| The existence of emerging contaminants such as pharmaceuticals and personal care products,antibiotic resistance genes and endocrine disruptors in water environment poses a new challenge to traditional sewage treatment technology.Persulfate-based advanced oxidation process is an emerging contaminants removal technology with efficiency.On the one hand,peroxodisulfate（PDS）has a higher redox potential than peroxymonosulfate（PMS）.On the other hand,PDS is commonly used as the preferred oxidant due to its ease of transportation and storage.Therefore,the development of low-cost,stable,and efficient PDS activators is urgently needed.Due to its advantages of low cost and easy availability,sewage sludge-derived biochar activators have been more often to be applied for oxidation of the emerging contaminants.However,the approach to improve its catalytic activity is still a key factor needs to be researched immediately.In order to develop a low-cost,high-performance persulfate activator,provide theoretical guidance for the removal of emerging pollutant using water treatment technology,this study focused on sulfamethoxazole（SMX）,sulfonamide antibiotic resistance gene（sul1）,the mobile genetic element（int I1）,as well as bisphenol A and its substitutes as target pollutants to discuss the removal efficiency and mechanism of emerging contaminants using advanced persulfate oxidation technology driven by sludge-based biochar.In this work,biochar BC400,BC600,BC800 were prepared from municipal sewage sludge by one-pot pyrolysis under 400°C,600°C,and 800°C,respectively.The degradation efficiency of SMX using peroxodisulfate activated by the mentioned biochar was evaluated.The degradation efficiency was BC800>BC600>BC400 in order.The effects of sludge-derived biochar concentration and initial p H on the SMX degradation efficiency in the BC800/PDS system were explored.The removal rate of SMX could reach 92.6%when the concentration of BC800 was 0.75 g L-1.The performance is stable in the PH range of 5.0-11.0.The characterization analyses showed that the higher degree of graphitization and the content of C=O functional groups on the surface of BC800 lead to its higher activation efficiency.The dominance of the electron transfer pathway in the BC800/PDS system was confirmed by electron paramagnetic resonance spectroscopy（ESR）,quenching experiments,and electrochemical tests.The possible degradation pathways of sulfamethoxazole were proposed.The acute and chronic toxicity of sulfamethoxazole and its degradation intermediates were predicted by ECOSAR software.The results showed that the predicted toxicity of most degradation intermediates was significantly lower than that of the parent.The feasibility of sludge-derived biochar/PDS system to remove sulfamethoxazole ARGs（sul1）and class I integrase gene（int I1）was investigated.The results showed that sludge-derived biochar/PDS system could effectively reduce the absolute abundance of sul1,int I1,and bacterial biomass compared with PDS treatment.At the same time,compared with the original water samples,the relative abundance removal rate of sul1and int I1 in PB=1:2.5 treatment reached 62%and 60%,respectively,which could effectively reduce the relative abundance of sul1 and int I1.While PDS treatment resulted in the increase of sul1 and int I1 to 5.1 and 3,4 times that of the original water samples,respectively,which indicates that the bacteria carrying the sul1 and int I1 genes had resistance capability to PDS treatment.Microbial community structure analysis results concluded that the PB=1:2.5 treatment exhibited better performance than that of other treatments for reducing the abundance of Actinomycetes and Bacteroidetes.While the relative abundance of Proteobacteria（58%）was much higher than of the other treatment groups.The PB=1:2.5 treatment system had a significant effect on the removal of various genera in the original water samples,while the relative abundance of some genera,mainly Sphingomonas,increased after the treatment.Correlation analysis was conducted,indicating that the absolute abundance of sul1 and intl1 was positively correlated,which shows that sul1 can spread and transfer within and between species.Furthermore,Hydrogenophaga,Solibacillus,Moheibacter,and Aequorivita may be the potential hosts for sul1 and int I1.According to the results of scanning electron microscopy,the damage of cell walls and membranes may be an important mechanism for the inactivation of bacterial cells.Seven strains of sulfonamide antibiotic-resistant bacteria were screened out using a selective medium,and all of these strains were detected to carry sul1 and int I1genes by PCR amplification with specific primers.Cell viability detection was performed on S1,S2,S3,S4,S6,and S7 under different treatment conditions by laser confocal microscopy.The results showed that the sludge biochar/PDS system could effectively inactivate the above-mentioned bacteria,confirming that a large part of antibiotic resistance genes,mobile genetic elements,and 16S r RNA detected by q PCR technology may be from extracellular or inactivated cells.The activation efficiency of PDS using sludge-derived biochar was improved by the application ofβ-cyclodextrin-modification.When the concentration ofβ-cyclodextrin-modified biochar（β-SB）was 0.4 g L-1,the degradation efficiency of BPA reached 91.6%.According to the quenching experiments,ESR tests,and electrochemical analysis,it is proposed that the degradation mechanism of BPs and its substitutes in theβ-SB/PDS system is dominated by the electron transfer mechanism.Bisphenol contaminants and substitutes act as electron donors to trigger the decomposition of PDS.During the process,the hydroxyl groups on the surface ofβ-SB promote the electron transfer process.By means of theoretical calculation and intermediates analysis,it was proved that the difference of substituents led to the difference in the degradation pathways of BPA and its substitutes.The acute and chronic toxicity of the four BPs and their intermediates were predicted by ECOSAR software.The results showed that the predicted toxicity of most of the intermediates was significantly lower than that of the parent,but parts of intermediates produced by the cleavage of the benzene rings were toxic to fish,daphnia,and green algae.The results of the ecotoxicological evaluation showed that the toxicity of BPA and its substitutes was generally reduced after degradation,but the attention should be paid to the possible production of some intermediates which may lead to the increase of toxicity. |
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