“… an excellent guide to membrane technology …”

― La Doc STI, No 385, June 2000, p 28

Membrane Technology in Water and Wastewater Treatment

By P. Hillis

The Royal Society of Chemistry

Copyright © 2000 The Royal Society of Chemistry
All rights reserved.
ISBN: 978-0-85404-800-7

Contents

Case Studies,
Keynote Lecture: Membrane Case Studies, Past, Present and Future J.S. Taylor and S.J. Duranceau, 3,
Sea Water Reverse Osmosis – The Largest Plant in British Waters N. Marsh, J. Howard, F. Finlayson and S. Rybar, 25,
Drinking Water Sources in Kuwait M. Safar and Y. Al-Wazzan, 32,
Nanofiltration for Colour Removal – 7 Years Operational Experience in Scotland E. Irvine, A.B. F. Grose, D. Welch and A. Donn, 41,
Ultrafiltration for 90 MLD Cryptosporidium- and Giardia-free Drinking Water. A Case Study of the Yorkshire Water Keldgate Plant F.N.M. Knops and B. Franklin, 49,
Application of a New Generation Microfiltration Process for Large Scale Water and Wastewater Treatment W.T. Johnson and A. Patterson, 57,
Water Quality and Treatment,
The UK System of Approval of Products Used in Contact with Drinking Water T. Ogunbiyi, 67,
Immersed Membranes for Drinking Water Production P. Côté, C. Güngerich and U. Mende, 71,
Phosphate and Iron Removal from Seepage and Surface Water by Microfiltration J.A.M.H. Hofman, N.C. Wortel, E.T. Baars and J.P. van der Hoek, 78,
Reuse of Filter Backwash Water as a Source for Drinking Water Production: Piloting and Implementation of a Full-scale Ultrafiltration Plant A. Brügger, K. Vossenkaul, T. Melin, R. Rautenbach, B. Golling, U. Jacobs and P. Ohlenforst, 85,
Improved Performance of Drinking Water Microfiltration with Hybrid Particle Pre-treatment T. Carroll and N. Booker, 93,
River Trent On Tap – Comparison of Conventional and Membrane Treatment Processes B.E. Drage, J.E. Upton, P. Holden and J.Q. Marchant, 100,
The Use of Electrodialysis at Amsterdam Water Supply J.P. van der Hoek, J.A.M.H. Hofman, P.A.C. Bonné and D.O. Rijnbende, 108,
Applying Electrodialysis (EDR) Technology to Underground Water Treatment E. Sgarbi, 118,
Nanofiltration for Drinking Water Treatment from a Eutrophied Lake in Taiwan H.-H. Yeh. S.-H. Lin, S.-J. Kao and G.T. Wang, 128,
Fouling and Cleaning,
Keynote Lecture: Membranes and Microorganisms – Love at First Sight and the Consequences H.-C. Flemming, 128,
Optimising Membrane Performance – Practical Experiences L.Y. Dudley, F. del Vigo Pisano and M. Fazel, 150,
Fouling Characteristics of Membrane Filtration in Membrane Bioreactors M.H. Thomas, S.J. Judd and J. Murrer, 158,
Cleaning of Membranes in Water and Wastewater Applications R. Krack, 166,
Water Reuse,
Water Reuse for the Next Millennium – Membrane Treatment at the Millennium Dome J.H Khow, A.J. Smith, A. Rachwal, A. Donn and C.V. Meadowcroft, 175,
Wastewater Reclamation Case Studies, the Benefits of Outsourced Membrane Systems D. Threlfall, 184,
Comparison between Different Out-to-in Filtration MF/UF Membranes for the Re-use of Biologically Treated Wastewater Effluent E. Van Houtte, J. Verbauwhede, F. Vanlerberghe and J. Cabooter, 190,
Industrial Applications,
Sulphate Removal Membrane Technology: Application to the Janice Field G.H. Mellor, R.C.W. Weston, G.F. Bavister and A. White, 201,
SASOL’s Experience in the Desalination and Re-use of Acid Mine Drainage and Ash Water J.G. Nieuwenhuis, G.H. Du Plessis, M.P. Augustyn, B. Steytler, A.J. Viljoen and I.W. Van Der Merwe, 211,
Recovery of Wool Scouring Effluent Utilising Membrane Bioreator (MBR) Technology as Part of the Activated Sludge System followed by Two-stage Reverse Osmosis (RO) Membrane Concentration A.R. Bennett, 219,
Performance on a Real Industrial Effluent using a ZenoGem® MBR D. Mallon, F. Steen and K. Brindle, 226,
Membrane Technology in Wood, Pulp and Paper Industries J. Wagner, 233,
Case Studies of Wastewater Re-use for Petrochemical, Power and Paper Industry B. Durham, 241,
Posters,
Practical Experience with a Membrane Bioreactor for Wastewater Treatment-semi-cross-flow Ultrafiltration S. Geißler, K. Vossenkaul, Th. Melin, P. Ohle, E. Brands and M. Dohmann, 251,
Treating Highly Coloured Waters: Design Innovations and Implications A.B.F. Grose, D. Welch and E. Irvine, 253,
Treatment of Leachate by the MBR Process (Membrane Bioreactor) A.H. Robinson, 255,
Operation of a Zero Discharge Wood Pulp Effluent Treatment Plant G. Bateman, 257,
Integration of Maintenance and Operation into the Design of Reverse Osmosis Membrane Networks H.J. See, V.S. Vassiliadis and D.I. Wilson, 258,
Microfiltration and Reverse Osmosis of Knostrop Final Effluent M. Barton, 260,
Modelling Temperature and Concentration Polarisation in Ultrafiltration of Non-Newtonian Fluid under Non-isothermal Conditions S.P. Agashichev, 261,
Novel Methods of Hollow Fibre Membrane Integrity Monitoring S. Williams, A.J. Merry and C.V. Meadowcroft, 262,
Comparison of Chemical Pretreatment Methods for Nanofiltration of Cold, Soft and Humic Waters J. Yli-Kuivila, R. Liikanen and R. Laukkanen, 264,
In-situ Ultrasonic Measurement of Fouling and Cleaning Processes in Spiral-wound Membrane Modules G.-Y. Chai, A.R. Greenberg and W.B. Krantz, 266,
A Novel Way to Treat Textile Wastewater with Nanofiltration and Adsorption Th. Melin and L. Eilers, 268,

