Draft PPS18: Renewable Energy
Annex 1 Technology: Ash
B37. The main solid bi-product of the conversion of biomass into energy is ash, usually termed ‘bottom ash’. Bottom ash is produced at a rate of around 1 per cent of the total weight of the biomass burned. If residues from forests are used, the inclusion of ‘tramp’ materials such as soil may increase this ash level to 3-4 per cent. The ash from most fuels, except perhaps MSW, can be safely returned to the soil as a fertiliser.