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Davis

Davis, California

Tuesday, October 26, 2021

Proposed wastewater treatment system looks to reduce costs and energy consumption in face of rising rates

Faced with rising water and sewer rates, the city of Davis is seeking to adopt a more efficient water treatment system.

Ed Schroeder and George Tchobanoglous, two UC Davis civil and environmental engineering professors emeriti, proposed their wastewater management plan at the Mar. 2 city council meeting.

Schroeder and Tchobanoglous led the planning and design panel, which consisted of six wastewater professionals. The two-day panel analyzed wastewater treatment and disposal alternatives. Experts devised a treatment process flow diagram that examines how the city can continue discharging treated wastewater to the Willow Slough Bypass.

Schroeder said he predicts the recommended flow sheet will be adapted in several other cities.

“The plan is unique because it takes advantage of some existing facilities and allows the city opportunities to develop,” Tchobanoglous said.

The most critical factor of the treatment plan is converting ammonia to nitrate because high levels of ammonia in water are damaging to aquatic species. The proposed system is a stable process, which will oxidate ammonia to nitrate, thereby decreasing the pH levels in the water, Schroeder said.

The current water filtration system allows a fairly high concentration of selenium to exist in Davis well water. High levels of selenium are fatal to aquatic waterfowl.

The incorporation of the oxidation ponds will result in a smaller main plant designed to hold 6 million gallons per day and will actually be able to provide 7.5 million gallons per day.

“The recommended system will be prudent – capable of operating at the flow allowed by the Regional Water Quality Control Board but with the principal units designed for a considerably lower flow rate due to incorporation of the current oxidation ponds in the plan,” Schroeder said.

Also, using the pre-existing oxidation ponds will reliably prevent waste, reduce costs and lower oxygen use, thus decreasing energy consumption, Schroeder said.

As the demand for water in California increases, the competition for water is increasing as well, and the value of treated wastewater will rise as well. Davis can use recycled wastewater for parks, greenbelts, golf courses and floorage crop, thereby reducing water costs, Schroeder said.

The recommended improvements will reliably meet adopted discharge requirements and provide flexibility to meet prospective stricter discharge requirements, said the city’s utilities engineer Keith Smith.

“You can add on or change the system in a cost effective manner,” Smith said.

The City Council directed the staff to develop cost estimates for the recommended plan. These costs will provide a baseline when other alternatives are considered.

Eventually, water rates will double from current rates. Sewer rates are estimated to increase by approximately 50 percent. Initial increases of 5 percent for water rates and 6 percent for sewer rates are recommended for the 2010-2011 fiscal year.

“Estimated average combined monthly increase for water and sewer is $4.27 or $51.24 per year,” said Assistant Public Works Director Sue Gedestad in an e-mail interview.

Actual rate approval will occur on May 4.

“The large projects in each utility are the main driver, Woodland-Davis Surface water project for the water utility and wastewater treatment plant upgrade for sewer,” Gedestad said. “The water utility has also had major replacement project such as East Area Water Storage Tank and two water wells.”

THERESA MONGELLUZZO can be reached at city@theaggie.org.

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