective in increasing injection efficiency. The most likely 

explanation for this is that after most of the C02 was absorbed, the remaining bubbles 

were so small that there was relatively little motion between the water and the gas. 

This resulted in the formation of a substantial local back pressure which greatly slowed 

absorption. The pH of these local volumes of water would have to have been about 5, 

depending on how much the bubble C02 content was diluted by nitrogen and oxygen 

absorbed from the water. The most effective manner of increasing the absorption efficiency would appear to increase the turbulence in the sump. In the actual operation 
Table 3-10. Summary of Outgassing Results 

Depth Velocity KL SD 

(m) h/s) (m/s> (m/s> 

of the ponds, this occurs--the gas is injected countercurrently into water flowing into and 

out of the sump. However, outgassing of oxygen (the concentration of which in the ponds 

was well above air saturation levels) may decrease absorption efficiency by decreasing 

the pCO in the bubbles. As discussed in Section 4, the estimated in situ efficiency is no 

higher t E an the efficiency measured in these tests, despite the countercurrent operation. If so, it may be necessary to install a system for capturing the gas and recycling it 

through the injection system. 

Outgassing of CO through the pond surface can be extensive if mixing is too energetic 

and pH too low. dowevet-, it can be made negligible by optimized operation of the ponds. 

Given the values of the outgassing coefficients, pH should be maintained above 8 to 

reduce outgassing losses to less than 10%. The effect of this on algal productivity is discussed in Section 5. 
4.0 OPERATION OF THE LARGE-SCALE SYSTEM 

Most of the activity concerning the two 0.1-ha raceways centered around the engineering 

analyses discussed in Section 3. In addition, however, the process of evaluating the biological performance of the large-scale system began during this subcontract period. The 

two raceways began operation in August 1988 with the inoculation of Tetraselmis 

etroselmis suecica TETRAI. Since it was evident that pond hydraulics were not yet 

optimized, the paddle wheel rotation speed was set at 5.3 rpm to try to alleviate in-pond 

sedimentation of biomass. This resulted in an average mixing velocity of 30 cm/s in the 

lined pond and 22 cm/s in the unlined pond. 

T. suecica grew from the middle ff August to the middle of September, averaging 

11 g ash free dry weight (AFDM)/m /d in the North (lined) pond and 10 g AFDM/m/d in 

the South (unlined) pond. Even with the higher mixing speed, frequent sweeping of the 

bottom of the North (lined) pond showed that settling of biomass was significant. Suspended solids ranged from 10% to 100% higher after sweeping This action may have 2 contributed to poor yield by the large ponds versus the 3-m ponds. In re latter, 

T. suecica grew stably through the fall and winter, averaging 15.2 g AFDM/m /d over a 

comparable time period. 

After the loss of T. suecica from the large-sfale ponds, Monoraphidium minutum was 

inoculated It was also cultivated in the 50-m inoculum pond for comparison, as well as 2 in the 3-m ponds. As shown in Table 4-1, productivity was highest in the smallest ponds, 

but not much higher than in the North (lined) ponds (the lined 0.1-ha pond and the 

inoculum pond). Productivity was lowest in the large, South (unlined) pond. Significant 

biomass settling was observed once again in both of the 0.1-ha ponds. The inability to 

clean the south unlined pond (by mechanical resuspension of settled matter) was a distinguishing characteristic. Whether this or some other factor was the reason for lower production from this pond is unknown. During the month of December, yields were low in all 

ponds because of the cold weather. 

An important aspect of the difference between membrane-lined ponds and unlined ponds 

is the loss of water through leaks and percolation. The average daily loss of water, 

including evaporation, is given in Table 4-2 for the large-scale system raceways. Initially, seepage from the unlined pond was visible as water around the pond periphery. 

