Chapter 14: Treatment processes, filtration and adsorption

14.8 Desalination

Desalination has been included in this section because at least some of the process can include membrane (reverse osmosis or RO) treatment. Distillation can also be used. Chapter 2 of WHO (2005) is titled Desalination Guidelines Development for Drinking Water. Chapter 12 is titled Health Risks from Drinking Demineralised Water. WHO (2011a) updates these and discusses related safety plans (WSPs).
WHO (2007) states that more than 12,000 desalination plants are in operation throughout the world producing about 40 million m³ of water per day. The number is growing rapidly as the need for fresh water supplies grows more acute and technologies improve and unit costs are reduced. As at 2010, desalinated water provides about 20 percent of Israel’s drinking water supply, and major expansions to cope with rising demand are predicted to increase this proportion to around 50 percent by 2020 (taken from WQRA (2011).
Desalination plants use waters impaired with salts (seawater or brackish water) or other contaminants as their sources. About 50 percent of the capacity exists in the West Asia Gulf region. North America has about 17 percent, Asia apart from the Gulf about 10 percent and North Africa and Europe account for about 8 percent and 7 percent respectively, and Australia a bit over 1 percent.
The principal distillation systems include Multistage Flash (MSF) distillation, Multi-effect Distillation (MED) and Vapour Compression Distillation (VCD). Distillation plants can produce water in the range of 1 to 50 mg/L TDS. As a comparison, RO processes can produce water in the range of 10 to 500 mg/L TDS.
Common membranes are polymeric materials such as cellulose triacetate or more likely polyamides and polysulfones. Membranes are typically layered or thin film composites. The surface contact layer (rejection layer) is adhered to a porous support, which can be produced from the same material as the surface.
In electrodialysis-based treatment systems a direct current is passed through the water, which drives the ions (not the water) through membranes to electrodes of opposite charge. In electrodialysis reversal systems, the polarity of the electrodes is reversed periodically during the treatment process. Ion-transfer (perm-selective) anion and cation membranes separate the ions in the source water. Electrodialysis reversal systems do not provide any barrier against pathogens, and electrodialysis reversal is, therefore, rarely considered to serve as the main treatment barrier for drinking-water production.
Desalinated water is stabilised by adding lime and other chemicals, and/or by blending with other water, both to offer a balanced mineral content and to reduce corrosion effects.
Most of the inorganic components will be significantly removed in the desalination process, either thermal or RO, although some sodium chloride and bromide may be present in the treated water from membrane plants and possibly from some older distillation plants. In terms of key contaminants of direct interest for health and environment, the most important is probably boron, which can be of significance in reverse osmosis plants since the rejection ratio of boron (probably mostly as borate) is less than that for most other inorganic determinands. Bromide is initially present in seawater in relatively large amounts (~70 to 80 mg/L), so even high (eg, >95 percent) percentage removals will allow some bromide of the order of 1 to several mg/L to be present in the finished water.
RO has been shown to remove bacteria and larger pathogens and, depending on the membrane applied, to remove all or a large fraction of viruses. High-quality RO processes are good treatment barriers to pathogens if properly selected and maintained.
Most vegetative pathogens are inactivated under flash pasteurisation conditions (temperature of 72°C for 15 seconds). The condensate is unlikely to contain pathogens after the distillation process because of the killing impact of heat and because pathogens are unlikely to be entrained. However, reduced pressures are used in some desalination processes to reduce the boiling point and reduce energy demand. Temperatures as low as 50°C may be used which might not achieve the required inactivation targets. Inactivation levels expected at temperatures typical of distillation processes are considered sufficient to inactivate most pathogens since they are equivalent or in excess to those used for pasteurisation.
Chlorine in various forms (sodium hypochlorite, chlorine gas) is generally used for disinfection because of its recognised efficiency as a disinfectant and because of the reduced level of disinfection by-product precursors. Protozoa have generally been removed in the desalination process.
Desalinated water is initially more corrosive than many other drinking-water sources, and it is important that the water be stabilised to minimise its corrosive effect on pipes and fittings used in distribution and plumbing systems in buildings, and/or that the materials used in contact with the water be selected with care. The Israeli Ministry of Health has announced that it intends to require water providers to supplement desalinated water with magnesium in order to prevent the potential adverse effects of magnesium deficiency (taken from WQRA 2011). See Spungen et al (2013) for a discussion on health issues related to drinking desalinated water without supplementary calcium and magnesium.

