Biogas from clean-water plants and other sources has potential to become a significant clean and renewable fuel in the nation’s energy portfolio.

Biogas-to-energy systems are common at clean-water plants, but not nearly as prevalent as they could be.

That’s the assessment of Patrick Serfass, executive director of the American Biogas Council. Serfass and his organization work to expand the use of biogas from anaerobic digesters at wastewater treatment plants, livestock farms and food waste recycling facilities.

The council’s mission is to create jobs, and foster environmental sustainability and energy independence by growing the biogas industry in the U.S. Serfass notes that the nation has more than 2,200 sites producing biogas in all 50 states.

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However, he says, that volume of projects lags far behind Europe, which has more than 10,000 operating digesters, some of which make their communities fossil-fuel free. Serfass talked about biogas, its potential as a mainstream renewable fuel, and obstacles to its broader adoption in an interview with Treatment Plant Operator.

TPO: Taking a broad view, how would you describe the status of biogas energy in the U.S.?

Serfass: While we have more than 2,000 operational biogas systems, there is potential to develop almost 14,000 new systems. Biogas-to-energy is a technology that is commercial and mature. There is always room for research and development, but it is a mature technology that has not been rolled out as much as it could be.

TPO: Where are these existing biogas systems?

Serfass: In addition to the systems at wastewater treatment facilities, there are 259 on farms, 39 stand-alone systems that digest food waste, and 645 systems at landfills. That sounds like a lot, but on farms there is potential for about 10,000, and in food waste there is potential for about 1,000. We have potential for biogas systems to be built all over the country, but a lot of places are only experiencing their first systems because there is no permitting process in place for building new systems. Several speed bumps along the way are slowing down development. The industry could be growing a lot faster than it is today.

TPO: What does the biogas picture look like in the wastewater treatment sector?

Serfass: The wastewater sector has 1,269 anaerobic digesters operational today, but only about 800 to 900 treatment plants are using the biogas they produce. The others tend to be facilities that are just flaring the gas. We estimate that another 3,000 to 4,000 biogas systems could be developed at treatment facilities greater than 2 mgd. There is a great deal of latent energy available in every wastewater treatment facility that could be better used.

TPO: Is there a minimum treatment plant size at which biogas energy becomes feasible?

Serfass: People differ on the minimum size, anywhere from 1 mgd to 5 mgd. We believe in the lower threshold because some treatment facilities are adding food waste to their digesters. When you do that you can have a feasible project even below 1 mgd because food waste produces 10 to 35 times more biogas than sludge does. Sludge is basically food waste from people that has already been digested once. Food waste hasn’t been digested and so contains a lot more energy. You can add about 10 percent food waste to a wastewater treatment biogas system and double the biogas yield. That basically doubles the revenue, or doubles the savings in the case of wastewater facilities, since they use biogas to offset their electricity and heating costs.

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TPO: In the wastewater sector, what are the main factors holding back development of more biogas energy?

Serfass: For wastewater treatment systems, running a biogas system is outside their primary job, which is to clean up the water, remove contaminants and return fresh, clean water back into the waterways. They don’t want to have a more complex system to operate. They want to stick to what they know and make sure that it’s as reliable as possible. And yet the energy cost at a treatment facility is almost always the second highest cost behind labor, and usually the largest energy cost for the entire city. The other main deterrent is the extra capital cost.

TPO: Are there any obvious ways to get around those issues?

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Serfass: Yes. One way we’ve seen that happen is for a private company to build or upgrade the digesters and manage the biogas at no up-front cost to the municipality. A good example of this is the village of Ridgewood, New Jersey. They had a digester and they wanted to accept food waste to help cities in the region recycle food waste and to increase the potential for biogas to offset their energy cost.

TPO: How did that community accomplish its goals?

Serfass: They brought in a private developer who promised them a long-term low and predictable energy cost. The developer upgraded their existing digester and got a long-term lease to run and manage the facility. The developer built it at no cost to the municipality. The system meets more than 100 percent of the facility’s energy needs. It includes a solar array that boosts energy production. The developer also gets an upside in that they can profit from tipping fees for taking the food waste and from running the biogas system very efficiently.

TPO: Are there any other creative development approaches?

