The Ralph W. Chapman Water Recycling Facility (Chapman Facility) is located in Rancho San Diego and recycles up to 1.3 million gallons per day (mgd) of raw sewage to full Title 22 recycled water standards. It is also considered a stripping treatment facility in that excess wastewater that is not treated by the facility for beneficial reuse is disposed of via the existing sewer disposal system within the Jamacha Basin.
In 1980, the Otay Water District started operation of the Chapman Facility.
The facility treats domestic sewage, going through the following steps:
Primary Treatment: Raw sewage flows in at the drum screen, also known as the “headworks” which removes a large amount of coarse organic and inorganic material that is either floating or in suspension. This is followed by a grit chamber, which removes heavy settled material.
Secondary Treatment: This is where the biological treatment begins. The first step takes place in the aeration tanks, also known as reactors or sedimentation basins, which contain a huge mass of bacteria that feed on the organic material in sewage. The bacteria are aerobic and therefore require a great quantity of pumped-in air to help them thrive.
The next step in the process is clarification where the sludge from the aeration tanks is allowed to settle to the bottom and the clear liquid, or secondary effluent, flows out over weirs at the surface. Some of the settled sludge is disposed of and some is returned to the aeration tanks to keep the process in balance. The secondary effluent flowing over the weirs is ready for the next step.
Tertiary Treatment: Just before filtration, a small amount of coagulant is added as a filter aid which helps suspended material in the secondary effluent “clump” on the surface of the filters. The filters consist of a layer of sand with a layer of anthracite coal on top. As the fluid moves through the filters, the liquid flows through a chlorine contact chamber where disinfection takes place.
The Chapman Facility’s conversion time from raw sewage to full Title 22 recycled water is about 20 hours.
Sludge is combined with excess non-treated waste water and is pumped to the city of San Diego’s Metropolitan Wastewater System.
Recycled water produced is used for landscape irrigation at golf courses, schools, parks and open space in the communities of EastLake, Otay Ranch, and Rancho Del Rey, as well as other areas of eastern Chula Vista.