August 2007, Vol. 19, No.8

Plant Profile

San Diego


Opened in 1963, the Point Loma Wastewater Treatment Plant treats approximately 175 mgd (662,000 m3/d) of wastewater generated in a 450-mi2 (1165-km2) area by more than 2.2 million residents in 12 municipalities. Located on a 40-ac (16-ha) site on the Point Loma bluffs in San Diego, the advanced primary treatment plant has a capacity of 240 mgd (908,400 m3/d).

Following screening and grit removal in the plant’s headworks, 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. Wastewater is pumped into sedimentation tanks for the solids to settle. Point Loma has 12 primary sedimentation tanks, eight of which are used on a regular basis. Each basin is 60-ft (18-m) wide by 22-ft (6.7-m) long by 16-ft (4.9-m) deep and holds about 1.6 million gal (6 million L). The plant’s National Pollutant Discharge Elimination System (NPDES) permit requires that the plant remove 80% of the total suspended solids (TSS) on a monthly basis and 58% of the biochemical oxygen demand (BOD) on a calendar year basis. For calendar year 2007 through May, the daily average TSS removal was 89% and the daily average BOD removal was 67%.

Since 1995 the plant has operated under a modified permit that eliminates secondary treatment requirements usually required by the Clean Water Act. Because of the plant’s industrial source control, advanced primary treatment of wastewater, a deep ocean outfall, and comprehensive environmental monitoring, both the U.S. Environmental Protection Agency and the California Regional Water Quality Control Board agreed that the Point Loma Plant fully protects the ocean.

Effluent is discharged by gravity through a 4.5-mi (7.2-km) ocean outfall 320 ft (97 m) below the surface. In 1993, the outfall was extended from a length of 2 mi (3.2-km) miles off the coast of Point Loma to its present length of 4.5 mi (7.2 km). Twelve feet (3.7 m) in diameter, the outfall ends in a Y-shaped diffuser to ensure wide dispersal of effluent into ocean waters.

Approximately 1 mgd (3785 m3/d) of raw solids settle out in the sedimentation tanks and are pumped into anaerobic digesters. Currently, seven out of eight digesters, each with a capacity of 3.6 million gal (13.6 million L), are in use as primary digesters with the eighth digester utilized as a storage tank. The raw solids undergo anaerobic digestion for approximately 30 days to meet Part 503 Class B sludge requirements. The digested solids are then pumped from Point Loma through a 17-mi (27-km) pipeline to the Metro Biosolids Center for further processing.

Methane gas from the digesters 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 any excess energy it produces to the local electricity grid, offsetting the energy costs at pump stations throughout San Diego. In addition, the effluent piping system on the plant’s north effluent outfall circuit has an elevation drop of 90 ft (27 m) allowing the facility to operate a hydroelectric plant. This additional power is also sold to the local energy grid.

Point Loma has received nine Gold Awards (one for each of the last 9 years) from the National Association of Clean Water Agencies (Washington, D.C.) for its complete compliance with all federal and state regulations.

The Point Loma Wastewater Treatment Plant will host a tour of its facility during WEFTEC.07. The tour is scheduled for 12 p.m. to 4 p.m. on Wednesday, Oct. 17.

City of San Diego Metropolitan Wastewater Department Environmental Monitoring and Technical Services Division Laboratory

Opened in 2003, the City of San Diego’s Environmental Monitoring and Technical Services Laboratory supports the city’s Ocean Monitoring Program. The 3440-m2 (37,000-ft2) facility houses 52 scientists and support staff who perform a variety of functions, including marine sampling and sediment analysis.

