Get with the Program

Biogas producers struggling to generate revenue from their digestate may find an opportunity to turn this around through the American Biogas Council’s Digestate Standard Testing and Certification Program.
By Ron Kotrba | September 05, 2019

Stonyvale Farm is family-run dairy operation in a remote part of central Maine, near Exeter. “It was started by my grandfather in the 1950s,” says John Wintle, project and facilities manager for Exeter Agri-Energy, a spinoff of Stonyvale Farm. Although Stonyvale Farm was officially formed in the mid-20th Century, its ancestors had been practicing crop and livestock husbandry in Maine since the 1800s. Today, the farm centers around roughly 1,800 cattle, including 1,000 milking cows and hundreds of calves and dry cows. In addition, Stonyvale Farm grows corn, grass, haylage and alfalfa to feed its livestock.

Exeter Agri-Energy was formed to run two anaerobic digesters built at Stonyvale Farm in 2011. “We built two anaerobic digesters to process cow manure and food waste,” Wintle says. “At first, we thought if we built one to process food waste, there would be waste haulers to bring us the food waste. But we quickly realized that’s not how it works. As a result, my brother formed Agri-Cycle Energy, which sources food waste and hauls it here to our site and to other digesters around New England.”

Approximately 25,000 gallons of food waste and 30,000 gallons of cow manure are fed daily into the digesters at Stonyvale Farm. “The food waste and manure are mixed together in the digesters and are digested together,” Wintle says. “They don’t come into contact with each other until they’re in the digester.”

The biogas produced by Exeter Agri-Energy from the anaerobic digestion (AD) of food waste and cow manure fires three 1-megawatt cogeneration units that turn generators in order to make power for Stonyvale Farm. Any power left over is sold to the utility company. The process is continuous based on hydraulic retention time, pumping in material to be digested and pumping out raw digestate, which is the leftover, nutrient-rich material undigested by the microorganisms used in the AD process. Raw digestate is a mixture of liquids and solids.
In Exeter Agri-Energy’s process, the raw digestate is pumped out of the digesters to a separator for removal of undigestible fiber, which is stockpiled in a building near the digesters and used as cattle bedding. The remaining liquid that comes off the separator is stored in a 10,000-gallon tank on-site, some of which is reused in the process. “The [food waste] organics tend to be thick, so when we get to the point when we need to pump it, we add digestate, so it is pumpable,” Wintle says. “We also mix some with the manure. Anything left over is stored in a lagoon until it’s ready to spread.”

Once ready to spread on the field as a soil amendment, tanker trucks are loaded with digestate and driven to the fields for application. “We usually spread with tanker trucks,” Wintle says, “but if it’s too wet, we’ll offload the liquid digestate into tanks pulled by tractors and spread it that way.”

All of Exeter Agri-Energy’s digestate is used locally. “I tried to figure out how many millions of gallons of digestate we make in a year, and I don’t really know—but it’s a lot,” Wintle tells Biomass Magazine. “We grow corn, grass, haylage and alfalfa, and we rotate crops with a local potato famer, so some of the digestate is spread on their field too. We don’t sell any at this point. I don’t think we’re at the point yet where people are willing to pay for it. As far as the reason, it’s hard to say.”

Many Uses, Little Value
Patrick Serfass, the executive director of the American Biogas Council, says digested manure from 1,000 cows on average will produce roughly 50,000 tons per year of raw digestate. Some fraction of digestate is always used as a soil amendment, Serfass says, with liquid being the most common because of its weight and expense to transport. “There is usually a symbiotic relationship between a digester site and a place to use the liquid digestate,” Serfass says.

According to Wintle, digestate is an even better fertilizer than cow manure for a variety of reasons. “We feel that we generate better crop yields as result—but to quantify this is a tough thing to do,” he says. One reason Stonyvale Farm likes digestate over manure as a fertilizer is the odor. “Digestate odor is much less offensive,” Wintle says. “It’s a subtler odor and goes away quicker.” He says the farm could not spread manure in summer because windows are open, and the odor would create issues with neighbors. “But we can apply digestate any time,” he says.

The other benefit of digestate over manure is its inorganic nitrogen content. “Nitrogen can take two forms, organic and inorganic, and crops can only use inorganic nitrogen,” Wintle says. “During the digestate process, nitrogen is converted from organic to inorganic, so as soon as it is applied, crops can take it up, which reduces the risk that it will run off the field or go away before the plants can use it. Organic nitrogen has to be broken down before crops can take it up.” 

