| The spread of antibiotics in water environment will promote the development and spread of antibiotic resistance.Therefore,how to reduce antibiotics in water environment and corresponding ecological risk has become an important proposition to protect the water environment and public health in recent years.As a technology with broad application prospect,constructed wetland and its role in risk control of antibiotics have received widespread attention.This study established an integrated vertical-flow constructed wetland(IVCW),by which the efficient purification of antibiotic containing wastewater was realized and the contaminants attenuation and ecological treatment efficiency was evaluated.Meanwhile,phytoremediation and microbial degradation pathways were investigated to reveal the degradation characteristics and mechanism of typical antibiotic(SMX)and nutrients in the IVCW.The main results and conclusions are as follows:(1)The IVCW could remove antibiotics efficiently and stably with the removal rate of SMX over 98%.The first stage(DS)was responsible for over 95% of SMX removal,and the upper layer played a major role.The second stage(US)exerted a supplementary removal effect of SMX and further reduced the ecological risk in the effluent.(2)In the presence of antibiotics,the IVCW still had an excellent COD removal effect,with the removal rate over 96%.Microbial degradation constituted the main pathway of organic pollutants removal in the IVCW,and DS was responsible for the most proportion.The TP removal efficiency was limited(less than 50%)and the average removal efficiency of TN fluctuated from 52.16% to 61.83%.The distribution of nutrients along the flow direction showed that the contribution of the upper layer of DS to nitrogen transformation was 61.07%,and that of COD reached 92.47%.(3)The presence of vegetation significantly enhanced the denitrification efficiency of IVCW with the average removal rate increased by 8.65% compared to the unplanted phase(p < 0.05).Whilst,the ecological risk of SMX in effluent was reduced with the risk to algae and invertebrates reduced to the lower level.The uptake of plants contributed a minimal part in that the accumulation content of TN and SMX in plants only accounted for 2.91% and 1.36% of the total removal respectively.However,the absorbed pollutants had an impact on the growth and defense mechanism of plants,which responded positively to the removal of SMX and nutrients,thus affecting the performance of the IVCW.Rizho-micro environment constituted by plant-microorganism interaction made up the main pathway of phytoremediation mechanism in the IVCW.The denitrifying bacteria Clostridium＿Sensu＿Stricto,Iignavibacterium,Rhodanobacter and Geobacter were found to be abundant in the rhizosphere due to root activities such as oxygen-secreting and root exudates,promoting the denitrification process of the IVCW.Meanwhile,the abundant plant growth promoting bacteria(PGPB),unclassified＿Burkholderiales(1.84%)and unclassified＿Betaproteobacteria(6.38%)in the rhizosphere ensured the growth of plants and the ecological function of the IVCW.(4)The results of high-throughput sequencing showed that the microbial community structure presented spatial differences along the flow direction.Plenty of unique bacteria were abundant in the upper layer of DS(DSU),named Chryseobacterium(12.00%),Comamonas(4.68%),Paracoccus(2.26%),Lysobacter(1.86%),Rudaea(1.57%),unclassified＿Cytophagaceae(2.36%),Lautropia(2.70%)and Flavihumibacter(1.94%),among which Chryseobacterium,Comamonas and Lysobacter were potential biodegradation bacteria of SMX.The selected pressure of antibiotics,the concentration level of pollutants and the corresponding removal process drove the spatial distribution characteristics of functional microorganisms.In addition,the internal environmental conditions also indirectly affected the spatial structure of microbial communities.(5)The analysis of carbon metabolism pathway results showed that the metabolic pathways related to xenobiotics biodegradation and metabolism in DS was significantly higher than that in US.The abundance of Cytochrome P450 was also enriched in DSU,which was 2.46-13.21 times higher than that in other samples.The analysis of nitrogen metabolism pathway results showed that under antibiotic stress,a variety of nitrogen cycling functional genes,such as pmo A-amo A,pmo B-amo B,pmo C-amo C,nxr A,nxr B,nar G,nar H,nor C,nos Z,nir K,nor B,nap A,nap B,nas A,nir A and nar L,were enabled,resulting in multi-pathways functioned in nitrogen cycling including nitrogen fixation,nitrification,denitrification,nitrogen assimilation reduction and nitrogen dissimilation reduction in the IVCW.DSU had a complete nitrification-denitrification pathway and the expression of corresponding functional genes.FAPROTAX was employed to predict carbon and nitrogen cycling ecological function and results showed that enriched bacteria in DSU might be involved in the carbon and nitrogen cycling served as multi-functional bacteria participating in denitrification and organic matters degradation process.The results of co-occurance network topology analysis showed that the bacteria enriched in DSU had unique ecological niches with growth-promoting relationship between each other,which constituted the main microbial degradation pathway for the excellent removal effect of the IVCW. |
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