Production of Drinking Water from Lake Water Sources with a Nanofilter Membrane to Prevent the Formation of Disinfection Byproducts

Small community systems that use surface water as a source of drinking water are frequently faced with elevated levels of naturally-occurring organic matter (NOM) that are not removed by conventional filtration methods. These residual levels of NOM may combine with chlorine used for disinfection and create disinfection byproducts (DBPs) potentially in excess of the regulatory limit for various DBPs. Frequently, additional treatment for removal of these DBPs is necessary to avoid non- compliance with the requirements of the Safe Drinking Water Act (SDWA). The formation of DBPs can be prevented by removing NOM, which acts as a precursor to DBP formation. This paper presents the results of field tests conducted on lake water using a nanofilter membrane, incorporating a method for cleaning the membrane using a foam ball. The system uses a tubular membrane with the ends connected to effectively form a single, long, membrane. The lake water is fed into the inside of the membrane tube and the filtrate is forced out, through the membrane into the membrane housing outlet. Using a timer, a foam ball is periodically passed through the inside of the membrane by reversing the flow direction. This foam ball serves to remove accumulated organic matter capable of fouling the membrane surface. This organic matter is flushed to drain as the foam ball passes through the inside of the tube. The system can be operated with the membrane reject water recycled to the system inlet or in a dead-end mode where no membrane reject water is produced until the 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 the system in producing drinking water was gauged by measuring the turbidity, color, and particle counts of the system inlet and outlet. Tests were also performed using the aerobic spore Bacillus subtilis (B. Subtilis) as a surrogate for bacteria removal.