Unraveling The Mechanism Of Oxysulfur Radical For Enhancing Waste Activated Sludge Deep Dewatering And Typical Pollutants Removal

Waste activated sludge（WAS）is a large amount of organic solid waste generated from the process of urban life.And the production of WAS has increased with passage of time,which has brought tremendous pressure on urban environmental management.Meanwhile,WAS has the attributes of pollution and resource,and its scientific treatment and disposal is crucial for the construction of ecological civilization.Therefore,in order to address the engineering roadblock of terrible dewaterability,high abundance of emerging pollutants and low resource conversion efficiency during the WAS treatment process,the pretreatment based on the oxysulfur radical（OSR）was used to enhance the deep dewatering,pollutant removal and anaerobic biological conversion of WAS in this study.The main research conclusions are as follows:1)The performance differences of the two types of pretreatment(S₂O₈^2-/Fe²⁺and SO₃^2-/Fe²⁺)in improving the deep dehydration of WAS,the disintegration of extracellular polymeric substance（EPS）and the removal of antibiotic resistance genes（ARGs）were comprehensively evaluate.The results revealed that S₂O₈^2-/Fe²⁺pretreatment was significantly better than SO₃^2-/Fe²⁺in enhancing WAS dewaterability and the removal of ARGs and coliforms.At the optimal dosage,after pretreatment with S₂O₈^2-/Fe²⁺（1.2/1.5 mmol/g-VS）,the CST reduction rate of WAS was as high as 68.4%,which was significantly better than SO₃^2-/Fe²⁺pretreatment（24.1%）.Statistical analysis indicated that the redistribution of LB-EPS and TB-EPS in WAS,especially the varitions of PN content,was the key factor affecting the change of dewaterability.The abundant of SO₄^·—generated form S₂O₈^2-/Fe²⁺pretreatment could quickly destroy the EPS structure through oxidative degradation to release bound water,accelerate the dissociation of WAS flocs,and cause cell lysis and DNA dissolution.However,due to the near-neutral p H value of WAS and low dissolved oxygen content,the generation effectively of SO₄^·—was limited by SO₃^2-/Fe²⁺pretreatment.Nortably,S₂O₈^2-/Fe²⁺and SO₃^2-/Fe²⁺pretreatment both could remove the 12 types of ARGs determined in WAS through destroying the plasmid,DNA structure and inducing cell death in EPS.Among them,S₂O₈^2-/Fe²⁺pretreatment has a more obvious removal effect on ARGs,the range of removal rate（0.96-2.17 log-units）,and reduced the propagation and proliferation potential of residual ARGs.In addition,compared with SO₃^2-/Fe²⁺pretreatment,the coliforms content in WAS decreased significantly after S₂O₈^2-/Fe²⁺pretreatment,and the lowest reached 1.84±0.24 log（MPN/g-TS）.Therefore,S₂O₈^2-/Fe²⁺pretreatment is an efficient,economical and green method to improve the WAS dewatering and the removal of pollutants.2)This study explored the effects of different dosages of S₂O₈^2-/Fe²⁺pretreatment on the dewaterability,floc characteristics of WAS floc,the DOM conversion and ARGs removal mechanism.WAS dewaterability was observably enhanced by S₂O₈^2-/Fe²⁺pretreatment,the water content of the mud cake was as low as 15.92±0.25%after 120s suction filtration,which is significantly lower than the raw sludge.During S₂O₈^2-/Fe²⁺pretreatment,the strong oxidation of SO₄^·—severely damages the EPS structure and leads to cell lysis,which greatly reduces the Zeta potential of WAS.Meanwhile,S₂O₈^2-/Fe²⁺pretreatment effectively degraded the hydrophilic organics in EPS,reduce the aromaticity of DOM,and increase the relative proportion of low-molecular-weight organics.The results of fourier transform ion cyclotron resonance mass spectrometry revealed that the increased concentration of tannins in WAS after S₂O₈^2-/Fe²⁺pretreatment is a potential factor for affecting the improvement of dewaterability.In addition,in the WAS pretreatment process,the cell structure of ARGs host bacterias were significantly deatroyed by S₂O₈^2-/Fe²⁺,such as Terrimonas,Gemmataceae,Blastocatellaceae and Anaerolineaceae,after removing the ARGs presented in cell-free DNA and EPS.Therefore,the removal rate of ARGs was up to 0.48-1.01 log-units.3)This study developed disordered mesoporous carbon/persulfate(S₂O₈^2-/DMC)pretreatment for sludge,and systematically explored the potential of this pretreatment to enhance sludge solubilization and anaerobic biotransformation.The performance of sludge solubilization and anaerobic bioconversion was observably improved by S₂O₈^2-/DMC pretreatment.The results revealed that S₂O₈^2-/DMC to produce sulfate radicals(SO₄^·—),facilitating cells rupture and sludge matrix dissociation by degrading the carbonyl and amide groups in organic biopolymers（especially proteins,polysaccharides and humus）.Under the action of S₂O₈^2-/DMC,the organic matter and microbial metabolites in EPS are oxidized and decomposed into inorganic matter and HA by SO₄^·—.At the optimal S₂O₈^2-/DMC dosage of 0.04/1.2 g-mmol/g-VS,biodegradable substances including PN and PS in WAS were released into the liquid phase in large quantities for promoting its subsequent anaerobic methane conversion,in which SCOD and methane production rate were enhanced by 1.47 and 1.63 folds with respect to raw sludge,respectively.However,the dissolved substances would re-oxidize in S₂O₈^2-/DMC pretreatment with an excessively high dosage（0.06/1.2 g-mmol/g-VS）for limiting the increase of methane yield.DMC could serve as electron mediator to accelerate electron transfer of microorganisms by building a more robust anaerobic metabolic environment.Modified Gompertz modelling analysis further demonstrated the crucial role of S₂O₈^2-/DMC pretreatment in biological degradation and methane productivity.