Solids are usually separated from digestate with a screw press or centrifuge. “It may or may not be dried further to reduce weight and make more transportable,” Serfass says. “Sometimes the fiber is further separated from the solids, which would be hay that wasn’t digested. It has a sawdust consistency, dark in color. It’s odor-free and earthy.” Sawdust and sand are the two most popular materials on which to bed dairy cows. “It keeps them comfortable,” Serfass says. “The fiber can be used to replace buying sawdust or sand to bed animals, so not only are they using a coproduct from biogas production, but they’re replacing a cost on the farm. Then, when they scrape the [manure-laden] material up after use, it’s very compatible with the digester.”

All kinds of interesting products can be made from digestate fractions beyond its most common uses as a soil amendment and animal bedding: Fiberboard, flower pots, peat moss replacement, fertilizer granules of various sizes, and much more. The problem, however, is that digestate has a low perceived value ranging anywhere from zero to $50 a ton, depending on what the digestate is replacing. “If you’re replacing a very specialized fertilizer, then companies are willing to pay a premium for it,” Serfass says.

Generating revenue from selling digestate is “a lot more difficult than it should be,” Serfass says. “Few people recognize its incredible nutrient and agronomic value today. It’s a perception issue.” As a result, in order to build biogas systems, project developers must rely solely on revenues from gas sales and tipping fees while trying to bring the cost of managing digestate as close to zero as possible. “We’ve got work to do as an industry to help educate consumers,” he says. “They just don’t know what it is. It’s not a known name. That’s why products don’t use ‘digestate’ in their name—it’s not a recognized word. ‘Hey, want some digestate?’ ‘What is that?’ It’s the lack of awareness, that’s the biggest reason its value is so low.”

The annual revenue-generating market potential for digestate when just three aspects of the material are considered—its nutrient-enriched fiber and recovered phosphorus and nitrogen—is roughly $1.4 billion, according to Serfass. Too often, however, managing digestate is an expense to producers, not an income generator. How, then, can the biogas industry effectively relay the true value of digestate to consumers and, more importantly, get them to pay for the product? The answer, according to Serfass, is by convincing them the product is safe to use, that it comes from a good source—digesters—and that it has the nutrients the producers say it does. Accomplishing this is the reason why ABC launched a brand-new effort: The ABC Digestate Standard Testing and Certification Program.

Program Details
The program is industry-led and creates a voluntary, third-party verification system of “quantifying, characterizing and communicating the physical and chemical qualities of digestate,” according to ABC. “The program provides standardized terminology, quality management systems and test methods administered by program-certified laboratories for characterizing digestate. The characterization allows digestate producers to relay important information regarding composition and appropriate beneficial uses of digestate to regulators and users of digestate. The program enables the biogas industry to effectively communicate the valuable environmental and agronomic benefits of digestate to key stakeholders and to serve as a model for any future local, state or federal regulation of digestate, not otherwise addressed by existing statute or voluntary compliance programs.”

Serfass tells Biomass Magazine, “We’ve looked at what’s preventing digestate from being sold more. It’s definitely a perception issue. There’s not enough awareness of what digestate has in it. Customers don’t necessarily need to know what digestate means, but they need to know what nutrients are in it, and that it’s safe. We designed this program to address those issues—to provide customer assurance that the product they’re buying has the ingredients the seller says it has in it and trust it’s safe.”

How the program works for biogas producers is simple. The first step is to achieve steady-state digester operation. Next, they sign up for the program and pay a fee based in part on digestate volume in order to access the program details and choose a lab. The fees range from four-tenths of a cent to 6 cents per ton. “The bigger a system is, the lower the cost is per ton,” Serfass says. The third step is to have the digestate tested, and the chosen lab determines if the product passes or fails. “We test for a few elements just like U.S. EPA does with wastewater products—pathogens, viruses, physical contaminations and heavy metals,” Serfass says. “If the product passes the tests, the customer can be assured it’s safe to use. Then we test for a number of agronomic levels—nitrogen, phosphorus and potassium (NPK)—and others like organic ammonia, nitrates, micronutrients, pH, the moisture content of the material, stability and a few other things. For someone who wants to know what they’re placing on their field or garden, this is really important. When a producer sells digestate as a certified product, then the customer can be assured and trust what’s on the label—that it’s safe and ready to use.” 

If a producer fails because, for example, heavy metal content is too high, then a protocol is in place to address this. “Based on what test the digestate fails, this will tell us what’s wrong with the biogas system,” Serfass says. “Digestate from any well-operating system will pass. They only fail if the digester is not running well or accepted feedstock that they didn’t know had some bad stuff in it. When it fails, we look at what part failed. Then we go back to the digester, talk with the operator, determine the cause and test again. They are suspended after a failure until a pass result is gained. Then they must test periodically, more frequently until a history of passing is built.”

