Point Loma Wastewater Treatment Plant
1902 Gatchell Road, San Diego, CA 92106
- 2010 San Diego 301(h) Modified Permit Final Decision Letter (PDF)
- 2010 San Diego 301(h) Modified Permit (PDF)
- Plant Monitoring Reports
- Plant Process (PDF)
- Take a video tour of the PLWTP
Opened in 1963, the Point Loma Wastewater Treatment Plant (PLWTP) treats approximately 175 million gallons of wastewater per day generated in a 450 square mile area by more than 2.2 million residents. Located on a 40 acre site on the bluffs of Point Loma, the plant has a treatment capacity of 240 million gallons per day (mgd).
The PLWTP Operations Building & Visitors Center houses the Control Center which monitors and controls every phase of the treatment process. The facility is staffed 24 hours a day, 365 days a year. Plant operations can also be monitored from Public Utilities Department's Communications Center in Kearny Mesa. The PLWTP Operations Building also houses Process Control Laboratories where samples of wastewater from every stage of treatment are analyzed.
Wastewater moves from Pump Station 2 on Harbor Drive to the top of Point Loma. From there, gravity takes hold and the wastewater (called "influent") flows into the headworks of the plant. The foul air from the influent passes through an odor control system which "scrubs" the foul smelling air with a bleach solution. The scrubbed air then passes through carbon filters before being released. There are 11 other odor control systems throughout the plant that operate during every stage of the treatment process. The wastewater then passes through screens which act as giant rakes to remove materials that would interfere with the treatment process. These materials, called "Rags," are a diverse assortment of paper, plastic, pieces of wood, toys, and vegetable matter.
The wastewater then flows into grit removal tanks, where heavy inorganic particles such as sand, gravel, coffee grounds and eggshells settle to the bottom. "Rags" and grit are dewatered and trucked off site for disposal.
Following grit removal, the wastewater is pumped into sedimentation tanks where organic solids settle to the bottom of the tanks and "scum" (primarily cooking grease and oil) float to the surface. Chemicals such as ferric chloride and organic polymers are added to the wastewater to help waste particles bond together in large enough mass to settle out. At this point, approximately 80 percent of the total suspended solids in the water have been removed. After a final screening, the treated wastewater, called "effluent," is now ready to be discharged to the ocean through the 4.5 mile long Ocean Outfall.
The Point Loma Ocean Outfall was built in 1963 for the discharge of treated wastewater into the ocean. In 1993, the Outfall was extended from a length of two miles off the coast of Point Loma to its present length of 4.5 miles. Twelve feet in diameter and operating via gravity-feed, the Outfall ends 320 feet below the surface in a Y-shaped diffuser to ensure wide dispersal of effluent into ocean waters.
The scum is skimmed off the surface of the water, dewatered and taken off site for disposal. The organic solids ("sludge") which have settled out of the wastewater are pumped into one of the eight digesters on site where they are reduced in volume through a heat and bacterial process similar to human digestion. After about two weeks, this digested sludge is pumped from Point Loma through a 17 mile pipeline to the Metro Biosolids Center for further processing.
Methane gas is a by-product of the digestion process. The gas is removed from the digesters and is used to power two Caterpillar engines in the plant's Gas Utilization Facility. These two engines supply all of the plant's energy needs, making the Point Loma Wastewater Treatment Plant energy self-sufficient. The plant sells the excess energy it produces to the local electricity grid, offsetting the energy costs at pump stations throughout the City. The plant also takes advantage of its location on a cliff's edge by operating a hydroelectric plant driven by effluent dropping 90 feet into the Outfall. This additional power is also sold to the local energy grid.
In November 1995, the City of San Diego received a modified permit (also called a "waiver") from Secondary Treatment requirements of the Clean Water Act. This modified permit was renewed in September 2002, and again in June 2010. Through a combination of factors, including industrial source control, Advanced Primary Treatment of wastewater, a deep ocean outfall and comprehensive environmental monitoring, both the Environmental Protection Agency and the Regional Water Quality Control Board agreed that the PLWTP fully protects the ocean.
The Point Loma Wastewater Treatment Plant recently received its 16th Gold Award from the Association of Metropolitan Sewerage Agencies for its 16th year of complete compliance with all Federal and State regulations.