The Sanitation Districts have a proud tradition of providing low-cost, high-quality wastewater management for Los Angeles County. This includes operating the largest engineered wastewater recycling program in the world.

Water recycling is very important in our arid Southern California environment where water must be imported from other parts of the state. The goal of the Sanitation Districts is to recycle as much water from its Water Reclamation Plants, as possible and, therefore, the Water Reclamation Plants (WRPs) play a major role in meeting our water needs. This recycling significantly reduces the Los Angeles Basin's dependence on costly imported water and helps to replenish the groundwater used by a large percentage of the region.

The WRPs literally replicate what happens in nature. They just speed up the process and do it in modern, high-tech facilities. They provide what is known as primary, secondary, and tertiary treatment for approximately 200 million gallons of wastewater per day. The following describes the wastewater treatment and water reclamation processes for all of the WRPs, with the exception of La Caņada WRP, Lancaster WRP, and Palmdale WRP.

Wastewater Treatment

A treatment plant is just like a natural river but in a concrete box. First, materials settle to the bottom (Primary Treatment). Second, microbes use air to breath while they eat up organic material, then the microbes settle out (Secondary Treatment). Third, sand and coal filter out leftover particles (Tertiary Treatment) like sand in the bottom of a river.

Typical Flow Schematic of a Water Reclamation Plant

Primary Treatment

Just as in nature, when runoff first enters a river, heavier solid particles settle to the bottom while lighter materials float to the top and are carried away. At the water reclamation plant, long concrete tanks replace the river. The heavier solids which settle to the bottom and the lighter materials, like plastic and grease, which float to the top are called primary sludge and are removed and returned to the sewers for further treatment at the Joint Water Pollution Control Plant, then the remaining wastewater containing dissolved and suspended materials (mostly organic) moves to the second phase of treatment in aeration tanks and secondary settling basins.


Secondary Treatment

As dirty water in a river flows downstream, naturally occurring microorganisms feed on the dissolved organic materials. As the river flows downstream, oxygen naturally enters the water so the organisms can breathe. In the secondary treatment aeration tanks, air is bubbled through the water to supply the oxygen. The same microorganisms in the wastewater grow as they feed on the organic materials in these tanks. In the secondary treatment settling tanks, the microorganisms clump together and settle to the bottom, where they are removed and recycled back into the treatment process.




Tertiary Treatment

Finally, in a natural river, the clean water soaks into the ground beneath the river and joins the underground water supply. The ground is replaced at the treatment plant by filters, which remove any remaining suspended materials from the water. The filters contain layers of anthracite coal, sand, and gravel. The reclaimed water is then disinfected. It is now free of harmful bacteria and viruses and safe for human contact, recharging groundwater, and for a wide variety of other uses. Following disinfection, any remaining chlorine in the purified water is removed to protect aquatic life in the receiving environment.


To learn more about the Sanitation Districts' reclaimed water programs, browse the Water Reuse Partnership and the current Water Reuse Summary.

Reclaimed Water Discharged Into San Jose Creek, Control Room, Reclaimed Water

Laboratory

Water quality measurements and analysis are completed at laboratories located at each water reclamation plant. The laboratory staff provides analytical services that meet all the requirements of the Regional Water Quality Control Board for all of the Districts' treatment facilities. A full spectrum of analytical services is available, including chemical, biological, and microbiological testing. Districts' scientists employ a combination of classical techniques and modern, sophisticated instrumentation to provide assessments of inorganic and organic chemicals, bacteria, viruses, and toxicity. More than 300,000 tests on 20,000 samples are performed annually. In addition, new and improved analytical methods are continually being evaluated and developed.