Application of sludge biochar combined with peroxydisulfate to degrade fluoroquinolones: Efficiency, mechanisms and implication for ISCO

Peroxydisulfate (PDS) is increasingly used for in situ chemical oxidation (ISCO) of organic pollutants in groundwater, but the efficient and applicable activator is still scarce. In this study, sludge-derived biochar (SDBC) was prepared by pyrolysis to activate PDS, which could effectively degrade the fluoroquinolone antibiotics (FQs, levofloxacin, enrofloxacin, norfloxacin and ciprofloxacin). Compared with pig manure and corn straw derived biochar, SDBC showed higher efficiency in PDS activation. Singlet oxygen (O-1(2)) was identified as the major reactive species, and the surface-bonded radicals also contributed to the FQs degradation. The selective oxidation of FQs by O-1(2) was first reported, which followed the trend of enrofloxacin similar to levofloxacin > norfloxacin similar to ciprofloxacin. The C=O and Fe2+ on SDBC were the dominant reactive sites for PDS activating. Products analysis revealed that FQs degradation proceeds via the cleavage of the piperazine ring, breaking of the quinolone ring, decarboxylation, and defluorination. Moreover, the tertiary amine of N (4) on enrofloxacin was more reactive towards singlet oxygen than the secondary amine of N (4) on ciprofloxacin, inducing the faster degradation and de-toxicity of enrofloxacin in the reaction system. SDBC showed high reusability in PDS activation and negligible metals leachates were detected. The column study proved the efficiency of PDS/SDBC in groundwater remediation.

Automated summary

In this study, sludge-derived biochar (SDBC) was prepared by pyrolysis to activate peroxydisulfate (PDS) for the efficient degradation of fluoroquinolone antibiotics (FQs). Singlet oxygen (O-1(2)) was identified as the major reactive species, and SDBC showed higher efficiency in PDS activation compared to other biochars. The selective oxidation of FQs by O-1(2) was reported, and the dominant reactive sites on SDBC for PDS activation were identified as C=O and Fe2+.