Many cities and counties are finding ways to generate energy through the operations of their wastewater treatment facilities, helping cut costs and moving the facilities toward self-sustainability. For most communities, generating energy through the wastewater treatment process is important for both financial and environmental reasons. As energy costs increase, the facilities get a break by producing their own power, and, because most self-sustaining wastewater plants generate green energy, they help reduce greenhouse gas emissions.

According to the U.S. Environmental Protection Agency (EPA), wastewater treatment plants account for approximately 3 percent of the electric load in the United States, and energy costs can account for approximately 30 percent of the total operation and maintenance costs of those plants. Finding ways to generate energy in-house does not just decrease the amount of greenhouse gas emitted from the wastewater treatment process; it also reduces energy costs and demands for outside energy.

Targeting 100 percent energy needs

Since 2005, Gresham, Ore., has made strides toward its goal of achieving 100 percent energy sustainability at its wastewater treatment plant by 2015. The facility treats 20 million gallons per day and serves 108,000 customers in Gresham and surrounding towns.

Using a cogeneration engine that Chicago-based Veolia Water North America operates on behalf of the city, the plant generates its own electrical power and heat from the biogas that is produced by the plant's digesters as a natural byproduct of the wastewater treatment process, says Alan Johnston, senior engineer for the city and manager of the wastewater treatment program. The generator takes the biogas, which is about 65 percent methane, removes moisture and contaminants, and produces about 60 percent of the energy needed to run the plant, Johnston says. Since the 395 kilowatt (kW) cogeneration engine became operational in November 2005, electricity costs at the facility have been reduced by an average of $20,000 per month.

The Energy Trust of Oregon, a nonprofit organization that manages energy efficiency programs statewide, gave the city a grant to pay for the cogeneration system's building and installation. The grant funded 8 percent of the project costs, and an Oregon Business Energy Tax Credit was used in partnership with a local private business to pay for another 30 percent of the costs, Johnston says.

Gresham's wastewater plant also produces energy with a 420 kW solar panel that supplies 8 percent of the plant's energy needs. To produce even more energy on-site, Gresham's wastewater department is designing a receiving system for fats, oils and grease from restaurants and food service establishments, which will be directly injected into the plant's digesters, dramatically increasing the plant's gas production, Johnston says. "It could turn into more than we need to power the plant," he says.

While management hopes the new collection program for fats, oils and grease will eventually bring the plant to 100 percent energy independence, there's no way to know for sure yet, Johnston adds. "It will need to be tested and proven." The city also is planning a micro hydropower project, which will involve placing small turbines in pipes that run from the treatment plant to the river. Johnston and his staff have completed a feasibility study and are attempting to secure permits and grants. The project would produce about 7 percent of the plant's electrical needs.

Because the region is bound to experience growth and an increase in demand for wastewater treatment, the city has extra land set aside so it can pursue a cost efficient solution to meeting those future energy needs. While there are no specific plans for using the available land, Johnston says it could be used to install additional solar panels or some yet-to-be-developed energy solution. "Our goal is to be energy independent with cost-effective renewable power production alternatives," Johnston says.

ARRA funds solar power

Although city officials in Pueblo, Colo., were interested in producing energy at the city's wastewater treatment plant, such a project was not financially feasible until the federal government passed the American Recovery and Reinvestment Act (ARRA).

Thanks to ARRA funding and with the partnership of Overland Park, Kan.-based Black & Veatch, Pueblo installed 309 kW of direct current solar panels on the site of the city's original water reclamation facility, which is now abandoned. The panels provide 465,000 kilowatt-hours of AC electrical power per year — about 40 percent of the energy needed to operate the current wastewater plant.

The majority of funding for the solar energy project came from a federal grant through the ARRA. Pueblo received a $1.5 million, zero-percent interest green infrastructure loan to help pay for the solar panels and their installation, and an additional $700,000 for the project came from city funds. In addition to stimulus funding, the city received a $200,000 renewable energy rebate from Black Hills Power, the local utility. The rebate was $2 per direct current watt, up to 100 kW. The city also will receive annual renewable energy credit payments from the utility of $115 per megawatt hour, which will be approximately $53,000 annually.

In addition to solar panels, the plant has anaerobic digesters for methane gas, which are used to heat the plant during the winter. Those digesters produce approximately 12 percent of the energy needed for the plant's operation.

Because the city plans to expand its wastewater treatment plant within the next few years, the percentage of needed energy that can be supplied by existing solar panels will drop to 15 percent, says Gene Michael, wastewater director for Pueblo. "But, we have a lot of open space and room for more solar panels. We have no current plans to add more, but as time goes on, it will be to our benefit to add more solar panels to control costs and ultimately to pass on the savings to our constituents," he says.

Improving environment, finances and reliability

The Orange County, Calif., Sanitation District worked with Black & Veatch to install central power generation facilities at both of the county's wastewater treatment plants. Those central generation facilities include three engine-driven generators at Reclamation Plant No. 1 and five engine-driven generators at Treatment Plant No. 2. The county uses the biogas produced in its solids digestion process to fuel the central generation engines. Excess heat from the engines is captured in exhaust heat boilers, which generate steam that is used to heat the digesters to 98 degrees Fahrenheit at both plants.

In addition to the engine-driven generators, Orange County recently installed a 300 kW fuel cell in its wastewater plant. The fuel cell will begin operations this month, generating electricity and producing hydrogen that will be dispensed at a hydrogen vehicle fueling station at one of the county's reclamation plants.

The hydrogen fueling station is located adjacent to the county's natural gas fueling station just off of a major freeway "and will be available to anyone with a hydrogen vehicle and a swipe card," says Jim Herberg, director of engineering for the Orange County Sanitation District. Orange County is contributing $500,000 for the project, and the remaining $800,000 will be paid by grants from the U.S. Department of Energy and the California Air Resources Board.

Orange County's central generation facilities produce about nine megawatts on average. The electrical power is used by the treatment plants, which have an average demand of about 13 megawatts. "So, the majority of the electricity required to treat wastewater at the Orange County Sanitation District is derived from renewable biogas that is generated from our treatment process," Herberg says.

For Orange County, operating wastewater treatment plants that generate their own energy makes sense for a number of reasons. "One thing we accomplish by having our own renewable energy source on site is improved reliability," Herberg says. "Our central generation facilities, along with power from the electrical grid, give us two independent sources of power."

It also promotes green energy, an important goal for the region, as "the operation of our electrical generation facilities is restricted by newer air quality limitations and potential future regulations," Herberg says. "Our goal for the future is to continue to utilize this green source of power while meeting air quality regulations."

As more cities and counties work toward sustainable operations, the EPA expects to see increasing numbers of energy-producing and self-sufficient, wastewater treatment plants. Local governments like Gresham, Pueblo and Orange County serve as viable models for other cities and counties in the quest for sustainability and energy conservation in the wastewater treatment process.

Nancy Jackson is a Huntsville, Ala.-based freelance writer.

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