Degradation of 4-chloroaniline in sulfidated nanoscale zero-valent iron loaded on biochar activated persulfate system: Batch and column experiments

• S-nZVI/BC with a sulfide species layer on the surface of nZVI was synthesized through co-sulfidation method. • S-nZVI/BC exhibited an enhanced PS activation capacity for the degradation of 4-CA in both batch and column experiments. • SO 4 •- , •OH and O 2 •- were generated and accounted for the degradation of 4-CA. • S doping enhanced the yield of ROSs , the stability of S-nZVI/BC and the utilization efficiency of PS. • A possible degradation pathway of 4-CA was proposed. Nanoscale zero-valent iron (nZVI) is widely utilized as an efficient transition metal material for persulfate (PS) activation. However, the intrinsic agglomeration and the passivation layer on nZVI surface limits its application in in-situ chemical oxidation (ISCO). Therefore, we synthesized sulfidated nanoscale zero-valent iron loaded on biochar (S-nZVI/BC) composite to enhance PS activation for efficient degradation of 4-chloroaniline (4-CA) under both batch and column experiments. S-nZVI/BC composite prepared at a S/Fe molar ratio of 1:5 and biochar pyrolysis temperature of 500 ℃ exhibited the optimum PS activation performance. The degradation rate of 4-CA was 98.86 % with the reaction rate constant of 0.684 min −1 in batch experiment. Meanwhile, the degradation rate of 4-CA was achieved 58.08 % in column experiment with a M S-nZVI/BC /M sand mass ratio of 1:200 and flowing rate at 1.0 mL·min −1 . By forming a sulfide species layer on the surface of nZVI, the yield of ROSs, the stability of nZVI/BC and the utilization efficiency of PS were enhanced in relation to the facilitated electron transfer property and the cycling of Fe 2+ . The electron paramagnetic resonance (EPR) analysis demonstrated the presence of SO 4 •- , •OH and O 2 •- and the contributions to the 4-CA degradation were 29.85 %, 44.93 % and 24.08 % verified by quenching experiment. 4-CA was gradually deaminated to monochlorobenzene, acetic acid, acetaldehyde, oxalic acid and ultimately mineralized to CO 2 and H 2 O with the total organic carbon (TOC) mineralization rate of 67.96 %, and the ecological toxicity of the system was significantly diminished from toxicity assessment. This study demonstrated insights into the enhancement mechanism of S doping in S-nZVI/BC activated PS system and provided a potential for the remediation of 4-CA contaminated groundwater in ISCO.