CHAPTER 1

MEMBRANE CASE STUDIES, PAST PRESENT AND FUTURE

J. S. Taylor, Ph.D., P.E.
Alex Alexander Professor of Engineering
Civil and Environmental Engineering Department
University of Central Florida
Orlando, FL 32816
USA

S. J. Duranceau, Ph.D., P.E.
Dir. of Water Quality and Treatment
Boyle Engineering Corporation
320 East South Street
Orlando, FL 32801
USA

1 INTRODUCTION

Membrane case studies have played an essential part in the development of membrane technology for drinking water treatment. Continuing advances in regulatory constraints and aesthetic criteria for consumer water quality have driven the water community to seek new technologies, which meet these criteria. Foremost among regulatory constraints are disinfection requirements, disinfection by-product and corrosion regulations. Consumers have become aware of regulatory violation through mandated public notification, and they have always been aware of the appearance, taste and odour of drinking water. Before the requirement of advanced technologies to meet higher water quality regulations, design, construction and successful operation of conventional water plants was well established and did not require pilot studies. However, such is not the case today. Pilot or case studies in all developed countries are establishing productivity, water quality and estimated cost for advanced treatment process construction and operation.

2 OVERVIEW OF MEMBRANE PROCESSES

Understanding membrane application requires understanding of the characteristics of drinking water membrane processes. Reverse osmosis (RO), nanofiltration (NF), electrodialysis reversal (EDR), ultrafiltration (UF) and microfiltration (MF) are the membrane processes, which have application to drinking water. Combinations of membrane processes with other processes have become known as integrated membrane systems. Although a conventional NF process consists of a pre-treatment and post treatment process before and after the NF, which could be described as integrated, this is described as conventional. The coupling of a MF and a NF or coagulation, sedimentation and filtration with a NF are accepted examples of IMS’s. The basic characteristics of these processes are shown in Table 1. Although many factors affect the solute separation by these process, a general understanding of drinking water application can be achieved by associating minimum size of solute rejection with membrane process and regulated contaminate.

