Performance And Mechanism Of Soil Aquifer Treatment For Polishing Antibiotics-Containing Effluent From WWTP

Wastewater reuse after advanced treatment is an effective way to solve the problem of water shortage.Soil aquifer treatment is a low cost and high efficiency method.Because of its advantages,it has been widely approved by scholars.However,antibiotics have brought new threats to wastewater reuse.On the one hand,antibiotics have toxic effects on aquatic organisms and can promote the generation and spread of antibiotic resistance genes,which directly affects the saf ety of reclaimed wastwater.On the other hand,they can inhibit microorganisms,resulting in indirectly affecting the wastewater reuse.At present,relevant studies mainly focused on the change of antibiotics concentration before and after filtration,and the removal mechanism of antibiotics need be further explored.Furthermore,the internal relationship between antibiotics,soil microbial activity and removal of conventional pollutants has not been established.At the same time,there are few studies on the ecological and environmental risk assessment of the reclaimed water.In this study,amoxicilin(AMX),tetracycline(TC)and levofloxacin(LEV)were used as targeted drugs to investigate the removal efficiency of antibiotics and conventional contaminants in soil aquifer treatment.The contribution of different soil column depth and different effects(abiotic,aerobic,anoxic/anaerobic)to antibiotic removal was quantitatively analyzed,and the changes of soil microbial community structure and metabolic function diversity under the influence of antibiotics were investigated.The risk assessment of reclaimed water w as carried out,and control measures were proposed.The results showed that soil aquifer treatment had a good performance on antibiotics removal,and the removal rates were AMX(90.4%)>TC(76.2%)>LEV(62.1%),respectively.Antibiotics were mainly enriched in the upper layer of soil column,and the enrichment of the three antibiotics in soil decreased gradually with the increase of soil depth.Under the influence of three antibiotics,the removal rates of chemical oxygen demand,biological oxygen demand and organic carbon decreased by 0.3%～4.8%,5.1%～9.1% and 3.1%～5.4%,respectively.Different from the performance of above pollutants,the infiltration of AMX and TC promoted the degradation of dissolved organic nitrogen and ammonia nitrogen,and the degradation rates increased by 2.9%～3.1% and 2.6%～3.7%,respectively.LEV still showed inhibition effect on dissolved organic nitrogen and ammonia nitro gen,the inhibition rates were 2.3% and 4.2%,respectively.The three antibiotics had almost no effect on total phosphorus removal.AMX,TC and LEV produced 3,7 and 5 intermediates,respectively.They were derived from β lactam ring desorption;isomerization,demethylation,decarboxylation;hydroxy-substituted fluorine and piperazine ring fracture.The results showed that aerobic microorganisms contributed 48.1% and 34.3% to the removal of TC and AMX in soil column,while anoxic/anaerobic microorganisms contributed 34.7% to the removal of LEV.Under different redox conditions,the antibiotics degrading bacteria at the level of phylms were: Bacteroidetes and Actinobacteria(AMX),Actinobacteria,Verrucomicrobia,Deinococcus-thermus and Armatimonadetes(TC);Planctomycetota(LEV).At the genus level,predominant organism were Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium(AMX);Verrucomicrobiaceae,Deinococcus,Paenarthrobacter and Rhodococcus(TC);Methylophilus(LEV).From the perspective of microbial structure diversity,the relative abundance of Nitrrospira and Nitrosomonadaceae in soil surface increased by 5.4%,2%,2.3% and 1.4%,respectively,under the selection of AMX and TC.It is the reason why the removal efficiency of ammonia nitrogen and dissolved organic nitrogen increased.From the perspective of microbial functional diversity,antibiotic infiltration significantly inhibited the metabolic activity of microbial carbon source,and the maximum AWCD values were blank(0.352)>AMX(0.225)>LEV(0.103)>TC(0.096),respectively.The inhibition trend of biological oxygen demand and organic carbon degradation is the same and similar.Through the analysis of microbial carbon source metabolic fingerprint,it was found that tetracycline enrichment had the greatest influence on the microbial carbon acid metabolism in the upper soil column,which directly led to the inhibition of fulvic acid removal in dissolved organic pollutants.Under the influence,the removal rate was blank(69.04%)>LEV(68.09%)>AMX(64.57%)>TC(61.42%).The ecological risk quotient of AMX,TC,and LEV decreased from 0.076,5.998,and 1.351 in the influent to 0.007,1.43,and 0.51 in the effluent.Under the influence of antibiotics,the effluent of conventional pollutants met the standards of landscape reuse and miscellaneous water.Combined with principal component analysis and analytic hierarchy process,the risk assessment was carried out on the reclaimed water.It was found that the risk of effluent was significantly lower than that of influent after the treatment of 100 cm soil column.In this paper,the behavior characteristics of three different antibiotics in the soil aquifer treatment was analyzed.On the one hand,it provides new ideas for further strengthening the removal of antibiotics in wastewater.On the other hand,it provides a reference for the reuse approach of the antibiotics-containing effluent from WWTP after soil filtration,and has important theoretical significance and practical value for the safety of reclaimed water reuse.