Bay Area wastewater utility to cut its greenhouse gas emissions by more than 90 percent

June 24, 2022

West County Wastewater (WCW), in Richmond, California, is conducting an infrastructure upgrade project to reduce the greenhouse gas (GHG) emissions from its 12.5 mgd Water Quality and Resource Recovery Plant by more than 90 percent. Much of the anticipated reductions will result from improvements to the solids-handling processes at the facility, particularly the elimination of its existing sludge drying beds.

The WCW owns, operates, and maintains a wastewater collection system comprising 249 miles of gravity sewer pipelines, 17 lift stations, and 6 miles of force mains. Serving several communities in the Richmond, California, area, the utility provides wastewater treatment for about 34,000 residences and 2,450 commercial and industrial customers, for a total population of nearly 100,000.

The upgrades to the WCW’s wastewater facility will include solids-handling improvements, power-generation capabilities, and treatment process upgrades. The overall project was designed by ENGIE North America, Inc., a regional hub of the low-carbon energy and services provider ENGIE S.A. ENGIE's design project team includes Pacific Advanced Civil Engineering, Inc. (PACE), Yorke Engineering, LLC, and The Process Group.

Major GHG emissions

Today, the WCW sends its biosolids to the landfill because they do not comply with requirements for beneficial reuse. Currently, the solids-handling process at the Water Quality and Resource Recovery Plant includes the use of a dissolved-air flotation system to thicken waste activated sludge. 

“Thickened sludge is transported to both primary and secondary digesters,” says Keith Reynolds, Jr., the senior project manager for the WCW. “The sludge is then actively transported to sludge lagoons utilizing water caps. Once the sludge has dried sufficiently, it is removed and used as landfill capping material.”  

Unfortunately, the sludge lagoons generate significant GHG emissions. “Even though the biosolids were previously anaerobically digested, the anaerobic reaction would continue in the presence of moisture to emit methane,” Reynolds says. 

A study commissioned by the WCW found that the storage of sludge in the drying beds generated approximately 3,953 metric tons of carbon dioxide (CO2) emissions annually, Reynolds says. The same study also determined that landfill disposal of biosolids by the WCW generated another 133 metric tons of CO2 emissions annually.

Major GHG reductions

Improvements to the solids-handling system at the Water Quality and Resource Recovery Plant will include rotary drum thickeners, two new digesters, centrifuges for solids dewatering, and a  thermal dryer system. Ultimately, these upgrades to the facility will help to reduce its GHG emissions by 93 percent, according to a June 7 news release from ENGIE.

Eliminating the sludge drying beds will result in the “principal reduction” in GHG emissions, Reynolds says. “The thermal dryer bypasses the sludge drying beds and reduces the volume of sludge shipped offsite by nearly a factor of nine,” he says.  

Power generation

As for improvements designed to facilitate onsite power generation, the project will include a 450 kW cogeneration system powered by digester gas and a 1.1 MW solar power system.

“Together, these systems’ onsite generation will meet close to 100 percent of the [WCW’s] facilities and wastewater treatment electricity needs,” according to the news release. 

The project also will entail the installation of LED lighting and electric vehicle charging stations. Treatment process improvements to the WCW’s treatment facility will include a new grit separation system, a high-efficiency aeration blower, and equalization basins. 

When all is said and done, the revamped Water Quality and Resource Recovery Plant will achieve a negative or neutral rate of annual GHG emissions, Reynolds says. “The final GHG emissions, counting natural gas used for the dryer, beneficial use of the methane from digestion in a cogeneration engine, and reduction of purchased electricity with solar PV, will result in a final emission of -617 metric tons of CO2 [emissions annually],” he says.  

Class A and its advantages

At the same time, the upgrades to the solids-handling system will enable the WCW to generate Class A biosolids suitable for agricultural and other beneficial uses.

“WCW will produce Class A biosolids by thermal drying and using newly installed centrifuges  – either by drying the sludge to 90 percent solids or more or by meeting the time and temperature requirements in 40 CFR Section 503,” Reynolds says, referring to the U.S. Environmental Protection Agency’s Standards for the Use or Disposal of Sewage Sludge.

Obviating the need to send biosolids to the landfill confers key benefits to the WCW. Along with reducing disposal costs, the shift to land application of biosolids will enable the utility to comply with the requirements of S.B. 1383, California’s organic waste recycling requirements that take effect this year. The requirements are intended to decrease GHG emissions by reducing the volume of organic material going to landfills.

Long-term savings

Project construction began in March 2022 and is scheduled to wrap up in January 2025. Estimated to cost approximately $81 million, the project is expected to save more than $83 million during the project’s lifetime.

After implementing the improvements, ENGIE will maintain the installed equipment for 20 years in accordance with an energy-savings performance contract. The company is “targeting a 4.2 million kWh reduction in WCW’s annual energy use,” according to the news release.

“This project is one of the most impactful energy, infrastructure, and process improvement programs in the United States," said Stefaan Sercu, managing director at ENGIE North America, in the news release. "Our alliance with WCW will serve as a proof point for the benefits of the comprehensive energy collaboration approach,” Sercu said.