Slowsand/Nanofiltration of Surface Water

Abstract

Since the spring of 1988 the University of Arizona has conducted nanofiltration research. The major emphasis has been the treatment of both Colorado River Water and municipal effluent. The work has been sponsored by the John F. Long Foundation Inc. and the Consolidated Water Utilities, Phoenix Az. Nanofiltration is a low pressure form of reverse osmosis. It operates at about 1/3 the pressure and 3 times the flux rate of older brackish water reverse osmosis systems. This reduces both the cost as well as the operating costs to approximately 1 /10 of the older reverse osmosis systems. The City of Ft Myers is projecting costs as low as $0.50-0.60/1000 gallons for their 20 MGD plant. Nanofiltration treats water the way it needs to be treated to meet the Environmental Protection Agency's (EPA) present minimum contamination levels (MCL) as well as projected future levels. Nanofiltration removes most of the bivalent inorganic molecules such as calcium and magnesium as well as some monovalent molecules such as sodium and chloride. It also removes pathogens and dissolved organics, thus reducing the trihalomethane formation potential (THMFP). The research on recharged effluent municipal effluent below the 91st Avenue Plant in Phoenix has shown the value of nanofiltration for reclaiming municipal wastewater to potable standards. A 20,000 GPD slowsand /nanofiltration pilot plant at Apache Junction has shown the effectiveness of the treatment on Colorado River Water at a 95% recovery over the past 2 years.