Utilization of sewage sludge in short-rotation energy forestry: a pilot study

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Abstract
Dewatered and non-dewatered sewage sludge from a secondary treatment plant was applied to plots planted with three Salix (willow) clones according to the Swedish short-rotation forestry concept. Stem biomass production was enhanced by the sludge application rate, which vaned between 2.5 and 20 t DS/ha/yr. Sludge metals in general accumulated in the soil within the layer in which the sludge was applied, whereas metal transportation below this point was less pronounced. Concentrations of nutrients and metals in plant tissues were not influenced by the sludge application rates, but decreased in general with stem and stand age. Improved sewage sludge quality in recent years is contributing to the possibilities of designing sustainable systems for sludge use on productive land—for instance, in short-rotation forestry for biofuel production.