Leaks were evident between the concrete mixing structures and the clay lining. After 

these were fixed, percolation still occurred. Nearly one-half of a centimeter per day 

more water was lost from the unlined pond than from the lined pond. However, after 

approximately 30 days of operation, the water loss from the ponds equalized at the lower 

rate of 0.4 cm/d. Apparently the unlined pond had sealed. Subsequently, the pond was 

emptied to take some engineering measurements. The pond bottom dried out completely. When refilled, the unlined pond again incurred a greater water loss than the 

lined ponds. Although the extra loss of water was now less (about 0.3 cmld, there has 

been no amelioration of the rate. Thus, it is likely that the drying process led to the 

formation of new leaks. This element will be examined next year. 

A preliminary mass balance for carbon was calculated for the North (lined) 0.1-ha raceway. The amount of CO injected into the sump was monitored with a calibrated mass 

flow meter. The mass ofcarbon fixed into biomass was estimated as half of the AFDM 

produced. Finally, carbon lost to the atmosphere through outgassing was estimated from 

the mass transfer coefficient as a function of average operating pH. The results of the 

trial mass balances are shown in Table 4-3. Overall utilization efficiency of CO -carbon 

varied from a low of 32%-65%. The low efficiency was caused by low, winter$iornass 

productivity. More C02 was lost to the atmosphere than was fixed in biomass. When 
SHPI 

Table 4- 1. Large-scale System Productivity (g AFDM/~*/~) 

Lined Pond Unlined Pond 2 50-rn Pond 2 3-m Pond 

* 1987 results. 

2 2 Note: 50-m pond is lined; 3-m pond is fiberglass. 

Table 4-2. Average Daily Water Loss from Large-scale Ponds 

(cm/day) 

Lined Pond Unlined Pond 2 50-m Pond 

Table 4-3. Carbon Utilization Efficiency in Lined Pond 

Carbon (kg) Efficiency (%) 

Injected Biomass Outgassed Overall Inject ion 
2 ~)roductivity averaged about 10 g AFDM/m /d, outgassing represented 30% of the 

injected C02 at pH 7.5 and 20% at an operating pH of 7.8. As noted in Section 3.8, to 

achieve over 90% overall C02 utilization efficiency, the pH of the ponds must be kept 

above 8.0. The injection efficiency of the sumps, operated countercurrently, was 78%- 

95%. 

In summary, the results from the large-scale raceways have been mixed One species, 2 T. suecica, was not as productive in the larger ponds versus the 3-m ponds, while 

another species, M. minuturn, was about as productive. The South (unlined) pond tended 

to have reduced yields and more difficulties with settling. Much more discriminating 

results wiIl be obtained when the ponds are operated over long periods during which 

yields are potentially high. In addition, some of the problems with mixing and suspension 

will have been examined by then. Operation of the South (unlined) pond consumed more 

water than the North (lined) ponds due to leaks and percolation. The leaks appeared to 

predominate; they also can probably be fixed. Under the worst conditions observed, 

water usage in the unlined system would be 50% greater than in the lined system. However, there is evidence that the unlined system can seal effectively. C02 utilization 

efficiency was low (60%), but this was mainly due to outgassing. This loss can be minimized by operating at a higher pH. 
5,0 OPERATION OF THE SMALL-SCALE SYSTEM 

5.1 Experimental Plan 

The small-scale system was used to test 15 species for growth in the mass culture 

environment, to assess the effects of moderately low C02 and moderately high pH (conditions which improve the economics of pond operation) on productivity and stability, and 

to evaluate capability for induction of high-lipid content in the organisms tested. 

Last year, we found that M. minutum grew stably during the cold seasons, even surviving 

freezes. It was cultivated during January, February, March, April, and May, and again 

during October and November of 1988. During January, February, and April, it was 

grown in unheated ponds as well as in heated ponds. During the first two months, each 

condition was performed in duplicate. Other heating experiments were also performed, 

for two weeks at a time, during May and June to see whether raising pond temperatures 

would increase productivity of warm weather species (e.g., T. suecica TETRAI) and 

affect species dominance. 

