| The sequestration of target pollutants in the dissolved air flotation(DAF)process involves two sequential steps.In the first step,the particles destabilize and agglomerate through pre-coagulation;in the second step,the microbubbles collide and attach to destabilized flocs to form microbubble flocs,which causes them to float upward to the surface where they are removed.However,the flocs formation was subject to the activity of coagulants and the types of pollutants,and the role of microbubble flocs for organic matter removal poorly studied.Based on the dissolved ozone floatation(DOF)process proposed by the research group in the early stage,the in-situ formed ozone microbubble flocs was selected to explore the modification characteristics of coagulants,organic matter,and flocs mediated by ozone microbubbles.The reaction mechanism and regulation methods of ozone microbubble flocs for enhanced organic matter removal were investigated,and the DOF process were applied to the petroleum wastewater treatment.The results provide theoretical basis and application basis for enriching the advanced treatment process of wastewater and strengthening the efficiency of wastewater regeneration.The main contents were as follows:(1)By constructing a reaction and observation device to characterize the physicochemical properties of ozone microbubble flocs,the results showed that compared with microbubble flocs,the average size of the ozone microbubble flocs increased from216.00 to 258.93 μm.The enrichment of ozone microbubbles on the surface of flocs increases the oxidation reduction potential of the flocs surface from 236 to 426 m V.Therefore,the ozone microbubble flocs have unique oxidation capacity during the flotation process,and affect the morphology and characteristics of organics,flocs and coagulants.Ozone microbubbles improve the gas-liquid mass transfer efficiency of ozone in solution,thereby transforming the C-CO and C-C functional groups in organic components into COOH and COH functional groups that were conducive to coagulation;Al-based coagulants promote ozone decomposition to form hydroxyl radical(·OH),which can simultaneously act on dissolved HA and insoluble solid flocs,thus increase the oxygen content in flocs;Ozone microbubbles can affect the distribution of coagulant hydrolysis species and induce the conversion of monomer Al(Ala)into medium polymeric Al(Alb)that was conducive to the complexation reaction and highly stable colloidal/large polymeric Al(Alc).(2)During the ozone microbubble flocs floating process,ozone microbubbles can enhance the capture characteristics of organic matter by flocs.The capture effect of flocs on organics increases with the increase of the content of hydroxyl and carboxyl oxygencontaining functional groups on the surface of flocs.By comparing the functional group changes before and after the floc reaction,it was found that the formation of hydrogen bonds by polar oxygen-containing functional groups was the main driving factor for organic matter removal,and COOH and OH were were identified as the surface hydrogen bond donors.Therefore,the modification of flocs by ozone can enhance the hydrogen bonding effect of polar functional groups,thereby improving the removal effect of organic matter.In addition,the surface hydroxyl group in the flocs acted as the active site for the connection between ozone and flocs.Ozone accelerated the transformation of tetrahedral Al to octahedral Al,which enhance ozone microbubble flocs generation.In addition,the ozone microbubble floc-HA(flotation product)showed higher surface hydrophobicity than the conventional flocs,which results in high flotation efficiency.(3)The DOF process with ozone microbubble flocs as the core significantly improves the organic matter removal efficiency,and broaden the ozone dosing range.It was found that ozone microbubbles can induce the conversion of organic matter and coagulants into modified intermediates with carboxyl,hydroxyl,and aromatic structures,as well as coagulant species with high complexation characteristics,respectively.Modified intermediate products and coagulant species characteristics can form coagulant organic complex through C-O-Al coordination bond.This complex has high stability,and avoid further oxidation modified intermediate organic products into small molecule organic compounds.As the reaction progresses,ozone can induce the transformation of dissolved small-scale complexes into insoluble flocs by promoting the formation of hydroxyl bridges between Al species,and gradually reduce the free aluminum content in the water.The flocs can be oxidized and modified by ozone,thereby enhancing their surface capture effect on organic matter and further improving organic matter removal efficiency.(4)Based on the interaction mechanism of ozone microbubbles,coagulants,and organic matter,the reaction characteristics of DOF process in the coexistence system of organic matter and hardness ions were revealed.During the reaction process,ozone modifies the surface functional group of organic compounds,providing chelating sites for Ca ions and inducing the formation of Ca-organic complex.Carboxyl and hydroxyl functional groups can serve as reaction sites for Ca-organic complexes.Ozone can enhance the Alc content in the hydrolytic species of coagulants,thereby promoting the formation of flocs.During the ozone microbubble flocs floating process,the Ca-organic complex in the solution was attached to the surface of the flocs by strengthening the hydrogen bonding of hydrophilic functional groups and the hydrophobic interaction of hydrophobic functional groups in the flocs.On the basis of the above research,in response to the removal requirements of organic matter and hardness ions in petroleum wastewater,the simultaneous removal of organic matter and hardness ions was achieved in an integrated device by utilizing the reaction characteristics of ozone microbubble flocs in the DOF process. 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