Role Of Zero-Valent Iron Activated Peroxydisulfate In Imporving The Dewaterability Of Sewage Sludge And Removing The Antibiotic Resistance Genes In Sludge

With the acceleration of urbanization and the development of industrialization in China,the production of municipal sewage sludge dratically increased.However,the high moisture content of sewage sludge seriously limited its subsequent treatment and disposal.Antibiotic resistance,which induced by antibiotic resistance genes(ARGs),have become one of the major global public health issues due to the long-term abuse of antibiotics.It has revealed that urban wastewater treatment plants(WWTPs)are hotspots for the dissemination of ARGs.Most ARGs in sewage influent are concentrated in the municipal sewage sludge during the wastewater treatment processes.Therefore,it is necessary to develop a new technology to effectively improve sludge dewatering and eliminate ARGs from sludge at the same time.Sulfate radical(·SO4-)-based sludge conditioning methods have received notable attention because of their usefulness in improving sludge dewaterability.Based on our previous studies,the present study use ZVI/S2O82-coupled with chemical acidification to condition municipal sewage sludge,in order to simultaneously increase sludge dewatering rate and dewatering extent,and eliminate the intracellular and extracellular ARGs in sewage sludge to attenuate antibiotic resistance.The present study aims to evaluate the usefulness of ZVI/S2O82-system in reducing sludge CST,sludge SRF,and the moisture content of dewatered sludge cake at different initial sludge pH;explore the mechanisms involved in improving the dewaterability of sludge by ZVI/S2O82-system;evaluate the feasibility of removing the intracellular and/or extracellular ARGs and intI1 in sewage sludge by using ZVI/S2O82-or Fe2+/S2O82conditioning system;explore the mechanisms for the elimination of intracellular and/or extracellular ARGs and intI1 during the conditioning process.The related results are shown as follow:(1)The conditioning of sludge using 0.353 g/g DS of ZVI and Na2S2O8 with a mole ratio of 1.25:1 at the initial sludge pH of 2.52 was the optimal conditions to improve sludge dewaterability.The moisture content of dewatered sludge cake could be reduced to 69.80%,and sludge CST and SRF could be reduced by 70.94%and 40.75%after the above sludge conditioning treatment.(2)The decrease of sludge pH reduced the moisture content of dewatered sludge cake via damaging sludge microbial cell lysis induced,while the oxidation of sludge extracellular polymeric substances(EPS)and the coagulation of disrupted sludge flocs achieved by ZVI/S2O82-system effectively reduced sludge CST and SRF.Specifically,ZVI/S2O82-oxidation was effective in breaking down high-molecular-weight substances and degrading tyrosine protein-like and tryptophan protein-like substances in sludge EPS,which has positive effects on sludge filterability.A kaolin suspension experiment revealed that the oxidation effectiveness was gradually inhibited and the coagulation effect offset the disruption effect on sludge flocs to improve the filterability of sludge with a decrease in system pH.(3)The conditioning treatments using ZVI/S2O82-or Fe2+/S2O82-system,at acidic initial sludge pH,is very useful to remove the intracellular ARGs and intI1(total ARGs:1.31 log units;intI1:2.85 log units)and the extracellular intI1 from sewage sludge,but led to the accumulation of total extracellular ARGs(0.45-0.82 log units).(4)During the sludge conditioning with ZVI/S2O82-or Fe2+/S2O82-,the bacterial hosts carrying ARGs and intI1 were seriously damaged or lysed to release the intracellular ARGs and intI1 into the extracellular environment,thus eliminating intracellular ARGs and intI1 in sewage sludge.Meanwhile,the released ARGs or intI1 can be readily degraded by the produced·SO4-to attenuate most extracellular ARGs and intI1,though the relative lower degradation ability of ·SO4-for extracellular ARGs of aadA-01,aadA-02,aadA1,aadA2-03 and strB,which led to their accumulation in conditioned sludge.Therefore,the ·SO4--based conditioning methods can be employed as effective conditioning ways to reduce ARGs in sewage sludge,but the subsequent treatment of sludge dewatering filtrate should be paid more attention.The results of the present study would provide insight into the mechanisms responsible for improving the dewaterability of municipal sewage sludge and eliminating ARGs in sewage sludge by employing·SO4--based sludge conditioning.