Removal Efficiency And Correlation Study Of Antibiotics And Related Resistance Genes In Sludge Drying Reed Beds

With the increasing use of antibiotics,environmental residual pollution has been increased.The removal of tetracycline and macrolide antibiotics in sewage mainly depends on the adsorption of sludge,so the surplus sludge is a important repository of antibiotics.In recent years,there has been a high concentration of antibiotic resistance genes in excess sludge produced by sewage treatment plants.The antibiotic resistance genes in the excess sludge enter the surrounding environment with landfill and open piling,which threaten the ecological safety and human health.Sludge drying and reed bed,a new type of sludge treatment technology,has the characteristics of simple process,economic efficiency and so on.The surplus sludge can be directly used for soil improvement after the sludge is stabilized by reed bed,but the study on the removal of antibiotics and antibiotics in the reed bed has not been reported.The experiment was divided into three beds with the same specifications,namely a conventional sludge drying bed with a ventilation structure,a sludge drying reed bed with ventilation structure and a sludge drying reed bed without ventilation structure.The sludge drying reed beds do not interfere with each other and operate independently.After three years of mud entering period,the surface and bottom sludge were collected synchronously in each bed in natural stability.According to the growth of reed,they were sampled in April,July,September and November.The residue concentration of target antibiotics(azithromycin,roxithromycin,Oxytetracycline)in the sample was detected by LC-MS/MS method.The results showed that with the extension of sludge stabilization time,the concentration of three kinds of antibiotics in the sludge decreased as a whole.Ventilation pipe and reed can effectively improve the efficiency of sludge drying reed bed for the removal of antibiotics in surplus sludge,and the contribution of the reed is greater.The average removal efficiency of RTM,AZM and OTC in the sludge drying reed bed with ventilation structure can reach 89%,80%and 91%,under the dual effects of ventilation pipe and reeds.The absolute copy numbers of target antibiotic resistance gene(msrSA,tetC,ermB,tetA and tetX)in samples was determined by real-time PCR.The absolute copy numbers of msrSA,tetC,ermB,tetA and tetX in he surface stabilized sludge were higher than the bottom stabilized sludge in traditional sludge drying bed and the sludge drying reed bed with ventilation structure and the sludge drying reed bed without ventilation structure.However,msrSA and tetC in the bottom stabilized sludge had the best removal effect in the sludge drying reed bed with ventilation structure.During the stabilization period of sludge,the absolute copies of msrSA and tetC in the bottom stabilized sludge in sludge drying reed bed with ventilation structure were reduced from 1.03×10~7 and 1.85×10~6 to 1.83×10~6 and 3.71×10~5 respectively.ermB and tetA in surface stabilized sludge and bottom stabilized sludge have the best removal effect in the traditional sludge drying bed with ventilation structure.The absolute copy numbers of tetA and ermB in the surface stabilized sludge were reduced from1.13×10~5 and 7.55×10~3 to 6.61×10~4 and 7.02×10~3 respectively and the absolute copies of tetA and ermB in the bottom stabilized sludge were reduced from 7.67×10~4 and 5.17×10~3 to1.06×10~4 and 3.80×10^3 respectively.The absolute copy number of tetX in the stabilized sludge in conventional sludge drying bed with ventilated structure and the sludge drying reed bed with ventilation structure and no ventilation structure.The correlation between antibiotics and antibiotic resistance genes was consistent in three beds.There was a significant correlation between msr SA and RTM and AZM(P<0.05)in the surface and bottom stabilized sludge of the three beds(P<0.05),and there was a significant correlation between tetA and tetC with the associated antibiotic OTC(P<0.05).The correlation between ermB and RTM and AZM was not significant(P>0.05),and the correlation between tetX and OTC was not significant(P>0.05).