Frequently asked questions
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Also known as Biogas Technology, it is a natural biological process for treating biodegradable waste by means of bacterial action in the absence of oxygen. It is a fully proven commercial process which generates a biogas which can be used via a CHP unit for electricity generation and heat for export (producing a substantial net surplus after powering the plant) and a liquid bio-fertiliser for application on land. Biogas plant will achieve in 30 days what a landfill site does in 25 years and without polluting the atmosphere and land. Compact Biogas Installation
From anaerobic digestion it is usually about 60-65% Methane, 35-40% Carbon Dioxide and trace elements of H2S depending on the process. The Carbon Dioxide has been previously sequestrated by plants and therefore does not add to Global Warming and the H2S is easily be removed before use. Biogas is also produced from landfill, but this is on less predictable quality (see landfill gas)
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 “real” 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 an imperative to reduce organic wastes going to landfill sites. Modern landfill sites capture a significant proportion of the gas, using 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 is 37% of the UK’s total renewable energy resource. The answer is that the organics being diverted from landfill, where they produce methane for 25 years) should be digested in anaerobic digestion facilities where the methane is efficiently and safely digested in 30 days!
Feedstock includes a wide range of biodegradable wastes, including farm manure, household waste including vegetables and meat, restaurants, schools, food processing factory wastes, supermakret and small retailer wastes and even textiles and paper. The most exciting recent trend is towards the digestion of crops such as sugar beet, ensiled maize, rye grass, wheat and others. Although green waste can be digested, it is obviously far better for households to compost their own wastes, thus avoiding unecessary additional household collections. Both Defra (UK) and SEPA (Scotland) stipulate that feedstocks must be source separated if the digestate is applied to land. (See Digestate)
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 displace commercial fertilisers on farm or parkland – see also Does the process reduce the mass of the waste
Yes. Biogas us a renewable energy source and eligible for Renewable Obligation Certificates (ROCs) under the Renewables Obligation Order 2002 if the biomass input is at least 98%. The biogas is normally used as a fuel in CHP plant which produces heat and electricity which displace fossil fuels. Biogas is also included in the Road Transport Fuels Obligation if it is reformed by removal of the carbon dioxide
The feedstock is a waste product which would otherwise be dumped in landfill sites, which 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 biowaste and finally returning to the soil as a valuable nutrient.
Life Cycle Diagram
It's complicated, but if, for instance, our feedstock was 100 tonnes of vegetable waste (with about 78% water content), 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 farmlan
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 (Composting). This means that every tonne of waste processed in a Biogas Plant can be counted towards re-cycling targets, by contributing towards Best Value targets within this category
Biogas technology is now classed with composting as the best way of dealing with biodegradable waste. It will be the preferred technology before incineration, gasification, pyrolysis and of course landfill. Waste Authorities can actually choose to classify it as energy recovery but understandably it cannot be both composting and recovery. Composting is an energy consuming process whereas anaerobic digestion produces a large surplus of renewable energy, so the latter should really be the first choice
Very much so, including, EU Landfill Directive, EU Animal By Products Regulation and Climate Change Legislation. see: Defra
EC Landfill Directive 99/31/EC, has set out mandatory targets for the reduction of biodegradable wastes sent to landfill. By 2020 these must amount to no more than 35% of that produced in 1995. Some Councils have decided to meet these targets by starting green collections which increase the total waste, and then composting or digesting the green waste to meet the required percentages; this is not logical – if there were mandatory reductions in actual tonnage, we would see green waste being composted at home, thus making substantial saving
Because of the risks to animal health from BSE and Foot & Mouth there was a temporary ban on household waste being composted or processed in a Biogas Plant and used on land to which animals had access. However, since 1st May 2003, bio-fertiliser from Biogas Plants is once again be available for use on land under certain strictly enforced regulations under the EU Animal By-Products Regulations 1774/2002
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
Yes, there are 100's of Biogas Plants in Europe and the UK, excluding sewage and farm manure operations and there is excellent UK based engineering, manufacturing and project management capabilit
Biogas plants are a more sophisticated method of waste disposal which of course require more capital investment than transporting waste to landfill. In the case of a plant dealing with municipal organic wastes, 25% of the income for a plant comes from energy, (covering the running costs) and the remaining 75% from Gate Fee for organic wastes. Rising landfill taxes and the increasing value of gas are all improving the commercial climate for building AD plant. If animal by products are excluded, capital costs are reduced and it is now feasible to build AD plants relying purely on energy sales without Gate Fee income. AD plant is being built in the UK in 2006 on a fully commercial basis without any government subsidy.
Yes. The entire process is contained in carefully monitored vessles on a 24-hour basis and there are no emissions of biogas froma well run plant. Modern communications ensure that any abnormal indications are relayed immediately to duty personnel for correction. Biogas is safer even than natural gas which we use daily in our home
One of the big advantages of Biogas Plant is that the entire process in carried out in sealed vessels. Even the waste reception and shredding process is done in a closed shed with biofiltration. There should be no smell from the process itself apart from waste that is actually in transit to the plan
For producing heat and electricity from a CHP unit, for re-processing into natural gas or used in vehicle
If the digestate has been produced from source separated feedstock, 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. It is safe for human and animal health. However, at present, a Waste Management Licence (WML) is required from the Environment Agency before any land application is allowed. This is an onerous process costing time and money, which has affected the commercial viability of some plants. However a Digestate Standard has been written for Scotland by a REA team led by David Collins, and this should shortly enable digestate which pases that standard to be used on farmland without the need for a WML licence. It isplanned that this Standard will be extended to the remainder of the UK.