Removal Of Antibiotics And Antibiotic Resistance Genes From Farm Wastewater By Modified Biochar-activated Persulfate

Antibiotics and antibiotic resistance genes（ARGs）are widely detected in wastewater as emerging pollutants,which will not only pollute the ecological environment but also pose a threat to human health.As an important aggregation site for antibiotics and ARGs,how to efficiently remove antibiotics and ARGs has become a research hotspot in recent years.Traditional chlorinated disinfectants,ozone or UV disinfection are ineffective in removing antibiotic resistant bacteria（ARB）and ARGs from wastewater,and horizontal gene transfer（HGT）between bacterial populations aggravates the drug resistance problems.Due to the low cost,stable performance and environmental friendliness,persulfate advanced oxidation process（PS-AOPs）is extensively used to remove pollutants from wastewater.Biochar is a commonly applied activator of peroxodisulfate,but it is limited in practical applications owing to the problems of insufficient activation sites and low activation efficiency.In this paper,two elemental doped modified biochar with nitrogen and iron were prepared and their structural characteristics were characterized.The influencing factors and activation mechanism of the modified biochar were further explored,and the efficiency and mechanism of the biochar persulfate（PDS）removal were revealed by the biochar persulfate advanced oxidation system.（1）The surface of nitrogen-doped biochar（NLBH）prepared with urea as nitrogen source showed loose porous structure.Compared with the pristine biochar,the nitrogen content and defect degree of NLBH surface increased.When the ratio of pristine biochar to nitrogen dopant was 1:2（NLBH2）,the highest content of defective structures and marginal pyridine nitrogen on the surface,both of which were also identified as reaction sites for activation of PDS.The NLBH2/PDS system was able to degrade 70.1%of tetracycline（TC）within 120 min under the optimal conditions of 4 g/L catalyst dosing and 10 m M PDS dosing,whereas antibiotic resistance bacteria（ARB,Pseudomonas sp.HLS-6）inactivated 71.5%within 90 min.In contrast to external ARGs（sul1 and sul2）and int I1,which accumulated markedly by 1.52-4.18 and 4.92 log,respectively,intracellular ARGs（i ARGs;sul1,sul2）and int I1 showed reduction efficiencies of 2.73-4.04 and 2.70 log,respectively.The primary mechanism of PDS activation,as determined by electron paramagnetic resonance（EPR）and free radical burst tests,was a non-radical pathway dominated by singlet oxygen（¹O₂）.The radical pathway involving sulfate radicals（SO₄·^-）and hydroxyl radicals（·OH）plays a limited role in the NLBH/PDS system.The main methods of TC degradation were hydroxylation,demethylation,and decarboxylation,and 8 intermediates were found based on different reaction characteristics and mass-to-charge ratios,and two possible degradation paths were deduced in the reaction.（2）The Fe SO₄·7H₂O was used as the iron source to load iron on the biochar.The fine particles were uniformly distributed on the surface of the modified iron-supported biochar（Fe-LBH）,and the analysis of surface element composition confirmed that these particles were Fe₃O₄.Further examination of Fe-LBH surface functional groups showed that Fe（II）and oxygen functional groups（e.g.-C-OH and-C=O）were the main active sites of PDS.When the concentration of iron dopant was 150 m M（Fe-LBH3）,the dosage of catalyst was 1 g/L,and the dosage of PDS was 5 m M,85.1%of TC could be degraded within 30 min.In addition,60.4%of HLS-6 were inactivated by the Fe-LBH3/PDS combination within 60 min.The removal rates of ARGs（sul1 and sul2）and int I1 were 0.05-0.60 and 1.54-2.74 log2 times,respectively.Furthermore,the results of EPR and free radical quenching experiments indicate that the·OH-dominated radical pathway and the ¹O₂-dominated non-radical pathway worked together to degrade the target substance during the oxidation of Fe-LBH/PDS system.The degradation process of TC was analyzed to find 13 intermediates as well as two possible degradation pathways,which were able to reach a mineralization level of 55.15%.