During the warm and sunny months of May through September, we could often operate 

the raceways on a two-day hydraulic detention time. However, extended periods of cloud 

cover can cause instability of culture density. Therefore, we compared productivity of 

cultures operated on a three-day detention to that of cultures operated on a two-day 

regime. A three-day regime is much more stable. Two warm weather organisms, which 

grow quite stably, were used in these two-week trials: Amphora sp. (RTF) and T. suecica 

TETRA 1 

Since C02 is a major input to the system, and its loss via outgassing is increased at low 

pH, experiments were performed to test productivity at pH 7.2, 7.8, and 8.3. Dissolved 

concentrations of CO (at the alkalinity of 3 to 5 milliequivalent/L) were about 285, 75, 

and 20 pm, respective T y, at these pH values. 

All of the organisms that were stable in culture (that is, could be grown for at least two 

to three weeks) were tested for the capability to produce lipids under nutrient stress. 

These experiments were usually conducted singly, but were repeated. Samples were preserved for subsequent lipid analysis at the Solar Energy Research Institute (SERI). 

5-2 Materials and Methods 

2 The small-scale system consists of six 2.74-m fiberglass tanks operated at 15-cm depth, 

mixed by paddle wheel, and pH controlled by injection of 100% C02 on demand. Two 

1000-W heaters were available per pond to maintain a given minimum temperature for 

experiments performed during the fall and winter. 

We prepared 900 L of media in each of three polyethylene tanks. The tanks were 

mounted at ground level, and media were pumped into the ponds. RTF Saw was the only 

water resource used (see Table A-1). Urea (3.6 mmol), anhydrous dipotassium phosphate 

(0.2 mmol), silica (as needed for diatoms, added at 4.7 mmol, neutralized with HCl on a 

2:1 mo1:mol basis), and chelated iron (0.1 mmol iron sulfate premixed with 2: 1, rno1:mol 

EDTA) were added to the nutrient tanks. Alkalinity was typically 3.5 mmol and derived 

from the water used. 

Daily measurements included minimum and maximum ambient temperatures and insolation (Li-Cor 1776 integrating solar monitor with 200SB pyranometer sensor), minimum/ 

maximum culture temperatures, pH, ash-free biomass density, and culture depth. The pH 

34 
was checked several times each day to see that it was within limits. Cultures were 

diluted continuously 8-14 h/d (depending on temperature and insolation) from MayOctober using Masterflex peristaltic pumps on both the influent and effluent lines. 

Effluents were sampled every hour and composited. The composite samples were kept 

fresh in a refrigerator. Daily productivity was calculated as grams AFDM harvested 

(mass ger liter of the composited samples, multipled by liters harvested) divided by 

2.74 m (pond area). Because of the continuous nature of the dilution, any given productivity that was calculated represented a smoothed average value. During periods of 

potential freezing temperatures, cultures were operated as sequential batches. 

Inoculum was grown indoors in 750-mL and 8-L cultures, incubated at 25O to 30°C at 

pH 7.5, unde? continuous illumination (cool, white fluorescent bulbs) at about 

200 & 20 HE m Is, and at saturating C02 (1.0% in air, injected continuously through glass 

bubblers at a rate of 0.33-0.5 v/v/min. 

We measured AFDM by filtering 5-10 rng of cells (estimated AFDM) on GF/C (Whatman) 

filters, rinsing with 50-100 mL of isotonic NaCl solution, drying at 103OC for 1 h, 

weighing on a five-place electronic balance (Mettler AE240), ashing for 20 min at 550°C, 

weighing again, and using the difference as the dry mass. The drying times were sufficiently long to reach constant weight. 

Heat of combustion was estimated at 6 kcal/g AFDM. Photosynthetic efficiency was 

calculated based on photosynthetically active radiation (using 45% of the cumulated outdoor energy input) and the estimated heat of combustion to convert from mass units to 

thermal units. 