References

American Society of Civil Engineers, Environmental Engineering Division. 1991. Slow Sand Filtration. GS Logsdon (ed). New York: ASCE. 0-87262-847-7, 230 pp.

ANSI/AWWA B101-12. AWWA Standard for Precoat Filter Media.

ANSI/AWWA B110-09. AWWA Standard for Membrane Systems (9/4/2009).

ANSI/AWWA B130-13. AWWA Standard for Membrane Bioreactor Systems.

ANSI/AWWA B604-12. AWWA Standard for Granular Activated Carbon.

ANSI/AWWA B605-13. AWWA Standard for Reactivation of Granular Activated Carbon.

AS/NZS 4348:1995. Water Supply: Domestic type water treatment appliances – Performance requirements.

AS/NZS 3497:1998. Drinking Water Treatment Units: Plumbing requirements.

AWWA. 1990. Water Quality and Treatment (4th edition). McGraw-Hill Inc.

AWWA. 1995. Precoat Filtration (2nd edition). Manual M30. Denver CO: American Water Works Association.

AWWA. 1999. Reverse Osmosis and Nanofiltration (1st edition). Manual M46. Denver CO: American Water Works Association.

AWWA. 2005. Microfiltration and Ultrafiltration Membranes for Drinking Water. Manual M53. Denver CO: American Water Works Association. Summarised in J AWWA 2008 100(12): 84–97.

Bonny E, Cameron D. 1998. Woodville’s diatomaceous earth plant. Water & Wastes in New Zealand 101: 20–2.

Brown TS, Malina JF Jr, Moore BD. 1974. Virus removal by diatomaceous-earth filtration – Part 2. Journal of the American Water Works Association 66(12): 735–8.

Cotte, et al. 2005. Distributed Water Quality after Three Years of Nanofiltration, pp 143–56. Water Quality in the Distribution System. Denver CO: American Water Works Association.

Drinking Water Inspectorate (DWI). 2011. List of Approved Products for Use in Public Water Supply in the United Kingdom. London: Department for Environment, Food and Rural Affairs. See www.dwi.gov.uk or http://dwi.defra.gov.uk/drinking-water-products/approved-products/soslistcurrent.pdf

EPA/NSF ETV. 2002. Protocol for Equipment Verification Testing for Physical Removal of Microbiological and Particulate Contaminants. NSF International, Ann Arbor, MI for USEPA.

EPA/NSF ETV. 2005. Protocol for Equipment Verification Testing for Physical Removal of Microbiological and Particulate Contaminants. 40 CFR 35.6450. NSF International, Ann Arbor, MI for USEPA. www.epa.gov/etv/pubs/059205epadwctr.pdf

Lang KP, et al. 1986. Diatomaceous earth filtration of Giardia cysts and other substances. Journal of the American Water Works Association 78(1): 76–84.

The New Zealand Ministry of Health’s Guides for drinking-water supplies can be accessed as Word documents on the Ministry of Health website: www.health.govt.nz/water then select publications and Water Safety Plans.

Ministry of Health. Public Health Risk Management Plan Guide PHRMP Ref: P6.2. Filtration – Slow Sand Filtration. Wellington: Ministry of Health.

Ministry of Health. Public Health Risk Management Plan Guide PHRMP Ref: P6.3. Treatment Processes – Cartridge Filtration. Wellington: Ministry of Health.

Ministry of Health. Public Health Risk Management Plan Guide PHRMP Ref: 6.4. Filtration – Diatomaceous Earth. Wellington: Ministry of Health.

