Feasibility of wet-extraction of phosphorus from incinerated sewage sludge ash (ISSA) for phosphate fertilizer production: A critical review

Incinerated sewage sludge ash (ISSA) is produced worldwide where incineration is used to manage sewage sludge. ISSA contains significant amounts of phosphorus (P) with high recovery potential, and may contribute to mitigate the global P supply problem. This study reviews P transformation in sewage sludge incineration, the characteristics of the resultant ISSA and processes for P recovery from ISSA focusing on wet-extraction methods due to their greater feasibility. The major drawback of the wet-extraction method is the co-dissolution of metal(loid)s. Hence, purification of the P-extract is necessary to produce a P fertilizer. Based on the analysis, three recommendations are made for further studies. One is optimizing the extraction process to produce a P-extract with a high content of P and low contents of impurities. The second is to develop a plant-available adsorption media, which can selectively adsorb P from the acid-extract of ISSA making the P-laden media as P fertilizers directly. The third is to form a high-purity P product that would be cost-competitive and attractive for use in diverse sectors. Finally, since the criteria for recovered phosphate fertilizer is incomplete, the agronomic effectiveness of newly produced P fertilizer from ISSA should be evaluated prior to large scale applications.