Ashes from Sewage Sludge and Bottom Sediments as a Source of Bioavailable Phosphorus

Phosphorus is an element necessary for the growth of plants. As phosphate rock gets depleted, it becomes an increasingly scarce resource. Therefore, it seems necessary to implement simple methods of cheap and effective phosphorus recovery from waste. The ashes of municipal sewage sludge and bottom sediments constitute particularly valuable sources of phosphorus. However, these materials usually carry significant amounts of pollutants, including heavy metals. Optimization of ash phosphorus sequential extraction methods from a thermal conversion of sewage sludge and bottom sediments allows to select an effective and simple technology of phosphorus recovery, while maintaining low heavy metal pollution, which is one of the main restrictions in use of ashes. Determination of an amount of bioavailable phosphorus is therefore a basis for estimation of the possibility of using it from waste. Extraction using the Golterman method or shaking out with calcium lactate or Trougs reagent indicates that the ashes from sewage sludge and bottom sediments are rich sources of bioavailable phosphorus, which could find use under field conditions as a viable alternative to fertilizers containing fossil phosphorus.