AWWA WQTC54997

The objective of this study was to evaluate the effectiveness of NF/RO membranes in treating filtered water from a conventional water treatment plant. The performance of these membranes was evaluated in terms of rejection of DBP precursors, fouling potential and cleaning frequency. All experiments were conducted with conventionally treated Ohio River water. Effluent from the plant filters was collected in a holding tank, pumped to the dechlorination tank upstream from the pilot plant, where sodium bisulfite was added, and allowed to flow by gravity to the skid-mounted RO feed tank. The pilot unit consisted of four pressure vessels, each with a dedicated feed pump, making it possible to operate four spiral wound membranes simultaneously. Each pressure vessel could hold two 2.5 inch diameter by 40 inch long membranes in series. Part of the reject stream could be recycled to the RO feed to achieve higher recovery rates. The membranes were chemically cleaned when the normalized permeate flux declined by 15% or when the feed to brine pressure drop increased by about 15%. Cleaning was done with hydrochloric acid solution at a pH of 4 and commercial cleaning solutions at pH 10.5 and 12. The feed, permeate, and reject streams were analyzed for conductivity and pH, and for various organic and inorganic constituents, including conductivity, hardness, alkalinity, barium, iron, manganese, fluoride, nitrate, phosphate, aluminum, sodium, potassium, silica, total dissolved solids (TDS), strontium, TOC, DOC, and UV254 absorbance. Simulated distribution system tests were performed on feed and permeate water at an initial chlorine concentration in the range of 2.5 to 3 mg/L, and at incubation periods of 2, 24, and 72 hours. In Phases I and II of the pilot study, eight NF/RO membranes from three manufacturers were evaluated over a relatively short period to determine the rejection characteristics. Membranes that achieved good DOC removal were subjected to further testing to determine the fouling tendencies and achievable flux. Includes 6 references, tables, figures.