R-98-05

The Desalting and Water Treatment

Membrane Manual: A Guide to Membranes

for Municipal Water Treatment (2nd Edition)

Water Treatment Technology Program Report No. 29

BY

Michelle Chapman Wilbert

Frank Leib

Ellen Abart

Bill Boegli

Kim Linton

Technical Service Center

Water Treatment Engineering and Research

Denver, Colorado

UNITED STATES DEPARTMENT OF INTERIOR * BUREAU OF RECLAMATION
ACKNOWLEDGMENTS

I would like to thank Susan Martella for her help in putting this work all together, Bob

Rodriguez and Scott Irvine for their help in contacting manufacturers, and Robert Rood,

Mary Voita, and staff for their presentation expertise. The manufacturers who sent in data on

their products are to be commended for their far sightedness. Above all, I thank my husband,

Ken Wilbert, for his support and encouragement when blank screen looked good enough.

ii
U.S. Department of Interior Mission Statement

The mission of the Department of the Interior is to protect and provide access to our Nation’s

natural and cultural heritage and honor our trust responsibilities to tribes.

Bureau of Reclamation Mission and Vision Statement

The mission of the Bureau of Reclamation is to manage, develop, and protect water and

related resources in an environmentally and economically sound manner in the interest of the

American public.

Through leadership, use of technical expertise, efficient operations, responsive customer

service and the creativity of people, Reclamation will seek to protect local economies and

preserve natural resources and ecosystems through the effective use of water.

Disclaimer

Information contained in this report regarding commercial products or firms was supplied by those firms. It

may not be used for advertising or promotional purposes and is not to be construed as an endorsement of any

product or fum by the Bureau of Reclamation.

The information contained in this report was developed for Reclamation: no warranty as to the accuracy,

usefulness, or completeness is expressed or implied.

.-.

111
From

SI Metric Conversions

To

fl

i n

ft2

kgal (U.S.)

Mgal (U.S.)

acre-ft

lb/in2 (psi)

“F

m

m

m2

m3

m3

m3

kPa

“C

Multiply by

‘0.3048

‘0.0254

‘0.09290304

3.785 412

3,785.412

1,233.489

6.894 757

’ “C=(’ F-32)/1.8

’ Exact conversion.

iv
CONTENTS

Page

Chapter 1 Introduction ................................................... 1.5

1.1 Recent Developments in the Membrane Industry ......................... 1.5

1.1.1 Wider Application ........................................ 1.5

1.1.2 Systems Integration ....................................... 1.5

1.1.3 Selection Criteria ......................................... 1.6

1.1.4 Module Integrity .......................................... 1.6

1.2 Basics of Membrane Technology ..................................... 1.7

1.2.1 What is a Membrane? ..................................... 1.7

1.2.2 Sieving ................................................. 1.8

1.2.3 The Solution Diffusion Model (briefly) ........................ 1.8

1.2.4 Pore Flow Model (even more briefly) ........................ 1.10

1.2.5 Basic System Design ..................................... 1.10

1.2.6 Membrane Configurations ................................. 1.10

1.2.7 Dead-End, Cross flow, and Transverse Flow Operation ......... 1.14

1.3 About This Book ................................................. 1.16

Chapter 2 Microfiltration

2.1 Definition ....................................................... 2.1

2.2 Background ...................................................... 2.2

2.3 Microfiltration Membranes .......................................... 2.2

2.4 Microfiltration Systems ............................................ 2.3

2.5 Operating Plants .................................................. 2.4

2.6 Demonstration or Pilot Plants ........................................ 2.6

2.7 Potential Projects ................................................. 2.7

2.8 Research and Development Efforts ................................... 2.8

Chapter 3 Ultrafiltration

3.1 Basics of Ultrafiltration ............................................ 3.1

3.2 Membrane Characterization ......................................... 3.1

3.2.1 Molecular Mass Cutoff .................................... 3.2

3.2.2 Clean Water Permeability .................................. 3.3

3.3 Process Design Considerations ...................................... 3.5

3.4 Process Instrumentation and Evaluation ............................... 3.6

3.5 Integrity Testing Methods .......................................... 3.12

3.6 Concentrate Issues ............................................... 3.14

3.7 UF Case Studies ................................................. 3.14

3.7.1 Removing TOC and Color ................................. 3.14

3.7.2 Enhancing UF Organic Removal With PAC ................... 3.16

3.7.3 Testing UF as Pretreatment for RO .......................... 3.16

3.8 Conclusions and Research Needs .................................... 3.18

V
Page

Chapter 4 Nanofiltration and Reverse

4.1 Process Fundamentals .............................................. 4.1

4.2 Module Configuration ............................................. 4.4

4.3 Pretreatment ..................................................... 4.4

4.4 Monitoring Performance ............................................ 4.6

4.4.1 Effect of Operation Parameters on Performance ................. 4.8

4.5 Post-treatment ................................................... 4.12

4.6 Applications .................................................... 4.12

4.7 NForRO? ..................................................... 4.16

4.7.1 ROandNFCostComparison .............................. 4.18

4.8 ResearchNeeds inNF and RO ...................................... 4.22

Chapter 5 Electrodialysis

5.1 Definition ....................................................... 5.1

5.2 Background...............-.~ .................................... 5.1

5.3 Membranes ...................................................... 5.1

5.4 Membrane Properties .............................................. 5.4

5.5 Electrodialysis Process ............................................. 5.5

5.6 Electrodialysis Apparatus ........................................... 5.8

5.7 Electrodialysis Operation .......................................... 5.10

5.8 Electrodialysis Applications ........................................ 5.10

5.9 Electrodialysis Economics ......................................... 5.11

Chapter 6 Pretreatment Processes

6.1 Particulates ...................................................... 6.1

6.2 Colloidal Fouling ................................................. 6.1

6.2.1 Avoidance .............................................. 6.2

6.2.2 Flocculation, Settling, and Filtration .......................... 6.2

6.2.3 Diatomaceous Earth Filtration ............................... 6.2

6.2.4 Ultrafiltration ............................................ 6.2

6.3 Iron andManganese ............................................... 6.3

6.3.1 Oxidation/Filtration ....................................... 6.3

6.3.2 Iron Removal With Lime Softening ........................... 6.3

6.3.3 Biological Removal ....................................... 6.3

6.3.4 Oxidation Of Manganese With MnO, ......................... 6.4

6.3.5 Biological Manganese Removal ............................. 6.4

6.4 Scaling ......................................................... 6.4

6.4.1 Acidification ............................................ 6.5

6.4.2 Lime Softening ........................................... 6.5

6.4.3 IonExchange ............................................ 6.6

6.4.4 Nanofiltration ............................................ 6.6

vi
Page

6.5 Biological Matter ................................................. 6.7

6.5.1 Oxidation ............................................... 6.7

65.2 MediaFiltration .......................................... 6.7

6.5.3 Ultrafiltration ............................................ 6.8

6.6 Deoxidation ..................................................... 6.9

6.7 Organic Compounds ............................................... 6.9

6.7.1 GranularActivatedCarbon ................................ 6.10

6.7.2 Air Stripping ........................................... 6.10

Chapter 7 Waste Disposal

7.1 Surface Water Body ............................................... 7.4

7.2 Wastewater Treatment Plant (WWTP) ................................. 7.6

7.3 Land Application ................................................. 7.7

7.4 Injection Wells ................................................... 7.9

7.5 Evaporation Ponds ................................................ 7.9

7.6 SolarPonds ..................................................... 7.10

Chapter 8 Cleaning and Storage

8.1 Cleaning Procedures ............................................... 8.1

8.1.1 Cleaning Regimes ........................................ 8.1

8.1.2 Equipment .............................................. 8.2

8.1.3 Generic Cleaning Process .................................. 8.2

8.1.4 WhichCleaning? ......................................... 8.6

8.1.5 PassiveCleaning ......................................... 8.8

8.2 Membrane Storage ................................................ 8.8

Chapter 9 Process Design

9.1 Introduction.........................................~............ 9.1

9.2 Solvent Flux Models ............................................... 9.1

9.2.1 Reverse Osmosis ......................................... 9.3

9.2.2 Nanofiltration, Ultrafiltration, and Microfiltration ............... 9.3

9.2.3 Estimation of Permeability Parameters ........................ 9.4

9.2.4 Estimation of Osmotic Pressure .............................. 9.5

9.2.5 Module Mass Balance ..................................... 9.6

9.2.6 Sample Design Problem ................................... 9.11

9.3 Membrane System Design ......................................... 9.13

9.3.1 System Equations ........................................ 9.17

9.3.2 Element-By-Element Analysis .............................. 9.19

9.3.3 Manufacturers’ Computer Programs ......................... 9.24

Chapter 10 Product Review

10.1 Product Listings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1

10.2 What Does It All Mean? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.21

vii
Page

10.2-l Water and Salt Transport Coefficients Versus Rejection

andProductivity ........................................... 10.21

10.2.2 Does Operating Pressure Make a Real Difference? ............ 10.24

10.2.3 Does Increasing Membrane Area per Module Improve

Productivity? .............................................. 10.25

10.2.4 Are Longer Modules Better? ............................. 10.25

10.2.6 Conclusions .......................................... 10.27

Chapter 11 Estimating the Cost of Membrane Treatment

11.1 Predicting Product and Concentrate Composition and Volume ........... 11.1

11.2 Estimating Membrane Cost Factors ................................. 11.3

11.2.1 MembraneArea ........................................ 11.3

11.2.2 Operating Pressure ...................................... 11.4

11.2.3 Pump Horsepower ...................................... 11.4

11.2.4 NumberofSkids ....................................... 11.5

11.2.5 ChemicalFeedRates .................................... 11.5

11.3 Calculating Costs ............................................... 11.7

11.4 Ultrafiltration Costs ............................................ 11.11

11.5 MicrofiltrationCosts.. .......................................... 11.11

11.6 Conclusions .................................................. 11.12

Chapter 12 Perspectives on Future Opportunities

12.1 Microfiltration .................................................. 12.3

12.2 Ultrafiltration .................................................. 12.3

12.3 NFandRO .................................................... 12.4

12.4 The Next Generation ............................................. 12.5

References............................................................. 13.1

References for Further Information . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.1

AppendixA............................................................ 15.1

f..

Vlll
Table

Tables

Page

1.1

1.2

2.1

2.2

2.3

3.1

3.2

3.3

3.4

4.1

4.2

4.3.

4.4

4.5

6.1

6.2

7.1

7.2

7.3

7.4

8.1

8.2

8.3

8.4

9.1

9.2

9.3.

9.4

9.5

10.1

10.2

10.3

10.4

10.5

10.6

10.7

11.1

Conventional and membrane process solutions to common water problems ... 1.2

Characteristics of the major types of water treatment membranes ............ 1.3

Characteristics of commercial microfiltration equipment .................. 2.3

Manufacturer’s estimate of system costs for units about 1 million gallons

perdaycapacity ................................................. 2.4

MF plants and plant expansions proposed for the near future ............... 2.8

UF instrumentation requirements .................................... 3.10

UF performance evaluation parameters used in recent case studies ......... 3.10

Integrity testing and monitoring techniques for UF membrane ............. 3.13

Treatment alternatives for Cheyenne, Wyoming ........................ 3.15

Typical NF and RO performance specifications ......................... 4.7

Troubleshooting guide for NF and RO systems .......................... 4.9

RO and NF applications ........................................... 4.13

Capacities and number of systems ................................... 4.14

Membrane characteristics used in treatment option comparison ............ 4.18

Qualities of oxidants for drinking water disinfection ..................... 6.8

Processes for removing organic compounds ........................... 6.10

Regulatory program authority by state as of January 1993 ................. 7.3

SDWA regulated contaminants (1997) ................................ 7.5

TDS threshold levels in applied irrigation water ......................... 7.7

Recommended maximum trace element levels in irrigation water ........... 7.8

Two tiered classification of membrane cleaning regimes .................. 8.1

Maximum pH/temperature limits for Filmtec BW-30 membrane ............ 8.4

Recommended feed flow rate per pressure vessel during cleaning ........... 8.6

Foulant characterization based on chemical composition .................. 8.7

Data for determining the relationship between osmotic pressure

andconcentration .............................................. 9.12

Sample spreadsheet for estimating spiral wound RO module

designperformance.. ........................................... 9.14

Sample spreadsheet for an element-by-element analysis .................. 9.20

Sample printout of a FilmTec RO system analysis using ROSA

Version 3.05d software .......................................... 9.24

Comparison of results from FilmTec’s ROSA program and the element-byelement spreadsheet analysis ...................................... 9.26

Membrane manufacturers .......................................... lo.3

Seawater membranes ............................................. 10.5

Brackish water membranes ........................................ 10.7

Nanofiltration membranes ........................................ 10.13

Ultrafilitration membranes ........................................ 10.15

Microfiltration membranes ........................................ 10.19

Change in performance statistics with operating pressure ................ 10.24

Direct construction costs ........................................... 11.7

ix
Table Page

11.2 Indirect construction costs ......................................... 11.8

11.3 Operation and maintenance costs .................................... 11.8

11.4 Assumptions used in comparing membrane treatment costs .............. 11.10

Figures

Figure Page

1.1

1.2

1.3a

1.3b

1.4

2.1

2.2

3.1

3.2

3.3

3.4a

3.4b

3.4c

3.5

4.1

4.2

4.3

4.4

4.5

4.4

4.7

4.8

7.1

7.2

7.3

8.1

9.1

Models for various types of membrane separation ....................... 1.5

General design of a membrane system ................................. 1.7

General membrane configurations .................................... 1.8

Generalized membrane configurations ................................. 1.9

Dead-end, cross flow, and transverse flow ............................ 1.11

Comparison of size range of various materials .............................

Alternatives for the Saratoga Water Treatment Plant ..................... 2.5

Comparison of molecular mass and retention rates for membranes with

narrow and wide pore size distributions .............................. 3.3

Difference in retention between clean and fouled UF membrane ............ 3.4

Comparison between membrane productivity for seawater and brackish

water RO, UF, and MF membrane as tested by the manufacturers.. ......... 3.5

Concentrate recycle operation with product backwash .................... 3.7

Batch operation with product backwash ............................... 3 8

Stages in series. Each stage flow and TMP are controlled separately ......... 3.9

Schematic for a Floe Blanket Reactor-UF system for removal of

organic contaminants ........................................... 3.17

Osmosis and reverse osmosis ........................................ 4.2

(A) Spiral wound membrane systems require 2 stages of 6 element pressure

vessels to attain a 75 percent recovery rate. (B) Hollow fine fiber systems

are designed with 1 element per vessel and only 1 vessel per series. With

this 1 stage configuration they are capable of a 50 percent recovery ........ 4.5

The effects of applied pressure, feed temperature, and water recovery on

membrane flux and product water quality of RO membranes ............ 4.10

Distribution of membrane applications. ............................... 4.15

Comparison of cost statistics for various membrane options ............... 4.17

Costs for plants to produce 500 mg/L TDS drinking water including

blendwater ................................................... 4.19

Costs for plants to produce 7569 m3/day including blend water ............ 4.20

Costs for plants to produce 7569 m3/day including blend water ............ 4.2 1

Typical municipal and industrial injection well construction .............. 7.10

Crosssectionofasolarpond ....................................... 7.11

Solar pond heat transfer for power generation .......................... 7.12

State-of-the-art cleaning system ...................................... 8.3

Schematic of pressure-driven membrane processes ....................... 9.2

X
Figure Page

9.2

9.3

9.4

9.5

9.6

10.1

10.2

10.3

10.4

10.5

11.1

11.2

11.3

11.4

Variables for module mass balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.7

Iterative solution for water permeation rate, Jv, every iteration has more

accurate estimates of recovery rate, product, and wall concentration . . . . . . . 9.15

Oscillation of recovery rate and the apparent rejection rate as the solution

becomes more accurate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.15

Diagram of a two-stage membrane system . . . . . . . . . . . . . . . . . . . _ . . . . . . . . 9.16

Generalized process diagram of the 4 lead elements of 1 st stage . . . . . . . . . . . 9.18

Relation between salt and water transport coefficients for seawater, brackish

water RO and NF membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.22

Close up of relationship between sea and brackish water RO membrane

transport coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . - . . . . . . . . . . . . . . . . 10.23

No relationship between rejection rate and productivity per unit area . . . . . . . 10.23

Effect of increased module area on module efficiency per m2 added area,

water (A) and salt (B) transport coefficients. . . . . . . . . . . . . _ . . . . . . . . . . . 10.26

Change in performance with longer modules . . . . . . . . . . . . . . . . . . . . . . . . . 10.28

Optimizing pump cost and the number of skids for a range of flow rates . . . . . 11.6

Membrane system costs with increasing capacity . . . . . . . . . . . . . . . . . . . . . . . 11.9

Membrane system costs with increasing TDS . . . . . . . . _ . . . . . . . . . . . . . . . . . 11.9

Effect of skid size on construction and O&M costs for a system to

produce 1,200 m3/day . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . 11.10

xi
Chapter 1

INTRODUCTION

1.1 Recent Developments in the Membrane Industry

Since the first Desalting and Water Treatment Membrane Manual was written in 1992, there

have been significant advancements in the development of membrane technology. Every

aspect of the technology has changed except, of course, for the basic principles of membrane

separations. There are now more manufacturers producing many more types of membrane

out of different materials, in different configurations. The latest catalogs feature modules

with greater membrane area, and modules that are 40 or 60 inches long. Many manufacturers

now have a product line with a range of productivity and rejection characteristics. Manufacturers of ceramic and stainless steel membranes, that were priced for high dollar, low

quantity separations in the early ‘9Os, are now trying to lower their costs to attract large-scale

applications. Microfiltration (MF) and ultrafiltration (UF) have also been reclaimed from the

dairy and paint industries and have taken their places in water treatment plants all over the

world.

1.1.1 Wider Application

While in the early 1990s most water treatment membrane applications were for brackish

water treatment, there are now more sites where membranes are being used or considered for

removing specific contaminants such as manganese, radium, fluoride, nitrate, or color. This

change in applications is a sign that communities are beginning to think more about their

“bang for the buck.” If one must spend $2 million to remove 0.5 mg& of manganese with a

greensand filter and still end up with poor tasting water, or $3 million to produce good tasting

water, which process should be endorsed? Communities striving to attract development

should be considering the latter.

Table 1 .l lists several undesirable water contaminants, the conventional solutions for them,

and corresponding membrane processes that can do the job. There are many variations on

these conventional processes that could be included, but the ones listed are sufficient to

illustrate that there is a membrane process alternative available to address most drinking

water problems.

1.1.2 Systems Integration

At the 1997 American Water Works Association (AWWA) Membrane Technology

Conference it seemed the question of conventional verses membrane treatment had been

settled. Presentations there were concerned with,which membrane process to use with which

membrane, under what conditions, and in what order. There was a session on Integrated

1.1
Table 1 .l .-Conventional and membrane process solutions to common water problems

Constituent of concern

Turbidity

Suspended solids

Biological contamination

Conventional process

Coagulation/flocculation

Media filtration

Disinfection

Color Activated carbon

Odor Cl, + media filtration

Volatile organics aeration

Hardness

Sulfates

Manganese

Iron

Heavy metals

Lime softening

ion exchange

Oxidation, filtration

Ion exchange

Coagulation/flocculation

Total dissolved solids

Nitrate

Distillation

Ion exchange

Membrane process

Microfiltration

Ultrafiltration

Nanofiltration

Reverse osmosis

Electrodialysis

Membrane Systems with studies on whether MF or UF should serve as pretreatment for

reverse osmosis (RO) or nanofiltration (NF) for treating surface water. Membrane

optimization was discussed in several of the sessions. Should the productivity of each stage

be balanced or not? Does it make a difference if recovery is increased by adding membrane

area, recirculating concentrate, or by lowering feed flow?

1.13 Selection Criteria

There were quite a few papers on membrane selection studies. Most compared all the

membranes at one permeation rate. Is this valid? In one of our screening tests, we tested

each membrane according to its manufacturers suggested operating pressure and feed flow

(Boegli, Chapman Wilbert, 1997). How should membranes from different manufacturers be

compared in a screening test? Should they be compared at the same pressure or the same

permeation rate? Or should the optimum performance for each membrane be found through

experimentation and then compared on that basis?

1.1.4 Module Integrity

Module integrity is another area of present concern. Communities would like to use their

membrane systems to ensure protection against viral and bacterial contamination. If a

membrane rejects salt, one would hope that it would also exclude viruses and bacteria, but

does it? Test data are discouraging on that point. During a pilot study in Avondale, Arizona,

1.2
bacteria were found in NF permeate when there was a high bacteria count in the feed water

(Jurenka, Chapman Wilbert, 1996). Another study of virus removal efficiency of MF, UF,

and RO found that RO could effect a 3-4.8 log removal while UF effected greater than

5.4 log removal (Kruithof, et al., 1997).

1.2 Basics of Membrane Technology

1.2.1 What is a Membrane?

A membrane is a film. A semi-permeable membrane is a very thin film that allows some

types of matter to pass through while leaving others behind. Some membranes are porous

and separate materials based on size compared to the size of the pores. Others are dense

films with no apparent pores that separate matter based on differences in diffusion rates

through the membrane.

Membranes are divided into indistinct classes based on the size of the materials they retain.

Table 1.2 gives an overview of the various types. MF membrane is very porous; it allows

water, dissolved salts, colloidal materials, and particles that are smaller than the pores to pass

through. On the other end of the spectrum, RO membrane is a dense film with no pores, only

spaces in its polymeric structure that are large enough to allow water and other small,

uncharged molecules to pass through.

Table 1.2.-Characteristics of the major types of water treatment membranes

ED MF UF NF R O

Materials

retained

Materials

transported

Water’

permeation

(m3m-‘d’)

Water,

microorganisms,

uncharged

molecules,

suspended

solids

Dissolved

salts

Practically

none

Particles

larger than

pore size

Dissolved

salts, small

particles

‘800 - 4,000

Molecules

larger than

the

molecular

mass cutoff

Small

molecules

and ions

0.4 - 2.5

>95% of

multi-valent

ions, 25-90%

of monovalent ions,

molecules

and particles

over 300

Daltons

Mono-valent

ions and

very small

molecules.

1 .o

>95% of all

ions, most

molecules

and particles

over 200

Very small

uncharged

molecules

0.8

’ Pure water at normal operating pressure. Actual values are extremely condition dependent.

* Depending on micron rating.

1.3
There are three primary mechanisms for the separation and transport of water and solutes

across a membrane: sieving, convection, and solution diffusion. Sieving in membranes is

the same as sifting sand and stones through a wire mesh. Molecules or particles that are

larger than the membrane pores are retained within the membrane if it is a cartridge type filter

or in the concentrate stream if it is a cross flow design. Convection is the mechanism

whereby solute is carried through the membrane with the solvent. Diffusion is the transport

of solute through the membrane once it has dissolved into the membrane polymer. The

concentration gradient across the membrane drives the diffusion of solute to the low concentration side (Allgeier and Summers, 1995). Figure 1.1 illustrates the differences in these

mechanisms and their controlling factors.

1.2.2 Sieving

The pore size distribution of the membrane and the particle shape and size distribution of the

solution are the important factors in the sieving mechanism of solute rejection. See the

chapter on MF for a more detailed discussion.

1.2.3 The Solution Diffusion Model (briefly)

There are three important aspects of a membrane that control the solution diffusion process

and, thus, the membranes performance:

1. The solubility and diffusion rate of the solvent in the membrane (in this case, water),

2 . The solubility and diffusion rate of the solute in the membrane (in this case, salts or

other impurities of water), and

3 . The thickness of the membrane

In the solution-diffusion model, material dissolves in the membrane and then diffixses to the

other side down a concentration gradient (see Wijmans, Baker, 1995 for more detailed

discussion and further references). In this way, the permeation of a component “l”of the

solution is described:

Ji =

Di(ciu(t7z) -ci~(tn$

I

Eq. 1.1

Where Di is the diffusion coefficient made up of the solubility of component 7” in the

membrane and the diffusivity of ‘7” through the membrane. The term in parentheses is the

difference in concentration across the membrane, and I is the thickness of the membrane. To

have a high water permeation rate, the membrane should be able to absorb water, move it

through quickly, and be very thin. Yet, the membrane must also have a low salt permeation

rate. Since the water is pouring through our “perfect” membrane, the salt concentration

1.4
(A) Sieving

D is very high for water and low

for salt in a good membrane.

(B) Solution Diffusion

Particles and salts

4

l

1 4

( C ) Pore Flow Model.

P

Figure 1 .l .-Models for various types of membrane separation.
gradient and thickness are helping to enhance salt permeation. The diffusion coefficient must

come to the rescue. If our membrane has a minuscule salt diffusion rate, we will still have a

perfect membrane.

1.2.4 Pore Flow Model (even more briefly)

Permeation through membranes that do have pores is described by the pore flow model

which looks similar to the solution diffusion model but is completely different.

J = kAp

1

I

Eq. 1.2

Where J, is the permeation of component “i,” k is the Darcy’s Law coefficient that has to do

with the number of pores large enough to accommodate “i,” Ap is the difference in pressure

across the membrane, and “l” is the membrane thickness.

1.2.5 Basic System Design

Each membrane process has three process streams: the feed stream, that may have undergone

some type of pretreatment; the product stream; and a concentrate stream. Using the term

“stream” is convenient, but in some applications the concentrate is actually a solid, such as in

some dairy applications and in sludge de-watering. Figure 1.2 illustrates the general design

of a membrane system. The feed stream is exposed to the semi-permeable membrane which,

under the influence of the appropriate driving force, separates the product from the

concentrate.

1.2.6 Membrane Configurations

Membranes can be made from many different materials and can be formed into a wide variety

of configurations. The most common are depth filters, plate and f&me, spiral wound,

pleated, tubular, and hollow fiber. Figures 1.3a and 1.3b show the differences between the

various configurations. No configuration is better under all circumstances; there are

advantages and disadvantages inherent in each of them. One must select the best for a

particular situation.

l Depth filters are used in MF to trap coarser particles. They are dense, thick walled

cylinders made fi-om spun polymer strands. They are formed such that the outside

has a more open structure than the inside so that as water passes from the outside in,

larger particles are trapped first.

1.6
Pretreated

Water

Cartridge Filter

F = Flow meter

P = Pressure

C = Conductivity

Cl = Chlorine

pli = pH meter

Pump Pr&ct

cF>C

F

Figure 1.2.-General design of a membrane system.
Feed in Vexar spacer

~ Product to promote turbulence

n, 1) /----XI Two halves of a

Depth Filter Retezate ~

, Membrane

Product water

carrier

\

Feed

Direction of flow

is reversed in

the next frame

Met Inlet

Product, two membrane sheets

are bound to

carrier sheet%

ether with a product

etween them Plate and Frame Product collected *

from bottom

Figure 1.3a.-General membrane configurations.
Feed + Product

RetfLate

Pleated Membrane Cartridge

Membrane Tubes or Hollow Fibers

Retentate

.Membrane

Support material

Permeate tube

Vessel wall

Cross section

Product

Feed water flows through the inside of the tube,

product water permeates through the membrane,

and the retentate exits through the other end

Tubular or Hollow Fiber Module

Figure 1.3b.-Generalized membrane configurations.
l Plate and frame configurations are used in electrodialysis and in high solids content

micro- and ultra-filtration because the units can be taken apart and cleaned very

thoroughly.

l The spiral wound configuration, which is used in the whole range of filtration

processes, provides a greater surface area per module than pleated or tubular

configurations in the same processes, but is much more difficult to clean.

l Pleated membrane cartridges are a cross between a solid depth filter and a spiral

wound membrane. The thinner, pleated, membrane material allows higher flux rates

than a depth filter. Because the membrane is supported on both sides, back-flushing

can be used to help extend membrane life.

l The hollow fiber configuration, used in RO and NF, has the highest surface area to

volume ratio attainable, but requires a higher level of pretreatment than the other

configurations.

l Tubular configurations can be used for MF, UF, and sometimes NF membranes.

They are easy to clean but have a low surface area to volume ratio. Tubular

configurations are used for high flow/high solids content feed streams.

l A more recent configuration, called transverse-flow tubular, uses small diameter

tubular membrane with the tube ends potted into the sides of the cylindrical vessels

to form a pattern like the webbing of a tennis racket. The feed water flows at a right

angle, or transverse, to the tubes. Product water permeates to the inside of the tubes

and is collected outside the vessel. The advantage of this configuration is that the

tubes are flexible enough to vibrate as the water flows over them. The motion and

flow pattern helps to wash foulants from the membrane surface.

l Another variation on the tubular membrane configuration has the membrane strands

submerged in the source water. Rather than pumping water into the filter, the filtrate

is pumped out of the source Corn the interior of the tubular membranes under a

vacuum. If you imagine sucking on a foam straw that is blocked off at the end, you

will see just how this system works. Blasts of air can be used to vibrate the tubes

periodically to prevent build up on the outside of the tubes.

1.2.7 Dead-End, Cross flow, and Transverse Flow Operation

Dead-end, cross flow, and transverse flow operation refer to the direction of flow across the

membrane. Figure 1.4 diagrams the differences between them. In dead-end filtration, there

is no liquid waste stream; all feed water passes through the membrane. Over time, particles

build up in the membrane structure or on the surface, limiting water passage. As the filter

cake accumulates, the AP builds until the maximum is reached, and then the membrane must

be replaced or cleaned.

1.10
Dead end flow: All

water passes through the

membrane, particles are

trapped within the

membrane structure.

Cross flow: Feed water

passes parallel to the

membrane surface,

product water permeates

through the membrane,

the concentrated stream

helps carry particles out

of the system.

Transverse flow: Feed

water meets the

membrane surface at

right angles, product

water permeates through

to the inside of the tube,

concentrate washes over

the outside of the tube

removing particle buildup.

Figure 1.4.~Dead-end, cross flow, and transverse flow.
In cross flow operation, the feed stream flows parallel to the membrane surface, limiting filter

cake thickness and density. A part of the stream permeates through the membrane, leaving a

zone of high particle concentration at the surface. Particles and/or solutes are drawn back

into the bulk feed stream by the flow of lower concentration water past the surface.

Transverse flow operation is used with tubular membranes configured such that the feed

stream flows past them at right angles. The product stream permeates to the interior of the

tubes. The higher turbulence across the membrane in this configuration enhances filter cake

disruption and thereby maintains a higher productivity rate than cross flow or dead-end

filtration operated under equivalent conditions.

1.3 About This Book

Answers to the questions raised in section 1.2 need to be found in the next few years if

membrane technology is to reach its full potential. They will be explored more fully in the

following chapters on each form of membrane filtration. A brief review of each process is

presented with a discussion of their similarities and differences, main operational

parameters, and most important aspects to consider in choosing a membrane for your

particular application. Examples of novel uses and methods of process optimization are

discussed. Since specific cleaning procedures are required to satisfy warranty conditions for

each manufacturer, the chapter on cleaning will provide a basic discussion of cleaning

philosophy rather than a reproduction of cleaning recommendations. The process design

section describes simple methods for designing membrane systems, determining membrane

area, and predicting performance. Cost and concentrate disposal options are covered in

chapters 8 and 9. The product listing has been updated with performance statistics calculated

from the manufacturers test data in chapter 10. An analysis is included to help determine the

functional differences between the new module configurations.

1.12
Chapter 2

MICROFILTRATION

Microfiltration as a process has received considerable attention in the United States in recent

years. Much of this has been under the impetus of legislation which has increased the

requirements on drinking water. In addition, improved methods of removing the fouling

layer from microfiltration membranes have considerably improved the economics of the

process. Highly varied equipment is available commercially. Existing microfiltration plants

are now providing operating experience. And a number of demonstration or pilot plants are

being used to provide comparison to alternative processes and to generate design data.

Research on a number of different applications relating to drinking water, including

pretreatment for desalting plants and watershed protection, is being carried out.

2.1 Definition

When we speak of microfiltration, we are talking about filtration through a coherent medium

with a nominal pore size range from slightly below 0.1 pm to slightly above 1 pm. This size

range refers to the pore size of the medium itself, not to that of any cake or fouling layer

which may accumulate on the medium. Thus, in terms of pore size, microfiltration fills in the

gap between ultrafiltration and granular media filtration. In terms of characteristic particle

size, this range covers the lower portion of the conventional clays and the upper half of the

range for hurnic acids. This is smaller than the size range for bacteria, algae and cysts, and

larger than that of viruses. Sizes of various materials of concern are shown in figure 2.1.

SIZE 0.001 pm 0.01 p O.lpm l.Opm 1ocnn loom 1OQOWJ

5i2EET

I I

MCROFlLTRA77ON

SUSPENDED

RAtE OF HUM/C ACIDS

ORGANIC AND

BIOLOGICAL

MAERIALS

Figure 2.1 .-Comparison of size range of various materials.

2.1
Over the years, a number of industrial applications have developed for microfiltration.

However, this paper covers only drinking water applications. The field of drinking water

supplies both a blessing and a curse to any treatment process. The blessing is that the

potential market is both volumetrically huge and worldwide. The curse is that the process

must be inexpensive.

2.2 Background

One of the principal reasons behind the considerable interest in microfiltration in the United

States has been recent regulations concerning drinking water. The 1986 Safe Drinking Water

Act Amendments required new drinking water regulations and treatment requirements. The

Surface Water Treatment Rule requires that disinfection or a combination of filtration and

disinfection be employed to achieve 99.99 percent (4 log) removal of viruses and 99.9 percent (3 log) removal or deactivation of Giardia cysts. Turbidity standards require that 95 percent of the water samples collected each month have a turbidity of less than 0.5 NTU

(Nephelometric Turbidity Units) and that filtered water turbidity never exceed 5.0 NTU. In

addition, the Disinfection Byproduct Rule targets trihalomethanes and haloacetic acids.

Interestingly, in the EPA (Environmental Protection Agency) manuals on Microorganism

Removal for Small Water Systems (SME-Martin Inc. Microorganism..., 1983) and Turbidity

Removal for Small Public Water Systems (SME-Martin Inc. Turbidity..., 1983) there is no

mention of membrane filtration. The fast manual mentions disinfection with chlorine,

chloramines, chlorine dioxide, ozone, and ultraviolet radiation along with the non-treatment

alternatives of watershed management, source substitution, and regional&&ion of supply.

The second refers to conventional flocculation, sedimentation, and filtration.

2.3 Microfiltration Membranes

Membranes for microfiltration, as defined above, have been available and in use for decades.

The 0.45 micron membrane used for silt density index measurements are microfiltration

membranes. Nucleopore membranes have been available since the early 1960s (Silk and

Barnes, 1955; Fleischer, e? al., 1963; Fleischer, et al., 1969). However, only in recent years

has there been the kind of commercial interest that we now see. In order for microfiltration

to become a commercial process, we need membrane apparatus with three characteristics:

1) Produce water at a reasonable cost,

2) Be essentially free of leaks and have good seals around pressurized units, and

3) Be capable of being cleaned.

2.2
2.4 Microfiltration Systems

There are four major suppliers of microfiltration equipment. Characteristics of equipment are

shown in tables 2.1 and 2.2.

Table 2.1 .-Characteristics of commercial microfiltration eauioment

Memtec Dow U.S. filter Xenon

Pore size

Material

Configuration

Flux

Flow pattern

Transmembrane

pressure

Chlorine

sensitivity

0.2 urn

Polypropylene

Hollow fiber

67 GFD

Dead end

3-15psi

Can only tolerate a

combined chlorine

residual

Chemical Sodium thiosulfate

addition for dechlorination

Cleaning Water/air backwash

every 15 minutes.

Citric acid used for

inorganic fouling.

0.1 to 0.2 urn

PVDF

Flat sheet

30-50 GFD

Crossflow

2to15psi

3mgR free

chlorine residual

desired

Periodic

backwashing

with permeate.

Every 1 to 3

weeks, clean with

sodium

hypochlorite or Biz

0.8um

Ceramic

Multichannel

400 GFD

Crossflow

Up to 20 psi

Tolerates

chlorine residual

Aluminum

chlorohydrate

for flocculation

Recirculation of

2% caustic,

chlorine and

possibly sulfuric

acid

0.2um

Polymeric

Hollow fiber

50-63 GFD

Crossf low

8 to 12 psi

Tolerates

chlorine

residual

Continuous

air scour.

Relaxation

or permeate

back-flush

cleaning.

An interesting aspect of the Memcor equipment is that it permits an automatic test for

membrane and seal integrity. Operation is periodically interrupted, and a pressure of air at

15 to 20 psi is applied. Too rapid a decline in pressure discloses the presence of a leak.

The problem with estimates like those above is that they are based on comparatively little

data. As a result, there is considerable uncertainty in these numbers. Because of the

recentness of this application, there are few data on the useful life of microfiltration

membranes in this service.

An excellent review of the overall status of microfiltration is provided by the NWRUOCWD

(National Water Research Institute/Orange County Water District) symposium (1994) held in

2.3
Table 2.2.-Manufacturer’s estimate of system costs for units about

1 million gallons per dav capacitv

Memtec Dow U.S. filter

Capital,

$/daily gallon

0.77 0.67 0.94

O&M,

$/l ,000 gallons

0.16 0.40 0.14

Energy,

kWh/l ,000 gallons

0.8 5.0 Not provided

Irvine, California. A recent paper presents results of a survey of microfiltration plants

worldwide (Adham et al., 1996). This study indicates that in 1996, based on the results of

their survey, there were a total of 40 microfiltration plants worldwide, with a total capacity

of 12 MGD (45,000 cubic meters/day). Over 90 percent of these plants were supplied by

Memtec. For plants with a capacity of 0.1 MGD or more, the installed membrane system unit

cost was between $0.50 and $2.00 per (gallon/day). The plant capital cost is about twice

that. Based on about 290 responses, the operating and maintenance cost ranges from $0.20 to

$0.25/thousand gallons.

Microfiltration can typically produce water of satisfactory turbidity with feed waters

exceeding 100 NTU. Giardia removal as high as 6 logs is reported. Bacteria removal is

satisfactorily high. Cryptosporidia is satisfactory. Virus removal of 0.5 log (68 percent).

Disinfection byproduct removal is about 10 percent.

The major difficulty for the technology in California, where there is a large potential market,

is the desire to treat wastewater and the necessity to meet the CDHS (California Department

of Health Services) regulations. For instance, at Grange County Water Factory 21, they treat

wastewater and inject it into a drinking water aquifer to prevent seawater intrusion. Their

treatment must have multiple barriers that must remove at least 4 logs of microbiological

species. They have found that microfiltration has been good at bacterial removal, but in order

to get the virus and cryptosporidium removal, ultrafiltration is needed. Interestingly,

cellulose acetate RO membranes have a better removal than thin film composite membranes,

but uhraf3tration has been shown to give a better removal than RO. One hypothesis is that

sealing the product stream from the feed stream is more of a problem in RO than UF, as the

equipment is configured. Many studies have been done to determine the different membrane

removal efficiencies.

2.5 Operating Plants

San Jose, CaZifornia (Yoo et al., 1994; Yoo et al., 1995). Faced with a requirement to

upgrade or abandon the existing Saratoga 5 MGD diatomaceous earth treatment plant, the

San Jose Water Company installed a microfiltration plant of this capacity. The major

2.4
alternatives considered were diatomaceous earth filtration, two-stage filtration,

microfiltration, and ultrafiltration. These were looked at on the basis of cost, regulatory

approval, operability, and environmental and design constraints. Cost estimates for these

processes are shown in figure 2.2.

Figure 2.2.-Alternatives for the Saratoga Water Treatment Plant.

Microfiltration equipment was manufactured by Memtec Ltd. consisting of six factory

assembled units, each composed of 90 modules, each of which contains 10 square meters of

membrane surface. Capital cost of the microfiltration equipment alone was $1.5 million

which equates to $0.30 per (gallon&y). Design flux is 86 GFD. It has successfully operated

since February 1994. Gere (1997) reports that in its fourth year, the plant continues to

operate reliably and to provide quality product water. Operating costs for the first year came

to 30.9 cents per thousand gallons, which includes a prorated cost for membrane replacement

based on six year membrane life. No membranes have been replaced yet. Periodically,

the membranes require chemical cleaning. Cleaning interval varies from 2 to 6 weeks,

depending on the quality of the feedwater.

Tams Brook, ?Grginia, has installed a plant with a capacity of 130,000 GPD (McClain,

1994). This treats part of the water being supplied to the communities of Toms Brook and

Maurertown. The water source being treated by microfiltration is a new well, Toms Brook

2.5
Well No 2. The fairly porous karst soil allows groundwater from this well to be influenced

by surface infiltration, so the Virginia Health Department indicated that they considered this

a surface water in terms of treatment regulation.

Because microfiltration is a new water treatment method, a pilot study was required to

demonstrate its efficacy. The pilot study, which was run with a 43,000 gallon per day unit,

ran successfully for more than 2 months. During this test, the turbidity was artificially

elevated to challenge the membranes. Parameters monitored during the test included

turbidity, particle counts, coliform and membrane integrity. Removal of Giardia,

Cryptosporidia, bacteria, and some removal of viruses are attributed to the microfiltration

membrane. However, post-chlorination is the primary means of removal of viruses.

The final plant consists of three units identical to the one tested with the option to install two

further units. It contains a 200 pm bag prefilter. After microfiltration, the water is

chlorinated and sufficient contact time is allowed before distribution. The plant is

sufficiently automated that it needs to be checked by the operator only at the beginning and

end of a shift. Thus, additional personnel were not required by addition of the filtration unit.

2.6 Demonstration or Pilot Plants

Scottsdale Arizona. Scottsdale is currently testing microfiltration for aquifer recharge and

for surface water treatment (Dueker and Hemken, 1994). They have a 720,000 gallon per day

Memcor unit. They are also investigating microfiltration as a pretreatment for reverse

osmosis units.

Orange County, California. Water Factory 21 tested a 2,800 GPD unit in 1992 (Sudak and

Dunnivan, 1994). Pleased with the results, they subsequently tested a 43,000 GPD unit.

Both units were from Memtec. Indications were that the MF would allow them to increase

RO flux rates from 10.3 to between 12 and 13 GFD. They are now embarking on a

demonstration project of 800,000 GPD.

Colorado River Aqueduct (Coffey et al., 1994). The Metropolitan Water District performed a

very thorough test corn August 1991 to March 1992 on a Memcor pilot unit containing 4

square meters of membrane. Based on favorable results, they requested that California

approve the microfiltration process for this application. The CDHS credited microfiltration

with 3 logs of Giardia and 0.5 log (68.4 percent) reduction of virus. Based on these results,

MWD procured microfiltration units for five of their desert stations.

Barrow, Alaska. A 40 GPM combined microfiltration and nanofiltration plant is described

by Lozier et al. (1997). The feed water is cold, contains high quantities of disinfection

byproduct precursors, and microbial contaminants, Giardia and Cryptosporidium. For the

first year of operation, the plant product exceeded all requirements proposed for water

treatment and removal of disinfection byproducts. The water treatment facility plans to

convert its existing conventional filtration and reverse osmosis system to the combined

membrane process.

2.6
2.7 Potential Projects

New York City. The New York City water supply serves half of the population of New York

State, or approximately 9,000,OOO people. This system, containing 19 reservoirs, provides

1.3 billion gallons (72,000,OOO cubic meters) of water daily. This works out to 144 gallons

(0.54 m’) per person, not an unusual usage for the United States. The Ashokan Reservoir, for

example, has a capacity of 123 billion gallons (6.8 billion cubic meters) and a residence time

of 8 months. The principal purification method is simply long residence time.

Once called the “Champagne of drinking water,” this water is being threatened by the effects

of development and agricultural practices in the watershed. Testing of the water shows a

number of potential threats to public health: cryptosporidia, Giardia Zamblia, and E. coli.

