The Allentown Wastewater Treatment Plant in Pennsylvania is one of at least 122 wastewater plants generating
renewable electricity and heat from CHP

Wastewater treatment plants are an essential part of urban and rural communities. Wastewater treatment plants, either under municipal or private ownership, process residential, commercial, and industrial wastes for conversion into benign liquid, gas and solid waste streams. Although the plants can be very energy intensive, the treatment process produces methane as a byproduct, which can be burned to generate electricity. The waste heat from the electricity generation can then be used to meet plant thermal requirements such as digester and space heating loads. Making use of the waste heat from onsite electricity production increases fuel efficiency and decreases energy costs.

Facts and Figures

• A typical wastewater treatment plant processes 100 gallons per day of wastewater for every person served.
• Each million gallons per day (MGD) of wastewater flow can produce enough biogas in an anaerobic digester to generate approximately 26 kilowatts (kW) of electric capacity and 2.4 million Btu per day (MMBtu/day) of thermal energy in a CHP system.
• 122 wastewater treatment plants in the U.S. have CHP systems using biogas, representing 254 megawatts (MW) of capacity.

Opportunity for Combined Heat and Power

CHP is an attractive option for wastewater plants that have, or are planning to install, anaerobic digesters. The biogas from the digester can be used as fuel to generate electricity in a CHP system. The thermal energy produced by the CHP system is then typically used to maintain the digester temperature, as well as for space heating in other plant buildings. A well-designed CHP system using biogas offers many benefits for wastewater treatment plants because it:

• Offers savings on electricity bills.
• Displaces purchased fuels for thermal needs.
• May qualify as a renewable fuel source under state renewable portfolio standards and utility green power programs.
• Enhances power reliability for the plant.
• Produces more useful energy than if the wastewater plant were to use biogas solely to meet digester heat loads.
• Reduces emissions of greenhouse gases and other air pollutants, primarily by displacing utility grid power.

Wastewater treatment plants are critical for maintaining public sanitation and a healthy environment, and must be able to operate in the event of a natural or man-made disaster, as well as a utility power outage. Because of CHP's ability to produce electricity and heat on site, it is a valuable infrastructure addition for wastewater treatment plants.

Project Profile

The wastewater treatment plant for the City of Allentown, Pennsylvania produces biogas as a byproduct of the wastewater treatment process. This biogas is used to fuel a 360-kW microturbine CHP system to produce electricity, and the heat is recycled back to the plant's anaerobic digester and buildings. A detailed project profile is available at www.maceac.psu.edu.

Additional Resources

• Opportunities for Combined Heat and Power at Wastewater Treatment Facilities: Market Analysis and Lessons from the Field, EPA CHP Partnership (2011)
• Biomass CHP Catalog of Technologies, EPA CHP Partnership (2012)
• Evaluation of Combined Heat and Power Technologies for Wastewater Treatment Facilities, Brown & Caldwell (2010)
• Strategic CHP Deployment Assistance for Wastewater Treatment Facilities, Association of State Energy Research & Technology Transfer Institutions (2009)
• Combined Heat and Power Potential at California's Wastewater Treatment Plants, California Energy Commission (2009)