Performance of large-scale biological filtrationfor removal of particles and biodegradable organic matterproduced by ozonation

摘要

Metropolitan Water District of Southern California (Metropolitan) is a water wholesaler supplyingrnmore than 50-percent of drinking water to over 17-million people in southern California.rnMetropolitan operates five regional water treatment plants (WTPs) that use conventionalrncoagulation, sedimentation, and multi-media (e.g., anthracite, sand) filtration with a combinedrndesign flow capacity of more than 2.5 billion-gallons-per-day. To comply with disinfectants andrndisinfection by-products (D/DBP) regulations set by the U.S. Environmental Protection Agency,rnMetropolitan is retrofitting its WTPs with pre-ozone (upstream of conventional treatment)rndisinfection. Following ozone retrofit, subsequent chlorination is postponed until after filtration,rnallowing filters to operate in a biologically-active manner (biofiltration). This allows forrnbiodegradable organic matter (BOM), produced by ozonation, to be significantly reduced prior torndistribution. Metropolitan’s H.J. Mills WTP began biofiltration in August 2004 and currentlyrnoperates biofilters with a 70-percent BOM reduction goal. This manuscript summarizes resultsrnfrom the first year of biofilter operations, including: BOM removal, bacterial sloughing, effects onrnfilter run length, and effect on the level of WTP-effluent, halogenated DBPs.