The Croton reservoir system supplies 10 percent of this water. It receives effluent from

53 sewage treatment systems in addition to a number of septic systems and surface storm

runoff. Estimated capital cost of a filtration plant is $600 to $700 million and $40 million

annually for operation. This works out to $5/(gallon/day) and $0.84/kilogallon. The Catskill

and Delaware systems which supply 90 percent of the water are less threatened. If water

quality drops below Federal standards, the city will have to construct a filtration system.

Such a plant would cost approximately $5 billion investment cost and $500 million per year

to operate. This works out to $4.20/(gallon/day) and $1.20/kilogallon.

The system has so far obtained “avoidance” agreements extending to the year 2002. An

extensive program of watershed protection and monitoring of species like Cryptosporidium

has been undertaken (Ashendorff, 1997). This includes a recently signed memorandum of

agreement for a cooperative effort on the part of all stakeholders. EPA’s Expert Panel (Okun,

1997) has concluded that disinfection alone will not provide adequate protection against

cryptosporidiosis for the users of this water. Both watershed protection and filtration will be

necessary for this water supply.

It is highly speculative whether microfiltration fits into this picture. At this time, there is no

“barrier,” as the water quality regulators express it, between the reservoirs and the taps in

New York City. This is a highly politicized issue and the best technical answer may not be

the best political answer. A variety of non-structural solutions, like land acquisition,

restrictions on land use, and tightened agricultural regulation have been proposed, and some

are being implemented. There will probably be a filtration plant on the Croton system. MF

would almost certainly meet or exceed their requirements. Where application of microfiltration seems most likely is in the treatment of some of the more seriously contaminated

waters that currently flow into the reservoir system. Draft regulations for sewage treatment

plants located within the watershed have been revised to include microfiltration. Kachalsky

(1994) presents the results of tests run on effluent from the City’s Brewster Treatment Plant.

Four microfiltration units and three ultrafiltration units were tested. Microfiltration was

recommended to achieve the required reduction of targeted organisms.

2.7
Others. It is estimated that over 300 million gallons per day of microfiltration and

ultrafiltration projects are on the drawing boards for startup in the next 4 years within the

United States. Table 2.3 is a summary of MF plants and plant expansions planned for the

near future. Among the plants being discussed are: 5 MGD by Los Angeles Water and

Power at Terminal Island and within 3 to 4 years expanding to 15 MGD; Orange County

Water District will be scaling up to 5 MGD of MF or UF, eventually going to 15 MGD; San

Diego is planning 24 MGD by 2000; West Basin Water District in California is starting with

2.5 MGD and will be expanding to a total of 5 MGD before 2000 to provide treated water for

industrial cooling; Sacramento is studying 22 MGD of MF or UF treated water from the

American River using Ranney collectors; Tampa Bay, Florida, is studying the pretreatment of

25 MGD for reverse osmosis; San Francisco is studying a 24 MGD project; Tucson, New

Orleans, and a city in Wisconsin are studying projects that total 140 MGD; and Minneapolis

is studying membrane treatment of their water supply.

Table 2.3.-MF plants and olant expansions proposed for the near future

City Capacity Remark

Los Angeles (CA) water and power

Orange County Water District, CA

West Basin Water District, CA

San Diego, CA

Sacramento, CA

Tampa Bay, FL

San Francisco, CA

Tucson, AZ, New Orleans, LA,

and a city in Wisconsin

Minneapolis

5 MGD

5 MGD

2.5 MGD

24 MGD

22 MGD

25 MGD

24 MGD

Total of

140 MGD

Expanding to 15 MGD

Expanding to 15 MGD

Expanding to 5 MGD

for industrial cooling

By 2000 year

For RO pretreatment

Water supply treatment

2.8 Research and Development Efforts

The plants and demonstrations suggest that microfiltration is an economically valid process

for water treatment where the desired results are Giardia and bacterial removal at a level of

3 to 3.5 log. Virus removal is very modest; the best estimate is about 0.5 log. However, if

there is not a great quantity of THM formation potential, the combination of microfiltration

with chlorination can be a satisfactory process.

Freeman (1994) has investigated treating backwash water from conventional filtration via

microfiltration. Cost estimates from this study were $0.67/gallon per day for MF and

$0.33/gaIlon per day for a plate settler. These were considered close enough to encourage

testing.

2.8
Vickers (1994; 1995) has studied use of microfiltration in conjunction with coagulation

processes. The objective of this process is the removal of organic matter, particularly

disinfection by-products. An advantage to MF or UF is that the coagulant and process can

be optimized for organic removal instead of particulate removal.

Jacangelo et al. (1995) have run extensive tests on the mechanism of cryptosporidium,

giardia, and MS2 virus removal by MF and UF. They have concluded, inter alia, that

initially removal is dominated by sieving action of the membrane, but that late in a cycle,

cake formation dominates in removal. Over a number of cycles, the irreversible fouling layer

dominates over cake formation.

Adham et al. (1995) have evaluated methods of assessing membrane integrity for several

low-pressure membrane technologies. Methods tested include bubble-point testing, airpressure-hold, sonic sensing, particle counting, particle monitoring, and turbidity monitoring.

The air-pressure-hold test, though not continuous, was found to be most effective. Particle

counting was most sensitive of the continuous methods.

Pretreatment for Water reuse and RO Pretreatment. Lozier and McKim (1994) carried out an

evaluation of the suitability of microfiltration for RO pretreatment. They concluded that

filtrate from some microfiltration equipment exceeds all industry criteria for RO feedwater.

However, the removal of metals and reduction of silica which occurs in lime softening does

not occur with MF. They found that MF provides from 2 to 4 log reduction of bacterial

viruses when used with alum coagulation. Jolis and Hirano (1994) noted that following

microfiltration they found negligible fouling or solids deposition on the sleeves of W lamps

used for sterilization. Their tests on operation of an RO system following a MF unit were

still in progress after 5 months.

2.9
Chapter 3

ULTRAFILTRATION

3.1 Basics of Ultrafiltration

Ultrafiltration (UF) is midway between MF and NF in degree of separation. Separation is

accomplished through sieving just as with MF, but while MF membrane retains particles and

allows macro molecules and colloids to pass through, UF membrane retains most molecules

and particles larger than its molecular mass cutoff (MMCO). Colloidal silica, protein, humic

substances, pyrogens, and viruses would be retained by a UF membrane but dissolved salts,

sugar, and mid-sized organic molecules would not.

UF is a relatively new process for municipal water treatment. It has been used more

extensively in industrial processes for concentrating milk, protein, and cells; recovering

process materials such as paint, colloidal metals, and dyes; and recovering oily waste water.

In the last 5 years, the application of UF in drinking water treatment has expanded profoundly

due to changes in drinking water quality regulations. The Surface Water Treatment Rule

(SWTR) of 1986 requires 3 log removal or inactivation of Giurdia cysts and a 4 log removal

of enteric viruses. An enhanced Surface Water Treatment rule may increase the required

reduction in Giardia and Cryptosporidium to 6 logs for some source waters. At the same

time, the Disinfectants/ Disinfection By-Product Rule (DBPR) will reduce the allowable

concentration of disinfection by-products, but drinking water must still contain a residual

disinfectant. It is difficult to meet all of these requirements with conventional media

filtration and coagulation/clarification processes. These processes typically rely on

disinfection to inactivate any remaining organisms, but they do not completely remove the

disinfection by-product precursors (naturally occurring humic and fulvic acids). So, when

the disinfectant is added, they will be able to meet the SWTR, but not the DBPR! UF

membranes do remove DBP precursors and can easily meet 6 log reduction in organisms

Giardia and Cryptosporidium if the MMCO is low enough.

UF membrane comes in all of the configurations shown in figure 1.3 (Spiral Wound, Tubular,

Compound Tubular, Flat Sheet) except hollow fine fiber. If the feed water suspended solids

content is low, spiral wound modules are best since they have the highest area/volume ratio

of all UF type configurations. But if the feed water does contain a high concentration of

suspended solids, one of the tubular configurations will be easier to maintain.

3.2 Membrane Characterization

There are four important aspects necessary to describe UF membrane: configuration, composition, molecular mass cutoff, and clean water permeability. Of these four, the only one that

is well described by manufacturers is the configuration. They are fairly good about telling

3.1
you the dimensions and whether the membrane is in a spiral wound, tubular, compound

tubular, or hollow fiber configuration. They will also give you an idea of the composition

such as PS (polysulphone), CA (cellulose di-tri acetate), PVF (polyvinylfloridine), or

ceramic. They may further assist the customer by pointing out that one has high fouling

resistance and the other is good for oily waste water. Maybe that is the best one can hope for.

Manufacturers do provide detailed information on the last two items; unfortunately, it mostly

serves to confuse matters when trying to compare one membrane to another, especially

among manufacturers.

3.2.1 Molecular Mass Cutoff

UF membrane is described chiefly by its MMCO which is more often called the MWCO

(molecular weight cutoff). MWCO is not entirely accurate since molecules are always

described by their mass rather than their weight. Weight is the mass of an object under the

influence of Earth’s gravity. A 100 lb weight will weigh much less than 100 lb on the Moon,

but it will have a mass of 45.45 kg no matter what planet it is taken to. This may seem

trivial, but some people are fanatical about being exactly correct in language. Whether it is

called MMCO or MWCO it is still determined in the same general manner, though there is no

standard method. The membrane is challenged with substances of known molecular mass

such as latex spheres, dextran, protein, or other organics. Retention rate is determined for a

range of molecule sizes; then the MMCO is defined as the molecular mass of molecules

retained at an arbitrary level. Most manufacturers use 90 percent.

There are problems with this method of characterization and also with the interpretation of

the results. Different companies challenge their membranes with different substances at

different concentrations and then use different methods for determining the retention rate.

Who can say whether a membrane with a MMCO of 100,000 Daltons determined using

2,000 mg/L of a “polymer marker” will perform similarly to one with the same MMCO

determined using polyethylene glycol at 1,000 mgL? Standard methods would help clear up

this confusion, but the MMCO statistic is still only an approximation. Membrane pores are

not homogenous or evenly spaced. Some will be much larger than the MMCO and others

much smaller. Figure 3.1 is a generic molecular mass versus retention curve for a membrane

with a sharp MMCO, or narrow pore size distribution, and one with an indistinct MMCO, or

wide pore size distribution.

Another problem with assigning a MMCO is that many organic molecules are adsorbed onto

the membrane surface forming a cake layer which reduces the effective pore size. The rate

of adsorption depends on the organic molecules present, their concentration, the pH, flow

velocity, pressure, temperature, ionic strength, and membrane material. As material builds

up at the membrane surface, the pores are closed in from the sides. Figure 3.2 illustrates the

difference in retention of a membrane before and after cake formation.

The Seventh Edition Perry’s Handbook gives a rule of thumb for estimating UF separation

abilities. The molecular mass should be a factor of 10 greater than the MMCO for a good

separation using UF membrane (Perry and Green, 1997). In practice, the customer must test

3.2
: MMCO

v

Molecular Mass

Figure 3.1 .-Comparison of molecular mass and retention rates for membranes

with narrow and wide pore size distributions.

a range of MMCOs and membrane materials, since the pores of one material may differ from

those of another, to determine which membrane will be adequate for the source water and

treatment objectives.

3.2.2 Clean Water Permeability

What is clean water? I am sure that the number of definitions for clean water is only limited

by the number of UF membrane mantiacturers. Some add sodium chloride, some use RO

permeate or local tap water. In reality, UF is not normally used for treating “clean” water.

The reason one wants to know the clean water permeability is to get an idea of the membrane

module productivity to estimate how many to purchase. But the module productivity has

nothing to do with the clean water permeability! It depends on the pressure, feed flow rate,

recovery rate, fouling rate, backwash frequency, and temperature and probably we’ll find that

the phase of the moon has a major impact when we reaZZy understand the process.

Manufacturers measure the clean water permeability so that they can tell you something

about the membrane. Its easier and more direct than giving lots of pilot test data from

different water sources that still may be inapplicable to your particular situation and may

3.3
Cross flow

m - .-

l

l &ean UF Membrane

0 Cross flow

-NY*,’

m

. m . -

.

l Fouled UF Membrane

Figure 3.2.-Difference in retention between clean and fouled UF membrane.
lead you to believe their product is not as good as another. The trouble is that UF is so

profoundly dependent on the feed water quality that it is complicated to predict how a UF

membrane will perform. The only way to get the best membrane for the job is to pilot test a

few different types and MMCOs. Luckily, there are more and more documented pilot tests

available now that may involve testing a feed water similar to the one you need to treat. The

AWWA Membrane Conference Proceedings from the last few years have several case

studies. The manufacturers will also have documented case studies and will be able to help

you choose a few good membranes to test.

3.3 Process Design Considerations

UF is most always operated in a cross-flow mode. There are references to operating in deadend mode (see Chan et. al., 1997), but these systems are designed to handle a wide range in

water quality. They are automated to switch to cross-flow mode when turbidity or some

other monitored parameter exceeds the setpoint. Figure 3.3 compares the averages of

productivity for all seawater (SEA) and brackish RO, NF, UF, and MF membranes listed in

chapter 10. UF membrane “clean” water permeability is about twice that of NF membrane

and 2.5 times that of brackish water RO membrane. In practice, however, these high flow

rates are only realized with feed water of the same quality as is needed for RO and NF

treatment. UF is not normally used on such clean water, though. With high turbidity water

(in excess of about 15 NTU in the Chan study), concentration polarization becomes a limiting

factor in UF productivity (for a perspicuous discussion of concentration polarization and UF

see’ Perry and Green, 1997, p 22-53).

1 0

1

0.1

Sea R O N F UF MF

Figure 3.3.-Comparison between membrane productivity for seawater and brackish water RO, UF, and

MF membrane as tested by the manufacturers. Productivity units are m3m“day”.

Concentration polarization is the build-up of material at the membrane surface. In MF, this

material is blown out periodically in the backwash. In RO and NF, it is minimized by

3.5
extensive pretreatment, high flow rates, and by using feed channel spacers designed to

promote turbulence. UF systems incorporate a combination of these strategies. The systems

are operated in cross-flow mode at high shear rates and low pressure; feed channel spacers

are designed to promote turbulence; and the systems are periodically backwashed. High

recovery is achieved by recirculating the concentrate stream to the feed tank, back into the

feed line, or into another stage of membranes. Figure 3.4 illustrates the three UF process

designs with pre-filters, permeate backwash, and concentrate recycle.

3.4 Process Instrumentation and Evaluation

There are three purposes for instrumentation in UF treatment processes. These are to

monitor:

. Hydraulic performance,

l Retention performance, and

l General water quality.

Hydraulic monitoring requires measurement of the feed and permeate pressure, feed,

permeate, recycle and backwash flows, and temperature of the feed stream. Retention

monitoring requirements depend on the source water and treatment objectives. Operators

should be able to tell, with a glance at the monitoring instrumentation, whether the product

water is within specifications or not. Surface water treated for drinking purposes should be

monitored for turbidity and particle count of the feed and permeate. General water quality

monitoring for UF is the same required of any drinking water process to provide docurnentation that the water meets Safe Drinking Water Standards. This should include at least

conductivity, pH, and chlorine residual. Table 3.1 summarizes monitoring equipment for a

UF water treatment system by purpose.

UF is evaluated in a number of ways depending on the treatment objectives. Table 3.2 lists

performance parameters used in various UF pilot studies reported recently. These are

explained in greater detail following the table. Some, such as the net permeate volume per

unit energy or average power consumption would only be monitored during a pilot study to

optimize system operation. Others, such as the heterotrophic plate count (HPC), Giardia and

Cryptosporidum enumeration, Total Coliform (TC), and Bacteria Virus Assay (BVA) would

be required of any drinking water treatment plant. The rest are necessary to monitor

performance of a UF system.

Transmembrane Pressure (TMP)

TMP should be monitored continuously or at least twice a day. In automated systems, the

backwash cycle is initiated either on a timed basis or by a specific increase in the TMP. It is

calculated as follows from three pressure measurements.

3.6
Coarse

Filter F

0

0 2 0F

Concentrate

I

A. Concentrate Recycle Operation with

Product Backwash.

Backwash

Pump

n

Product

Figure 3.4a.-Concentrate recycle operation with product backwash.

..w.

. .
Coarse

Filter

Concentrate Waste F

.o

1 I

Feed r Concentrate Recycle

Tank

I I I

I

B. Batch Operation with Product Backwash.

Backwash

Pump IIProduct

Figure 3.4b.-Batch operation with product backwash.
Coarse

Filter

Feed

Tank

Stage 1 Stage 2 Stage 3

+

Product

l-l

Flow

Ratio

Control

Concentrate

Recycle

1

Concentrate

Waste

Figure 3.4c.-Stages in series. Each stage flow and TMP are controlled separately.

At a minimum feed, individual product, and concentrate recycle flows and

pressure across each stage must be monitored.
TMP = 0.5(Pf + P$ - Pp Eq. 3.1

Where: P, = Feed pressure

P, = Recycle pressure

P, = Permeate pressure

Table 3.1 .-UF instrumentation requirements

Function Parameter Feed Permeate Recycle Concentrate Backwash

Hydraulics Pressure X X X

Flow X X X X

Temperature X

Retention Turbidity X X

Particle Count X X

Water quality Conductivity X

PH X

Chlorine Residual X

Table 3.2-UF performance evaluation parameters used in recent case studies

Obiective Performance parameters Reference

Optimizing operation

using backwash time and

powedered activiated carbon (PAC)

addition as variables

Removal of color and TOC from

surface water w/ and w/o chemical

addition.

Testing pretreatment for RO in

recovering waste water from

petrochemical plant.

Determining effect of charge and

coagulant dose on NOM Removal

and fouling rate.

Color, TOC, iron, bacteria removal.

Microbial removal and integrity

verification.

Net permeate vol/unit energy

Net permeate vol/average

power requirement

Water quality, TMP, and run

length.

Permeation rate and turbidity.

Permeation rate, UVQ254 and

TOC.

Water quality, TMP,

permeation rate

Permeation rate, particle count,

turbidity, SDI, TMP, TOC,

UV@254 HPC, TC, BVA,

Ctypto, and Giardia

enumeration.

Marriott, Clark and

Lain& 1997.

Scanlan et. al., 1997.

Wong et. al., 1997.

Fu and Dempsey, 1997.

Chan et. al., 1997.

Jacangelo, Adham and

Lain& 1997.

3.10
Net Permeate Flow (Qp,,,J

Q P?lt?f is used to evaluate performance using different backwash frequencies and durations. It

accounts for product water used during backwash and cleaning. It should be calculated from

actual flow rates, not the temperature normalized flow.

Q Pnet = QP - QB, - QC Eq. 3.2

Where: Q, = Total product flow (Lhr-‘me*)

Q BW = Product used for backwashing (Lhr-‘mm*)

Qc = Product used for cleaning (Lhr-‘mm*)

Normalized Permeate Flow (Qp,J

Permeate flow may be normalized for temperature to allow comparisons over time with large

temperature fluctuations. This is not as critical as with NF and RO processes, though,

because UF is not operated at its full permeation capacity. Manufacturers generally provide a

temperature normalization equation specific for each type of membrane they produce that

adjusts for the change in viscosity of water and changes in the membrane with temperature.

The following equation corrects for changes due to viscosity only (Streeter and Wiley, 1985).

* e -O.O239(T-20)

Qpn = Qpnet Area Eq. 3.3

Where: Qp,, = Permeate flow (Lhr’m-*) adjusted for viscosity at temperature T

Q Pm-r = Net Permeate flow (Lhr-‘me*)

T = Temperature (“C)

Area = Membrane area (m’)

Net Permeate/Net Energy (QJE,,) and Net Permeate/Average Power Consumed (Qp,/W&

Q&E, and Qpr/waVg are parameters used by Marriott and associates (1997) to optimize a UF

process using backwash frequency and duration, permeation rate, and PAC addition as

variables. The energy and power terms, as defined in the reference, are given below. Qpn is

as described above.

Eq. 3.4

3.11
w = %I

wz

td + ‘bj

Eq. 3.5

Where: E = Pump energy (joules)

P

= Pressure (Pascal)

Q = Flow rate during time At (m3/s)

At = Time period (set)

Kvg = Average power consumption (watts)

t = Total time during each cycle (set)

Summations are of one second intervals (or any other convenient time interval) over the

duration of the test. Subscript “n” means “net,” “ bf’ refers to the backwash cycle, and “d”

refers to production cycle .

Using compound parameters such as these helps to normalize cost/benefit tradeoffs for

different scenarios. The volume per energy term is based on the total energy required. An

efficient process would have a high Q,/E, value. The volume per average power term is

based on the power consumption averaged over the same time period. If the process is

efficient and timely, then the Qp,,/Wavg value would also be high. Operating with a very

conservative permeation rate and backwash cycle would be reflected in a high Qp,/En value

and relatively low Qr,,,fWaVg value. Even though the system would operate smoothly, it would

be not be operating to its full potential3.5 Integrity Testing Methods

If a UF membrane is the main barrier between pathogenic organisms and the public, it is

reassuring to be able to monitor its integrity. On-line monitoring would be the most

desirable, but it is difficult to make a direct correlation between measurable parameters and

the presence of pathogens. Jacangelo and associates (1997) reviewed a number of methods

classified as direct or indirect methods, though the distinction between the two classes is

rather gray. Direct methods monitor for a change that is directly traceable to a flaw in the

membrane module and/or system. Examples of direct monitoring are air pressure hold and

bubble point testing. Indirect methods monitor changes that infer a flaw in the membrane

and/or system such as particle counting and turbidity monitoring.

The objective of the Jacangelo study was to determine the ability of UF and MF membrane to

remove microbes. One spiral wound, one tubular, and four hollow fiber membranes were

compared on five different source waters. The membranes were subjected to pin pricks and

cut fibers during the integrity testing described in Jacangelo’s report. Only the direct

methods of air pressure hold and bubble point testing were able to detect the induced flaws

in the spiral wound membrane. The problem is that a spiral wound membrane has a

3.12
Technique

Table 3.3.-Integrity testing and monitoring techniques for UF membrane

Description Comments

Air pressure hold test Permeate side of the membrane is drained and pressurized with

air. Pressure is monitored for 10 minutes.

Sonic sensing

Bubble point test

Particle counting

Sound wave sensors are attached to the membrane module

during the air pressure hold test to listen for leaking bubbles.

Mainly used for determining MF pore size. UF membrane pores

are too small. The method can be used to detect broken fibers

in a bundle, though.

Light scattering used to enumerate particles in one or more size

ranges.

Particle monitoring Measures fluctuations in light intensity, output is an index of High upper limit, but feed may still exceed limit. Not sensitive

relative water quality. Less complicated and expensive than enough for small flaws. Need correlations between particle

particle counters. detection and bacteria/virus/spore concentrations.

Turbidity monitoring Measures degree of light scattering by suspended solids. Not sensitive enough for small flaws. Need correlations

between turbidity and bacteria/virus/spore concentrations.

Silt density index Measure of fouling potential. Calculated from the difference in

time required to filter 100 ml at constant pressure through a

0.45pm filter at the start and end of 15 minutes.

System must be shut down.

System must be shut down. Extraneous noise could interfere

with the test.

Module must be taken offline. Cannot detect leaks in the

system piping and gasketing. Only good for fibers.

Low upper limit on particle counts: feed particles are too

numerous to count. Not sensitive enough for small flaws.

Need correlations between particle size and

bacteria/virus/spore concentrations.

No correlation between SDI and presence of

bacteria/virus/spores. Not sensitive enough to detect small

flaws.

(Based on Jacangelo et. al. 1997).
far greater surface area than the hollow fiber and tubular modules tested. In this way the

spiral wound module is a good model for a large membrane system of any configuration. A

small flaw in a large system will be difficult to detect by any of these methods.

3.6 Concentrate Issues

UF concentrate consists entirely of backwash and cleaning water. The volume of waste

depends on the frequency of backwashing and cleaning. A survey of full size UF and MF

plants revealed a range in recovery rates of 70 to 99 percent. Extremely high recoveries,

without additional treatment of the backwash, can result in build up of pathogenic organisms

in the system and is not recommended for drinking water treatment. Scanlan and associates

(1997) had trouble with accumulation of algae in their backwash solution. They had saved it,

though, for batch treatment at the end of raw water testing. Algae growth can be prevented

by keeping sunlight out of the system. If only a portion of the backwash is constantly

recycled to the feed, the problem of pathogen build-up and algae growth should be minimized. Since the mineral make up of the backwash water is similar to the feed source, it can

be discharged to a settling pond, disinfected, and then recirculated to the feed stream or

discharged to the source. Some plants use the backwash for irrigation (Jacangelo, 1997).

Its high natural organic matter content makes it an excellent fertilizer.

Cleaning solutions need to be neutralized before disposal. Depending on the solution used,

they could be discharged to the sewer or disposed of with the backwash. Typical cleaning

solutions are sodium hypochlorite, sodium hydroxide, hydrogen peroxide, or detergents.

3.7 UF Case Studies

Examining case studies of an unfamiliar process is a good way to illustrate how the process is

used and what kind of problems may come up when testing the process. The following are

studies reported in the AWWA Membrane Technology Conference Proceedings from 1995

and 1997.

3.7.1 Removing TOC and Color

Scanlan and associates compared MF and UF with conventional sedimentation and dissolved

air floatation (DAF) for treating mountain runoff with low turbidity, moderate alkalinity, but

high color and TOC to produce drinking water for the city of Cheyenne, Wyoming. Their

objective was to remove particles, disinfection bi-product precursors (DBPs), color, and

soluble manganese with minimal chemical addition. Table 3.4 shows the various treatment

combinations.

A Memcor, 0.2 - 0.5 micron, MF system with automated backwash using air and water was

used. Between tests, the membranes were cleaned with citric acid and caustic. The Koch,

3.14
Table 3.4.-Treatment alternatives for Cheyenne, Wyoming

1 2 3 4

Alum or Ferric Alum or Ferric

Flocculation Flocculation

Tube settler Solids floatation

Dual media filter Dual media filter

Strainer Alum, Ferric or PAC

200pm bag filter Strainer

U F M F

0.05 pm, UF system was backwashed at 30 minute intervals with a water/hypochlorous

acid/caustic solution and cleaned between tests with a proprietary caustic solution. Because

of the system configurations, the two systems were operated on different principles. Constant

permeate flow was maintained on the MF system, while constant pressure was maintained

on the UF system. It would be best if both systems could be operated in the same manner,

because when the pressure is increased to maintain a given permeation rate, fouling becomes

more difficult to remove with ordinary backwash cycles. One must work with what one has

though; since they could not compare TMP changes or energy usage differences

meaningfully, they compared run length and volume and quality of water produced.

During the test, the water was analyzed for alkalinity, turbidity, color, chlorine, manganese,

TOC, total trihalomethane (TTHM), and particle counts in the range of 2 to 15 pm, the

approximate size of Cryptosporidium and Giardia. Their findings are listed below.

l All the treatments reduced turbidity to 0.15 NTU or less.

l All treatments did a satisfactory job of reducing color, though increasing ferric

sulfate doses resulted in increased color removal.

l MF and UF had 2.6 and 3.6 log removal of particles, respectively, compared to 1.5 to

2.2 log removal with sedimentation and DAF.

l UF and MF removed significant amounts of manganese without chemical addition.

Sedimentation and DAF removed manganese to the same extent when alum was

used as coagulant.

l UF and MF were not able to remove TOC to the target 45 percent level. Even with

50 mg/L coagulant or PAC, MF TOC removal increased to only 36 percent. DAF

and sedimentation were able to remove 44 percent TOC with the same coagulant

dose and 49 percent with 70 mg/L.

l MF had longer run times than UF. The UF system was unable to maintain the design

permeation rate, but did perform consistently at l/4 the design rate.

In this case, the UF membrane was unable to perform as desired. but if they had tested a UF

with a much smaller MMCO (0.05 pm- 100,000 Daltons). or used PAC pretreatment with the

3.15
UF, they could have come to completely different conclusions. Here. the objective of

attaining high water quality with minimal chemical addition will not be met because the

apparent winners of the test are the conventional sedimentation or DAF processes with 50 to

70 mg/L alum or ferric sulfate.

3.7.2 Enhancing UF Organic Removal With PAC

In another example, a group at the University of Illinois piloted a UF system in conjunction

with a floe blanket reactor (FBR) and PAC to remove organic contaminants (Schirnmoller,

1995). Organic molecules are adsorbed onto PAC at a rate dependent on the concentration of

organic compounds and the retention time. As organic concentration increases in the UF

concentrate stream, the PAC can be more fully utilized. The extended retention time in the

FBR also helps improve PAC utilization. Figure 3.5 illustrates the configuration of such a

system. The PAC is injected just ahead of the UF system. PAC that remains in the reject

stream is recycled back to the UF. When the membranes are backwashed, the PAC that has

built up on the surface is recycled to the FBR. Solids are removed from the FBR as needed.

It turns out that the PAC in the UF feed stream actually slows the rate of flux decline. This

could be due to the scouring effect of the PAC particles, and/or the PAC could improve the

permeability of the filter cake layer by making it less compressible.

Groundwater from Urbana, Illinois, was used as feed water for this study. It had 2.5 mg/L

TOC and turbidity from 0.1 - 1 .O NTU. The FBR effluent was treated with hollow fiber UF

membrane with 100,000 Dalton MMCO. The concentrate was recycled to the UF feed tank.

After reaching steady state performance, the FBR removed about 1 mg/L, and the UF system

removed another 0.75 mg/L for a final reduction from 2.5 to 0.75 mg/L, an overall 70 percent

reduction in TOC.

3.7.3 Testing UF as Pretreatment for RO

Wong and associates (1997) describe a pilot test to recover waste water from a petrochemical

plant. This plant has three waste streams: the cooling tower blowdown (CTB) and the

organic and inorganic waste water treatment system effluent (OWWTS and IWWTS

respectively). Since the IWWTS has very high TDS, the OWWTS and CTB were selected

for recovery and reuse. An elaborate pretreatment system was designed using potassium

permanganate oxidation and greensand filtration to precipitate and remove manganese, iron,

and cobalt, followed by a GAC and cartridge filter to remove organics and particulates. UV

irradiation was used before the membrane systems for disinfection. They conservatively

tested and optimized each process in turn all the way up the line. The GAC filter was taken

out of line to see if it was really necessary. but that caused an increase in the UF TMP so the

GAC was returned to the process stream.

The UF system used was designed for a waste water treatment plant. but not such a treatment

plant as this! The feed to the UF system was of such high quality that they where able to

replace the permeate flow restricting valve with a partially open globe va1L.e thereby

3.16
Alum,

Clay, & Polymer

Rapid

Mix

Product

Solids

lCon6entrate -

c

L

-

Mix Tank (IT==== Flocculator

Figure 3.5.~-Schematic for a Floe Blanket Reactor-UF system for removal of organic contaminants.
increasing productivity by 45 percent. This in turn improved the RO system performance by

17.5 percent through providing an optimum feed flow rate. The system operated consistently

for the entire 2000 hour test. The only adverse effect on the UF system was the formation of

a black layer of material on the membrane surface that could not be removed with the usual

NaOCl cleaning. It was removed successfully with HCl and NaHSO,, though.

This system was conservatively designed with the idea that components could always be

excluded from the final design if they proved unnecessary, which is always better than

finding the design won’t work because proper pretreatment is not in place. UF systems do

not need to have such stringent pretreatment systems, but there are trade offs. The UF system

would probably have operated satisfactorily at a reduced permeation rate without the GAC,

but then more membrane area would be needed to meet the RO system feed flow

requirements. In this case, it was more economical to keep the GAC in the design and

operate at a higher UF permeation rate.

3.8 Conclusions and Research Needs

From the case studies referenced here, it seems that applications of UF for waste water

recovery, microbial removal insurance, and pretreatment for RO and NF are growing in

numbers and interest. Still, there are shortfalls in three major areas:

l Membrane Characterization - Standard methods need to be established for evaluating

UF membrane retention characteristics. Preferably, a method similar to that

described above will be adopted where a range of sizes of differently shaped

molecules would be tested and the whole retention versus molecular mass curve for

each shape would be used to describe the membrane.

l Membrane Specifications - UF membrane specifications are diverse and confusing.

Standard methods for evaluating and reporting permeation rates need to be

developed. The standard method should include specifications for operating

pressure, flow rate, temperature, and water composition.

l Integrity Monitoring - There does not seem to be a reliable on-line method for

integrity monitoring. If a method cannot be found, then correlations should be

developed between microbial activity and a parameter that can be measured reliably

on-line.

3.18
Chapter 4

NANOFILTRATION AND REVERSE OSMOSIS

4.1 Process Fundamentals

Nanofiltration (NF) and reverse osmosis (RO) are unlike the previous filtration processes

discussed. MF and UF use pressure merely to provide convective flow of liquid through the

membrane. NF and RO require hydraulic pressure as well to overcome the osmotic pressure

of the feed solution. Osmosis is a natural process whereby water is transported through a

semi-permeable membrane from a solution of low concentration, to one of high concentration. Plants use this phenomena to draw in water from soil. Reverse osmosis occurs when

pressure in excess of the osmotic pressure is exerted on the high concentration side of the

membrane inducing pure water to diffuse through the membrane to the low concentration

side, as depicted in figure 4.1.

The osmotic pressure of a solution, 7c, is the pressure that is exactly enough to prevent

osmosis from occurring. It is approximated by the following equation:

Where:

II

T

I

Y

2,

number of moles of ions per mole of solute,

the universal gas constant, 8.314 m’ Pa%-’ mole-‘,

“K,

ionic strength of the solution,

activity coefficient of the solution.

concentration of the z* species,

charge of the zti species.

log y = A

A

B

7

= 0.5091 for water at 298.15”K,

= 0.2 for monovalent species,

&+, Z- are the charges on the anion and cation.

TC = yInRT Eq. 4.1

Eq. 4.2

Eq. 4.3

4.1
4.2
A rough approximation is:

n (7b/in2)= 0.0 1 * TDS mg/L Eq. 4.4

Non-ionized solutes, such as sugar or other organic molecules, have only one mole of

particles per mole of molecules and therefore have a fraction of the influence on osmotic

pressure that solutes which dissociate in solution, such as NaCl, have. A solution with one

gram of NaCl per liter would have an activity coefficient of 0.877, ionic strength of 0.017,

2 moles of ions per mole of solute, and an osmotic pressure of about 74 kPa (10.8 lb/in’).

The key descriptive parameters for RO and NF membrane are their water and salt transport

coefficients. The transport coefficients determine the amount of water or salt that passes

through, or permeates, a unit area of membrane over a given range of salinity, pressure,

temperature, and pH. Water transport is often called the “flux” and the salt transport is

usually discussed in terms of the salt rejection rather than the salt passage. But flux and

rejection are dependent on the operating conditions, while the transport coefficients are

supposed to be intrinsic qualities of the membrane. Actually, the transport coefficients are

also dependent on the operating conditions, but over the normal range of operation, the

effects are minimal. Generally, it is assumed that the transport coefficients can be used to

compare membranes operated under fairly similar conditions.

The water transport coeffkient, normally denoted as “A,” measures the permeation, or flow,

of water through a membrane for a unit of applied pressure.

Eq. 4.5

Where:

A = water transport coefficient in m see-‘Pa-‘,

F, = water flux, or volume of liquid passing through a unit area of

membrane expressed as m3 mm2 set“

AP= difference in pressure across the membrane in Pa,

An = difference in osmotic pressure across the membrane in Pa.

The salt transport coefficient is the rate at which dissolved salt passes through the membrane.

4.3

Eq. 4.6
Where:

c, = concentration of salt in the product stream in mol/L,

c, = concentration of salt in the concentrate stream in mol/L,

v,= -volume of concentrate produced per unit time in m’/sec,

Area = active area of the membrane in m2,

cc-c, = difference in salt concentration across the membrane in mol/L,

B = salt transport coefficient for the membrane in m/s.

Salt rejection is the percentage of salt that does not pass through the membrane:

R = (5 - 5) 1()(-j

5

Eq. 4.7

Where:

cp =

Cf =

concentration of salt in product water in mol/m’,

concentration of salt in feed water in mol/m’.

4.2 Module Configuration

The most common commercial configurations for RO and NF elements are spiral wound and

hollow fine fiber (HFF). They are similar to those shown in figure 1.3. The main difference

between HFF elements and those depicted is that HFF fibers are like strands of hair. HFF

modules contain the largest amount of surface area per unit volume of any configuration;

there are over 840 m2 in a 20 x 122 cm module compared to 37 m2 in a similar spiral wound

element. The flux for HFF membrane material is only about one tenth that of spiral wound

membrane, but because of the tremendous amount of active surface area per module, HFF

modules have three times the productivity of spiral wound elements. For this reason, a

typical spiral wound system for treating brackish water usually has two parallel sets of

pressure vessels, containing 6 elements each, in series with two or three stages of vessels,

while HFF systems are generally configured with parallel vessels of one or two elements each

and have only one stage. Figure 4.2 shows typical spiral wound and HFF membrane systems.

4.3 Pretreatment

RO and NF are intended only to remove dissolved salts. Ideally, the feed water to these types

of systems should have turbidity levels under 1 NTU and silt density index (SDI) level less

than 5. HFF modules have even higher standards of pretreatment; they require under

0.5 NTU and SD1 under 3. In addition, thin film composite membranes are not tolerant of

free chlorine or other oxidants, such as ozone, in the feed water. Generally, manufacturers

recommend less thar 000 mg/L- hours of contact with free chlorine. This means that the

membranes are warranted for up to 1000 hours of contact with water containing 1 mg/L free

4.4
P

in

High Pressure Pump Co

(A) Two stage spiral wound membrane system.

(B) One stage hollow fine fiber membrane system.

Cartridge

Filtration High Pressure Pump

00C,

0

F, P‘

Product Concentrate

Figure 4.2.-(A) Spiral wound membrane systems require 2 stages of 6 element pressure vessels to attain a 75 percent recovery rate.

(B) Hollow fine fiber systems are designed with 1 element per pressure vessel and only 1 vessel in series.

With this 1 stage configuration they are capable of a 50 percent recovery.
chlorine, or 200 hours with 5 mg5. Biological contamination and large organic molecules

should also be removed in the pretreatment system as they tend to accumulate on (or foul) the

membrane surface and cause a decline in performance. Of course, such pristine conditions

are difficult to attain, but should be strived for in designing a pretreatment system. At the

very least, there should be some method of disinfection and particle filtration. There are

systems that incorporate chemical precipitation methods for clarifying the RO feed water, but

often the added chemicals cause fouling problems in the membrane system. The real beauty

of the membrane separation process is that it can be tailored to remove only what is necessary

without adding more undesirable chemicals to the product water. The membrane processes

described above can provide excellent pretreatment for NF and RO. Aside from possible

clarification chemicals, there are a few chemicals that are commonly used to enhance NF and

RO membrane performance and longevity. Acid is generally added to adjust the feed pH for

cellulose acetate (CA) membranes. Anti-scalants may also be added to prevent scaling

(precipitation of slightly soluble salts) in the concentrate stream.

4.4 Monitoring Performance

Temperature, pressure, and feed concentration generally determine the productivity of an NF

or RO system. The membrane specifications in table 4.1 give the manufacturers limits for

these parameters. These three parameters appear in the osmotic pressure equation, indicating

their obvious importance in the process, but they also affect the membrane itself. You may

be able to imagine what happens to a plastic wrapper in the microwave oven. Membrane in

hot water behaves in the same way. It becomes loose and deformed, or even perforated, by

the mesh spacer material, and the glue lines weaken. Water and salts are transported at a

higher rate. Excessively high pressure can also cause the membrane to be deformed by the

mesh spacer. Any fouling material on the membrane surface becomes compacted under

pressure, resulting in a less permeable and more persistent layer. If the feed concentration

should become higher with time, with no change in other design parameters, there could be

problems with scaling or compaction, leading to possible loss in productivity. For all these

reasons, it is important that the following parameters be monitored with instrumentation on

all NF and RO systems, if possible:

l Feed, concentrate, and product conductivity for each stage.

l Feed, interstage, and concentrate pressure.

l Feed temperature.

l Feed pH, turbidity, and free chlorine concentration.

Conductivity is used as an estimate of concentration for real-time performance tracking.

However, since performance is dependent on a number of factors, it is inadequate to track

any single parameter. Instead, normalized permeate flow (NPF) and the AP across each

pressure vessel are used to track performance. NPF is the permeate flow normalized for feed

concentration, temperature, and applied transmembrane pressure.

4.6
Manufacturer: A

Table 4.1.-Typical NF and RO performance specifications

B B B” C

Process Seawater RO

Configuration Spiral Wound

Membrane polymer Polyamide

Area 27.67 m (306ft ) ’

Minimum salt rejection 99.6%

Permeate flow 19 m /day (5 kgal/day)

Max applied pressure 6.3 MPa (1200 lb/in )

Max feed flow Process dependent

Max operating temperature 45 “C (113 “F)

Feed water pH range 4.11

Max feedwater turbidity 1.0 NTU

Max chlorine concentration 0

Single element recovery 17%

Max pressure drop per element Process dependent

Brackish RO

Spiral Wound

Composite Polyamide

37.16 m’ (400 ft’)

99.0%

45.4 ma/day (12 kgal/day)

4.16 MPa (6db lb/in’)

264 Umin (75 gal/min)

45 “C (113 “F)

3-10

1.0 NTU

~0.1 mg/L

15%

69 kPa (10 lb/in )

Brackish RO

Hollow Fine Fiber

Aramid

845.4 m * (9100 ft*)

95.0%

140 m3/day (37 kgal/day)

4.14 MPa (600 lb/in*)

176 Umin (46.5 gallmin)

40 “C (104 “F)

4-11

1 .O NTU

0

50%

69 kPa (10 lb/in’)

Brackish RO

Spiral Wound

Cellulose Acetate Blend

49 m * (528 ft’)

98%

39.7 m’/day (10.5 kgal/day

4.14 MPa (600 lb/in’)

137.8 Umin (36.4 gallmin)

40 “C (104 “F)

4-6

1 .O NTU

1 .O mglL

20%

104 kPa (15 lb/in*)

N F

Spiral Wound

Composite Polyamide

37 m * (400 ft2)

70% NaCI, 95% MgSO

47 m3/day (12.5 kgal/day)

1.7 MPa (250 lb/in’)

265 Umin (70 gal/min)

35 “C (95” F)

3-9

1 .O NTU

~0.1 mg/L

15%

Process dependent

Data from manufacturer’s literature.
NPF = F Nuy,,,,

’ NDP;,,,

TCF Eq. 4.8

NDP = Pa-PO-P P

Where:

F, =

NDPjnir =

NDP,&,, =

P, =

P, =

P, =

TCF =

Eq. 4.9

product flow,

net driving pressure at startup,

current net driving pressure,

applied pressure,

osmotic plus the hydraulic back pressure of the permeate,

osmotic pressure of the feed water calculated as above,

temperature correction factor calculated from an equation

supplied by the manufacturer. It has the effect of

decreasing the NPF above 25 “C and increasing it below

25 “C. At 25 “C, the TCF is equal to one.

Whenever there is a 10 percent change in NPF or AP, or a significant change in any of the

individual operating parameters, some corrective action, such as rinsing, cleaning, or system

maintenance, is required. Sudden changes during normal operating mode usually indicate a

mechanical problem with the system. Sudden increases in AP can indicate a blockage in one

of the pipes or in the lead end element. Sudden decreases usually mean that one of the

O-rings which prevent feed water from leaking around the membrane (and thus avoiding

treatment) has deteriorated. In any case, it is something that needs to be addressed right

away. In the author’s experience, most of the parameters that are monitored stay fairly

constant until the system needs attention (backwashing media filters, replacing cartridge

filters, replacing O-rings, etc.). Changes that indicate a problem with the membrane may be

gradual, such as a slow creep in AP or steady increase in product flow. Table 4.2 lists the

changes that can occur, possible causes, and solutions.

