Digestate use and management eventActivity by Jacqui Colgate | added on Feb 01, 2011 | United Kingdom
Sponsor(s): Aqua Enviro Technology Transfer
A Defra strategy is now in place hopes to see a large increase in the number of anaerobic digesters constructed in England and Wales over the coming decade with a target of 1,000 new digesters to be built by 2015.
Digestate use and management event
SCI HQ, London, UK
11 May 2011
Organised by SCI's Science and Enterprise Group and SCI's Environment Group
A Defra strategy is now in place hopes to see a large increase in the number of anaerobic digesters constructed in England and Wales over the coming decade with a target of 1,000 new digesters to be built by 2015. The feedstock for these new digesters will be predominantly food waste and the organic fraction of municipal waste, currently sent to landfill, together with farmyard manures that are spread to land. Financial incentives to encourage the take-up of anaerobic digestion are provided by the government in the form of Renewable Obligation Certificates (ROC’s), Feed in tariffs (FITs) and Renewable Heat Incentives (RHI). In addition to this, digestion facilities will derive income from gate fees for the waste and from the energy produced in the form of methane gas. However for many facilities it is the fate of the digestate, which is an end-product of the digestion process, that will determine the payback period and in many cases dictate the overall financial viability of the scheme.
It is recognised that digestate is a valuable source of plant nutrients and thus should have some value as a fertiliser. In view of the finite global availability of phosphorus, the so called “peak phosphorus”, and the inexorable rise in prices of mineral fertilisers it would suggest that the economic future of digestate is secure. Unfortunately digestate is produced at a very low total solids concentration, typically between 4 and 6%. Thus unless the digester is sited conveniently close to the point of digestate recycling, then transport costs will be high. Although digestate does dewater easily to a product with around 25 to 30% solids, this option means that much of the nutrient value is in the dewatering liquor. This not only reduces the market value of the digestate, it leaves a liquid residue that requires expensive additional treatment to render it environmentally benign. A number of options have been proposed to handle this liquid residue and produce a solid, slow-release fertiliser with a high market value and low transport costs, but these have not been evaluated in the UK market place.
At present the market for both digestate and dried fertiliser is rather immature with few established supply chains in position. As a result it is difficult to predict the potential future value of digestate and thus determine whether digestate recycling will represent an income stream or an operating cost for the digester. It is the aim of this event therefore, to review the present status of digestate and its management. It will consider the legislative background and highlight the key restrictions on digestate recycling and indicting where changes in legislation might be anticipated. It will consider the technologies currently available for dealing with digestate and indicate the economics of these options. The agronomy of digestate and the value it offers the end-user will be discussed. It will also examine the status of the marketplace and anticipate the opportunities and threats that will arise from a product that is likely to become much more readily available.Programme
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SCI HQ, London, UK
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