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Watts from Wastewater New Jersey is already a top-ranked state in on-site utilization of biogas produced by wastewater treatment plants, but ongoing research could help craft incentives to push it even higher. BY LISA GIBSON
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f New Jersey’s 28 wastewater treatment plants employing anaerobic digestion (AD) systems, at least 10 have infrastructure in place to utilize the resulting biogas, many producing heat and/or power. It may not seem like an overwhelmingly high count, but the number is more impressive when also considering the fact that the entire country has a total of 1,500 wastewater treatment facility AD systems. With only 250 of those wastewater treatment plants using their biogas, New Jersey’s position is suddenly much more progressive. “It’s certainly in the upper-middle third of all states,” says Patrick Serfass, executive director of the American Biogas Council. New Jersey is close behind its fellow northeastern state of New York, which has 16 wastewater treatment AD systems that use their biogas, and behind Connecticut, at 21. Oregon has 22 that use the methane they produce, and California tips the scale at 50, with several others having one or two, Serfass cites. The remaining plants with AD systems that choose not to use their methane for energy, simply employ the process because it reduces the volume of the waste, much like a cow’s stomach digests food, Serfass says. In addition, it improves the quality of the waste on the backend. “The active digestion upgrades the product that you’re digesting,” he says. Typically, without an anaerobic digester, the material is classified as a Class B biosolid, which is a hazardous material. “If you take that sludge and put it through a digester, you make heat, you make biogas, and then you make digestate, which is both in a liquid and solid form.” The solid that comes out of the digester, in comparison to the solid that comes out of the primary wastewater treatment, is a Class A biosolid and nonhazardous. It can be sold as compost or fertilizer, in addition to occupying a much lower volume. “Therefore, depending upon how much biogas they’re making and what the will is of the municipality, they may or may not even want to use the biogas, which we think is a total waste,” Serfass says. “But that’s their own business decision, and we’re trying to encourage folks to use that biogas.”
Exploring Options The New Jersey Board of Public Utilities agrees that unused biogas is a waste and is tasking the state’s newly formed Renewable Natural Gas Work Group with three assignments: identify the number of locations currently producing biogas through AD, identify plants without digesters that would OCTOBER 2011 | BIOMASS POWER & THERMAL 39