Background

The City of Holtville, through its Public Works Department, is responsible for providing wastewater collection and treatment services. In 2013, wastewater collection coverage was estimated at more than 98% through 1,372 residential and commercial sewer connections. All of the collected wastewater is treated at the city’s wastewater plant, which currently uses a Modified Ludzack-Ettinger (MLE) treatment system and has a treatment capacity of 0.85 million gallon a day (mgd). The plant provides service to city residents, residents located
immediately outside the incorporated city boundaries and residents of the Barbara Worth Country Club located within an unincorporated area of Imperial County. Current flows into the plant average 0.65 mgd.

The plant has experienced persistent problems with effluent toxicity resulting from high ammonia levels associated with high organic loadings. The non-compliant effluent impacts the Pear Drain, Alamo River and the Salton Sea, which are listed as impaired water bodies for nutrients. Its current National Pollutant Discharge Elimination System (NPDES) Permit contains stringent ammonia nitrogen removal requirements, with allowable limits for ammonia set at a maximum daily concentration of 3.6 milligrams/liter (mg/L) and an average monthly concentration of 1.9 mg/L. Between February and October
2013, the plant’s daily ammonia concentrations exceeded the maximum limit on a monthly basis with readings ranging from 5.04 to 16.24 mg/L. Since the existing trickling filter process has limited capacity to remove ammonia, the plant requires extensive upgrades and
rehabilitation in order to comply with the NPDES ammonia discharge limits.

In addition, the existing operations building is approximately 40 years old and requires extensive modification to meet various code requirements and energy efficiency guidelines.

Description

The project consists of rehabilitating and upgrading the wastewater treatment system with a BIOLAC® Wave Oxidation System, which includes the installation of an automatic bar screen and a single-cell activated sludge system with high-efficiency moving and flexible aeration chains to improve treatment effectiveness. Facilities to be rehabilitated include the effluent pump stations, UV disinfection system, and storm water tanks, and the operations building will be replaced.

Benefits

The project will improve the quality of the effluent discharged from the plant in compliance with federal and state requirements for ammonia and other pollutants, thereby contributing to the protection of aquatic ecosystems and helping to improve water quality conditions in the Pear Drain, Alamo River and Salton Sea.