It is possible to spend ones entire life in fascination with the various ways RO membranes

can be ruined; those listed in table 4.2 merely scratch the surface. More detail can be found

in chapter 8 on membrane cleaning and preservation. Remember, pretreatment, close

monitoring, and timely cleaning are the keys to longevity in membrane systems.

4.4.1 Effect of Operation Parameters on Performance

Membrane performance depends on the chemical make up of the feed water, but given a

standard feed water, performance varies with pressure, water temperature, level of water

recovery, and the oxidation potential of the feed water. The first three of these factors are

4.8
Table 4.2.-Troubleshooting guide for NF and RO systems

Symptom Possible problems Solutions

Sudden T AP, no change in

rejection.

Sudden 1 AP, 1 rejection

Gradual I NPF 1st stage

may be a slight T rejection

Gradual I NPF 2nd stage

with I 2nd stage rejection

Gradual 1 NPF 1st stage

with I 1st stage rejection

Gradual T NPF 2nd stage,

with I 2nd stage rejection

Clogged cartridge filter

Blocked pipes, or front end of

membrane element

O-ring or brine seal failure,

cracked permeate tube

Biological or particulate fouling

Scaling

Lead end degradation caused

by reaction of free chlorine with

transition metals, or advanced

biofouling

Advanced scaling

Replace cartridge filter, Check

flows and front end of

membrane.

Isolate point of failure by

probing permeate tube with

conductivity sensor, then

replace defective part.

Clean 1st stage with high pH,

high temperature solution.

Clean 2nd stage with low pH

solution at standard operating

temperature.

Check dechlorination system,

check for sources of iron

directly ahead of membrane

system. Can sacrifice 1st

element to protect rest of

system. If problem is

advanced biofouling, replace

element and check prefiltration

and disinfection system.

Replace element and check

pretreatment system. May

need NF.

related to the feed water composition. The last is related to the material used in the

membrane. Figure 4.3 illustrates how applied pressure, feed water temperature, and water

recovery affect RO membrane flux and water quality. The graphs are generalized curves

intended to show trends; they are not based on actual data points.

E#ect of Pressure

The graph in figure 4.3 and the equation for “A” show that water flux is directly proportional

to applied pressure. After a certain point, though, higher pressures cause problems that result

in a decline in water flux. At high pressure, the feed water is forced against the membrane at

a higher velocity, forcing a greater number of foulants in the feed stream to interact at the

membrane surface. Material that might flow out of the system at lower pressure gets

impacted onto the membrane surface and hung up in the spacer at higher pressure. The added

layer causes a decline in water flux and may also aid in deterioration of the membrane

material and provide protection to bacterial colonies.

4.9
Membrane ;a p---j 5; m

Temperature Temperature

Membrane

J

Water Recovery Water Recovery

Figure 4.3.-The effects of applied pressure, feed temperature, and water recovery on

membrane flux and product water quality of RO membranes. (From Riley, 1990.)

Scaling problems increase at high pressures. If the water flux is greater than the system is

designed for, concentration polarization can cause precipitation of slightly soluble salts at the

membrane surface. Concentration polarization is the normal phenomena of salt build up at

the surface of a semi-permeable membrane. As the concentration builds, the local osmotic

pressure increases. Under normal operating conditions, ions diffise away from the membrane surface and the bulk flow carries them out of the system. But at higher operating

pressures, a higher surface osmotic pressure is required before diffusion away from the

membrane can take place, thus increasing the potential for scaling.

Membrane compaction and deformation are caused in part by excessive pressure. In the first

stages of compaction, the membrane structure is compressed, restricting the flow of water

and salt. The result is a decrease in water flux accompanied by an increase in product quality.

If the condition continues, the membrane can be forced into the mesh of the product water

carrier, causing minute tears to form (Kaakinen and Moody, 1985). An irreversible stage of

compaction begins, characterized by an increase in water flux as well as an increase in salt

passage. The time factor for compaction depends on other operating parameters. High

temperatures, high pH, and the presence of oxidants will speed up the process.

4.10
Effect of Temperature

The effect of temperature on RO and NF membranes is the result of an increase in enthalpy

of the system. Bonds within the membrane matrix are more relaxed, and salt molecules are

more active at higher temperatures (22.5 “C). Water passes through the membrane with

lower applied pressure than is required at lower temperatures. To a certain extent, salt flux is

also increased as temperature is increased, but the effect is not important at normal operating

temperatures.

Membrane manufacturers provide a table or formula for determining TCF (temperature

correction factors). The TCF is equal to 1 .OO at 25 “C and is proportional to the change in

pressure needed to maintain the 25 “C flux rate. Some manufacturers divide by the TCF to

equate flux at one temperature to flux at 25 “C, in which case the TCF is less than 1 .OO for

temperatures below 25 “C and greater than 1 .OO above 25 “C. Others choose to multiply flux

by the TCF to correct for temperature so their TCFs are inverted. Just remember that at low

temperatures the membrane flux will be lower, and to compare it to a high temperature flux,

one must increase the low temperature flux value.

Most cellulosic and thin film composite membranes listed in chapter 10 have maximum

temperature limits of 40 to 45 “C, which should be adequate for most surface and

groundwater sources. Streams at higher ambient temperatures should be used in a heat

transfer process before treatment. Excessive heat in the RO system can cause a variety of

problems. Carbonate scaling is more likely at higher temperatures, membrane compaction is

enhanced, and fouling caused by increased water flux is also more likely. Most membranes

can handle feed water at temperatures as low as 1 “C without problem. The membrane

matrix becomes more rigid at low temperatures and water flux decreases.

Effect ofpH

The pH of the feed water can affect the membrane structure and the scale formation potential

of the concentrate stream. Cellulosic membranes have a narrow operational pH range of 4 to

6. Some membranes have pH ranges as narrow as 5.5 to 6.0 (see tables 10.2 through 10.6).

If exposed to a pH outside this range, hydrolysis occurs. Bonds in the membrane matrix are

broken and replaced with hydroxyl ions, leaving holes in the matrix (Murphy, 1990). Thin

film composite membranes generally have a much broader operational pH range, some as

large as 2 to 11. Ceramics and metallics are untiected by pH.

The pH of the feed water may need adjustment to control scaling of the concentrate conveyance system. For example, silica solubility increases dramatically above pH 7.7, and at

higher temperatures. A silica scaling problem could be controlled by either raising the pH or

the temperature of the feed water. Calcium carbonate, on the other hand, is more soluble at

low temperatures and at a pH less than 8.0. A carbonate scaling problem can be relieved by

lowering the pH, temperature or adding anti-scalants. However, if the concentrate is

saturated in both silica and carbonate, changes in temperature or pH can cause one or the

other to precipitate. Care must be taken to find the best condition to prevent scaling.

4.11
Tolerance to Oxidation

Oxidants are added to water supplies to control biological growth, to improve taste and odor,

to remove iron and manganese, and to speed the decomposition of vegetable and animal

matter (Weber, 1972). In the past, chlorine has been used very reliably. The CA membranes

are chlorine tolerant. Non-cellulosic thin film composite membranes are not tolerant to

oxidation; yet some method of biological treatment is still needed. Systems that use chlorine

with thin film composite membranes require dechlorination just ahead of the RO unit.

Ozone, an aggressive oxidant, is useful for color removal, taste and odor removal, disinfection, iron and manganese removal, phenol oxidation, and cyanide oxidation (Weber, 1972).

Ozone is bubbled into the feed water allowing sufficient time for reaction. Ultraviolet light

is used to remove excess ozone before the feed water enters the membrane modules

(Zoccolante, 1990). UV irradiation also can be used as a disinfectant, but is only active

while the water is exposed to the light. Organisms that survive exposure can recontaminate

the system. When used with ozone, however, irradiation has a synergistic effect.

4.5 Post-treatment

Water produced from RO or NF processes is not exceptionally good for drinking. Depending

on the level of desalination, it may be corrosive to distribution lines. It is necessary to add

back some of the hardness by adding lime, which is another reason for using NF if possible.

Adding lime will also raise the pH, which is necessary if CA membranes were used. Water is

practically de-aerated in the RO and NF processes, so some aeration is needed to improve

flavor. Finally, chlorine is added to maintain the required residual disinfection prior to

distribution.

4.6 Applications

The use of RO membranes on a large scale for water treatment originally began in the 1960s

using CA membrane to remove salts ITom brackish water or seawater. The applications

evident in the 1990s include the traditional potable water applications, industrial and waste

water treatment, boiler feed water purification, irrigation return flow remediation, and

production of ultrapure water for the pharmaceutical and electronics industry. Commercial

applications have grown in diversity as listed in table 4.3.

Several manul?acturers in the U.S. were surveyed to find out how their membranes are being

used. A compilation of two of the top manufacturers (DuPont and Fluid Systems) indicated

that the they sold close to 5 1 percent of the systems to prepare potable water and 49 percent

of the systems for “other purposes.”

The information provided by these two companies has been compiled and organized in

table 4.4 and figure 4.4. A complete list of the information is provided in appendix A.

This is not intended as an extensive survey of manufacturers; however, this listing of over

4.12
Table 4.3.-RO and NF applications

Application Purpose

Potable water

Municipalities, cities, and towns

Resorts, hotels, and motels

Offshore drilling and production platforms

Mobile home parks

Realty developments

Island communities

Industrial applications

Rinsing electronic components

Boiler makeup

Process water

High-purity water

Electrodeposition paint processing

Special applications

Pharmaceuticals

Medical

Concentrating cheese whey and juice

Laboratories

Car washes

Small cooling towers

Humidifiers

Flower growers

Water bottlers

Ice rinks

Fish farms and hydroponic farming

Photographic wastes

Campgrounds

Soft (bottled) drink manufacturers

Ice manufacturers

Private home systems

Landscaping gardens, golf courses

Removes alcohol

Drinking water, bathing, laundry

Drinking water, bathing, laundry

Drinking water, bathing, laundry

Drinking water, bathing, laundry

Drinking water, bathing, laundry

Drinking water, bathing, laundry

High quality, uncontaminated components

Increases heat transfer by reducing scaling

Reduces waste, improves quality of process

Formulations, rinsing and cleaning metals,

polymerization reactions

Recycle stream reduces waste water

Create a pure product

Hemodialysis, separating proteins

dehydration

Reduce TDS

Prevent spotting

Reduce contaminant

Prevent scale

Better yields and quality

Reduce salinity

Smoother ice

Consistent quality

Potable

Remove organic& better taste

Reduce TDS

Improve quality

Reduce TDS, improved plant growth

Preserves flavor

Source: Dupont’s Guide to Products and Properties, Amjad, 1993.

4.13
Table 4.4 Capacities and number of systems

Application

Average

capacity

(1,000 gal/d)

Number of Capacity

systems (% of total)

Number of systems

(% of total)

Other applications:

Commercial

Electronics

Power

Industrial

Boiler feed water

Waste water

Subtotal

Potable water:

Potable - Brackish

Potable - Seawater

Potable - Groundwater

99 2 1 1.1 6.4

330 6 4 3.7 19.4

609 8 6.9 2.4

722 2 8 8.2 8.5

890 3 3 10.1 10.0

1,119 7 12.7 2.1

910 2 7 10.3 8.2

1,311 131 14.8 39.7

2,850 1 1 32.2 3.3

42.7 48.8

Total 8,840 330 100.0 100.0

300 installed applications is assumed to be a reflection of the variety of applications for these

processes. Many smaller firms exist and may be seeing different trends in their sales. More

detailed information which fully analyzes the world market may be available from the

Wangnick Consulting report from Germany (listed in the bibliography).

Several broad conclusions can be made regarding this compilation. Three of the top four

capacity applications are associated with the production of potable water. Treatment of

groundwater uses the highest amount of RO membranes at 32 percent of the total capacity.

After potable water, the largest applications are wastewater, boiler feed, industrial, power,

electronics, and commercial applications. Potable sea water had the largest number of

systems put in place with nearly 40 percent of all the systems. Next was the electronics

field at 19 percent, then boiler feed water at 10 percent.

Manufacturers are sorting out the market niches for RO membranes. One manufacturer has

dropped development of new applications and no longer sells spiral wound CA membranes.

They now concentrate on their most profitable hollow fine fiber membranes for sea or

brackish water purification sold primarily in Europe and the Middle East. Another

manufacturer indicated that the current driving force of expansion in the industry was

probably municipal water treatment.

4.14
Percent of Total Non-Potable Water Capacity

Commercial

Water

Percent of Total Capacity

Brackish

Percent of Total Non-Potable Water Systems

Boiler Feed Waste Water Commercial

Percent of Total Number of Systems

Seawater Non - Potable

Brackish

Figure 4.4.~-Distribution of membrane applications.
The other applications serve as a flourishing testing ground for new approaches to problems.

A review of the recent articles in the Chemical Abstracts indicates that many countries, in

particular India, Korea, and Japan, are highly involved in RO research. Surveying the

literature provided by the manufacturers points out that global application of this technology

was strong in the early 1980s and continues to expand throughout the 1990s.

4.7 NF or RO?

The RO and NF membranes available today are very similar. It seems that, rather than

marketing “RO” and “NF” membranes, manufacturers are producing different membranes to

cover a wide range of rejection characteristics. For this discussion, any membrane with

greater than 95 percent rejection of sodium chloride is considered an “RO” membrane, those

with between 45 and 95 percent rejection of sodium chloride are considered to be “NF”

membranes. So, how does one choose which to use for a particular situation? The following

questions can be answered with a good water analysis and will help with the decision.

l What is the TDS? If the TDS is over about l,500 mg/L, RO will probably be best.

l What is the target product water quality? If a reduction in TDS greater than -

90 percent is needed, RO will be necessary.

l What is the percentage of multi-valent ions? If the TDS is made up of mostly

multivalent ions, NF may be best.

l Which constituents exceed primary or secondary drinking water standards?

RO permeate can often be blended with water from another source, but if there are

contaminants that will exceed drinking water standards even when blended with RO

permeate, the cost of treating the blend water must be considered. If the cost is high

and/or there is a high percentage of multivalent ions, then NF may be a better choice.

l Are there size and cost restrictions? Systems can be designed to minimize any

parameter, but there are tradeoffs.

l What are the concentrate disposal options ? In some locations with only marginal

water quality, surface disposal may be possible if the concentrate TDS is not too

high. What is “too high” depends on the local soils, amount of precipitation, and

type of plants to be grown in the area. In other locations, concentrate volume will be

the most important factor.

The options for tailoring a membrane system to meet the specific objectives for cost and

concentrate stream characteristics at a tictitious site are explored in figure 4.5. Salinity of the

feed water is 1800 mgL TDS, 28 percent of which is multi-valent. The source water also

exceeds the secondary drinking water limit for manganese (0.05 mg/L) by 0.5 mg/L. NF

membranes with three different rejection characteristics are compared with RO using three

4.16
Analysis of Waste Stream For Different

Membrane Treatment Options

Treatment Option

Cost and Size Comparison for Different

Membrane Treatment Options

I+ Construction Cost 1

6 O&M cost

+ No. of 8” elements

Treatment Option

J

Figure 4.5.-Comparison of cost statistics for various membrane treatment options. Costs are based on

producing 2,000 m?day with a target TDS of 500 mg/L. The raw water is assumed to have 1,800 mg/L TDS,

28 percent multi-valent, with 0.55 mg/L Mn (secondary standard is 0.05 mg/L). B is blend with raw water.

RB is remediated blend, meaning the Mn in the blend water has been removed using green sand. NFB is

blend with NF-A product water which would have 788 mg/L TDS and less than 0.05 mg/L Mn.

4.17
different blending options to assess differences in the concentrate stream volume, concentration, total mass of salt produced, construction cost, O&M cost, and plant size. The

membrane characteristics used in this comparison are listed in table 4.5.

Table 4.5.-Membrane characteristics used in treatment option comparison.

Assumptions: 80 percent recovery; feed water has 1800 mg/L TDS; 28 percent

multi-valent ions, 0.55 mg/L manganese

NF-A NF-B NF-C RO-D

Element productivity m3/day 28.3 4 7 3 9 3 4

Mono-valent rejection 40% 70%’ 90%’ 98%’

Multi-valent rejection 98% 95% 95% 99.5%

’ Rejections are estimates based on laboratory tests.

The options of using selective NF membranes for treatment of water to be blended with

product from membrane NF-C, or RO-D, produce the lowest total concentrate volume. If

the concentrate stream had to be disposed of in an evaporation pond or brine concentrator,

low volume would be an important consideration because it controls the cost of disposal.

However, these two options also require the largest number of elements and are among the

most expensive to build.

Because of the low blend ratio, membrane NF-B with NF-A blend option has the lowest

concentrate TDS, but the highest volume. In this scenario, the product of membrane NF-B

has a concentration of about 400 mg&, just slightly below the standard of 500 mg/L.

Treatment of the blend water with membrane NF-A allows a 23 percent blend rate, but then

the concentrate stream is augmented with that of the NF-A system which is also operated at

80 percent recovery. However, if the concentrate stream TDS is low enough that it can be

used for irrigation, swimming pools, or dischtiged to surface water, the higher construction

cost and larger plant size would be out weighed by the lower disposal cost.

4.7.1 RO and NF Cost Comparison

There are two key interrelated cost controlling parameters for RO and NF. Both of these, the

operating pressure and the membrane capacity, are dependent on the difference in osmotic

pressure (or TDS) between the feed and product water. Figures 4.6- 4.8 show the change in

cost for three types of NF and brackish water RO treatment systems with increasing salinity

and volume. Figure 4.6 shows change in cost with total capacity, including blend volume.

Feed water is assumed to have a TDS of 1,800 mg/L for all membrane types except NF-A,

which is assumed to have 1,100 mg/L. NF-A would not be able to produce the target TDS of

500 mg/L from such a high salinity water. Capacity is directly related to membrane area,

which explains the linear aspect of the capacity-cost relationship. The hierarchy of the curves

is a function of blend ratio. If costs for plants with equivalent membrane area were compared, the hierarchy would be determined by operating pressure.

8
-0- NF-A cc

+ NF-B AC

+ NF-B CC

+NF-C AC

-e NF-C CC

+RO-DCC

-+- RO-D AC

8ooo 10000 12000

Cubic Meters per Day Capacity

14om 16000 18000 2oooa

Figure 4.6.-Costs for plants to produce 500 mg/L TDS drinking water including blend water. Multi-valent ion concentration is 28 percent. Interest rate is 7 percent for 15 years. Plant is assumed to operate 85 percent of the year. Brackish water RO costs jump at 1,100 and 2,700 mg/L because the high rejection rate produces

a large osmotic pressure differential which must be overcome with a higher operating pressure.
$6000

* $5ooo -O- NF-A CC

2

s

B

-A- NF-B CC

B@OoO

+ NF-C CC

-H- RO-D AC

ir $3ooo + RO-D CC

$

l,@JO w3.3 3,000 4WJ 5,000 6,oCQ 7,ooo

CC = Construction Cost Total Dissolved Solids (mg/L)

Figure 4.7.-Costs for plants to produce 7,569 mYday including blend water. Multi-valent ion concentration is 28 percent. Interest rate is 7 percent for 15 years.

Plant is assumed to operate 85 percent of the year. Brackish water RO costs jump at 1,100 and 2,700 mg/L because the high rejection rate produces a large

osmotic pressure differential which must be overcome with a higher operating pressure.
$2500

$500

$

500 700 900 1,100

CC = Construction Cost

AC = Annual Operation and Maintenance Cost + Interest

1,300 1300 1,700

Total Dissolved Solids (mg/L)

1,900 2,100 2,300 2,500

-8- NF-A AC

-eNFA CC

+I- NF-B AC

+ NF-B CC I

+-F-C AC

+ NF-C CC

4-RO-D A C

+ RO-D CC

Figure 4.8.-Costs for plants to produce 7,569 m3/day including blend water. Multi-valent ion concentration is 28 percent. Interest rate is 7 percent for 15 years.

Plant is assumed to operate 85 percent of the year. Brackish water RO costs jump at 1,100 mg/L because the high rejection rate produces a large osmotic pressure

differential which must be overcome with a higher operating pressure.
In both figures 4.7 and 4.8, costs are calculated to produce 7,569 m3 per day (2 million

gallons per day) assuming that TDS is the only problem with the source water and that the

product can be blended back with raw water to achieve 500 mg/L TDS. In figure 4.7, the

curves level out at the point where the TDS is too high to allow blending. Notice that the

RO curves take two sudden jumps at about 1 ,100 and 2,600 mg/L. This is because of the

additional equipment costs involved with operating at higher pressures, such as higher quality

pumps and high pressure piping. The NF membrane pressures do not exceed

1,700 kPa (about 250 psi). At low concentrations, shown in greater detail in figure 4.8,

the NF-C still has a slight advantage over RO because of the lower operating pressure.

One might wonder why the lower rejection NF membranes would be used if they are more

expensive. Concentrate disposal cost is not accounted for in this cost comparison, but as

discussed above, NF-A concentrate is more likely to be acceptable for surface discharge or

application than RO concentrate. Also, when there is the potential for scaling, RO feed water

would need more pretreatment than if a selective membrane, such as the NF-A, were to be

used. To bring the total cost of desalting treatment down, scenarios such as these need to be

analyzed thoroughly. There is a limit to the economies available if each process is evaluated

separately.

But when the complete treatment process is evaluated as a whole, from pretreatment to

concentrate disposal, there may be large economies that arise from having the flexibility to

choose a design that fits the disposal options available.

4.8 Research Needs in NF and RO

l Development of more robust systems. Improvements in water transport and salt

rejection are meaningless if they are accompanied by increased fouling potential.

The newer thin film composite membranes do have superior transport qualities but

they are extremely sensitive to fouling and difficult to clean (Chapman Wilbert,

1997). A new design is needed that promotes self-maintenance of the membranes,

perhaps an improved spacer, and/or membrane material that has a lower fouling

potential.

. A new method of dealing with biological fouling is needed. If organisms cannot be

kept from the feed stream, there will be biological fouling that will be difficult, if not

impossible, to remove without destroying the membrane. There are two possible

approaches to this problem: either find a way to keep the biofilms permeable so that

they cause a minimal increase in resistance to water transport, or find a way to

induce the biofilms inhabitants to leave on their own. Progress is being made in both

of these areas. Hopefully, it won’t be too long before research bears fruit in

application.

4.22
l Concentrate utilization is urgently needed. There must be beneficial uses for

concentrated salt solutions. When people spend $30.00 or more for 10 oz. of Salt

Lake mineral supplements it is hard to believe that RO concentrate is useless. It may

take selectively removing some components and adding others. We need to get some

nutritionists working on this problem.

4.23
Chapter 5

ELECTRODIALYSIS

5.1 Definition

Electrodialysis, ED for short, can be described, in the most general terms, as a process that

moves ions (charged molecular species) from one solution to another, employing an electrical

potential as the driving force and using some sort of semipermeable membrane as a separator.

This process can be used for concentration, dilution, or segregation of ionic species. The

classical reference on electrodialysis of water, for breadth of approach and depth of research,

is the book by Wilson (Wilson, 1960).

5.2 Background

A primitive form of electrodialysis has been used for salt removal from solutions since the

beginning of the twentieth century, primarily in the laboratory. With the invention of the

synthetic ion-exchange membrane in 1948, it became a practical means for water

desalination. Electrodialysis was publicly demonstrated in 1952 (Lawrence, 1952). The

introduction of current reversal electrodialysis in the early 1970s made operation with no

chemical addition possible.

5.3 Membranes

The synthetic ion-exchange membrane contains fixed charges usually of only one sort

(positive or negative) attached to a polymer backbone. Because of the fixed charges, the

material is usually highly hydrated. The membrane has pores of molecular dimensions,

undoubtedly irregular in shape and size, bounded by fixed charges of one sort filled with

water containing the mobile ions having a charge opposite to that of the fixed charges. In the

membrane, ions of opposite charge to the fixed charges are called “counterions” and ions of

the same charge as the fixed charges are called “coions.” There is a low concentration of

coions in an ion-exchange membrane.

One material commonly used in making ion-exchange materials is styrene, C,H,, which has

the following structural formula:

5.1
Styrene: or more

H=\ //

C

simply:

H

Styrene is a commonly available organic compound, currently available at a bulk price of less

than $0.40 per pound. It is a pungent, volatile aromatic liquid at room temperature. Under

fairly gentle conditions, i.e., at temperatures slightly above room temperature and at room

pressure, and with a suitable catalyst, this can be converted to a linear polymer of high

molecular weight. The linear polymer, a thermoplastic, has the structure like a chain of

beads. The chain is drawn as a straight line for convenience. Subject to steric limitations,

fairly free rotation around the single carbon-carbon bonds is expected.

- HC-C/i,- HC-CH,- HC-CH,- HC-CH,- HC-CCH,

o@fJo(J

HY - CH,-

0/

\,/

Divinyl benzene, CIOHIO, a fairly common organic compound, is similar to styrene but it

contains a second vinyl group attached to the ring. It has three isomers, the para isomer is

shown.

HC = CH,

Divinyl

\

-3 benzene:

/

I

HC= CH,

This is used as a cross-linking agent for styrene-based polymers. The sketch below shows

two polystyrene chains with a single crosslink.

5.2
-HY

-CH,- HT-CH,- HC-CH,- Hy-CH,- HT-CH,-

Crosslinking makes the polymer thermosetting, causing hardness in the polymer and

decreased solubility, depending on the mol ratio of divinyl benzene to styrene.

A third compound is normally added to the chemical mixture before polymerization to

improve this polymer for use as an ion-exchange membrane, a material soluble in the

styreneldivinyl benzene mixture, but incapable of polymerization. Such a material is diethyl

benzene, C,oH,,.

benzene:

H,k-CH,

This will cause the resulting polymeric network to be more open and will increase the water

content of the finished membrane.

A sulfonate group can be added to a benzene ring of the polymerized crosslinked polystyrene

by exposing it to strong sulfuric acid.

5.3
-ljC-CH,- -ljC-CH,-

+ H,O

Typically, there will be slightly less than one sulfonate group per benzene ring. This reaction

supplies a fixed negative charge to the polymer and converts a piece of plastic into an ionexchange material. When equilibrated in water, the material, though electrically neutral, has

mobile positive charges and fixed negative charges. Note that the hydrogen ion is not

associated with a particular sulfonate group but is reasonably free to wander about in the

aqueous phase of the membrane. Ions in the pores of the membrane can, subject to

quantifiable rules of mass transport, exchange with ions in solutions surrounding the

membrane. Of particular importance to ED, motion of ions is infhtenced by electrical

potentials applied across the membrane.

In a manner analogous to the creation of this membrane, the polymerized polystyrene can be

treated with a tertiary amine to produce a membrane with a fixed positive charge.

Strength and flexibility are gained by casting this polymer mixture on a fabric backing. By

such means, one obtains an ion exchange material in sheet form suitable for use in

electrodialysis. The resulting product can be called a “cation-passing,” “cation-exchange,”

“cation-transfer,” or, simply, “cation” membrane. All these terminologies are used in the

literature and in the field. Curiously, since the membranes are named after the mobile species,

a cation membrane is actually a polyanion.

High conductivity ion-exchange membranes usually have a high water content. They are

translucent and generally tan in color, somewhere between ivory and brown. When exposed

to dry air, high water content membranes lose water and can lose physical integrity. Under

this condition, the membrane turns opaque due to small cracks in the polymer structure.

A variety of other approaches can be used to generate ion-exchange membranes. In addition

to the procedure described above, “homogeneous” membranes can also be produced by

sorbing monomer, like styrene, into existing polymer films, such as polyethylene.

“Heterogeneous” membranes can be made by using a binder to adhere finely divided ionexchange particles to each other and, if desired, to a fabric. Kesting (197 1, chapter 7)

describes a number of approaches to manufacture ion-exchange membranes.

5.4 Membrane Properties

A number of properties of ion-exchange membranes can be measured. Those of interest to

the electrodialysis process are resistance, permselectivity, and flexural or burst strength.

5.4
Electrical resistance in a membrane is analogous to electrical resistance in an electronic

conductor. It is the ratio of potential drop to current passed. The difference is that in the

membrane, current is being carried by ionic species rather than by electrons.

Permselectivity is the ratio of the current carried by the mobile, or counterions, to the total

current. While it might appear that all of the current should be carried by the counterions,

there is usually a small fraction which is carried by ions of the same charge as the fixed

charges in the membrane. For a given membrane, permselectivity may be significantly

affected by the concentration and ionic composition of the solutions in which the membrane

is immersed. Temperature and pressure, in the range used in water desalination, have little

effect on it.

Flexural strength is a concern only when one looks at use of the membrane in ED equipment,

described below. Typically, a membrane is optimized in terms of polymer/crosslinker/nonpolymerizable ratios to give good transport properties. Then it is left to the equipment

engineer to design a system which can contain and support the resulting membrane. Because

the pressure applied across a membrane in an ED system is very modest, membranes are

rarely taken to the point of bursting. However, the burst strength test is a useful means of

quality control on membrane manufacture and a convenient measure of membrane

degradation in use. Lior (1986, chapter 2.7) provides details of performing these tests.

5.5 Electrodialysis Process

The basis of the process is straightforward.’ When dissolved in water, salts, acids, and bases

dissociate into ions. An electrical field can be produced across a solution by immersing a

pair of electrodes into an ionic solution in a container or cell and applying a direct current

potential difference to the electrodes. This produces a general motion of ions. As indicated

below, negatively charged anions, like chloride ions (Cl-) or hydroxide ions (OH-), migrate

toward the anode, and positively charged cations, like sodium ions or magnesium ions,

migrate toward the cathode. In a solution of sodium chloride, about half the current is carried

by cations, migrating to the left in the diagram, and half by anions migrating in the opposite

direction. This discussion focuses on the motion of the ions. What occurs at the electrodes

will be covered later.

’ To avoid a frequent repetition of “usually,” “ often,” or “generally,” the text below is written to

express the common phenomena. The author recognizes that there are fi-equent exceptions.

5.5
In such a solution, an ion-exchange membrane acts as a one-way street, permitting migration

of ions of only one charge. If a cation membrane is inserted between the electrodes, one will

observe a depletion of cations (and thus of salt) on the side facing the anode and an increase

of cations on the side facing the cathode.

CathodeG-

-0

Q-- 1.Anode

If an anion membrane is inserted in the cell between the cation membrane and the anode, one

will observe a general depletion of salt in the compartment between the membranes.

Cathode- ~ Anode

C. A4 A. Ad

If the membrane positions are reversed with respect to the electrodes, passage of current will

cause an increase in concentration of salt within the compartment.

5.6
CathodeA. A4 c. M

In an alternating series of membranes, three membranes are shown below, we find a diluting

compartment next to a concentrating compartment. The grouping consisting of a cation

membrane, a diluting compartment, an anion membrane and a concentrating compartment is

the fundamental building block, termed a “cell pair,” of which an electrodialysis stack is

made.

Cathode- IAnode

c. A4 A. M C. M

Conceptually, it is only a small step from one cell pair, as shown above, to the large number

of cell pairs between one pair of electrodes which comprise an electrodialysis stack.

At the electrodes, electrochemical reactions occur. These reactions change the current from a

flow of electrons to a flow of ions. The most common reactions are the following:

At the cathode: 2H’ + 2e- + I-$ (g)

At the anode: 20H- - H,O + i02 (g) + 2eor

2Cl- - Cl, (g) + 2e5.7
The effect of the electrode reactions is minimized by using a large number of cell pairs

between one pair of electrodes. However, a certain amount of gas is evolved that must be

disposed of.

5.6 Electrodialysis Apparatus

Commercial electrodialysis apparatus is operated on a continuous flow basis. The description

above is for a batch cell, but similar principles apply to continuous apparatus. Mason and

Kirkham (1959) provide a very thorough analytical treatment of electrodialysis as a process.

Another good general reference on electrodialysis is the article by Solt (Meares, 1976). See

also (Li, 1972).

A variety of commercial systems are available. The physical structure of the equipment is

quite varied. These are based on membranes having an area of 0.5 to 1.5 square meters. The

compartments between the membranes are formed by gaskets or spacers between 0.5 and

1 mm thick. These gaskets support and separate the membranes and control and direct the

flow of water through the compartments. As many as 600 cell pairs may be placed between a

pair of electrodes. When the entire assemblage is placed between a pair of compression

blocks, the result is the basic building block of an electrodialysis system, usually termed a

“stack.” For no obvious reason, the membranes in American electrodialysis stacks are

oriented horizontally and those in stacks made in Japan are oriented vertically. The residence

time of water in the stack is a small number of seconds.

Some structural details may be of interest. Water is fed into and removed from the

compartments by holes cut in the membranes and the frames of the spacer which are aligned

to form manifolds, In the areas which connect the open area of the compartment to the

appropriate manifold, the membranes need to be supported to prevent leakage from the

manifold to the alternate compartment. Two general forms of spacers are in use. The “sheet

flow” spacer is an open frame containing a net like material which allows passage of water

parallel to the membrane surfaces and passage of current normal to the membrane surfaces.

Fluid flow is essentially parallel to the long dimension of the stack. The other sort of spacer

is the “tortuous path” spacer in which the flow path bends back and forth on itself yielding a

path length which is about four to eight times the length of the longer dimension of the

membrane. This type of spacer contains “turbulence promoters” which are half the thickness

of the spacer in height and designed to promote mixing at the membrane surface. Because

they are chemically more stable, cation membranes are used next to both the cathode and the

anode. A more robust, i.e., thicker, membrane is used next to the electrodes.

While it is not the purpose of this paper to provide sufficient detail to allow the reader to

design an electrodialysis system, some quantitative relationships may be useful. A large

number of variables must be set in design of an ED plant, which is best done by the

manufacturer of the equipment. The following estimating equations are given to show the

relationship of required area and power for a given desalination. The cell pair area, AP, is

given by

5.8
A, =

cdiFRpofoFd

Te

and the power, P, in watts, is given by

P = ‘pCdi FfoFd

e

Eq. 5.1

Eq. 5.2

Variables in these equations are explained below. The factor Tis constant.

F = 96,500 Asleq

Certain variables depend on the application; i.e., what is the salinity of the feed, how much

this is to be reduced, and how much water is to be treated.

Cdi = inlet feed concentration, es/m3

f. = “Cut” =

feed concentration - product concentration

feed concentration

, dimensionless

F, = feed rate, m3/s

Other variables are determined by the equipment used:

e = current efiiciency, dimensionless

R, = resistance per cell pair, Q.mL

VP = cell pair voltage, V

For estimating purposes, one can take e = 90%, I$, = 0.01 Q.~~, and VP = 2 volts. l-he

approximation for area in equation 1 becomes inaccurate for cuts greater than 50 percent. If a

cut of 75 percent is required. for example, it is best to assume that there will be two stacks

each operating at 50 percent and total the area required.

5.9
5.7 Electrodialysis Operation

Passage of current through the stack causes ion removal from the solution being desalted. The

ion removal occurs right at the membrane solution interface. Almost 100 percent of the

current in the membrane is carried by the counterions, while only about 50 percent of the

current in the solution is carried by ions of the same charge. This leads to lowering of

concentration at the interface. This deficiency of ions at the interface is made up by

convective mass transfer and diffusion from the bulk solution. The rate of convective transfer

determines the maximum current flow through the stack. Thus, considerable design effort has

gone into the problem of improving convective mass transfer to the membrane surface, and

fluid velocity through the compartment is an important design variable. Marincid and Leitz

(1972) reported detailed studies on the effect of turbulence promoters on mass transfer to a

flat surface like that of the ED membrane.

As the solution passes between the membranes bounding the diluting compartments, salt is

gradually stripped from the solution. This salt is transferred into the concentrating

compartments. As one moves down the path from the feed end, the cell pair resistance

gradually increases, and since the driving potential is constant, the current density slowly

decreases. In practice, the system is usually designed so that the salt concentration in the

diluate is decreased to no more than one half in a single stage, i.e., between a single pair of

electrodes. A sufficient number of stages is used to get the desired total degree of

desalination.

If the same spacers are used for the diluting and concentrating compartments, then the same

flow velocity is normally used to keep the pressure drop across the membranes to a

minimum. If the concentrate stream were discharged directly after a single pass, one of the

best features of electrodialysis would be lost. Very high recoveries can be obtained by

recirculating most of the concentrate stream, i.e., by operating in the feed-and-bleed mode.

A comparatively recent development has been electrodialysis reversal, often abbreviated to

EDR. In this process, the polarity of the applied voltage is changed periodically, every 15

minutes or so. Reversing polarity converts the concentrating compartments to diluting

compartments and vice versa. This means that the plumbing connections need to be reversed

and for a few seconds after reversal, the product is out of specifications. The electrodes need

to be able to function as both anodes and cathodes. What these modest inconveniences

provide, however, is a self-cleaning stack. Any solid matter which may have been pushed

against the membrane surface by the current is now carried in the opposite direction away

from the membranes.

5.8 Electrodialysis Applications

The principal application of electrodialysis in the United States is for the desalination of

water. Other applications include whey deasbing (desalting) and recovery and concentration

of metals from spent plating solutions. In Japan, the principal use has been for concentration

5.10
of salts in sea water to produce table salt. An extensive list of references showing the breadth

of applications is given in the chapter on electrodialysis in Weissberger and Rossiter (1971).

Wangnick (1994, 1996) provides data on the worldwide application of electrodialysis for

water desalting. The total capacity of land-based ED desalting plants with a product capacity

of 100 cubic meters/day (26,400 U.S. gallons/day) in 1996 is reported to be 1.16 million

cubic meters per day (307 million U.S. gallons per day). The 1994 report lists a total of 828

plants with a product capacity of 100 cubic meters/day, of which 13 are reported as out of use

or removed. The 1996 report lists a total of 389 plants with a capacity of 500 cubic meters

per day, including hybrid process plants of which 7 are reported as out of use or removed. Of

the 389 plants, 327 are listed as reversal plants. The great majority of these plants have been

supplied by Ionics, Incorporated. Recently, a number of plants have proceeded from Asahi

Glass Co., Ltd. Other suppliers over the last three decades have included Asahi Chemical

Co., Ltd.; Christ AG; Deutsche Babcock Anlagen AG; Ebara-Infilco Co., Ltd./Tokuyama

Soda Co., Ltd.; FISIA SpA; Japan Organ0 Co., Ltd.; Mitsubishi Heavy Industries, Ltd.;

Nippon Rensui Co., Ltd.; Permutit Company, Inc.; Portals Water Treatment, Ltd.; ShinkoPantec Co., Ltd.; and Societtc Recherche Technique et Industrielie. Whether some of these

companies are still producing or selling electrodialysis equipment is not known.

5.9 Electrodialysis Economics

Electrodialysis costs are difficult to generalize. They are specific to feedwater and sensitive

to the economic climate in which the plant is built. Probably the best generalization is that

below a feed salinity of 3,000 mg/L ED can be competitive with and may be economically or

operationally advantageous over RO.

A very detailed study on operation and costs of electrodialysis plants in the United States is

that done by DSS Engineers (Latour, 1980), Volume III. This group visited each ED plant

and interviewed the operators on site. While slightly dated, this study goes into considerable

detail. For comparison of processes, this group reported on 13 RO plants in Volume II of the

same study.

More recently, results of a survey based on responses to a one-page questionnaire received

from 17 owners of electrodialysis reversal plants are presented by Leitner (1997). This study

also covers RO and membrane softening plants.

An interesting comparison of plant performance and cost for ED, RO, and NF under a single

set of operating conditions will be provided by the Port Hueneme demonstration plant. This

plant, described by Thompson et al. (1997), contains a train of each of these processes

designed to reduce water with total dissolved solids of 1,015 ppm to 370 ppm. In the case of

RO and NF, the product salinity will be obtained by blending with bypass water. Operation

is expected to begin in 1998.

5.11
Chapter 6

PRETREATMENT PROCESSES

The importance of pretreatment prior to membrane separations cannot be stressed enough.

Membrane performance and life expectancy depend heavily on the quality of the feed water.

Ideally, feed water to RO and NF systems should be clean, containing nothing but dissolved

salts. In reality, many of these systems are run with a lower quality feed water, which causes

problems with fouling, decreased capacity, and increased cleaning and replacement costs. An

extensive comparison of pretreatment technologies is beyond the scope of this work, but

pretreatment is so important that a summary of common problems and technologies for

remediation is offered.

6.1 Particulates

Cartridge microfilters are designed to remove at least 90 percent of particles larger than their

nominal rated size. Most are depth filters, which trap particles within tortuous passages as

the water runs through. They are dead-end systems that process all the water passing through

after an initial wetting period. When the back pressure reaches a specified level (65 to 240

kPa), the filters are replaced. Particulates are disposed of with the filter as solid waste.

Cartridge life expectancy depends on the particulate loading and the flow rate. Costs for

cartridge filtration depend on the micrometer rating, size, replacement rate, and type of

cartridge housing.

6.2 Colloidal Fouling

Colloids are metal oxides, soaps, detergents, proteins, organic matter, silicates, and clay

usually found in surface water. These substances generally have a negative surface charge.

Water molecules and positively charged ions form a double charge layer around colloidal

particles. Positive molecular poles and cations are attracted to the surface of the particle.

The negative poles of water molecules around the particle cause a repulsive force between

particles. Conditions of high pressure and ionic concentrations at the membrane surface

cause these repulsive forces to be overcome and attractive van der Waals forces then cause

the particles to coalesce. The result is the formation of a colloidal slime on the membrane

that is difficult to remove. For this reason, the SD1 (silt density index), a measurement of

colloid concentration, should be no higher than 5.0 for spiral wound membranes and no

greater than 3.0 for HFF membranes. See van Olphen (1977), Iler (1979), or Hiemenz (1986)

for more extensive discussions of colloid and surface chemistry.

6.1
6.2.1 Avoidance

Since colloids occur naturally in surface water, one way to avoid the problem of colloidal

fouling is to locate intake pipes in wells adjacent to the surface water source. In this way, the

soil and rock can be used as a natural filter. This method is used at some seawater RO plants.

By using the beach sand as a filter, both SD1 and turbidity of the intake water are reduced.

6.2.2 Flocculation, Settling, and Filtration

Colloids can be removed by co-precipitation with Al(III), Fe(III), or Si(IV) hydroxides. The

negatively charged colloids are surrounded by the metal cations and thus form a nucleus for

their precipitation. The same thing happens when lime is used for softening. When polymer

is added for coagulation the long chains can act as bridges linking colloidal particles and

aiding in floe formation (O’Melia, 1972).

Effectiveness of colloid removal is dependent on pH, the concentration of colloids, and the

charge of the metal cation used in co-precipitation. Higher charged cations, such as Fe(III)

and Si(IV), are more effective than sodium and Magnesium (with +l and +2 charges). The

optimum pH depends on the precipitant. The optimum pH for AI( precipitation is about

6 while that for Fe(OH), is 8.

6.2.3 Diatomaceous Earth Filtration

DE (diatomaceous earth) is the fossilized remains of siliceous shells of marine origin. It is

composed of grains with diameters from 5 to 100 pm. Colloids, emulsified oils, and other

hydrocarbons are adsorbed onto the rough, porous surface of these grains (Degremont, 1991).

Diatomaceous earth may be treated with a substance such as alum to enhance surface

retention of small particles, just as microbial slimes enhance retention in sand filters (Bell

and Himes, 1982). However, DE filters are prone to plugging if the feed water bas an SD1 of

6 or higher (Permasep Engineering Manual #506,1982).

