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A B S T R A C TFlocculants are used in combination with coagulants to agglomerate suspended particles for removal by filtration. This technique is used extensively in all types of surface waters to reduce the silt density index (SDI) and minimise membrane fouling. Although organic cationic flocculants are particularly effective, their widespread use in membrane applications is limited because of perceived problems with flocculant fouling at the membrane surface causing irreparable damage. Reference material from some of the major membrane manufacturers on the use of flocculants is given.Autopsies show that more than 50% of membrane fouling is caused by inadequate, deficient or poorly operated pre-treatment systems. The Authors suggest that if the correct chemistry is considered, the addition of an effective flocculant can be simple and safe. The paper discusses the use of cationic flocculants and the fouling process that occur at the membrane surface. The paper explains the types of coagulants and flocculants used and considers cationic flocculants and the way they function.Operational results when using a soluble polyquaternary amine flocculant (Genefloc GPF) developed by Genesys International Limited is presented. Genefloc GPF has been in extensive use for several years and a review of the results clearly shows no detrimental effect on membrane performance.A case study shows the effectiveness of Genefloc GPF in reducing SDI and increasing particle size prior to filtration. In every case a significant improvement in plant performance is seen with a reduction in cleaning frequency and extended membrane life. New particle counting techniques [1] have assisted us in optimising flocculant dosage rate and monitor on-going performance.

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A B S T R A C TOver the last 10 years, there have been significant developments in new devices for energy recovery, new membrane materials and new sizes and orientations of reverse osmosis (RO) plants, all designed to reduce costs and improve efficiency. The fundamental issue of keeping membrane surfaces clean to ensure efficient RO plant operation has seen relatively few recent developments. This is surprising as any fouling of the membrane surface will have a dramatic effect on energy consumption and plant efficiency. Many researchers have focused on identifying and studying the foulants in great detail, but there have been few studies in how to remove it. Commodity acid and alkali compounds are still widely used due to the perceived lower application costs. Specially blended cleaning chemicals incorporating detergents, surfactants and chelants are also in wide use and are increasingly accepted by the market to be economically and environmentally viable. "Strategically pairing chemical agents that have complementary cleaning mechanisms so a higher cleaning efficiency can be attained" has been described by Wui. The authors have established a research project to explore in detail the use of novel physical and chemical cleaning methods. These included effervescent chemicals, physically generated bubbles and high ionic strength cleaners designed to agitate the cake layer on the membrane surface, assisting deposit removal. A series of experiments using flat sheet test rigs and pilot plant have been completed and the results presented in papers at IDA Tianjin 2013. This paper explains how the multiple cleaning mechanisms remove foulants and presents new data from a food processing plant which recycles wastewater through an RO plant is presented. Historically, cleans were conducted every one to two weeks due to the very high fouling rate. An air inductor and specially formulated cleaning compound cleaners A & B incorporating effervescent and high ionic strength demonstrated that the plant could be cleaned more efficiently and in a shorter timescale than using conventional cleaners. The presence of microbubbles has a dramatic effect on cleaning efficiency as a result of agitation of deposits on the membrane surface. The differential pressure of the first-stage plant was reduced for 4.5 bar to consistently less than 1 bar. The quantity of permeate produced increased from 15 to 24 m 3 /h. The underlying fouling rate was dramatically reduced so cleans are now conducted on a 6-8 week cycle rather than a 10-day cycle. These improvements occurred because cleaning using microbubbles has been more effective and the membrane surface much cleaner than previously. A clean membrane surface does not foul as quickly as a dirty membrane surface due to surface roughness. The potential for enhanced membrane cleaning by combining different chemical and physical mechanisms is an exciting area of research.