Where you live determines which treatment plant your wastewater is cleaned. (Where does my sewage get treated?) There are two 24-hour treatment plants that operate 365 days a year. We also have a third facility called a "wet-weather facility" that only operates during rain events. Wastewater treatment is separated into liquid and solids processing components.
2 Treatment Plants and 1 Wet-Weather Facility
Treating the Liquid Stream
For the most part, the treatment processes at each plant are very similar. We separate liquids from solids and treat each one separately. Here is a brief and simplified version of the liquid treatment process.
|Step One: Screening and Primary Treatment
||A screen is used to remove large objects when wastewater first arrives
at the plant. Then the wastewater is put into large settling tanks where
heavier solids settle at the bottom, and floatables like oil and grease
are scraped off the top.
|Step Two: Secondary Treatment
||Secondary treatment uses pure oxygen to excite microorganisms in the
wastewater stream. The microrganisms mulitply and more rapidly consume
organic material helping purify the wastewater. Afterwards, the
wastewater is put into a second round of settling tanks where the
microorganisms are separated from the purified water.
|Step Three: Disinfection and Discharge
||Treated wastewater, now called effluent, at the Southeast Plant is
disinfected before being discharged 800 feet into the San Francsco Bay.
Effluent at the Oceanside Plant is discharged 4.5 miles into the Pacific
Ocean, where the high salt concentration and cold temperatures help to
kill any remaining bacteria. Effluent at North Point Facility is also
disinfected before being discharged 800 feet in the San Francisco Bay.
The beaker on the left is what wastewater looks like when it first arrives at one of our treatment plants. Compare it with the beaker of effluent on the right that is discharged into the Bay or Ocean. Big difference, right? Now let's find out what happens to all the solids we've extracted.
Next Step: Treating the Solids