UTVINNING AV FOSFOR VID SUPERKRITISK VATTENOXIDATION AV AVLOPPSSLAM / Recovery of phosphorus in supercritical water oxidation of sewage sludge
A theoretical and experimental study has been performed to give a basis for recovery of phosphorus and Other products from sewage sludge and ash with application to Henriksdal wastewater treatment plant (Hultman et al., 2002). Special attention is given in this article on the use of supercritical water oxidation followed by phosphorus recovery (Aqua Reci). Studies of the Aqua Reci process have recently begun; the process is under development. Experiments have been performed (both at KTH and Feralco) to give information on recovery of phosphorus from sewage sludge with the application to digested sludge from biological treatment and chemical precipitation with iron.
High chemical demand is required by use of thermal technology and addition of acids to release phosphorus. Addition of bases is by interest since aluminium and phosphate are released first, while iron, calcium and magnesium ions are not released in the same step (if a preceding washing step is used). To release phosphorus appr. 100-200 kg NaOH/ ton DS is required and the total chemical demand is appr. 200 kg/ ton DS of lime and NaOH to release phosphorus and obtain calcium phosphate as a phosphorus product.