Wastewater treatment requires a lot of energy, and energy is expensive. In an effort to reduce costs and greenhouse gas emissions, NapaSan implements projects at the treatment plant to increase energy efficiency and generate our own electricity.
When the solids that are removed from the wastewater are treated (digested), it produces a lot of methane gas. Lucky for us, methane gas is a great energy source. NapaSan installed generators that can burn this methane to produce electricity that then powers the wastewater treatment process. This process, called cogeneration, produces electricity that replaces the electricity and natural gas that would normally be purchased from PG&E.
Waste heat, a by-product of the electricity generation, is recovered from the cogeneration engines and exhaust. This heat is used for heating the digester where the solids are treated, and for heating nearby buildings at the plant.
The average amount of energy produced each month by the cogeneration unit is equivalent to the amount of electricity used monthly by about 185 homes. For every kilowatt-hour generated at this facility, that's one less kilowatt-hour of energy purchased, and creating a cost savings for NapaSan's ratepayers.