Serfass: One concern of wastewater facilities is that they don’t want the complexity of dealing with variability in food waste — they don’t want to handle the receiving end of it. That’s where a company like Waste Management comes in. They create a transfer station, separate the food waste from the trash they’re hauling anyway, and create a liquid slurry from the food waste. Then they deliver that high-energy slurry to the treatment plant. One place they’re doing this is at the Los Angeles County Sanitation District’s wastewater treatment facility.

TPO: Is there any momentum toward plants converting from aerobic to anaerobic digestion in order to produce biogas?

Serfass: It depends mainly on the age of the system. If the aerobic system is old, there is substantial benefit in turning it into an anaerobic system. Historically, digesters were installed in wastewater facilities to reduce the volume of sludge, and not to produce energy. Aerobic systems were often put in to do just the bare minimum needed to treat the material. But when you look at all the benefits of an anaerobic digester, it becomes clear pretty quickly that it might make sense to invest in one.

TPO: What would be a good way to quantify the potential benefits of greater biogas system development?

Serfass: We see biogas systems having potential to electrify 7.5 million homes or to reduce greenhouse gas emissions by the equivalent of removing more than 15 million passenger cars from the road. Optimal development would catalyze an estimated $40 billion in capital deployment. It would also generate 335,000 construction jobs and 23,000 permanent operations jobs. That’s for all potential biogas systems, not just the wastewater sector.

TPO: As for stand-alone biogas systems, such as food waste digesters, what factors tend to hinder development?

Serfass: First, being able to sell all the energy as gas or electricity. Many states have difficult net metering policies like net metering caps. Also, facilities looking to sell the biogas to a utility need to be able to access the natural gas pipeline easily and at reasonable cost. And long-term feedstock contracts are essential. To finance a food waste system, for example, it’s necessary to show the bank that feedstock will come in very consistently for five to 10 years. Some states have policies that require commercial organic waste to be recycled, and those policies can really help in getting feedstock contracts.

TPO: What forces are driving or hindering development on the agricultural side?

Serfass: There are plenty of farmers who just want to farm. Like wastewater operators, they don’t want to operate a biogas facility — and yet they have manure and nutrients that need to be managed. A lot of issues with spreading raw manure on fields can be alleviated by first digesting the manure.

TPO: Can local politics and public objections get in the way of biogas projects?

Serfass: Most biogas systems are well run and valued in their communities, but some biogas facilities around the country have experienced objections. Some complaints they hear are unbelievable, like a complaint about odor when the wind is blowing in the opposite direction. But sometimes there’s an issue with the digester that the operator hasn’t noticed. So it’s necessary to have a validation process and an openness on both sides to reach an understanding. The most common issue is fear of the unknown. So, communication with the local community when putting in a digester is key. If people are unfamiliar with the technology, you need to tell them about it, be available to answer questions and respond quickly to any issues after startup.

TPO: Are most biogas-to-energy facilities combined heat and power projects?

Serfass: Yes. A digester has heating needs, and the engine-generator is usually right there, so CHP is easy to do. You’re almost always producing renewable heat as a part of the biogas system.

TPO: Are there any issues in meeting standards for export of biogas to utility pipelines or using it for vehicle fuel?

Serfass: No. Biogas upgrading systems can meet all those standards. We have a pipeline specification on our website ( that is a mix of gas quality standards from all across the country. In practice, every utility has a different standard. There’s not much standardization among utilities, and they tend to have a lot of autonomy to do what they want. And while electric utilities are required to allow interconnection, gas utilities are not required to allow renewable gas into their pipelines, even though gas from biogas facilities that has been processed properly is of higher quality than the gas already in the pipeline. So the issue is usually not the gas quality, but getting permission to inject into the gas pipeline.

TPO: In your opinion, how important is it to maximize the use of biogas in terms of energy supply, clean energy, and reducing carbon emissions?

Serfass: It’s so very important that we utilize our resources to their highest potential. At present, less than 3 percent of food waste is recycled in our country. So we have a huge opportunity to use that material. In the process, we’d probably save businesses money because they have to pay to handle that material anyway. In biogas systems we create renewable energy and lots of great products that return nutrients to the soil, turning food back into food.

TPO: What parting advice would you offer to operators of clean-water facilities?

Serfass: I would encourage them to be bold and to explore how adding or upgrading a digester could benefit not only their facility but also the community. We are rolling out a series of operations and maintenance training programs for digesters this year. Operators can learn more by visiting our website.

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