3 REGULATIONS

The US water quality requirements determine membrane selection. Many of the regulatory constraints for drinking water can be related to control of inorganic, organic or pathogenic solutes in the finished product. The specific application of membrane processes to drinking water applications is shown in simplified format in Table 2. The word Yes indicates the membrane process can remove significant amounts of contaminate specified by the rule, and No indicates the membrane process can not remove the regulated contaminate.

Examples of community water quality objectives are total hardness, taste & odour, and colour. Some community water quality objectives may be classified as secondary standards or those standards, which do not affect consumer health. Community water quality objectives are shown in simplified form in Table 3. Once the treatment objectives are known, potential membrane systems can be determined for meeting these goals. Some general statements can be made regarding current treatment concerns:

1. Diffusion controlled membranes (RO & NF) are required for control of inorganic contaminates such as total dissolved solids (TDS), total hardness (TH), chlorides, etc. and DBP precursors.

2. Charge controlled membranes (EDR) can remove TDS, TH, chlorides etc.

3. Size exclusion controlled membranes can control particles, turbidity and cysts.

4 REQUIREMENTS FOR CASE STUDIES

4.1 Documentation

Case studies are investigations of singular or combined processes with specific goals for production, water quality and cost. Accurate project documentation is required to develop and report pilot production and water quality. Documentation of laboratory work should be associated with a change of custody and quality control. Determination of precision and accuracy of analytical samples in the laboratory or field is essential for meaningful interpretation of results. A traceable paper trail of sample analysis should be described in project documentation and referenced in a project report. Work and sampling logs should be used for documentation of fieldwork. Work or operational logs have daily entries that describe taking operational data, mechanical repair or any other activity that is associated with operation of pilot systems. Sample logs are separate from work logs in that specific data is recorded. Typical examples of field data include pH, pressure, flow, and temperature.

4.2 Productivity

Productivity is essential to any water treatment facility. Productivity is affected by design of the membrane process and fouling. Designers can select membranes for specific treatment characteristics. Once selected, a designer can select operating conditions for that membrane process. A primary consideration affecting productivity is fouling. The four primary mechanisms of fouling are scaling, plugging, adsorption and biological growth. The primary means of controlling fouling by mechanism and unit operation are shown in Table 4. General Comments can be made regarding pre-treatment requirements.

1. Scaling control is typically required for all RO/NF membrane systems in either surface or groundwaters and is achieved by acid and/or antiscalent addition.

2. Plugging control is typically required for all RO/NF membrane systems in either surface or groundwaters and is achieved by feed water turbidities and SDI’s less than 0.2 NTU and 2 respectively.

3. Bio-fouling control is typically required for aerobic surface or groundwaters and is achieved by NH2Cl or addition of other bactericidal agents.

4. Organic fouling can occur in surface water systems with TOC > 3-6 mg/L and is typically reduced by coagulation, sedimentation and filtration. However, the significance of organic fouling is not known.

4.3 Evaluation of Membrane Systems

Performance of membrane units can be measured in the field or laboratory by functioning membrane systems in the form of (a) small cells, (b) bench units or (c) pilot plants. Small cells have historically been used to test film characteristics and have not yet been shown to be representative of actual production. A testing protocol for small cells has been published. There results indicated that the Phase II MCLs for DBPs could be met in four of the five waters tested, the rate of productivity decline was exceptionally high and that DOC was diffusion controlled. While the DBP results were comparable with previous studies, the productivity results were not. Their results have shown that small cells are suited for membrane screening quality studies but are not adequate for productivity assessment.

