Advanced BioFuels USA

by Ron Kotrba (Biomass Magazine)  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.  —  … 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.”

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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.”

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According to (John) Wintle (project and facilities manager for Exeter Agri-Energy, a spinoff of Stonyvale Farm), 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.”

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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 (Patrick Serfass, the executive director of the American Biogas Council) 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.

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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.” 

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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.” 

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“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.” 

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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.

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“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 (Brian Langolf, director of the biogas program at the University of Wisconsin-Oshkosh) 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.”   READ MORE