Improving the phosphorus bioavailability of sludge: Comparison of oxidation treatments based on Mn(VII)-Fe(III) catalysis

Sludge serves as an alternative to traditional sources of phosphorus. However, the low phosphorus bioavailability limits its utilization. In this study, different oxidation treatments based on permanganate-ferric chloride (Mn(VII)-Fe(III)) catalysis were employed to improve the phosphorus bioavailability of sludge. The phosphorus bioavailability was evaluated using sequential extraction. Comparative experiments showed that the group of Mn(VII)-Fe(III)/peroxydisulfate (PDS) was more effective than Mn(VII)-Fe(III)/sodium percarbonate (SPC) and Mn(VII)-Fe(III)/hydrogen peroxide (H₂O₂) in increasing the phosphorus bioavailability of sludge. The extracellular polymeric substances (EPS) of sludge were disintegrated under the oxidative treatment through destructing the bonds of C–H and O–H, leading to the release of phosphorus. Meanwhile, the bond of O=P=O was broken down, which caused the degradation of organic phosphorus into inorganic phosphorus. This process reduced the amount of residual phosphorus and insoluble phosphorus in sludge, as well as increased the amount of phosphates. Some of the phosphate was deposited in sludge solid phase due to the adsorption of MnO_x and FeO_x. Phosphates combined with added and released Fe ions to form Fe–P complex enhanced the phosphorus bioavailability. The stronger destruction on O=P=O and higher disintegration on EPS promoted the achievement of better enhancement of phosphorus bioavailability under Mn(VII)-Fe(III)/PDS treatment. Furthermore, three types of oxidation treatments based on Mn(VII)-Fe(III) have all been shown to improve heavy metals leaching and reduce sludge dewaterability. Therefore, oxidation methods based on Mn(VII)-Fe(III) have excellent effects on the resourcefulness, harmlessness and minimization of sludge. This work provides ideas for selecting more practical sludge conditioning methods in engineering.