Removal Of Antibiotic And Resistance Genes From Swine Wastewater In Constructed Wetlands

The phenomenon of antibiotic abuse in livestock breeding has caused extensive attention to the society.Once antibiotics entered the environment,it will cause pollution of water and soil,also resulting microbial communities to have resistance genes,which bring unestimated damage to the ecological balance.As a kind of economical,efficient and easy-manageable sewage treatment ecosystem,constructed wetland is widely used in dealing with treatment of waste water from livestock breeding,life and industry.However,at the present,the previous study of effects of antibiotics and their resistance genes in distribution and removal of constructed wetlands is not specific.Through continuous sampling in summer and winter,the followings are monitored and detected,all together 14 kinds antibiotics(tetracycline,chlortetracycline,oxytetracycchloramphenicol,sulfacetamide,sulfadiazine,Sulfathiazole,sulfamethazine,sulfamonomethoxine,trimethoprim,ofloxacin,norfloxacin and ciprofloxacin),nine common tetracycline resistance genes(tetA,tetB,tetC,tetD,tetM,tetO,tetQ,tetW and tetX),three sulfa antibiotic resistance genes(sulI,sulII and sulIII),three quinolones(qnrA,qnrB and qnrS),and one integrase gene(Int1).At the same time,environmental indexes,such as concentration of nitrogen,phosphorus and COD,also pH,DO were detected.Based on this,the analysis of main factors concerning removal antibiotic and its resistance genes was made,in order to offer a basis for assessing the environmental and ecological risks of antibiotics.The chief results of the experiment are as follows:(1)By calculating the average removal rates of NH4+-N,TN,COD and TP in constructed wetland water samples,the removal rates were showed as follows: NH4+-N> TN> COD> TP,with the values of 92.51%,89.9% and 81.25% 79.15%.It can be seen the average removal rate of each index was higher than 79%.Constructed wetlands efficiently decreased the concentration of each pollutants,so it can found it has good purifying capacity for livestock sewage.(2)The constructed wetlands had efficient removing effects on tetracyclines,sulfonamides and quinolone antibiotics in high,medium and low concentrations of sewage in summer and winter.The average removal rate was 91.8%,81.6% and 99% respectively.It was also found that the concentration of tetracycline antibiotic in winter was as twice as that in summer.(3)According to the detection of content of antibiotics in soil samples in summer and winter,it was found that whether tetracycline or sulfa antibiotics,the antibiotic content of constructed wetland soil samples in summer was significantly higher than that in winter.And the content of tetracycline antibiotics was significantly higher than that of sulfonamide antibiotics,which increased the polluted risks of constructed wetlands from these antibiotics.(4)In this study,antibiotic resistance genes(ARGs)were detected in both tetracyclines and sulfonamides.But through the PCR detection,ARGs in quinolones were unable to be found.The contents of TetO and tetC were higher in tetracycline-type ARGs,followed by tetW,tetX.The content of tetX was the lowest in the tetracycline.And in sulfonamide ARGs,the content of sul1 and sul2 were the highest.It was showed through the study,after being treated by constructed wetland,the contents of resistance genes of tetracycline and sulfa antibiotic have been greatly reduced.Therefore,it can be seen constructed wetlands play an important role in removing resistance genes.