Energy-lightbulb_TransparentEnergy is recovered in the water treatment process in two ways. Microbes that digest the solids removed from the water produce biogas as a byproduct of their metabolism. Essentially, they are converting the energy that is already in the biosolids to a form we can use directly to power the plant. Biogas consists mainly of methane and carbon dioxide. This methane is used to fuel a cogeneration system that produces electricity used at the Facility. The heat given off by the engine is then redirected to warm the anaerobic digesters where the microbes live to the appropriate temperature for their growth. This cycling of energy ensures that the maximum potential of the solids from your water goes towards productive applications.

WRRF Energy Efficiency Project: Energy Measures

The City recently completed a “first phase” of the WRRF Project — the WRRF Energy Efficiency Project.  This project was a partnership with PG&E and included:

  • Cogeneration system for producing electricity
  • Replacement of aging, inefficient equipment: belt-press, filter tower components, initial screening processes, and grit-removal system
  • Upgraded SCADA (Supervisory Control And Data Acquisition) system to help optimizes processes

WRRF Project: Energy Measures

The WRRF is one of the largest energy consumers in the City. Because of this, every decision made in the project first considers energy efficiency.

  • “Right-sized” design processes
  • Advanced, energy efficient equipment and technology
  • Solar panels on multiple buildings and structures
  • Biogas storage for cogeneration system
  • Future fats, oils, and grease receiving station – increasing biogas production


The cogeneration system shown here produces electricity for the WRRF from biogas made in the digesters.