Calibrations of pond areas, pond depth-volume relationships and effluent tank depth- 2 volume relationships were made. The pond area was 2.74 m . Potential shading from 

sidewalls was reduced by minimizing sidewall freeboard (at 15-cm depth, freeboard was 

8 cm) and by orienting the ponds so that the short dimension was in the north-south 

direction. Although this exacerbated sidewall shading in the winter when the sun is in 

the southern sky, pond depth could be raised if the problem was significant (as discussed 

later, temperature was the limiting factor in the winter). Paddle-wheel shading was minimized by building the wheels of clear polycarbonate. No adjustments in the productivity 

were made for any of these potential shading problems. The volume per centimeter of 

pond depth was less at the pond bottom because of the rouding of the bottom-sidewall 

joint and the very slight trapezoidal shape of the ponds. Above the first few centimeters, each pond contained contained 28.5 + 0.5 L/cm. When necessary, the actual 

depth-volume calibration for each pond was used. The effluent tanks were straightwalled cylinders with conical bottoms. Each was independently calibrated for depthvolume. The typical relationship was: volume (L) = 18 + 4.9 x depth (cm). 

5.3 Results 

5.3.1 Overall Results 

Fifteen organisms were inoculated into outdoor cultures. Two species invaded: the 

Amphora sp. that was present during the previous year and a CycZoteZla sp. that was isolated from a bloom in the 0.1-ha raceways. Six of these could be cultured: Chaetoceros 

muelleri CHAET9, Chaetoceros muelleri CHAET63, the indigenous Amphora, the 

indigenous Cyclotetla, T. suecica TETRA 1, and M. minuturn MONOR2. The 10 that could 

not be cultured were Chlorella sp. 12P, Nitzschia sp. NIT2, Chaetoceros muelleri 

CHAET61, Green 7.1, Green 7.2, Nannochloropsis sp. NANNP2, Nannochloris sp. 
NANN02, Cyclotella crypt ica CY CLO 1, Thallasiosira fluviat il is, and Thallasiosira sp. 

THALl. 

Of the unsuccessful cultivation attempts, a few may have been caused by the poor 

quality of the inoculum used. Both Cyclotella cryptica CYCLOl and THALl failed, 

never showing any significant growth. This response was certainly unexpected with 

CYCLOl since it had grown so well last year. Other species did show initial growth, but 

soon became contaminated with the indigenous Amphora and then dominated by 

TETRAI. For instance2NANNP2 grew from 50 to 300 mg/L (with a maximum productivity of 16 g AFDM/m /d) but was lost after successive blooms of the two competitors 

along with other indigenous green algae. The same pattern was observed with NANNOZ. 

The daily insolation for 1988 is shown in Figure 5-1. The ambient and typical pond 

temperatures are shown in Figures 5-2 and 5-3, respectively. The overall productivity 

results for the year are shown in Table 5-1. Two strains were found to be stable during 

the coldest months: M. minutum and T. suecica. Five species performed well during the 

warm season: T. suecica, Cyclotella sp. RTF, Amphora sp. RTF, Chaetoceros muelleri 

CHAET9, and Chaetoceros muelleri CHAET63. All of the results shown in this table are 

from unheated cultures. The weather was quite similar during 1987 and 1988, as was the 

species succession. 

Productivities were very low during the coldest months (December, January, and 

February). Severe conditions of ice or slush in the small ponds every day limited our 

ability to dilute the cultures. Of c rse, growth was very slow anyway. The produc- OY tivities averaged 25 to 30 g AFDM/m /d during the warm months of May, June, July, and 

August. Because of our efforts to screen many species, the most productive organi YS were not cultivated during most of July and August. Yields of about 20 g AFDM/m /d 

were obtained from several strains during the transition months of September and 

October. These months have 10% to 20% less insolation than the months of April and 

March, but are much warmer. We believe the pryuctivities may be improved for the 

months of March and April. If 15-20 g AFDM/m /d were attaine5 during these two 

months as we15 the yearly average would be close to 20 g AFDM/m /d rather than the 

16 g AFDM/m /d achieved in 198% The greater thermal insulation of the large-scale 

raceways compared with the 3-rn raceways will help keep pond temperatures higher 

during the transition months, which may improve yields. 

The results from all the species (in unheated ponds) are shown in Table 5-2 and 

Figures 5-4 through 5-7. As we have seen in previous years, the diatoms were more productive than the green algae. 

