Prior to the upgrade detailed in this case study, the wastewater treatment plant (WWTP) serving the city of Corcoran, California, employed a conventional aerated/facultative (A/F) lagoon to treat primary effluent. The conventional lagoon was ineffective and the effluent often exceeded the discharge limits of 40 mg/L for five-day biochemical oxygen demand (BOD5) and 45 mg/L for total suspended solids (TSS). In 2001, the plant exceeded the average monthly discharge limits four times for BOD5 and nine times for TSS. Most of the violations occurred during the summer months.
In spite of effluent reclamation on land, the California Regional Water Quality Control Board (CRWQCB) insisted that the plant adhere to the discharge standards. Frequent notices of violation (NOV) were sent by the CRWQCB to the city of Corcoran regarding the ineffective plant. In response, the city chose to upgrade the existing A/F lagoon using a dualpower, multicellular aerated (DPMC) lagoon system to bring the plant into compliance. The use of a DPMC lagoon as a secondary treatment process is innovative. This paper describes and analyzes the project and its results.