7.5. The Challenge of Water Treatment Plant Design

When water treatment engineering first evolved in the early part of the twentieth century, its main goal was to ensure that infectious organisms in drinking water supplies were removed or inactivated. Chlorination and filtration practices were applied with tremendous success to the point that major death-causing waterborne disesase outbreaks in the United States were virtually eliminated by the 1930s (Lane, 2005). As a result, for engineers trained in the 1960s, 1970s, and 1980s, both education and industry belief were that all concerns of microbiological contamination in surface waters could be eliminated by providing filtration to produce water of sufficient clarity and then chlorinating. Groundwater was thought to be already filtered, requiring only chlorination to maintain a distribution system residual. Any additional treatment was generally considered necessary only to address non-health-related parameters, such as excessive hardness or discoloration caused by iron and manganese (Lane, 2005). In the 1970s and 1980s a new drinking water concern arose: the potential long-term health risks posed by trace amounts of organic compounds present in drinking water. In the 1990s the old concern about microbiological contamination reemerged as a primary focus of water treatment engineers (Lane, 2005).Recently, new health effects research has led to reconsideration of the safe drinking water concentrations for several inorganic contaminents. In the United States the MCL for arsenic was reduced dramatically from 50 to 10 ppb. This has created new treatment challenges for many utilities (Lane, 2005). The effects of planned and unplanned recycling of municipal wastewater into raw water sources are gaining increased attention. A new class of constituents emanating from modern human life has been discovered in trace amounts in water supplies. These include personnel hygiene product and pharmaceutical compounds. Additionally, new “emerging” pathogens are being discovered and their potential occurrence and treatability in water supplies evaluated. The potential impacts of these developments on the design requirements for water treatment facilities have yet to be determined. In the last decade, new water treatment technologies have continued to be developed and older technologies improved. Finally, since September 11, 2001, there has been increased recognition of the vulnerability of municipal water systems to acts of terrorism and vandalism. New approaches to siting and designing critical system components, including water treatment plants, are evolving to reduce his vulnerability (Lane, 2005).