Use of Soil Filtration and UV Disinfection for Advanced Wastewater Treatment

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Abstract

While guidelines exist, currently there are no federal regulations governing treatment requirements for reclaimed water. In their absence, many states have adopted California’s reclaimed water regulations, found under Title 22 of the California Code of Regulations (CCR) as well as the UV Disinfection Guidelines for Water and Water Reuse, published by the National Water Research Institute and the American Water Works Research Foundation in 2003 (NWRI/AwwaRF 2003 Guidelines). These documents provide treatment requirements based on the type of reclaimed water application being proposed (e.g. irrigation, aquifer recharge, streamflow augmentation).

The City of Dinuba, California has been using percolation as a disposal method for their unfiltered secondary wastewater effluent for some time. Now viewed as a resource, the City plans to extract up to 4 mgd of percolated municipal wastewater from recovery wells for use in landscape and golf course irrigation. The extracted effluent will be disinfected through an invessel UV rector to meet Title 22 recycled water criteria for unrestricted landscape irrigation. Title 22 includes limits on turbidity (2 NTU average 24 hour), coliforms (2.2 MPN/100mL 7-day median), and a minimum 5-log reduction of poliovirus during operation.

While not directly written into Title 22, the California Department of Health Services (CaDHS) closely abides by the UV design guidelines in the 2003 NWRI/AwwaRF Guidelines. These guidelines are meant to ensure that UV systems are adequately sized to meet treatment objectives. The guidelines vary depending on the type of treatment prior to UV disinfection. For post media filtration UV systems it is recommended that a UV design dose of at least 100 mJ/cm2 and a design UV transmittance of 55 percent be required for this application. Post membrane filtration, the recommended UV design dose is 80 mJ/cm2 and design UV transmittance is 65 percent.

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