Phosphorus release and recovery from treated sewage sludge

Abstract: In working towards a sustainable society, recycling and recovery of products together with handling of scarce resources must be considered. The growing quantities of sludge from wastewater treatment plants and the increasingly stringent restrictions on landfilling and on agricultural use of sludge are promoting other disposal alternatives. Sludge fractionation, providing sludge volume reduction, product recovery and separation of toxic substances into a small stream, has gained particular interest. In this thesis, the potential for phosphate release and recovery from treated sewage sludge is investigated as an alternative for agricultural use in urban areas. Leaching and recovery experiments were performed on sludge residue from supercritical water oxidation, ash from incineration and dried sludge at different temperatures. Results showed that acid or alkaline leaching is a promising method to release phosphate from sewage sludge treated with supercritical water oxidation, incineration, or drying at 300°C. The leaching is affected by a number of factors, including how the sludge residue has been produced, the origin of the sludge residue, the quantity of chemicals added and the presence of ions in the leachate. The implementation of any particular sludge treatment technology would depend on cost, environmental regulations, and social aspects. The results of this thesis may be beneficial for minimizing the use and cost of chemicals, and give increased knowledge for further development of technology for phosphate recovery.