A Win-Win Situation
The Donald C. Tillman Water Reclamation Plant (DCTWRP) in Los Angeles began operation in 1985. The plant’s treatment scheme consists of primary sedimentation, activated sludge, secondary clarification followed by traveling bridge sand filters, a chlorination pathogen removal process and dechlorination prior to water reclamation or discharge. The flow design criteria for the plant are 80 million gal per day (mgd) average dry weather flow (ADWF), 120 mgd dry weather peak flow (DWPF) and 160 mgd peak wet weather flow (PWWF).
In recent years, the traveling bridge sand filters have experienced serious mechanical, structural and performance degradation. Chemical enhancement, as well as repeated shock chlorination, have been necessary to maintain acceptable filter performance. These tertiary filtration issues made it difficult for the Bureau of Sanitation operational and maintenance staff to guarantee long-term performance and reliability, so DCTWRP needed a solution—one that included expanded flow capacity.
After evaluating the options for a resolution, eight AquaDiamond cloth media filters were installed at the plant. These filters were selected because they are specifically designed for retrofitting into existing sand filter beds with minimal modification to the existing civil works. They also can provide more than twice the hydraulic capacity than sand filters with an equivalent footprint, and produce high-quality filtered effluent to meet California’s stringent reuse requirements.
The diamond laterals are covered with 10-micron OptiFiber PES-13 cloth filtration media, which is constructed of polyester pile fibers woven into a polyester support backing material. The cloth media provide an increased filtration surface area with higher solids and hydraulic loadings per square foot compared to sand media. These benefits minimized spatial requirements and construction costs for DCTWRP.
Each AquaDiamond filter is designed to handle an average flow of 12.5 mgd and a maximum flow of 24 mgd. Under these flow rates, the filters must achieve Title 22 California Department of Public Health Water Recycling Criteria, which stipulate that a turbidity daily average effluent must not exceed 2 NTU, while influent filter turbidity values range from zero to 10 NTU. The specifications also required the filter units to run without continuous backwashing with average influent TSS concentrations up to 10 mg/L and maximum TSS concentrations of 17.6 mg/L.
DCTWRP conducted field performance tests on four diamond filters installed during the first phase of the project. The testing ran from Dec. 4, 2009, to Jan. 21, 2010, to confirm compliance of the filters’ performance with design specifications.
The performance tests were successful, and indicated a 240% average increase in treatment capacity while exhibiting comparable solids removal rates at design flow with a superior ability to achieve elevated performance. During a 24-hour test period, average daily backwash rates were low—generally less than 0.45% of the forward flow. No continuous backwashing occurred during the tests.
The AquaDiamond filters are able to consistently achieve reuse quality effluent at the designed hydraulic conditions of 12-mgd-per-filter average flow and 24-mgd-per-filter peak flow.
AquaDiamond Filter Performance Data - DCTWRP
1.3 - 3.6
0.5 - 1.4
2.4 - 14.2
The remaining four filter units went online soon after the successful field performance testing. The AquaDiamond filters continue to meet the expectations of DCTWRP with expanded treatment capacity in a smaller footprint and consistent reuse-quality effluent.