6.2.4 Ultrafiltration

Ultrafilters with MWCOs between 200 and 20,000 Daltons can be used to remove silica and

colloids. These filters are operated at low pressure and high recirculation rates so that fouling

is not as much of a problem as it would be with RO membranes. Some are durable enough to

be cleaned under harsh conditions that RO membranes cannot tolerate.

The absence of sludge and the compactness of the process are some of the benefits of using

UF as opposed to the traditional precipitation processes. UF requires the same type of

equipment as RO. In fact, depending on the feed water composition and the type of

6.2
membrane used, ultrafilters could be incorporated into the RO system ahead of the RO

membrane. Booster pumps may be needed to get the pressure up to the level required for

RO.

6.3 Iron and Manganese

Iron is found in groundwater and deep surface water low in dissolved oxygen. It may be in

either the soluble ferrous state (Fe”); the ferric state (Fe’3); in inorganic complexes with

silicates, phosphates, polyphosphates, sulfates, cyanides, and others; or organic complexes

with humic, fulvic, and/or tannic acids (Degremont, 1991). Underground water usually has

iron as ferrous bicarbonate. When dissolved ferrous bicarbonate is exposed to air, the iron

may become oxidized to the ferric state in which it forms an insoluble hydroxide that is

difficult to remove from membrane surfaces. Manganese is usually found with iron and

behaves similarly.

6.3.1 Oxidation/Filtration

Iron can be precipitated by increasing the oxidation potential and/or the pH. When iron

concentration is between 5 to 10 mg/L and no other problems exist with manganese, color,

turbidity, or organic acids, the iron can be precipitated by oxidation with air. The rate of

reaction is directly proportional to the pH and dissolved oxygen content. After oxidation, the

treated water requires filtration with media capable of removing 0.5- to 1 -mm particles.

If iron concentration is higher or other contaminants are present in the water, a coagulant

such as aluminum sulfate or ferric chloride is added to enhance removal of organics. A

settling tank between the oxidation and filtration steps is used to remove larger precipitates.

6.3.2 Iron Removal With Lime Softening

When softening is required, iron can be removed in the same step. At a pH of about 8,

practically all iron is precipitated as FeCO,.

6.3.3 Biological Removal

Under the right conditions, certain bacteria will convert Fe3+ to Fe(OH), within or on the

sheaths surrounding their bodies. The optimum conditions are:

Dissolved oxygen 0.2 to 0.5 mg/L

P H 6.3

Redox potential 100 mV

Any H,S should be removed by aeration prior to the fermentation tank (Degremont, 1991).

6.3
6.3.4 Oxidation Of Manganese With MnO,

The reaction rate of oxidation of Mn*’ with air is too slow to be practical; manganese dioxide

(MnO,) works much faster. When mixed into a sand filter, MnO, reacts with Mn*’ by the

following reaction:

Mn*’ + MnO, - MnO,*Mn*’ Fast Rate

MnO,*Mn*’ + 0, - 2Mn0, Slow Rate

Eq. 6.1

In this way, manganese is held in the sand filter, giving oxygen in the water a chance to

oxidize it. Eventually, the filter bed becomes saturated with manganese dioxide, leading to

the formation of Mn20,, and the bed must then be regenerated with potassium permanganate

(KMnO,). The regeneration follows the reaction:

Mn,O, + 2MnO; + 2H,O - 5Mn0, + 4H’ Eq. 6.2

Theoretically the required ratio of KMnO, to Mn is 1.9: 1 .O.

Potassium permanganate or ozone can be added directly to the water to oxidize Mn*+ in the

same manner. The ratio of KMnO, to Mn*+ is 1.9: 1; the ratio for ozone is 0.9: 1 .O. The

addition of excess oxidant will produce MnO,, which turns the water pink (Degrkmont,

1991).

63.5 Biological Manganese Removal

Manganese can be removed by biological processes similar to iron removal. However, they

cannot be removed in the same bioreactor. Bacteria that accumulate manganese do so in an

environment with a redox potential of at least 400 mV. At lower potentials, MnO, will be

dissolved into Mn** instead of the reverse. Culturing a sufficient bed of manganeseaccumulating microbes takes about 3 months (Degrkmont, 199 1).

6.4 Scaling

Scaling is caused by the precipitation of slightly soluble salts such as MgCO,, CaCO,,

CaSO,, BaSO,, SrSO,, Cal?,, and SiO, within the membrane module and the concentrate

removal system. Solubility of these salts depends on temperature and PH. Higher

temperatures and pH facilitate precipitation of carbonates and sulfates. The concentration of

these salts in the feed must be low enough that the concentration in the reject is still below

saturation.

The LSI (Langeher Saturation Index) is the standard measure of scaling potential given by the

simplified equation:

LSI = pH, - pH, Eq. 6.3

6.4
The pH, is the pH of the reject; the pH, is the saturation pH of the reject stream calculated

from total dissolved solids, temperature, calcium concentration, and alkalinity of the feed

water and the percent recovery. If the LSI is negative, CaCO, tends to dissolve; if it is

positive, CaCO, tends to precipitate. The LSI is not a quantitative measure. It does not

predict scaling, only the tendency toward scaling or corrosion. Some manufacturers void

their guarantee if membranes are used with a positive LSI; others recommend limits.

Because of reaction time, and the fact that the actual amount of CaCO, over the saturation

level may be small, running an RO or NF system with a slightly positive LSI may be possible.

Softening techniques to lower the LSI involve shifting the carbonate system by:

l Acidification - converts HCO, to CO,;

l Addition of lime and soda ash - causes precipitation;

l Ion Exchange - replaces cations with sodium; and

l NF - removes dissolved divalent salts.

6.4.1 Acidification

The addition of HCl or H,SO, causes the reduction of bicarbonate ion to water and carbon

dioxide. At atmospheric pressure, the CO, bubbles out of solution and is no longer available

for carbonate production. Bicarbonate is a potent buffer, the amount of H’ required to change

the pH is logarithmically proportional to the concentration of HCO,-.

After acidification has forced the bicarbonate ions out of solution, the metallic cations are

balanced by Cl if HCI was used, or SOi, if H,SO, was used. Sulfuric acid is stronger than

hydrochloric acid, so the pH can be lowered with a smaller amount, but the fact that SO; can

cause scaling problems with barium, lead, and calcium should be taken into consideration.

6.4.2 Lime Softening

Lime, Ca(OH),, reacts with bicarbonate ions in the following manner:

Ca(OH), + Ca(HCO,), - 2CaCO,l+ 2H,O and

Ca(OH), + Mg(HCOJz - CaCO, 1 + MgCO, + 2H,O

Eq. 6.4

Additional lime will precipitate Mg? to its theoretical solubility under existing conditions:

Ca(OH), + MgCO, - CaCO, 1 + Mg(OH)* 1 Eq. 6.5

Lime softening is an old, reliable process, but it produces massive quantities of sludge that

require settling ponds and filter presses for dewatering. To remove 160 mg/L of Ca(HCO,),

and 160 mg/L of Mg(HCO&, from one cubic meter of water by the above equations, 15.5 g of

lime are required that produce 3 10 g of carbonate solids. The solids are mixed with water

6.5
though, after settling and pumping off the supematant, the sludge is still about 75 percent

water by weight, resulting in a total weight of 1,240 g. Multiply these amounts by a modest

5,000 m3/d plant, and the sludge is increased to 6,200 kg/d.

6.4.3 Ion Exchange

Another approach for softening is to use cationic resins to replace the calcium ions (or other

divalent cations) with sodium ions, which do not form insoluble salts with carbonate ion.

Resin beads have multiple sites of ionic attachment. These sites are preferentially taken up

by multivalent cations. During the service phase of operation, two sodium ions are displaced

by a calcium cation. The number of sites per volume of resin (capacity) is supplied by the

manufacturer. The depth of the resin bed and the necessary flow rates can be calculated from

the resin capacity, the divalent ion concentration in the feed water, and the volume of water to

be treated.

When most of the attachment sites have been taken up, calcium begins to appear in the

product water and the resin must be regenerated. During regeneration, a strong sodium

chloride solution is passed through the resin bed until the amount of calcium in the product

water falls off. Rohm and Haas (1978) recommend 3 to 10 L of 10 percent NaCl solution per

liter of resin at a flow rate of 130 mL/min per liter of resin for complete regeneration of their

Amberlite@ IR-120 Plus (Rohm and Haas, 1978).

Ion exchange is well suited for incorporation into an RO system. Depending on the salinity

and pH, the RO concentrate may be used as regenerant solution. Cation exchange resins can

be adequately regenerated at lower concentrations than 10 pet with lower flow rates and

longer regeneration cycles (Haugseth and Bietelshees, 1974). However, precipitation of

CaCO, may cause problems because the cations removed from the resin are reintroduced to

the concentrated bicarbonate ions in the concentrate.

6.4.4 Nanofdtration

NF membranes preferentially reject divalent ions over monovalent ions at a rate of about 95

percent to 75 percent. Chloride ions tend to pass through the membrane while divalent

carbonate ions are retained. It is unclear whether bicarbonate ions are rejected at the same

rate as chloride. The rate of rejection really depends on the composition of the water. The

calcium and magnesium must be balanced by an equivalent negative charge. If divalent

anions are scarce then ion size will be the determining factor. Larger monovalent ions will

tend to be retained and bicarbonate is almost twice as large as chloride (61:35).

The reject from NF contains approximately 95 percent of the divalent (and higher) cations,

50 to 75 percent of the monovalent cations, and an equivalent percentage of the higher

charged, and larger anions in 10 to 15 percent of the water. Because some bicarbonate passes

through the membrane, scaling may not be a problem in the reject conveyance system. Only

a pilot test can tell exactly what the reject carbonate concentration will be. If supersaturation

6.6
occurs, the carbonate balance of the reject must be adjusted. CaCO, crystals can be seeded at

this point, encouraging the scale formation on the crystals instead of the plumbing, or acid

can be added to shift the carbonate balance toward CO, formation rather than CaCO,.

The benefits of NF are that no sludge is produced, little if any additional chemicals are

needed, and it is compact in size. The disadvantages are the difficulty in predicting anion

rejection, the need for cleaning and proper storage of the membranes, pretreatment for

bacteria, and the disposal of the concentrate stream.

6.5 Biological Matter

Biological matter refers to micro-organisms, living or dead, and pyrogens, which are

biological waste products excreted on the outer surface of micro-organisms or bits of

micro-organisms. When live microbes are present in the feed water they form colonies on

membranes and other surfaces on or in the pressure vessel. Microbial colonies plug the pores

of the membrane, decreasing productivity. Ridgeway et al. (1984) found that these colonies

did not cause a decrease in salt rejection and the productivity leveled out at a sustainable

level. However, when the feed water was heavily dosed with chlorine to kill the microorganisms and then dosed with an excess of ammonia to convert the free chlorine to

chloramine, biological fouling was enhanced. Productivity continued to decline until the end

of testing. The accumulation of dead microbes on the membrane surface is similar to

colloidal fouling. Colonies are not formed, but the gelatinous slime of decomposing bacteria

inhibits water passage. To alleviate this problem, a 0. 1 - to 1 .O-pm filter should be used with

disinfection processes that do not involve filtration.

6.5.1 Oxidation

Several oxidants can be used for disinfection of drinking water. Table 6.1 compares relative

efficacy, remanent effect, speed, and required dosage for each. Chlorine and chlorine dioxide

can be used for both initial disinfection and residual protection from reinfection, but they

cannot be present in water used with most thin film composite membranes. Ozone and UV

(ultraviolet radiation) are the best candidates for use with TFC membranes. They are

effective for initial disinfection, but ozone dissipates rapidly, and W is effective only while

the water is exposed to it. As mentioned above, a micro filter is needed with any oxidant to

remove the dead and living microbes ahead of the membranes.

6.5.2 Media Filtration

Media filtration is a well known, effective treatment process for lowering SD1 by removing

particulates, colloids, and bacteria. Sand media acts as both a filter and settling chamber,

trapping suspended solids within the bed. Filtering action is enhanced by biological growth

within the bed. Microbes break down large organics and nitrates and excrete a gelatinous

substance which enhances filtration of sub-micron particles (Bellamy, et al., 1985).

6.7
A media filtration system may have one, two, or three layers of progressively finer graded

material. Mono-media sand filters have only a bed of sand. Dual-media filter systems have a

layer of anthracite on top of the sand. A layer of garnet below the sand also may be added to

form a multi-media filter. The layers have progressively smaller grain size from top to

bottom (1.1 mm anthracite to 0.2 mm garnet), and higher specific gravity (1.5 for anthracite

to 4.2 for garnet). The layering of coarse to fine media improves the flow rate of water

through the bed and promotes filtration in depth. Single media filters are run as high as 122-

163 L min-‘me2 ; dual and multi-media filters can be operated as high as 244-6 10 L min-‘mb2

(Parekh, 1991).

Table 6.1 .-Qualities of oxidants for drinking water disinfection

Ozone CIO, Chloramines u v

Efficacy +++

Remanent effect 0

Speed +++

Dosage 0.4 mg/L 4

min.

Conditions No Mn2+:

oxidizes to

MnO,

++ ++ + ++

+

++

0.5 mg/L

30 min.

atpH8

Remove

THMPs

+

++

0.2 mg/L

15 min.

Forms

CIO; in

oxidation

of NOM

++

+

Used for

remanent effect

after 0, or UV

Used for post

treatment with

0, and UV

0

+++

20-25

mW-s/cm2

Turbidity <l

NTU,

no iron, NOM,

thin stream of

water, clean

equipment

NOM is natural organic matter, mWa/cm2 is milliwatts second per square centimeter, and THMPs are

trihalomethane precursors. Adapted from Degremont, 1991.

Dual and multi-media beds are back-washed to remove trapped solids at higher flow rates

than used in operation. Because of the gradation in specific gravity of the layers, the media

settle back in the same sequence (Parekh, 199 1). Single media beds, such as slow sand

filters, are not generally back-washed. Instead, when the flow rate declines, the top layer of

filtration cake, or schmutzdecke, is scraped off. When cleaning reduces the sand depth to 0.3

to 0.5 m, the bottom sand is removed, and new sand is added to the bottom. The top layer is

replaced with the old sand to maintain the flora and fauna of the bed (Bellamy, et al., 1985).

6.5.3 Ultrafiltration

As discussed earlier, UF is useful for reducing bacteria, virus, pyrogens, organics including

color and odor causing compounds, and trihalomethanes and their precursors. In sewage

treatment, ultrafilters can be used to filter effluent from bioreactors. Effluent is recirculated

at a rate sufficient to keep the membrane surface clean. In this way, organics are retained in

6.8
the reactor until they have been broken down to a MW below the MWCO of the ultrafilter.

Bacteria cannot pass the membrane and so are also retained in the bioreactor. Because no

added coagulants or granular material are present, the sludge volume remains low, requiring

disposal only once every month or two (Stavenger, 1971).

6.6 Deoxidation

The presence of free oxidants is destructive to thin film composite membranes; eventually it

breaks down even cellulosic membranes that can tolerate up to 5 mg/L of free chlorine.

Unfortunately, oxidation is usually required to keep microbial life in check. If halogens are

used, dechlorination is required just before feed water enters the membrane modules.

Dechlorination can be achieved by adding some form of SO, or filtering with granular

activated carbon (GAC). Reduction with SO, is a fast reaction, which can work in the feed

pipes on the way to the RO system. SO, can be sulfur dioxide gas, crystallized sodium

sulfite, or sodium bisulfite. The reactions are as follows:

SO, + H,O - H,SO;

With free chlorine: H,SO, + HClO - HCI + H,SO, Eq. 6.6

With monochloramine: H,SO, + NH,CI + H,O - NH&l + H,SO, Eq. 6.7

GAC takes longer to deoxidize water than SO,. A reaction chamber is required to keep the

water in contact with the carbon for a few minutes. Unfortunately, an activated carbon bed is

perfect for culturing bacteria. Organic molecules adsorbed by the carbon provide

nourishment. With the water free of oxidants, nothing keeps microbes from flourishing

downstream in the RO module.

The presence of fine carbon dust mixed with the grains is another reason not to use GAC for

deoxidation, If the GAC is just ahead of the RO system, some carbon fines will deposit in

the membrane module where they erode the membranes and clog membrane spacers. If GAC

must be used for dechlorination, a sub-micrometer filter should be placed after the reactor,

and the quality of the GAC effluent should be monitored closely for bacterial contamination.

6.7 Organic Compounds

Organic compounds are a diverse group of water contaminants. They come from a variety of

sources: humic and fulvic acids from the breakdown of vegetative matter and oils, phenols,

pesticides, surfactants, tannins, and chlorinated methanes from precipitation runoff from

cities and farms, not to mention industrial wastes. Table 6.2 compares processes for

removing organic compounds based on polarity, size, and functional groups. Some organics

are removed at each stage of pretreatment: aeration removes volatile organic compounds;

polar organic compounds are adsorbed during flocculation; and filtration removes organics

adsorbed into floes too small to have settled. Flocculation and filtration are discussed above.

Air stripping and granular activated carbon filtration are discussed in this section.

6.9
6.7.1 Granular Activated Carbon

Activated carbon has a high adsorbent capacity per volume and can be used on a supporting

layer of cellulose, Diatomaceous earth, or in a column by itself to remove organics as listed

above. GAC also will remove free chlorine remaining in water after disinfection as discussed

above. So, if a remanent effect is desired in the water, chlorine should be added after the

GAC.

Table 6.2.-Processes for removing organic compounds

Process Type of organics removed Mode of action

Air stripping Volatile compounds

Coagulation - Humic and fulvic acids

flocculation - settling

Ozonation Phenols, detergents, polycyclic hydrocarbons,

certain pesticides

Activated carbon High MW, low polarization, sapid compounds

(flavor), phenols, surfactants, saturated

hydrocarbons, pesticides

Ultrafiltration Globular shaped molecules over MWCO, some

linear molecules significantly over MWCO.

Adapted From Wafer Treatment Handbook, Degrkmont, 1991.

Evaporation

Adsorption

Oxidation

Adsorption

Separation and

concentration

6.7.2 Air Stripping

Volatile organic compounds can be removed from water by aeration. Air can be incorporated

into water in several ways: cascading the stream down a series of steps; bubbling air into the

water; or spraying the water up into the air in a fountain. The idea is to bring an excess of

oxygen in contact with the water so that volatile organic compounds can escape.

6.10
Chapter 7

WASTE DISPOSAL

Typical waste products from membrane systems include the pretreatment sludge, cleaning

and storage chemical solutions, the concentrate, and used membranes. Ways to minimize or

avoid sludge production are discussed in the chapter on pretreatment. Cleaning and storage

chemicals each have their own characteristic disposal requirements and are usually

considered industrial wastes. Currently, used membranes are considered solid waste, but

possibilities for reconditioning and recycling exist.

Usually the most significant waste disposal issue for membrane systems is the concentrate.

The major difficulty is that the concentrate has significantly higher TDS than both a typical

wastewater discharge and the receiving water. Source water quality, pretreatment, membrane

type, process-added chemicals, and process configuration (recovery) influence the quality and

quantity of the concentrate. The method generally accepted for determining the expected

strength of the concentrate assumes 100 percent rejection of salts. The concentration factor

(CF) is calculated by the following equation:

cF=L

1-Y Eq. 7.1

Where Y equals the recovery portion in decimal.

From this equation, the concentrate from a 75 percent recovery system processing feed water

with 3,000 mg/L TDS would have 12,000 mg/L TDS. At 90 percent recovery, the

concentrate would have 30,000 mg/L TDS. A membrane system with 10 Mgal/d product

water capacity will also produce 3.3 MgaVd of concentrate at 75 percent, or 1.1 Mgal/d of

concentrate at 90 percent. This trade-off between quantity and quality of concentrate can

strongly influence, and be influenced by, the disposal options. Sometimes it is advisable to

blend the concentrate with some other water or wastewater in order to make disposal more

practical or economical. Some examples are blending with treated sewage, an industrial

waste stream, or power plant cooling water.

How the concentrate or blend may be disposed of depends on its quality and quantity,

geographic availability, and potential impacts on the receiving water, soil, or use. The most

common disposal options for membrane system concentrates are:

l Surface water body,

l Wastewater treatment plant,

l Land application,

l Injection well,

l Evaporation pond, and

l Solar pond.

7.1
The quantity and quality of the concentrate or blend and the disposal method determine

which regulatory requirements apply. Concentrate disposal is regulated under several Federal

laws, and state and local governments may impose additional regulations. Any or several of

the following Federal laws may be applicable to a specific case of concentrate disposal:

.

.

.

Clean Water Act (CWA), includes

- National Pollutant Discharge Elimination System (NPDES) program,

- National Pretreatment Standards program, and

- Water Treatment Sludge Disposal regulations (Sec. 503).

Coastal Zone Management Act (CZMA).

Comprehensive Environmental Response, Compensation, and Liability Act

(CERCLA).

Hazardous Materials Transportation Act (HMTA).

Occupational Safety and Health Act (OSHA).

Resource Conservation and Recovery Act (RCRA), includes

- Solid Waste Disposal Act (subtitle D), and

- Hazardous waste regulations (subtitle C).

Safe Drinking Water Act (SDWA), includes

- Underground Injection Control (UIC) program, and

- Wellhead protection program (state-administered).

Toxic Substances Control Act (TSCA).

States may assume regulatory/permit authority for the NPDES, Pretreatment Standards, and

UIC programs if their requirements are at least as stringent as EPA’s. Table 7.1 lists state

authorities for these programs. In some states, membrane system concentrate may be

classified as industrial waste and must therefore meet different disposal requirements than

municipal water treatment waste.

A key issue in determining the applicability of some USEPA regulations is whether the

concentrate meets the definition of “hazardous” or “toxic.” Solid waste is defined broadly

and includes waste in liquid, semi-liquid, and solid forms. Membrane system concentrates are

generally considered a solid waste. A solid waste is considered hazardous if (1) it is

specifically identified on any of the lists published in the RCRA regulations, or (2) it exhibits

any one of the four specific characteristics of hazardous wastes: ignitability, reactivity,

corrosivity, and toxicity. A “toxic” concentrate would be one which contains substances

regulated as toxins under the TSCA as “presenting an unreasonable risk of injury to health or

the environment” (15 U.S.C. $2601(a)(3)). In general, membrane system concentrates are not

likely to be classified as a hazardous or toxic waste but this possibility should be evaluated,

particularly if the raw water quality is unusual or the concentrate disposal options are limited.

The relative cost of permit and regulatory requirements should be considered when selecting

a disposal option. In addition to Federal programs, state and local regulations may vary

greatly and some agency requirements may conflict. Because regulatory requirements and

agency personnel can change with time, care should be taken to ensure that decisions made

by agencies are explicitly documented throughout a project.

7.2
Table 7.1 .-Regulatory program authority by state as of October 1997

(Does not include Indian lands and some Federal facilities)

USEAP region and state NPDES program Pretreatment program

Region I

Connecticut yes yes

Maine n o n o

Massachusetts n o n o

New Hampshire n o n o

Rhode Island yes yes

Vermont yes yes

Region II

New Jersey yes yes

New York yes n o

Virgin Islands yes w

Puerto Rico n o n o

Region Ill

Delaware yes n o

District of Columbia n o n o

Maryland yes yes

Pennsylvania yes n o

Virginia yes 9s

West Virginia yes yes

Region IV

Alabama yes yes

Florida yes Yes

Georgia yes yes

Kentucky yes yes

Mississippi yes yes

North Carolina 9s yes

South Carolina yes Yes

Tennessee yes ye=

Region V

Illinois yes n o

Indiana yes n o

Michigan Yes yes

Minnesota yes yes

Ohio yes yes

Wisconsin yes yes

Region VI yes

Arkansas yes yes

Louisiana yes yes

New Mexico Yes n o

Oklahoma Yes yes

Texas yes n o

Region VII

Iowa yes Yes

Kansas yes n o

Missouri yes yes

Nebraska yes yes

Region VIII

Colorado yes n o

Montana yes n o

Nevada yes n o

North Dakota Yes n o

South Dakota yes yes

Utah Ye yes

Wyoming yes n o

Region IX

Arizona n o n o

Hawaii yes yes

California yes yes

Region X

Alaska n o n o

Idaho n o l-t0

UIC program

yes

yes

yes

yes

yes

yes

yes

n o

n o

yes

yes

n o

yes

n o

n o

yes

y:,”

yes

n o

yes

yes

yes

n o

y::

n o

n o

yes

yes

yes

yes

yes

yes

yes

n o

yes

yes

yes

n o

yes

yes

y:;

yes

yes

n o

n o

11)

(1)

yes

Oregon yes yes yes

Washington yes yes yes

’ Primacy for UIC is shared with EPA.

7.3
7.1 Surface Water Body

The primary concern about discharging membrane system concentrate to surface waters is

degradation of the receiving water. Receiving water quality influences whether treatment of

the concentrate is required before discharge. In general, concentrates may have low dissolved

oxygen, high hydrogen sulfide, and low pH. The concentrate may also have “common ion

toxicity” which occurs when the concentrate has an excess or deficiency of one or more

common ions relative to the ion composition of the receiving water.

An alternative to discharging membrane system concentrate directly to surface water is to

combine it with treated sewage or storm water runoff. If seawater membrane concentrate is

mixed with 1,000 mg/L TDS water (very high for treated sewage) at a ratio of 2: 1 (concentrate:sewage), the TDS can be reduced to that of the ambient seawater. Similar dilution of

brackish membrane system concentrate would make it compatible with an inland surface

water. Concentrates may also be combined with power plant cooling water which provides

thermal dilution for the power plant discharge and TDS dilution for the concentrate.

All discharges into the navigable waters of the U.S. (all streams, lakes, rivers, and oceans) are

required to be permitted through the NPDES program. The five-year permits generally

contain numerical effluent limitations for specific pollutants

If good circulation is present at the concentrate outfall, the high TDS should dissipate rapidly,

but discharging large volumes of high TDS water into small lakes, enclosed bays, shellfish

beds, or valuable fishing waters might pose some hazards. The influence of local currents

may also assist in dispersing the plume concentrations. Impact studies of the effect of

discharge on aquatic life may be required before an NPDES permit is issued. Wetlands are

regulated under the CWA. Wetlands protection laws are an important consideration in the

siting and construction of membrane systems and concentrate disposal facilities.

The concentrate must meet the enforceable MCLs (maximum contaminant levels)

promulgated under the SDWA if it is disposed of into a protected drinking water supply

source as determined by the state (SDWA, 42 U.S.C.A. 3 300g). Table 7.2 lists the SDWA

regulated contaminants. The MCLGs (Maximum Contaminant Level Goals) are recommended, but not enforceable, limits. Local regulations must also be complied with. For

example, in Florida, discharges into surface water also must meet requirements for Class III

waters that are to be kept suitable for recreation and the propagation and maintenance of fish

and wildlife populations. These requirements involve regulations limiting hydrogen sulfide,

dissolved oxygen levels, sulfide toxicity, low pH, corrosiveness, and toxins (Malaxos and

Morin, 1990).

Most coastal membrane systems discharge concentrate to the sea. If the raw water was

obtained from some inland source, the TDS of the concentrate will be less than or equal to

the TDS of seawater. However, if the raw water is seawater, the TDS of the concentrate will

be significantly higher than the seawater TDS. Salinity affects density, osmotic pressure, and

buffering properties of seawater and supply of oxygen. Measurements of seawater

7.4
Contaminants

Tabte 7.2.-SDWA regulated contaminants (1997)

MCLG MCL

PWL) @g/L) Contaminants

MCLG MCL

(mgn) (mg/L)

Fluoride 4.0 4.0

Trichloroethylene

Carbon Tetrachloride

1 , 1.1 -Trichloroethane

1,2-Dichloroethane

Vinyl Chlorite

Benzene

p-Dichlorobenzene

1,l-Dichloroethylene

zero

zero

0.2

zero

zero

zero

0.075

0.007

0.005

0.005

0.2

0.005

0.002

0.005

0.075

0.007

Total Coliform

Turbidity

Giardia lamblia

Viruses

Standard plate count

Legionella

zero

N/A

zero

zero

zero

zero

<5%

l-r

l-r

l-r

l-r

l-r

Tetrachloroethylene

Chlorobenzene

trans-1,2-Dichloroethylene

cis-1,2-Dichloroethylene

o-Dichlorobenzene

Barium

Cadmium

Chromium (total)

Mercury (inorganic)

Nitrate (as N)

Selenium

Asbestos (fiber >lO,um)

Lindane

Methoxychlor

Toxaphene

2,4-D

2,4,5-TP (Silvex)

Aldicarb

Chlordane

Carbofuran

Alachlor

Epichlorohydrfn

Totuene

PCBs

Atrazfne

Acrylamide

Dibromochforopropane (DBCP)

1,2-Dichloropropane

Pentachlorophenol

Ethylene dibromide (EDB)

xyletles (total)

zero

0.1

0.007

0.07

0.6

2

0.005

0.1

0.002

10

0.05

7 MFL

0.0002

0.04

zero

0.07

0.05

0.003

zero

0.04

zero

zero

1

zero

0.003

zero

zero

zero

zero

1 0

0.005

0.1

0.007

0.07

0.6

2

0.005

0.1

0.002

1 0

0.05

7 MFL

0.0002

0.04

0.003

0.07

0.05

0.003

0.002

0.04

0.002

l-r

1

0.0005

0.003

l-r

0.0002

0.005

0.001

0.0000

510

Ethylbenzene 0.7 0.7

Styrene 0.1 0.1

Heptachlor zero 0.0004

Heptachlor epoxide zero 0.0002

Nitrite (as N) 1 1

Aldicarb sulfoxide 0.001 0.004

Aldicarb sulfone 0.001 0.002

Lead zero l-T+

Copper 0.07 l-r++

Dichloromethane zero 0.005

1,2,4-Trichlorobenzene 0.07 0.07

Hexachlorobenzene zero 0.001

Antimony zero 0.006

Nickel 0.1 0.1

Thallium 0.002 0.002

Beryllium 0.004 0.004

Cyanide 0.2 0.2

Endtin 0.002 0.002

Dalapon 0.2 0.2

Diquat 0.1 0.1

Endothall 0.1 0.1

Gfyphosphate 0.7 0.7

Di(2-ethylhexyl)adipate 0.4 0.4

2,3.7.8-TCDD (Dioxin) zero 3x10”

1 ,l,2-Trfchloroethane 0.005 0.005

Oxamyl (Vydate) 0.2 0.2

Simazine 0.004 0.004

PAHs Benzo(a)pyrene zero 0.0002

Diethylhexyl Phthalate zero 0.006

Picloram 0.5 0.5

Dinoseb 0.007 0.007

Hexachlorocyctopentadiene 0.05 0.05

Radionuclides (Proposed)

Radium 226

Radium 228

Gross beta Particle and Photon

Emitters

Uranium

Gross alpha Emitters

Radon

Sulfate (Proposed)

Arsenic (Interim)

zero

zero

zero

zero

zero

zero

500

0.002

2OpciiL

2OpWL

4mRem/y

~Opcll

15pCii

3OOpcwL

Disinfection By-Products

(Interim)

Total Trihalomethanes 0.01

0.05

0.1

+

K

Source:

Action Level = 0.015 mgfl

Action Level = 1.3 mg/L

Treatment technique requirement

USEPA

7.5
characteristics show natural salinity variations of the order of +/- 1,000 mg/L due to tidal

actions, fresh water runoff, and seasonal variations. Conservatively, it would appear that a

benthic ecosystem could easily tolerate a salinity perturbation of 1,000 mg/L, which is about

3 percent deviation from the ambient.

Marine organisms can tolerate gradual increases in salinity, but sudden changes are fatal. A

specific gravity of 1.030 g/cm’ is the upper limit of tolerance for most species outside of the

Mediterranean. Assuming a linear relationship between specific gravity and TDS, an

increase of 0.008 g/cm’ (normal specific gravity = 1.022 for seawater) equates to an increase

in TDS of only 36 percent (from a normal 35,000 to 47,727 mg/L). Mobile creatures can

move away from the concentrate discharge but immobile species will die if the TDS suddenly

increases too much. Denser seawater RO concentrate sinks rapidly to the ocean floor and may

harm benthic organisms because of the high salinity.

NPDES permits for ocean outfalls for regular wastewater treatment plants (WWTPs) often

require a certain depth of discharge so that the rising plume of the lighter-than-seawater

effluent has adequate time to mix and dilute before reaching the surface. In contrast, the

higher density of seawater membrane system concentrate results in a directly discharged

plume which sinks to the ocean floor. So an NPDES permit should require a certain depth of

discharge and/or mixing zone. Mixing and dispersion may also be accomplished by

discharging the concentrate through a seabed distribution system of pipelines, or one pipeline

with many outlets.

The CZMA is administered by the Office of Coastal Zone Management in the National

Oceanic and Atmospheric Administration, which is part of the U.S. Department of

Commerce. Water development and construction projects which are within designated

coastal zones and that require one or more Federal permits are subject to CZMA

requirements. This would include construction or modification of an ocean outfall. The

coastal zone states are all states adjacent to the Great Lakes and the East, West, and Gulf

coasts. Each state defines its own coastal zone; some have included river segments more

than 100 miles (160 km) from the coastline.

7.2 Wastewater Treatment Plant (WWTP)

As indirect dischargers, membrane systems which discharge concentrate to WWTPs are

exempt from NPDES regulation. Rather, they are subject to USEPA National Pretreatment

Standards and to any additional regulations imposed by the state or the WWTP. Municipal

sewer authorities may restrict concentrate disposal to sanitary sewers because of concern that

the high TDS would adversely affect their biological treatment processes. Discharge quality

limitations and conditions may be imposed by the WWTP through a permit, a local

ordinance, or both. Many WWTPs set limits to enable them to achieve compliance with their

own permit requirements. If the use of an existing permitted wastewater ocean outfall is

proposed for additional concentrate disposal, the mixing characteristics of the combined

7.6
discharge may require a NPDES permit modification. WWTPs also need to control the

pollutants that enter their sludge to ensure that they will be able to continue managing and

disposing of their sludge in accordance with USEPA regulations (CWA, section 503).

7.3 Land Application

The interrelated actions of soil filtering, plant uptake, plant metabolism, soil biochemical and

physicochemical reactions, and soil particle adsorption must all be considered in evaluating

the impacts of land application disposal of concentrate.

Permit requirements will usually depend upon the ultimate destination of the concentrate.

State and local regulations usually govern, and an NPDES permit may be required if ultimate

discharge is to surface water. In general, application of irrigation water must not adversely

affect the groundwater being recharged, its users, or the surrounding environment. State and

local wellhead protection programs may limit land application disposal that could adversely

affect local drinking water wells. Spray irrigation results in concentrate entering the

groundwater unless under-drains are provided. Careful planning is required to prevent

groundwater contamination. An NPDES permit will be required if under-drains are designed

to discharge to surface water.

If the concentrate TDS is low enough, or if it can be blended with another water (e.g.,

wastewater effluent) which will result in a sufficiently low TDS, the concentrate may be

usable for irrigation of certain crops. However, even salt-tolerant crops require irrigation

water with a chloride concentration of 1,000 mg/L or less. Table 7.3 lists threshold levels of

irrigation water TDS for several crops. These are levels above which yields begin to decrease

with increased TDS. The levels are based on the conductivity of saturated soil extract from

the root zone; a factor of 640/l .5 was used to convert the conductivity of soil extract in

deciSiemens/meter to irrigation water TDS in mgk.

Table 7.3.-TDS threshold levels in applied irrigation water

Crop

Maximum

TDS Crop

Maximum

TDS

Lettuce 555

Cotton lint 3,285

Carrots 427

Wheat 2,560

Oranges 725

Grapefruit 768

Onions 512

Corn 726

Celery 768

Potatoes 725

Strawberries 427

Almonds 640

Peaches 725

Alfalfa 853

Grapes, table 640

Cantaloupe 1,422

Dates 1,707

Sugar beets 2,987

Lemons 768

Beans 427

Cabbage 768

Peppers 640

Spinach 853

Sweet potato 640

Berries/plums 640

Avocados 427

Source: Lohman, Milliken, and Dorn, 1988, p. 23.

7.7
Because certain crops bioaccumulate certain minerals, irrigation water should not contain

excessive amounts of trace elements or metals. Table 7.4 lists guidelines for maximum trace

element levels in irrigation water. Of course, the degree of this risk is also influenced by the

type of crop, the soil, and irrigation frequency and timing.

Table 7.4.--Recommended maximum trace element levels

in irriaation water

Element

Suggested maximum

irrigation water level

O-wU

Aluminum (Al) 10.0

Arsenic (As) 0.1 - 2.0

Beryllium (Be) 0.1 - 0.05

Boron (B) 0.5 - 2.0

Cadmium (Cd) 0.01 - 0.05

Chromium (Cr&) 0.5 - 1 .o

Cobalt (Co) 0.1 - 5.0

Copper (Cu) 0.2 - 5.0

Fluoride (FI) 1.8

Iron (Fe) 5.0 - 20

Lead (Pb) 5.0 - 10

Lithium (Li) 2.5

Manganese (Mn) 0.02 - 10

Molybdenum (MO) 0.01 - 0.05

Nickel (Ni) 0.2 - 2.0

Selenium (Se) 0.02

Silver (Ag) 4.0 - 8.0

Vanadium (V) 0.1 - 1.0

Zinc (Zn) 2.0 - 10.0

Source: Edwards and Bowdoin, 1990.

Soil permeability problems occur when the rate of water infiltration into and through the soil

is reduced by the effects of salts in the water. The infiltration rate can be reduced to such an

extent that the crop is not properly supplied with water. Generally, three factors determine a

water’s long-term influence on soil permeability: (1) sodium content relative to calcium and

magnesium; (2) bicarbonate and carbonate content; and (3) total salt concentration of the

water. Most salts in irrigation water are left behind in the soil as water is taken up by the

crop. These salts may accumulate and reduce the availability of water in the root zone. This

is called the osmotic effect and can be measured as a force the plant must overcome to obtain

the water. Soils behave as cation exchangers. Various cations in the soil can be replaced by

each other by proper choice of concentrations.

The potential impacts of the concentrate on the existing irrigation distribution system should

also be evaluated. What are the impacts on aquatic organisms, on canal system materials, on

field runoff areas, etc.?

7.8
Another option for land application is irrigation of constructed saline marshes.

studies of this concept have been conducted by Reclamation and others.

Some pilot

7.4 Injection Wells

Direct discharges to groundwater are subject to the UIC regulations set by USEPA under the

SDWA. The UIC program deals with the construction and operation of underground

injection wells. UIC regulations prohibit subsurface disposal through a well unless

authorized by rule or by permit. Five classes of well are established, and disposal of certain

types of wastes within each class are authorized by rule. The class of well that may be used

and the associated requirements depend on the quality of the concentrate. Generally,

injection of any fluid is prohibited if it will cause an underground source of drinking water

to exceed any SDWA maximum contaminant level or otherwise affect public health.

Depending upon the site-specific circumstances, RCRA and TSCA may also have some

effect, but generally, state legislation or regulation covers the specifics.

Disposal by injection well is a simple, effective means of disposing of large volumes of concentrate continually under varying weather conditions. However, the development and construction of this option is very complicated. There are very particular geological requirements; the site must be over a confined aquifer which is unsuitable for drinking water, is

below all drinking water aquifers in its vicinity, and has a relatively high transmissivity in

order to accept the injected concentrate at economical pressures. The operation should be

designed not to degrade the transmissivity of the aquifer. A considerable amount of testing

occurs during the construction of an injection well. Water samples are collected during

drilling to correlate water quality with depth and to identify underground sources of drinking

water. Drill cuttings are collected to establish site-specific lithology, and pumping tests may

be performed to locate production zones. Geophysical logs are run to help identify aquifer

characteristics and interpret other field data. Field testing is used for determining preliminary

water quality parameters such as chlorides, conductivity, temperature, and pH. Because

concentrate has been classified as industrial waste by EPA, deep injection wells are required

to have a liner from the wellhead to the receiving aquifer in addition to the casings which

protect successive geologic layers from leakage from lower layers. Figure 7.1 illustrates the

geologic strata and well construction requirements.

7.5 Evaporation Ponds

Evaporation ponds are a practical disposal method in locations with relatively high

evaporation rates, low precipitation rates, and suffkient inexpensive land area. Ponds are

typically lined and protected from flooding. They are designed so that no liquid is discharged

to surface water or groundwater; thus, no permits are required. However, local regulations

may require leak detection or monitoring or underdrains to assure groundwater protection.

7.9
Municipal Injection Well Industrial Injection Well

Figure 7.1 .-Typical municipal and industrial injection well construction.

From Florida Underground Injection Control Program Handbook, FDER, 1983.

Residual solids must be periodically removed and transported to a landfill for disposal. The

Solid Waste Disposal Act requires states to establish solid waste management plans governing non-hazardous waste disposal activities. USEPA regulations set minimum criteria for

municipal solid waste landfills, and a state program must be at least as stringent. In general,

landfill disposal rules apply to the residue remaining after evaporation of membrane system

concentrates. If the residue is classified as a hazardous waste or toxic substance, RCRA and

HMTA, or TSCA rules apply to its storage, transport, and disposal.

7.6 Solar Ponds

Solar ponds are heat traps that use high TDS water to trap heat from the sun which can then

be used to generate electrical power or desalt water. A solar pond is 3 - 7 m deep,

constructed in three distinct layers as on figure 7.2. The surface has a thin layer of fresh

water. Convective currents created by wind and evaporation move vertically through this

layer just as they do in any other body of water, though wind currents are kept to a minimum

with wave suppression netting on the surface. Below the surface layer is a zone of increasing

salinity, from near fresh at the top to about 20 percent (by weight) sodium chloride or other

suitable salts, at the bottom. Normal convection currents cannot circulate water in this zone

because of the density gradient. The bottom of the pond is the thermal storage zone. This

7.10
Upper Convective Zone

Pond

1-0-r.3m -

z

lniwmediate Zone

(Stable Gtadient)

t

l.O-5.4m 5

Lower Conveotive Zone

(lBennal Stomge)

Salt Concentmtion orDen&y

Figure 7.2-Gross section of a solar pond (From Boegli et al., 1984).

layer has a uniform concentration as high as ten times that of seawater and is the heaviest

layer in the pond. This layer has convective currents, but they do not circulate into the

salinity-gradient layer above. The bottom of the pond is lined to prevent seepage into the

groundwater.

The sun’s energy penetrates the upper layers, warming the thermal storage zone just as in any

lake, but the heat cannot circulate and dissipate into the atmosphere as it normally would. It

becomes trapped in the dense lower layer of the pond. The temperature of the storage zone

becomes as high as 70 to 100 O C (160 to 2 12 “F) within a few months after the salinity

gradient is established. Heat in the storage zone may be used as process heat, or may be

converted to electricity with thermal effkiency of up to 15-20 percent. Even during the

winter when the surface of the pond may be frozen, the storage zone will be hot enough to

generate electricity. (Boegli et al., 1983).

The first solar pond in the U.S. to generate electricity was Reclamation’s El Paso Solar Pond.

The El Paso Solar Pond project began as a University of Texas at El Paso research project

sponsored by Reclamation and the Bruce Foods Corporation and was later cost-shared with

the Texas Energy and Natural Resources Advisory Council and the El Paso Electric

Company. After some experimentation with process heat production, the solar pond was tied

to the El Paso Electric Company power grid and began producing electricity on September

19, 1986. Figure 7.3 diagrams the process of electricity generation that is used at the El Paso

7.11
CONOLNSIR

Figure 7.3.-Solar pond heat transfer for power generation (From Boegli et al., 1984).

