What Happened
The city of Wilmington, Delaware, is awaiting approval on the second phase of a greening initiative that will save nearly $1 million every year, and will reduce greenhouse gas production by 13,000 metric tons annually.
The Challenge
Minimizing the environmental footprint of a local wastewater treatment facility was the key objective, for several reasons. First, the Hay Road Wastewater Treatment Plant is a major source of greenhouse gas emissions. That’s because methane gas is continuously burning at the location; methane gas is a naturally occurring byproduct of the wastewater treatment process. Second, the facility uses significant electricity from the grid. And third, the facility hauls biosolids out of state for disposal. That’s a big environmental footprint to minimize, but it wasn’t the only objective: the other was saving money.
The Solution
The solution, which is part of a $50.5 million city initiative to reduce energy consumption and greenhouse gasses, consists of two parts:
- Using the Gas for Power: Instead of just burning the methane gas generated at the plant, the methane will be captured and combined with similar gasses produced by an adjacent Cherry Island Landfill. Those gasses will create a renewable, self-perpetuating fuel source to power the plant. The plant would then stop purchasing more costly electricity from a power utility.
- Breaking Down Waste: The plant would also employ a thermal drying technology, utilizing excess heat from electricity generation, to greatly reduce the volume of biosolids produced by the plant (biosolids are the naturally occurring byproduct of treating wastewater).
Regarding the latter initiative, above, it is estimated that biosolids will decrease from 135 to 35 tons per day. More importantly, the “pelletized” end product is a marketable additive to fertilizer or fuel.
The City will seek to finance the project through municipal bonds or a 20-year municipal lease. Under the city’s Guaranteed Energy Performance Contract, annual savings to the city are guaranteed to exceed financing and other project related costs.
Other Cities
When the project is completed, Wilmington will join several other major cities that have switched from the land application of biosolids to thermal drying, including Philadelphia, Washington, D.C., and Baltimore.
Other approaches have also been taken. In San Jose, California, for example, a biosolids facility will employ “anaerobic digestion” to process 270,000 tons of organic waste annually sent to a landfill. This system actually converts the waste into composting material for use as soil or fertilizer. Excess renewable bio-gas will be used to power garbage vehicles. Details were covered in a broad study of California digestion facilities in Oakland, Santa Barbara County, Chino, as well as Toronto, Canada. Also available for review is San Jose’s RFP seeking companies to build a new anaerobic digestion facility.
A feasibility study conducted by the City of Palo Alto to research the economics of an anaerobic digestion facility is also available; the study looked at five different scenarios, and reviewed greenhouse gas emissions as well. The city determined that the greatest emissions savings came from the renewable power generated by the new plant.
More Resources
An introduction to methane capture, written for students, was published by the EPA, and a more detailed report was released by the Congressional Research Service. The EPA actually has a landfill methane outreach program, which includes details on projects, programs, partners, tools, resources, and more.
More specific details on recovery of methane gas in landfills were aggregated by U.S. Power Partners, including related links and relevant projects. The Mississippi Technology Alliance, which also is pursuing methane gas projects, as published a briefing on anaerobic digestion and methane gas capture.