Full Description

Metropolitan Water District of Southern California operates five pumping plants along the Colorado River Aqueduct. At each facility employees and their families receive potable water from a pressure sand filtration system. These systems would not meet current regulations and could not be retrofitted. Microfiltration was investigated as an alternative. Microfiltration performed well as a solid-liquid separation device. Most beneficial was its high efficiency in removing turbidity and microorganisms. With no chemical coagulation or disinfection, microfiltration removed all measurable coliform bacteria and Giardia cysts and reduced MS2 bacteriophage levels by 1.7 to 2.9 logs. As expected, microfiltration did not remove significant amounts of soluble inorganics or DBP precursors. However, the excellent removal of microorganisms might allow reduced chlorination or chloramination, resulting in lower DBP formation. The membrane integrity test allowed easy monitoring of both membrane and system integrity. The sensitive integrity test would signal a membrane failure much earlier than turbidity or particle breakthrough. Not all backwashes are 100-percent efficient, so periodic chemical cleaning of the membranes is required. The pilot study indicated that chemical cleaning would be needed every 4-6 weeks. Based on these results, Metropolitan requested that the State of California Department of Health Services (CDHS) approve the microfiltration process, as supplied by the Memtec America Corporation, as an alternative filtration technology. The CDHS granted approval of the process and credited microfiltration for removing 3 logs (99.9 percent) of Giardia and 0.5 logs (68.4 percent) of virus. To comply with the SWTR by June 1993, Metropolitan is now proceeding with the installation of microfiltration facilities for each of its small desert domestic water systems.

Product Details

Published: 01/01/1993 ISBN(s): 0898677076 Number of Pages: 24File Size: 1 file , 1000 KB