Catalytic pyrolysis coupling to enhanced dewatering of waste activated sludge using KMnO₄Fe(II) conditioning for preparing multi-functional material to treat groundwater containing combined pollutants

Sewage sludge, the major by-product during the primary treatment and subsequent biotreatment of wastewater, is increasingly generated around the world. KMnO₄Fe(II) consists both oxidation properties of KMnO₄ and flocculation ability by in-situ formed Fe(III) and is widely used in water treatment. In this study, KMnO₄Fe(II) was used as chemical conditioners to synchronously improve sludge dewatering performance and catalyze the biomass pyrolysis of waste activated sludge for preparing multi-functional material to remedy arsenic containing groundwater. The results showed that the sludge dewaterability was significantly improved due to the moderate pre-oxidation of extracellular polymeric substances by KMnO₄, and then the sludge particles were re-flocculated by Fe(III) generated from KMnO₄Fe(II). The conditioned sludge cake was then utilized for preparing sludge-based carbon (Fe-Mn-SBC) which was systematically characterized. The surface area of Fe-Mn-SBC was characteristic of high surface area (100.08 m²/g) which had a great adsorption capacity on arsenic. Besides, Fe-Mn-SBC could effectively oxidize As(III) to As(V), and addition of low dose of H₂O₂ can further improve total arsenic removal due to catalytic peroxidation of Fe-Mn-SBC. Besides, it was found that the presence of humic acid could inhibit the hydroxy iron formation and compete for the active adsorption sites and then resulted in the decrease in arsenic removal, and the co-existing humic acid could also be removed by adsorption of Fe-Mn-SBC. This work proposed a novel sludge treatment process by combining enhanced sludge dewatering with catalytic pyrolysis for preparing multi-functional materials, and they are promising in treatment of water containing combined pollutants.