| The use of chlorine in drinking water treatment produces disinfection byproducts (DBPs) that have been shown to be deleterious to health. DBPs are currently under regulatory consideration by the U.S. Environmental Protection Agency. If the currently proposed regulatory levels are accepted, many utilities will be forced to adopt additional expensive treatment processes such as membranes for DBP precursor control.; The loss of membrane flux due to fouling is one of the main impediments to the development of membrane processes for use in drinking water treatment. The objective of this work was to determine the nature of membrane foulants for a number of surface waters that had different water qualities and pretreatments. Knowledge of the nature of the foulants responsible for flux decline would lead to optimal pretreatment and cleaning selections.; The foulants from pilot nanofiltration membrane elements fed conventionally-treated Ohio River, Harsha Lake, and Manatee Lake waters for extended times were analyzed for organic, inorganic, and biological parameters. All three systems had foulants with strong biological natures as determined by heterotrophic plate counts, phospholipid analyses, and pyrolysis-GC/MS analyses. The inorganic contribution to the dried foulants was low (less than 15 percent by weight).; A 70-day study with conventionally-treated Ohio River water showed that controlling biological growth with chloramines and severely reducing the feed water temperature resulted in greater flux decline than without these additional pretreatments. Chloramination was found to change the organic characteristics of the foulant to a more proteinaceous nature. This was likely due to the interaction of chloramines with the organic foulant and the absence of biogrowth and its obligatory increase in extracellular biopolymers rich in polysaccharides. The ozone pretreatment, ozone/biofiltration pretreatment, and no additional pretreatment systems had better flux characteristics compared to the chloramine and low-temperature systems. They also had high levels of biological growth as determined by heterotrophic plate counts, phospholipid analyses, and pyrolysis-GC/MS analyses. Therefore, the large biological growth in these systems lessened the impact of fouling due to inorganics, organics, or particulates presumably by creating a foulant layer with diffuse properties. This was successfully modeled with a modified resistence-in-series theory. |