The ocean monitoring program is conducted by staff from three different sections of the Environmental Monitoring and Technical Services Division: Marine Biology and Ocean Operations (e.g., marine biologists, ecologists, taxonomists, toxicologists); Marine Microbiology and Vector Management (e.g., biologists, entomologists); and Wastewater Chemistry Services (e.g., chemists). The Wastewater Chemistry Services division is located about 15 mi away with the city’s Water Department chemistry lab.
Those staff members rely on two of the program’s greatest assets, the department’s ocean monitoring vessels, to help collect samples for testing. The 48-ft (14.6-m) Oceanus and the 42-ft (12.8-m) Monitor III are used to conduct more than 200 sampling days each year. These boats collect samples of seawater, sediments, and marine life (fishes and invertebrates) from an area encompassing more than 300 mi2 of coastal waters.
The City of San Diego Metropolitan Wastewater Department Environmental Monitoring and Technical Services Division Laboratory uses the 48-ft (14.6-m) Oceanus (pictured) and the 42-ft (12.8-m) Monitor III to collect samples covering more than 300 mi2 of coastal waters.
(Photo by City of San Diego Metropolitan Wastewater Department)
The sampling area stretches from Del Mar, Calif., to northern part of the Baja California peninsula in Mexico, according to Alan Langworthy, deputy director of the laboratory.

Staff members use specialized oceanographic instrumentation, standard benthic and epibenthic sampling gear, a remote operated vehicle (ROV), and dive surveys to collect the wide array of information necessary to define the ecological health of the ocean environment. They also identify potential health concerns associated with the recreational use of San Diego’s coastal waters, and evaluate the structural integrity of the Point Loma Wastewater Treatment Plant outfall pipes. Specific sites are monitored to assess water quality conditions, sediment quality, the health and status of bottom dwelling marine fishes and invertebrates, and the accumulation of contaminants in tissues of marine fishes.

The scientists look for both spatial and temporal changes and differences in water quality conditions (e.g., bacterial concentrations, physical and chemical water column parameters), sediment quality (e.g., grain size distribution, chemical contaminant concentrations), and the health and status of marine invertebrate and fish communities living on or near the seafloor. They compare those findings to what are considered natural or reference conditions and evaluate whether or not significant environmental changes have occurred.

If changes or differences are present, they also attempt to evaluate whether these are related to manmade causes, such as wastewater discharge, stormwater runoff, or dredging activities, or if natural factors, such as storms, current patterns, or El Niño-La Niña events are the culprit.

A tour of the Environmental Monitoring & Technical Services Laboratory is scheduled during WEFTEC.07. The tour will be held on Monday, Oct. 15 from 9 a.m. until 1 p.m.

Padre Dam Municipal Water District Santee Water Recycling Facility and Santee Lakes Recreation Preserve

The Padre Dam Municipal Water District (Santee, Calif.) operates a 2-mgd (7600 m3/d) water recycling facility (WRF) that produces effluent that meets California’s Title 22 reuse requirements. Half of the effluent is sold to irrigation and commercial users, and the other half flows into the Santee Lake system. The current lake system consists of a series of seven lakes flowing from one to the next from the treatment facility on the north. Any excess water flows into the San Diego River with a discharge permit.

The system receives 5.2 mgd (19,700 m3/d) from the communities of Santee, El Cajon, and Lakeside. The WRF captures 2 mgd (7600 m3/d) for treatment and passes the rest on to the Point Loma Wastewater Treatment Plant in San Diego. The original facility was built at the south end of the property in 1959 as a way to allow local development without paying to transport wastewater to the San Diego Metro system. The lakes were built one at a time from south to north to use as oxidation ponds for part of the treatment. Percolation beds were also constructed with an underdrain system to collect the processed water to put into the lakes.

The Padre Dam Municipal Water District Water Recycling Facility uses its effluent for irrigation and commercial reuse and to maintain the seven lakes of the Santee Lakes Recreation Preserve. The treatment facility’s effluent meets California’s restrictive Title 22 requirements for water reuse. (Photo by Padre Dam Municipal Water District) Eventually the recycled water was deemed clean enough by the health department and Regional Water Quality Control Board to allow public access for boating, fishing, picnics, and other activities.

In 1967, the facility was moved 3 mi (4.8 km) north to its current location and upgraded to 1-mgd (3800 m3/d). Three oxidation ponds totaling 40 million gal (151 million L) were added for the secondary treatment process as well as 11 percolation ponds for the effluent. After passing through percolation ponds, the water was captured from underdrains, chlorinated and dechlorinated, and released to the lakes. In 1997, an upgrade in size and processes brought the facility to 2 mgd (7600 m3/d) and Title 22 compliance. The plant no longer needs the oxidation and percolation components of the system. The oxidation
ponds, now used for storage, enable the district to meet recycled water demands in the summer.

