UK strategy for centralised anaerobic digestion

Experience to date with on-farm anaerobic digestion in the UK has been poor. For a number of reasons, many of these plants have not performed to expectations. The technology has been very much environmentally driven, often requiring integration with other farm activities. The resource is generally considered too widely dispersed for most individual farms to economically exploit. There are opportunities for improving the economics through co-operative ventures at medium- to large-scale centralised anaerobic digestion facilities. These would be highly tuned, generally thermophilic CHP systems; typical installations would lie in the size-range 0·1–1·0 MWe. These facilities would be fed primarily with farm wastes, together with non-toxic, industrial, organic wastes from food processing/preparation activities. A pasteurisation stage is required to ensure a more complete pathogen kill. The liquid digestate fertiliser would be returned to the land when the timing for application was right, thereby ensuring its nutrients were better utilised. Digestate fibre would be processed and marketed as a peat substitute or soil conditioner. Although useful experience is available from Denmark, where centralised anaerobic digestion facilities are well established, there are likely to be problems implementing such schemes in the UK. The strategy outlined recommends a two-phase approach. Phase 1 is aimed at gathering sufficient information with which to form an opinion about the viability of centralised anaerobic digestion in the UK. Proceeding to project implementation in Phase 2 is dependent on the findings of Phase 1.