EWA operates a cogeneration plant that utilizes internal combustion engines and generators to produce electricity and usable heat in a single operation.  The cogeneration engines are fueled by a renewable resource called biogas (methane), which is produced from the treatment of wastewater solids in vessels called digesters.  This treatment process, known as anaerobic digestion, converts volatile organic solids to carbon dioxide and methane.  The conversion occurs in a liquor filled tank that is maintained at a temperature of 95 to 98 ˚F. 

Gas produced by the anaerobic digestion process is a mixture of approximately 60-65% methane, 35-40% carbon dioxide, and small quantities of nitrogen, hydrogen and sulfur compounds.  As the gas leaves the digesters, it is cooled, which releases moisture, and then filtered to remove particulates.  The conditioned gas is then pressurized and sent to the cogeneration engine generators via mixed gas blowers.

During the EWPCF Phase V plant upgrade, four new Caterpillar G3516 engine generator sets were installed.  These sixteen-cylinder, turbo-charged, low-emission engines are capable of generating 750 kilowatts of electricity.  They can be fueled by either imported natural gas or methane.  Waste heat from the engines’ jacket water and exhaust is also utilized to heat the plant’s solids digesters, thereby increasing overall system efficiency.

Over 60% of the electricity used by the EWPCF is provided by the cogeneration facility. In addition, use of thermal energy from the cogeneration process to heat the digesters reduces the amount of natural gas that must be purchased.  As a result, operation of the cogeneration facility saves the Encina Wastewater Authority about $2 million dollars a year in energy costs.

The average home electricity use in Southern California is about 6,000 kilowatt hours (KWh) per year.  The EWPCF’s cogeneration plant produces about 12 million KWh per year, which is enough to power 2,000 homes.