Physical And Chemical Characteristics Of Ozone Microbubble Flocs And Its Mechanism And Application For Removal Of Organic Matter

The hybrid ozonation-coagulation（HOC）process is an integrated water treatment technology that combines microbubble ozone,coagulation and air flotation organically.The HOC process is characterized with high efficiency and short process.In the HOC process,ozone microbubbles react with coagulants and organic matter to form ozone microbubble flocs.By that,the ozonation and coagulation process are simultaneously realized in one treatment unit.To explore the role of ozone microbubble flocs in the HOC system,this paper proposes to study the physical and chemical characteristics of ozone microbubble flocs and its mechanism of removing organic matter.Furthermore,ozone microbubble flocs are used to treat the drilling wastewater from oil and gas production.The structure characteristics of ozone microbubble flocs were determined by analysis of images collected by the stereomicroscope.Under different conditions,the average diameter of the microbubbles adsorbed and encapsulated by flocs is in the range of 75.85～99.65μm,the fractal dimension of flocs ranges from 1.499 to 2.050,and the contact angle is between 93.81°and 115.37°.Compared to traditional aerated flocs,ozone microbubble flocs have smaller microbubbles and larger fractal dimension and more compact structure due to the interaction between ozone,coagulants and organic matter.The microelectrode determination showed that the average REDOX potential in the layer of ozone microbubble flocs is 454.14 m V,higher than that in the traditional aerated flocs layer（234.22 m V）,providing conditions for modifying organic matter.The mechanism of organic matter removal by ozone microbubble flocs was inferred by determination of free radicals in the system by probe method and the evolution of aluminum salts and organic matter on the flocs.The coagulants are hydrolyzed and complexed with organic matter to form flocs,where ozone acts on the Lewis acid active site（ⅣAl）and consumes hydroxyl groups,producing hydroxyl radicals and modifying organic functional groups on flocs surface.Compared with Al Cl₃ and Al₂（SO₄）₃,the PAC ozone microbubble flocs have moreⅣAl sites,which induces ozone to generate more hydroxyl radicals.Also,the structure of PAC ozone microbubble flocs is more open,which benefits the attachment of microbubbles,making it better for removal of pollutants.The effect of the treatment of actual drilling wastewater by ozone microbubble flocs was investigated,and the characteristics of the reaction process were further summarized.Under the condition of p H 7,PAC 40 mg Al/L,ozone concentration 0.8 mg/L,reaction for 15 minutes（aeration for 5 minutes）,the removal rates of UV₂₅₄,UV₂₈₀ and DOC in drilling wastewater reached 20.07%,37.97%and 14.51%,respectively.It was shown that the benzene ring compounds,proteins and humic acids in the wastewater were markedly reduced after the treatment.XRD and Al-Ferron analysis showed that ozone could induce the increase of polymerization degree of aluminum hydrolysates.NMR analysis showed that the hydrolysate component of Al₁₃,which is beneficial to coagulation,increased in ozone microbubble flocs.When the secondary effluent of drilling wastewater is treated by the HOC process,ozone will act on the organic matter in the flocs and solution at the same time,affecting the composition and structure of the surface functional groups,so that the flocs and organic matter can be combined through the bond of hydrophilic groups.