A Class Act: City of Davis Pilots Class A EQ Biosolids Technology 

AC24 PREVIEW: Digestion to Dewatering Biosolids, Wednesday, April 10 
Roni Gehlke, Clean Water Magazine editor , Resource Recovery


The CWEA Annual Conference in 2024 will bring together wastewater industry experts to discuss the latest innovations and emerging technologies in wastewater maintenance. One of the key topics of discussion will be the various methods for treating and disposing of biosolids, also known as sewage sludge. The focus will be on exploring newer and more cost-effective approaches. Kathryn Gies from West Yost Associates will be hosting a session to discuss her current pilot program with the City of Davis.

“The City of Davis is conducting pilot testing of the Dry Vac system, which is an innovative wastewater biosolids dewatering technology,” Gies explained. “By demonstrating the efficacy and feasibility of this technology, the City hopes to identify a viable strategy to decrease in energy consumption of the solids processing train and reduce hauling and disposal costs while regaining anaerobic digestion capacity and producing a beneficial product that qualifies as Class A EQ biosolids.”

Biosolids are classified as “Class A” and “Class B” based on their treatment methods. The two classes have different requirements for treating pollutants, pathogens, and vector attraction, as well as general management practices. Part 503 treatment processes are used for Class A biosolids, which effectively eliminate pathogens, including viruses.

The DryVac system used in Davis’ pilot program is a thermal vacuum steam desiccation process that uses a combination of physical, chemical, and thermal processes to stabilize biosolids. It is a mechanical dewatering system that employs a plate-and-frame design, along with steam drying.

The first step of the process involves dewatering the solids under pressure, yielding filtrate that’s as pure as the source water. In the second phase of the cycle, the solids are dried up to 98% solid under a partial vacuum with the help of steam. This stage also kills pathogens via heat, causing biological cell material to lyse and release biologically held water. This water is then purified through filtration and distillation.

“The two major advantages are that it is one piece of equipment and the reduced hauling cost of the end product,” Gies said.

The DryVac process does not involve biological oxidation or conversion. This means that most of the nutrients in the raw material are preserved in the dried sludge, except for any soluble ammonia and phosphorus in the transfer water. Additionally, the DryVac system can be used before digestion, eliminating the need for thickening, digestion, heating, and dewatering equipment that would otherwise be required.

During the conference session, Gies will discuss the pilot program’s results and its effectiveness in achieving Class A standards for various solid streams produced by the City’s wastewater treatment plant. The implementation of this technology will be defined by the study, including operational requirements, capital costs, and potential savings in operational expenses.

“The City intends for the study to support not only the adoption of this new technology for the City’s WWTP, but also provide information needed for other agencies to consider this option at their facilities as well,” Gies said.

Gies has worked for West Yost Associates for more than 23 years providing planning and regulatory compliance support for wastewater treatment and recycled water projects. Her expertise lies in process design, planning, natural wastewater treatment, sustainable infrastructure, biological nutrient removal (BNR) systems, recycled water master planning, NPDES and biosolids regulatory permitting, and groundwater quality studies.
Gies is currently vice president of CWEA’s state Board of Directors. She has been actively involved with CWEA since 2002 serving on both local and state committees.

Join this session at the Annual Conference in Sacramento on Wednesday, April 10 at 3:25 p.m. Details here.