- Anaerobic Digestion (AD): is a biological process in which microorganisms break down biodegradable material in the absence of oxygen creating two important products: biogas and digestate.
- Thermal gasification (Gasification): is a physico-chemical oxygen depleted process in which the carbon containing components of the biomass break down to syngas instead of being completely combusted
- Feedstock: AD can process almost any biogenic material including solid and liquid manure; energy crops; catch crops; agricultural waste and residues; industrial food and beverage waste; and sewage sludge and the organic fraction of municipal solid waste. Gasification can theoretically process any carbon containing material and is a complementary technology to Anaerobic Digestion (AD), since it can treat high-solids feedstock with low anaerobic biodegradability; these include lignocellulosic feedstocks such as wood chips, and non-recyclable waste fractions of biomass origin currently landfilled or incinerated for energy recovery.
- Biogas: the primary product of AD is a methane-rich renewable gas composed of 50 to 65% methane and 35 to 50% carbon dioxide.
- Digestate: remaining part of organic matter treated by AD, rich in nutrients and nitrogen, commonly used as an organic fertilizer in agriculture.
- Syngas: the primary product of gasification is a mixture of carbon monoxide and hydrogen, with traces of methane and carbon dioxide. It may be used directly for electricity generation, or further transformed to increase its share of methane.
- Ashes: all non-nitrogen nutrients contained in the resulting ash, which are recycled to the producing lands, e.g. forests. To maximize the recycling of nitrogen, all feedstock high in nitrogen should always be treated through AD.
- Biomethanation: besides methane formed spontaneously during gasification, syngas can be transformed into methane through two catalyst aided reactions: the water-shift reaction (hydrogen and carbon dioxide formed from carbon monoxide and water) and the Sabatier reaction (methane formed from carbon dioxide and hydrogen).
- Biomethane: when carbon dioxide and trace gases in biogas are removed, a methane rich renewable natural gas substitute is left in the form of biomethane. Biomethane can be injected into the gas grid, used as a vehicle fuel or used for combined heat and electricity generation.
Gasification and anaerobic digestion (AD) contribution to key European policy areas:
- European climate targets: high-rate dedicated anaerobic digesters using organic wastes as feedstock reduce the need for the landfilling of organic materials thereby cutting greenhouse gas emissions, avoiding groundwater pollution and helping to replace mineral fertilisers. Anaerobic Digestion cuts methane emissions from landfill and slurry pits while reducing the use of fossil fuels, commercial fertilisers and chemical inputs. Large scale production of biomethane from biomass gasification will also significantly increase the availability of renewable alternatives to fossil fuels.
- European energy security: biomethane from gasification and AD is a locally generated, decentralised, flexible and storable energy supply, balancing the intermittent production of other renewable energy sources and improving energy security. Large scale thermal biomass gasification makes it feasible to create truly renewable natural gas fuelled balancing power schemes for the future. Gasification and AD are the most cost-effective and energy efficient ways to produce green gas for grid injection. Biogas and syngas powered CHP plants, with over 40% power efficiency and over 85% total efficiency, are among the most energy efficient ways to cogenerate heat and power. High-solids lignocellulosic waste fractions can be transformed into higher value energy carriers such as automotive fuels or electricity, depending on the needs of the market. Fully implemented, AD and gasification combined have the potential to make all gas in the European natural gas transport system renewable.
- Food security and resource efficiency: AD is the technology which currently delivers the most benefit from organic wastes and crops, extracting energy whilst recycling the nutrients and organic matter. Crops grown for biogas production can be integrated into food crop rotations, thus improving the overall productivity of farming and providing preceding crop value and soil quality improvements. Gasification utilizes feedstocks high in solids and lignocellulose and therefore does not compete with AD for waste food feedstocks. It has the potential to make the valorification of high-solids waste fractions more versatile and flexible, when adding the choice of fuel generation and injection of biomethane into the natural gas transport system.
- Improved air quality: biomethane used as a transport fuel reduces particulate matter (PM10) and NOxemissions by over 95% and 25% respectively, when compared to diesel engines with catalytic converters.
- Bioeconomy: the Biogas industry generates thousands of green jobs, invigorates the European countryside and reduces energy and agricultural bills through the local production of bioenergy and bio-fertiliser. Short-rotation forestry on fallow lands in agriculture expands the options for the European farmer, and represents an opportunity to complete the nutrient cycle for bio-fertilisers from waste streams that may not be suitable for food production, such as wastewater treatment plant sludge. Biomethane production from biomass gasification will invigorate the European market, by increasing the versatility and value of the European waste streams. It represents a great opportunity for industries based on forest resources, by adding a new market outlet for wood chips, and making it possible for the paper and pulp industry to add automotive fuels to its product line. It may also create a new export market since many of the leading technology suppliers are European.
- Bioenergy: Anaerobic Digestion facilitates the sustainable use of feedstocks by enabling the use of crops which support biodiversity and deliver high ecological standards.
- Prevention of contamination:in many EU Member States manure is spread on fields without any treatment to control pathogens, potentially causing biological contamination. Treatment through AD at higher (>50°C) or at mesophilic temperatures greatly reduces the number of plant and animal pathogens within a feedstock. AD carries the benefit of also destroying most weeds.