Membrane manufacturers use 4″x40″ elements, 2.5″x40″ elements or 2.5″x20″ elements in pilot studies for plant scale up. The preliminary results of the information collection rule (ICR) were presented at the 1999 WQTC in Tampa, FL. In excess of forty membrane studies have been done through the United States to comply with the ICR requirements. The studies typically consist of flat sheet laboratory work; single element field work, multi-staged pilot plants and full scale plant documentation. The studies have shown that DBP precursor removal requirements were exceeded for haloacetic acids for either stage 1 or 2 MCLs, but that the ninety-fifth percentile of THMs exceeded the stage 2 MCL (40 ug/L). The higher THMs were attributed to high bromide concentrations (>30 ug/L) and variable bromide rejection (70% to 0%) by membranes.

Membrane case studies require that mass transport of water and solutes through the membranes be described quantitatively. The equations used to describe flow through a single element are shown in (1) through (7) with reference to the membrane element shown in Figure 1.

Mass transport in pressure driven membrane processes can be described as convection or diffusion controlled. Models for describing mass transfer in membrane systems have been presented by several investigators. These equations can be used to predict permeate water quality of any membrane system. Although membrane systems have been shown to produce water quality that exceeds most regulatory requirements, models as shown in equation (8) or (9) are essential for predicting the cost and performance of membrane systems from pilot plant data. Equation (8) is used to describe diffusion controlled mass transfer, which includes inorganics, i.e., alkalinity, hardness, TDS, sodium, chlorides, etc. Equation (9) is used to describe sieving controlled mass transfer, which includes TOC, DBP precursors, most SOCs and organics in general.

However, TOC has been shown as diffusion controlled in a surface water application at Tampa FL for CA and CTF membranes. The TOC from the CTF membrane was so low that no limit for flux and recovery was projected for precursor control, however flux and recovery were limited for the CA membranes as TOC rejection was significantly less.

Existing research has clearly shown consistent production and concentrate disposal are the limiting constraints for membrane systems. Concentrate disposal is essentially a regulatory problem but consistent production is a research and development problem. There is simply inadequate information on the fouling of membranes by moderate organic surface waters.

Reference Equations:

FW = KW(ΔP – ΔΠ) = Qp/A (1)

FS = KS(ΔC – QpCp/A (2)

R = Qp/Qf (3)

Qf = Qc + Qp (4)

QfCf = QcCc + QpCp (5)

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (6)

r = Qr/Qf (7)

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (8)

Cp = ΦCv (9)

ΔC = Concentration gradient (M/L3, ((Cf + Cc/2-Cp)

Cf = Feed stream solute concentration (M/L3)

Cc = Concentrate stream solute concentration (M/L3)

Cp = Permeate stream solute concentration (M/L3)

Cs = Solute concentration at the membrane surface (M/L2)

k = Diffusion coefficient from the surface to the bulk (L3/L2t)

ΔP = Pressure gradient (L), ((Pf + Pc)/2-Pp)

Δπ = Osmotic pressure (L) ((πf + πc)/2-Δp)

Kw = solvent mass transfer coefficient (L2t/M)

FW = Water flux (L3/L2t)

FS = Solute flux (M/L2t)

Ks = Solute mass transfer coefficient (L/t)

Qf = Feed stream low (L3/t)

Qc = Concentrate stream flow (L3/t)

Qp = Permeate stream flow (L3/t)

R = Recovery

A = Membrane are (L2)

r = Recycle ration

φ = Sieving pass coefficient

Fouling indices can be used to indirectly estimate pre-treatment requirements for membrane systems. These investigations have shown that fouling indices do not statistically correlate to the rate of productivity decline in diffusion controlled membrane systems. Regardless, fouling indices can be used to get a crude estimate of membrane pretreatment requirements. The silt density index (SDI), modified fouling index (MFI) and the mini-plugging factor index (MPFI) are shown in equations (10), (11) and (12).

SD1 = 100(1 – ti/tf)/T (10)

MFI = (QV)-1 (11)

MPFI = Q/t (12)

Where: ti = time to collect initial 500 ml; tf = time to collect final 500 ml; T = time between ti and tf, (15 min); Q = flow; V = volume

(Continues…)Excerpted from Membrane Technology in Water and Wastewater Treatment by P. Hillis. Copyright © 2000 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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