Innovators Aim to Give Anaerobic Digestion a Shot in the Arm

As headlines cry out we have to move faster to cut greenhouse gas emissions and reverse climate change, anaerobic digestion (AD), with its ability to trap methane and turn it into renewable commodities, is gaining attention. Still the technology is slow to catch on in the U.S., but some industry players are working to pick up the pace through innovations to make the process more efficient, cheaper, and to expand its capabilities. From AI-driven add-ons to experiments with some unlikely feedstocks, new concepts are starting to take shape.

Processing highly variable feedstocks, each with their own makeup of sugars, fats, and other organic compounds is a complex job. Researchers at the University of Iowa are turning to automation to address associated challenges.

A team there is toiling to develop a fully automated system, at scale, that includes sensors and machine learning to gain more insight on feedstocks to bolster operational efficiency.

“We are seeing that, coupled with real-time feedstock composition sensing, mathematical models can inform AD operations to increase biogas production and expand the range of organics feedstocks that can be used,” says Craig Just, Donald E. Bently associate professor in Engineering, University of Iowa.

With these capabilities, automation can reduce staffing costs and lost revenue from downtime and ultimately make projects more profitable more quickly, he says.

This past year was a good one for discovery. That’s when the Iowa University team demonstrated that data from a supervisory control and data acquisition system (SCADA) collected at a municipal co-digestion facility could forecast biogas production, which Just calls a first step toward a digital twin model – these virtual representations of real-life scenarios can spot potential issues before they happen, monitor and maximize performance.

But cutting-edge innovations are slow to evolve, despite the demand for technologies to sustainably manage burgeoning organics loads while putting them to use. Just points to his home state as an example.

“In Iowa, we have enough feedstock to support over 1,000 digesters, yet we have less than 100 of them in operation. So, AD is hindered by the overall lack of innovation.”

What is needed as much as technology he says is a paradigm shift towards capitalizing on underutilized, heterogeneous organic feedstocks “to turn the carbon we have into the carbon we need.”

Researchers at UC Davis are investigating methods to pelletize manure and compost, and in the future may apply the technology to manure digestate from ADs.

Frank Mitloehner, professor and air quality specialist, UC Davis, has been involved in a pilot-scale pelletization project for application at an almond orchard while a colleague of his has run a similar project on a dairy farm to produce manure pellets.

The research in this space has been limited due to that these are energy- intensive and expensive processes.

Mitloehner and his team are working to improve the economics of treatment methods to increase the biodegradability and biogas production rate.  They are homing in on maximizing nutrient recovery from digestate as well as shortening treatment times.

“With all of these improved efficiencies we should be able to drive down cost, energy consumption, and emissions and more rapidly speed adoption,” he says.

Another UC Davis project entails investigating ways to enhance processing of liquid and solid fractions for applications such as barn bedding, soil amendment, or concentrate used as a liquid fertilizer.
And Mitloehner and colleagues are measuring methane emissions of manure lagoons before and after digester installation to assess outcomes.

“The goal of this research is to collect data that can improve the usefulness of technologies already in place. Sustainability is a journey, not a destination. And a lot of our work is about precise improvements to existing systems that will have big impact,” he says.

Scientists from Iowa State University, Penn State University, and Roeslein Alternative Energy are assessing how perennial grass and winter crops fare as feedstock, which is being co-digested with manure.

The USDA grant-funded project called C-CHANGE: Grass2Gas aims to incentivize farmers to plant these new crops and prairie grass on environmentally sensitive lands or where the corn and soybean they typically grow don’t yield well. In essence farmers get paid to cut their emissions and help grow a renewable energy market. The innovators powering Grass2Gas get to be at the forefront of this movement.

In mixing manure with new agricultural feedstocks, the partners’ ambition is to demonstrate that it’s possible to create more diverse products and increased value throughout the supply chain, says Lisa Schulte Moore, professor and co-director of the Bioeconomy Institute at Iowa State University. Schulte Moore leads the multi-institutional, transdisciplinary effort.

Plants produce a lot of methane. That’s good for AD if the technology is soundly designed to capture the potent gas. But not so good if the methane releases to the atmosphere. The team has kept this reality in mind.

“Our technoeconomic and life-cycle assessment modeling indicates that

efforts to make AD systems really, really tight and avoid methane leakage during production, cleaning, injection, transport, and utilization are crucial,” Schulte Moore says.

At an industry level, more widespread understanding is also being developed regarding the importance of covered storage for digestate liquids and digestate solids.

More concepts slowly come to life intended to someday take the 2,400 or so operational U.S. biogas facilities (mostly small operations) further and to bring more of them up from the ground. A handful of regions are moving faster to scale.

“Anaerobic digestion is a fascinating space right now. Seeing it at the scale we are in California is exciting,” Mitloehner says. Though he shares one particular pain point that’s on his mind.

“I think how we use the resulting biogas is still working itself out, and research exploring new avenues to use biogas will allow the technology to continue to be used in the future.”