A Study On The Degradation Of Sulfamethoxazole By Red Mud-sludge Derived Biochar Activated Peroxymonosulfate

Recently,sludge derived biochar（SDBC）is produced by pyrolysis of sewage sludge and employed as the catalyst of peroxymonosulfate（PMS）for various pollutants degradation,which has became a promising technology for sewage sludge disposal.For the strategy of“treat waste by waste”,red mud,a Fe-rich solid waste,was employed to modify SDBC.In this effort,SDBC and Red Mud-Sludge Derived Biochar（RSDBC）were prepared to activate PMS for sulfamethoxazole（SMX）degradation.The main research contents and results are listed as follows:（1）The optimal reaction conditions are:SDBC and RSDBC dosage:1.5 g/L,PMS concentration:0.15 m M,SMX concentration:0.02 m M.Under the optimal conditions,92.1%and 82.5%of SMX was removed in SDBC/PMS and RSDBC/PMS system,respectively.（2）Influences of various reaction conditions on the degradation of SMX by SDBC/PMS and RSDBC/PMS systems were studied.Along with increase of temperature and humic acid concentration,SMX removal decreased.SDBC/PMS system maintained high efficiency in a wide p H window（2-10）,however,a sluggish performance was achieved in RSDBC/PMS system under alkaline conditions.Different inorganic anions showed different inhibition effects.In SDBC/PMS system,the inhibitory effect of SO₄^2-was obvious,and that of Cl^-was negligible.In RSDBC/PMS system,the trend was in contrast.RSDBC showed a better reuse performance than SDBC did,and Fe leaching from RSDBC（0.67 ppm）was much lower than that of SDBC（3.07 ppm）.（3）In SDBC/PMS system,three Reactive Oxygen Species（ROS）,SO₄^·-,·OH,¹O₂were responsible to degradation of SMX.These ROS were generated through the activation of PMS by heterogeneous Fe species,ketone groups and graphitic carbon,contributed equally to degradation of SMX.In RSDBC/PMS system,SMX was mainly degraded by ¹O₂（97.67%）,¹O₂was generated through the activation of PMS by oxygen vacancy,ketone groups and graphitic carbon.In addition,it was found that some ¹O₂was converted from dissolved oxygen.（4）In RSDBC/PMS system,¹O₂attacked the 2C,4C,6C and 7N atoms of SMX,and five transformed products（TPs）were finally detected.Quantitative Structure Activity Relationship（QSAR）model in Ecological Structure Activity Relationship（ECOSAR）program was used to predict the toxicity of the TPs,and the results identified the five TPs with low toxicity.The residual toxicity was studied by the inhibition assays of Lactuca sativa germination,and the results showed a lower residual toxicity in RSDBC/PMS system.In SDBC/PMS system,because of the attacking of SO₄^·-and·OH,8S-11N bond was broken,amino groups were oxided,benzene rings were hydroxylated and isoxazole rings were opened.Besides,¹O₂attacked the 2C,6C and 7N atoms of SMX.Finally,13 TPs were detected in this system,among which TP99 and TP198 were highly toxic.In addition,residual toxicity was higher in this case.