3.3.2 Effects of Heating 

Results of experiments with heating as a variable are shown in Table 5-3. As was 

observed last year, heating had little effect on the productivity of the cultures. The 

ponds were only heated during the day, from 0600 (or 0800) to 1300 (or 1600). Thus, the 

minimum and maximum temperatures reached in the heated ponds were about the same 

as those reached in the unheated ponds. Any effects due to low overnight temperatures 

would have been the same in both cases. The conditions, coupled with the generally 

unfavorable growth conditions during the winter, kept all productivities low during this 

time. The heated ponds were more productive, but still productivity was very low (photosynthetically active radiation efficiency was also very low). The major effect of the 

heating was to raise pond temperatures 10°C by 0900-1000 hours during the winter and 

15"-20°C by that time during the spring. Although not much effect was expected during 

the winter, little was seen during April either. However, there were mitigating factors. 



Table 5-1. Monthly Productivity Results from 3-rn2 Algal Cultures 

Insolatifn Ambient Temperature Productivijy Efficiency 

Month (cal/cm id) max (OC) min ("C) (g AFDM/rn /d) (%PAR) Species 

Jan. 

Feb. 

Mar. 

Apr. 

May 

June 

July 

Aug. 

Sept. 

Oct. 

NOV. * 

MONOR2 to 

AMPHO 

AMPHO 

AMPHO 

AMPHO 

CYCLO or 

AMPHO 

AMPHO 

*Half month. 

Note: Standard deviation in ( ). 

For example, one week of dilution of the ponds was lost during April because of the collapse of one of the cultures (a large dose of chlorine was measured in the make-up 

water). In general, the dilution rate may not have been fast enough to attain maximal 

productivities. On the other hand, last year we found that with Me minuturn, responses to 

heating are minimal. This finding was again observed in the May experiments. 

A heating experiment was performed using To suecica TETRA1 during June. Unlike the 

other experiments, this one was conducted sequentially and without replication. However, the average conditions of insolation and ambient temperature were quite uniform 

during this time. For 12 days in early Sune, a culture was heated to 20°C 24 h each 

day. For I1 days during the Iast two weeks of June, the culture was not heated. When 

we compared the results of these experiments, we found that productivity was 
Table 5-2. Productivity of Algal Strains Cultivated in 3-rn2 Ponds (1988) 

Insolat ion Productivi y 1 Efficiency Species Date (cal/crn2/d) (g AFDM/m /dl (%PAR) 

RTF CYCLO 9/27- 1 1 /8 

RTF AMPHO 5/17-713 

8/16-11/16 

TETRA1 5114-1 1/16 

unchanged. The only noticeable difference was that the small amount of contamination 

of these cultures by Amphora was absent in the heated culture. 

5.3.3 Effects of Reduced pC02 

Amphora sp. RTF, 2'. suecica TETRAl, and C. muelleri CHAET9 were grown at several 

pHs to test the effect on productivity of reducing the concentration of CO in the bulk 

liquid. Although the pH had to be raised to accomplish this, we assumed t t at with the 

values that tested higher, pH would not affect productivity (Weissrnan, in press). Three 

pH values were used. At pH 7.2, CO concentration was about 285 pm; at pH 7.8, it was 

75 urn; and at pH 8.3, it was about 28~1-n. Thus, outgassing losses of Cog could be significantly lowered by operating at a higher pH. 

The results of cultivation at different pH values are shown in Table 5-4. Productivity 

was significantly lower in a statistical sense (t test for difference of correlated means, 

data not shown). However, in a practical sense, the 10%-15% lower productivity at higher 

pH is not important. We will continue to study whether the difference r Y ains small 

when such an experiment is performed at productivities above 30 g AFDM/m Id. 

5.3.4 Effect of Rate of Dilution 

T. suecica TETRAl and Amphora RTF were grown in continuous culture with either 35% 

or 50% of the volume diluted per day. As shown in Table 5-5, no significant difference in 

the yield occurred in either case. However, the slower rate of dilution is more stable in 

a climate with variable insolation. The slower rate of dilution allows the pond to 

maintain a standing biomass during cloudy days. 

