“Waste not, want not,” Philadelphia resident Benjamin Franklin famously said, and the home of the Liberty Bell has taken his words to heart. Instead of flaring off waste gas from the city’s wastewater treatment plant, the Philadelphia Water Department has teamed up with the renewable energy company Ameresco to build a $47.5 million wastewater-to-biogas facility with a capacity of 5.6 megawatts.
Though small compared to conventional energy generation, the new Northeast Cogeneration Facility will be fairly large for biogas. Beating out a Texas-sized, 4.3 megawatt wastewater-to-biogas facility planned for the City of Dallas, also by Ameresco, it’s a good example of how budget-stressed local governments are turning to sustainable technologies in order to squeeze every dollar out of untapped resources.
Biogas helps municipal budgets
Ameresco has been something of a pioneer in the municipal wastewater-to-biogas field. In 2010 the company partnered with the City of San Antonio to open the first grid-connected wastewater-to-biogas facility in the U.S., enabling the city to sell biogas on the open market.
Philadelphia won’t be selling off the biogas of its worthy citizens, but it does expect the new facility to cut its energy bill for wastewater treatment by $12 million over its 16-year contract with Ameresco.
That’s part of a broader renewable energy goal the city set under its sustainability plan. In 2008 Philadelphia received only 2.4 percent of its electricity from alternative sources, and the aim is to get that up to 20 percent by 2015.
No magic in biogas production
Wastewater treatment plants naturally produce copious amounts of biogas, since they involve the fairly straightforward process of decomposition. As microorganisms digest the organic material in wastewater, they produce gas. In the past, the gas was simply flared off for safety and odor prevention, but with impurities removed biogas can be stored, transported and used just like any other gas.
Some treatment plants, including Philadelphia’s, already capture at least some waste biogas and use it to keep the decomposition process running at an optimal temperature. The Ameresco project takes it a step farther by using biogas to run a turbine to generate electricity on site.
The electricity will be used to run pumps and other equipment at the plant, which previously depended on fossil fuels. The result is an expected cut in carbon emissions for wastewater treatment by almost 22,000 tons each year, the equivalent of taking more than 4,800 cars off the road.
Lightening the load of municipal infrastructure
If that sounds like a lot of carbon emissions from one treatment plant, consider that a large municipal wastewater facility handles millions of gallons of liquid per day, at more than eight pounds per gallon. Though gravity comes into play as much as possible, at one point or another all of that liquid must be pumped from place to place. Factor in screens, scrapers and other equipment, and you are talking about one gigantic piece of energy-sucking infrastructure.
Harvesting biogas is one way to glean some energy value out of the muck. Some localities are also taking advantage of the available acreage at sprawling wastewater facilities to set up solar arrays.
Fertilizer and even bioplastics are two other potential sources of revenue from wastewater.
Home grown biogas
When President Obama talks about “American-made energy,” wastewater treatment might not be at the top of his mind, though in fact the Philadelphia project was funded through the President’s signature American Recovery and Reinvestment Act.
More to the point, wastewater is on the way to playing a significant role in the tapping of unmined energy resources on American soil.
In addition to biogas from human waste, the U.S. EPA Agstar initiative has prompted an increased interest in livestock waste-to-biogas operations, and biogas recovery from biorefineries is also in the future.
Follow Tina Casey on Twitter: @TinaMCasey.