MICROORGANISMS IN NON-POTABLE RECLAIMED WATER DISTRIBUTION SYSTEMS IN THE SOUTHWESTERN UNITED STATES

摘要

Diminishing fresh water supplies coupled with increasing municipal water demands in highly populated areas around the world highlights the significance of water reuse. The microbial quality of reclaimed water is one of the reasons for its restricted use. The goal of this project is to characterize the nature and extent of water quality deterioration in reclaimed water distribution systems, including microbial fouling, regrowth, impacts to the end user, and impacts on reuse and other related regulations. Samples from reclaimed water distribution systems in seven metropolitan areas in California, Arizona, Texas, and Nevada were collected and assayed for Cryptosporidium oocysts, Giardia cysts, and indicator microorganisms such as total coliforms, fecal coliforms, male specific coliphages, and somatic coliphages. Cryptosporidium oocysts and Giardia cysts were detected in 24% (12/50) and 46% (23/50) of the samples, respectively. Total coliforms and fecal coliforms were detected in 45% (40/89, 1-6×10~4 cfu/100 mL) and 20% (18/90, 1-1×10~2 cfu/100 mL) of the samples, respectively. Male specific and somatic bacteriophages were detected in 14% (7/52, 1-28 pfu/10 mL) and 15% (8/52, 1-30 pfu/10 mL) of the samples, respectively. Sporadic peaks in the concentrations of coliform bacteria and coliphages in tertiary treated water samples indicate that the plants often failed to remove or disinfect these microorganisms. In other words, the chlorination practices used by the reclaimed water utilities were not sufficient to even inactivate coliphages and coliforms. An increase of the number of total coliforms between the point of water entry and the point of water use in reclaimed water distribution systems was observed, whereas, as expected, no such increase of the number of male specific and somatic bacteriophages was noticed.