Carlsbad project that turns human waste into electricity
Carlsbad CA— The Encina Wastewater Authority in Carlsbad has received national recognition for creating a green power supply that fuels 83% of its wastewater treatment plant’s electric demand and saves $2 million a year in power costs. The authority is owned by the cities of Carlsbad, Vista and Encinitas and the Vallecitos Water District, Buena Sanitation District and the Leucadia Wastewater District. Under a joint powers agreement, the agency is responsible for treating wastewater generated from approximately 379,000 residents in north San Diego County.
The U.S. EPA’s Green Power Partnership ranked the Encina Wastewater Authority number one for the percentage of total power produced onsite and 16th for the total quantity of power produced. Other honorees recognized for producing power on site include such major companies as Apple, Proctor and Gamble, General Motors, Intel, Toyota and Walmart.
Wastewater treatment is an energy-intensive process. The Encina Wastewater Authority utilizes methane gas produced naturally by the treatment process to fuel internal combustion engines that produce usable heat and electricity. The Encina Wastewater Authority’s cogeneration system produces over 14 million kWh per year, enough electricity to power over 2,000 homes for a year.
How it works
The treatment process that creates biogas is known as anaerobic digestion. Solids are heated to 98°F in covered tanks for 15-20 days. This process breaks down organic matter to form carbon dioxide and methane. Gas produced by the anaerobic digestion process is a mixture of 60-65% methane, 35-40% carbon dioxide. As the gas leaves the digesters, it is cooled, releasing moisture, and then filtered to remove particulates. The conditioned gas is then pressurized and sent to cogeneration engine generators.
Four engine generators receive this gas and convert it into electricity. Each of these 16-cylinder, turbo-charged, low-emission engines can generate 750 kilowatts of electricity. Waste heat from the engines’ jacket water and exhaust is also utilized to heat the plant’s digesters, which further reduces energy demands and costs.
About the EPA Top 30 On-site Power Generation list
The EPA’s Top 30 On-site Power Generation list represents organizations generating and consuming green power on-site within the EPA’s Green Power Partnership. The Green Power Partnership is a voluntary program that supports the use of green power by offering expert advice, technical support, tools, and resources.
About the Encina Wastewater Authority
The Encina Wastewater Authority is a public agency located in Carlsbad, California. EWA provides wastewater treatment services to more than 379,000 residents in northern San Diego County. EWAs facilities are essential for protecting the local ocean environment and preserving public health.
EWA is owned by six public agencies governed by a Joint Powers Agreement.