Dublin San Ramon Services District has started a major capital improvement project at the Regional Wastewater Treatment Facility in Pleasanton that will increase efficiency to improve the wastewater treatment process and reduce energy costs.

The $19 million project is the largest undertaken by the District since a treatment plant expansion in 2000.

Contractors began work in April on the Primary Sedimentation Expansion and Improvements Project, which will increase the primary treatment capacity by 33 percent. Construction is estimated to continue through fall 2021.

Currently there are four primary sedimentation tanks at the facility. The project involves constructing a fifth tank and partially demolishing and replacing an existing one. These two new tanks will be 100 feet long, 20.5 feet wide, and 15 feet deep. The project will also replace the internal mechanisms of the three remaining tanks (100 feet long, 20.5 feet wide, and 10.5 feet deep) as well as the motor control center, and an additional grit tank will also be added.

The grit tanks remove small material, such as gravel and sand, to protect equipment and prevent clogged pipes at the plant. Once the wastewater reaches the primary sedimentation step, scum is skimmed from the water’s surface and solids are scraped from the bottom of each tank. From here, the sewage is split into two separate streams of treatment for liquids and solids.

Currently the primary treatment capacity is undersized for the facility’s average dry weather flow of more than 10 million gallons a day. Insufficient primary treatment capacity can add stress to the next steps in the wastewater treatment process.

Once the project is complete, having two deeper tanks as well as improving the internal mechanism configuration will allow the wastewater to spend more time in the primary tanks, which will improve separation of solids and liquids. Removing solids earlier in the process will also help reduce energy use in secondary treatment.

The improvements will also enable the plant to send more solids to digesters that create biogas, a renewable fuel used to generate electricity to heat and power the plant. The expansion and improvements will provide the needed primary treatment capacity for both current flows as well as anticipated community buildout.