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THE USE OF ALTERNATE MICROBIOLOGICAL INDICATORS OF WATER TREATMENT PLANT PERFORMANCE

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Previous studies have shown that current microbial indicators used to evaluate the performance of water treatment plants cannot be correlated with the removal of certain pathogens such as Giardia, Cryptosporidium and enteric viruses. To meet water quality standards established by federal agencies, various methods have been developed in order to assess existing treatment facilities for their capacity in treating drinking water and to obtain the required treated water quality. As part of an investigation conducted in Puerto Rico to improve the quality of the drinking water, a pilot study approach was adopted and involved the installation of a pilot plant. The pilot plant was installed in the largest Caribbean water treatment plant, the Sergio Cuevas Water Treatment Plant located in San Juan, Puerto Rico (100 MGD). The treatment units found include a coagulation-flocculation- sedimentation unit, dual-media filters, micro-filtration units, ozonation contact columns as well as a biological filtration unit. The clarification unit can be operated under two different flocculation and settling modes: typical conventional flocculation with lamellar settling and micro-sand ballasted flocculation with lamellar settling. Two identical filtration skids, each equipped with two 8-inch filtration columns, are found at the pilot plant site. One skid is used for conventional mono or dual-media filtration and the another skid is used for biological filtration. The micro-filtration units consist of two different membrane technologies found on the market: pressure vessels and submerged membranes. The ozonation unit consists of an ozone generator, two contact columns connected in series for ozone transfer. Included in the study is the evaluation of the physical bacterial removal through the different treatment steps described. To do so, Bacillus subtilis spores and coliphages are being used as alternate indicators of treatment plant performance because they may more closely mimic the removal of enteric pathogens during treatment processes. The procedure consists of injecting of Bacillus subtilis spores, and coliphages and to evaluate the percent removal at each treatment stage. Molecular fingerprinting is being carried out to track the seed bacteria through the system. Preliminary results have shown a removal range of 76.6-99.9 percent of Bacillus subtilis spores depending on a type of treatment. The ease as well as the apparent specificity of detection of the aerobic Bacillus spores indicate that these microorganisms may be an excellent alternative to currently used indicators of water treatment efficiency.
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Document Type: Research Article

Publication date: 2001-01-01

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