Implementing NWRI Guidelines for UV Disinfection for Water Reuse: Pitfalls and Practical Advice

The City of Manteca (City) discharges secondary effluent to the San Joaquin River near Stockton in Northern California. The Manteca Wastewater Quality Control Facility (WQCF) is a 7.5 mgd activated sludge-biofilter plant that has been recently upgraded to full nitrification. Chlorination and dechlorination of secondary effluent has been accomplished historically with chlorine and sulfur dioxide gas utilizing a converted sedimentation basin as a chlorine contact tank. Because of poor hydraulics and a nitrified effluent, satisfying NPDES coliform requirements consistently with conventional chlorination practices has proven difficult. As part of a $47 million Phase III expansion and upgrade of the Manteca WQCF, the City will replace the existing chlorine contact basin with tertiary filtration and UV disinfection. Following completion of the Phase III Project, the plant capacity will increase to 10 mgd and tertiary effluent will be suitable for unrestricted reuse in accordance with California Title 22 reclamation criteria. This paper will focus on both pitfalls and practical advice for developing a design acceptable to the California Department of Health Services (DHS) while complying with the National Water Research Institute (NWRI) guidelines for UV disinfection. Discussion topics will include the following:Facility and reliability requirements dictated by NWRI guidelinesDevelopment of design criteria for full-scale UV disinfection systems including the role of pilot studies and wastewater characterization activitiesSelection of upstream filtration processes to ensure effective disinfectionConsultation and coordination with UV equipment suppliers and DHS staff during project planning, design, and implementationOptimizing facility layout to facilitate expansion and routine maintenance activitiesPower, control, and instrumentation issues associated with several thousand UV lamps arranged in multiple banks in dual disinfection channelsProcurement practices and implementation suggestions to meet a fast-track construction schedulePlanning and design of a UV disinfection system for the City has evolved over a three-year period during which application of NWRI guidelines has been in flux. Activities to date have included numerous site visits to operating UV facilities in the United States and Europe, bench scale and pilot scale feasibility studies, formal evaluations of alternative UV systems, liaison with regulatory staff, preparation of procurement documents, and completion of final design documents. The UV system at the Manteca WQCF will be capable of treating nearly 20 mgd of filtered secondary effluent with a low pressure-high intensity system. The $5 million disinfection facility will begin construction in early 2005 with completion scheduled in mid-2006.