Water and Energy Efficiency: How CHP and Energy Efficiency can Lead to Energy Neutrality for Wastewater Agencies

The scale of potential energy savings from optimizing energy use and recovering energy in wastewater treatment plants has led to the concept of energy neutrality for a segment of the wastewater treatment sector.

The energy contained in a given amount of wastewater and its biosolids can equal 10 times the energy required to treat that wastewater, according to the Water Environment Research Foundation (WERF). One significant method for capturing the embedded energy in wastewater is through cogeneration, also known as Combined Heat and Power (CHP). Wastewater treatment plants, having an anaerobic digestion process, are prime candidates for CHP because of the biogas that can be used as fuel to generate electricity and heat.

Potential for CHP

Despite the opportunity for CHP in wastewater treatment plants, there is room for greater penetration of CHP in the U.S. wastewater sector.

• An analysis done by the Environmental Protection Agency (EPA) found that 1,351 wastewater treatment facilities with anaerobic digestion treat more than 1 million gallons per day, but do not have CHP. The EPA estimates the technical potential for new CHP capacity in these treatment plants at more than 400 MW of biogas-based electricity and about 38,000 MMBtu/day of thermal energy output.
• Currently, 104 wastewater treatment facilities with anaerobic digestion utilize CHP with biogas as a primary fuel source. Together, these 104 plants generate 190 MW of electricity.

Barriers to CHP

One significant barrier is that CHP tends to be economically feasible for the larger wastewater treatment facilities. Since larger wastewater treatment plants can capture the majority of the energy efficiency potential from CHP, adoption of CHP by such plants can yield significant energy savings.

A cultural challenge of developing organizational commitment to energy efficiency can present as another barrier.  In addition, some states' energy efficiency resource standards set up regulatory obstacles, such as the lack of inclusion of biogas-based CHP.

Wastewater Agencies Leading the Way

Several wastewater agencies in the United States have implemented energy efficiency, including CHP, and have achieved energy neutrality. One such agency is the East Bay Municipal Utility District (EBMUD) in San Jose, Cali. EBMUD has undertaken several measures as part of its energy portfolio to improve energy efficiency, including CHP from biogas. It has enabled EBMUD to generate more than 55,000 MWh annually, which it uses internally; and sells excess power into the grid.

With a strong focus on optimizing the energy efficiency of its motor-driven systems, the Sheboygan, Wis., Wastewater Treatment Plant has been able to reduce its energy use by 20% from its 2003 baseline. Motor system upgrades and variable speed drives enabled the plant to reduce energy use by 157,000 kWh per year. With CHP, the plant now produces 70% to 90% of its own energy.

Starting in 2004, the Metropolitan Syracuse Wastewater Treatment plant in Onondaga, N.Y., implemented a combination of energy efficiency measures and CHP to achieve annual energy savings of 2.6 million kWh and 270 MMBtu in natural gas purchases.

Getting on Board: The Roadmap to Sustainability

To help the wastewater treatment sector, the Water Environment Foundation (WEF) is developing a roadmap to energy sustainability. This roadmap is being designed to help wastewater agencies understand how to achieve energy neutrality by implementing CHP and other energy efficiency measures.

For WEF Vice President of Research Barry Liner, “The roadmap will be applicable whether plants choose simply to increase energy efficiency or to build a full scale cogeneration system.”

WEF will release the draft roadmap and a technical summary by the end of summer 2012 and will produce a guidance document in time for WEFTEC 2012.