Fate of heavy metals after application of sewage sludge and wood–ash mixtures to short-rotation willow coppice

Short-rotation willow coppice (SRWC), grown on farmland in Sweden for energy-biomass production, was fertilised with sewage sludge and wood–ash mixtures on the basis of the permitted annual phosphorus supply. Two identical experiments were conducted in central Sweden, on two newly harvested commercial SRWC fields. The maximum legally permitted amount of the sludge-ash mixture, sludge only, ash only, and twice the maximum permitted sludge-ash amount, were applied. The aim was to assess the effect of pH changes following treatment, on the ability of SRWC to take up large amounts of Cd and other metals. The remediation effect of SRWC was also studied. Under the experimental conditions applied, uptake by SRWC was unaffected by pH changes. The differences between the amounts of metals experimentally applied, less the uptake by SRWC after a potential harvest, were broadly within the permitted limits. For Cd, a reduction of total amounts in soil was observed.