Pyrolysis of hydrothermally dewatering sewage sludge: Highly efficient peroxydisulfate activation of derived biochar to degrade diclofenac.

The resource utilization of sewage sludge can solve its disposal issue essentially. Meanwhile the removal of diclofenac (DCF) in wastewater is an emerging environmental problem. In this study, a novel strategy of sludge utilizing via hydrothermal - peroxydisulfate (PDS) dewatering coupled pyrolysis process was proposed. The obtained sludge-derived biochar (HSC) could be as candidate to activate PDS to degrade DCF. Results indicated that exceed 90% of DCF was eliminated within 30 min in HSC-PDS/DCF ternary system under the optimized condition (0.6 mmol/L PDS and 0.5 mg/L HSC, without temperature and pH pre-adjusting). The inner mechanism of HSC-PDS/DCF system was revealed as follows: (1) Major: CO in quinones and ketone structure in HSC accelerated the degradation of DCF via non-radical pathway (electron transfer and 1O2). (2) Minor: Graphitic N structure accelerated the electron transfer and O2•- originated from defective sites involved into the redox. Several by-products were identified and two tentative degradation pathways of DCF (eg. dechlorination and C-N cleavage) were proposed.