AWWA JAW6787

In this article, the authors report on recent outbreaks of waterborne diseases such as cholera and typhoid fever. Each one of these outbreaks can be attributed to the lack of filtration or to faulty operation and maintenance of the process. Pilot plant data and results from full-scale operation are presented to illustrate the effectiveness of various forms of filtration in reducing microbial populations to concentrations that are easily controlled by disinfection. Slow sand filters, rapid sand filters, and diatomaceous earth (DE) filters are discussed relative to their ability to remove coliforms, reduce total microscopic count, remove viruses, and remove Giardia cysts. All three filters are capable of removing bacteria, viruses, and cysts if designed and operated properly. The authors caution that operators should recognize the vulnerability of filters, especially their lowered efficiency for removing bacteria, virus, and cysts, in the 30 minutes to one hour after backwashing. Includes 25 references, tables, figures.