NANOFILTRATION FOULANTS FROM A TREATED SURFACE-WATER

The loss of membrane flux due to fouling is one of the main impediment s in the development of membrane processes for use in drinking water t reatment. The objective of this work was to determine the nature of na nofiltration membrane foulants for a pilot system fed conventionally t reated Ohio River water for 15 months. The foulant responsible for flu x loss was shown to be a film layer 20-80 mu m thick with the greatest depth in the first of three elements in series. Heterotrophic plate c ount, 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/deter gent cleaning yielded only short-term flux recovery, although they wer e independent of each other. Neither acid cleaning, alkaline/detergent cleaning, nor hydraulic flushing removed the thickness of the film la yer, nor changed its organic characteristics. Only alkaline/detergent cleaning inactivated a large percentage of the film-layer microbes. Th e short-term flux recovery without loss of biofilm thickness suggests a morphological change upon chemical cleaning. The results suggest tha t feedwater pretreatment to prevent cell deposition and subsequent bio growth would he more successful than chemical cleaning the membrane af ter biofouling.