5.3.5 Growth under Nitrogen or Silicon Deficiency 

A number of experiments were performed to monitor production of biomass and lipids 

under nutrient-deficient conditions. Nutrient-sufficient biomass was taken from continuously diluted cultures, diluted with nitrogen-free or silicon-free growth medium, and 

allowed to grow in batch. Sampling was made daily. The cell density (and thus, time) at 




Table 5-3. Effects of Heating on Algal Productivity in 3-rn2 Ponds 

Temperature Productivity 

Heated Pond Unheated Pond Heated Unhqated 

Month rnax(OC) min(OC) max("C) rnin(OC) (g AFDM/m /d) Species - -pp 

Jan. 21.5 0 7.1 (0 3.05 0 -8 

Feb. 24.6 1.5 9.6 0 3.3 1.95 MONOR2 

Apr . 23.6 5 .7 21.8 4.4 12.6 11.9 MONO 

R2 

May 29,O 12.0 27.1 11.7 25.2 28.3 TETRA 1 

14-23 

June 30.5 19.5 29.7 13.7 24.6 -- TETRA 1 

4-15 

June -- -- 30.3 15*3 -- 25.2 TETRA 1 

15-25 

Table 5-4. Effects of 902 on Productivity 

(g AFDMIm /d) 

Species pcOZ Productivity n 

RTF AMPHO 0.0090 

0.0024 

Note: pCOZ of 0.0090, 0.0024, and 0.0006 correspond to pH 7.2, 7.8, and 8.3, respectively. 

0.01 atm = 320 pm. 

Standard deviation given in ( ). 
Table 5-5. Effects of aflution Rate on Productivity 

(g AFDM/m /d) 

Detention Time 

Species (days) Productivity n 

RTF AMPHO 3 

2 

Note: Standard deviation given in ( ). 

which the cultures reduced intracellular nutrients below levels typical of nutrient sufficiency was estimated from the initial concentration of nutrient (that is, by diluting 

nutrient-sufficient medium plus any additions). Nitrogen sufficiency was assumed to end 

when biomass nitrogen content dropped below 8%, and silicon sufficiency was assumed to 

end when biomass silicon content dropped to 20%. The experiment was terminated when 

calculated intracellular nutrient concentration reached half of its sufficiency value. 

Lipid samples were saved for subsequent analysis at SERI. 

The effect of nutrient deficiency on biomass productivity is shown in Table 5-6 and Figures 5-8 through 5-13. Without the nutrient analyses, it is difficult to determine where 

the optimal stopping point of the induction should be, as well as to what extent the lipid 

productivity increased or decreased. In general, the biomass productivities of the induction batches were less than concurrently operated, nutrient-suf ficient continuous 

cultures, even before the nutrient became limiting. An experiment with T. suecica was 

the only exception perhaps because the cultures were both too dilute for optimal production at the beginning of the batches, and then not adapted to the shade conditions as the 

batches got denser (Weissrnan and Goebel, 1988). Setting the initial conditions of an 

induction batch will prove to be an important controlling factor. For the most part, biomass productivity dropped after nutrient-suf f icient growth turned to nutrient-limiting 

growth. 
Table 5-6. Productivities of Nutrient-s f f icient and deficient 'I Algal Cultures (g AFDM/m- /d) 

N- or Si-sufficient Induction Batch 

Species Continuous Cultures Before Depletion After Depletion Overall 

CHAET63 

Nitrogen 18 9.8 (4)* 13.4 (5-7)** 11.4 

Nitrogen 20 14.2 (3) 1 9.2 (4-6) 12.2 

CHAET9 

Nitrogen 22 

Nitrogen 22 

MONOR2 

Nitrogen 16 

Nitrogen 13 

RTF CYCLO 

Nitrogen 22 

Nitrogen 20 

Silicon 20 

TETRA1 

Nitrogen 26 

Nitrogen 24 

Nitrogen 16 

RTF AMPHO 

Nitrogen 40 

Nitrogen 37 

Nitrogen 27 

Silicon 38 

Silicon 35 -- 

*Number of days of nutrient-sufficient growth. 

