Treatment Process

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Basic Treatment ProcessIn addition to processing wastewater discharge for the cities of South San Francisco, San Bruno, and the Town of Colma, the Plant also provides the dechlorination treatment of chlorinated effluent for the cities of Burlingame, Millbrae, and the San Francisco International Airport prior to discharging the treated wastewater into San Francisco Bay. The average dry weather flow through the facility is nine million gallons per day (MGD). Peak wet weather flows can exceed 60 MGD.

Wastewater treatment at the facility consists of:

  • Screening
  • Grit removal
  • Chemical addition to aid settling of solids
  • Primary settling under vacuum
  • Aeration
  • Clarification
  • Disinfection by chlorination
  • Removal of excess chlorine prior to discharge

More About the Process

  • Anaerobic bacteria in the five digesters convert the volatile solids removed during the treatment process into methane, carbon dioxide, and other trace gases.
  • The methane is then used as fuel to drive our 400 kilowatt generator. This provides a significant subsidy to our use of power supplied from Pacific Gas & Electric Co.
  • The sludge which is left following digestion is treated with polymers to aid in separation and the solids are then pumped to a dewatering facility.
  • The water drained in this process is returned to the plant for further treatment.
  • Finally, the solids left behind after the dewatering process are hauled to a landfill where it is used as ground cover.