Pilot-Scale Evaluation of Cloth Media Filtration Technology

The Sanitation Districts of Los Angeles County (Districts) operate 11 wastewater treatment facilities. Ten of these facilities are classified as water reclamation plants (WRPs) producing approximately 200 million gallons per day (MGD) of reclaimed water suitable for reuse. The Districts' Palmdale WRP treats approximately 10 MGD using primary treatment followed by stabilization ponds. This facility is currently undergoing design upgrades to tertiary treatment with biological nitrogen removal. The Districts initially planned to design and operate deep-bed mono-media (anthracite) gravity filters. However, due to potential capital and operating cost savings, cloth media filters (CMFs) were subsequently considered. While the Districts have extensive experience with the operation and performance of mono-media filters, CMFs are a relatively new technology without a long track record of successful operation. Based on preliminary information gathered by Districts' staff, potential performance issues were identified that could make this technology less attractive when compared to mono-media filters. One issue was the potential for matting of the CMFs with polymer used to enhance secondary clarifier performance. Polymer addition is typically employed at Districts' facilities and is planned for the Palmdale WRP. There is also a lack of well documented data on CMF effluent particle size distribution (PSD) compared to conventional granular media filtration processes. If CMF effluent PSD is relatively poor, it may impact disinfection performance, in particular UV disinfection. To address these issues and to evaluate the overall performance of this technology, pilot-scale testing was conducted in January of 2007. This paper summarizes the results of the pilot testing.