| Recent years,antibiotics,as a typical organic micro-pollutant,have been detected frequently in environmental water,especially in drinking water sources.As a sustainable drinking water pretreatment technology,Riverbank Filtration(RBF)technology can effectively remove plenty of pollutants in surface water,including antibiotics.Its operational efficiency and ecological stability are of great significance to drinking water safety.In this paper,RBF system was studied.Sulfonamide antibiotics(SAs),a typical antibiotics with frequent environmental detection and high environmental and human health risks,were selected as the target pollutants to study their environmental behavior and ecological effects in the RBF system.Firstly,metagenomics sequencing were used to identify distribution pattern of antibiotics and antibiotic resistance genes(ARGs)in typical surface drinking water sources,at the same time the occurrence and risk of SAs in drinking water sources were confirmed.Furthermore,indoor batch experiments were conducted to reveal the migration-transformation behavior and mechanisms of typical sulfonamides(SAs)sulfamethazine(SM2),in different RBF sand matrix,which provided a scientific reference for efficiency evaluation and stability optimization of SAs removal in RBF system.Indoor column simulation experiments were used to further reveal the ecological response of in-situ microbes to long term and low level SAs stress,to provid theoretical basis for retaining the biological stability of RBF system.The in-situ RBF system operation and SAs pollution condition were further restored to explore the effects of matrix characteristics and hydraulic resistance time on SAs'removal efficiency,and optimization suggestions on technical parameters of RBF system were proposed based on the parameter-efficiency model fitted by multivariate linear regression analysis.The main results are as follows:(1)In the typical surface drinking water sources of the Huaihe River Basin,the total concentration of SAs,tetracyclines and quinolones range is 84.85-707.03 ng/L.The average concentration of sulfanamides was 34.66 ng/L,among which sulfamethoxazole and sulfamethoxine(31.1%-82.6%)are the main category with potential health risk.That of tetracyclines and quinolones were 177.29 ng/L(68.56632.13 ng/L)and 6.29 ng/L(0.00-22.33 ng/L).Based on the 16S rRNA and metagenomics sequencing,Actinobacteria and Proteobacteria are the dominant ones(30.4%-53.8%and 17.1%-37.4%).Nine bacterial taxa were identified as biomarkers,and 14 types of ARGs(71 ARG subtypes)were detected in the research area.Opitutales was significantly enriched in the drinking water sources from middle-lower reaches,carrying mainly bacA?mdtB,mrdA,arnC and arnD ARGs.Flavobacterium was significantly enriched in upper reaches,carrying tetA ARG.It is speculated that the distribution pattern of unique ARG hosts might be responsible for the specific biogeographic pattern of ARGs in drinking water sources.(2)A typical SAs-sulfamethazine(SM2)was selected to conduct the experimental.The results indicated that SM2 show a fast adsorption and then desorption to equilibrium.The fast adsorption subject to the first-order kinetics equation,and the adsorption rate constant differs among RBF sand(9.51-21.65 h-1)while the equilibrium adsorption amount were almost the same(0.31-0.39 mg/L).Three strains of SAsdegrading bacteria were isolated and purified from different RBF sand,belonging to Bacillus aryabhattai(strainl),Acinetobacter pittii(strain2),and Lysinibacillus xylanilyticus(strain3)respectively,which were the main functional trains responsible for SAs removal in RBF systems.The degradation ability was strain 1(0.150 d1)>strain 2(0.121 d-1)>strain 3(0.096 d-1),and the main metabolites were 2-amino-4,6-dimethylpyrimidine and deaminated sulfamethazine.Adsorption and biodegradation coupling effects contributed the apparent removal of SM2 in RBF system,among which proportion of adsorption was about 15.52%and 5.94%under under anaerobic and oxic condition,while biodegradation took 84.48%and 94.06%under anaerobic and oxic condition respectively.(3)Under long-term low level SAs stress(ng/L),the microbial community structural in RBF system changed significantly.Among them,the main decrased taxa belongs to Comamonadaceae,Xanthomonadaceae and Oxalobacteraceae,while the increased taxa belongs to Bacillaceae,the main family with SAs degradation ability in RBF system,which indicated that the microbial community in RBF system has evolved with higher environmental tolerance.Under the long-term low level of SAs stress,the total abundance of ARGs in RBF system also increased(from 1.2×10-1 to 1.7×10-1 capc).The relative abundance of synthesis of dihydrofolate reductase folP gene(relative to SAs ARGs emerging)significantly increased,indicating a potential SAs resistance with the mechanism of target modification.From the perspective of substance and energy metabolism,the relative abundance of microbial transporter,ABC transporter and ribosome related functional genes significantly increased(average deviation>0.1%),showing significantly higher exchanging potential of genetic material and energy compared with original community.The abundance of metabolic pathways of exogenous organic compounds increased significantly,but the carbon source metabolism showed obvious reduction,indicating SAs stress stimulated the cometabolism process of in-situ microbial community in RBF system.(4)RBF column system with different sand matrix was constructed to simulate the in-situ RBF operation condition.The results indicated that the degradation efficiencies of SAs were significantly different(half-life 49.87-462.10 d).The main matrix influential factor of the removal efficiency in RBF included clay content(positive correlation),organic matter and typical minerals(negative correlation).Under the influence of different hydraulic retention(HRT)time,there is an obvious oxic-anoxicanearobic distribution pattern,and the increase of HRT benefit the removal of SAs in RBF system.Multiple linear regression model of RBF systems' parameters-efficiencies was constructed,which can be used to optimize the hydrodynamic parameter of RBF sites.Besides,during RBF sites selection,construction and operation,it is suggested to evaluate the matrix characteristics and HRT,especially the biological stability of in-situ microbial community,in order to ensure the effectiveness and sustainability of RBF system,as well as drinking water safety.The main innovations of this research including:(1)The adopted metagenomics sequencing technology overcame the defects of low coverage and high specificity of traditional methods.The diversity characteristics of microbial communities and ARGs in typical surface drinking water sources were systematically revealed,and it was proposed that specific bacteria was responsible for ARGs propagation and accumulation in drinking water sources.(2)The succession characteristics of RBF insitu microbial communities under long-term SAs stress(ng/L)were systematically analyzed,and the main microbial groups with SAs resistance and degradability were identified.the ecological response mechanism of microbial communities in RBF system under typical antibiotic selection pressure were revealed,which provided support for biological stability maintenance of RBF system.(3)Column setups were restored to simulate the RBF in-situ operating conditions and SAs pollution characteristics.The effects of matrix characteristics and HRT on the SAs removal efficiency in RBF system were quantified,and the multivariate linear regression model of parameters-efficiency was fitted to optimize RBF technical parameters and ecology sustainability,which provided support for the application of RBF technique and drinking water safety guarantee. |
PDF Full Text Request