AWWA ACE63189

The water treatment industry has put greater emphasis on the removal of microorganisms in the 2-10 µm. Well operated water treatment plants have generally been recognized as able to provide excellent removal of particles over 2 µm size. However, field findings indicate that the passage of large, live zooplankton (200 µm to 1400 µm) was common at treatment facilities that use nutrient rich lake or impoundments as a raw water source. This paper presents field data of zooplankton prevalence in treated water supplies, and the efficiency of ozonation, clarification, dissolved air flotation, dual media filtration, and membrane filtration in removing or inactivating zooplankton at several water treatment sites. Live zooplanktons were found after low dose ozone treatment. High ozone doses were required to inactivate copepod nauplii, a common nuisance species of zooplankton in treated water supplies. Live zooplankton passage through dual media filters was commonly observed. Membrane filtration provided the best physical barrier against zooplankton. Includes 13 references, tables, figures.