Biogas digestate is a key byproduct of anaerobic digestion, offering significant benefits for agriculture and environmental sustainability.
As biogas production expands, digestate plays an essential role in nutrient recycling and the circular economy.
What is biogas digestate?
Biogas forms when organic materials like food waste, agricultural residues, and energy crops decompose in an oxygen-free environment – anaerobic digestion. While biogas is the primary output, the remaining substance, biogas digestate, is rich in essential nutrients like nitrogen, phosphorus, and potassium.
These qualities make it an excellent organic fertilizer for sustainable farming.
How is biogas digestate used in the EU?
The European Union manages biogas digestate in various ways, depending on environmental policies and market demand. Typical applications include:
- Fertilizer – Due to its high nutrient content, wet digestate is commonly applied to agricultural fields or processed into pelletized fertilizer, meeting EU standards for organic farming.
- Composting & further treatment – Some digestates undergo composting or drying for stability, easier storage, and odor reduction. Separating them into solid and liquid fractions enables precise nutrient application.
- Biogas recovery & advanced processing – Secondary digestion can extract additional biogas.
At the same time, technologies like ammonia stripping and membrane filtration help recover nutrients. - Limited disposal – While landfill disposal is discouraged, incineration may be necessary if digestate is contaminated or produced in excess.
The EU actively promotes digestate valorization through subsidies and policies, supporting its use in agriculture and soil restoration as part of a broader circular economy strategy. EU regulations, such as the Fertilizing Products Regulation (EU 2019/1009), set safety standards for nitrogen levels, heavy metals, and pathogens.
Is untreated biogas digestate safe for human health?
While biogas digestate is a valuable fertilizer, untreated digestate can harm human health and the environment if not managed properly.
One primary concern is pathogens and microorganisms, as raw digestate may contain harmful bacteria and viruses. However, proper
anaerobic digestion combined with post-treatment methods such as drying, pasteurization, or composting significantly reduces these risks.
Another issue is the potential presence of heavy metals and other contaminants, particularly in digestate derived from industrial waste or sewage sludge. This requires strict regulatory oversight to prevent harmful substances from entering the soil and food chain. Manure-based digestate can harbor antibiotic-resistant bacteria, raising concerns about its long-term environmental impact and prompting ongoing research.
Nitrogen and ammonia pollution is another challenge. Over-application of digestate can cause nitrate to leach into groundwater, affecting water quality. At the same time, ammonia emissions contribute to air pollution. The EU enforces strict regulations to tackle these risks, including a one-hour heat treatment at 70°C to ensure digestate safety before agricultural use.
Why further treat biogas digestate?
Biogas digestate contains a high moisture content, making storage, transport, and handling challenging.
Wet digestate can promote bacterial and mold growth and emit strong odors.
Drying digestate provides several advantages:
- Easier storage & handling – Dried digestate takes up less space, resists spoilage, and can be transported efficiently over long distances.
- Lower emissions – Proper digestate drying reduces greenhouse gas emissions compared to wet digestate.
- Sterilization & nutrient retention – Drying eliminates pathogens while preserving essential nutrients. ExergyPSSD® also sterilizes the digestate during drying.
However, the drying process must be carefully managed to maintain the integrity of organic compounds and prevent nitrogen loss through ammonia volatilization. This occurs when ammonium, a nitrogen-rich compound found in fertilizers and organic matter, converts into ammonia gas and escapes into the atmosphere. Effective drying techniques can minimize this loss, ensuring that digestate remains a valuable and sustainable resource.
Exergy drying technologies for biogas digestate
Choosing the right dryer is critical to ensuring digestate quality and sustainability. Drying is often one of the most energy-intensive stages in further digestate processing, making efficiency a key concern. Inefficient methods are costly and can negatively impact the environment, product quality, and the bottom line.
Exergy’s pressurized superheated steam dryer (ExergyPSSD®) offers an energy-efficient and sustainable solution:
- Up to 85% lower energy consumption – Compared to conventional dryers.
- Excess steam recovery – Steam generated during drying can be recovered and reused for energy or heating other applications.
- Complete sterilization – High-temperature steam sterilization kills pathogens, producing Class A biosolids.
- Preserved nutrients – Unlike traditional hot air dryers, ExergyPSSD® prevents nutrient degradation, oxidation, and uneven drying.
- Environmental sustainability – With no emissions released into the atmosphere, ExergyPSSD® contributes to a greener processing solution.
Maximizing the value of biogas digestate for a sustainable future
Biogas digestate is more than just a byproduct—it is a vital resource for sustainable agriculture and renewable energy. Its rich nutrient content plays is crucial in soil enrichment and the circular economy. Advanced drying technologies, such as Exergy’s superheated steam dryer, enhance digestate’s efficiency and environmental benefits by improving storage, reducing emissions, and ensuring safer application.
Combined with stringent EU regulations, these innovations help maximize digestate’s potential while minimizing risks.
Sustainability in the biogas industry goes beyond energy production. Responsible digestate management—from raw material selection to anaerobic digestion and post-processing—is crucial for a circular system. A sustainable biogas future relies on optimizing each process stage, with environmental responsibility at the heart of renewable energy production.
