California WWTP increases its energy efficiency with new UV equipment
The American Canyon (Calif.) Wastewater Treatment Plant (WWTP) began operation in October 2002 with then-state-of-the-art secondary treatment that featured one of the nation’s first uses of tandem membrane bioreactor/UV disinfection in the process chain. As with many other early membrane bioreactor treatment plants, this facility had a number of design deficiencies, which became apparent over time as the equipment aged, the utility’s customer base expanded and more stringent environmental regulations were enacted.
By 2011, power bills for the plant had reached $27,000 per month ($324,000 annually), imposing a strain on the municipality’s $5-million wastewater utility fund budget. In an effort to contain costs, the City of American Canyon—located 35 miles northeast of San Francisco in the Napa Valley—took part in the California Wastewater Process Optimization Program (CalPOP) sponsored by Pacific Gas & Electric (PG&E). The program helps wastewater utilities reduce their energy usage through energy efficiency improvements, allowing PG&E to meet growing customer demand.
A CalPOP audit team worked with the WWTP staff, the local office of Carollo Engineers and a Xylem Wedeco field rep to identify opportunities for energy savings at the plant, including improvements to the existing 144-lamp/single channel Wedeco TAK 55 UV disinfection system, its dose control and other UV system components that were reaching the ends of their expected lives.
The audit is one of the services offered through Xylem TotalCare, a comprehensive portfolio of services that ensures equipment from all Xylem brands—Flygt, Godwin, Leopold, Sanitaire and Wedeco—will always run at its best.
At the time of the TotalCare audit, the UV system was operating all three banks of UV lamps in the channel at full power instead of modulating the arrays. Recommendations included a complete re-lamping with Wedeco’s newer, more energy-efficient Ecoray UV lamps and ballasts; a PLC processor enabling monitoring by the plant’s SCADA; improved instrumentation; and a transmissivity monitor in the influent channel, along with UV intensity sensors in the dosing zones.
Energy savings from the UV system updates were conservatively projected to reach 50%. However, with the upgrades, added modulation and power use on balanced demand, the Wedeco TAK 55 UV disinfection system now achieves the desired disinfection with only one bank operating at only half power. The result has been an up to 80% reduction in energy use.
Data collection for measurement and verification occurred between October 28 and November 13, 2013, revealing an estimated annual savings of $26,511 (314,624 kWh) for the UV system alone. Given the initial UV upgrade cost of $124,586, the improvements will generate a simple payback within 7.1 years, or 6.2 years when the cash incentive of $31,915 provided through CalPOP for the UV upgrade is deducted from the capital cost.