The Digested Sludge Dewatering Facility project will free up 750 acres of San José-Santa Clara Regional Wastewater Facility (RWF) land for alternative uses, reduce odors in the community and comply with new organic waste regulations. The $177 million project, which includes the dewatering facility and associated support facilities, is expected to come online October 2025, transitioning the facility from open-air drying beds and lagoons to an enclosed mechanical dewatering process.

Notably, by using the dewatering facility’s four new powerful centrifuges, this new development reduces sludge drying time and biosolids production from four years to just 24 hours.

Left: Diagram of the current biosolids drying land footprint at the RWF. The new dewatering facility frees up 750 acres of land for other uses. Right: A project rendering of the new Digested Sludge Dewatering Facility with other supporting facilities at the RWF.

More efficient biosolids dewatering and drying helps distill a product that has a variety of beneficial reuses, such as:

• alternative daily ground cover on Newby Island Landfill, that reduces pest access to garbage and odors for the surrounding community
• processing into soil
• land application
• agricultural uses
• after additional treatment, compost

The Digester and Thickener Facilities Upgrades Project, a complex, $218 million undertaking to retrofit existing facilities, design and construct new tanks, and elevate gas lines from underground tunnels, was completed April 2022.

Using a two-phased, high-temperature process known as Temperature-Phased Anaerobic Digestion (TPAD), the upgraded digesters more efficiently produce biogas that helps generate power for the RWF by using anaerobic bacteria and heat to break down biosolids. The heat used for this process is a byproduct from the Cogeneration Facility.

A construction worker in the interior of one of the four renovated digester tanks.

Left: Installation of 87-inch and 136-inch pipes that transfer biosolids to the new digesters. Middle: Construction workers install rebar around the wye structure. Right: Interior work on a digester.

Work continues with the Additional Digester Facility Upgrade project, scheduled to begin in 2025.

The Headworks Improvements and New Headworks Project, completed in 2023 with a total project value of $169 million, offers better performance and reliability and provides for a safer and more efficient work environment with a new and more accessible wastewater pre-treatment system. 

The Headworks pre-treatment of raw wastewater enhances and protects downstream treatment processes by removing any debris and grit that finds its way into our wastewater. This project replaced the aging Headworks 1 with a new Headworks 3 and made modifications to improve operational reliability of the existing Headworks 2.

The new Headworks 3 improves the Facility’s performance and dependability, preparing the Facility to handle any changing climate conditions, such as rising sea level, natural disasters, and population growth. Thanks to the new Headworks, the Facility can now treat up to 400 million gallons of wastewater a day.

The Headworks project was delivered on time and on budget even through the pandemic. It is recognized with the 2024 Project Achievement Award by the Construction Management Association of America (CMAA) for outstanding construction management, two national awards from the Design Build Institute of America (DBIA), and an award from the California Water Environment Association (CWEA).

Top left: During pretreatment, headworks bar screens remove grit and debris from wastewater. Top right: Primary treatment tanks. Bottom left: Aeration tanks pump air into wastewater during secondary treatment. Bottom right: Wastewater flows through serpentine tanks to remove remaining bacteria during tertiary treatment.

The Cogeneration Facility Project completed in 2020, was intricately built to meet our goals to convert digester gas (biogas) more efficiently into energy resources for the RWF and optimize operating costs. A team with diverse backgrounds and expertise collaborated on this complex project.

With a with a total value of $113 million, this project replaced the RWF’s old cogeneration engines, well-worn due to nonstop use for over 35 years.

Four new engine generators were installed, along with heat recovery and gas treatment systems. The treatment systems clean the digester biogas used in the engines and backup boilers will use heat from the engines to provide hot water for RWF building services.

The new Cogeneration Facility improves reliability, energy efficiency and enables full reuse of biogas that makes the RWF much more sustainable moving forward.

The Cogeneration Facility Project was recognized by the Design-Build Institute of America (DBIA) with the 2021 National Award of Merit and the 2021 Award of Excellence for Innovation & Resiliency – Large Agency by the California Association of Sanitation Agencies (CASA).

Above: Exhaust gas is cleaned before being discharged through exhaust stacks.