Energy is top of mind with today’s clean-water plant operators. They’re looking not just to save energy but to produce it, mainly using biogas from anaerobic digestion of biosolids.

The most efficient way to produce energy from biogas is combined heat and power (CHP), also called cogeneration. By using engines or turbines to generate electricity, and capturing heat from the prime mover, plants can extract the maximum energy from their biogas.

The U.S. EPA promotes biogas-fueled CHP as a source of clean, renewable energy. The agency’s Office of Infrastructure and Assistance, as part of its charter, offers clean-water plants information and technical assistance on CHP projects. Valerie Breznicky, a project officer, shared information about CHP and the EPA’s resources with Treatment Plant Operator.

TPO: What is the basic value proposition for CHP?

Breznicky: It is an efficient and clean approach to generating electric power and useful thermal energy from a single fuel source. CHP can produce energy twice as efficiently as older electric-generating systems. And because the energy is generated close to where it is needed, very little is lost in transmission. CHP can be a reliable, cost-effective option for WWTPs that have or are planning to install anaerobic digesters. For most treatment plants, a biogas-fueled CHP system has potential to offset energy consumption by up to 40 percent.

TPO: How does CHP using biogas affect greenhouse gas (GHG) emissions?

Breznicky: A CHP system can significantly reduce a plant’s direct and indirect GHG emissions. According to the EPA’s 2004 Clean Watershed Needs Survey data, a total of 2.3 million metric tons of carbon dioxide emission reductions could be achieved through increased use of CHP at wastewater treatment plants. These reductions are equivalent to planting about 640,000 acres of forest, or eliminating the emissions of about 430,000 cars.

TPO: Does biogas-fueled CHP qualify as renewable energy under utility and government incentive programs?

Breznicky: Yes. The use of biogas is often eligible for renewable fuel credits and clean energy funding. For example, biogas-fueled electricity generation qualifies as a renewable energy source in the District of Columbia and the 22 states that have renewable portfolio standards. National voluntary renewable energy credit [REC] programs also consider new electricity generation fueled by biogas from wastewater treatment plants as eligible sources for RECs.

TPO: What exactly are renewable energy credits?

Breznicky: A renewable energy credit [sometimes called a renewable energy certificate or “greentag”] is a commodity that represents the added value, environmental benefits and cost of renewable energy above conventional methods of producing electricity. Purchase of these credits is a widely accepted way to reduce the environmental footprint of a facility’s electricity consumption and help fund renewable energy development.

TPO: What factors determine how much biogas and energy can be recovered from anaerobic digesters?

Breznicky: The overall energy recovery depends on a combination of factors, including the effectiveness of the digestion process, the efficiency of the CHP system, the type of treatment processes, and the efficiency of the treatment plant’s liquid stream treatment. The addition of fats, oils and grease [FOG] and other highly digestible waste streams to the anaerobic digestion process can dramatically enhance digester gas production.

Regardless of their capacity, treatment plants operating or considering CHP should evaluate the potential to add FOG or other digester feedstocks to the digestion process. The increased gas production translates directly into cost offsets for electric power and greater heat production for processes. Additional process heat can offset a large portion of supplemental fuel needs.

TPO: How can a facility determine whether a CHP system would be technically feasible and economically beneficial?

Breznicky: A feasibility analysis is a first step in determining the viability of CHP. Whether a system is economically viable depends on site-specific factors such as the facility’s energy consumption, the prices of fuel and retail electricity, and the cost of installing and maintaining the CHP equipment. The analysis can provide enough information on project economics to allow plant personnel to decide whether to make the investment, while minimizing up-front time and expense. The EPA’s CHP Partnership can assist with a feasibility analysis.

TPO: In summary, what does a feasibility analysis include?

Breznicky: The first step is to identify the system size and electrical demand of the treatment plant. Electrical demand can be determined from a utility bill analysis, available plant data and site information. This information is used to determine which type of CHP technology will be best for the facility.

An economic analysis included with the study is usually a simple payback calculation. It considers the amount of power to be produced by the CHP system and the amount to be used on site, the expected savings from offsetting purchased energy, the energy and cost associated with running the CHP system, and the cost to install and maintain the system. Further analysis may show the benefits of available grants or incentives and the costs and benefits of being able to use the system to provide backup power during utility outages.

TPO: What are the preferred prime mover technologies for CHP in clean-water plants?

Breznicky: Treatment facilities have successfully incorporated CHP systems using a variety of technologies. Internal combustion engines are the most widely used. Combustion gas turbines are another common technology. Microturbines, a relatively new CHP technology, have become more popular in recent years due to their clean emissions and relatively small sizes. Microturbines are fully packaged modular machines that comprise the smallest-capacity CHP units available.

TPO: What kinds of funding resources are available to support CHP project development?

Breznicky: Energy efficiency upgrades at water and wastewater treatment facilities are eligible for low-interest rate loans through the EPA’s Clean Water [CW] and Drinking Water [DW] State Revolving Fund [SRF] programs. These upgrades can be individual projects or part of a larger overall upgrade.

Many states implementing the CWSRF and DWSRF programs award priority ranking points for applications that include energy-efficient upgrades and other sustainability, climate change and resiliency elements. In the past few years, the CWSRF program has required states to provide a percentage of its EPA capitalization grants to projects that meet “green reserve” criteria. These include green infrastructure, energy efficiency, water conservation and environmentally innovative projects. The priority ranking points and green reserve requirements have led to many projects receiving low-interest financing and subsidies. General information and specific state contacts for the programs can be found at:

• http://water.epa.gov/grants_funding/cwsrf/cwsrf_index.cfm
• http://water.epa.gov/grants_funding/dwsrf/index.cfm

TPO: What are some basic technical resources clean-water plants can turn to as they evaluate the potential of CHP?

Breznicky: An interim report, “Evaluation of Combined Heat and Power Technologies for Wastewater Facilities,” serves as a planning tool and examines commonly used and emerging CHP technologies for converting biogas to electric power and process heat. The EPA has also established the CHP Partnership [www.epa.gov/chp], a voluntary program that promotes efficient CHP technologies. The Partnership works closely with energy users, the CHP industry, state and local governments, and other clean-energy stakeholders to facilitate the development of new projects and to promote their environmental and economic benefits.

TPO: What specific kinds of resources does the CHP Partnership provide?

Breznicky: It offers a variety of tools and services designed to facilitate and promote CHP development. For example, CHP project qualification tools help to determine whether CHP is worth considering at a particular facility. The CHP Emissions Calculator compares the anticipated CH4, CO2, CO2e, SO2, N2O, and NOx emissions from a CHP system to the emissions from a separate heat and power system.

The CHP Partnership also offers resources for education and outreach, such as information for regulators, policymakers and utilities to encourage energy efficiency and CHP; peer-to-peer marketing and networking at workshops and conferences; examples of model state policies for promoting CHP; information about CHP markets; and topical email announcements highlighting Partnership activities, funding opportunities and upcoming events.

Other resources include information about the CHP project development process, including access to tools and recommendations to facilitate successful projects, information about CHP prime movers including cost and performance characteristics, current information on state and federal incentives applicable to CHP, and technical white papers and other clean energy resource documents.

TPO: In a nutshell, what words of encouragement would you offer to clean-water agencies considering CHP?

Breznicky: As a cost-effective means of making energy-efficiency gains, CHP represents a tremendous opportunity. The ability to add this technology to a wastewater treatment plant — and the benefits that can be gained through energy generation using the byproducts of an existing treatment process — is an opportunity that cannot be wasted.