Archaea Augmentation and Coliform Reduction at an Arizona Water Reclamation Facility

Wastewater contains many types of human enteric organisms that are associated with various waterborne diseases, and the destruction of these organisms is an essential process design consideration to meet applicable state and federal standards intended for the protection of public health. The selection of a disinfection process for a water reclamation facility is further driven by extremely low-level compliance targets with regard to total and fecal coliform, biological nutrients, and disinfection by-products (DBPs). In 2001, the City of Phoenix installed an open channel, medium pressure ultraviolet disinfection system at the Cave Creek Water Reclamation Plant, to specifically address the State of Arizona's low-level coliform and DBP regulations. Since the installation, UV system performance has been relatively effective with regard to effluent compliance. However, there have been difficulties, as the system has been encumbered with lamp and ballast failures, resulting in higher than expected operational and maintenance effort and cost. To increase the overall reliability of the disinfection system, the City currently feeds sodium hypochlorite after UV disinfection as a dual barrier to consistently meet compliance regulations. The City embarked on a study to determine the best means of providing a disinfection system with a high degree of reliability, while also providing the required flexibility for multiple means of effluent reuse and disposal. An assumption of the study was that an iterative pre-treatment process that reduces indicator organisms by one or more log cycles would theoretically reduce the disinfection burden. A year-long, full-scale pilot study was performed at the Cave Creek WRP that showed Archaea bio-system augmentation consistently drove total coliform and fecal coliform counts down one or more log cycles in the activated sludge plant without reducing plant operations efficiency, modifying procedures, or increasing operating costs.