THE POWER OF DIGESTER GAS, A TECHNOLOGY REVIEW FROM MICRO TO MEGAWATTS

The County Sanitation Districts of Los Angeles County (Districts) operate and maintain both a regional wastewater treatment and a solid waste management system that provide services to approximately five million people in Los Angeles County. This involves treating approximately 520 million gallons a day of wastewater and managing the final disposal of half of the 40,000 tons per day of nonhazardous solid waste in the county.The Districts have a long history of utilizing biogas for the production of electricity. In 1938 the Districts employed gas from wastewater digesters to fuel internal combustion engines that provided all the power requirements for a treatment facility. This proved to be so successful that the facility was disconnected from the local electric utility. From this beginning the Districts have continued to pursue the economic and environmental benefits of “waste gas“. At the Districts' wastewater treatment plants, digester gas is used to generate the electricity needed for plant operations. The gas generated at the Districts' landfills is also used to generate electricity that is sold to the local utility.Many benefits can be derived through the use of renewable resources available as a byproduct of wastewater treatment and solid waste management. For wastewater facilities, biogas offers a source of low cost electricity independent of foreign fuel supplies. Landfills can use the gas produced to provide power for the local communities they serve. In many cases this displaces imported power, thus reducing the cost and environmental consequences of high voltage transmission facilities.The following provides a brief description of all the Districts' electrical generating facilities followed by a detailed discussion of the 23 megawatts of digester gas fired generation at the Districts wastewater reclamation plants (WRP). These facilities include gas turbines, internal combustion engines, a fuel cell and a microturbine. The discussion will cover the unique aspects of dealing with a waste fuel, operating and maintenance costs, plant reliability and air emissions.