Solar Pond. The hot concentrate can be circulated to the food processing plant to be used as

preheat for boiler feedwater as needed, to a lOO-kW organic Rankine cycle power conversion

module, or to a multistage flash desalting system. (Reid and Swift, 1987).

To build the solar pond, the storage layer concentrate must be concentrated to 10 times the

sahnity of sea water, or about 350,000 mg/L TDS. The normal RO recovery rate for sea

water is 30-40 percent, which produces a TDS of only 50,000 to 67,000 mg/L. At another

solar pond at the California Department of Water Resources, Los Banos, California,

Demonstration Desalting Facility, concentrate was supplied by a three stage RO system

designed to obtain 90 percent recovery from a feed water with 8,930 mg/L TDS. Thermal

evaporation was used to increase recovery to 96 percent, resulting in a TDS of 223,250 mg/L.

Further concentration of the RO concentrate could be carried out with heat energy from the

solar pond, but to start with, energy was supplied by the local power utility (Smith, 1990).

The Israelis have since developed an enhanced evaporation system that quickly concentrates

the concentrate by spraying it down into evaporation ponds. This system is currently being

used successfully at a saltworks.

The density gradient is important in maintaining a high temperature in the heat storage

region. The density and temperature are monitored daily to ensure that the gradient is intact.

If it is upset by physical mixing or operator error, the pond will become convective,

transferring heat away from the bottom layer to the atmosphere. Gradient maintenance is

accomplished periodically with diffusers that can be raised or lowered to inject concentrate at

the right levels.

7.12
Solar ponds are a beneficial solution to the concentrate disposal problem. The initial block of

power produced can be used to run pumps for the membrane system. Power production

depends on the membrane system for a source of concentrate, so as long as replacement

concentrate can be made from salt when needed, excess power can be sold to utilities to

defray expenses. During the first thirty years of the project, the salt concentrate can be

disposed of by constructing additional solar ponds. When the initial capital cost has been

amortized, the excess power can be sold to pay for the disposal of excess RO concentrate by

further concentration, deep well injection, or other means.

7.13
Chapter 8

CLEANING AND STORAGE

Each membrane manufacturer publishes specific instructions for cleaning and storing

membranes when necessary. Rather than repeating these instructions, which may change

with time, general cleaning and storage procedures are discussed in this chapter. Cleaning

and storage are critical operations that can extend or shorten the life of membranes. It is

important to the success of these touchy processes that the “why” is well understood.

8.1 Cleaning Procedures

Over time, even membranes with optimum pretreatment systems need to be cleaned. As

mentioned earlier, this should be one of the action items triggered by a 10 percent change in

AP, NPF, or salt rejection.

8.1.1 Cleaning Regimes

There are two basic types of cleaning regimes as described in table 8.1. One for organics and

biological fouling, and one for scaling. Organic and biological films are best broken down

with a high pH solution at the maximum temperature and pH limits for the membrane.

Sodium hydroxide works well. Some suggest adding enzymes to help break down cellular

matter, surfactants to help penetrate and dissolve the film, and a chelating agent to bind

calcium ions. Calcium is an important component in extra-cellular polysaccharides (EPS, or

extra-cellular polymeric slime) which is produced by well-established bacteria. EPS protects

them from disinfectants and cleaning agents. Depleting the EPS of its calcium building

blocks helps the cleaning solution penetrate the biofilm.

Table 8.1 .-Two tiered classification of membrane cleaning regimes

Wkhelate

W/detergent

Wkhelate and/or

enzymes

Low temperature, low pH

Soluble inorganic substances

(carbonates, sulfates)

High temperature, high pH

Inorganic colloidal materials (i.e., silica,

metallic hydroxides, etc.)

Soluble organic substances (precursors

of trihalomethanes)

Microorganisms (bacteria, protozoa,

fungi, algae)

8.1
Membranes with scaling problems are cleaned with a low pH, room temperature solution at

low pressure and moderate flow rate for longer periods of time. Citric acid works well

because it is also a chelating agent; it binds higher charged cations so that they cannot

re-precipitate before they exit the system.

There may be layers of biological and scaling material in the same element. In this case, it

will be necessary to use both solutions, one after the other, repeatedly. Since some

precipitates are less soluble in hot water, the unheated, low pH solution should always be

used first.

8.1.2 Equipment

Figure 8.1 is a diagram for a state of the art cleaning system. There are advantages to having

a special skid just for cleaning, but if your system is designed with flexible plumbing

connections, it is often possible to improvise. The most important components are:

l Mix tank with some method of mixing (volume should be twice the capacity of the

vessel or stage that is to be cleaned)

l Pump with some method of flow control

l Flexible plumt . _ connectors (to isolate stages or vessels)

. Temperature control

l Cartridge filter

l Temperature/pH sensor (portable or hand-held model will do)

8.1.3 Generic Cleaning Process

No more than one stage should be cleaned at a time. Ideally, only one element would be

cleaned at a time, but that would be far too labor intensive. As a compromise, each stage

should be cleaned separately so that the cleaning solution needs to go through only one vessel

before returning to the mix tank. When two stages are cleaned at once, the foulants from the

first stage have to be moved all the way through the second stage. It is difficult enough to get

them out of the first stage; the likelihood of getting them all through the second is very low.

The following cleaning procedures were generalized from FilmTec’s “Cleaning and

Disinfection” chapter of their Technical Manual.

8.2
From Membranes

!%licron

To Membranes

Cartridge Filter

I

’ Valve

1 Diaphram

I-112 HP, J-phase

Centrifugal

IOO-Mesh

316 SS Strainer

Drain

Figure 8.1 .-State-of-the-art cleaning system.
8. I. 3. I Preparation

l Isolate the vessel or stage that is to be cleaned.

l If pump does not have a variable speed drive, be sure that plumbing allows for flow

bypass of pressure vessels so that flow can be controlled without increasing pressure

to the membranes.

l Check temperature control system. If there is none, use sealed buckets of ice in the

mix tank to keep the cleaning solution temperature from exceeding maximum

limitations (may sound strange, but temperature is vitally important). See table 8.2

for maximum pH./temperature limits for Filmtec BW-30 membrane. Other

membrane temperature limits can be found in chapter 10.

Table 8.2.-Maximum pH/temperature limits for Filmtec BW-30 membrane

pH range 2-10 l-11 l-12

Maximum temperature 50 35 30

l Temperature can be monitored by hanging a temperature probe in the tank.

However, be sure not to let the water level drop below the level of the probe.

l Fill the mix tank with an adequate volume of RO product water, at least two times

the volume of the piping and pressure vessel that is being cleaned.

l Begin mixing and warming the RO product water with a heater or 100 percent

bypass.

8.1.3.2 Cleaning Solution Preparation

Bring the water to the appropriate temperature by mixing and heating or by pumping with

100 percent bypass back to the mix tank. Except perhaps in very cold climates, heating is

necessary only during cleaning solution preparation. Once the cleaning cycle has begun,

cooling is more important.

Add the cleaning chemicals slowly while mixing. If dry chemicals are added all at once, it

will be more difficult to get them dissolved. Some dry detergents and thick surfactants are

very difficult to get into solution. Be sure to allow enough mixing time to ensure the

chemicals are dissolved. They will not work if they are not completely dissolved! They will

likely cause further fouling and/or degradation, or else they will be removed by the cartridge

filter and never get to the membranes. Take samples of the unused cleaning solution to

compare before and after cleaning chemical analyses.

8.4
8.1.3.3 Fill System

Introduce the cleaning solution into the vessel or stage at a low flow rate with the concentrate

stream going to drain. To determine when the system is completely filled, monitor the pH of

the concentrate and divert the concentrate stream back to the mix tank when it matches that

of the cleaning solution.

8.1.3.4 Low Fiow Pumping

Pump the mixed, preheated cleaning solution at a low flow rate with solution recirculating to

the mix tank for about 15 minutes or until the return solution looks cleaner. The back

pressure valve should be completely open so that no permeate is produced. The objective of

this cycle is to dislodge larger particles and remove them from the system. Table 8.3 lists

sample cleaning flow rates for different sized elements.

8.1.3.5 Moderate Flow Pumping

Increase to moderate flow rate with the solution still recirculating for another 15 minutes with

the back pressure valve still open. Check solution appearance and make note of any cloudiness or suspended solids accumulation.

8.1.3.6 Soak

Reduce flow to lowest possible level for the soak period. Soaking helps to dissolve stubborn

films and precipitates. The membranes should soak for anywhere from one to fifteen hours,

depending on the degree of fouling. It is important to control the temperature during long

soaking periods. The cleaning solution should be kept at the optimum temperature. In most

cases, this means keeping the temperature from rising too high; however, if the ambient

temperature is low and the optimum temperature is high, heating may be necessary.

8.1.3.7 High Flow Pumping

After soaking, slowly increase the flow rate to the maximum allowable for your system.

Filmtec’s specifications are given in table 8.3. The pressure drop must be monitored during

the high flow cycle. Maximum pressure drops for each element type are listed in chapter 10.

Flow rate should be increased slowly to flush out any large material loosened by soaking.

Then the high flow may remove stubborn material and particles stuck in the spacer material.

8.5
Table 8.3.--Recommended feed flow rate per pressure vessel during cleaning

Cleaning cycle Feed flow rate, Umin (gal/min)

Module diameter 64 mm (2.5”) 102 mm (4”) 203 mm (8”)

Soaking 2 (0.5) 3 (1) 15 (4)

Low flow 10 (2.6) 19 (5) 75 (20)

Moderate flow 15 (4) 30 (8) 100 (26)

High flow 20 (5) 38 (10) 150 (40)

8.1.3.8 Flush and Sanitize

Take samples of the spent cleaning solution for chemical analysis. Drain tank and piping.

Rinse the tank, and refill it with RO permeate. Flush out the system at a moderate flow rate

with the concentrate stream diverted to drain. After flushing, refill the tank and add a

sanitizer recommended by the membrane manufacturer. Sodium bisulfite or chlorine can be

used with CA membranes. Formaldehyde or hydrogen peroxide can be used with thin film

composites. Use caution with these chemicals, though; high concentrations may cause

damage.

After the cleaning process, some cleaning solution will still be on the permeate side of the

membrane; so, after putting the clean stage back on line, divert product to drain until quality

is acceptable.

8.1.4 Which Cleaning?

It is often possible to determine what has happened to a membrane system by noting changes

in the NPF, AP, and rejection for each stage over time. Table 8.4 describes the symptoms of

major types of fouling and which cleaning regime is called for. Generally, a decrease in NPF

in the first stage means particulate fouling. Particulates could be mineral, vegetable, or

animal in nature. Both spiral wound and HFF membranes serve as excellent cartridge filters -

most particulates are trapped in the first couple of elements. The cleaning strategy indicated

for front end fouling of this sort is a high pwhigh temperature regime.

Precipitative fouling, or scaling, occurs at the tail end of the system where the feed stream is

at its highest concentration. Effects are a decrease in rejection and NPF and an increase in

AP. A low temperature/low pH cleaning regime is needed for scaling. Low temperature

means normal operating temperature. Since calcium carbonate is less soluble at higher

temperatures, it is best to use a low pWlow temperature cleaning solution first if more than

one type of cleaning will be used.

8.6
Table 9.4.-Foulant characterization based on chemical composition

Soluble inorganic substances Soluble organic substances

Colloid materials (water insoluble inorganic

compounds: silica, iron hydroxides, etc.) Biological materials (bacteria, algae, lungi, etc.)

Causes Over saturation

Presence of crystallization centers

Oecrease In salt rejection in end stages

Increase in pressure drop in end stages

Decrease Normalized Permeate flow

W’F)

Scale formation on membrane surface or In

bulk w/subsequent deposition

Formation of ‘salt bridge’ facilitating protein

adsorption

High concentration at membrane surface

can cause denaturation of proteins which

then are more of a fouling problem

Prevention Softening

Acidification

Use of chelating agents

Remediation Low pH w/ chelale

Normal operating temperature

“Soak cycle

Physical methods: ultrasound, magnetic,

Humic and fulvfc acids natural to

surface waters

Lack of adequate pretreatment

Over utilization

Formation of H bonds on contact w/

membrane

Partial diffusion through membrane -

dependent on degree of branching

Ultraftltratton

Coagulationlsedimentation

“Same as Colloids

Over utilization

Inadequate sedimentation period

Gel formation on membrane surface

Decrease in salt rejection

Decrease in NPF

Symptoms most likely to appear in last stage

Softening

High pH

High temperature

High flow rate

“Detergent

Inadequate pretreatment

Inadequate flow through module - dead spaces

Hydrophobic attraction between cell and

membrane surfaces

Production of extracellular polymeric substances

Cell fimbriae may help attach bacteria to

molecular matrix of the membrane

Decrease in NPF

Initial increase in salt rejection

Increase in pressure drop

“Symptoms most likely to appear in first stage

Accumulation of byproducts of metabolism

Eventual detedoration of the membrane resulting

in a decrease in rejection

Decrease in llow at membrane surface can

exacerbate concentration polarization

phenomena

Prefiltration

Use of surfactants during normal operation has

been shown to prevent bacterial attachment

Reduce recovery rate

“Same as Colloids

Use of enzymes has been shown to help loosen

biofilm

hyarouynamw

Adapted from Saran, A.A. 1990.

l * DHP: Paul, 1993.
8.1.5 Passive Cleaning

Passive cleaning is a milder form of cleaning that does not use chemicals or even a separate

pump. If, say at 5 percent change in AP, NPF, or rejection, passive cleaning is performed, it

may be possible to extend the time between chemical cleanings. The following are some

procedures that can have a beneficial effect without voiding the manufacturers warranty.

l Turn off the system for an hour. Osmotic pressure will draw product water through

the membrane to the concentrate side. This can help lift foulants off the surface. If

live bacteria are present, stopping flow could encourage a growth spurt, so this

method should be used only when disinfectants are present.

l Reduce back-pressure for a short time. Permeation rate should drop, and flow rates

through the system should increase. This changes flow patterns through the system

and can disrupt films that may be in process of taking root. It also washes away the

high concentration layer right at the membrane surface and, in doing so, could slow

the scaling process.

l Perform a high flow, low pressure flush with product water. RO product water is

very aggressive in dissolving precipitates. The change in flow pattern will also have

the effect described above.

These are experimental procedures at this point, but there is nothing in them that

manufacturers would object to. For more information about fouling and membrane cleaning

philosophy, see Chapman Wilbert, 1997.

8.2 Membrane Storage

Membrane systems work best when they operate continuously. It is unavoidable to have

occasional shutdowns, though. When a membrane system is to be down for a few days, flush

the process water from the system and replace it with RO product water pumped into the

system at low pressure.

If the concentrated process water and pure product water are left in the membrane vessels, the

difference in concentration across the membranes will cause osmotic flow from the product

side to the concentrate side. This can be beneficial in lifting foulants from the membrane

surface in small quantities, but too much back flow can destroy the glue lines.

For thin film composite membranes, the storage water should be oxidant-free. Otherwise, the

membranes will degrade over time. CA membranes should be stored in chlorinated water,

though. While the danger of biological growth is the same for both types of membrane,

damage from oxidation would be worse than biofouling for thin film composites.

8.8
If the membranes are to be stored for longer than about a week, a biostat, such as

glutaraldehyde or sodium metabisulfite, should be added as a preservative. The solution

must be changed periodically, and the elements should be kept in a temperature-controlled

environment away from direct sunlight.

Alternative methods for storing membranes for long periods have been investigated at the

Yuma Desalting Plant. While some have proven successful, the final report of findings is

still under review. For more information, check the Water Treatment and Engineering

Group’s intemet library home page at (http://www.usbr.gov/water/water.html).

8.9
Chapter 9

PROCESS DESIGN

9.1 Introduction

The purpose of this section is threefold: first, to illustrate a simple solvent flux modeling

approach for estimating the overall performance of a pressure-driven, liquid filtration,

membrane module; second, to demonstrate an element-by-element analytical procedure for

the preliminary design of membrane desalting systems; and third, to present several vendorsupplied computer programs for estimating membrane system performance. More accurate

and complex models and algorithms are available in the literature, and the reader is referred

to those for detailed design projects (Hwang and Kammermeyer, 1975).

9.2 Solvent Flux Models

Simple models are useful for exploring the effects of changes in membrane characteristics

and module operating conditions. A “simple approach” means the solution can be obtained

without complex numerical computation techniques. Ideally, a spreadsheet program could be

used to perform “what if’ case studies. The reader is cautioned at the outset that, because of

the assumptions required in a simple model, significant differences will probably exist

between the actual performance and the estimate.

The model presented here assumes perfectly mixed feed and permeate compartments, with

consideration of concentration polarization. This model is the simplest to use and provides a

conservative estimate of module performance. In the general case, solution of the design

problem requires an iterative (trial and error) method, but in special circumstances, an

algebraic solution can be obtained.

This module model can be used for RO, NF, UF, and MF with appropriate modifications.

The overall material balances and boundary layer aspects are essentially the same for all these

applications. The definition of the flux, membrane resistances, and the concentrations can be

modified to suit the specific type of filtration. Therefore, this discussion will begin with the

specific flux models for the different types of filtration. The overall material balance

equations will be developed using the RO flux model and boundary layer estimation

techniques. Finally, a sample design problem will be presented.

Figure 9.1 is a diagram of the dynamics of a pressure-driven filtration process. A gel layer is

shown to illustrate how solute build up at the membrane surface affects the flow of solvent

through the membrane.

9.1













Jv

-5 &J-J6 _ _._............_...

Ii

2

$j 2E-06 - -~.~~~~~.~~~~-~--~~~~....~~.~~~~-..~...~~~.~~.-~~~..~...~.~~~~~.~. .. .- ...... .~~~--.~..~~~...~~.~~~..~.~~.~~~- .. ....._ ........ ... ...._.... ..

2

OE+OOi : : I : : : : I : : : I ; : I I :

I 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Calculation Iteration

L-tJvJ

Figure 9.3.~Iterative solution for water permeation rate, Jv, every iteration has more accurate estimates of

recovery rate, product, and wall concentration. The solution is found when the calculated values

level out at the most accurate estimate.

1 3 5 7 9 1 1 1 3 1 5 1 7 1 9

Calculation lteration

--+--Recovery -t- Intrinsic Rejection, RB +-Apparent Rejection Ra

Figure 9.4.-Oscillation of recovery rate and the apparent rejection rate as the solution becomes more accurate.

9.15
--________--____________________I

Stage One

I

4

,

I

(_________-___--________________

I

I Stage llvo

Permeate

Figure 9.5.-Diagram of a two-stage membrane system.
system operating conditions, i.e., feed pressure, temperature, etc., and the type and number of

elements loaded in the vessels, a percentage of the feed will diffuse through the membranes

and will be collected as permeate. The feed flow to each succeeding element in a vessel will

be lower, by the amount of permeate developed, and the concentration will be higher.

Concentrate (reject) flows from the two 1” stage vessels are then combined and proceed to a

2”d stage where additional desalting takes place. Permeates from both stages are collected

and represent the total system production. The array and number of elements per vessel are

generally dictated by feed water quality, element hydraulic limitations, and economic

considerations. A 2:l array, as shown in figure 9.5, can be used to recover about 70 to

75 percent of the system feed, while a 4:2:1 array can recover up to 90 percent. Several other

configurations are also commonly used.

9.3.1 System Equations

A generalized process diagram of four lead elements of a membrane desalting system is

presented on figure 9.6. This type of diagram is used to develop material balance and other

equations around individual elements to accommodate system design calculations. Although

only four elements are shown on this figure, the computations apply to the entire system.

Definitions of the symbols used in the diagram are as follows:

5

- Feed water flow

Fp, - Permeate flow

Fri - Reject flow

c/i - Feed water concentration

cpi - Permeate concentration

cn - Reject concentration

pl - Feed pressure

ppi - Permeate back pressure

pri - Reject pressure

AP- Differential pressure

Where i represents the element number.

Applicable equations describing the first element on figure 9.6 would include:

Mass Balance - FflCfl = F& + F&I G Fp& + Wr,

Differential Pressure - AP=Pfl-P,,

Average Feed Pressure - Pmg = (Pfl + PfJ2

Average Salt Concentration - Cmg = (Cfl +Cd/2

Net Driving Pressure - NDP = Pfl-P/P,,

Where PO is the element osmotic pressure.

9.17

Eq. 9.36

Eq. 9.37

Eq. 9.38

Eq. 9.39

Eq. 9.40
Element 1

Ffl API

Cfl

Pfl

11

FPI

CPl

PPl

Element 2 Element 3 Element 4

AP2 A P3 AP4 Fr4

F!2

O-2 7Pf2

I-------- F!3

0-3

Pt3

7

Fp3

CP3

PP3

FP~

CP2

PP2

4 * Cr4

Ff4 Pr4

CM

Pf4

7

FP4

Cp4

Pp4

Figure 9.6.-Generalized process diagram of the four lead elements of 1st stage.
9.3.2 Element-By-Element Analysis

A fairly good estimate of system performance can be determined using an element-byelement analysis developed by David H. Paul (Paul, 1993). As the name implies, this

procedure steps through the proposed membrane desalting system one element at a time,

calculating individual productivities based on net driving pressure (NIP). A spreadsheet

program such as Excel or Lotus l-2-3 is typically used to perform the calculations.

The following sample problem, used to illustrate the element-by-element design procedure, is

based on treatment calculations for a high-nitrate (64 mg/L NO,-) and slightly brackish [599

mg/L TDS (total dissolved solids)] groundwater in southern California. Treatment objectives

were to remove sufficient NO, and TDS to allow blending with filtered well water to

optimize net recovery while still meeting state and Federal drinking water standards and the

Santa Ana River Basin water quality objective of 400 mg/L TDS. The well in question has

an average production rate of 1500 gal/min at a wellhead temperature of 22.5 “C. Based on

pretreatment calculations and total product requirements, it was decided to design a lowpressure RO system to desalt 1125 gal/min at a recovery rate of 75 percent and then blend the

resulting permeate with 375 gal/min for filtered well water, for a total net recovery (permeate

plus filtered well water) of slightly in excess of 81 percent.

The required system permeate flow would then be determined as follows:

F, = (75/l 00) I I25 = 844 gal/min Eq. 9.41

The first step in the design process is to select a membrane element and element configuration required to produce the total amount of permeate desired. This determination will

be affected by the achievable recovery of the pretreated water to avoid scaling by sparingly

soluble salts. FihnTec’s BW30-8040 thin-film composite membrane element (now

designated as BW30-330) was chosen for evaluation. The characteristics of this element are

shown at the top of table 9.3. Based on a design element productivity of 5.2 gal/min

(well/softened water supplies), an initial estimate of the total number of elements required

would be:

Number of elements = 844 gallmin = 162

5.2 gallmin Eq. 9.42

9.19
Table 9.3.-Sample spreadsheet for an element-by-element analysis

. ..““......*...“*.**..*..**..*..***.***.**.*..***..**.*..*..*.**.*...*..*..**....**...*..*.~**.**..**.***.**.**~*..**.***..**.**.***.

Fmjott1-

Wellhcxl Twatmcnt 8tudy

Van Bum Well No. 8

Sye&an Design Pammckx

RO Feed Row. gal/min -

Bknd Flow. gallmin -

kited Reawety. % -

Rcq’d Permeate, gallmin -

Sydcm Amy -

Fed Tempemtumc, oC -

1125

315

75

844

24:12

22.5

MtmbmuEl~Dtsaiplioal

Mmlufactum - Fi1mTc.c

Modcllrypc - BW30-330. Thin-Film Composite

Max Operatin Pnrsure. psi - 600

l Mas Feed Flow. gallmin - 6 2

Was Fkkmcam Flow. gallmin - 5.2

Was Ekmcm Remwy. 46 - 1 9

Average Cl- Rejcaion. % - 9 9

=well watcr/softcd Wmcr Supply

I

FIRST STAGE IX1Elem EknlxL Elem 83 Elem#4 Elem 15 Elem 16

Feed Flow. gallmin 46.88 42.29 37.81 33.62 29.49 25.48

Feed C!onam&on, mgfL 599.0 663.4 739.9 832.7 948.1 1096

Feed Ptwurc, prig 187.0 180.6 175.3 171.0 167.4 164.6

Osmotic Rururc. psi ht.) 5.99 6.63 7.40 8.33 9.48 IO.96

Net Driving Pressure. psi 181.0 174.0 167.9 162.6 157.9 153.7

Pcrmcam Flow. gallmia 4.59 4.41 4.26 4.13 4.01 3.90

Rrmcstc COW.. mgn 6.0 6.6 7.4 8.3 9.5 11.0

Element Recovmy. 96 9.79 10.4 11.2 12.3 13.6 15.3

Pmssulr: Dmp. prid 6.36 5.31 4.37 3.53 2.80 2.15

Rejea Flow, gal/min 42.29 37.87 33.62 29.49 25.48 21.59

Rcjeu Pmmrc. psi8 180.6 175.3 171.0 167.4 161.6 162.5

Reject Ccaoat~ioa, mg/L bb3.4 739.9 832.7 948.1 1096 1292

Pcmcdc Flow. gal/min

Rcjcct Flow. gal/min

Pcrmatc Cow.. me/L

Reject Conantrdtion. mg/L

Rccowy. %

Pressure Drop. psid

J!s?s! ld Staec

25.29 607.1

21.59 518.0

8.04 8.04

1292 1292

53.% 53.%

24.52 24.52

SECOND 8TAGE

Feed Flw. gal/min

Feed Canatmuion. m8fL

Feed Rurum. psi8

Osmotic Fnmm. psi (est.)

Na Driving Pmuurc. psi

Elem #I ucmrz Elemn Elm a4 Elem I5 Elem 16

43.17 39.50 36.01 32.67 29.47 2b.41

1292 1410 154b 1702 1885 2101

157.5 151.9 147.1 143.0 139.6 136.7

12.92 14.10 15.46 17.02 18.85 21.01

144.6 137.8 131.6 126.0 120.7 115.7

Fwmde Flaw. gUmin 3.67 3.50 3.34 3.20 3.06 2.93

Pattune Chc., men 12.9 14.1 15.5 17.0 18.8 21.0

EkttiUU~.% 8.49 8.85 9.27 9.78 10.39 11.11

Pressurn Drop. psid 5.59 4.80 4.08 3.44 2.88 2.37

Rcjea Flow. gellmin 39.50 36.01 32.67 29.47 26.41

R&u Fbessum. psi0 151.9 147.1 143.0 139.6 136.7

wectCocumurion.mgn 1410 1546 1702 1885 2101

23.48

134.3

Permcuc Flow. gallmin

Rcjcct Flow. gaUmi5

pcrmatec4ac.. mgn

Rejcu CoPuurslion, mg/L

Reawy. 96

Rururc Dmp. psid

3ks! 2nd stppc Ae?!!

19.7 236.3 843.4

23.5 281 .‘I 281.7

16.4 16.4 10.4

2361 2361 2361

45.6 45.6 75.0

23.2 23.2 52.7

Blended Pmdua Flow. gdlmin 1218

Blended Pmdua Cont.. mgtL 192

Na Renavery. % 81.2

9.20
Assuming 6 elements per pressure vessel:

Number of pressure vessels =

162 elements = 27

6 elementslvessel Eq. 9.43

Using this number of pressure vessels in a 2-stage system (based on 75 percent recovery), the

resulting array would be 18:9. The feed flow per first stage pressure vessel would be:

Feed flow per vessel = 1125 gallmin

18 vessels

= 62.5 galfmin Eq. 9.44

This feed flow rate is higher than the maximum recommended feed flow of 62 gal/min for the

element (refer to top of table 9.3), and could result in a higher fouling potential. Therefore, it

was decided that a more conservative 24: 12 array would be used which would result in a 1”’

stage feed flow per vessel of 46.9 gal/min.

Referring to table 9.3, element 1 of the 1” stage, entries for feed flow and concentration

would be 46.9 gal/min and 599 mg/L, respectively. Feed pressure will be varied, as will be

explained later, to obtain a system recovery of 75 percent. An estimate of the osmotic

pressure gradient can be calculated as:

P = 599 lb/in2 feed pressure = 5 99 Ib,in2

0

100 Eq. 9.45

The net driving pressure (NDP) for each element can be calculated by subtracting the osmotic

pressure gradient and permeate back-pressure (assumed to be zero in this case) from the

element feed pressure. For the first stage lead element, this would be:

NDP = PI - PO - Pp = 187 - 5.99 - 0 = 181 lb/in2

This NDP is then used to determine element productivity (permeate flow):

Fp = Design Productivity NDp*alla,

NDpdesi*

= 5 2 181 lblin2

205 lblin2

= 4.59 gallmin

Eq. 9.46

Eq. 9.47

Eq. 9.48

9.21
Where NDPdesrgn is equal to the design pressure of 225 lb/in* minus an estimated osmotic

pressure of 20 lb/in* (design concentration of 2,000 ppm divided by 100). This design

information, based on manufacturer’s test data, is available in FilmTec’s technical bulletin

for the BW30-330 element.

Permeate concentration is calculated using the published average salt passage of 1.0 percent

(average salt rejection of 99 percent) for the membrane element:

Cp = Feed TDS x % Salt Flux = 599 x 0.01 = 6.0 mglL

Percent recovery for the element is:

Element Recovery = 3 100 = 4.59 100 =

Fs

9.79 %

46.88

Eq. 9.49

Eq. 9.50

For this example, the interstage pressure drop was assumed to be 5 lb/in*, and element

pressure drops were computed based on the following formula provided by FilmTec:

APE,em = 0.01 [(Ff + F,)/2)]‘-’

= 0.01 [(46.88 + 42.29)/2-j’-” = 6.36 Zb/in2

Where:

Fs =

F, =

element feed flow, gtimin,

element reject flow, gal/mm.

The element reject flow, pressure, and concentration are determined as follows:

Fr = F/ - F, = 46.88 - 4.59 = 42.29 gallmin

Pr = pr - ApeleIn = 187 - 6.36 = 180.6 Iblin2 Eq. 9.53

Eq. 9.51

Eq. 9.52

9.22
Eq. 9.54

= (46.88 x 599) - (4.59 x 6.0) = 664 mg,L

42.29

This completes the calculations for the lead element of the 1” stage. As shown in table 9.3,

the first element reject flow, pressure and concentration are now used as input (feed)

parameters for the second element. Once the equations for the first element are input to the

spreadsheet, they can be copied and pasted to the remaining columns to complete the

analysis.

Vessel, stage, and system summaries can also be included in the spreadsheet, as shown in

table 9.3. Notice, at the bottom of the table, that the overall membrane system recovery

(prior to blending) is 75 percent, which is equivalent to the original requirement. This was

achieved iteratively by adjusting the value of the permeate flow for element 1 of the 1” stage.

9.3.3 Manufacturers’ Computer Programs

A number of manufacturers provide software for predicting the performance of their

membranes for site-specific design applications. Among these are Dow FilmTec (ROSA),

Fluid Systems (ROPRO), Hydranautics (RODESIGN), Desal (Solutions), and DuPont

Permasep (CPP). All operate in the Windows environment except for the Desal program

which is DOS based. These programs are not for final design specifications, and each of the

manufacturers includes a liability disclaimer stating that final designs should be reviewed by

an appropriate applications engineer. These programs provide estimates of water production

and quality from given input parameters and are useful for examining alternative system

configurations.

An example of a Dow FihnTec computer analysis using Reverse Osmosis System Analysis

(ROSA) software is shown in table 9.4. Input parameters include the feed water analysis,

design temperature, system configuration, percent recovery, fouling factor (indicates degree

of membrane fouling; set at 1 .OO for new membranes), and desired feed <or> permeate flow

rate. Interstage booster pumping and concentrate recirculation options are also available. As

shown on table 9.4, the results of the analysis include system flows and pressures; average

permeate flux; ion concentrations for the feed, reject and permeate streams [for the system

and individual stages (referred to as arrays in the program)];estimated permeate pH; and

scaling calculations.

This computer analysis was run with the same input parameters used for the earlier elementby-element analysis (refer to figure 9.4). The results of the computer and manual

(spreadsheet) methods compare very favorably as shown in table 9.5.

9.23
Table 9.4.-Sample printout of a FilmTec RO system analysis using ROSA Version 3.05d software

FilmToe Ravarro OIIlorfr Syrtom Analyrir, Marah 95 Voxrion 3,056

Pzoparod Forr Euroau of Roclauuxtion

Analysir by% W-S.8

Date : 03-19-1997

Ford t 1125.00 QPM, 603 MWL. 22-s Dog c

Recovrry I 74.9 Parcont

Wayz a 2

MO.Of Pv: 24 1 2

Elaont f BW30-8040 EWBO-8040

IPO*El/PvX 6 6

Ex,Total: 144 7 2

Baakp <PSfQ?t 0.0 0.0

Fouling Factor: 1.00

-CT AvHEuaE

Prarsurr (PSIQ) 196.9 138.7 167.6

o-tic Proamuro (PSXG) 4.1 16.8 8.8

BDP (Moan) = 158.9 PSI0

Avorago Po-at0 Flux- 17.0 aFD, Permeate Plow- 842-78 GPM

erry El .#o.

1 a

2

3

4

5

6

RoaovOry

(Po~Foad)

-096

-103

-111

,122

,135

,152

PO-to

GPD #o/L

6505 4 46.9

6279 5 42.4

6084 6 38-O

5915 7 33-8

5765 9 29.7

5628 11 25.7

2 12 -0848 5284064 i's

3 -0939 4866 4686 21 18

5 -106 4520 25

6 .a14 4361 31

Array: Total May1 Array2

Rojoct <aPa t 522.1 282-2

Rojoat (yp/t) t 1292 2373

PW (GPP) ~1213601 868225 345376

P- <Mu/m I 3.1 7 20

Pozmoator

irrryr

xE4

L

s

ar

Ea

xc03

m3

C l

Y

so4

8102

<Mm/L u

TO-1

O-0

0-I.

O-6

0.2

t::

0.0

3.2

2.3

a.1

O-0

O-6

O-8

x-1

Axrav 1

0.0

0.0

0.4

0.1.

x.2

:::

2.x

$2

0.0

0.4

0.5

Array 2

0.0

::;

0.3

3-4

O-0

O-0

:::

1.9

0.0

1.0

1.6

43.5

39.8

36.3

32.9

29.7

26.5

Food Ford

Ma/L PRSSS~PSSG)

603 asa.

667 185-S

743 180.2

835 175.8

950 172.2

1097 169 .I

a292 162.2

a410 156.5

1545 152.7

r701 147.5

1886 144.0

2105 a4i.x

9.24
Table 9.4.~Sample printout of a FilmTec RO system analysis using ROSA Version 3.05d software (continued)

FilcaToc Reverts0 Oamoein Syrtrm ZLrrrlymis, Match 95 version 3 *OSd

Prepared Fort Bureau of Raclamatio~

Analysis byr BILL BOBQLX

Date: 03-19-1997

Feed/Rej *et,

NE4

K

101

MS

C a

sr

B a

EC03

x03

C l

F

SO4

a.02

8X804

CaF2

8102

<MQ/L at3 Ion)

Feed Reject 1

0.0

3.0

39.0

11.0

110.0

0.0

19x::

64.0

95.8

0.1

56.0

26.2

0.0

6.4

83.6

23.6

235.7

0.0

0.2

424.3

136.3

205.5

12::z

55.9

aojeat 2

0.0

11.8

153.6

43.3

433.1

8::

779.7

248.1

378.6

22::::

102.0

& Davirr -:

T&y (Molal) :

CI&g/L)f

(MS/L) t

OWL) 8

(9 Saturatioxa) :

(% Saturation) :

(+ Saturrtion) t

<% Satuzatioa):

(% Saturatioxk) I

PI-w Scaling Calculations

Feed Adjusted Food eat Rej

7-60 7.60 8.03

0.30 O-36 1.91

0.85 0.85 1.92

0,012 O-012 O-047

603.2 603.2 2372.6

198.0 198.0 779.7

11.8 11.8 11.8

0.3 0.3 1.4

1.3 1-S 11.8

147-o 147.0 1222.0

0.0 0.0

2::: 21-6 O0 81-l. 0"::

Etstimatmd Permeate pH is 5-7

To Balanae 0.0 MQ/L Sodium and 0.0 MG/L Chloride added to faad,

Feed titer io Well or 8oftzaxuM water mw) SDX 5 3

DI8-t MO-* -ssHDoHIKptIED,AlmMowAmummr

OF BABXLXTY OH FX'EIRPSS, Ib: QIVEW. Weithclr FilrnToo

Corporat+orr aor The Dow Chemkaal w- liability for

rerrultr cb- or damagmr incntrrcrdfrcm the application of

thir ipforuuoa. Any fS.naX dmrign rlwuld lm rrpimd by eke

approprirtm applfcat%oaa angineu&mg pmr6onnol.

9.25
Parameter

Table 9.5-Comparison of results from FilmTec’s ROSA program and

the element-by-element spreadsheet analysis

1 st Stage 2”6 Stage System

Spread Spread Spread

sheet ROSA Sheet ROSA sheet ROSA

Permeate flow, gal/min

Reject flow, gal/min

Permeate concentration, mg/L

Reject concentration, mg/L

Recovery, %

Pressure drop, psig (stage AP only;

excludes interstage connections)

607 603 236 240 843 843

518 522 282 282 282 282

8.0 7 16.4 2 0 10.4 1 1

1,292 1,292 2,361 2,373 2,361 2,373

540 53.6 45.6 45.9 75.0 74.9

24.5 24.7 23.2 23.5 52.7 53.2

9.26
Chapter IO

PRODUCT REVIEW

The last 5 years have seen the number of membrane products skyrocket. Even since this

publication was begun, there have been many new products released. Fortunately, the

membrane manufacturers have also made great strides onto the information superhighway! It

was possible to update the product lists as the rest of this publication was being reviewed.

Table 10.1 lists the membrane manufacturer’s addresses, phone numbers, web sites, and

contacts. Many of them have complete product information on the Internet.

10.1 Product Listings

The tables of membrane specifications are categorized as seawater, brackish water,

nanofiltration, ultrafiltration, and microfiltration. The products were categorized as the

manufacturer had them. Seawater membranes are those with high NaCl rejection rates

designed to withstand 7 to 8 MPa (approximately 1000 lb/in2). Brackish water membranes

have rejections from 99.7 percent to 85 percent with maximum pressure ratings of 2 to 4 MPa

(275 to 600 lb/in2). Nanofiltration membranes have rejections between 20 percent and

85 percent, with a wide range of pressure ratings from 1.7 to 7 MPa (250 to 1000 lb/in2).

Ultrafiltration membranes are those characterized by a Molecular Mass Cutoff, and

microfiltration membranes are those with micron pore sizes.

For seawater, brackish water RO, and NF membranes, there are three categories of

information supplied by the manufacturer and one category of calculated parameters.

l Physical Dimensions. The physical dimensions given in tables 10.2-10.6 are the

membrane composition, and configurations, total module length, and diameter. Ml?

membrane information includes pores size, bubble point, and foam point if available.

. Performance Under Test Conditions. Production rate and rejection are the

primary performance parameters for RO and NF membrane. UF and MF membrane

performance specifications give only the productivity. Percent variability is included

for RO membrane, but was left off the NF tables since few manufacturers provided

the information. The test conditions are very important here as the performance is

directly related to the conditions. Whenever available, the standard test conditions

for each company are provided. A complete description of test conditions should

include feed flow rate, test solution composition, temperature, pH, operating

pressure, and recovery rate. Usually, the feed flow rate is not provided. It must be

calculated from the recovery rate and production rate. A few companies persist in

stating their products are tested with “San Diego Tap Water” or “Typical Brackish

Water.” While this may be convenient for people in San Diego, it is not very

meaningful to the rest of the world.

10.1
UF and MF manufacturers are consistent in testing their products with “clean water,”

which is fine since performance of these types of membrane is not significantly

affected by dissolved solids concentration.

l Operating Limits. RO and NF operating limits are given for feed flow, concentrate

flow and/or recovery, operating pressure, pressure drop across the module, SDI,

turbidity, temperature, pH during operation and cleaning cycles and exposure to

oxidants. Optimum pH is provided by one company. UF and MF membrane

limitations are given only for pressure, temperature, and pH.

. Calculated Parameters. The calculated parameters are the water (A) and salt (B)

transport coefficients under the specified test conditions calculated as described in

chapter 4 (RO and NF), equations 4.4 and 4.5, and also the productivity per unit

module volume. The productivity per unit volume is simply the claimed production

rate under standard test conditions divided by the module volume calculated from the

given dimensions. It must be emphasized that the values of these parameters are

highly dependent on the operating conditions. For that reason, A and B are not listed

for the NF membranes that were not tested with a di-valent solution. The B value for

these membranes would be inordinately high and incomparable to the B values for

those calculated from test data using divalent test solutions such as MgSO,. They are

included in figure 10.1 for comparison.

There are no calculated parameters for UF and MF membranes. One could calculate

a water transport coefficient and productivity per unit volume, but it would not be

meaningful for anything but clean water. The best way to evaluate UF and MF

membrane is to compare them side by side on the same test solution using the best

operating conditions for each membrane.

Data for these tables has been gathered from manufacturers specification sheets in hard copy

or from web sites. It has been reviewed by the company’s representative for accuracy. As

many different manufacturers as possible were included. If someone has been left out, we

apologize. The paucity of data from those outside the United States is due to the difficulty in

obtaining data from such companies and not entirely due to our preference for supporting

domestic industry.

In using these tables, remember that performance is always different with “real” water. All of

the membranes listed were tested with salt solutions made from clean water, RO product

water in most cases, and food grade NaCl or MgSO, (if not laboratory grade). Complex

solutions of salts, organic compounds, colloids, suspended solids, and wildlife will have

different rejection and productivity rates.

10.2
Company/Address

Table 10.1 Mcmbrr

lPhone Numbers

Advanced Membrane Technology, Inc

10350 Barnes Canyon Rd

SanDiego, CA 92121

Phone: 619 4574488

FAX: 619 457-4422

An&&&iv. W&Grace &Co.

72 Cher$Hill Dr.

Beverly&A k315

’ Phone: 5087775622

Fi% 5118 92MO38-

Aoglinn Water/Fluid Systems

10054 Old Grove Rd.

San Diego, CA 92131

800 525-4369

Phone: 619 695-3840

FAX: 619 695-2176 ‘. j: ,:. : i P&&: 6i9 727”$71.1

Aqua Source, North America

2924 Emerywood Parkway

Richmond, VA 23294

Phone: 804 756-7620

DesaVOsmonics

760 Shadowridge Dr.

Vii CA 92083-7986

800 423-3725

Phone: 619 598-3334

FAX: 619 5983335

Du Pont Permasep* Products

P.O. Box 6101

Newark, DE 19714-6101

Phone: 302 45 l-968 1

I

Graver Scparatious, Inc

200 Lake Dr., Pencader Corp. Center

Glasgow, D E 19702-3319

I Phone: 302 731-1700

FAX: 302 731-1707

I

Lo&s, Inc.

65 Grove Street, POB 9 13 1 617 926-2500

Watertown, MA 02272-g 13 1

I Phone:

e Manufacturers

Web Site - bttp://www. Products Conlig

: ’

.

. .

: :. ..:. :

. ..* .‘.&&

t

+

.: ..:, : i: ,::: . .

advancedmembrane.com RO, NF, UF, SW, TU

M F

fluid-systemscorn IRO,NF,UF~ SW

: appliedmembranes.rom

‘. ::

+ UF l-IF

.:

:

osmonics.com RQ m, m, S W

IUF

dupontcom RO, NF HI3

gmversom h4F

I I

T u

..;. :.

,.::... : : : : :

:. . ..j. :... ::,.:: . .

.:, . . . . . :: jj.j . .

. . .j

.

:... .: ..:;.

