Adapting membrane system operation and cleaning to varying raw water quality

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Membrane technologies are commonly used for water treatment applications throughout Canada and Internationally. The relatively rapid adoption of this novel technology over the past decade is largely due to its ability to produce high quality drinking water. During treatment, material that is retained at/in the membrane must be removed to prevent an excessive increase in the resistance to the permeating water. Hydraulic cleaning is typically used to remove most of the retained material (i.e. foulants). However, some of the foulants can only be removed chemically. Although effective at removing residual foulants, it is becoming increasingly evident that the use of chemical agents for membrane cleaning can negatively impact membrane performance. Over time, as a result of the impact of multiple chemical cleaning events, the membrane material is considered to have 'aged' beyond a trigger point and must be replaced. Coagulation-flocculation is commonly used prior to membrane filtration to improve the removal of contaminants in membrane systems, particularly components of dissolved organic matter that contribute to fouling. Because coagulation/flocculation affects the raw water matrix, it is also expected to impact the retention and accumulation of material by the membrane, and therefore chemical cleaning requirements as well as membrane ageing. Variations in source water quality are also expected to affect the performance of coagulation-flocculation and membrane systems and therefore chemical cleaning requirements. However, to-date, limited knowledge exists with respect to the effect of raw water quality and coagulation/flocculation practices on chemical cleaning requirements. The specific objectives of this study are to develop coagulation/flocculation protocols targeted specifically at the treatment of raw waters with highly variable characteristics, with the aim of identifying conditions that minimizing chemical cleaning requirements while maintaining water quality targets (concentration of organics, DBP precursor reduction).