| With the rapid development of economy,the production of activated sludge in wastewater treatment plants has been increasing drastically.However,the high moisture content and the accumulated pollutants are two major factors that limit the resource reuse of activated sludge.Hence,the synergistic reduction of sludge volume and accumulated pollutants is one of the important goals of sludge reclamation.Recently,antibiotic resistance genes(ARGs),as one of the emerging environmental pollutants,have been listed as one of the six major environmental problems by United Nations.It was reproted that activated sludge is one of the important hotspots for ARGs,which poses a high risk of antibiotic resistance transmission and spread during the resource reuse process of activated sludge.Therefore,the reduction and control of ARGs is significantly important in the treatment and reuse of sewage sludge.The conditioning of sludge is indispensable for the dewatering of sludge.Recently,some studies suggested that some proper conditioning methods synchronously improved the dewaterability and removed the ARGs in sewage sludge.Fenton conditioning has been proved to be effective in improving the dehydration of sludge.However,the effect of Fenton conditioning on the removal of ARGs was rarely studied.Actually,previous study showed that the conditioning of sludge with bioleaching and Fe[?]/CaO could attenuate ARGs effectively,while the traditional conditioning of sludge using Polyacrylamide(PAM)reagent was ineffective to remove ARGs in sludge.However,it is still unclear how the composts derived from the three kind of conditioned sludge mentioned above influence the variation of ARGs in soils during the land application.Hence,the research on the control of ARGs during the Fenton conditioning and land application of composts derived from various conditioned sludge is necessary,which is meaningful to control the transmission and spread of ARGs from sludge to natural environment.The objectives of this paper are(1)to explore the effect of pre-acidification on the synergetic improvement of dewaterability and removal of ARGs when the sludge was conditioned using Fenton's system;(2)to compare the variation of ARGs and the decay of ARG subtypes during the land application of composts derived from various conditioned sludge(PAM conditioning,bioleaching conditioning and Fe[?]/CaO conditioning),and(3)to reveal the mechanisms for the differences in the changes of ARGs in soils during the land application of composts derived from various conditioned sludge via the analysis of soil microbial community.Main conclusions were drawn as follows:(1)The effect of pre-acidfication on the improvement of dewaterability was limited when the sludge was conditioned using Fenton's system.The conditioning of sludge using Fenton's reagent without pre-acidification improved the dewatering extent and rate of sludge.The moisture content of dewatered sludge cake was reduced from 87.41%to 73.32%,and the Capillary Suction Time(CST)and Sludge Resistance to Filtration(SRF)of sludge were reduced by 85.02%and 92.17%.Meanwhile,the conditioning of sludge with preacidification coupled with Fenton's reagent reduced the dosage of Fenton's reagent.(2)The pre-acidification played an important role in synergistically improving the dewaterability and removing the ARGs when the sludge was conditioned using Fenton's system.The total ARGs,ARGs in dewatered sludge cake and dewatering filtrate were reduced by 2.10,1.44 and 1.51 log units,respectively,when the sludge was conditioned with pre-acidification coupled with Fenton's reagent.However,the accumulation of tet34,tet32 and intll should be paid more attention,because of the potential transfer of tetracyclin resistant gene.The lysis of sludge microbial cells was the key reason for the synergetic improvement of sludge dewaterability and removal of ARGs.(3)Even that the conditioning of sludge with bioleaching or Fe[?]/CaO reagent can effectively attenuate the ARGs in sludge,the variation of ARGs in soils showed difference during the land application of composts derived from bioleaching-conditioned sludge or Fe[?]/CaO-conditioned sludge.After a 170-days' incubation,the abundance of ARGs in the red soil amended with the compost derived from bioleaching-conditioned sludge was close to the red soil,which was 1.53 times the orginial abundance of ARGs in red soil.While the abundance of ARGs in the red soil amended with the compost derived from Fe[?]/CaOconditioned sludge was 4.79 times that of red soil.The decay of 5 major ARG subtypes(aac(6')-?,floR,mexF,Sul2 and tetG-01)achieved a good result during the land application of the compost derived from bioleaching-conditioned sludge compared to other conditioned sludge.(4)The species diversity and richness were lowest when the soils were ammeded with the composts derived from bioleaching-conditioned sludge.The abundance of potential hosts were most when the compost derived from Fe[?]/CaO-conditioned sludge was added into the soil,thus posing the highest risk of ARGs transmission and spread.The physical and chemical indicators such as pH,WSOC,WSON and mobile genic elements were highly correlated with some specific potential hosts,and Planctomycetes,Proteobacteria,Actinobacteria and Bacteroidetes were four dominant potential hosts that leading to the transfer of ARGs in soils.The results of the present study revealed that pre-acidification coupled with Fenton's reagent was useful to synergistically improve the dewaterability of sludge and remove ARGs in sludge.Meanwhile,the compost derived from bioleaching-conditioned sludge was much more effective than that of raw sludge,PAM-conditioned sludge and Fe[?]/CaO-conditioned sludge to control the spread of ARGs in soils when the sludge composts were land applied.Our study suggested that specific sludge conditioning methods can reduce the spread of ARGs in the soils receiving sludge composts,which provides a new way to control the antibiotic resistance in the environment. |
PDF Full Text Request