.: i memb++s.cqm +;&jg ;: :;“;;$iy ..:

; : . ..‘...‘, .j:” ..f :: .:

ionicscorn RO, ED, NF, Systems

m,m

10.3

. .
Company/Address

Table 10.1 Membrane Manufacturers (continued)

Phone Numbers Web Site - http://www. Products

Millipore Corporation

80 Ashby Road Phone: 617 275-9200 millipore.com UF HF

Bedford, MA 01730-2271 FAX: 617 275-5550

@m&i&.:. & :890-8+1750

5951i@!e3yt~~ Dr. j : hone: 612.-933&!?7 yxkewm : i; gqNF,LiF; ,sw

ti&*glti :5536y945 .Fti:61293&#K41 .: :: ::..m.

.:: .:

.y:

PCI Membrane Systems Ltd.

Laventoke Mill Phone: 44 0 1256 896966 * RO,NF, UF TU

Whitchurch, Hants RG28 7NR, England FAX: 44 0 1256 893835

:, .;. ‘:, ,:’ . . 1: ..y;. ,, :ii:. .;;; ‘!i; .,,. ;,,j ,’

.:$ha&&& .; ; 1: .i I:.. ;I:: -lid

rj*~**t.*: 94550

: . . ;..:

+::51&@fif42,., .: ..;.i; ;::: ‘..’ :

Trisep Corporation

93 S. La Patera Lane Phone: 805 964-8003 trisep.com RONF, UF, SW

Goleta, CA 93 177 FAX: 805 964-1235 MF

Water Equipment Technologies 800 6844844

832 Pike Rd Phone: 407 684-6300

W. Palm Beach, FL 3341 l-3855 FAX: 407 697-3342

l M F S W

10.4
Table 10.2. Seawater Membranes, 203 mm (8”) diameter or equivalent.

Physical Characteristics Performance at Test Conditions Test Conditions

Manufacturer Model No.

I Du Pont 6835T

.:; . : Dir l%nt ..“” :. .:

EiayJy l&ii.‘t’&

X.’ ,. : . . ...,.: .,;.-

DuPont 6882TM B-10 Twin

Du.Font~ “, &~(i’g~&~~,~.: 1.1:: :, :,

I

Du Pont SW-H-8540

I

FilmTec SW30-8040

FilmTee SW30IfR-8040

Flitid~!f@ema. ,’. ’ 2822SS j,-,$:

Fluid Systems 2822SS Premium

F.~y~rj:~#ii: ,’ Z~~s;s..M~p;-:.;:: :?;.,:

Hydranauttcs 8040~HSY-SWCl

ffydranauiicj 804t)-ffSY~W~.

. .

OsmonicUDesal Desal-11 ADSOlOF

Permeate Nominal

Effective Permeate Flow Salt

Diameter, Length, Membrane Flow Rate, Variation, Rejection,

Comp. Configuration mm mm Area, m* m’/d % %

B-IO I

999 26.5 I5 99.35

‘1810 ‘-60.5 .* 993

B-IO

aramid HFF 219 2108 2283 68.9 * 99.35

.,, Ai.Y&..:‘:, ..j..@$:f;, 2ig, i@o 700 265 IS 99.3

B-1OT

asymmetric

aramid HFF 216 1032 1219 30.3 15 99.6

thin film I

thin film

composite SW 201 1016 27.1 I 1 5 -5 to +15 99.4

Feed

Feed TDS, Pressure, Recovery, Temp.

m8L MPa % ‘C pH

32,000 5.5 ‘ID 25 ,8

35,000 6.89 3 5 25 *

35,000 .’ 6.89 ,3$ : 25 * :’

32,000 6.89 3 5 25 *

35,OdO 6.9 35 25 ‘; *

35,000 6.89 3 5 25 *

32,000 6.85 35 25 i :

35,000 5.5 I O 25 ,8

32,000 5.5 8 ‘25 ,‘a

35,000 5.5 8 2 5 8

32,890 5.52 7 25, ,735 :

32,800 5.52 7 25 1.5

32;soo 5.52 1.1 23 .: .:“:‘7‘5

32,000 5.5 I O 25 6.0 “’- 7.0

32,000 5.5 10 $5 6.t& 7.6

32,000 5.516 15 25 7.5

.3w’~0. 5.516 !$.. .:,.:15. ‘:.. .;,:--:jj:.$.

10.5
I

FiimTec sw30-8040

FiimTec SW30HR-8040

. .

Fluid Sj@ms 2822SS,.. . . . . . ::...::.x’.. : . . . :.,.:.,.:.. . . . . : . ._ . . . . Fluid Systems 2822SS Premium

@~@y:.@ ; .G ...z~g3s.img,~. i::;c:. : . ..I. . .

Hydranautics 8040-HSY-SWCl wjiatitiiciici

: $(i&&@jyqyy~~.

Osmonics/Desai Des&11 AD8040F

Table 10.2. Seawater Membranes, 203 mm (8”) diameter or equivalent (continued)

Operating Limits

Max Feed

Flow, Umin, Optimum

Max% Max Max Max/Highly Chlorine

Rec. Max. pHRange; pH

pH for

Recovery or Opcr Press Max

Min Brine PreS., Drop, Feed Turbidity, Oper

Tolerance, Rejection

continuous Range; iv or and or

Flow (Jfmin) MPa kPa SD1 NTU Temp. “C operation cleaning (ppm days) Permeatio

132(11) 8.3 69 5 l 30 4-9 2.5 - 12 co.1 *

,.: ,,.,.: ..,,: ,..: .:. :. ::: .:,: . . . . . . . . ‘,:, . . . . . ::;,:,:,:,: ” “. ‘..’ ” ‘.

. . . . . . . . . . . . . . . . . . . ...:.:. . . . . . . . > .:.>,.>::. ~:i . . . . . . . . .

.,;;,:., ‘:;;, .‘. ..:

. > ..:.. . ..A . . ..:: .:.. . . . . . .: . . .

.v. ./.. . . . . .

.

.:.: :(.))):.).. ~ . . . . . . . .,,, .,,....................(. :, ,,.,., :.: .,.,.. , ’ “, : :’ ‘.‘.

iiii:iiiiii~s~~~~~~~~~~~~~::~~,~.~.~-I.I~~,:iil-l::::~~~~ ,.,,, 1,; *’ ..,’ ‘, jij’. ,, 4; b; : 2,s i ii”

:..:::.. k0.J *

15% 6.895 69 ~5 <l 5 0 4-11 2- 11.5 6.5 - 7 ,, . . . . . . . y ,..:: (41.5)

.

,,, , , ,, ,.

.... .:.:.:.: . . . .:.. . . . . . . . .

,::.:.::i:i:i::.:.i~~,~“.’ 6 :.......I.,::.::i::::.:~~~~~~~~~,~ ,., ~~~~il:::.~~~~~:~:~:~ 1; ,I, .;<1.,. ,,,,,,,,.

..: . . :. :. . . . . . . . . .:. :. ::. . . . . . . . . .

.::.$@ :y. ::.: 2,.t. 11 I- 11.5 :.;. .(20;& 5.5-7

Calculated Parameters

Salt

Water Transport

Transport Coef.

Coef. A* JO”, B*106, Mod. Etf

m3m’*Pd’sec“ mkec m’day”m’

2.88 ‘ , ().oss”‘- ,,::.7&&

0.10 0.002 361

‘.

0,12 0.001 482..

0.10 0.002 535

0.14 0.002 730

0.09 0.001 801

2.79 0.029 .-:, 713 ‘,

2.56 0.036 465

2,95 :~o;qj.:. ..‘578.

2.95 b.015 578.

2.65 0.038 591

ls90

10.6
Table 10.3. Brackish Water

Physical Characteristics

IManufacturer Model No.

Adv;MenuTech; +TFRCj$~tj4OH:~~“: .I:.

Adv. Mem. Tech. ATFRO-8040

&I~~#&:..~~~~, *Cf#04ri;a ::i.?...: . . . . ..:. :. .:.:: Adv. Mem. Tech. M-T4040AHF

pyJ?@n( .,, .,,I { ‘ , .J.y.4I1;1qiR’. f,, ;$;.&y:. : j :j:j

Du Pont BW-L-8540

‘~imi;cc &&j j$;::: ‘.:.;,;~;:;:. :~ ::i;

FilmTee BW30-365

,.,., . . . . . .

FtliiiTtc~~ ‘. .swjo~~~~~.:.~~~,~~~.:.: ‘;i .:.: .;.:‘:.

FilmTee BW30LE-400, High P . . .,., -

B~3OLB~OO;f;oS.lp”

BW30LE-440

8221Hrk ‘,., :c :

IFluid Svstems 8821ULP

Len. Eff. Area,

Thin Film SW 200 1.016 34

Asymetric

aramid HFF 216 1.032 1280 .,. . . . , , . . .

:.:&yp~/p~::.’ .. ..pJ:

‘..

‘: :.!J()1 1@6 ‘. 28

PAlPSlPE SW 201 1,016 34

~a~~~~:i~:::::‘:;r~4~~ ,““. ‘.;&ji, ” :‘. i,qifj :‘, .:...:.37

201 1,016 ..:.

za1. I;016 :;

PAIPSIPE SW 200 I .ooo 41

CA Blend SW 203 1,016 31.6 :&:,,g,&d” .‘$&W ,,. :&3 i;524 4p.1

CABlend SW 203 1.524 49.1

Fluld Systems 8822HR Premium

~&p&~~~&L~ : ,~~~~jj~.+:~~.‘.‘:. .. ,, ;,;,

Fluid Systems 8822HR-400 Premium

FtidiLSystems 3,J@XR :.j::.:-:. ‘ j

Fluid Systems 8822XR-400

ifhiidSJist&is lw#r@ieg) ; ” :,

Hvdranautics 8040-LHY-CPA2

1,016 30.7

i&16 ., 37.2

1,016 37.2

1,0t6 30.7

1,016 37.2

.:.T’F’c’:. : ..m! “, -::.203 ii524 47.4

Comp.PA SW 201.9 1.016 37.2

Permeate Nominal

Permeate Flow Salt

‘low Rate, Variation, Rejection,

m’/d % %

.‘. 54 ,: “,,, 15 99.5

i0 15 98

” 284 -15 97.5

7.57 96

60 92

41.6 I O 97.3

28 15 995

36 7 99.5

40 7 99.5

54 15 99.0

34 I5 98.0

44 15 99.0

23.9 IS 98.0

30.3 I5 95.5

39.7 15 98.0

49.2 I5 95.5

20.1 1 5 98.0

27.3 I5 98.5

4t:6 is 99.0

23.8 I5 98.0

..32.2 15 98.5

49.2 I5 99.0

a.?’ 15 ?ii5.

32.2 15 99.7

39.7 15 $9.5

39.7 I5 99.7

25.7 15 99.6

31.4 15 99.6

49.2 15 99.5

41.6 15 99.0

Test Conditions

Feed Feed

TDS, Pressure,

ma MPa Rec. (%) Temp. ‘C pH

2,000 1.6 15 .25 8.

2,000 1.55 I O 25

2,000 1.55 10 ” 25’ ” -585

2,000 1.55 10 25 8

1,500 2.76 75 ,2$” *..

1,500 1.55 75 25 t

2,000 1.55 15 ‘25 8

2,000 1.55 15 25

2,000 1.55 .15 25

2,000 2,0do 1.55 1.07 15 25 8”.

2,000 1.03 15 25 8

2,000 2.9 1 0 25 5.i

2,000 2.9 I O 25 5.7

VO? 2.9 1 6 25 :s.7

2,poo 2.9 1 6 25 5.7

500 0.524 -10 is 7.5

500 0.69 1 0 25 7.5

500 1.04 1 0 ‘ . 25 7.5

500 0.524 10 25 7.5

500 0.69 lb .25 7.5

500 1.05 1 0 25 7.5

ZQPO 1.55 rii 25 .7.5 .,

2,000 1.55 10

::

7.5

i;Oai, 1.55 lfj: ” 7-j..

2,000 1.55 1 0 25 7.5

2,000 2.24 10 25 .“’ ,i):5

2,000 2.24 10 25 7.5

2,000 1.55 1 6 24 7.5

1,500 1.55 1 5 25 6.5 - 7.c

10.7
I

Table 10.3. Brackish Water Membranes, 203 mm diameter or equivalent (continued)

Operating Limit3

I

Calculated Parameters

Manufacturer Model No.

‘Adii’i.&$@‘&‘.i .,j~IL1pIQ+B*go4o;H.f” ,:

,... .,...... c: . . . . . . ::t:..:. . ...’ ,.......

Adv. Mem. Tech. ATFRO-8040

&j$K~e~+:y”&~; ,, ,&$&j&J& .;:i . ..I. .::

Adv. Mem. Tech. M-T404OAHF

pq.*li;jt.-.,, .: .: :. :::::. $,p; &jiiR.$ .; jj::;:;.;.: :.:. . : j:

Du Pont BW-L-8540

F@jg&F: ‘,::. ” : ~&3&i)::: : : :.:. ‘:.::

FilmTec BW30-365

..... :\

Max Feed Flow, Optimum

Umin,Max% Max Max Max/Highly Max. Chlorine pH for

Recovery or Oper Press Max Rec. CPer pH Range; Tolerance, Rejection

Min Brine Flow Pres., Drop, Feed Turbidity, Temp. continuous pH Range; ppm or (ppm and or

(Umin) MPa kPa SD1 NTU ‘C operation cleaning days) Permeatior

j:j::). *

. .

. . . . . . :.qg :.:

;. .,. . .,.

.:‘:::i~.:g.:.‘..::-:.....:~~~. ,, $ .,.::::: .,.. F. . . : ..:. !, . , ,, ,, q :,/ :.:::, 4+‘9, l;L? 0

303 4.2 * 5 1 46 2-11 1 - 12 co.1 +

..:: . . ..:.yq ” .;... &1.. .‘$:, .; ..j ,:(. 1 ,, 40 4-6 0.3’t.O.5 *

I 4 5 2. II 0 *

+: 40 .4;tt 2.3- tt.9# .C&l *

. .Y.Y V,‘......” “--““,- ““I” 4.14 69 5 110.2 40 4-6 2.5 - I 1 5.7

Flo!dl!&temr iJq#f~ &Rig ::i:;;, ‘,:.j, : ij:;: ::.. .; : . $g&::::;;;. ..:::.A ::::. +;p::. .:j 44::::. . . . 5 i I 0.i 4b 4 4 ‘i;.s. 7. 1 5.7

uluid Systems 8231SD Mag 20% 4.14 104 5 110.2 40 4-6 2.5 - 8 1 5.7 i...i .:. :,, ,,,

I~&Syjtemj., 88z.lap. ‘.:. :.I,, :“;,;, ~::jl::, ..-:.@g;;: :i ::i.: YJqQ- ., ‘,::;69:.::.: 1, : j

,‘,I IO.2 4 5 4 -:l.l 2.5 i 1.1 0 8

‘luid Systems 88211JLP 17% 2.44 69 5 110.2 45 4-11 2.5-11 0 8 ,..

‘#iii$$y~~~:f@ .:. .: .~~jlq&~. ::‘. : :, :. ‘. ::.;i:. : ..g”/o. .:~::::::.::::::..:::&g$::: ~6$:;.I:.:. .;5 -I/b,? : 45 4~-..11. 2.5 - 1 I 0 8

‘luid Systems 8821rJLP-400 17% 2.44 69 5 110.2 45 4-11 2.5-11

:Q~&#j&ii~~ ,’ :~@@@~L&$i~,, ,;. :..$ ::::;z;~:~:irsR::.~.~~~~~~~~~~: ; y . . A .,;+t+:::; ,,I;. . . .s :. 1-j a;& ,%s 4 * .I 1 i:s-11 ;. :;

‘lutd Systems 8821ULP-400 17% 2.44 69 5 110.2 45 4-11 2.5- 11 ..I.... ..,.... . . ytjr;iisfj!+ ~ :: k $8 if@& ::‘.:l:: ‘::.;::ii:::~I:::::.:.~,~: .::j$ .y:jl:$ :j j!c@~:?:r ;:j:j:; ~.:::.:;:.L$+.:::~. . : : ,.l&i ~;,f:: : : ,.:j’ :,, : .,::i j 0.2 ,‘,;;45.1 “’ 4-11 ” :2.5+li ..:

‘tuid Systems 8822HR Premium 17% 4.13 69 5 110.2 4 5 4-11 2.5 - 11 0 8

;ia:;sj;i*etis 8822HB-& ~:f.‘jj’?~~~~’ “:. .x.:.: .~‘i.i~.‘li:,,:~::i~~~~::bd4: ,,,,, :,. :&::,.,. ” ,s ‘i .I 9.2 ‘ . 45 4-.&I 2;5 - t’l 0, : a

8822HR-400 Premium Ii% 4.13 69 5 110.2 4 5 4-11 2.5 - I1 0 8

8822@4 ‘,.. .,‘: ,, -~i:ia~:,:::::..~~::~~~~ ,: %ii$.;.: :: .j 1/0;2 45 4’11 25 - 11 0 8

8822XR-400 17% 4.13 69 5 1 IO.2 4.il 2.5-11 0 8

+, .I.. @@#.&qg:, .y?; .:;:,::,-:.g(jy*,y:;:::.,. ‘.:f::,:;#<J$:~ .I,. 1’ ;tijp::, ::.: J, 11012’ ::. 4-11 2.5.if, 0 s

rti”rfrrnrutiw. 8040-LHY-CPA2 283 4.2 69 4 I 4 5 3-10 3-10 <O.l *

Salt

Water Transport

Transport Coef.

Coef. A* 1012, Bt 106, EfTicienc

m3mS*Pd’sec“ mlsec m3day-‘m

12.8 ” 0.0~~:~~~~ ” .f719

7.4 0.197 940

r * 363.

* * 968

0.220 0,019 1043,

0.302 0.004 1100

-85 ‘. O.OS?: .’ ‘. 869::

9.0 0.057 1117

9.1 :- 0.05.8 124I’;

12.3 0.157 1675

11.9 0.199 lpss

14.6 0.115 1401

3.2 .: 0.169 ‘/27..;..

4.1 0.495 921

3.4,’ O.i74

-...

805

4.3 0.499 997

15.8 0.147 611

15.9 0.148 830

15.7 tJ:‘l50 1265

15.4 0.143 724

8.8 0.0s~ 997

9 2 n 171) 1370

10.8
Table 10.3. Brackish Water Membranes, 203 mm diameter or equivalent.

Physical Characteristics Performance at Test Conditions Test Conditions

Manufacturer Model No.

@&~~gJ~~~~~~~ ‘ : : jBo;lii~~~~~~~~:~~:~.~:~:~~

Hydranautics 8040-LHY-CPA4 &#&&g&, ,: : ~o&imy;y&~ 1,1.1: 1,

Hydranautics 8040-MSY-CAB1

l$4~ki~auticf

. . .

: 8o~qls~+q.lz ”

Hydranautics 8040-MSY-CAB3

.,. ,. .(

Whwt!es ,804ij &‘Ai ,: A-” :” :‘,

Hydranautics 8040 ESPAZ ., ,. . .

HygtWiii@4 .8049 EsPAj..~ : ,:

Hvdranautics 8040 LFCl

Osmonics 811~HR

Len. Eff. Area,

Composition Config. Dia. (mm) (mm) (m*)

;:j &@y~rl;~~~.~:~:~yg$.z? .i:::,‘,.&::;21)1 ;g: ‘,:;.:. +-jr B’ ,,. : .: j, ;2

Comp. PA SW 201.9 1,016 37.2 . .,.,., ,.

GlqjJQ.....:~> sw...:.;'.::._.ser;a;..::.,, (j-16 .' 33;9

201.9 1,016 31.6

~‘-~~~~~:i?~ :;C$ 3ii6

CABlend SW 201.9

:‘,pog’;.lp;hi’ .::.::.:.:.:.;’

l

,,, . ..$W ‘ , ,2os.y,: I:djc ‘ ,

S W 201.9 1.016 *

:. ,,,’ ,‘,‘$“‘,‘, : . . . .

.,.

, . I SW:. ~:~;20&9 ,,,l;Oi6 *

l

S W 201.9 1.016 l

Permeate Nominal

Permeate Flow Salt

Flow Rate, Variation, Rejection,

m’ld % %

22.7 15 99.5

24.1 15 99.0

32.2 15 95.0

25.7” 15 98.0

17.0 15 99.0

45.4 IS 99.0

34.1 15 PP.5

56.8 15 98.0

37.8 15 99.0

.41.6 15 95.0

27.4 97.5

33.4 “’ .’ :: 87.0’

34.6 95.0

30.5 .‘.,

:i

97.5

37.1 15 87.0

38.7 15 35.0

CDTA SW 201 1,016 29.4 24.3 15 97.5

. . .

.... -..‘+g~ : j, :.+Jyj..: .. .:.::,2(y ,,Q16 ” ‘29.4 ., ‘, ‘.,gis,- 15 87.0 . . . . .

CDTA SW 201 1,016 29.4 30.7 15 95.0

‘,‘$=+A ,,,,,,.:-../,++$:Y ~,;ibl’:~~::..l,d16 3f ‘, 27.2 15 97.5

CDTA SW 201 1,016 3 1 33.2 15 87.0

:: :%D;Tk.,. ::. $W, ,, ~‘::..‘.jOl..~.: 1;yfj ::,,,’qr 34.5 1s 950

Polyamide SW 2il 1,016 38.6 38.i 15 99.0

;~~~j~~& .;,, . -:,sw~.~.:,:,;:~:~l.~,, . . . . .:.q$i6 34.8 31.8. IS 9P.i-i

Polyamide SW 211 1,016 37.62 34.7 15 99.0

P$$.tijiki~. c/ ~::l~,~~::.::::.‘.‘:.::~:i~i:.’ : ,1,01.6.:... : !4.4 ‘j4.1 ‘, 15 PP.?

Polyamide SW 201 1,016 31.6 28.4 15 99.0

~~‘~$f@j$~~~.~.f:~.~ . . . . li:$*,: h :; , :,.&*i, ,,,, ,.: ii . . . . 1. jji . . ~G,::: : , ‘: ” +jorg I5 ,......

,:.: .-jj;g:;. ,.,... 99.q: ;

Polyamide SW 201 1,016 37.16 39.7 15 99.0

Thin Film

Membrane SW 201 1.016 32.52 I 39.69 15 99.4

Feed Feed

TDS, Pressure, I mti MPa Rec. (%) Temp. ‘C pH

i,soo 1.55 iy’:. ;‘.‘25 :: :.‘ks:K7,q

1,500 1.55 15 2 5 6.5 - 7.0

1,500 i.55 15 2$ m-‘Y’ 7.0.

2,000 2.89

+ooo 2.89 1; 2;

5.0 - 6.0

‘5..0 - q.rj

2,000 2.89 10 2 5 5.0 - 6.0

1,500 1.05 15 -2s &:$ -.7.0

1,500 1.05 15 .25 6.5 - 7.0

1,500 1.05 is -12s. ,.6.j i i.0

1,500 1.55 15 25 6.5 - 7.0

1,500 1.55 ,s. .25 6.5 -‘ii;6

2,000 2.9 15 2 5 6-j

2,000 2.21 1S 2s ,:5.-7

2,000 2.9 15 2 5 6-7

2,000 2.9 10 25 c-7

2,000 2.21 10 i5 6-7

2,000 2.9 10, ,25 ‘, 6+7,.

2,000 2.9 I5 2 5 -

1,000 2..21 15 ‘.2i ;:L.:

2,000 2.9 15 2 5 2,000 2.9 ld 25 ,g::

2,000 2,000 2.21 2.9 10 2s2 5 i::

2,000 2.21 15 ‘is 7-8

2,000 2.21 15 ,’ .2.5 ‘-7.8’

2,000 2.21 I O 2 5 7-8

2,000 2.21 15 25 ..,.i -.$

2,000 2.21 15 2 5 7-8

2,000 2.21 10. : ‘:‘25 ,7-g

2.000 1.55 * 2 5 i

2,000 1.551 15 25 7.5

‘.‘.... 2.000 1.951 15’ 25.:. ‘,“‘&.s, .’

10.9
Table 10.3. Brackish Water Membranes, 203 mm diameter or equivalent (continued)

Operating Limits

Max Feed Flow, Optimum

Urnin, Max% Max Max Max/Highly Max. Chlorine pH for

Recovery or Oper Press Max Rec. OPer pH Range; Tolerance, Rejection

Min Brine Flow Pres., Drop, Feed Turbidity, Temp. continuous pH Range; ppm or (ppm and or

Manufacturer Mode

qjg&&~j&+$:;:, .:, .:::#&,j:

Hydranautics 8040. tiga;iki.iiti ioiti;

Hydranautics 8040.

tf+dqnr.utJkc~, ‘. @i?O.

Hvdranauties 8040.

Osmonics 811-1

Calculated Parameters

Salt

Water Transport

Transport Coef.

Coef. A* lo’*, R+ 106, Efficiency

m’m-‘Pd’sec” mkec m’day”m

9.2 :,: KO60. ‘... .::.J2?9, ”

5.0 0.033 698

8.2 “’ 6.ios .. lo45

4.3 0.588 990

3.5 @32 790.

2.3 0.060 523“”

15.4 O.lSf ‘..:.~9(s:~~~:

* * 1048

l ì, 1746.

I: * ë*

+ ,í *, .: .c ë...

3.4 0.215 773

5.4 ‘ . 030 :‘: $42~::

4.2 0.558 916

4.0 0,264 :fjsf)-

6.4 I .870 1044

5.0 0.687 : . . ~lW...

3.5 0.225 756

5.7 :‘J,.,600’~~ ‘9.liJ .I.

4.4 0.585 952

3.7 0.241 ‘ . ~‘84f ‘,

6.0 1.755 1030

4.7 .0.642 , ’ !OiO

5.6 o.io8 1075

5.2 fi&jS 895

10.3 0.078 1231

10.10
Table 10.3. Brackish Water Membranes, 203 mm diameter or equivalent.

Physical Characteristics Performance at Test Conditions Test Conditions

Manufacturer

Osmonics/Desal

Model No.

Desal3 Stand. Pres.

SE8040F

I

OsmonicslDesal Duratherm?O Thin Film

SC804OCZH Membrane SW

Desal-3

DurathermTMRO

SG804OCZH

g.&Qiiiamcjar : D~sa.f;~~.~~~~~o,~.~~::

Osmonics/Desal Desal-CA CE8040F aj~ojji&~tJal, :: ,De~~l~c~pp~~~O;~‘.‘.‘::.:.

TriSep Corp. 8040-ACMl-TSA

Ti#js+@+p; :’ : ” ..” .. ...‘.. ““‘. “““.‘.“.‘. ”

:, ~~tp+ZMNJ.WiC~.~.

..,.,.. . .

TriSep Corp. 8040-ACM2-TSA

y4s’+p c&-p.. ::.,$(J~~~~~~&.Jyv&‘$ : ::.

TriSep Corp. 804t%ACM3-TSA

%~l$Q.gi~~.’

,, saaolAcM4;~a,....:i::: . , TriSep Corp. 8040-ACM4-TSA ,,

. . . . .

TriScp Corp. 894~~SBlO-TQA

:

TrlSep Corp. 8040-SB20-TSA

~+#$+i, .j.+NJ&J@i@& I. .’ .,

TriSep Corp. 8040-SB90-TSA

Osmonics/Desal

Len. Eff. Area,

Composition Contig. Dia. (mm) (mm) (m’)

Thin Film

Membrane SW 200.2 I.016 32.52

201.9 1.016 32.52 19.44 15 99.0

201.9 I.016 32.52

::.::$Qjg 1” ‘. ,y:$$y

Thin Film

.20&J

Membrane SW :..

1,018 32.52

CTDB SW idii 1,016 32.52 . . . y:‘.,,Q@ :..: ::.&$, ‘2b6,2~ -1,016 32.52

PA(ACM) SW 202 1,016 33.5

.J&&4$~::::: ::.::..$A!;:<, y :.,:gi : !,016 33.5

PA (ACM) SW 202 1,016 33.5

:...1p’,A.(~@$~:‘:: ;y~$,q.:~~::. ‘.:.:&I~ ‘: ...l,Ql6 ,,,, 33.5

. .

PA(ACM) SW 202 1,016 33.5

; p&q$y -.z:::$Ji::~,. ,:;,::::::.::~fp ” l;jjld- 3Lf.s

PA(ACM) SW 202 1,016 33.5

:Q$Bl&if.:.. .,.-SW : ‘. .: :!ij@ 1,Offj 31.6

CABlend SW 202 1,016 31.6

: :-.C&BlCtg ::: ; ‘ . ‘,‘: s:w:::. : ~yz202 : ‘: I,0 16 31.6

CA blend SW 202 1,016 31.6

. . . . . . .f&+≧if’. ~y$i~.~ ,..., ,, 392 : :,, 1,016.. .ppj ..

CABlend SW 202 1,524 47.4

::i f2f4fl&i$j ‘,’ ..-‘.T.QJ 202 1,524 43.4

PA(ACM) SW 211 596 34.6 . . . .; . .

:

.&p&“: ‘,:~::\$g’,,, ,,,,‘::;;$jj .. !,Oii 32.6 :,‘,

CA blend SW 211 1,016 32.6

@f&&j’? ~‘!‘;:&$f:- “.2)6 l,Ql& : 35.3.

CA blend SW 2i6 I.016 35.3

Permeate Nominal

Permeate Flow Salt

Flow Rate, Variation, Rejection,

m3/d % %

29.1 I I5 98.9

.‘. .’

‘27.22 ” I5 98.2

‘24.6. IS 98.9

24.6 I5 98.2

22.68 IS iJi.0

30.24 I5 97.0

127.59 IS 87.0

28 I5 99.5

34.. I5 99.5 ”

34 I5 99.5

39.7 1 5 99.5

39.8 I5 99.0

53 15 99>2

21 I O 98.0

.I? 15 99.0

26 I5 98.0

32 15 95.0

2 5 I5 85.0

30.3 I5 99.3

51 I5 98.0

51 ., 15 4LOi0 I5 99.0

26 I5 98.0

32 I5 95.0

-3b I5 98.0

3x IS 95.0

Feed Feed

TDS, Pressure,

m@ MPa Rec. (%) Temp. “C pH

2,000 2.93 I5 2 5 6.5

. .

2,ObO 1.551 iS ‘:“25 6~5’

2,000 2.93 15 2 5 6.5

2,000 I.551 I5 2 5 6.5

2,000 2.93 15 25 *

2,000 2.93 I5 2 5 *

2,000 I.551 I5 2 5 *

2,000 1.55 I5 2 5 8

2,000 1.55 I5 25 8

2,000 1.55 15 2 5 8

2,000 1.55 I5 2s 8’

2,000 1.55 I5 2 5 8

2,000 I.55 I$ 25 8

2,000 0.69 I5 2 5 8

2,000 2.9 15 :i& 5~6

2,000 2.9 I5 2 5 5-6

2,000 2.9 15 25 ‘5-6

2,000 2.9 I5 2 5 5-6

2,000 I.55 15 25 : 8

2,000 2.9 I5 i5 5-6

2,000 2.9 IS 25 .5-6

2,000 I.55 I5 2 5 8

2,ObO 2.9 I5 25 5+6

2,000 2.9 I5 25 5-6

2,000 2.9 15 ; @ ..’ 5-6

2 non 2 9 I5 35 5-h

10.11
I I

Table 10.3. Brackish Water Membranes, 203 mm diameter or equivalent (continued)

Operating Limits

I Calculated Parameters I

Max Feed Flow, Optimum

Umin,Max% Max Max Max/Highly Max. Chlorine pH for

Recovery or Oper Press Max Rec. DPer pH Range; Tolerance, Rejection

Min Brine Flow Pres., Drop, Feed Turbidity, Temp. continuous pH Range; ppm or (ppm and or

(Urnin) MPa kPa SD1 NTU “C operation cleaning days) Permeation

15% 3.448 69 ~5 <I 5 0 2-11 I - 11.5 (20.8) 5.5 - 7

I

OsmonicslDesal DurathermTMRO

SC8040CZH I 15% 4.131 69 ~5 Cl 7 0 4-9 - 1 I .5. T< 120.8. T<501 6.5 - 7

Osmonics/Desal DurathermmRO

SG8040CZH 15% 4.137 69 <5 <l - 11.5, T< (20.8, T<50) 6.5 - 7

Ojl~oiji&j&$&f:~. ~~:~.j$jqal;t& @$#I@ :,,,

..,, . :.:..i:. Desal:ti .--.ib40F :+jii~';,z~#~ ,,,,,,: i:,:,i:;.$;$& .... ,!$+J ,j? -'<y '<:1 3:: 8 1,. *

15%

. . . . . Osmonlcs/Desal 3.103 69 <5 <I 3 0 5 - 6.5 3-8 I *

.,. . , .,.,. . .

I)~mwd@ilWif

. . . . . . . . . . . . . . . . . . . . -~~~~i~~~~6~~~~~F,:~,.. : , , ::tqp.:.. , , . ...3.103, ‘. @ *5 <I 3 0 S-4.5 3-8 1 *

TrlSfp Corp. 8040-ACMl-TSA 300 4.1 69 5 1 4 5 4-11 2.5 - 11.5 co. I *

,. . . . . . . . . . . . 

. . . . . . . . .: pi&q Q+; ;

tjp~t&~~yA*~& .;. ?: ~::‘::~BOO”‘:‘.:~~’ ;...#.;z:: “‘. ,.j’, :;, 5 I 45. 4-1.1 2.5 - 11.5. ::. co.1 t

TrlSep Corp. 8040-ACMZ-TSA 300 4.1 69

+;. ~~o;.:;;.~'~,~,~.:~.:.~i:~~,l .; jiq::.. ..:,,

1 4 5 4-11 2.5 - 11.5 co.1 *

Tk&%p .$YoqJ; fjo4&l(r;&Q&j$& ,: .I " 45 4-,I1 2.5 -11:5 40.1 *

TriSep Corp. 8040-ACM3-*iA 300 4.1 69 5 I 4 5 4-11 2.5 - II.5 co. I *

Trl~s@cwp~ t?J+A&+%k~~ ., ,, ,, ,,,,, ,,,.

:...G:~&j :,,. x:.:.i.'~j 69,:. 5 I 4s. 4-11 <OS *

Triqep Corp.

8040-ACM4i+ii

300 4.1 69 j

2.5 - 11.5

1 4 5 4-11 2.5 - 11.5 co. 1 *

y,&-&j+; . .

. , . . . . ,.,..... . ...\.. . . . &,4@@)1&~~::::.: ........... '.ii~:iiii~:~~,~::'~~:~~~:" ~,.',:~~~:;,;..~ ..:.&J .,,x . .../ j : :, ,I,' 1 : 40 23 - 7.5 1 * +'* 7

TriScp Corp. 8040-SB20-TSA 300 4.1 69 5 1 4 0 4-7 2.5 -1.5 1 *

f~~$g&&.. ~~4~@$j+jj&$~~ .‘.‘. , : 1: .::::.i$@jj;,, ,,::--:,.:..‘:‘::l:~~i:~‘:::;~. : $9 “3 1

40 4-7 2.5 -7.5 1

i

TriSep Corp. 804OSB90-TSA 300 4.1 69 5 I 40 4-l 2.5 - 1.5 1

1

+ij++&jP;.. ,:,, F .; :g~~o;~oi~~~::~~..:...:'.:~:..~.i. :i.:.;.: ,.:.. : s$)Q ; : ../ . . .:;.;.:::;;.;::;4. 1, . . ~ .@i:... .'5. ..:. 1 : 4s. 4 ; ,I 1 23 i 11.5' co.1 *

TriSep Corp. 8060SB20-TSA 300 4.1 5 I 40 4-7 2.5 - i.5 1 *

~l~ep~,~,~& aos~np;lrsc4i.::;.:.:~.~.:~~~~ yy,, JOti :, :,:: ,: ” . . ;1;,1: ‘ : . ..@I : :$ 1. 40 4.3 1 *

TrlSip Corp. $340~ACMl-TSA

,a.$ - 7.5,

300 1

.‘..“” :.:::,::.:..:::;j : ‘. ” j, ..:. -: ,,. 1

4 5 4- I1 2.5 - II.5 co. 1 *

‘T&&$.&;iiia’ g~~o~~B~~*~~.‘.:.:~:;:. ‘::, ‘.j;:j:;::::.:: ‘yjo 40 4-7 i.5-7.5' I *

TrlSep Corp. 8340-SBSO-TSA 300 ‘4.1 69 5 1 4 0 4-l 2.5 - 1.5 1 *

~~&j&;~~,p,, Y.5 .I.. .

8j&$jgj~~q~~.j~ ,.j : ~,;;;j’::,;:.$@ :,:.:, j::;:j ~~:~~~.:~~;;,,~,;~~:~~~:;: ,..j” ” ,:..j ,A0 477 2.5 -7.5 1*

TriScn t-nm. 8540-SB50-TSA 300 4.1 69 5 1 40 4-7 2.5 - 7.5 I *

Salt

Water Transport

Transport Coef.

Coef. A* 1012, B*106, Effkieng

m3m-2Pa3ecp’ m/set m3day”m’

3.8 0.106 910

7.1 0.163 837'

2.5 0.064 598

:

:..

3.2 0.089 ” 736 ‘.’

6.4 0.147 756

2.9 0.151 io9. "

3.9 0.306 946

7.1 1.348 863

7.1 0.045 860

8.6 o&4 ..:..j&J :

8.6 0.054 1044

10.0 ” :o.ow : .I219

10.0 0.128 ii22

13.4 0.136 Hi?

14.1 0.135 639

2.3' Q.lg ""sz2

3.5 0.179 799

4.3 'dj67 983

3.3 1.485 168

7.6 O@$ " wt

4.6 0.234 1044

4.6 0.602 .,,’ 1044

7.3 0.093 844

3.4 Oil73 132

4.2 0.549 901

3.6 XL184 806 ':

A6 tifai tn7i

10.12
I

Table 10.4. Nanofiitration Membranes, 203 mm (8”) diameter or equivalent.

I

Physical Characteristics Performance at Test Conditions Test Conditions

I

Dia. hen. Eff. Area,

Typical

Permeate Chloride

Flow

Typical

Rej., % Divalent Rej.,

..a 6 0 9 5

4 7 6 0 9 5

?g.’

..&j 9s ”

49.2 7 5 4i

‘29 8 5 9 s

3 5 8 5 9 5

56.8 .;; i

31.3 6 0 9 4

-3y .40 4s

36.4 4 0 9 5

30.3 4 0 $3

32.2 4 0 9 5

36.24 * 9 8

30.24 * 9 8

1.. 38.56 l 9 6

... 38.56 l 9 6

43+ 20 t

41.7 4 0 9 8

30.3~~: ia *

3 0 8 0 9 8

J3.4 R t

34.5 6 0 9 4

27.8 6 0 9 4

30.9 6 0 9 4

Feed

NaCi Divaient PXSSW,

Cont. for Cont. for

&, mg& &, mg/L Test solution (diz:nt)

Recovery,

% Temp.“C pH

:2,000 2,000 MgSO, 0.5 13 : “. .25 7

2,000 2,000 McKh 0.5 I5 2 5 I

2,qoo 2.4300. M&h OS 1s. ‘T.25 7

2,000 2,000 ‘WQ 0.9 * 2 5 t

2,000 2,000 Ma% 0.5 !5 2 5 .. 8

2,000 2,000 N&h 0.5 is 2 5 8

2,000 2,000 MgsO, O S is “ . 25 ,‘.

2,000 ’ typical BW 1.55 16 2 5 i.3

500 * typicat BW 0.552 IO 2 5 75

500 * typical BW 0.552 10 2 5 7.5

soa 250 San Diega TW i .a5 1s .25 ‘X3.. 8.2

500 * * 0.52 I5 2 5 6.5 - 7.0

.5ou.. *, * OS2 IS 23 ,a.5 i 7-O

I 2.000 Na>SO, 1.59 10 2 5 6-7

.’ 2,000 NqSO, 0.93 ‘0 ‘25 ,, *

I 2,000 NalSOr 0.93 10 2 5 *

* 2.000 NatSO 0.93 I O 25 . ..*

* 2,000 NalSO, 0.93 10 2 5 l

l 1,000 M&O, 0.69 10 25’ *,:

:. 1,000 @SO, 0.69 I O 2 5 1 *

i;OOO M’$O, 0.69 IO 25 ,‘?

l 1,000 MgSQ 0.69 10 2 5 *

500 l NaCi 0.72 15 ‘25 8

500 500 M&N’4 0.69 I5 2 5 8

sgi, : Nat21 0.72 13 2j

“ioo

8

500 MaSO, 0.69 1 5 is 8

2,000 t fiiC!l~ 0.72 1.5 25 8’

1 2.000 NaSO, _ I .59 IO 2 5 6-7

* 2,ood Na$Oa I .59 10 15 .;6.7

1 2,000 NalSOl 1.59 1 0 2 5 6-7

10.13
Table 10.4. Nanofdtration Membranes, 203 mm (8”) diameter or equivalent (continued)

Operating Limits Calculated Parameters

Max Feed Flow,

Ymin,Max% Max Max. Chlorine Salt

Recovery or Min Oper. Pressure Max/Highly Mm. pHRnnge; pH Tolerance, opt, pH for Water Trhmport Transport

Brine Flow Prcs., hop, Max Feed Recommended Operating continuous Range; ppm or (ppm Rej. end/or Cocf. A*lO’*, coef, p106, Mod. Eff. m’dal

Manufacturer Model No. (Ymin) MPa kPa SD1 Turbidity, NTIJ Temp. ‘C operation cleaning days) Permeation m’m.*Pa-‘xc” mlsec Im”

&:$f$&T~~; : . j -;4Tp~~so’1o:,i,i~~~;..:::,~ iii:.~l:.~:,:;~~J.,:,~ijii~::-:.:,:’ii:’~::~~::.:..;~?~~.:.~~~:‘ ‘ : 5, ” ‘,y:::‘: f .‘: :$o -4-4’-::“.3.!0 Q .* 30.1 ,8,245 ” 12’73

Ad”:&. Tech. ATtiO-B-Sti& 265 4.1 103 5 1 50 4-9 3 - 10 0

. 26.9 4638 iil4”

&flvi~.n;r+:~~~, ., :-~~~-&~z$.:;;z:::;:.: ;:; ;.;;:;;; .::,:;@;j ::., c::f;;+f;.q;j+, .~f~~.+~~.~~: y .,:, : ,. . . . 1 : ,JO -?:-S, .j-jo.. 0 *.. 27.5 2.165 j114

FilmTec NF4!!-8040 245 4.1 * 5

. 45 3 - 1 0 2- I1 co.1 * l l 901 ./

It/lMT& ,.Y.. ~~~~~~:.” ..;ii;,;,.:;:.‘.:; .:(:.:~:.~,.~6~,:~~,~~~,~::~:~:~~~,~~’:,.,~~:~~~:..,:,~‘,~~, .j.. jj. 3i9- I - I1 * 0.1 * 34% 0.700 1273 . .

FilmTec NF70-408 265 I.7 * 5 I 35 3-9 I - I1 co.1 *

35.4 0.71 I 1496

FlldhT*e,;,:T;~;.,. .; .~@@#o.:. :.:-;. . .+ ..y.<..:.:tJsj$..;.yy .;: ;;y;;;p$$$ ; ~:::;,:: ,.:‘:-‘: 3’. “: . . . 1.‘. “’ ,35 3-9 .l-11 =z 0.1 l 29.4

: ,.... ,,:.,

o.qo iT$l

,,, .,, .,., ,... ,,, ,, ,, ,,,,,,.... . . . . . . . . ..c Fluid Systems 8231LP Mag 20% I .655 104

ht&&yiiijl... ; pms .:,.::,, :::.$.;,.;;;,:i.. :, I;,:;; ~~.:,:,!?~~..~,.:...~~~~:~~~~:~~~~~~:::~.~~:.:~.6~’ .:j:::y:::: ;.