Now, influent passes through two rectangular sedimentation tanks, a five-stage Bardenpho biological nutrient removal process, two rectangular secondary sedimentation tanks, two flocculation–sedimentation tanks for aluminum sulfate injection, coagulation, and sedimentation via lamella plate settlers, four denitrification filters, and a chlorine (gas) contact tank for disinfection.

The facility’s effluent is typically far cleaner than it is required to be by the Title 22 standards. For example, while its biochemical oxygen demand limit is set at 15.0 mg/L, the facility averages less than 2.0 mg/L. Likewise, total suspended solids are permitted at 15 mg/L, but the actual average concentration is only 1.03 mg/L.

The facility now is conducting a feasibility study on expanding the plant to 4 mgd (15,000 m3/d) to keep up with local recycled water demands. It is also part of a regional effort to expand the facility further and provide advanced treatment (microfiltration, reverse osmosis, ultraviolet disinfection) to provide a new raw water source for a groundwater recharge effort under study.

For more information on the district, see For more information on the Santee Lakes, see

The Padre Dam Municipal Water District Santee Water Recycling Facility will host a tour of its facility during WEFTEC.07. The tour is scheduled for 9 a.m. to 1 p.m. on Wednesday, Oct. 17.

City of San Diego South Bay Water Reclamation Plant

The South Bay Water Reclamation Plant is located near the border of Mexico in the Tijuana River Valley. The 15 mgd (56,775 m3/d) plant relieves a significant interceptor system and provides local wastewater treatment services and reclaimed water to the southernmost region of San Diego. Its average flow is between 6 and 10 mgd (22,700 and 37,900 m3/d). The plant, which opened in May 2002, incorporates the newest technologies, including UV disinfection and strict odor control measures.

Throughout the plant, fans draw the foul air from the surface of the wastewater. Scrubbers spray a bleach solution through the air, neutralizing odor-causing sulfide compounds. The scrubbed air then passes through carbon filters that remove any additional odors before the air is released into the atmosphere.

Influent passes through bar screens and grit chambers on its way to the plant’s five primary clarifiers. Each clarifier can hold up to 179,600 gal (679,700 L). The flow passes through anoxic chambers on its way to eight aeration basins. The total aeration basin volume is about 5.1 million gal (19.3 million L). After secondary clarification in nine tanks, each with a volume of about 292,000 gal (1.1 million L), the secondary effluent is split.

Between 3 and 5 mgd (11,400 and 18,900 m3/d) of the flow undergoes tertiary treatment for reuse. In tertiary treatment, anthracite coal beds filter any remaining solids and ultraviolet light inactivates pathogens. At this stage the now-reclaimed water meets California’s Title 22 full body contact requirements.

The flow that it not reclaimed is discharged into the ocean though the South Bay Ocean Outfall. Located near Imperial Beach, the South Bay Ocean Outfall extends approximately 3.5 mi (5.6 km) offshore and discharges effluent approximately 100 ft (30 m) deep. A tunnel-boring machine was used to excavate the tunnel for this project. The tunnel has an 11-ft (3.4-m) diameter and is 19,000 ft (5800 m) long. Barges were used as platforms to trench the ocean floor, install pipe, and then cover the 1.5 mi (2.4 km) of exposed pipeline with more than 400,000 ton (363,000 tonne) of rock to protect the outfall from ocean waves and ship anchors.

Both primary and secondary solids are returned to the sewer system and sent to the Point Loma Wastewater Treatment Plant for processing.

The South Bay Water Reclamation Plant will host a tour of its facility during WEFTEC.07. The tour is scheduled for 9 a.m. to 1 p.m. on Tuesday, Oct. 16.

City of San Diego North City Water Reclamation Plant

The North City Water Reclamation Plant (NCWRP) is the first large-scale water reclamation plant in San Diego’s history and part of the single largest sewer system expansion in the area in more than 35 years. This state-of-the-art facility can treat up to 30 mgd (113,600 m3/d) generated by northern San Diego communities. The plant relies on a series of treatment and purifying steps using the latest technologies to supplement the water supply of the region.