**Day of change to nutrient-deficient growth minus last day of experiment 

Note: Biomass is nutrient sufficient until depletion of nutrient from medium. 






6.0 CONCLUSIONS AND FUTURE WORK 

Several important conclusions can be reached based on the data collected. The use of 

equations for uniform flow in open channels in the design of large raceways (Weissrnan 

et al., 1988b) is justified and practical when adjustments are made for head losses not 

associated with channel roughness. For the 0.1-ha raceways, these additional losses were 

just as significant as those due to the pond bottom. Even for larger raceways, the design 

of the slope and the mixing system must be modified to accommodate increased losses 

caused by bends and sumps. From the overall mixing system efficiencies, it is evident 

that before a larger pond system is built, the design-mixing velocity must be specified 

rather closely. Otherwise, power consumed for mixing will be much greater than 

actually needed to satisfy the hydraulic power consumption. In terms of operating large 

raceways, the data indicate that operation will be easier and more economical if the 

design depth is larger than the present operating depth of 14 cm. During most of 1989, 

the operating depth will be increased to 18-20 cm. If lower depths are desired, then 

grading costs will certainly increase greatly for large pond construction. 

The methods used for measuring velocity and power were chosen as a compromise 

between precision and accuracy on the one hand, and cost (both for instruments and time) 

on the other. The methods are adequate, but the degree of error limits the scope of the 

analysis. At present, we do not plan to spend more funds to significantly lower the measurement errors. However, when the next set of measurements are taken, the pond depth 

will be greater. This should improve the precision of all depth measurements and reduce 

the influence of depth variations on velocity and kinetic energy measurements. Thus, 

operation at greater depth will not only improve hydraulics, but also improve hydraulic 

measurements. At that time, we will determine whether to improve the grade of the 

system by filling low spots with sand. This determination will be based on cost, convenience, and whether the increased depth resuits in sufficient improvement in hydraulics. 

The analysis of the carbonation system indicates that although injection efficiency is 

good, averaging above 80% in the tests, it needs to be as hi9 as 90%. Carbon is one of 

the most critical cost centers in the technology. In the 3-m ponds we found that losses 

via outgassing can be kept minimal by operating at pH 8 and above. The impact on biomass productivity appeared to be small. This finding must be confirmed at the highest 

rates of production. The errors in the carbonation sump tests also need to be reduced. 

This will be accomplished by measuring actual total inorganic carbon in the water, rather 

than by estimating it with buffer equations. 

The performance of the 0.1-ha raceways was hampered by start-up problems. Depths 

were too shallow for the uneven grade, leading to excessive in-pond settling of cells; 

operations were interrupted to reexamine some of the engineering measurements; and 

adjustments in baffling were ongoing to improve hydraulics. Some of these problems 

cannot be avoided in a research environment. Improvements need to be tested. However, emphasis will be placed on reducing in-pond settling because its effects on yield are 

serious. 

Annually averaged biomas~yields, estimated on the basis of performance in the 3-m 2 

ponds, were 16 g AFDMJm /d. The months of March and April are being targeted for 

yield improvement. Insolation is high, although temperatures are variably cool. If a 

strain can be found that grows well in the large raceways during these months, in addition to the kind of gr wth achieved during the summer, then productivity average will 9 exceed 20 g AFDM/m /d. We have evidence of much greater yields for very short 

periods. At resent, there is virtually no understanding why yield can be above 9 50 g AFDM/m /d on isolated days. In the future, research needs to be conducted to elucidate the conditions favorable for such high yields. 
7.0 REFERENCES 

Barclay, W.R., K.L. Terry, N.J. Nagle, J.C. Weissman, and R.P. Goebel, 1987, "Potential 

of New Strains of Marine Inland Saline-Adapted Microalgae for Aquaculture," J. World 

Aquaculture Soc., Vol. 18, pp. 218-228. 

Daugherty, R.L., and J.B. Franzini, 1977, Fluid Mechanics with Engineering Applications, 

New York: McGraw-Hill. 