I I0.i 40 3-7 2.5 - 8 I 5.1 a.2 3.530 991

l/O.2 4s 4-1L 2.5 l II 0 8 21.3 1.828 8d2

Fluid Systems 89215400 17% 2.41

; p;4e pq)&$:;.:::‘::::,; .:.:...: :,:, .;;:.;A .:.:.:. #&.:.;.:.:.y :.:~.:.:;cw,:::.i.~:.~~. :& ; ‘.,

I IO.2 45 4-11 2.5 - 11 b 8 21.2 1.821 1064

qzJ&j~~~~~,::::::‘:’ :, 1 4 0 2-i ‘ 8 2.8 1

*

13.95 Lti64. 1279 ,“’

Hydranautics 8040 ESNAl 280 4.14

.,,,.ë:j-ii;:;pg~ ,::f:. .+,:j::./ :,,$t;f:$)f. ..:g :.ë.

i 45 3-10 l >O.l * * 1 1279

&.&-~w& ..go!a,asN~,ë::::~-::i..: ; : ë:: ) .. 1 .45 ‘id!0 * bO.1 l . * I: : .í!?Pb.

Osmonlcs all-NFlOO (CA) l 6.9 l l

1 80 2-12 l 4I 7.5 0.6i4 818

:. .A.. :::

q&&fg;F :: : ,:,.s~*$yfy(pyyf ,::..., :j:.:I.ilila:i~~.~~~~~~~~~.:~::, ,:,: ;~:,l.i,ii::i:~.~:::~~ :. : .:ëIí; : .50 ..:: 2 ^. $, :

. . . * 2 l

14.6 om-- !iill.

Osmonics 813-NE300 (PA) 1 3.44 * l L 50 2-8 l 2

I 14.7 0.605 IO21

@iii~hliq 8l~N@qPP). :. ‘ . :.‘: :.:;.,‘ij, ‘y. . j;+$&:. + “’ ;;. 9 ’ S O 2-8 l 2

*

, , . . . . . .,. 14.4 0.595 ,850

Osmonica 81FNF300 (PA) * 2.07 l *

* 50 2-8 * 2l 14.5 0.596 903

Cji&ii&sal

:.

.l+i*ei$.Dcgf#~ .: .::. :::: ;: II,;;(! $TT- :;::..i,: “$$&J:::,:~ ?59. ::, ? f ” 50 I*ll l-II.5 (41.5) 416.6 o.ti$ ..930.’

OsmonicsITksal Desal-5 DK8040F 15% 3.448 69 *

l 50 2-11 1 - II.5 (41.5) * 16.6 0.21 946

(,&,,&,~l,,&&l, ., * 56 l-11 1 ^ 11.5

. . . .:.:

. fl+&$:Q&j$$@,::::: :.:.I. .~~~::.:.:.;.:~~~~~; ‘:I., .; .:: i,4&.‘: ,I; ,3$ ‘,,+r; ” :‘+ (415) F 21.2 osii 1 i&s.

Osmonicskal

. .. . .

Desal-5 DLg040F .i5% 3.448 69 ’

I 50 2-11 1 - 11.5 (41.5) * 21.2 0.542 1206 . . . .,...

ql$tp Pi+..:. ,&j~&f@@j”~:~: ;., ;‘::;.j.. , : j& y?:, ..: . ..2.&;. :. .‘6~,,;,:,:::::,.‘,:.. 3,: 1' i 45 4-11 2~5 - 11.5 1 * l .* 1339

TriSep Corp. 8040-TS40-TiA 302 2.1 69 5

f ..:.... :;.

4-11 2.5 - 11.5 I * 21.8 0.27i 1281

p&$pg.#, :::. :

.,.>... : ..:~~~~~~~~~i:!:::::~.~ :::‘:::+ iliii~~(ii.ii::~:~~,~:~~~~~:~:~:~~~~~~,:~ ::: .J.i :lj ‘:‘. ::. .,: .T&Jl ”

i

2.5” 11.5 I ìí í l

Lí .í 931.

TriSep Corp. 8040-TSSO-TSA 303 2.1 69 5 45 4-11 2.5 - II.5 0 * 15.7 0.195 921

T;i$$t$+; : ‘~04OX89iY&&” : . :.;i+‘.:&jz ‘..(‘: . . . ~~;$..:;:.L :q ‘.‘. ‘-3 “f, 45 p-il 2.5 - 11.5 0

. , 1.: 1026

TriSep Corp. 813-NFlOO (CA) l I

..;:;.j ,:,I ë;ë, l

. * 80 2-12 l -4 l 7.7 0.696 967

~ii$i@i&~ 8i+l$@$&, ;, ;:.. ,,* ,", ,>,,, ,. * ,: -!QQ 0.5 * 13 * 25 *,, ,, 7.4 0.662 779

TriSrn t-!wn. 817-NFlOO (CA) l 6.9 l 1 100 0.5-13 * 25 l 1.1 0.693 866

10.14
Manufacturer Model No.

,.,. :.:..

Afqpamil6gy

~~ia;e&&~ 1:“‘.

, , ,,,, ,,

A/G Technology UFP-100-E-85

AlC; i‘e+oiogy ..tjtiijb&tii$j: ,:,;g; ..,... ,................

Adv. Mem. Tech. AESlO-D-8040-I-I

. . ‘ .

Ad@,Mem. Tech,

: ,... .c’

,., . . . . . .

AIlS3OW304t@:~~

.‘. ..‘. .,.,. ..>,. .,.....

Adv. Mem. Tech. AFlO-D-8040-H

k&biqn. Tech AFi&j..a.ti*ir

&. Mem. T&h. AF3C-B-8040-H

A&. Mem. T&r. .4+?0;&&4Q~H.:.

Adv. Mem. Tech. AGS5B-8040-H

Adn ,M&n, ‘l’etlu -ASlao+8p4ojH.‘r

App. Mem. Inc. MC2020M7SH ,,..... . . .

App.$Wit;Ific j@$$j~@p~s :: ..:

App. Mem. Inc. M-U8040D3

.,. +p@+¶+ Inc. “‘~&fq.Jjj@j&b~:.; j;. 1.;

App. Mem. Inc. M-U804OD500 ~i~i,$6&rec,. .NA @j$$.;.~:.~i-~i”~ j

Aaur Source. NA MIA35

I CeraMem Sep. Inc. PMA-0010-G

I

FPI Sep. & Sys. KC-840-OlOSL :

k:

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

....

.... .:.: ..:: j:.:: ,: :.:.: . . ... ..:.:. . .

.3?lwm.~sYs~ .....

IsGt?4u?nwL.,::::‘I:

..... :........

I

FPI Sep. & Sys.

Table 10.5.

Physical Characteristics

Dia. Lo,,, Eff Are;3 ,

polysulfone HF 108 1,310 8.8

. . . . ..A

:I~dys;ylfm. ~:?$:j:.. :.. my .;: 10s 1,JlO 8.8

polyether

sulfone S W 200 I .ooo 34.4

polyether

sulfone

PES S W 203 1.524 30.7

Polyether

sulfone S W 200 1,000 25.5

~,‘ijij;&+j~i~; ,: .:. ..

polyoie@r:~-~,,, ,$W :;

‘,

,,,, 203 I,OIb ti.3

Polvsulfone S W 203 1.016 23.3

UltratIltrrtion Membranes.

Performance at Test Conditions

Nominal Permeate

Permeate Flow

Flow Rate, Variation, Productivity

Feed

Pressure,

ml/d %

:.

32 25

Test Fluid

ciean water

MPa

0.14

Feed Temp. ‘C Recovery, %

2 5 >dO.

5 0 2 5 clean water 0.14 2 5 >90

100 2 5 clean water 0.14 2 s 290.

2 6 2 5 clean water 1.0 2 5 1 0

33: 2 5 clean water 0.28 2 5 10

2 6 2 5 clean water 1.0 2 5 IO

65 2 5 clean water 0.2 2 5 rp

3 3 2 5 clean water 0.28 2 5 10

6 5 2 5 clean water 0.2 2 5 10

2 6 2 5 clean water 1.0 2 5 1n

6s 2 5 clean water a;2 24 ii:.

5.4 l clean water 0.5 2 5 2

23 2 5 clean water. 0.3 2 5 I O

2 6 2 5 clean water 1 2 5 10

2 1 25 clean water O S 2.5 10

136 2 5 clean water 0.2 2 5

zo

In._

150 IO clean water 0.04 * ‘,’

i9 2 clean water 0.04 2 0 l

ëi.8 N/A clean water 0.17 2s ‘. N/A

3.2 N/A clean water 0.17 2 5 N/A

49.2 20 SDTW 0.345 25 *

64.3 * SDTW 0.482 2 5 *

88.9 15 clean water ‘0.2 25 15

110 10 Dl water 0.34 2 5 90

135 IO DI water 0.34 2 5 9 0

165 I O DI water 0.34 2 5 90

26.5 * Dl water 0.2 25 ,lo-io

51.1 * D I water 0.2 2 5 IO-20

10.15
I I

Table 10.5. Uitraiiitration Membranes (continued)

Rejection Characteristics I Operating Limits

Manufacturer Model No.

Nominal

MOiCCUl~~ Feed Max. Chlorine

Mass Cutoff Test Solute Pressure, Feed Max. Operating Operating pH Range; pH Range; Tolerance, ppm

(NMMC) Test Solute Concentration, mg/L. MPa Temp. “C Pressure, MPa Temp. ‘C continuous cleaning or (ppm days)

Adv. Mem. Tech. AESlO-B-8040-H 3.5 K polymer marker 2,000 0.34 2 5 2.8 5 0 2-I! 2- I2 .,

(16,600)

““‘. : .&, M&,:T&$, ,... .:: .:;;;; .;., .:.;: ‘... ” ‘,.’ ,,, .., ;.:,;,.;,.,.. ;.j...;,,‘, ,” ~~~g.B;Bo&~. ‘.‘;. .‘.: ‘:: .; ‘: ‘: . . . . ..j-..;: <;, ..:

;

. . . . : . . . . . . .

.: .: :.

.

. . . . . . .,.,

A&o-B-8040-H

: :.~,:~~:!~:~..~,:,:~:,..pa~ymw,~~er.,, ;. ” ‘2,000 ” ,, Oi? 25’ 2.8 50 2-11 2.12 {16,@0) :

Adv. Mem. Tech. 3.5 K polymer marker 2,000 0.34 is 2.8 5 0 2-11 2- I2

$tiy! ,&ii&l&h, A;#j&j&j~&~::::::::'- :,i,i:.:'~3~~~.~:~~~:~:::~~~~.~~t~~~.:. :, : .,,qgj 0;33 : 25' 2.8 ,', 50 2-11

(1 yq

10K

2- 12 (16$oO) : :

Adv. Mem. Tech AFJC-B-8040-H polymer marker 2,000 0.34 2 5 2.8 so 2- 11 2- 12

AAdP* Mrin.T4&.

. , A~~i)i)i&$j,@i~i- .‘,,’ :. ~~~.sdo,~~;~.:.~‘~!ymei @jr@ 2$&j

(16,600)

il.34’ 25 ',, :, 2.8 so 2-If 2- I2 (li$mi).. :

I Adv. Mem. Tech. AGSS-R-8040-H

.4+.&erii Tjkh. : &~@k$j#iX&Hi:~~

App. Mem. Inc. M-CZOZOM’ISH

.&jp;++ti~ Inc.

. . . . . . MyU864~D$5 ‘:. .:.

App. Mem. Inc. M-U864OD3

A$ .MLirn. Jrjc. .: . .

,’M+Ji(t+~ ::. ::I::

App. Mem. Inc. M-U8040DSOO

. . . . .: . : . : AqUStiurce, NA

Lrtr;75; .:,::. :‘::,;, :,; :...

,. , .

Aaua Source. NA MIA35

. . . ,..,

c&#&f&&p$;r;l’::

. . . ..:. ,,, ;,. ‘.’

CeraMem Sep. Inc. PMA-0010-G

Fittid~.t$!&?rms. ,,:.

KGGAj”:gX3XDF’.:.:.:

. .

Mag&gyj ;:;: j.:_ :~j:::::.::j::::

Fluid Systems

Ultra7 8321UF

Magnum

. . . . . . . . .,. .

m,s:wx&ms,’ ‘. ;;;,:,.,:., ,.,.,.:.~ ,.,., ....,, ,,’ ‘.,.

$~i~;$j~ii~~x~A:ai:i;li:i

::’ . . ., . :........,........:

. , .:. :. .

I

FPI Sep. & Sys. KC-840-010-SL

. . . .,. . , . , . . . . . . ‘, ,:.:.;~:::::,:::,,j,, . ::

FpIJ~~j,i&SY&. i. : . . Kc;~?~~~~~~~:::~:~.:.~:~

. . . . .... . . . . ...’.,..’..,, ..

,..... . . .

. ,., ,.

:‘;:‘.:,,.,;~;,~ ,.,.,.:.::::::,:.:,:. ..... .c......

FPI Sep. & Sys. KC-840-100-SL

2.5 K polymer marker 2,000 0.34 2 5 2.8 5 0 2-11 2- I2

:.:;i.~.~Ficjlic,:~~~~~~~ j&&&i : ,,:, ; ,Qoo ti.34, .2s

(16,600)

2.8 50 2-11 2-12 ticgmj :

20000 l * l + 0.5 4 0 2- I2 l +

.ë.~~~ìì.ìí .::.:ë..-:;.~;+~.,~::,,.:;;,;~~ :. ,, +í + * * * I I + .. 

I + i t l * * 1

I ) . . . * .;* * * l l l .í

500060 * I l * + l * l I

:.; . . . . :.roo:~:,:..~~::::::~::~~~lt~~~, ; ,í ë..i,j(oo ,0:2 20 e.is’ .‘. 3 0 4 - 8.5 4-8.5 56

IOOK Dexirane 2,000 0.2 2 0 0.18 3 0 4 - 8.5 4 - 8.5 5 0

0.2 25 .;, 0.35 121 (WI) 4-9 4-9 ‘. Totemnt

Poiyvinyi250 K pyrroiidone 1,000 0.2 2 5 0.35 121 (as) 3- I2 3- 12 Tolerant

,. .: . . . .“.

,. _. . : : . . ?.. ,‘,z.‘.:,: :.;, ;,., ./. .:.

; ..:::. 1o:~,ID:#:‘:‘:i::;,:.~I:-:-s);‘~~~,I::,. 1; .,’ ,;i ‘. o:j45”

,.. . . . . . . . . . . " 2s 1,034 4 0

I .034@25, .827@

4-6 2.5-a 1

I - 13@25, 150@50,

6-IOK PEG l 0.482 2 5 5 0 5 0

. . , ,.,,,.,., ,.

I-11@50 pH7-8

,,.,;;...... ::,

,:, ‘. . . . .,.

. . . . . . . . pi@~ijt&fe~~.-: ,, .:, ‘ , .,. . . :. :. :,

,., ,,,,, . . .

.:~:.a.~.~~~~.~~:~:~.~:~ :~:;&cal -.:.j::::. :: . . ‘~.l:,@o : 0.2:. :: : -2s

.:

2.7 45 2- 12 2* 12.5’ “ ; .J(J

200 ppm

IOK Myogiobin 1,000 0.38 2 5 0.69 5 0 2- 10 i.s- 13 cleaning

.;-; F : ~ii ;;; : & ;, :;,

: ..50 2.10

: ‘I. $opijiii y. 1;$ . ..i’3 . . ,‘, ag&ih&

200 ppm

1OOK Globulin 2,000 0.38 2 5 0.69 5 0 2-10 i.5- 13 cleaning

.:. ‘:‘.‘:: “’ ..i:::: ,.,,,, Ip ,..,,; y ,..:.. .’

. . ,.. . :: ‘Z,’

.::gi&.30 ~:+:.-.:;i.:- -.‘.*EG ,,:,. ,:,:::- ,, :. ,, y” “” :............. ..;;:., . . . : .:,, .b.i.. :~.is. I,] ..:. 45 . ’

2- I2 1.13 :

IOOK PEG

,.i>o..

* 0.2 2 5 I.1 4 5 2- 12 1 - I3 I50

10.16
r

I Osmoniw 815~PTl CA

., ....

Osfn~ilics

I)i’gj$ps’.: ‘;. :[Z.

Osmoniw 815.PTl VS

I Osmoniw 815~PT2 PS

,.,.. ,..,. . .

osmbkF.,: ,, ‘,, ‘, 815-HP2 .VS ,;, <.:::,

:.. ’ ,,:..; ,: .,... ,,, ..: ,,..,.

Osmoniw 815-PT3 CA

I Osmontw P-Series PW8040F

Dia. Lo,.,, Eff. Arer

Comp. Cornfig. (mm) (mm) m’

i;:::..thin. ne:.:~~:i:~i::::::~~:~sw.::~::::~.:~:~~ 200.: ; : :.{f ,jj&;, :39: 8

. . . . . . . . . . . . . . . ,.,.,.,.,. .

l S W I t * - .

:::it';itj~ii@ii+<.ii.:. . : -flF'.:::.:, :,, p:S '.;. " 1,OQi 2.4

Polvsulfone HF 0.5 1,092 5

Homogenous

fluorocarbon S W 201 1.016 28.1

Cellulose di-hi

acetate S W 201 1.016 28.1

’

. . . . . .. .~h~bgep$lsl:‘:~,:... ‘ : :, ,,,::,:

.,. p&&j& j:::c . .

,,

$k : ,; ,, 20, I.016 28.1

Polyether

sulfone S W 200.2 1,016 32.5

.,.‘,T$n.pi)m :;:, :,;, .” :‘.‘.

~.Afii~~tt0~ s. ‘zlw :j .zod.z 1,01.6” 32.5

Thin Film

Membrane S W 200.2 1.016 32.5

sulfone S W 202 1,016 33.4 49.1 15 clean water 0.2 2 5 15

Table 10.5. Ultrafiltration Membranes.

Physical Characteristics Performrnce at Test Conditions

Nominal Permeate

Permeate Flow Feed

Flow Rate. Variation, Productivity Pressure,

m’ld % Test Fluid MPa Feed Temp. “C Recovery, %

î &&: ë: l

DI yatei 0.z 2 5 10 220 ...

15.5 I * 0.1 * *

3.45 - 460 402.5 Dl wrttq 0.14 * +

23 - 126 75 DI water 0.14 l *

36.68’ 5 2 01 water 0.14 * *

9-50 29.5 DI water 0.14 1 I

137.-256 197 DI water 0.14 1 t

2000 ppm

46.2 * NaCl 0.69 2 5 10

7 2

2OtlQ ppm

l Nad’ 0.69 25 10 :

2000 ppm

118

56.9

NaCl

2000 ppm

NBC1

0.69 2 5 10

0.34 2 5 10

7 2

2000 ppm

* NaCl 0.34 2 5 10

99.3 1

2000 ppm

NaCl 0.34 25 10

2000 ppm

62.2 + NaCl 0.34 2 5 10 2000

ppm

90:2 + NaCl 0.34 2s IO

119.07 2 5 clean water 0.207 2 5 10

25.7 2s clean water I .034 2 5 10 .’

21.17 2 5 clean water 1.034 2 5 10

23.44 25 clean Water. 0.517 2 5 ‘ . 10 .:

32.81 2 5 clean water 0.276 2 5 10

40.6.

‘...

1 5 clean water 0.72 25 15

10.17
Manufacturer Model No.

I

Osmonies 815-PTl VS

I

Osmonics 815-PT3 C A

I

Osmoniu P-Series PW8040F

ci;~x.i~&..l.

,:..,. ,.:..: .......... . ..

.c,io.:::~~~~4ur~~~~:::,

., ....... ...............//..: . ......A

:.,: ,,,,,,........: :

OsmonlcsIDesal G-20 GK8040F

I

OsmonfcsIDesal G-80 CN8040F

ITrtSep Corporation 8040.UESO-TSA

Table 10.5. Ultrafdtratlon Membranes (continued)

Rejection Characterlstlcs Operating Limits

Nominal

Molecular Feed Max. Chlorine

Mass Cutoff Test Solute Pressure, Feed Max. Operating Operating pH Range; pH Range; Tolerance, ppm

(NMMC) Test Solute Concentration, mg/L MPa Temp. ‘C Pressure, MPa Temp. “C continuous cleaning or hvm day.4

..,.,.,. .( @~;-~.~&p::‘~j~~::px~.& : : ,:., 5:.:, :. Of1.7 + O.iS 6 0 1.5-13.0 * ‘,’ *

ibK PVP K-30’ * 0.07 1 0.18 60 1.5 - 13.0 l *

ì.í fO;(iKI:ìëI:i-.~p~,~~.~.. ë.:: ë? .ë. a.07 * 0.18 60 1.5 * 13.0 1 l

3 K Insulin* l 0.07 l 0.18 6 0 I.5 - 13.0 * 1

jb j&; :,::, ..:‘gg”m$& .‘.’ * d.ci7 * 0.18 6 0 I.5 - 13.0 1 l

5-10 K + l l *I l

l I l l

5-10 K l + l *I l * 1 * *

SO-100 * * l *I* )I 1 * l

,. ,.... ‘..‘.“’

.~~~.~*~:::..:.‘~.:::i”:~‘.::~:.: “.,,:.;, ‘i * * : s‘ 4 1 l i

ë.ë.

>96% rejection

of CytochromeIOK C, MM=l3,300 + 1 2 5 1.379 5 0 2-11 2- 11.5 (~,OW

:. 50 2-11 2- 113 :,

~.& ,,

3.5 K PEG 1,000 0.827 2 5 2.785 5 0 2-11 2- II.5 (500) .

,,,,,, :. . : ::..: ,‘,‘,’ ,,,.’

. . .

..,...,,,

:.,. . . . .

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

. . . ..

,‘,‘,‘:‘,‘,::‘,‘,&‘fWWI:-: :::::‘iii~::;i~:~:~~~:~:~~:,::::.,~:::~,,~ ,:. jj::T i,:f;aoo I’: :. ;, : f i:q,eij:.

.

” 2s.

.;.. ,...., . . .. . . . 5 0 2-11 ; i ,jTp 1. 2 _ il.5 .‘:I; ~jj&-jJ ’

IOK PEG I.000 0.827 25 1 I .379 5 0 2-11 2- II.5 (I .ooo\

IOOK col 1,000 0.2 25 1 2.7 4 5 i- 12 2 - 12.5 I O

10.18
Table 10.6. Microfiltration Membranes.

Physical Characteristics

I

Foam

Point

Bubble Point (IPA),

Manufacturer Model No. Conlig. Comp. Dia. (mm) Len. (mm) Eff. Area, m2 Pore Size, micron (IPA), kPa kPa

&$g,f$;y$&. : .‘. . . . ~~1U+B&jijfj&~ .,.. .yyy :.‘i:~~~: :::‘:.:.;;.:.:j.+: : :gqgJp;” 200,. ~,tmJ 34. I 0.04 * *.

Adv. Mem. Tech.

,f&&j& &p. inc.

CeraMem Sea. Inc.

‘Graver Seo. Inc.

Gijlrni sei. fnc.

Osmonics/Bcsal

0slpciiki/&sa~

OsmonicsLlesal

.

,&tq@;.‘.‘. .’ ‘.‘..

Setec, Inc.

~pr#$::@tifJ$i:

IWater Equip Tech.

Witer-Equip. Tech.

I

Water Equip. Tech.

Vi’~ter.Eqnip; &ch.

Water Eouio. Tech.

AF JU-B-8040-H S W PVDF 200 1,000 34.1 3.0 * *

. ..., ., . ,. . , .

:..:.p~;Q~ooIG”.:.:‘:~:“. ;,j $Y+@$&,i,~bu!‘E;,.:

.. AlphaAlumina ‘: 144 864 11.1 0.2 t *

PMA-0500-G Cmpnd. Tubular Mixed Oxide 144 864 11.1 0.5 * l

:.;, ;yjgl;ir .,..,.. jo!yi+r 6 5 250 0.68 0.6 * *

Various Tubular polyester 6 5 500 1.36 0.6 l *

“’ ” .+Jubf&~\r...:. ..; :, ,,; polyester : 6 5 ‘is0 2.04 0.6 * +

Tubular polyester 6 5 1,000 2.12 0.6 l * VLfioii.. . . . ..A . . . .,

î ìi :. .: .,.. .:: . . . . . .J,,l@yi::: ~~~Ji&S~l&Sís St&] 25 - 1200 600 + 6100 &OS - 750 0.1 * *

E-500 EW804OF SW polysulfone 200.2 1,016 32.52 0.04 * *

.,. ,._ . . . . . . .

Jx8@4OF :

, . .,;;; .’ .‘i :..:~.sy/ ” PVDF 200.2 1,016 32.52 0.3 138 .i52

K8040 SW PTFE 200. I 1,016 18.58 .I, .2, s, 1,3 * *

.~~q@.;+..~,.+?~; ‘...:;I: : : : . . . . . . .,:‘..:I:il:i~~~~!.~:~~~~ ;;, ~‘~~,~.:~o!ri;fbdrienk 38 ‘460 .0.5 9.2 * : ,*

SC170 Tubular polypropylene 5 0 1,060

l;OlS &

0.2 * *

..:; ,i:irl::.i:::i:i:~~~.:~::‘I::i.::i.l.~ j ~~::.;pJqjf?~.:.~, :. zag.: ,‘, 0.2 .*’ .*-

SW CPVUPolypropylene 114.3 247.1 1.11 0.2 * *

. : + ‘) &&y :. .‘~pv(J&,g.~pylene 114.3 247.7 Lil 0.4

WBC-1.0-15

I

S W Cotton/Polyester 114.3 247.6 1.39 I + *

d&jgi~;is:.,: ,+:, ; ; .:;.::...&j$;; :,~:;:@diio&ojyester 114.3 247.6 1.39 5 * f

WVSS-20-15 S W Cotton/Polyester 114.3 247.6 1.39 20 t l

10.19
Table 10.6. Microfiltration Membranes (continued)

I Performance at Test Conditions Operating Limits I

Permeate MaX. Chlorine

Nominal Flow Feed Max. Operating Operating

Permeate Flow Variation, Productivity Pressure, Feed

Tolerance,

Recovery, Press., kPa or Temperature, pH Range; pH Range; ppm or (ppm

Manufacturer Model No. Rate, m’/d % Test Solution kPa Temp. “C % (Pressure Drop) OC continuous cleaning days)

,$jy$M&QIeeh;. : A~:@+&(t4~;f:i~.~: ,:::j. :,:.:.:.J 5O:i.:i%.::.: ::..: .j .%5.:: ,;:;:i clean- y@r 02 ‘,25’.; J(-J .‘; 1,030. 50 2. II a- !Z . ’ (16,609).

Adv. Mem. Tech. AF 3U-B-8040-H 300 25 clean water 0.2 2 5 I O 1,030 50 2- 11 2- I2 .

(16,600)

Cr~Mmni $+p+k HJ&$+.t)~~&~ ,., :j : : .:Y:‘, @f:.:j : :::f:.j., :-N/&:. . . : $@j :w&ter 0.i 7 2 5 W/A 345 121 3- 12 3; I2 ?k$+ri~ :

CeraMem Sep. Inc. PMA-0500-G 12.8 N/A clean water 0.17 2 5 N/A 345 121 3 - 12 3- 12 Tolerant

. . .

.,.

!$jy!c~;@qk& : : ~a~~~~~~;:.i::~~:i:,~.~,~, ; . , ,.,., ,,.,.,.,.,.,. ;;. -:;:i:,.ts.~~(.~~.:i::..: g;::+.:;;-:;. ;, ..\Hi& :,” 2.9.:,: :’ .:g *‘.’ 5.i.7 “60 4;g.j NIA t,. : Graver Sep. Inc. Varlous 38.2 5 water 2.9

,:.;.

t 517 60 4 - 9.5 N/A +

,gjgjfg@Si;&:Xhi:, i:,: ,: ,: . , :, x??@~ ,:.‘I. J., ‘.‘; .j:g :,:; : .::~~.:I:::.I.:~~,~.~:~:~~~~~:~:,~:.~~ :::.,: ::‘$+);:: ~ :v : :+v@ . . . .:: .;: $2 .’ .. T 517 60 4 - 9.5 N/A t

Graver Sep. Inc. Varlous 76.4 5 water 2.9 25 + 517 60 4 - 9.5 N/A *

ei&~,$$.:j& .: : , . .., vj@niij- .:’ ,:,:;: ;, ,.....,. :. .: .:. ::. .,...... ..f y::v@Q#::.,:::; :.T. ë.:.10 :;:.,I::,í c!~~tr$r$i ! ë9 l . @ilo .; ..li l 300 0 +99 unlimited 4im o* 14 .-o l 14

E-Sod tiW8040F

.v&sOsmonics/Desal 136.08 25 clean water 0.207 25 1 0 1,030 5 0 2-11 2- 11.5 ., . . . . . . . . . . .,.,. . . . .

#$hMitiWDt% -- .’ 0,207.::: :. j5

i5,OOO)

.

Jx8o~oF;:... ,:,.I ~. I::.;, ;16u;~..:~I.::::~.:.~;~ 25’::., . . ‘&@ $& i,o34 5 0 2-11 I’- 13 (s;aoti):.

Osmonics/Desal K8040 * i * + l * 138 5 0 l-11 l-13

..,. !&@$$:Jjg-= ‘; ,,: .st#ii;; ..:. :..:.,. .‘T. :: :;.~I.::.::17~1:::::i.l’-;‘,‘:’ .” : ’ , J 0.:;: ‘.. . .:. .&!&f&$&

(5,000+)

70. 21 IO ” 209 .40 1 - 14 .‘I - 14. -...d ”

Setec, Inc. SC170 230 I O clean water 7 0 il 209 40 1 - 14 1 - 14

+&i$$@;:$hi+pi . . . : : : :. .:: @J!&~~~&~$% ‘Y.: : ;:\ :‘.:: ;& .;A:’ :;i:. f ::;:::::.. , : I$: “.. ..:+ +iiu$jl;i~~.. : 70.0 . . ‘., .2s 15” 2;m 45’ 2- 12 2 L,.lfL;S po..

Water Equip. Tech. WBC-0.2P9-15 102 + clean water l * * 20 90 12@35de *’ Tolerant giiei; ,&&;i;. kj$&. WBc+B;4p47# 1.1 ‘,: :.I”” i@; “T.’ “’ + .‘.

,, . , &aiih&er * f * 20 90 12@35de * “’ $$jJafmt .., : . Water Equlp. Tech. WBC-1.0-15 245 * clean water 0.275 * l 34 90 -12at35 * Tolerant

W&t& &$.tip.,Tech, WBRS*5d3’~’ .’ .: ,: 272 ‘. ,*,;;. :. C’lash \iret;i’ 6.275 + * 27.5 90 -12at35 * Tolerant

Water Equip. Tech. wvss-20-15 272 * clean water 0.275 * * 20.6 90 -12at35 * Tolerant

10.20
10.2 What Does It All Mean?

There are so many products available with slightly different rejection and production rates

that are tested under different conditions! How is one to decide which one to get? The bad

news is that the most important information is not on the specification sheet. Cost and

service are the most important aspects of the membrane. Cost could be a deciding factor, but

it changes with time and depends on the quantity purchased and other nebulous site specific

situations. Service contracts are crucial. Membranes are a large part of the cost of a

treatment plant and they can be ruined in a matter of minutes if not used properly. Be sure

that the supplier will back up the warranty and be sure that none of the exclusionary

conditions occurs in your facility.

Here are a few tips for ensuring a successful membrane treatment experience.

l Make sure the company that supplies your membranes is going to help you get

started and will be available later when problems come up.

. Make sure there is a good warranty on the membranes.

. Invest in your operators. Well trained and empowered operators save money and

aggravation.

l Consider automatic data acquisition and controls so that operators can tune in on

gradual performance trends rather than day to day changes. Membrane data needs

normalization to detect real changes, shift to shift changes in the raw data are not as

meaningful.

l Calibrate sensors regularly to ensure data is as accurate as possible.

10.2.1 Water and Salt Transport Coefficients Versus Rejection and Productivity

Water (A) and salt (B) transport coefficients are difficult to get a handle on. They are

extremely small numbers calculated from the productivity, rejection, and test conditions.

A is the volume of water produced per net unit of pressure, area, and time at test conditions.

B is the quantity of salt that passes through the membrane per unit of difference in salt

concentration across the membrane for a unit of area in one second under test conditions.

As discussed in chapter 4, if one wants to produce a large quantity of low salt water, one

would want a membrane with a relatively large A value and a small B value. Figure 10.1

compares the A and B values for seawater, brackish water RO and NF membranes. Figure 10.2 focuses on RO membrane specifically, which will be the basis of the rest of this

discussion. Generally, seawater membranes have very small A and B values, brackish water

membranes have slightly higher values, and NF membranes have large values. The entire

range of desalination membranes is close to zero to 4x 10” m/set for B and close to zero to

35x1 O-l2 m3m-*sec~‘Pd’ for A.

10.21
3.0

o^0

: 2.5

:

2g 2.0

m 1.5

1.0

0.5

0.0

0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0

A (m3m~zPa~‘sec-1g1012)

Figure 10.1 .-Relation between salt and water transport coefficients for seawater, brackish water RO

and NF membrane. There are two different optimization strategies apparent here: one group of

membranes is for minimizing salt passage and concentrate volume, the other is for selective

salt passage and minimizing concentrate TDS.

Though it might look from these graphs like there is a linear relationship between A and B,

there is not. The value B/A is merely an artifact of the test conditions; it is the product of the

salt passage for the test solution and the NDP under test conditions. Remember that these

parameters are calculated from observed performance of the entire module, not from physical

characteristics of the membrane as they should be. Still, the visual aid is helpful in portraying

the performance of the a large population of membranes. A more informative graph would

be A or B versus applied pressure and feed water TDS. Alas, this data is not available for all

membranes. But what about the plain unprocessed specification sheet data? Salt rejection

and productivity per unit area are explored in figure 10.3. As with A and B, there is

absolutely no correlation between the two, except that in this figure it is readily apparent. It

would be difficult to predict which of these membranes would be best for a particular

application. There are too many variables that are not taken into consideration. Are the

differences in productivity for a given rejection rate due to test conditions or could the

module furthest to the top right actually have better circulation than the others? This is

because productivity and rejection are extremely sensitive to the operating conditions. There

must be a better way to determine the efficiency of a membrane module. One needs to be

able to decide whether it is better to pay extra for a module with 99.5 percent rejection if it

produces 6 m3 less per day than the 99 percent rejection membrane.

Unfortunately, there is no way to be sure which membrane will be best for a particular

application until it is tested on site. Until all membranes intended for a given purpose are

10.22
l BWR0 r-l q SWRO

6 8 1 0

A (m3m* Pa%ee1*1012)

1 2 1 4 1 6

Figure 10.2.-Close up of relationship between sea and brackish water RO membrane transport coefficients.

9 8

90-

8 8

l l + l +

86 -.

l

84 -I

0 0.2 0.4 0.6 0.8 1

Production Rate (m3mqday1)

1.2 1.4 1.6

Figure 10.3.-No relationship between rejection rate and productivity per unit area.

10.23
under the same conditions, or at least with the same feed solution at the same pH and

temperature, there is no meaningful way to compare them. With performance test data on

many different membranes, though, one can make some comparisons between different

configurations and testing methods.

10.2.2 Does Operating Pressure Make a Real Difference?

If a membrane will have the same rejection at a lower pressure with perhaps a small reduction

in productivity, it may be cost effective to use the lower the pressure. However, there is a

minimum pressure necessary to overcome the resistance due to osmotic pressure difference

between the feed and permeate; the membrane resistance, which is a function of the polymer

and its thickness; and the module resistance, which is a function of the flow channel width

and surface roughness. There is a trade-off involved in optimizing any of these three

resistances.

l Lowering the osmotic pressure difference means more salt in the product water,

l Decreasing membrane resistance usually is accompanied by increased salt transport,

and

l Lowering module resistance could mean less contact time and lower permeability.

But, are the current module designs at the optimum point? Conveniently, a few

manufacturers supply performance data for a membrane at more than one operating pressure

Table 10.7 lists differences in performance parameters when tested at different operating

pressures.

Table 10.7.-Change in performance statistics with operating pressure. Membrane X

may have better performance at the higher pressure

Membrane

Net driving

pressure

&Pa)

Productivity Rejection

( m3/day) (“W A B

861 34 98 11.9 0.20

X

1,369 54 99 12.3 0.16

481 20.1 98 15.8 0.15

Y 646 27.3 98.5 15.9 0.15

996 41.6 99 15.7 0.15

481 23.8 98 15.4 0.14

Z 646 32.2 98.5 15.5 0.14

1006 49.2 99 15.2 0.15

10.24
The only real difference in performance at higher pressure is the decrease in salt transfer (B)

for membrane X at higher pressure. Membranes Y and 2 have essentially the same

performance no matter what pressure they are operated at. They may have a slight

improvement in efficiency at mid-range pressures, but the increase in productivity per unit

NDP is too small to be significant. Membranes Y and 2 cannot be compared fairly with

membrane X because they were tested with only 500 mgL NaCl solution while the latter was

tested with 2000 ppm NaCl. Table 10.7 should be used only to compare each membrane to

its own performance at a different pressure.

10.2.3 Does Increasing Membrane Area per Module Improve Productivity?

Several of the membranes listed are available in “high area” module designs. One way to

measure the benefit of adding more area to a module is to look at the overall module

efficiency. Module efficiency, as it is used here, is the production rate under standard

conditions divided by the module volume. Figure 10.4 compares the module efficiency per

square meter of added membrane area and performance statistics for 20 pairs of modules

made with the same membrane, but constructed such that one has a greater surface area than

the other. All increases in area resulted in a net increase in the modules production rate;

otherwise, they would not be on the market. From figure 10.4, however, it is apparent that

some increases are more effective than others. There are only a few ways to increase the area

in a spiral wound element without increasing the volume.

l The membrane envelopes can be constructed such that the edge seam is very

narrow. Hand glued envelopes can have edges that are 6 - 10 cm wide on three

sides! Using a mechanical sealing machine could increase the area per envelope by

25 percent. This method should not change the A or B values. Small changes are

probably due to the error in the area measurement of the regular modules. There is

also an added value in that there are no longer dead spaces on the module edges that

can trap particles and provide good places for fungal growth.

l Thinner spacer materials can be used Thinner spacer material could improve or

hinder overall performance depending on whether the new material is better at

promoting mixing than the regular materials.

l The membrane envelopes can be wound more tightly. This method is sure to hinder

performance which will show up as a decrease in A and an increase in B over the

regular module. Tighter winding inhibits circulation and will promote fouling.

10.2.4 Are Longer Modules Better?

One recent change in module construction is to increase the length by one half so that two of

the newer “MAC” modules should be equivalent to three regular size modules. The benefits

of having longer modules are:

10.25
92’01

Percent Change in Module Effkiency and Transport Coeffkien
l Once the capital expense of the new equipment for manufacturing the modules has

been realized, it should cut production expenses by about one third.

l Fewer connectors are needed, which means a small equipment savings and fewer

opportunities for leaks.

l Greater active membrane area due to fewer seams and opportunities for an edge

effect.

On the down side:

l The modules are heavier and will require an hydraulic lift to load them into the

pressure vessels. They will also be more difficult to extract.

l Since the manufacturers had to up grade their equipment to produce these longer

elements, they will probably be more expensive than the equivalent number of

standard size elements.

How should a longer element perform in comparison to the standard size? Figure 10.5

compares five sets of modules that come in a 1 m length and also a 1.5 m length. Each pair

was performance tested with the same feed solution, NDP, temperature, and pH. The

recovery rate was higher for the 1.5 m module, as should be expected. Theoretically, A and

B should not be affected by a change in the module length. The increase in productivity

should be due to a reduction in edge effects caused by poor circulation in the membrane

envelope comers. Since the specifications are based on single module performance, though,

some of the improvement is probably the result of the higher feed flow necessary for a longer

element. But if both size modules were tested in full pressure vessels, both would have the

same feed flow, and the only differences would be due to the reduction in edge effects.

10.2.6 Conclusions

There are countless membrane products to choose from in a wide variety of materials, configurations, and sizes, with a wide range of rejection rates and production rates, and there wil

surely be many more in the future. They all operate under the same principles, however. As

long as one can find out how they were tested to produce the advert&d rejection and

production rates, one can normalize the data for testing differences and compare the

performance of different products. It is very important to look at more than two parameters,

though, when the products are tested under different conditions or are of different sizes.

While module efficiency may be not quite as important as UkWhr, it is still helpful when

deciding between modules of different configurations. Transport coefficients are useful by

themselves only when products of the same configuration are tested under the same

conditions.

10.27
6

-6

-.._ -- .~ ~..

..~_.

__-.-_.-.--

___._-_ .-----

I

1 2 3 4 5

Membrane Pairs

Figure 10.5-Ghange In performance wltn longer moaules.

No matter what the specifications are, service is still the ultimate consideration. Membranes

are an expensive part of a water treatment plant and can be easily ruined. Whether you are

purchasing membranes for your kitchen sink or a whole plant, your supplier should work

with you to ensure you are getting the right product for your application.

10.28
Chapter 11

ESTIMATING THE COST OF MEMBRANE TREATMENT

The cost of membrane processes depends primarily on the quality of the source water, the

method of concentrate disposal, and the quantity of water to be produced. The feed water

quality and treatment objectives dictate the type of membrane to use, which, in turn,

influence the operating pressure and the composition and volume of the concentrate stream.

For this reason, concentrate disposal must be a part of the overall treatment objectives. There

are two general approaches to disposing of concentrate. The first is dependent on volume

and the second is dependent on concentration. A goal must be established at the start of the

planning process: either to minimize concentrate volume or to minimize its salt content.

Blending the membrane product water with filtered feed water is one way to help control

concentrate characteristics, but first one needs to predict what the concentrate and product

composition will be.

11.1 Predicting Product and Concentrate Composition and Volume

There are four important pieces of information needed to predict the product and concentrate

composition and volume:

1) Recovery rate, (Ret) in decimal form. The recovery rate is limited by the

concentration of sparingly soluble salts in the feed water. Lowering the pH and

adding anti-sealants can increase the potential recovery rate. The other determining

factor is the configuration of the membrane system. Each element can recover

approximately 10 percent of the feed flow as product. Generally, 50 percent recovery

is assumed for a 6-element vessel. Therefore, a 2: 1 array should be expected to

achieve 75 percent recovery, and a 4:2: 1 array should be capable of 87.5 percent.

2) Rejection rate, Rej in decimal form. Manufacturers list a rejection rate for chloride

and one for sulfate or other divalent ions for NF membranes. For greater accuracy,

use a weighted average based on the feed water composition. For instance, if the

feed water has a ratio of 3: 1 mono-valent to multi-valent ions and the rejection rates

are 90 percent for chloride and 99.5 percent for sulfate, the weighted average

rejection rate would be:

Rej,, =

0.75*0.900 + 0.25*0.995 = o 924

0.75t0.25

Eq. 11.1

If the goal is to minimize concentrate volume, choose a membrane with a very high

rejection. However, if the goal is to minimize concentrate TDS, choose a membrane

that will produce the target water quality. NF membranes are suffkient in many

cases.

11.1
3) Feed water dissolved solids concentration, C, in mg/L.

4) Target delivery water concentration after blending, C, in mg/L.

