Treatment Facilities
Northeast Treatment Plant (NEP)
The current NEP treatment processes include: influent pumping, screening, grit removal, primary clarification, activated sludge, trickling filters, secondary clarification, trickling filter clarification, nitrification towers, cloth media filtration, and chlorination/dichlorination. The NEP rated design average flow (DAF) is 17.3 MGD with a rated design maximum flow (DMF) of 34.6 MGD, and excess flows treatment up to 22.75 MGD. Total treatment design capacity for all processes is 57.35 MGD.
Solids management facilities at the NEP include gravity belt thickeners to thicken waste activated sludge (WAS); a sludge receiving station that receives thickened waste activated sludge (TWAS) from the UCSD Southwest Plant (SWP), industrial WAS, high strength waste (HSW) from grease-hauling trucks and a small amount of food waste from the University of Illinois–Champaign-Urbana Grind2Energy program; a sludge blending tank that blends sludge from the receiving station with NEP TWAS; four anaerobic digesters; a digested sludge storage tank; and three centrifuges to thicken the digested sludge. The dewatered biosolids meet Class B biosolids requirements and are land applied as soil amendment to agricultural fields.
Digester gas produced in the anaerobic digesters is currently used in combined heat and power (CHP) engines to cogenerate electricity and heat for the NEP, as well as to export electricity to the NEP grid. A small fraction of the digester gas produced is burned in a gas flare.
Southwest Treatment Plant (SWP)
The existing SWP consists of headworks, secondary treatment, tertiary treatment, disinfection and excess flow treatment. The current design average flow is 7.98 MGD with a peak design flow of 17.25 MGD. The SWP can treat a maximum flow of 48 MGD, split into 28 MGD through excess flow and 20 MGD through the main treatment process when utilizing the advanced treatment bypass (ATB).
The headworks consist of four raw sewage pumps, two fine screens, and two aerated grit tanks.
Secondary treatment consists of two anaerobic selector basins, five aerobic activated sludge basins, and five secondary clarifiers. Tertiary/Advanced treatment consists of two nitrification towers and five cloth disk filters. No disinfection of the main plant effluent was required or provided from 1989 thru 2020. Prior to 1989 disinfection was accomplished through a chlorine contact tank using chlorine gas. Waste activated sludge is thickened through gravity belt thickeners. Thickened WAS is stored on site in a glass lined steel tank before being trucked to the District’s NEP for additional treatment and resource recovery. Excess flow treatment is completed through two excess flow clarifiers including disinfection chemical feeds. The excess flow is a blended discharge with the main plant effluent. Phosphorus removal is achieved solely through biological phosphorus removal. The plant does not currently utilize any primary treatment.