Biomass Production and Nutrient Removal from Municipal Wastes Using Willow Vegetation Filters

Abstract

Short rotation forests, consisting of various willows (Salix spp.), are suitable vegetation filters with regard to removal of nutrients from municipal sewage sludge, wastewater, leakage water and bioash (wood ash). As long as contents of heavy metals and known organic compounds are kept below accepted limit values, such waste oducts can be regarded as valuable nutrient resources, and particularly when the vegetation is produced for energy purposes instead of for direct or indirect human consumption. The benefit is three-fold: (i) purification of municipal waste using natural circulation, (ii) production of biomass for energy purposes, (iii) reduction of air pollution when burning wood instead of fossil fuels. Most Salix plantations can be used as recipients of sludge and ash as well as be irrigated with wastewater from sewage plants or with leakage water from dumps. Regarding waste and leakage water irrigation, a combined artificial wetland for winter conditions and a willow vegetation filter during the growing season can be used for the purification The welland should be planted with a suitable vegetation cover, which can be harvested in order to remove maximal amounts of nutrients from the system. This biomass can be used as fuel or in compost. There are also indications that some willow clones are capable of taking up certain heavy metals, while others are not. This is beneficial when growing willow on contaminated soils, which either could be purified or just be used for such plantations.