Phosphorus extraction from sewage sludge ash by the CO 2 blowing method

Abstract

Sewage sludge ash (SSA) often contains high levels of phosphorus (P) and has been considered as one of important secondary P resources. However, SSA also contains toxic heavy metals such as Cd, As, and Hg which can cause contamination problems in the recovery of P from SSA. Alkaline earth metal phosphate salts, which are present in SSA, can be preferentially dissolved by blowing CO 2 into the aqueous suspension of SSA. The dissolution mechanism involves the formation of soluble hydrogen carbonate by the CO 2 blowing which allows alkaline earth metal phosphate salts to form bicarbonate salts having high solubility in water. This chapter describes the selective extraction of phosphate from SSA using the CO 2 blowing method.