NEW DEVELOPMENTS IN MEMBRANE TREATMENT PROCESSES: PART 1 - DESALINATION R Tarr softening to facilitate further treatment stages, etc. T he membrane treat ment industry is In general, pilot testing of a proposed undergoing rapid changes and should be performed, design d evelopments, including the emergence particularly for large plants o r when and refin ement of new membranes and treating potentially d ifficult water. T his associated p roducts, novel membrane is especially so when con templating the treatment plant design and operating use o f a novel o r complex process techn iques, minimisation of capital and design. T he cost of a pilot trial is operating costs, and reduction in waste minimal compared with the total cost p roduction. Exciting new fields of of a large plant, and compared to the research are being pursued, and major cost of fixing the plant sho uld Figure 1. Assortment of spira l wou nd thin fi lm advances in memb rane treatment preventable p roblems emerge. To composite (TFC) RO elements (Koch Membrane should be realised over the next decade. highl igh t this, the p retreatment San Diego, USA). Systems, These papers provide an overview o f problems at the US$ 1 10M Tampa Bay advancements in the membrane Desalination Plant in Florida, have led treated water, or major p rocess problems, treatment fie ld, including key areas of to a 12-month plant shu tdown. A $29M increases. develop ment ro watch over the coming con tract has recen tly been awarded to repair memb rane Various design tech niques and years. It does not delve in to the minutiae the plane faults and return it to service configurations can be considered d uring the of technological advancements, but rather (using precoat MF pretreatment - cartridge of an RO plan t. Each design stage provides a summary of the broad trends in fi lters coated with diatomaceous earth). combination and sequence will produce the industry and key developments being d ifferent results. Some common tech niques made in various branches of memb rane The Cost of Desalination to consider are: rreannem. W hile RO desal ination costs keep fa lli ng • Permeate splitting - drawing high quality Part 1 of this paper looks at the fie ld of as tech nology improves, conventional water permeate from the feed end o f the tube for RO based desalination. Part 2, to be treatment technology costs remain relatively p roduct water, .and low quality permeate published later, will cover advanced stable. Figure 2 indicates the fall ing wholefrom the opposite end for additional wastewater treatment and re-use. of-life cost of desalinated water over the last treatment. decade. (Note that the Singapore N EWater • Treatment of part flows - as in permeate Background plam water cost is shown to provid e a splitting, but also includes bypassing a I n 2003 the author was awarded a comparison between desalination and ROportion of a permeate stream from a Fellowship from the Winston Churchill based wastewater treatment.) su bsequent stage to achieve a req uired Memorial Trust of Australia to undertake a T he price reduction of RO desalination quality in the combined flow. project focusing on recent developments in is d ue to small imp rovements in many membrane-based desalination and advanced A overview of advancements in the membrane wastewater treatment.
Abstract
T he p roject took in visits to treatment plants, membrane man ufacturi ng faci lities, research centres, the I nternatio nal Desalination Association 200 3 World Congress and workshops, with rime spent in the USA, Bahamas, Canada, England, UAE and Singapore. These papers are the culmination of the Fellowship.
Desalination Techniques There are many ways to design an RO train for a desalination task. T hese choices can make a marked difference to the bottom line of a project. Too conservative and money will be thrown away; too aggressive and the potential fo r substandard
40 NOVEMBE R 2004 water
treatment field, including key areas of development to watch over the coming years. • Combinations of different treatment stages - a SWRO array, fo llowed by a BWRO array for mating the SWRO permeate; ion exchange systems fo r permeate polish ing for ultra-pure product water, or ion-specific resin for softening, boron removal, etc. • Water conditioning - p H adj ustment to reduce scaling or precipitation, or to increase rejection of specific ions; degasification fo r CO2 removal; water
areas, ranging from membrane performance and energy reduction through to cheaper power and financing costs.
Pretreatment Systems To customise a popular phrase, RO is all about pretreatment, pretreatment, pretreatmen t. The majority of problems experienced in the R O train can be related back to pretreatment inadequacies. RO p retreatmen t has h istorically been performed using conventional processes.