PRODUCTION OF DRINKING WATER FROM LAKE WATER SOURCES WITH A NANOFILTER MEMBRANE TO PREVENT THE FORMATION OF DISINFECTION BYPRODUCTS

摘要

Small community systems that use surface water as a source of drinking water arefrequently faced with elevated levels of naturally-occurring organic matter (NOM)that are not removed by conventional filtration methods. These residual levels ofNOM may combine with chlorine used for disinfection and create disinfectionbyproducts (DBPs) potentially in excess of the regulatory limit for various DBPs.Frequently, additional treatment for removal of these DBPs is necessary to avoid noncompliancewith the requirements of the Safe Drinking Water Act (SDWA). Theformation of DBPs can be prevented by removing NOM, which acts as a precursor toDBP formation. This paper presents the results of field tests conducted on lake waterusing a nanofilter membrane, incorporating a method for cleaning the membraneusing a foam ball. The system uses a tubular membrane with the ends connected toeffectively form a single, long, membrane. The lake water is fed into the inside of themembrane tube and the filtrate is forced out, through the membrane into themembrane housing outlet. Using a timer, a foam ball is periodically passed throughthe inside of the membrane by reversing the flow direction. This foam ball serves toremove accumulated organic matter capable of fouling the membrane surface. Thisorganic matter is flushed to drain as the foam ball passes through the inside of thetube. The system can be operated with the membrane reject water recycled to thesystem inlet or in a dead-end mode where no membrane reject water is produced untilthe system is foam ball cleaned. Tests were conducted in both modes of operation.The system requires no pretreatment of the feed water other than a coarse (3mm)screen to prevent large solids from entering the system. The effectiveness of thesystem in producing drinking water was gauged by measuring the turbidity, color,and particle counts of the system inlet and outlet. Tests were also performed usingthe aerobic spore Bacillus subtilis (B. subtilis) as a surrogate for bacteria removal.