Enhanced Sludge Dewaterability via Oxone Activated by Biochar Pyrolyzed from Iron-Rich Sludge at a Low Temperature: Role of Iron Species

In this study, enhanced sludge dewaterability via oxone activated by biochar synthesized from the pyrolysis of iron-rich sludge at a low temperature of 300 °C (Fe-300 biochar) was achieved and compared to that at a high temperature of 800 °C (Fe-800 biochar), without the aid of extra pH adjustment. Multivalent iron species were identified in the Fe-300 biochar (including FeO and Fe3O4) and Fe-800 biochar (including FeO, Fe3O4, and Fe0). Experiments with model iron phases indicated that under the studied conditions, Fe3O4 failed to activate oxone. However, FeO and Fe0 were capable of activating oxone. Although Fe0 in the Fe-800 biochar also effectively activated oxone, part of the generated Fe(III) was further reduced back to Fe(II), decreasing the Fe(III) concentration in the dewatered sludge cake (0.4 vs 9.3 mg/g of dry solids), compared with the Fe-300 + oxone system. The superiority of Fe(II)-activated oxone in enhancing the sludge dewatering performance over Fe0-activated oxone was further proved with changes of radical generation, degradation of hydrophilic proteinaceous components, and surface thermodynamics. As such, this study for the first time systematically revealed the advantages of low-temperature pyrolysis of iron-rich biochar at 300 °C in activating oxone for enhancing sludge dewaterability.