American Canyon is a city of 20,000 located in Napa County, Calif. Its water reclamation facility (WRF) was commissioned in 2001 as one of the first membrane bioreactor plants (MBR) in the U.S. MBR filtration combined with disinfection produces a tertiary recycled water product with multiple non-potable uses.
The recycled water increases the city’s water supply portfolio by providing a reclaimed water source. In conjunction with producing the recycled water, the city launched the infrastructure plans to make the water available.
As effective as the bioreactor membranes are, they are sensitive to debris buildup. As debris buildup occurs, the filtration capability of the membranes is reduced. The membranes can be damaged by the extensive cleaning required to maintain an MBR system being overwhelmed by debris. A typical cleaning of a single membrane cassette at American Canyon took two to three workers half a day and produced 10 gal of debris.
While the membranes are the heart of an MBR plant, the preliminary phase, or headworks, of a plant will determine the efficiency of the process. In this phase, mechanical screens remove debris from the wastewater stream as it enters the plant.
American Canyon had traditional screw screens at its headworks for many years. When the screw screens required replacement, plant personnel looked for a screen with higher debris capture. They chose the Enviro-Care SAVI Flo-Drum VSA1400 with independently verified 86% capture. This product is a perforated plate, in-channel, rotating drum screen with 2-mm openings. It was installed in 2016 and replaced two of the screw screens. Since the plate was installed, sampling of the screen effluent has shown that nothing larger than a 2-mm particle has been found flowing into the MBR system.
American Canyon WRF wants to insure that all flow going to its MBR system in the future will first pass through a high-capture screen. To meet this commitment, it recently purchased two more Flo-Drum screens to complete its headworks.