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.

It is well known that any fouling of the membrane surface has a dramatic effect on energy consumption and plant efficiency; this is particularly true for waste water reverse osmosis (RO) plants due to the higher fouling rate. Such fouling can be very difficult to clean using commodity chemicals or even speciality chemicals. This paper explores the use of a novel cleaning process designed to increase the efficiency of membrane cleaning using microbubbles. The microbubbles were created by both a physical and chemical process, which circulate in the cleaning solution increasing turbulence at the membrane surface. These bubbles create shear forces which agitate and dislodge the foulant giving greater removal in a reduced time period. In order to demonstrate that there was no damage to the membrane surface or element using this cleaning method with microbubbles, we selected a number of 8´´membranes from the major membrane manufacturers and performed repeat cleans over a 12 month period. Membranes were autopsied to analyse presence of damage, flux and salt rejection performance, results showed that no damage was caused by using this method. These compatibility results were presented in papers at IDA Tianjin 2013. This paper explains how the multiple cleaning mechanisms (both physical and chemical) help remove foulants and restore performance at a tertiary treated sewage effluent treatment plant producing high quality water for reuse. The 6,800 m 3 /d plant treats conventional activated sludge with microfiltration and RO. Cleans were conducted every 2 or 3 months due to reduced flows and high differential pressures. The new cleaning method using microbubbles with specially formulated cleaning compound cleaners demonstrated that the plant could be cleaned more efficiently and in a shorter timescale than using conventional cleaners.

ab s t r ac tPhosphorous containing antiscalants, which are commonly used in RO desalination process, have become an environmental concern for RO concentrate disposal. These chemicals are suspected of contributing to algal blooms in the water bodies where RO concentrate is discharged. Therefore, phosphorous-free antiscalants are increasingly being required for both brackish and seawater membrane desalination systems. Nalco recently developed a phosphorous-free antiscalant (PC-1611T) to address this environmental concern. In the laboratory testing, this product performed similar to ATMP (commonly used phosphonate based antiscalant) for CaCO 3 scale inhibition up to 3.0 LSI (Langelier Saturation Index). It also inhibited CaCO 3 scale in presence of up to 1 ppm Fe 3+ and residual levels of poly(DADMAC) based pre-treatment coagulant. It also showed 2-5× lower bio-growth contribution potential than polycarboxylates and is compatible with polyamide RO membranes. Full-scale evaluation of this product is in progress and the results for first 4 weeks show stable RO performance, indicating successful scale-control.