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Biogas Council leader says digestate can help with fertilizer crisis

The leader of the American Biogas Council says digestate from anaerobic digesters is a great source of crop nutrients.

Patrick Serfass with the American Biogas Council says, “All of the nitrogen, phosphorus, and potassium, all of that N,P, and K that we all need is in our waste if we can just extract it.”

Serfass tells Brownfield that digestate from anaerobic digesters can’t replace all the commercial fertilizer, but it can make a significant contribution to farm nutrient needs. “We’re talking millions of tons of organic waste that can be recycled, and of that, you end up with millions of tons of fertilizer, so it’s a huge amount.”

Serfass says the organic waste from digesters is a domestic, concentrated nutrient source that can help alleviate the cost and availability problems with commercial fertilizer.  He says having more digesters also puts the supply of digestate closer to the demand. “There are people and animals everywhere. Most importantly, where there are people and animals, that’s normally where the fertilizer is needed, so it’s distributed all around the country where it’s needed. It’s just a matter of us utilizing it.”

Serfass says more biogas systems should be built to utilize the nutrients and the methane produced by digesters.  Right now, he says there are 26-hundred biogas systems in the U.S. with at least one in every state, but that’s less than 15% of the potential market.

AUDIO: Patrick Serfass from the American Biogas Council discusses digestate as a fertilizer source with Brownfield’s Larry Lee.

• Digestate as a crop fertilizer sounds like a win-win solution but it has its fatal flaw – lack of ongoing rigorous testing for PFAs (as well as other serious contaminants like microplastics and antibiotic resistant bacteria strains). In Fremont, Michigan, the digestate from the Fremont Regional Digester tested positive for PFAS in December 2024. It was only through local concerned citizen petitioning that the tests were conducted. They are NOT currently required in Michigan nor any other state that I am aware of.

  The following from a Michigan Environment, Great Lakes, and Energy (MI EGLE) letter to the owner of the digester and accompanying digestate lagoons regarding the presence of PFAs at levels that were cause for concern due to
  lack of data out there on the threat of PFAs in digestate causing build up in local surface and well water.

  “Eleven different PFAS compounds were detected in the samples, and two PFAS
  compounds, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS)….
  evaluation of the data and the characteristics of the digestate is required to fully
  understand the risk posed to soil and groundwater from its land application. Even with
  additional evaluation, it may not be possible to determine with any certainty, the nature
  and extent of the impacts to soil and groundwater…..The detection of multiple PFAS compounds makes the inertness of the digestate questionable. Further, Section 7 of the AUA makes clear that if materials that are land applied are determined to pose an unacceptable risk to
  public health, safety, welfare, or the environment, the person responsible for placement of the materials (* name redacted ) will be liable for the performance of response activities and response activity costs under Part 201.
  • The effect of land applying PFAS contaminated digestate is unknown. The science related to acceptable concentration of PFAS in soils, crop uptake of PFAS compounds, and risks to agricultural properties is still being developed.
  Applying PFAS impacted digestate may contaminate groundwater, nearby residential wells, soil, and crops grown on impacted fields…”

  Until it can be adequately regulated and tested for things other than just the standard N, P, K values, and other minerals valuable for crops, digestate should not be deemed the wonderful “organic” fertilizer that the biogas industry claims it to be. It’s generally given to local farmers for free! Free “organic” fertilizer? Something doesn’t add up. Digestate is the biogas production wastewater, plain and simple. Untested for the presence of PFAs and microplastics, it’s just unregulated waste that may pose a threat to land and water. American farmland should not be serving as a cost free landfill for the biogas industry’s waste.

  Reply

  • “What goes in must come out”, agree that there could be better oversight, but it has zero to do with the fact that it comes from an anaerobic digestion system. They don’t contribute to PFA’s, they are either present in in the incoming material or not. If material with PFA is going to waste water treatment, landfill or compost, the output is the same. WWTP’s can’t remove PFA’s, and pass them through to your drinking water, landfills leach PFA to groundwater, as does compost. If EPA and local authorities want prevent PFA contamination, it has to be removed i.e. banned, which would be celebrated by all.

    This was a dumb and shortsighted decision in Michigan, because of odor complaints which were being remediated, nothing more.

    Countries around the world use digestate safely, as the majority of AD feedstock is upstream, your “villain” here are the chemical company that continues to produce PFA’s in there ever changing form, and EPA who’s mandate to regulate those materials is increasingly pulled by the political winds.

    Reply