TROUBLESHOOTING AND OPTIMIZING THE PERFORMANCE OF A UV DISINFECTION SYSTEM APPLIED TO FILTERED EFFLUENT

An evaluation of UV disinfection system operations at the City of Santa Rosa's Laguna Subregional Water Reclamation Facility (Laguna WRF) was conducted because of total coliform excursions in the last 2 years. Several operational modifications have been implemented to ensure effective disinfection and to minimize the impacts of particles on disinfection performance. For example, a mechanical propeller mixer located upstream of the UV channels, previously used for chlorine mixing, has been turned on in an attempt to reduce the mean size of particles in the filtered effluent. Despite these actions, the Laguna WRF continues to experience periodic total coliform excursions. Recently, potential uneven flow split between channels has been identified and is being corrected by adjusting the effluent overflow weirs. Subsequent investigations may include assessing the extent of particleassociated coliform bacteria and optimizing the filter media configuration to further reduce mean particle size.