Phosphorus recovery from incinerated sewage sludge ash (ISSA) and reutilization of residues for sludge pretreated by different conditioners

Abstract

• Effect of different sludge conditioners on P recovery from ISSA was first studied. • Fe and Ca elements in sludge conditioner influenced the P speciation in ISSA. • Higher Ca content in ISSA resulted in lower P leaching efficiency. • Heavy metals mainly existed in residual specie with low mobility risk in ISSA. • Acid-leaching residue of ISSA could be reused as cement mortar additives. Phosphorus (P) recovery from incinerated sewage sludge ash (ISSA) has attracted increasing attentions in recent years. In this study, the P recovery was comparatively investigated on two types of ISSA for sewage sludge pretreated by Fenton's reagent, and a composite conditioner of Fenton's reagent and lime (referred to as ISSA-F and ISSA-FL, respectively). ISSA derived from raw sludge (referred to as ISSA-RS) was studied as the control group. The P species results showed that the proportions of AP (Ca-bound P) and NAIP (Al/Fe-bound P) in the ISSA samples were significantly affected by the added Fe and Ca elements in the sludge conditioner. The order of leaching efficiency of P in different ISSA samples was ISSA-F (100%) > ISSA-RS (94.4%) > ISSA-FL (83.1%), which was significantly related to the Ca content in those ISSA samples. Higher Ca content in the ISSA-RS and ISS-FL samples induced calcium oxalate precipitation during leaching process, which hindered the release of P from ISSA. P recovery product mainly composed of aluminum hydroxyphosphate was prepared from the purified solutions leached from different ISSA samples. Moreover, acid-leaching residues of different ISSA samples after P recovery were proposed to be reutilized as cement mortar additives by replacing 15 wt% of cement. The mechanical strength of the test cement mortar specimens with acid-leaching residues was comparable to that of the control cement mortar specimen without residue.