Nanofiltration Foulants from a Treated Surface Water

Abstract

The loss of membrane flux due to fouling is one of the main impediments in the development of membrane processes for use in drinking water treatment. The objective of this work was to determine the nature of nanofiltration membrane foulants for a pilot system fed conventionally treated Ohio River water for 15 months. The foulant responsible for flux loss was shown to be a film layer 20−80 μm thick with the greatest depth in the first of three elements in series. Heterotrophic plate count, phospholipid, and pyrolysis-GC/MS analyses showed the film layer had a strong biological signature. The inorganic contribution to the dried film layer was low (less than 15%). Both acid and alkaline/detergent cleaning yielded only short-term flux recovery, although they were independent of each other. Neither acid cleaning, alkaline/detergent cleaning, nor hydraulic flushing removed the thickness of the film layer, nor changed its organic characteristics. Only alkaline/detergent cleaning inactivated a large percentage of the film-layer microbes. The short-term flux recovery without loss of biofilm thickness suggests a morphological change upon chemical cleaning. The results suggest that feedwater pretreatment to prevent cell deposition and subsequent biogrowth would be more successful than chemical cleaning the membrane after biofouling.