The primary objective of the AWTF is to reduce total dissolved solids, silica, organics, and other undesirable constituents such as contaminants of emerging concern. RO currently is the best available technology for removal of dissolved constituents. Water treated by RO can be blended with tertiary effluent from the WPCP to reduce the concentrations of these constituents and to improve the overall quality of recycled water.
The presence of foulants, such as particulate or suspended solids, could adversely affect performance of the RO membrane. Since the mid 1990s, microfiltration has become the industry standard practice for pretreatment of RO feed in wastewater applications because of its ability to consistently provide a near-absolute barrier to particulate material. UV disinfection will be provided at the AWTF to fulfill Title 22 disinfection requirements (California Code of Regulations) for recycled water.
Operation of the AWTF
Two different strategies were developed to provide additional flexibility for the South Bay Water Recycling system and to increase the tertiary filter capacity at the WPCP during winter periods. The summer period is defined from May through November and the winter period from December through April.
Summer Operation
Under the summer operation mode, nitrified secondary effluent from the WPCP will be conveyed to the AWTF where it will be pretreated by MF, then demineralized through the RO process, and disinfected through UV disinfection. The product water will be stored in a 2.25 million gallon storage tank and flow-paced, using a flow control valve, to the SBWR Transmission Pump Station to blend with WPCP tertiary effluent.
Winter Operation
The AWTF will be able to meet the low recycled water demand during the winter period without blending WPCP tertiary effluent. It also will be capable of generally meeting a lower SBWR TDS goal of 400 mg/L. This would increase the tertiary filter capacity at the WPCP during winter periods. The initial AWTF treatment capacities alone may not be sufficient to meet projected maximum day winter demands for year 2015 and 2020. If so, tertiary effluent from the WPCP would supplement flows from the AWTF.
Estimated Cost
The current construction cost is $42.38 million plus the value of the land owned by the WPCP, which is leased to the district for $10/year. In April 2007, the California Department of Water Resources awarded an approximately $3 million state grant to this project. In addition, the district and the city recently received an additional $8.25 million in federal funding through the American Recovery and Reinvestment Act, administered by the United States Bureau of Reclamation.
