Degradation of tetracycline by peroxydisulfate activation on sludge-derived biochar modified with tannin extract

In this study, the waste sludge was modified by tannin extract, and the modified material Tannin Extract-Sludge Derived Biochar (TE-SDBC) was prepared by high-temperature pyrolysis at 700 degrees，while tannin extract dosage was 3.17 g, pH value was 7.69. TE-SDBC was used to activate peroxydisulfate (PDS) for the degradation of tetracycline(TC). The sludge-based biochar was characterized by ATR-FT-IR spectroscopy, BET, SEM, XRD, XPS. The following preparation conditions for TE-SDBC were tannin extract dosage was 3.17 g, pH value was 7.69 and pyrolysis temperature was 717.3 ℃. TE-SDBC had more defect sites and higher pyridinic N content, which was conducive to promote the PDS activation, indicating that TE-SDBC had better catalytic performance. The TE-SDBC obtained optimal conditions were as follows: the initial mass concentration of TC was 20 mg/L, TE-SDBC dosage was 0.15 g/L, PDS dosage was 0.1 g/L, initial pH of pollutant solution was 5.76 and the reaction temperature was 25 ℃. The degradation of TC by TE-SDBC/PDS and SDBC/PDS was explored. After 120 min reaction, the degradation efficiency of TE-SDBC/PDS was 40% higher than that of SDBC/PDS, and the optimization of the conditions indicated that the TE-SDBC/PDS system had a better removal effect on TC degradation. Under the action of reactive oxygen species, the breakage of CC bond happened, the functional groups, i.e., amino, methyl and hydroxyl, were removed, and the ring opening reaction occurred in TC molecule, then the small molecular intermediates were ultimately formed. Finally, the intermediate products were mineralized into CO2, H2O and various inorganic substances.