Ministry of Health. Public Health Risk Management Plan Guide PHRMP Ref: P6.5. Treatment Processes – Membrane. Wellington: Ministry of Health.

Ministry of Health. Public Health Risk Management Plan Guide PHRMP Ref: P10. Treatment Processes – Pump Operation. Wellington: Ministry of Health.

Ministry of Health. Public Health Risk Management Plan Guide PHRMP Ref: P11. Treatment Processes – Plant Construction and Operation. Wellington: Ministry of Health.

Ministry of Health. 2005. Drinking-water Standards for New Zealand 2005, revised 2008. Wellington: Ministry of Health.

NSF/ANSI 53-2002 (plus Addenda 1 and 2). Drinking-water treatment units health effects. Ann Arbor MI. Note that NSF are continually updating their standards. The latest version is: NSF/ANSI 53-2009e: Drinking Water Treatment Units: Health effects (23rd edition), 120 pp.

NSF. 2005. Feasibility of an Economically Sustainable Point-of-Use/Point-of-Entry Decentralized Public Water System. NSF International for USEPA. Available online at: www.nsf.org/business/drinking_water_treatment/GrimesFinalReport_Dec05.pdf

Ogilvie D. 1998. Diatomaceous earth treatment. Water & Wastes in New Zealand 101: 17–18.

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Schijven JF, et al. 2012. A mathematical model for removal of human pathogenic viruses and bacteria by slow sand filtration under variable operational conditions. Water Research

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Spungen JH et al. 2013. Desalination of water: Nutritional considerations. Israel Medical Association Journal 15(4): 164–8.

USEPA. 1984. Design Manual: Removal of fluoride from drinking water supplies by activated alumina. Rubel and Hagler, Inc. under contract 68-03-2917 for USEPA ORD.

USEPA. 2003a.* Membrane Filtration Guidance Manual. Proposal Draft, June. United States Environment Protection Agency. The draft version is/was available at: www.epa.gov/safewater/lt2/pdfs/guide_lt2_membranefiltration_draft.pdf see USEPA (2005) for latest version.

USEPA. 2005.* Note: the final Guidance Manual (USEPA Office of Water, EPA 815-R-06-009) was published in November 2005 and can be accessed at www.epa.gov/ogwdw/disinfection/lt2/pdfs/guide_lt2_membranefiltration_final.pdf or go to www.epa.gov/lawsregs/rulesregs/sdwa/lt2/compliance.cfm

USEPA. 2003b. Long Term 2 Enhanced Surface Water Treatment Rule: Toolbox Guidance Manual, Chapter 8: Bag and Cartridge Filters. Draft. EPA-815-D-03-009. Washington: United States Environmental Protection Agency. See USEPA (2009) for latest version.

USEPA. 2003c. Arsenic Treatment Technology Evaluation Handbook for Small Systems. USEPA, Office of Water, EPA 816-R-03-014. 151 pp. Available on the internet at: http://water.epa.gov/lawsregs/rulesregs/sdwa/arsenic/compliance.cfm

USEPA. 2003d. Small Drinking Water Systems Handbook: A guide to ‘packaged’ filtration and disinfection technologies with remote monitoring and control tools. EPA/600/R-03/041. Office of Research and Development. Water Supply and Water Resources Division, United States Environmental Protection Agency. 73 pp. See: www.epa.gov/ordntrnt/ORD/NRMRL/pubs/600r03041.html

USEPA. 2004. Protocol for Equipment Verification Testing of Volatile Organic Chemical Removal. Environmental Technology Verification Protocol (ETV). 04/9209/EPADWCTR. Prepared by NSF. 138 pp. www.epa.gov/etv/pubs/049209epadwctr.pdf

USEPA. 2006. Investigation of the Capability of Point-of-Use/Point-of-Entry Treatment Devices as a Means of Providing Water Security. EPA/600/R-06/012, February 2006. 54 pp. USEPA, Office of Research and Development, National Homeland Security Research Center. See www.epa.gov/nhsrc/pubs.html