Loewenthal, R.E., and C.V.R. Marais, 1984, Carbonate Chemistry of Aquatic Systems: 

High Salinity Waters, Boston: Butterworths. 

Neenan, B., D. Feinberg, A. Hill, R. McIntosh, and K. Terry, 1986, Fuels from Microalgae: Technology Status, Potential, and Research Requirements, SERllSP-231-2550, 

Golden, CO: Solar Energy Research Institute. 

Stumm, We, and J.J. Morgan, 1980, Aquatic Chemistry, New York: John Wiley & Sons. 

Weissman, J.C., and R.P. Goebel, 1985, Production of Liquid Fuels and Chemicals by 

Microalgae, Final Report, SERI/STR-231-2649, Golden, CO: Solar Energy Research 

Institute. 

Weissman, J.C., and R.P. Goebel, 1987, Design and Analysis of Microalgal Open Pond 

Systems for the Purpose of Producing Fuels, Final Report, SERIISTR-231-2840, Golden, 

CO: Solar Energy Research institute. 

Weissman, J.C., and R.P. Goebel, 1988, Production of Liquid Fuels and Chemicals by 

Microalgae, Final Report, IXK-3-030 135- 1, Golden, CO: Solar Energy Research 

Institute. 

Weissman, J.C., R.P. Goebel, and D.M. Tillett, 1988a, Design and Operation of an Outdoor Microalgae Test Facility, Final Report, Subcontract XK- 1-06 1 1 3- 1, Golden, CO: 

Solar Energy Research Institute. 

Weissman, J.C., R.P. Goebel, and J.R. Benemann, 1988b, "Photobioreactor Design: 

Mixing, Carbon Utilization, and Oxygen Accumulat ion," Biotechnol. Bioeng., Vo1. 3 1, 

pp. 336-344. 
corm Nc. 0069 (3-25-82) 

- -.... 3 Rec~plent's Access~orl No ' Document Control 1 sER~ Separt No 2. NTlS Access~on No 

Page . 

4 Title and Subtltle 

Design and Operation of an Outdoor Microalgae Test 

_ SERIISTR-231-3569 

5. Publ~catton Dare 

October 1989 

DE89009493 

Facility, Final Subcontract Report 6. 

7. Author(s) 8. Perform~ng Organ~zat~on Rept. No. 

J.C. Weissman, D.M. Tillet, R.P. Goebel 

9. Performing Organtzatlon Name and Address 

Microbial Products, Inc . Vacafille, California 95688 

12. Sponsor~ng Organizat~on Name and Address 

Solar Energy Research Ins ti tut e 

1617 Cole Boulevard 

Golden, Colorado 80401-3393 

r 

10. Project/Task/Work Unrt No. 

L 

11. Contract (C) or Grant (G) No. 

(C) XK-7-06113-1 

(GI 

13. Type of Repon & Period Covered 

Technical Report 

14. 

15. Supplementary Notes 

SERI Technical Monitor: W. Bollmeier (303) 231-1450 I 

16. Abstract (Lim~t: 200 words) 

The objective of the project covered in this report is to establish and operate 

a facility in the American Southwest to test the concept of producing microalgae 

on a large scale. This microalgae would then be used as a feedstock for producing liquid fuels. The site chosen for this project was an existing water 

research station in Roswell, New Mexico; the climate and water resources are 

representative of those in the Southwest. For this project, researchers tested 

specific designs, modes of operation, and strains of microalgae; proposed and 

evaluated modifications to technological concepts; and assessed the progress 

toward meeting cost objectives. 

17 Document Anaiysls 

a. Descriptors Microalgae ; outdoor test facility ; liquid fuels ; mass culture 

b. Ident~fiersiOpen-Ended Terms 

c. UC Categories 2 7 1 

18. Avallabllrty Statement 

National Technical Information Service 

U.S. Department of Commerce 

19. No. of Pages 

67 

5285 Port Royal Road 

Springfield, Virginia 22161 20. Pr~ce 

A04