Genesys International Limited

Microbubble RO membrane cleaning reduces fouling on WWRO plant.


Over the last ten 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. Specialty 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 waste water 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 15mVhr to 24mVhr. 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 have 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.

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