SAWS uses biogas as renewable energy source and creates revenue stream

SAWS uses biogas as renewable energy source and creates revenue stream
SAWS partnered with Ameresco to generate revenue from its biosolids production at the Dos Rios Water Recycling Center. (Photos courtesy of SAWS)

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With electricity costs on the rise, now is the time for wastewater treatment facilities to consider digester methane as a source of renewable energy and revenue.

San Antonio Water System (SAWS) has partnered with national energy company Ameresco to generate revenue from its biosolids production at the Dos Rios Water Recycling Center. SAWS was the first wastewater utility in the United States to partner with a private-sector company to sell biogas.

SAWS produces 140,000 tons of biosolids per year, yielding about 1.5 million standard cubic feet of biogas each day. “We use about 10 percent of what we produce,” says Meg Conner, SAWS director of environmental services. “We reserve enough to run our boilers that heat the digesters.”

Now instead of flaring off excess biogas gas, SAWS sends it via pipeline to the 1-acre Ameresco facility on the plant site where it is processed into natural gas. Ameresco delivers a minimum of 900,000 cubic feet of the natural gas each day to a commercial pipeline to sell on the open market.

The sale of biogas is the third leg of SAWS’ environmental trifecta. “That’s a term we coined for the three major programs in which we beneficially use our products from the wastewater treatment process,” says Conner. “They include making compost out of biosolids, recycling treated effluent, and providing biogas as a fuel.”

SAWS put in $800,000 and Ameresco invested $6.5 million in 2008 when the partnership started. “We issued a request for proposal for beneficial use of our biogas,” says Conner.

“We were very generic and open-ended; we did not specify anything to the proposers about what we wanted. We let them propose their ideas on how they would use our gas. Ameresco’s proposal was the most beneficial for SAWS.” The two entities signed a 20-year lease.

Renewable energy in the United States is increasingly necessary, and wastewater facilities generating revenue from biogas are setting the stage for change. Biogas is clean-burning, naturally produced domestic fuel.

Improved air quality for residents around the wastewater treatment plant is major environmental advantage of selling the biogas rather than flaring it off. By using some of the biogas for its own needs, the plant also reduces its dependence on traditional power plants that use fossil fuels.

Selling the gas has financial benefits: “We receive a 12 percent royalty from all the gas Ameresco sells on the open market,” says Conner. “We estimate we save about $20,000 to $50,000 per year in maintenance costs for not having to maintain the flare and various equipment.

“My recommendation is if you can make it work, do it. Companies like Ameresco, this is their business and they’re good at it. They’re in it for a profit, so they run it efficiently. They’re experienced and they have a wide background of resources to call on.”

Ameresco helps organizations meet complex energy management challenges with an integrated comprehensive approach to energy efficiency and renewable energy. 


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