The Watercare Mangere Wastewater Treatment Facility, which treats wastewater from the greater Auckland New Zealand region, is undergoing a major expansion/upgrading to add advanced treatment and disinfection prior to discharge into a harbor. One important goal of this project is to protect the receiving water from microbial contamination. Since sufficient information on the fate of various microorganisms through wastewater treatment plants in New Zealand was not readily available, extensive pilot- and bench-scale studies were undertaken to develop specific design criteria for the treatment and disinfection systems. The specific objective of this study was to evaluate the removal and inactivation of enteric pathogens and other microbial indicators through treatment processes that employs UV irradiation as a final disinfection process. The removal of indicator organisms through secondary treatment was typically between 2.5-log (99.7% removal) and 2.8-log (99.8% removal) for fecal coliforms and enterococci, respectively. Indigenous F-specific bacteriophage exhibited a mean removal of 1.6-log (i.e. 97.7% removal) and Clostridium perfringens spores showed a mean removal of 1.3-log (i.e. 95% removal). The UV dose required to achieve a one log reduction in the concentration of indigenous F-specific bacteriophage was found to be approximately 20 mWs/cm2 per log removal. The concentration of enterovirus and adenovirus were consistently reduced to the limit of detection (1 TCID50/100L) at UV doses of 35 to 40 mWs/cm2 and 40 to 45 mWs/cm2, respectively. Clostridium perfringens spores were the most resistant indicator organisms, being reduced to less than 200 MPN/100 mL at a UV dose of 75 mWs/cm2.
Decentralized wastewater treatment is frequently used worldwide in those locations where additional water supply and shortages of potable water make reuse of highly treated wastewater more acceptable. Treated wastewaters often are less costly than development of other potable water supplies.The use of decentralized treatment facilities, which are commonly referred to as 'scalping' or 'sewer mining' facilities, typically produce a high quality level of wastewater effluent. Irrigation usage is often accomplished with only secondary levels of treatment followed by filtration and high levels of disinfection. Other indirect and direct potable water schemes require very extensive process configurations, including ultra filtration, reverse osmosis, and advanced oxidation. This paper will discuss several of the drivers for decentralized wastewater treatment, such as irrigation, water supply augmentation, stream flow augmentation, and industrial reuse. Several case histories of various wastewater treatment plants around the world will be presented, including design criteria, effluent standards, and other descriptive information.
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