A very simple model of membrane separation is used here for the purpose of estimating

costs. Accurate product and concentrate concentration prediction calculations that take

concentration polarization into consideration can get quite complex, but do not provide that

much more accuracy in a first pass cost estimate.

Product concentration, C, in mg/L:

c = cf (1 -&I

P Ret

Concentrate concentration, C, in mg/L

c = 5 Rej

c

1 - Ret

Eq. 11.2

Eq. 11.3

The maximum amount of blend water that can be mixed with the membrane product and still

achieve the target water quality is calculated as follows, assuming filtered feed water is used

for the blend water:

Q =Q, (C, - C,)

b

c/ - c

P

Eq. 11.4

Where Qb is the maximum blend volume in m3/day, Q, is the target volume in m3/day, and C,

is the target dissolved solids concentration in mg/L. If there is a component of the blend

water that is more limiting than the total dissolved solids, there are two options. Either plan

to remove that component from the blend water or use the concentration of that component in

the blend water for C, and the estimated remaining concentration of it in the membrane

product water for C,. As an example, consider the following situation:

c, = 900 mg/L with 0.5 mg/L manganese

Rej = 0.95

Ret = 0.85

c, = 300 mg/L with less than 0.05 mg/L manganese

c, = 900*( l-0.95)/0.85 = 56 mg/L

c, = (300-56)/(900-56) = 0.29 or 29 percent blending with feed water.

11.2
But, when the manganese concentration is considered as the limiting component:

Cf =

Rej =

Ret =

c, =

c, =

c, =

0.5 mg/L manganese

0.95

0.85

Less than 0.05 mg/L manganese

O.S*(l-0.95)/0.85 = 0.03 mg/L

(O.OS-0.03)/(0.5-0.03) = 0.04 or 4 percent blending with feed

water.

If the blend water is filtered with greensand or the manganese is removed in some other way,

the higher level of blending is possible, otherwise not. However it is decided, once the blend

volume has been established, the membrane process feed, product, and concentrate flows are

set (all in m3/day):

Qp = Q, - Qb Eq. 11.5

Qf= 2

Q, =

Q,., (1 -Red

Ret

Eq. 11.6

Eq. 11.7

11.2 Estimating Membrane Cost Factors

The primary factors for estimating membrane system costs are the membrane area, operating

pressure, pump horsepower, and the number of skids.

11.2.1 Membrane Area

Membrane productivity per day is normally measured under some standard operating

conditions and listed as m3/day or gal/day. At this point, most manufacturers have there own

standards. The listed productivity will do for a preliminary estimate of membrane area

requirements, but a pilot test will be needed to verify the productivity on site. Perusing the

tables in chapter 10, you will notice quite a variation of productivity levels available even for

the same kind of membrane. For a preliminary estimate, take a moderate value from the

range listed. The number of modules needed is simply the required membrane capacity

divided by the module productivity:

11.3
Q

No. of modules = 2

Q, Eq. 11.8

Where Q, is the module productivity in m3/day. Of course there should be a full compliment

of modules in each vessel and enough vessels for a complete array. If a 2: 1 array is planned,

then the number of modules should be evenly divisible by 3. Likewise for a 4:2: 1 array, the

number of modules should be a product of 7.

11.2.2 Operating Pressure

The operating pressure is a function of the type of membrane used and the difference between

the osmotic pressure of the feed water and product water. For this level of estimate, we will

use the pressures recommended by the manufacturers. See chapter 10 for sample operating

pressures.

11.2.3 Pump Horsepower

Using the following assumptions:

l Feed water is being pumped from a tank of approximately the same height as the

membrane skid,

l 10 meters of pipe, and

l Pipe is 10 cm (4 in.) in diameter for 20 cm (8 in.) modules and 5 cm (2 in.) for 10 cm

(4 in.) modules.

hp =

(Ah g + 0.5 v2 + AP) (1 -JQ) e, 1000

746 E,,

Eq. 11.9

Where:

Ah =

g

=

V

=

Ap =

E ret =

Qf

1000 z

height difference between top of tank and membrane inlet in m,

gravitational constant, 9.81 m/s*,

velocity = Qdpipe area, m/s,

pressure difference between tank and operating pressure in kPa,

energy recovery in decimal, 0.20 - 0.30 depending on concentrate

pressure,

membrane feed flow, m3/sec,

mass of one m3 of water in kg,

11.4
746 = conversion factor from J/s to hp,

Eeff = combined pump and motor efficiency in decimal, try 0.75.

11.2.4 Number of Skids

There are several cost items that are directly tied to the number of skids in the system. The

most important item is the high pressure pump. The flow rate used in the horsepower

calculation above is the flow per skid. If all the flow is assumed to go to one skid for large

flowrates, the cost of the pump skyrockets. When choosing the number of skids, there are

three important considerations:

1) There must be a complete array on each skid. If a 2: 1 array is planned, then a

complete 2: 1 array should reside on each skid.

2) It is good to have two medium sized skids rather than one large skid. This is true

especially if the system is in operation 24 hours a day. If there is a problem with

one system, the other can still provide some water while the problem system is

being maintained.

3) It is less expensive to build fewer large skids.

As always, there is a trade off between expense and flexibility. The designer has to balance

the pumping costs with the other per skid costs such as chemical feed systems, controls and

data acquisition and the extra lab costs for testing the water quality of each skid. Figure 11.1

shows that, for smaller capacity systems, one skid is most economical, but very quickly the

extra cost associated with multiple skids is more than outweighed by the lower pump costs.

11.2.5 Chemical Feed Rates

Chemicals needed for RO and NF pre- and post-treatment and an estimate of the dose rate:

l Acid for pH adjustment to prevent scaling or for membrane preservation when using

CA membrane. Dosage depends on the buffering capacity of the water and the target

pH. Jar tests are best.

l Anti-scalar& for scaling prevention. A typical dosage is about 5 mg/L.

9 Chlorine, for disinfection after treatment. 5 mg/L is a good estimate for RO or NF

product water. Blend waters will require more, depending on the organic content.

11.5
1 0 I

0 0.1 0.2 0.3 0.4 0.5

m%ec

0.6 0.7 0.8 0.9 1

..-. Q ._.__ 2 skids

4 3 skids

. . . . . . a .._ 6 skids

Figure 11 .l .-Optimizing pump cost and the number of skids for a range of flow rates (0.1 m%ec = 2.2 Mgal/d)

Operating pressure is 1,350 kPa; pump efficiency is 75 percent.
11.3 Calculating Costs

The cost relations presented here for direct and indirect construction costs and O&M costs

have been adapted from a paper by William B. Suratt of Camp Dresser and Mckee (Suratt,

1995). They apply particularly to RO and NF systems; with modifications, they could also

apply to UF and MF as will be discussed below.

Cost item

Table 11 .l .-Direct construction costs

Equation Comments

Membrane modules

Skids with plumbing

Building

Electrical hookups

Instrumentation and

controls

Booster pumps

Product water degasifiers

Odor control

Process piping

Yard piping

Chemical feed systems

Cartridge filters

Membrane cleaning

equipment

$67,000

Concentrate treatment $1 5*(m3 concentrate/day)

Generator $150,00O’MWO.” + $50,000+

Site work

Contract engineering and

training

$‘number of modules

$* number of vessels

(21 m* l number of skids + 50 m2

admin. space)‘$l,000/m2

$61 4’m3/day o.65

$100,000+$80,000*

number of skids

$*(hp/lOO) ‘.”

1.5006 * m?day +3766

320.9’(m3/day)0-6

1 5.852’(m3/day)

1 OO*(m3/day)0-75

Storage (L) +$“skids’

chemical injection points/skid

1 35,000’skids’(m3/sec)o~

$15 * (m3/day)

$50,000

Use $700 for 20.2 cm (8”) diameter, $500

for 10.1 cm (4”) diameter and $250 for

6.4 cm (2.5”) diameter vessels

Assume 6 or 7 elements per vessel, use

$5,000 for 20.2 cm diameter,

$2,000 for 10.1 cm diameter and

$900 for 6.4 cm diameter vessels

Based on number of skids

Based on capacity

Based on number of skids

Use $85,000 for vertical turbine 316L

stainless steel with variable speed motor,

$58,000 for vertical turbine 316L

stainless steel with single speed drive

and $35,000 for a single speed ANSI

stainless steel horizontal pump

Based on capacity

Basedoncapacity

Based on feed flow (capacity/recovery)

Based on feed flow (capacity/recovery)

Based on chemical dosage rates and

$1/L of storage + $30,000 for acid or

caustic metering systems and $20,000

for antiscalant and chlorine metering

systems.

Based on the capacity per skid and total

number of skids. includes filters, filter

housing, and plumbing.

Two 4,000 m3 tanks, recirculation pump,

cartridge filter, mixer, piping, and

electrical.

Conservative estimate for in-line aeration

and surface water discharge.

Based on building and pumping power

costs. Assume 4 W per m3/day feed

capacity plus 746 W per hp for each

pump.

Based on total plant capacity (membrane

product + blend)

11.7
Table 1 1 .2.-Indirect construction costs

Cost item Equation

-~

Comments

Mobilization, insurance

and bonds

Contingencies

0.05 * total direct cost

0.40 * total direct cost

Table 11,3.-Ooeration and maintenance costs

Cost item Equation Comments

Electricity $/kWhr l kW l hr/yr

Labor

Chemicals

Cleaning supplies

$/yr ’ Employees

VL l Uyr

1.3 l vol of system(m3) *

cleanings/yr * $50

Membrane replacement

Cartridge filters

Repairs and replacements

# modules l $/module

life expectancy

(23,100 l m3/sec-6.25) l skids

* 12 times/yr

0.005 l DCC

Insurance 0.002 * DCC

Lab fees 800 * skids ’ 12

Capital recovery cost Use payment function in your

favorite spreadsheet program

Normal estimates are $.04 -

$.08 per kWhr

$40,000 per year average

Assuming an acid and a caustic

cleaning for each cleaning

session at a cost of $50/m3

cleaning solution

Assume 3-year life expectancy

Based on skid feed capacity

Based on direct construction

cost

Based on direct construction

cost

$800 per skid for each set of

analyses, 12 analyses per year

Based on given interest rate

and amortization time

Figures 11.2 and 11.3 show how construction and O&M costs change with capacity and with

total dissolved solids. Assumptions involved are listed in table 11.4. These costs are very

sensitive the number of vessels per skid. There are many cost items that depend on the

number of skids: pumps, instrumentation, chemical feed systems, and building size. O&M

costs are not as sensitive to skid size. For example, energy costs would be similar if used on

one large pump or two smaller ones. Figure 11.4 illustrates the effect on cost of unit size or

the number of vessels per skid.

11.8
3 5

3 0

2 5

2 0

1 5

1 0

5

6

0 10,000 20,ooo woo0 WJoo =sQo @2~

Capacity, m’lday

Figure 11.2.-Membrane system costs with increasing capacity. Assumed TDS is 1,800 mg/L,

blending allowed, target concentration is 500 mg/L.

5 1 0 1 5 2 0

Total Dirolved Solids (g/L)

2 5 30 3 5

Figure 11.8-Membrane system costs with increasing TDS. Capacity is 40,000 m3/day, blending is used

to the extent possible, target concentration is 500 mg/L.

11.9
Table 11.4.-Assumptions used in comparing membrane treatment costs

Cost item Assumed value

Total dissolved solids for capacity comparison 1,800 mg/L

Capacity for total dissolved solids comparison 40,000 m3/day

Target dissolved solids 500 mg/L

Average molecular mass 38.8 g/mole

Chemical addition and pretreatment 3.3 mg/L antiscalant, cartridge filtration,

Post treatment Aeration, 3 mg/L hypochlorite

Recovery rate 85%

Blending? Yes, if possible to achieve target quality

Membrane average rejection 99.1%

Membrane productivity 20 m3/day for 20.3 cm diameter module

Membrane life expectancy 3 years

System life expectancy 40 years

Interest rate 7 %

0 1 2 3 4 5 6 7

Number of RO Skids

I, TCC. 6 modtves

0O&M,6mc&es

0 O&M 7 ves/mod

Figure 11.4.-Effect of skid size on construction and O&M costs for a system to produce 1,200 m3/day

(3.17 MgaVd). Assumptions are the same as those listed in table 11.4.

11.10
11.4 Ultrafiltration Costs

The model presented above could be used to estimate UF costs, with a few modifications.

Unfortunately, because of the wide variety of matter retained by UF membrane, pilot studies

are necessary to estimate UF performance.

. Use retention rate instead of rejection rate. Manufacturers list nominal MWCOs

which are the size of particles retained at the 90 percent level. Pilot studies are

necessary to determine the actual retention rate of the substances of interest at a

particular site.

. UF systems are often operated in a recycle mode. To estimate the number of

modules needed, the on site productivity, at the optimum recycle rate, needs to be

determined through pilot testing.

. UF systems are operated at much lower pressures than RO and NF. Therefore, the

pumping costs would be driven by the piping configuration more than the system

operating pressure.

. Pretreatment is not necessary with UF systems. Chemical feed systems would be

unnecessary.

. Cartridge filters are not necessary. An in-line screen filter would be sufficient.

11.5 Microfiltration Costs

Cost estimating for MF systems is as particular as UF systems. Cost is still dependent on the

membrane area required. While MY membrane has high permeability, it can be fouled

quickly. The pilot study must focus on backwash duration and frequency. If the water

requires further processing, a portion of the backwash stream may be recycled to the feed.

However, if the water is to be for potable uses, it is best to discard the backwash to prevent

build up of pathogens in the system. Other differences between MF and the RO model:

. Rejection or retention is not considered in the MF cost model. A membrane must

be tested to ensure that it will perform adequately; the flow rate, backwash duration,

and frequency are determined so as to best keep the membranes working.

. There is no blending with MF. All water must be filtered.

. Operating pressure is minimal. Pump requirements are determined by the skid

capacity.

. No pretreatment is necessary, though coagulants can be added to enhance filtration.

11.11
l Cartridge filters are unnecessary.

l Waste stream is minimal; may be a sludge with some types of MF or some kinds of

feedwater.

11.6 Conclusions

It is possible to estimate RO and NF membrane system costs from the feed water quality and

the capacity. The model presented here includes default values for all other parameters. The

model is very sensitive to unit size, as well as several other parameters used in the example.

Accurate information on all the variables, but especially rejection, productivity and energy

cost, will produce more accurate results. UF and MF costs can be estimated from the same

model but require pilot testing to determine the cost parameters of membrane area and

pumping requirements.

11.12
Chapter 12

PERSPECTIVES ON FUTURE OPPORTUNITIES

The water treatment industry has found increasing value in membrane processes during the

last ten years. A snapshot from today’s technology landscape presents some perspectives on

infrastructure and technology developments that will possibly contribute to future growth.

However, in a field as dynamic as membrane separation processes, it is likely that both users

and technology developers will create innovation far beyond our current forecast horizon.

1. Expanded education of users to better understand the differences between the

membrane separation processes.

The trend in water treatment applications is for combinations of membranes to be used in one

system. For instance, MF or UF may be used as pretreatment for RO or NF membrane

systems. As a result, it is very important that users understand the differences between these

types of separations. It is very easy for operators to assume that what is good for RO is

also good for UF systems. After all, the equipment looks the same! In actuality, the two

processes involve very different separation mechanisms and require different O&M

procedures.

2 . Standard methods of membrane characterization and testing must be developed

to enable comparison of different membrane formulations and configurations.

Membranes are complex; researchers of the desalting community are still trying to figure out

exactly how they interact with feed water. However, a general understanding is not going to

happen if manufacturers continue to describe membrane characteristics in their own separate

ways. Users should not have to go through complex analyses to come up with equivalent

operating conditions in order to compare membranes from different manufacturers. There

needs to be some standardization within the industry. Sea water membranes, at least, are all

tested on 35,000 mg/L simulated sea water, but they are tested at different pressures,

production rates, and recovery rates. With brackish water membranes, the situation is even

worse. Some are tested with 2,000 mgL NaCI, while others are tested on “San Diego tap

water.” The feed solution should be adequate to test the general performance of the

membrane as it is intended to be used. For instance, brackish water membranes could be

tested with an industry standardized 5,000 mg/L NaCl solution, NF membranes could be

tested with a combination of mono- and multi-valent ions, UF membranes could be tested

with some predetermined macromolecule mixture (polyethylene glycol, for instance), and

MF membranes could be tested with a specific type and loading of suspended solids.

At a minimum, procedures should specify testing pressures and feed crossflow velocity

sufficient to produce a standard product flux, which should be consistent within a type of

filtration. It also would be very useful to measure what the membrane’s performance would

be under different conditions. Detailed standard testing methods would facilitate preliminary

12.1
application modeling and help end users narrow their field of potential candidate membranes

much more quickly. A variety of groups are currently working on this issue, and we can be

optimistic for progress in the future.

3 . Methods should be established to describe water composition, product water

quality goals, and desired production capacity such that a few good membranes

can be identified for the job from improved manufacturers specifications.

Current practice in membrane selection is generally driven by the manufacturer’s reputation

and the cost. Since we know little about the membranes (see 2 above), we need to depend

on the supplier for expert advice, support, and fair pricing. Hopefully, the supplier has

experience from many pilot tests and knows which membrane will work best, or at least

knows what pretreatment will be needed to make the system work with specific membranes.

However, if the membrane/feed water interactions were understood well enough to select

membranes compatible with the feed water, the pretreatment would not have to be quite as

extensive. Though groundwater and surface waters are complex, it is possible that they fall

into a finite set of categories. If these categories were described adequately and the

membrane/water interactions were described in similar terms, it might be possible to tailor

membranes specifically for major water types. Research addressing these goals is currently

being undertaken in a number of academic, government, and industrial laboratories.

4 . There should be a way to predict membrane performance under any water

condition if the membranes and the source water are well described.

Accomplishing this final task would decrease the initial development costs for

implementation of membrane processes.

5 . Correlations need to be developed among process monitoring data, membrane

integrity, and the likelihood of biological contamination of the product water.

One of the benefits of using membrane-based water treatment processes is that they provide a

physical barrier to biological contamination. However, it is often very difficult to determine

when that banier has been compromised. The product water is so clean, particularly with

UF, NF, and RO, that particle counts, turbidity, and other monitoring parameters give little

indication of impending problems. Integrity testing studies currently are underway, and the

ASTM has established a committee to develop consensus standard methods for RO and NF

membrane integrity tests. Hopefully, the problem will be resolved within the next 10 years.

6 . Cost models need to be developed relating production capacity, water quality,

membrane area, and power requirements for MF and UF to assist planners in

estimating preliminary costs without pilot study data.

Cost models for RO and NF are well developed, but cost models have not been developed for

MF and UF. Recirculation rates, backwash duration and frequency, and recovery rates will

need to be included as variables that affect the membrane area and power requirements.

12.2
12.1 Microfiltration

The potential for MF for removing suspended solids and biological contamination in

municipal water treatment systems is great. There are many promising studies ongoing at

this time. Recently published technical papers (as cited in chapter 2) show a possible

economic advantage of MF over strictly conventional treatment and pretreatment systems

for the following reasons:

. MF equipment takes up less space than conventional filtration or coagulation/

clarification equipment.

l Product water quality is independent of feed water quality.

l In some cases, chemical conditioning can be eliminated from the treatment train

altogether.

l When MF alone is insufficient, it can be incorporated into conventional coagulation

or biological processes to eliminate the large clarification basins or media filtration

beds that are normally used.

12.2 Ultrafiltration

Tight UF can remove viruses, pesticides, and large organic molecules that cause color and

odor problems and form DBPs (disinfection by-products). Since the use of UF and MF for

water is still fairly new, there are only rough guidelines as to when MF should be used and

when UF would be more effective. Current research results indicate that the membrane

material and water chemistry interact in a complicated way that does not lend itself to simple

rules of thumb. As case study documentation grows, it may be possible to establish more

concrete rationale for choice.

Unlike MF, there have not been sufficient studies to say for sure that UF is a more

economical treatment than the conventional processes of oxidation and media filtration.

With UF, the choice is driven by increased awareness of water quality and the inability to

achieve treatment goals with conventional processes. The many brands of UF membranes are

more diverse than MF membranes, and characterization is even more difficult and critical to

successful piloting. The case studies covered in chapter 3 demonstrated that the appropriate

choice of membrane can determine the success of a study. In the future, manufacturers and

suppliers may be able to provide enough information on the membranes for an intelligent

choice to be made.

Fundamental understanding tells us that if UF membranes could be made more porous and

with a more uniform pore size distribution, the task of classifying their solute removal

12.3
characteristics, and therefore correctly choosing which membrane to use, would be easier.

Advances in membrane materials development along these lines will likely increase the

opportunities for UF in municipal water production.

12.3 NF and RO

NF and RO can be designed to accommodate a variety of treatment objectives when

excessive dissolved salts are present. Either membrane type may be more appropriate,

depending on the water composition and the concentrate disposal options available.

Consequently, the concentrate disposal options should be examined at the beginning of the

planning process before selection of the treatment method.

More cost effective and beneficial uses for NF and RO concentrate would increase the

potential applications and have a large economic impact on membrane water treatment costs.

There are currently four good long-term alternatives for concentrate use or disposal, as

follows:

1) Mix it with a low TDS water or wastewater and disperse it into the ocean or other

body of water with a similar TDS.

2) Inject it into a confined aquifer that already has a high salt concentration.

3) Evaporate it completely in evaporation ponds or brine concentrators to recover and

sell the dried salt as a product, or dispose of it in a lined landfill.

4) Evaporate it partially and use it in a solar pond, providing an interim concentrate

storage which produces process heat for additional desalting and brine

concentration. Dispose of the dried salt in a landfill.

Improved robustness of membranes, modules, and systems would decrease maintenance costs

for municipal water treatment systems. Improvements that are generally recognized and

subject to current research and development are:

l Enhanced turbulence and transport of fouling matter out of the system so that

excursions in the pretreatment system can be more easily tolerated.

.

Increased chlorine resistance of thin-film composite membranes so that excursions

in the dechlorination system can be tolerated.

. Inclusion of an on-line normalized performance trending display with instrumentation so that operators can tell at a glance whether performance is changing and take

corrective action before irreversible problems occur.

Research is also needed into the source of counter-productive membrane/feed water

interactions. Flux decline (especially the irreversible, or hard-to-clean kind) due to

12.4
solute-membrane adsorption can be reduced when we have a broader range of membrane

surface material choices and a more complete database for quantifying solute-material

interactions.

12.4 The Next Generation

What will the next generation of membranes be like? Hopefully, they will represent such a

paradigm shift that any predictions are woefully inadequate. Current research and development described in the public literature focuses on the following attributes:

. Highly controlled surface energy, pore size distribution, and solute transport

coefficients

l High permeation rates

. Low fouling potential under intended operation conditions

l High resistance to any thermal or chemical degradation

The module advances include:

. Complete mixing within the feed flow channel

. Leak-proof seals

. Built-in sensors to monitor individual module performance

Advanced materials processing techniques could include tuning membranes for a particular

water source through post-production membrane surface treatments. But implementation of

this still requires the advances in describing and matching water composition and membrane

characteristics mentioned earlier. Developments in facilitated transport are finally producing

commercial applications. If this trend continues, and economical facilitated transport

membranes become widely available, economical removal of specific undesirable

components in individual processing steps can be realized.

Finally (and certainly more under our control), the third version of this manual may be

published on the Internet, with color pictures and some real-time data.

12.5
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and Biochemisby. John Wiley and Sons. 1979.

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99- 104, 1994.

Jurenka, R., and M. Chapman Wilbert. Maricopa Water Treatment Study. Water Treatment

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Kaakinen, J. W., and C.D. Moody. “Characteristics of Reverse-Osmosis Membrane Fouling

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Kachalsky, L. A., NWRI/OCWD Symposium on Microfiltration for Water Treatment, 77-84,

1994.

Kesting, R.E. Synthetic PoZymer Membranes, McGraw-Hill Book Company, New York.

1971.

Kruithof, J-C., P. Hiemstra, P.C. Kamp, J.P. van der Hoek, J.S. Taylor, and J-C. Shippers.

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Proceedings ofA WWA Membrane Technology Conference, Feb. 23-26, New Orleans,

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Lozier, J., G. Jones, and W. Bellamy, JAWWA, 89, No. 10,50-64, 1997.

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13.3
Malaxos, P.J. and O.J. Morin. “Surface Water Discharge of Reverse Osmosis

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13.4
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13.7
REFERENCES FOR FURTHER INFORMATION

“Eastern Municipal Water District RO Treatment/Saline Vegetated Wetlands Pilot Study,”

Boegli, W.J.; Thullen, J.S. U.S. Bureau of Reclamation, Water Treatment Engineering and

Research Group, Denver CO. Water Treatment Technology Program Report No. 16.

September 1996.

“Effect of Brine Blowdown Discharge from a DesaYPower Plant on Marine Life,” Chandy,

J.P.; Al-Tisan, I.; Manshi, H.A.; Abd El Reheim, H. Saline Water Conversion Corporation

Research and Development Center, Al-Jubail, Saudi Arabia. Research Activities and Studies,

Vol. 2 - 1411H, 1991.

“Proceedings of the IDA and WRPC World Conference on Desalination and Water

Treatment: Session A-6, Environmental and Health Issues.” Desalination, Vol. 97, No. l-3.

August 1994.

“Regulations Governing Membrane Concentrate Disposal,” Pontius, F. W.; Kawczynski, E.;

Koorse, S.J. Journal ofAmerican Water Works Association, Vol. 88, No. 5. May 1996.

14.1
APPENDIX A

Manufacturer Applications

Source: DuPont and Fluid Systems, U.S.A.

Location

Arizona

California

California

California

California

Canada

Canary Islands

Canary Islands

China

India

Iraq

Iraq

Iraq

Mexico

Mexico

Morocco

New Mexico

Pennsylvania

Pensylvania

Singapore

Spain

Spain

Spain

Spain

Spain

Spain

Spain

Texas

Texas

Texas

Tunis

Tunis

Utah

Texas

TOTAL

Capacity

(1,000 Capacity

GPD) M’ID

680 2,574

3,600 13,626

100 379

274 1,037

1 8 68

400 1,514

26 98

26 98

900 3,407

1,000 3,785

17,000 64,345

1,300 4,921

1,200 4,542

100 379

158 598

400 1,514

432 1,635

360 1,363

30 114

400 1,514

4 15

48 182

48 182

8 30

1 3 49

26 98

5 1 9

500 1,893

110 416

20 76

254 961

254 961

410 1,552

144 545

30548 114,489

Application

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boilerfeed

boiler&d

boilerfeed

boilerfeed

boilerfeed

BOILERFEED

startup

8 7

8 7

8 6

86

7 8

81

81

79

90

86

8 3

81

8 3

8 2

7 8

76

78

86

85

8 5

84

84

84

80

86

87

87

8 7

Mexico

Pennsylvania

California

West Virginia

China

China

China

Maryland

6 1 231 commercial - sofl drink

60 227 commercial - soft drink

272 1,030 commercial - textile waste reuse

30 114 commercial - ultra pure

60 227 commercial-acid mine drainage

6 3 238 commercial-beverage

127 481 commercial-beverage

127 481 commercial-beverage

24 9 1 commercial-beverage

190 719 commercial-beverage

8 7

86

81

86

87

15.1
Capacity

Location

Japan

Florida

Georgia

Michigan

South Carolina

Massachusettes

California

France

Ohio

(1,000 Capacity

GPD) Mm Application startup

I6 6 1 commercial-food 8 2

36 136 commercial-medical 8 5

IO 38 commercial-medical 8 5

120 454 commercial-medical makeup

66 250 commercial-pharmaceutical 8 5

7 2 273 commercial-precious metal plating rinse

15 5 7 commercial-process rinse water

300 1,136 commercial-ultrapure 8 5

200 757 commercial-ultrapure 8 5

Spain 7 26 commercial-ultrapure 8 6

Spain 4 15 commercial-ultrapure 8 0

Switzerland 320 1,211 commercial-ultrapure 77187

Total 2,180 8,251 COMMERCIAL

Arizona 320 I,21 1 electronic rinse

California 50 189 electronic rinse

California 30 114 electronic rinse

California 30 114 electronic rinse

Florida 260 984 electronic rinse

California 300 1,136 electronic rinse

San Salvador 50 189 electronic rinse water

Texas 320 1,211 electronic rinse water

Arizona 251 950 electronics

Arizona 1,420 5,375 electronics

Arizona 180 681 electronics

Arizona 6 1 231 electronics

Austria 50 189 electronics 8 7

Bulgaria 116 439 electronics 86

California 100 379 electronics

California 30 114 electronics

California 50 189 electronics

California 201 761 electronics

California 201 761 electronics

California 200 757 electronics

California 42 159 electronics

California 251 950 electronics

California 100 379 electronics

California 634 2,400 electronics

California 124 469 electronics

California 750 2,839 electronics

California 1 5 51 electronics

California 2,016 7,63 1 electronics

California 151 572 electronics

California 150 568 electronics

California 6 1 231 electronics

California 100 379 electronics

California 450 1,703 electronics

China 123 466 electronics

Colorado 600 2,271 electronics

Erie 37 140 electronics

France 300 1,136 electronics

G.D.R. I.000 3,785 electronics

15.2

86

8 5

8 4

86

79

77

82
Capacity

Location

(1,000 Capacity

GPD) Ml/D Application startup

Germany 19 72 electronics

Idaho 750 2,839 electronics

Idaho 71 269 electronics

Italy 7 7 291 electronics

Maine 8 7 329 electronics

Massachusettes 201 761 electronics

Mexico 4 5 170 electronics

New York 145 549 electronics

New York 79 299 electronics

New York 500 1,893 electronics

Oklahoma 600 2,27 1 electronics

Oregon 201 761 electronics

8 6

85

Pennsylvania

Poland

Spain

Texas

34

395

20

1,000

129

1,495

76

3,785

electronics

electronics

electronics

electronics

7 3

80

Texas 576 2,180 electronics

Texas 600 2,271 electronics

Texas 58 220 electronics

Texas 1,100 4,164 electronics

Texas 341 1,291 electronics

Texas 115 435 electronics

Texas 1,200 4,542 electronics

Utah 885 3,350 electronics

Vermont 481 1,821 electronics

Virginia 600 2,271 electronics 8 0

Maine 120 454 electronics - ultrapure

TOTAL 21,424 81,090 ELECTRONICS

Argentiana

Bahrain

California

California

Chile

Chilie

F.D.R.

Jordan

Mexico

Mexico

Mexico

Ohio

Peru

Peru

Saudi Arabia

Saudi Arabia

Saudi Arabia

U.S.S.R.

Venezuela

w. Germany

Conneticut

Wisconsin

100 379 industrial

600 2,27 1 industrial

4 15 industrial

100 379 industrial

160 606 industrial

50 189 industrial

4,640 17,562 industrial

800 3,028 industrial

80 303 industrial

60 227 industrial

140 530 industrial

120 454 industrial

50 189 industrial

50 189 industrial

1,044 3,952 industrial

84 318 industrial

1,500 5,678 industrial

3,300 12,491 industrial

500 1,893 industrial

70 265 industrial

820 3,104 industrial-metal finishing waste

60 227 industrial-process

200 757 industrial-process

8 3

79

84

8 3

8 6

7 7

7 7

8 2

8 3

82

8 2

8 7

82

7 8

8 6

8 4

8 2

8 0

85

86

82

15.3
location

Mexico

Netherlands

New York

W. Germany

Algeria

Saudi Arabia

TOTAL

Capacity

(1,000 Capacity

GPD) MVD

300 1,136

300 1,136

1,030 3,899

6 3 238

1,200 4,542

3,500 13.248

20,925 79,201

Application

industrial-process

industrial-process

industrial-process

industrial-process

industrial-ultrapure

industrial/potable

INDUSTRIAL

startup

17

7 5

86

8 6

7 9

8 5

Kuwait 4 15 irrigation

Saudi Arabia 134 507 irrigation 8 4

California 5 0 189 irrigation of seedlings

Arizona 73,100 276,684 irrigation/waste treatment

TOTAL 73,288 277,395 IRRIGATION

California 1,300 4,92 1 potable-brackish

California 900 3,407 potable-brackish

California 500 1,893 potable-brackish

California 500 1,893 potable-brackish

California 250 946 potable-brackish

Canada 700 2,650 potable-brackish

Florida 4,000 15,140 potable-brackish

Florida 1,800 6,813 potable-brackish

Florida 1,500 5,678 potable-brackish

Florida 1,500 5,678 potable-brackish

Florida 864 3,270 potable-brackish

Florida 576 2,180 potable-brackish

Hawaii 500 1,893 potable-brackish

Ireland 1,000 3,785 potable-brackish

Massuchettes 1,152 4,360 potable-brackish

Minnesota 288 1,090 potable-brackish

New York 422 1,597 potable-brackish

New York 360 1,363 potable-brackish

North Carolina 3,000 11,355 potable-brackish

Ohio 432 1,635 potable-brackish

Spain 300 1,136 potable-brackish

Spain 240 908 potable-brackish

Tailand 300 1,136 potable-brackish

Texas 800 3,028 potable-brackish

Texas 670 2,536 potable-brackish

Texas 576 2,180 potable-brackish

Utah 800 3,028 potable-brackish

Utah 260 984 potable-brackish

TOTAL 25,490 96,480 POTABLE-BR4CIUSH

9 3

8 8

90

8 9

90

88

89

9 3

9 3

89

90

9 1

93

8 9

87188

88

8 8

8 9

89

8 9

90

8 9

93

8 8

87

8 8

88

California 1,300 4,921 potable-ground water

California 500 1,893 potable-ground water

Florida 12,000 45,420 potable-ground water

Florida 5,000 18,925 potable-ground water

Florida 3,000 llJ55 potable-ground water

Florida 2,000 7,570 potable-ground water

Florida 2,000 7,570 potable-ground water

Florida 1,800 6,813 potable-ground water

15.4
Caoacitv

location

( i,ooo* Capacity

GPD) M’/D Application startup

Florida

Florida

North Carolina

South Carolina

TOTAL

1,500 5,678 potable-ground water

1,500 5,678 potable-ground water

3,000 11,355 potable-ground water

600 2,27 1 potable-ground water

34,200 129,447 POTABLE-GROUNDWATER

Algeria 900 3,407

Bahamas 7 26

Bahrain 12,000 45,420

Bahrain 12,000 45,420

Balearic Island 132 500

Canary Islands 925 3,501

Canary Islands 264 999

Canary Islands 662 2,506

Canary Islands 80 303

Canary Islands 32 121

Canary Islands 1,325 5,015

Canary Islands 132 500

Canary Islands 160 606

Canary Islands 132 500

Cape Verde Island 150 568

Caribbean 150 568

Caribbean 400 1,514

Caribbean 130 492

Caribbean 50 189

Caribbean 400 1,514

Caribbean 100 379

Caribbean 100 379

Equador 1 0 38

Florida 300 1,136

Florida 4,500 17,033

Florida 300 1,136

Florida 2,000 7,570

Florida 600 2,271

Florida 1,000 3,785

Florida 100 379

Florida 110 416

Florida 6 23

Florida 1,000 3,785

Florida 1 0 38

Florida 930 3,520

Florida 1 0 38

Florida 72 273

Greek Island 80 303

Greek Island 320 1,211

Greek Island 320 1,211

Greek Island 132 500

Greek Island 132 500

Iran 1,400 5,299

ldY 135 511

IdY 340 1,287

Japan 79 299

15.5

potable

potable

potable

ootable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

potable

8 3

90

84

8 5

89

89

8 7

8 7

8 7

86

84

8 4

8 3

8 3

85186

90

89

87

86

86

8 5

86

8 2

80

79

74

74

potable

ootable

potable

potable

potable

potable

potable

potable

stable

potable

90

89

89

8 3

8 1

76

85186

8 5

8 1
Location

Capacity

(1,000 Capacity

GPD) M’ID Application startup

8 3

84

86

81

80

9019 I

88

86

8 3

8 3

82

Jordan 150 568 potable

Kuwait 264 999 potable

Libya 130 492 potable

Libya 50 189 potable

Madieira Island 132 500 potable

Malta 5,600 21,196 potable

Malta 1,100 4,164 potable

Malta 3,700 14,005 potable

Malta 1,585 5,999 potable

Malta 5,300 20,06 1 potable

Mexico 500 1,893 potable

Mexico 5 0 189 potable

Mexico 50 189 potable

Oman 125 473 potable

Puerto Rico 150 568 potable

Saudi Arabia 1,600 6,056 potable

Saudi Arabia 3,600 13,626 potable

Saudi Arabia 7,900 29,902 potable

Saudi Arabia 150 568 potable

Saudi Arabia 4,500 17,033 potable

Saudi Arabia 6,900 26,117 potable

Saudi Arabia 100 379 potable

Saudi Arabia 260 984 potable

Saudi Arabia 60 227 potable

Saudi Arabia 100 379 potable

Saudi Arabia 130 492 potable

Saudi Arabia 150 568 potable

Saudi Arabia 150 568 potable

Saudi Arabia 189 715 potable

Saudi Arabia 2,600 9,841 potable

Saudi Arabia 5,000 18,925 potable

Saudi Arabia 150 568 potable

Saudi Arabia 600 2,271 potable

Saudi Arabia 600 2,271 potable

Saudi Arabia 1,000 3,185 potable

Saudi Arabia 1,cOo 3,785 potable

Saudi Arabia 1300 4,921 potable

Saudi Arabia 2,100 7,949 potable

Saudi Arabia 1,300 4,921 potable

Saudi Arabia 5,300 20,061 potable

Saudi Arabia 7,900 29,902 potable

Saudi Arabia 10,200 38,607 potable

Saudi Arabia 16,000 60,560 potable

Saudi Arabia 7 5 284 potable

Saudi Arabia 400 1,514 potable

Spain 132 500 potable

St. Thomas 39 148 potable

U.A.E. 300 1,136 potable

U.A.E. 300 1,136 potable

U.A.E. 300 1,136 potable

U.A.E. 1,200 4,542 potable

U.A.E. w@ 4,542 potable

15.6

81

82

87

8 7

86

86

86

86

8 5

85

8 5

84

84

84

84

84

84

84

8 3

8 3

83

82

8 1

8 1

8 1

80

79

79

79

78

76

76

82

84

90

9 0

90

90

90
Capacity

Location

( i,ooo- Capacity

GPD) Ml/D Application startup

U.A.E.

U.A.E.

U.A.E.

U.A.E.

U.A.E.

U.A.E.

U.A.E.

Argentina

Australia

Bahamas

Bahamas

California

California

California

Canary Islands

km

Indonesia

Korea

Kuwait

Lybia

Mexico

Mexico

Ras AI Khaima

Saudi Arabia

Saudi Arabia

Saudi Arabia

Saudi Arabia

Saudi Arabia

Spain

Spain

Tahiti

Turkey

U.S. Virgin Islands

1,200 4,542 potable

1,200 4,542 potable

2,400 9,084 potable

2,400 9,084 potable

1,200 4,542 potable

1,200 4,542 potable

2,400 9,084 potable

5 3 200 potable-sea water

106 400 potable-sea water

30 114 potable-sea water

100 380 potable-sea water

1 6 60 potable-sea water

2 1 8 0 potable-sea water

581 2,200 potable-sea water

251 950 potable-sea water

1,000 3,785 potable-sea water

793 3,000 potable-sea water

151 570 potable-sea water

264 1,000 potable-sea water

2,642 10,000 potable-sea water

300 1,135 potable-sea water

48 180 potable-sea water

132 500 potable-sea water

7 5 284 potable-sea water

1,321 5,000 potable-sea water

3,170 12,000 potable-sea water

317 1,200 potable-sea water

100 380 potable-sea water

1,321 5,000 potable-sea water

201 760 potable-sea water

1 6 60 potable-sea water

6 6 250 potable-sea water

80 303 potable-sea water

90

90

90

89

8 8

8 8

86

Venezuela 151 570 potable-sea water

TOTAL 173,093 655,158 POTABLE-SEA WATER

Shipboard 6 5 246 potable/ship

Shipboard 7 5 284 potable/ship

Shipboard 63 238 potable/ship

TOTAL 203 768 POTABLE/SHIP

86

8 6

8 5

U.S.A 3,000 11,355 potable

U.S.A 125 473 potable

Utah 30 114 potable

Algeria 12,200 46,177 potable-process

Algeria 300 1,136 potable-process

Canary Islands 50 189 potable-process

Saudi Arabia 2,400 9,084 potable-process

Argentina 20 76 potable/arsenic removal

Chilie 132 500 potable/arsenic removal

Saudi Arabia 1,200 4,542 potable/industrial

Venezuela 1,000 3,785 potable/power

80

8 5

79

8 3

79

76

83

15.7
Location

Algeria/Mobile Unit

Venezuela

Bahamas

U.S.A

TOTAL

Capacity

(1,000 Capacity

GPD) My/D

77 291

100 379

240 908

160 606

21,034 79,613

Application

potable/process

potable/process

potable/resort

potable/resort

POTABLE/VARIOUS

startup

8 6

81

86

818

TOTAL POTABLE 2,010 7,606 POTABLE - ALL TYPES 85

California 412 1,559 power 8 4

Canada 310 1,173 power 8 4

Texas 970 3,671 power 8 5

Venezuela 1,000 3,785 power 8 0

Colorado 432 1,635 power - cooling tower blowdown

New Mexico 2,300 8,706 power plant waste water

California 6 23 power-gas turbine injection

California 30 114 power-gas turbine injection

California 25 95 power-gas turbine injection

TOTAL 5,485 20.761 POWER 333

California 50 189 waste sewage - rclamation

California I68 636 waste sewage - reclamation

California 225 852 waste sewage - reclamation

California 5,000 18,925 waste tertiary effluent -process

California 30 II4 waste water treatment

California 750 2,839 waste water treatment

Colorado 125 473 waste water treatment

Saudi Arabia 2,600 9,841 waste water treatment

TOTAL 8,948 33,868 WASTE WATER

not included in TOTALS:

U.S. Amlv 50,198 190,000 potable-sea water

15.8
c

REPORT DOCUMENTATION PAGE I

Form Approved

OMB No. 0704-0788

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1. AGENCY USE ONLY (Leave Blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

July 1998 Final

4. TlTLE AND SUBTR-LE 5. FUNDING NUMBERS

The Desalting and Water Treatment Membrane Manual: A Guide to Membranes for

Municipal Water Treatment (2nd Edition)

Water Treatment Technology Program Report No. 29

6. AUTHOR(S)

Michelle Chapman Wilbert, Frank Leitz, Ellen Abart, Bill Boegli, Kim Linton

7. PERFORMING ORGANlZATlON NAME(S) AND ADDRESS 8. PERFORMING ORGANIZATION

REPORT NUMBER

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Water Treatment Engineering and Research R-98-05

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11. SUPPLEMENTARY NOTES

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13. ABSTRACT (Maximum 200 words)

The second edition of the membrane manual provides an overview of microfiltration, ultrafiltration, nonfiltration reverse osmosis,

and electrodialysis processes as they are used for water treatment. Performance evaluation, cost models, cleaning, and

concentrate issues are presented as well as an extensive listing of membrane products currently available. Membrane listing

includes physical characteristics, performance data, operational limits, and comparative statistics for each.

14. SUBJECT TERMS 15. NUMBER OF PAGES

membrane cost model, microfiltration, ultrafiltration, nonfiltration reverse osmosis, electrodialysis, 203

brackish water treatment, nanofiltration, membrane optimization, membrane selection criteria, viral and

bacterial contamination, module integrity, membrane technology, membrane dasses, membrane

configuration, membrane characterization, diffusion, sieving, pore flow model, molecular mass cutoff, 16. PRICE CODE

process instrumentation and evaluation, integrity testing, case studies, module configuration

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