– What is Anaerobic Digestion?
Now 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
– What is Biogas
It is about 65% Methane and 35% Carbon Dioxide depending on the process
– What goes into the Biogas plant as feedstock?
Feedstock includes a wide range of biodegradable waste, including sewage, farm manure, household waste including vegetables and meat, green waste and even textiles and paper. However, this website is primarily concerned with the biodegradable fraction of household and restaurant waste
– What comes out of the process?
Three quarters of the 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
– Is Biogas Renewable Energy?
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
– Is Biogas Technology sustainable?
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
– Does the process reduce the mass of the waste?
It's complicated, but our usual feedstock would be roughly 77% water and 23% solids. Three quarters of those solids would be converted to Biogas
– How can AD help Council's achieve government Best Value objectives?
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 will now contribute towards Best Value targets within this category.
– Where does it stand in the waste hierarchy of Reduce, Recycle, Compost, Recovery, Disposal?
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
– Can Biogas Technology help with Legislative targets for Councils?
Very much so, including, EU Landfill Directive, Draft EU Biowaste Directive, EU Animal By Products Regulation and Climate Change Legislation. see: Defra
– EU Landfill Directive
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
– EU Animal By-Products Regulation
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
– 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 fuels
– Is the technology proven?
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 capability
– Is it commercially viable?
Biogas plants are a more sophisticated method of waste disposal which of course require more capital investment than transporting waste to landfill. 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 case for building AD plant. AD plant is being built in the UK in 2006 on a fully commercial basis without any government subsidy.
– Is a Biogas Plant safe?
Yes. The entire process is monitored on a 24-hour basis and Biogas is safer even than natural gas which we use daily in our homes
– Does it smell?
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 household waste that is actually in transit to the plant
– What can Biogas be used for?
For running a CHP unit, for re-processing into natural gas or used in specially adapted vehicles
– 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. It is safe for human and animal health
For local Councils, biodigestion has proven an excellent way of meeting liabilities over government targets.
Engineering costs prove greater value as these are directed toward funding actual construction and not into consultants and middle men's pockets.