Reclaimed water produced at NCWRP is distributed throughout the northern region of San Diego via an extensive reclaimed water pipeline. More than 79 mi (127 km) of distribution pipelines are installed in Mira Mesa, Miramar Ranch North, Scripps Ranch, University City, Torrey Pines, Santaluz, and Black Mountain Ranch to provide reclaimed water for irrigation, landscaping, and industrial use. NCWRP also provides reclaimed water for the City of Poway. Reclaimed pipelines, sprinkler heads, meter boxes, and other irrigation equipment are color-coded purple to distinguish reclaimed water pipes from drinking water systems.

Influent enters the plant through an 84-in. (2100-mm) pipeline beneath Interstate 805 and flows into North City’s influent pump station. Four pumps at the influent pump station push the wastewater up 90 ft (27 m) to the headworks for bar screening and aerated grit removal.

During the 90 minutes the flow spends in the primary sedimentation tanks, about 99% of the settleable solids, 50% of the suspended solids, and 25% of the biological oxygen demand (BOD) are removed from the water.

Following aeration and secondary clarification, the flow can either be returned to the sewer system to flow to the Point Loma Wastewater Treatment Plant or sent through tertiary treatment for reclaimed water applications.

In tertiary treatment, secondary effluent flows into anthracite coal beds, where it is filtered of remaining solids. A portion of the filtered effluent is sent to the demineralization facility which uses an electro-dialysis reversal (EDR) process to reduce the salinity of the reclaimed water. Filtered effluent is blended with demineralized water then chlorinated in chlorine contact tanks for a minimum of 90 minutes for proper disinfection. The demineralized water now is available for industrial purposes for irrigation or agricultural purposes that require low salinity.

Primary and waste-activated sludges are blended and pumped to the Metro Biosolids Center for further processing.

All the power required to operate NCWRP is provided by an onsite cogeneration facility operated by Minnesota Methane (Roseville, Calif.). The cogeneration plant is powered by methane piped from the Miramar Landfill and Metro Biosolids Center digesters. Approximately 75% of the power produced is used for plant electrical needs, and the remainder of the power is sold to the local electric grid.

During WEFTEC.07, NCWRP will host Workshop 210, Activated Sludge and BNR Process Control: Hands-On in the Real World. The workshop will be held on Sunday, Oct. 14 from 8:30 a.m. until 4:30 p.m. Due to the level of hands-on activities in this workshop, space is limited to 90 participants.

City of San Diego Metropolitan Biosolids Center

The Metropolitan Biosolids Center (MBC), which began operation in 1998, is the City of San Diego’s state-of-the-art regional biosolids treatment facility. Located on 39 ac (15.8 ha) adjacent to the Miramar Landfill, MBC is an essential component of the region’s wastewater treatment system, processing nearly 99,800 kg (110 dry tons) of Class B biosolids per day.

MBC’s location required construction of two pipelines to feed the facility: the 17-mi (27.4-km) Miramar Pipeline from the Point Loma Wastewater Treatment Plant (PLWTP) and a 5-mi (8-km) pipeline from the North City Water Reclamation Plant (NCWRP).

MBC provides two treatment operations: thickening and digestion of the raw solids generated at NCWRP; and the dewatering of the wet biosolids from PLWTP as well as the biosolids MBC processes for NCWRP.

NCWRP does not have digesters on site. Raw solids from its primary and secondary treatment processes are pumped to receiving tanks at MBC. Then they pass through degritters to remove any abrasive material that could damage the processing equipment. The grit is removed and disposed of offsite.

The raw solids are thickened by centrifuges before being pumped into one of three anaerobic digesters. Under normal conditions one of the five thickening centrifuges is in service. From the anaerobic digesters, the biosolids are sent to a digested biosolids storage tank, where they are mixed with biosolids from the Point Loma Wastewater Treatment Plant.

The mixed biosolids are pumped to dewatering centrifuges. Under normal conditions, six of the eight centrifuges are in service. The centrate is returned to the sewer system for treatment at Point Loma, and the dewatered biosolids are pumped into storage silos before being trucked offsite.

MBC will host a tour of its facility during WEFTEC.07. The tour is scheduled for 9 a.m. to 1:00 p.m. on Monday, Oct. 15.

For more information on these tours, see