Analysis of the foulants isolated from fouled reverse osmosis (RO) membranes reveals simple scale deposits and, more frequently, composites of colloids, particulates and biomass that are difficult to remove. The common scales appear to be limited to calcium carbonate, calcium fluoride and the sulphates of calcium, strontium and barium, plus phosphate when present. Responses to specific cleaning formulations have confirmed the identity of the scales. Scaling is generally a problem with ground waters of varying mineral content, and not crucial for seawater feeds. Biofouling, on the other hand, can be a serious threat to all RO operations. Biomass accounts for the major part of the organic material in foulants. It is essential to minimise favourable growth and attachment conditions. The most effective control of biofouling is, of course, prevention of the colonisation or proliferation of microorganisms by disinfection.
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