Study On Contact Oxidation Of Benzene Series In Groundwater By Ozone Micro-nano Bubble Water

Groundwater is one of important water sources in China,but it is currently facing serious organic pollution,and it is particularly urgent to develop green and new technologies for groundwater remediation.Ozone micro-nano bubble oxidation is a new advanced oxidation technology with great potential in the field of groundwater remediation.This study aims to explore the oxidation efficiency and mechanism of ozone micro-nano bubble water on benzene series compounds in groundwater environment,and investigate the impact of environmental factors such as p H,dissolved organic matter,inorganic ions and pressure.Firstly,four benzene series compounds,toluene,ethylbenzene,p-xylene,and o-xylene,were subjected to contact oxidation using ordinary ozone water（OW）and ozone micro-nano bubble water（OMBW）with the same ozone concentration,to explore the mechanism and investigate the impact of environmental factors on oxidation.Research has found that OMBW with the same ozone concentration had a stronger ability to oxidize benzene derivatives than OW.This was because ozone micro-nano bubbles could adsorb pollutants,thereby improving the oxidation efficiency of hydroxyl radicals（OH·）,and the ozone stored in the micro-nano bubbles had a longer lifetime,so more oxidants could be provided when the initial ozone concentration was the same.The reaction rate constants k _P-OH·of hydroxyl radicals was OW at p H=8 for toluene,ethylbenzene,p-xylene,and o-xylene are 4.70×10⁹ M^-1s^-1,6.27×10⁹ M^-1s^-1,4.19×10⁹ M^-1s^-1 and 6.79×10⁹ M^-1s^-1 respectively.When micro-nano bubbles were added,k P-OH·increased to 7.88×10⁹ M^-1s^-1,1.02×10¹⁰ M^-1s^-1,8.99×10⁹ M^-1s^-1 and 9.83×10⁹ M^-1s^-1.Micro-nano bubbles could only improve the utilization rate of hydroxyl radicals,but had no significant impact on the utilization rate of ozone molecules.When investigating the influence of environmental factors,it was found that micro-nano bubbles enhanced the inhibition effect by acidic environment,inorganic anions and dissolved organic matter on the oxidation of benzene series compounds by OMBW,and the inhibition effect by OMBW was more significant than that by OW.The economic benefit evaluation indicated that OMBW oxidation was more energy-efficient than OW oxidation.Secondly,three different types of landfill leachate,humic acid and fulvic acid were used as typical dissolved organic compounds to study the selective oxidation behavior of toluene in ozone micro-nano bubble water.It was found that when OW was used as an oxidant,DOM did not affect the reaction rate of toluene with OH·.When OMBW was used as an oxidant,DOM inhibited the reaction rate of toluene with OH·,indicating that DOM occupied the adsorption site of micro-nano bubbles,inhibiting the catalytic effect of micro-nano bubbles on oxidation.In the presence of DOM,micro-nano bubbles reduce the percentage of ozone used to oxidize toluene.The average ratio of ozone（f_t）used to oxidize toluene for OW in five solutions with DOM was 45.3%,which was 10.0%higher than that of OMBW system.There was no significant difference in the oxidation behavior of DOM between OMBW and OW on indicators such as E₂/E₃,SUVA₂₅₄ and TOC.However,after OW oxidation,the products of DOM had higher content of humic acids,while the oxidation products of OMBW had more soluble microbial metabolites.Finally,the oxidation rate of toluene by OMBW under different pressure was investigated,and the oxidation potential of OMBW in groundwater environment was evaluated.The results showed that the water pressure of 2.5 m increased the oxidation rate of toluene by 18.4%for ozone micro-nano bubble water,but only 2%for ordinary ozone water.When the pressure reached 2.5 m,the particle size decreased by 42.1%,resulting in faster gas-liquid mass transfer and improved ozone storage capacity,and ultimately improving the oxidation efficiency of ozone micro-nano bubble water for toluene.In summary,this study had revealed the oxidation mechanism of ozone micro-nano bubble water,clarified the impact of environmental factors such as p H,inorganic ions,dissolved organic matter and water pressure on the oxidation of ozone micro-nano bubble water,and provided a scientific basis for the practical application of ozone micro-nano bubble in groundwater remediation.