Research On The Treatment Of Antibiotic-containing Domestic Sewage By Bioretention Cells Amended With Black Carbon

Antibiotics are widely used in agriculture,animal husbandry,human and animal disease prevention and control.Due to the low absorption and utilization of antibiotics by animals and plants,most antibiotics ultimately enter the environment in the form of original compounds or conjugates.However,the traditional wastewater treatment processes cannot effectively remove antibiotics.The residual antibiotics in effluents are discharged directly into the environment,resulting in elevated levels of antibiotics in the aqueous system,shifts of the microbial community structure,as well as the spread of antibiotic resistance genes and bacteria.Bioretention cells,previously developed as rainwater runoff treatment facilities,have been successfully applied to sewage treatment in recent years along with the technical improvements.However,the efficiency of nitrogen and removal is unstable.The enhanced treatment efficiency and removal mechanisms for typical emerging pollutant—antibiotics remain unclearThe modification of substrate is crucial to improve the performance of bioretention cells.Compared with conventional substrates,black carbon has high porosity and good antibiotics adsorption capacity,and can provide attachment sites for microorganisms.Activated carbon(AC),known as the most widely used black carbon,had been successfully used for modifying bioretention cells and was found to effectively remove a sole antibiotic during a short-term operation.However,the long-term performance of bioretention cells,the shifts microbial communities and the responses of antibiotic resistance genes under the stress of antibiotics remain unknown.In this study,we constructed three bioretention cells,including a conventional control cell(BRC),a activated carbon amended cell(AC-BRC),and a activated carbon&zero valent iron scraps cell(AC-Fe-BRC).The long-term performance of the cell in treating sulfamethoxazole(0.8 mg/L,205d)wastewater was comprehensively investigated(COD,TN,NH4+-N,TP,SMX).The shifts in in microbial community structures,denitrification functional genes(nirK,nirS,nosZ)as well as antibiotic resistance genes(sulⅠ,sulⅡ)were tracked to further reveal the mechanisms.According to the findings in the above cells,we established a second set of bioretention cells with another typical black carbon,biochar(BC),to increase the bioavailability of electrons.Meanwhile,an attempt was made to couple the biochar bioretention cells with the microbial fuel cell(MFC)to further enhance the system performance in treating wastewater containing multiple antibiotics.The five bioretention cells were composed of a control cell(PBR),a biochar amended cell(BC-PBR),a biochar-zero valent iron scraps cell(BC-Fe-PBR),a biochar-microbial fuel group(EBC-PBR)and the biochar-zero valent iron scraps-microbial fuel cell(EBC-Fe-PBR).COD,TN,NH4+-N,TP and antibiotics removal during 60 days of 0.2 mg/L SMX and 0.2 mg/L tetracycline(Tetracycline,TC)exposure were measured.Also,microbial communities,key functional genes and fate and transport of antibiotic resistance genes were carefully studied.The main findings are as follows:(1)Activated carbon and zero valent iron could significantly enhance the long-term performance of the bioretention cells when treating SMX wastewater.AC-BRC and AC-Fe-BRC exhibited much higher pollutants removals than BRC.The removal efficencies for COD,TN,NH4+-N and TP in AC-BRC and AC-Fe-BRC were 90.50±3.39%and 89.99±2.75%、69.65±15.01%and 87.19±4.65%、78.33±14.31%and 84.60±10.20%、75.27±9.86%and 95.86±1.07%,respectively.The removals of SMX in these two cells were greater than99%;(2)Under the stress of 0.8 mg/L SMX,Proteobacteria was the predominant phylum in BRC,AC-BRC,and AC-Fe-BRC.The relative abundance of Proteobacteria increased as it contains a lot of antibiotic resistance gene carriers.The function prediction based on FAPROTAX database suggested that the denitrification function in submerged layer of BRC was partially inhibited,while the denitrification function of AC-BRC and AC-Fe-BRC was significantly enhanced.Moreover,the iron respiration,dark iron oxidation and sulfate respiration in submerged layer of AC-Fe-BRC were significantly enhanced.Combined with the abundance of dominant genera,the main functional genera were identified as Nitrospira,Rhodoplanes,Desulfomicrobium,Geobacter.Under long-term SMX stress,substrates tended to become the sul gene reservior,with an abundance of 107-108 copies/g,and the order of sulⅠ>sulⅡ.Fe0 significantly reduced the effluent resistance genes.In addition,co-occurrence network analysis revealed that the potential hosts of resistance genes in the filter layer and the submerged layer were distinct;(3)Biochar/zero valent iron scraps and/or coupling with microbial fuel cell could facilitate pollutants removal in bioretention cells when treating 0.2 mg/L SMX and 0.2 mg/L TC.The overall performance was BC-Fe-PBR≈EBC-Fe-PBR≥EBC-PBR≥BC-PBR≥PBR.Biochar amended system coupled with MFC tended to favor nitrogen and phosphorus removals.Under the stress of mutipleantibiotic,the removal efficiencies of COD,NH4+-N,TN,TP in EBC-PBR were 88.91 ±2.93%,99.46±0.75%,60.09±5.19%and 84.95±4.53%respectively.BC-Fe-PBR exhibited the best removals for conventional pollutants in the presence of SMX and TC.The removal efficiencies of COD,NH4+-N,TN and TP were 90.52±3.72%,81.43±1.92%,88.60±3.12%and 98.71%±0.71%respectively.The removal of SMX/TC by BC-PBR,BC-Fe-PBR,EBC-PBR and EBC-Fe-PBR were all greater than 99%within 60 days operation;(4)Under the stress of SMX/TC,the most dominant phyla in the submerged layer of PBR,BC-PBR,BC-Fe-PBR and EBC-PBR were Proteobacteria,while that the filter layer was Actinobacteria.Nitrospira,Denitratisoma and unclassified_Rhodocyclaceae were selectively enriched in BC-Fe-PBR.SMX/TC tended to stimulate the growth of multi-resistant bacteria,such as Sphingomonas(submerged layer)and Pseudonocardia(filter layer).According to the results of functional prediction and the relative abundances of key microorganisms,the main functional genera were identified as Nitrospira,Nakamurella,BIrii41,and Denitratisoma.The relative abundance of resistance genes in the submerging layer was higher than that in the filter layer.The amendment with Fe0 and the coupling of microbial fuel cell played an important role in controlling resistance genes in the substrates.Under the stress of SMX/TC,the abundances of sul and tet gene in PBR,BC-PBR,BC-Fe-PBR,and EBC-PBR were approximately 106-108 and 104-106 copies/g.