Wastewater Treatment Plant

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The City’s Wastewater Treatment Plant (also called the Water Pollution Control Plant), located near the Yolo County Landfill, is owned and operated by the City of Davis. The facility is permitted to treat 7.5 mgd (million gallons per day) of wastewater. The existing treatment system design capacity is 6 mgd based on average dry weather flow. There are two permitted discharge points from the plant. Treated effluent is discharged to the Willow Slough Bypass and the Conaway Ranch Toe Drain.

Davis WWTP Aerial June 2018 - 2

The Treatment Process

The current treatment process consists of:



Screening – using a mechanical bar screen to sift out large material such as rags, wood, or rocks.
Aerated grit removal – particles of sand and/or silt are removed from the wastewater in an aerated chamber where heavier particles sink to the bottom of the tank.


Sedimentation – Wastewater velocity slows to a point where heavier material sinks to the bottom of a tank and is removed for additional treatment while the remaining wastewater flows to secondary treatment.


Activated sludge – Naturally occurring bacteria are cultivated in tanks. Wastewater from the primary treatment flows into the tanks and the bacteria consume the organic waste in the water. Oxygen is added to create the ideal environment for the bacteria to thrive. The mixed water then flows to clarifiers to allow the bacteria to sink to the bottom and be recycled back to the aerated tanks while the remaining water flows to tertiary treatment.


Filtering – Water from the secondary process flows to filters that remove any remaining particulate material.


Just before water leaves the treatment plant, it is injected with a chlorine solution to provide disinfection. After the chlorine has disinfected the water, sodium bisulfite is added to remove the chlorine from the water prior to being sent to the Willow Slough Bypass.

Davis Wetlands

wetlands-aerial-current              wetlands-birds

The Davis Wastewater Treatment Plant treats water at the tertiary level, the final cleaning process that produces high quality treated wastewater. This is reused in the wetlands to support habitat, benefiting wildlife and humans alike. The wetlands also provide drainage for stormwater during the rainy months. The City is looking at long-term objectives for the wetlands now that tertiary treated water is available due to the changes in the wastewater treatment process with the recent upgrade.
More information on the Davis Wetlands.