Environment
The production of biogas is a good idea for society in general, but also for the individual farmer, because:
- It produces renewable energy
- The farmer gets a better fertilizer from livestock manure
- Odor nuisances are limited
- The environment is saved from emissions of greenhouse gases
- The environment is saved from discharges of nutrients
- Organic waste is utilized and contributes to recycling
The physical and chemical change that occurs with the slurry in the biogas reactor gives a changed fertilizer effect in the field. The most significant change is the increase in the content of plant-available ammonium nitrogen. This is an advantage, as it is primarily the ammonium nitrogen that the plants can utilize. By using the degassed biomass as fertilizer, there is therefore the possibility of a higher harvest yield and a saving on the purchase of nitrogen in commercial fertilizer.
The thin and easy-flowing degassed slurry penetrates the soil relatively quickly. It helps to reduce the risk of ammonia evaporation.
When slurry is degassed, a number of substances which are always in the slurry are broken down. When using degassed slurry, the odor nuisance that may be associated with the application is reduced.
The risk of infection is reduced by processing the livestock manure in a biogas plant. The relatively long residence time at high heat reduces any infectious germs in the biogas reactor. If necessary, sanitization can be established at the biogas plant.
Society
In connection with the establishment of biogas plants, increased employment is typically created in an area. Especially in the establishment phase, local craftsmen can benefit. After establishment, an effort must be made in connection with operation and maintenance of the facility.
The local community can be proud of contributing to the solution of society-created climate and environmental problems and at the same time contributing to the production of local renewable energy.
In biogas plants, significant volumes of residues from agriculture, households and industry are digested, ensuring the recycling and reuse of the content of nutrients as fertilizer. With an intelligent use of biogas, these can be used to ensure the recirculation of phosphorus, which is a limited resource.
Biogas production has the potential to make a substantial contribution towards EU climate target for 2030.
The net climate impact of biogas exceeds the CO2savings from substituting fossil fuels.
Not only does biogas substitute fossil fuels, but it also reduces the carbon footprint from methane emissions during agricultural manure storage. However, biogas production also has a climate impact in the form of methane loss, energy consumption, and transportation of biomass and manure.
Proper management of the stables, combined with biogas, can significantly reduce the climate impact of livestock manure.
General Recommendations for the Mitigation of Environmental Impacts
Biogas production from manure and agricultural residues is widely recognized as a sustainable practice. The produced biogas can be used to generate both heat and electricity through combined heat and power (CHP) systems, or upgraded to biomethane for direct use as a renewable substitute to natural gas. However, despite the potential of these biofuels as green solutions, their overall production chain contains critical environmental hotspots that should be thoroughly examined.
To better understand the environmental outcomes of biomethane production, it is important to evaluate its environmental performance throughout its entire life cycle. By applying the Life Cycle Assessment (LCA) methodology, all environmental impacts linked to biomethane production are quantified and grouped into various representative categories. Thus, aggregated environmental factors such as Global Warming Potential (GWP), Terrestrial Acidification Potential (AP) and Freshwater Eutrophication Potential (EP) offer valuable insights into all impacts associated with climate change, soil integrity, and aquatic ecosystems, respectively.
Global Warming Potential (GWP)
The GWP impact category evaluates the potential contribution of a product or process to climate change, by quantifying all produced greenhouse gas (GHGs) emissions such as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). These gases are converted based on their heat trapping ability compared to CO₂, leading to the utilized metric unit of kg CO₂eq. The most common GHG emission sources in a biomethane production plant, alongside some reflective mitigation strategies are presented in the following table.
GWP Source |
Impact Mitigation Strategy |
Transportation of biomass to the biomethane production plant (fuel consumption)
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Optimization of transportation logistics, reducing fossil fuel consumption and subsequent GHG emissions.
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Operation of the upgrading unit (high electricity demands)
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Installation of renewable energy sources to meet the plant’s electricity and thermal demands.
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Operation of the Anaerobic Digestion unit (natural gas boilers)
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Operation of the upgrading unit (CO₂ emissions during purification)
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Capture and valorization of CO₂ as material for chemical compounds and building materials.
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Upgrading & Anaerobic Digestion units (biogas/methane slips)
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Frequent equipment maintenance to ensure gas-tight operating conditions.
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Storage of digestate (methane emissions)
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Implementation of closed storage conditions.
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Spreading of digestate (methane emissions)
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Further digestate processing for ammonium sulfate ((NH₄)₂SO₄) production as soil fertilizer.
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Terrestrial Acidification Potential (AP)
The AP impact category measures the capacity of acidifying substances, such as sulfur dioxide (SO₂), nitrogen oxides (NOₓ) and ammonia (NH₃) to affect the pH of soil, significantly reducing its quality. All the aforementioned compounds are converted based on their acidifying potential compared to SO₂, leading to the utilized metric unit of kg SO₂eq. Emission sources linked to AP in a biomethane plant and mitigation strategies are shown below.
AP Source |
Impact Mitigation Strategy |
Storage of manure/digestate (NH₃ emissions)
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Implementation of closed storage conditions.
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Spreading of digestate (NH₃ volatilization)
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Low-emission application techniques (e.g., trailing hose spreaders, injections).
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Anaerobic Digestion unit (SO₂, NOₓ from boilers)
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Installation of renewable energy sources for heat and electricity.
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Spreading of digestate (soil acidification)
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Regular soil testing to optimize digestate application rates.
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Freshwater Eutrophication Potential (EP)
The EP impact category evaluates the potential of unregulated nutrient discharge, like phosphates (PO₄³–) and nitrates (NO₃–), into water bodies. This nutrient release causes excessive algal blooms that deplete oxygen levels and harm aquatic life. The following table lists key nutrient discharge sources and mitigation strategies.
EP Source |
Impact Mitigation Strategy |
Storage of digestate (PO₄³– & NO₃– leaching)
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Closed storage and maintenance to ensure leak-proof conditions.
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Spreading of digestate (nutrient leaching)
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Controlled spreading based on soil nutrient needs.
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Spreading of digestate (excessive nutrients)
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Further processing (separation, extraction, evaporation) to produce commercial fertilizer substitutes.
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Upgrading unit (nutrient-rich wastewater)
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Wastewater treatment using appropriate filtration systems before discharge.
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