Biogas Energy Recovery Project

A new biogas energy recovery facility, developed in Texas by the City of Dallas Water Utilities (DWU), represents the kind of promising and productive partnerships being forged across the country between municipal governments and the private sector. In models such as this, city agencies collaborate with private corporations that provide know-how and technical support, conduct research, cover capital costs, and oversee operations. For this project, agency leadership sought ways to convert the biogas emitted from anaerobic digesters at city-owned wastewater plants into a usable source of energy.

DWU, a not-for-profit department of the City of Dallas, provides water and wastewater services to about 2.5 million people in Dallas and 27 nearby communities. The DWU wastewater biogas-to-energy facility, which went online in April 2011, converts methane or biogas into energy. Projects such as this one are notable as they take an otherwise harmful greenhouse gas—methane, which is significantly more toxic than carbon dioxide (by a factor of 21)—and use it to generate electricity and thermal load to power wastewater facilities.

Taking the “waste” out of wastewater
Wastewater is the used water that goes down the drain in homes and businesses. Currently, the DWU facility can treat up to 110 million gallons of wastewater per day. Traditionally, as required by law, excess gas at a wastewater facility is burned off by flares. Flaring is safe and generally effective, but often represents money wasted for a utility.

DWU worked in a public-private partnership to design, build, and operate the 4.3 MW biogas capture and refining facility. With municipal budgets shrinking and energy and infrastructure “to do” lists expanding, this kind of public private-partnership is garnering attention and accolades—and for good reason. This new facility is expected to save the City of Dallas at least $1.5 million annually, and offset approximately 60% of the electricity that the DWU currently pulls from the grid. This facility has already shown to be clean, green, and cost-effective, and is capable of treating and delivering up to 1,200 standard cubic feet per minute of biogas to power the wastewater plant. The city already has plans to incorporate future production increases.

In addition, the project was designed to convert waste heat, efficiently making use of it as a renewable resource. This approach allows DWU to utilize about 80% of the biogas resource. In comparison, a typical electrical production plant might only be able to utilize 35% of its energy product. The biogas facility was designed with a capacity to reduce greenhouse gas emissions, and its operation is equivalent to reducing annual greenhouse emissions from nearly 35,000 passenger vehicles, or the reduction of the carbon dioxide emissions from over 20 million gallons of gasoline consumed (according to the US Environmental Protection Agency’s emission reductions and environmental benefits calculator).

Market potential
DWU is leading the way for other wastewater utilities in the US with its decision to recycle biogas energy. The first sewage facility in the States to refine biogas for the natural gas grid went operational in September 2010, when the San Antonio Water System (SAWS) opened a new biogas facility at the Dos Rios Water Recycling Center. This methane capture technology is commonly constructed at landfills across the country, but there is growing interest among municipal leaders throughout the country who are looking to increase energy savings in other settings.

Both of these Texas-based projects in Dallas and San Antonio should serve as a model to other wastewater treatment plant managers and operators throughout the country. There are other opportunities to build these projects, and these projects showcase the revenue opportunities—whether in the form of royalties for the gas, or a cost-effective source of energy, and particularly in markets where energy prices are high.


Author Michael T. Bakas is senior vice president of Renewable Energy at Ameresco, Inc.

Ameresco, Inc.
www.ameresco.com