Updates on City of San José Services and/or Operations . (English | Español | Tiếng Việt | 中文)

Treatment Process

After wastewater enters the San José-Santa Clara Regional Wastewater Facility, it undergoes a three-step treatment process to remove solids, pollutants, and harmful bacteria. Machinery and gravity separate solids from the wastewater. Added bacteria remove pollutants before the wastewater enters the advanced filter process. The treatment process produces water that is 99% purified and then discharged into South San Francisco Bay.

Headworks (Pretreatment)

  • In the pretreatment process, large bar screens remove rags, sticks, rocks, and other debris that could otherwise clog machinery. Grit chambers remove heavier objects like sand and gravel.
  • Debris are taken to the landfill.

Primary Treatment

  • This 24-hour physical process removes about 50 percent of wastewater contaminants. In large tanks, the flow is slowed to allow gravity to separate large particles. This process mimics the natural processes of creeks and rivers, where sediments settle to the bottom.
  • Fiberglass bars, or flights, rotate to skim off fats, oils, and grease from the surface of the water and to scrape solids that sink to the bottom.


  • The pollutants and solid material removed during the three treatment steps are put in digester tanks.
  • In the digester tanks, naturally occurring anaerobic bacteria digest sludge and produce methane gas that helps meet 60 percent of the Facility’s energy needs.

Secondary Treatment

  • Aeration: Aeration tanks pump air into the wastewater to nurture the growth of naturally occurring aerobic bacteria that remove organic pollutants in the wastewater
  • Clarifiers: After aeration, the wastewater is piped into clarifiers, where the aerobic bacteria settle. Mechanical arms scrape away the settled material to transfer to the digester tanks or reuse again in the aeration tanks.

Tertiary Treatment

  • Tertiary treatment is the third and final process. During tertiary treatment, wastewater flows through several filter beds composed of gravel, sand and anthracite coal to remove small suspended solids.
  • The water flows through serpentine tanks where chlorine is used to kill any remaining viruses or bacteria. The chlorine is then neutralized to protect aquatic life.
  • This advanced treatment is needed to ensure that our water meets state and federal water quality regulations for the shallow waters and sensitive ecosystem of South San Francisco Bay. Water is 99% pure after tertiary treatment.

Outfall Channel

  • After tertiary treatment, about 80% of the treated water is piped to the outfall channel. From here, it flows to Artesian Slough, through Coyote Creek, and eventually into the South San Francisco Bay. Many birds and fish are found at the outfall channel, including stripers, black bass, and salmon.
  • The remaining 20% of the treated water is sent to South Bay Water Recycling and used to irrigate food crops, parks, schools, golf courses, street medians, and business park landscaping.

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