USEPA. 2006a. National Primary Drinking Water Regulations: Long Term 2 Enhanced Surface Water Treatment Rule: Final Rule. (LT2ESWTR). Federal Register Part II, 40 CFR Parts 9, 141 and 142. Washington: National Archives and Records Administration. See www.epa.gov/fedrgstr/EPA-WATER/2006/January/Day-05/w04a.pdf www.epa.gov/fedrgstr/EPA-WATER/2006/January/Day-05/w04b.pdf www.epa.gov/fedrgstr/EPA-WATER/2006/January/Day-05/w04c.pdf or go to www.epa.gov/lawsregs/rulesregs/sdwa/lt2/compliance.cfm

USEPA. 2009. Long Term 2 Enhanced Surface Water Treatment Rule, Toolbox Guidance Manual Review Draft. Go into www.epa.gov/safewater/disinfection/lt2/ and then enter: toolbox guidance manual review draft in the ‘search’ box. See USEPA (2010) for Final.

USEPA. 2010. Long Term 2 Enhanced Surface Water Treatment Rule, Toolbox Guidance Manual. EPA-815-R-09-016. 375 pp. www.epa.gov/safewater/disinfection/lt2/pdfs/guide_lt2_toolboxguidancemanual.pdf

WHO. 1974. Slow Sand Filtration. ISBN 92 4 154 037 0. 122 pp. Out of print. Available only in electronic form: www.who.int/water_sanitation_health/publications/ssf/en/index.html

WHO. 2004. Guidelines for Drinking-water Quality (3rd edition). Geneva: World Health Organization. Available at: www.who.int/water_sanitation_health/dwq/gdwq3/en/print.html see also the addenda.

WHO. 2004a. Water Treatment and Pathogen Control: Process efficiency in achieving safe drinking water. MW LeChevallier, K-K Au. 136 pp. Published on behalf of WHO by IWA Publishing. Available on the internet at: www.who.int/water_sanitation_health/publications/en/index.html

WHO. 2005. Nutrients in Drinking-water. WHO/SDE/WSH/05.09, 210 pp. See Chapter 2: Health Risks from Drinking Demineralised Water. This is available on the internet at www.who.int/water_sanitation_health/dwq/nutrientsindw/en/index.html

WHO. 2007. Desalination for Safe Water Supply. World Health Organization, Geneva. 173 pp. www.who.int/water_sanitation_health/gdwqrevision/desalination.pdf

WHO. 2009. Scaling Up Household Water Treatment Among Low-Income Populations. 84 pp. http://whqlibdoc.who.int/hq/2009/WHO_HSE_WSH_09.02_eng.pdf

WHO. 2011. Guidelines for Drinking-water Quality 2011 (4th edition). Geneva: World Health Organization. Available at: www.who.int/water_sanitation_health/publications/2011/dwq_guidelines/en/index.html

WHO. 2011a. Safe Drinking-water from Desalination: Guidance on risk assessment and risk management procedures to ensure the safety of desalinated drinking-water. Geneva: World Health Organization. WHO/HSE/WSH/11.03. 34 pp. www.who.int/water_sanitation_health/publications/2011/desalination_guidance/en/index.html

WQRA. 2011. HealthStream – Quarterly Public Health Newsletter of Water Quality Research Australia. March issue. www.wqra.com.au

1^ The volumetric percent of feedwater that is converted to filtrate in the treatment process over the course of an uninterrupted operating cycle. This excludes losses attributable to backwashing and CIP.

2^ The difference in pressure from the feed to the filtrate across a membrane barrier.

3^ The throughput of a pressure-driven membrane filtration system expressed as flow per unit of membrane area (eg, L/m²/h).

Guidelines for Drinking-water Quality Management for New Zealand 2015
Chapter 14: Treatment Processes, Filtration and Adsorption – October 2015