Biogas is a high-value clean and renewable fuel potentially available at thousands of clean-water plants that have anaerobic digesters.

Many facilities already put biogas to good use, such as to feed boilers that supply heat for the digesters, other processes and buildings; and to fuel combined heat and power systems.  Today the value of biogas is growing with government financial incentives for gas-to-energy projects and for conversion to renewable natural gas for pipeline delivery.

One area gaining attention is the addition of food waste and other high-strength organic material to biosolids digesters to boost gas output significantly. Still, many facilities still simply flare their digester gas. One business aiming to lead in drawing more value from biogas is Anaergia. The company specializes in projects that turn wastewater into RNG, fertilizer and clean water using innovative technologies.

With experience on four continents, Anaergia helps clean-water agencies implement high-efficiency anaerobic digestion and optimize biogas production and usage. The company serves the municipal solid waste, wastewater, agriculture and food processing sectors.

Last May Anaergia was named Net Zero Carbon Champion in the prestigious Global Water Awards, presented by Global Water Intelligence. Yaniv Scherson, chief operating officer, talked about trends and potentials in biogas in an interview with Treatment Plant Operator.

TPO: Taking a high-level view, how would you rate the value of biogas?

Scherson: The biogas market is a booming space and can play an essential role in decarbonization, for two reasons. First, it can be converted to RNG, which is the only fuel that has carbon-negative intensity. It sequesters carbon when produced, unlike solar and wind, which are carbon-neutral. Second, it is immediately dispatchable. No change in infrastructure or distribution is necessary.

TPO: In biogas development, where do you see the greatest potential at present?

Scherson: We’re focused on biogas-to-RNG projects, which constitute a huge opportunity. At present only a couple dozen of the roughly 1,300 treatment plants in the U.S. that have digesters are producing RNG. Most others are either running CHP or flaring. There are about 13,000 wastewater plants that don’t have digesters, but could.

TPO: Why does digester performance need to be improved?

Scherson: Digesters are using mixing technology that is decades old and is inefficient. Basically, we require the tanks to be very large because digesters typically run at 2% solids. If we thicken it any further, the viscosity gets too high for most conventional mixers to be able to operate efficiently. If we thicken the solids — for example, if we triple the solids concentration — we can make the digester one-third the size, or achieve three times the throughput from the same tank.

TPO: How can that improvement be accomplished?

Scherson: It’s very simple to do. The mixers are basically boat propellers installed on the inside circumference of the tank. They’re placed at various heights to create a swirl in the horizontal plane and a swirl in the vertical plane. They work at low speed and high torque; imagine a spoon mixing honey. This configuration can achieve a mixing performance standard that to our knowledge no other technology can meet, which is 90% of the mixing volume above the critical velocity all the time.

TPO: How significant a contribution can biogas make in reducing greenhouse gases and combating climate change?

Scherson: One statistic that adds perspective relates to California, which has a waste diversion law designed to get organic waste out of the landfills. Wastewater treatment plants are the best places to go with that waste. In California, 156 wastewater plants have digesters. If that state’s food waste were sent to those digesters to produce biogas, the reduction in greenhouse emissions would be equivalent to taking 3 million cars off the road.

TPO: Does the biogas-to-energy market benefit from any recent federal legislation?

Scherson: Yes. The Inflation Reduction Act includes an incentive under the investment tax credit that provides direct reimbursement against the capital cost that wastewater treatment plants and utilities incur for projects that generate RNG. It can cover up to 40% of the capital cost.

TPO: What incentives exist for RNG after it has been produced?

Scherson: There are two broad categories. First are renewable fuel credits from federal and state governments. Second, there is the voluntary market in which companies buy RNG for decarbonization purposes. They are basically buying RNG at a premium price, and that provides an economic incentive for utilities to pay for the needed infrastructure upgrades.

TPO: What do you see as deterring clean-water agencies that have anaerobic digesters from investing in some form of biogas-to-energy?

Scherson: I prefer to think in terms of opportunity. Everybody has barriers, but they all can be overcome with new tools in the toolbox. One tool is the economic incentive by way of the Inflation Reduction Act. Another tool is an alternative project delivery model called P3, which stands for public-private partnerships. In that model, a private company invests in all the infrastructure while the utility pays no money upfront. In return, the utility receives an ongoing revenue stream to help fund capital improvement programs and rate stabilization.

TPO: How does the P3 model differ from traditional project development?

Scherson: The traditional design-bid-build model is very time-consuming. There is an RFP process to select an engineer. The engineers do the design, which goes to bid. The bids are too high, so the project goes back for value engineering. Each step takes a long time, during which prices go up. In the P3 model, the technology, construction and engineering team is together from day one, sitting with the client to design the system and deliver it faster and more economically. Technical and economic risks are shifted away from the utility onto private companies that have expertise in delivering and operating biogas projects.

TPO: How would you assess the potential for co-digestion as a way to increase biogas production?

Scherson: Food waste is so good because it has a very high energy yield, double that of wastewater sludges. That’s simply because the food waste has not been already digested by humans. All the energy that our bodies would otherwise consume when we eat the food is available to the digester. Every wastewater treatment plant that has digesters can co-digest. There is no limitation. The question is what technologies and what design configurations are needed to retrofit the plant to make it work.

TPO: What forms of food waste are the most viable?

Scherson: The keys to success are homogeneity and scale. The preference is for high energy density, so high COD. Brewery waste, dairy waste, expired packaged goods, all qualify. Then we look at what is available in large quantities, such as material from grocery chains and other businesses. The kind of machinery used to slurry it up doesn’t matter.

TPO: How would you rate the potential for capturing post-consumer food waste, such as from green bin programs, for co-digestion?

Scherson: That has wide applicability. California is unique in having a statewide mandate, and that is a huge opportunity for the 156 treatment plants in the state that have digesters. Some states in the Northeast also have source-separated food waste streams, or requirements for large generators to have source-separated collection. Another driver is the high cost of disposal in many places, including the Northeast. So there is a pure economic incentive for food waste generators to find lower cost outlets. Wastewater plants are ideally positioned to serve that function.