biogas FAQs
One of our primary products, Bio-fertiliser, is natural chemical-free fertiliser which includes all the necessary nutrients for plant growth as well as lots of micro-organisms for healthy soil.
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What is landfill biogas?
This is produced by anaerobic degradation of organic materials in landfill sites, and although sometimes called biogas, is not as reliable in terms of quality as biogas produced from anaerobic digestion. It is estimated that 30% of anthropogenic methane emissions emanate from landfill, which is why the EU Landfill Directive has introduced the requirement to reduce organic residues going to landfill sites.
Modern landfill sites capture a significant proportion of the gas, using Combined Heat and Power technology (CHP) to convert it to electricity, but because landfill sites are situated away from other human activity, the heat element is rarely utilised. Landfill gas production gives the UK the dubious honour of being the largest producer of ‘biogas’ in Europe and it accounts for approx 37% of the UK's total renewable energy resource.
In landfill the organics produce methane for 25 years and if this could be diverted to anaerobic digestion facilities instead, the methane can be efficiently and safely digested in 40-80 days.
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What goes into the biogas plant as feedstock?
Feedstocks include a wide range of biodegradable residues, including:
- Animal by-products (Category 3)
- Food processing industry waste (bulk)
- Food processing industry waste (liquid)
- Food and drink obsolete/surplus stock (bulk)
- Food and drink obsolete/surplus stock (liquid)
- Kitchen food waste
- Local authority kerbside collection food waste
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What comes out of the process?
Three quarters of the dry solids are converted to biogas and the remainder is a nutrient rich bio-fertiliser in liquid form which can be used to replace commercial fertilisers on farm or park land.
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Is biogas renewable energy?
Yes. Biogas is a renewable energy source and eligible for Renewable Obligation Certificates (ROCs). The biogas is normally used in place of fossil fuels in a CHP plant which produces heat and electricity. Biogas is also included in the Road Transport Fuels Obligation if it is reformed by removal of the carbon dioxide.
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Is biogas technology sustainable?
Yes. Many of the feedstocks are by-products which would otherwise end up in landfill sites, and can produce methane adding to global warming, and liquids which pollute waterways. The bio-fertiliser can be used on soil to displace chemical products and this completes the life cycle of plants growing in soil, being processed, sold, becoming bio waste and finally returning to the soil as a valuable nutrient.
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Does the process reduce the mass of the residues?
It's complicated, but if, for instance, our feedstock was 100 tonnes of vegetable residues (with about 78% water content), and after digestion we would be left with 84 tonnes of digestate, the missing 16 tonnes having been converted to biogas. After de-watering the 84 tonnes of digestate we would be left with 68 tonnes of liquor and 16 tonnes of solid fibre; both the liquor and the fibre contain substantial amounts of nitrogen and other soil nutrients plus large amounts of organic material useful for application to farmland.
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How can AD deliver best value to Councils?
In December 2002 the Minister for the Environment, Michael Meacher, agreed in principle that Biogas Technology/Anaerobic Digestion should be re-classified within the definition of BV82b (Performance indicator for the percentage of household waste sent by the Authority for composting). This means that every tonne of residue processed in a biogas plant can be counted towards re-cycling targets, by contributing towards best value targets within this category.
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Where does it stand in the hierarchy of Reduce, Recycle, Compost, Recovery, and Disposal?
AD biogas technology is classed as recycling ahead of Composting as it is an energy consuming process whereas anaerobic digestion produces a large surplus of renewable energy.
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Can biogas technology help with legislative targets?
Very much so, including EU Landfill Directive, EU Animal By-Products Regulation and Climate Change Legislation.
Scotland's Zero Waste Plan
It aims to drive change and inspire households, businesses, community groups, local authorities and the wider public sector to change the way they view and deal with waste. It contains a broader approach to tackle all waste, not just waste collected by councils.
EU landfill directive
EC landfill directive 99/31/EC, has set out mandatory targets for the reduction of biodegradable residues sent to landfill. By 2020 these must amount to no more than 35% of that produced in 1995.
EU Animal By-Products Regulation
Since 1st May 2003, bio-fertiliser from biogas plants can be spread on land under the EU Animal By-Products Regulations 1774/2002.
Climate change legislation
A biogas plant meets the objectives of climate change legislation because it prevents the uncontrolled emission of methane and carbon dioxide to atmosphere, because it enables organic waste to be recycled as a fertiliser, reducing the need for artificial fertilisers and because it produces a renewable energy which is able to replace fossil fuel.
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Is the technology proven?
Internationally proven with thousands of biogas plants in mainland Europe and a growing number in the UK.
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What can biogas be used for?
For producing heat and electricity from a CHP (Combined Heat and Power) unit, for re-processing into bio methane or used to power vehicles.
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What can the Bio-fertiliser be used for?
It can be used on farmland as whole digestate, or, using belt-press equipment, de-watered to form a fibre compost and a liquid. All these products contain Nitrogen, Phosphates and Potash which can be used to replace expensive mineral fertilisers. The Bio-fertiliser also contributes to the organic matter content of the soil, enhancing biological activity, availability of nutrients and water retention.
