THE TAKE UP OF HEAVY METALS BY WOOD FUEL CROPS - IMPLICATIONS FOR EMISSIONS AND ECONOMICS

Abstract

ABSTRACT A series of trials investigating the use of sewage sludge as a fertiliser for short rotation wood fuel crops involved the intensive monitoring of heavy metals take up into the crop's above ground biomass. This indicated that the concentrations of heavy metals in the leaf and stem of several Salix varieties were equal or greater than the soil concentration of the metal and in some cases were above normally accepted phytotoxic levels. The presence of elevated levels of metals in the plant tissue was independent of sewage sludge addition and arose from soils which contained normal background concentrations. Combustion will result in the concentration of the metals in the ash, with consequences both for ash disposal and the recycling of nutrients in the ash to the crop. This paper summaries the heavy metal take up by the willow and poplar varieties investigated and reviews the implications for the use of wood as a fuel. This work is funded by Anglian Water Services Ltd and Severn Trent Water Ltd.