Once a producer passes, the fourth step is following program instructions on logo use and marketing for the product’s applied use, including whether this is “restricted” or “generally unrestricted.” “If you are just land-applying digestate broadly, then you don’t need all the tests in the unrestricted category,” Serfass says. “We wanted digesters that are never going to sell their product and just land-apply it to be able to show regulators or neighbors that the material is safe.” If, however, the digestate will be used to grow crops that people eat, for gardens or other uses in which more intimate contact with customers will be made, then the “generally unrestricted” category is recommended. “We just test for few additional things such as volatile solids, micronutrients, pH, soluble salt,” he says. “But if it’s just being applied to land for crop growth later, this is not as important, so the ‘restricted’ certification will save money.” 

Laboratories that wish to be part of the program must first sign up and pay an annual fee of $1,300. Then, a third-party verifier validates registration and responds to the applying lab and the administrator if the quality assurance and control procedures are approved. The program administrator then adds the applicant to the list of certified labs. Afterwards, the newly certified lab is directed to follow program instructions. Finally, an inter-lab validation must be completed in the next 12 months.

The inter-lab validation is run by a third-party verifier. The validation process entails one liquid sample be sent to all labs with instructions on the tests needed to be performed, or the product’s intended end-use classification. Once testing is complete, the results are sent to the third-party verifier, which confirms the test results and advises a pass or fail to each lab and ABC.

Brian Langolf, director of the biogas program at the University of Wisconsin-Oshkosh, is on ABC’s board of directors and digestate standard committee. Langolf was integral in developing the digestate certification program and runs the supervising lab used for third-party verification.

“Program development stemmed from what ABC and the digestate standard committee saw as a need for industry to help create the market and add value to digestate, which adds value to projects in general,” Langolf tells Biomass Magazine. “The program sets standards for people to follow to operate properly, ensuring the material meets those standards in order to provide assurance in quality and value when digestate is used in fertilizer or as a soil amendment. I definitely think it’s important to the industry, and to the future of biogas projects. It will help in securing funding from project developers as well, if they make sure they’re ABC-certified and meet industry standards. The big thing is getting more word out, advertising the certification program and its benefits, and getting more people signed up.”

So far, the program is being received positively, according to Serfass. “The challenge is just starting out,” he says. “We need a lot more producers so we can share their experiences with others. We’re looking forward to developing a body of data to show how consistently valuable and safe digestate is. Over time, even though the data we collect is confidential, we will aggregate it and show what the performance of digestate is, build more trust and show customers how valuable it is.”

Program benefits go beyond increasing the awareness, salability and marketability of digestate. It is also a way for the industry to self-regulate without policymakers jumping in and creating additional regulations with which producers must comply. “It is a standard to which [government officials] can refer without creating additional regulations,” Serfass says.

Biogas producers unable to sell their digestate now could sell it for $1 to $20 a ton once the market develops and certification provides added value. For small producers, this may mean $5,000 a year, and for the larger ones, maybe $20 million.

If ABC has its way, producers such as Wintle should find value in ABC’s digestate certification program. And while Wintle couldn’t say for sure why consumers are unwilling to pay for digestate despite its benefits, he has some guesses.

“Purchased fertilizer from fossil fuels is still cheap enough that it’s not worth the effort,” Wintle surmises. “To make a more salable product, especially in Maine where we are—it’s very remote—we would have to dewater our digestate further in order to haul it more cost-effectively. We have a separator that removes the fiber material, and we use that for bedding for cows, but that’s the only step we do at this point. We’ve looked at technologies to take this further, and we may end up there at some point, but it’s still in its infancy, at least for dairy-farm applications. For dairy farms, it’s still new and expensive, but we’ll keep our eye on it.”

Langolf certainly understands this perspective. “We’re competing against fossil fuel-based products—natural gas-derived fertilizers—so compared to products derived from renewable natural gas or digestate, it is definitely a challenge,” he says. “But there are other ancillary benefits from digestate that petroleum-based fertilizers don’t provide. If you add digestate, you’re adding organic content. Studies show improving the organic makeup of soil improves moisture and provides for a better microbial population so less fertilizer has to be added in the future. It’s about the long-term health of the soil from digestate versus the short-term benefits from fossil fuel products.”

Author: Ron Kotrba
Senior Editor, Biomass Magazine
218-745-8347
rkotrba@bbiinternational.com