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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.

ab s t r ac tWithin the lifetime of most reverse osmosis (RO) systems some fouling will adversely affect membrane performance. The major constituents of foulants found on the first position during six years of membrane autopsy at the Genesys Membrane laboratory are clay minerals chemically known as aluminosilicates. Clay is a naturally occurring material found in all RO feed waters composed primarily of different fine-grained minerals, which exhibit a degree of plasticity (deformation under pressure) depending on the amount of water held by polar attraction in the mineral crystalline structure. Clay deposits are difficult to remove with traditional specialty and commodity cleaning chemicals. This is due to the characteristic of plasticity, the presence of different structural cations and also the impermeability of clay to water. Clay deposits fouling the membrane rapidly reduce flux rates. In order to maintain product water output operators invariably increase feed pressure which compacts the deposit making it less porous and harder to penetrate with traditional cleaning chemicals. Ineffective deposit removal leads to more frequent cleaning and enhanced potential for membrane damage. Clay mineral fouling of membranes therefore requires immediate removal through effective cleaning. This paper explores the chemistry of clay and the mechanisms involved in membrane fouling. The process of developing and testing a new cleaning product Genesol 703 which removes clay deposits from RO/NF/UF systems is described. Comparative results with conventional cleaning products and commodity chemicals are presented. Product efficacy was determined by comparison of membrane flux rates before and after cleaning. The results demonstrate that Genesol 703 is a technically and economically viable cleaning chemical product for the removal of clay deposits from membranes.

He serves as the Head Officer Representative of the Chemical Engineering Club.

ab s t r ac tDespite the current economic turmoil the need for good quality drinking water continues relentlessly. In the last eight years 11,825 reverse osmosis (RO) plants have come on line with a combined output of 25 million m³/d. Although large seawater plants take most of the 'desalination news, awards and headlines', a large number of small and medium sized plants (requiring less energy) are being commissioned that use other water sources. Recent data shows that some 8,500 of these systems are producing 62% of the extra water capacity installed since 2000; these plants use brackish, surface or waste water as a feed source. The increasing demand for the minerals that are found in arid and desert areas has increased the need for desalinated water in many mining areas. In these regions ground waters frequently contain high levels of calcium, magnesium, silica and sulphate; in such cases water desalination increasingly demands sophisticated speciality antiscalants and dispersants. This paper examines the use of new antiscalant compounds developed specifically to inhibit the formation of calcium sulphate. The chemistry and deposition mechanisms are presented along with details of formulating Genesys CAS a sulphate specific antisclant. Results from an operating plant are presented showing the improvement in plant performance and a simple model is developed to equate the improvement in plant operation associated with high recovery to actual cost savings. Membrane systems will continue to be built and operated with increasingly poorer quality feed waters. For this reason it is essential that new and improved speciality antiscalants are developed so that plants can continue to operate at their highest efficiency thereby saving water and energy.