Phosphorous recovery from sewage sludge via chemical and thermal technologies

Phosphorus (P) recovery is important to reduce the dependence on natural and limited resources of phosphate rock, which can simultaneously prevent phosphorus discharge into the environment, thereby creating environmental issues such as eutrophication. One of the possible approaches to recycle phosphorus is to directly use sewage sludge as a fertilizer on arable land. Sewage sludge contains a high concentration of phosphorus, which can be suitable and alternative source of phosphate fertilizer. However, purification and removal of trace levels of phosphorus from the sewage sludge is necessary. In this review, information on appropriate strategies to the recovery of phosphorus from the sewage sludge through chemical treatment processes are collected from Scopus, Web of Science, PubMed and Embase to find the necessary literature on phosphorus recovery from the sludge using thermal or/and chemical treatment methods. The chemical methods such as adding calcium hydrate silicate, sulfuric acid, electrodialysis recovery, burning, hydrothermal and struvite have been explored to recover phosphorus from both sludge and sludge ash obtained from burning. The chemical/thermal methods have high efficiency for phosphorus recovery along with the simultaneous removal of heavy metals; these methods are considered promising for extracting the phosphorus from sewage sludge and ashes.