Vanadium Oxide Based Fenton-like Reactions For Diethyl Phthalate Degradation And Its Mechanism To Soil Bacterial Community

Diethyl phthalate?DEP?is one of the six types of phthalate?PAEs?contaminants that are preferentially controlled by the US Environmental Protection Agency?EPA?,which can interfere with human endocrine,and high concentrations of prolonged exposure can leading to mutations in the body,,and even having carcinogenic risk to our body.The chemical oxidation based on Fenton is widely used in the remediation of organic contaminated sites.The interaction of soil components such as organic matter,metal minerals and H₂O₂ has been the current research hotspot,but it is mainly focused on the interaction of iron and manganese minerals with H₂O₂.The content of vanadium in the soil is 0⁴00 mg/kg.It is very important to study the mechanism of vanadium mineral activation or H₂O₂ interaction for the degradation of pollutants.Based on this,the degradation effect of H₂O₂ activated by V₂O₃ on the DEP in aqueous solution was studied.The effects of pH condition,H₂O₂ concentration,anion and small molecule acid on DEP degradation were also investigated.Electron paramagnetic resonance EPR)and benzoic acid?BA?were used to characterize the hydroxyl and hydroxyl groups,and revealingthe molecular mechanism of the generation and degradation of hydroxyl.The concentration of V?IV?/V?V?in the system was determined by the method of chrome cyanide R?ECR?cetyltrimethyl-ammonium bromide?CTA?and N-benzoylhydroxylamine spectrophotometry respectively,and revealing the mechanism of ion dissolution and transformation of V in the system.In addition,vanadium dioxide?VO₂?and vanadium pentoxide?V₂O₅?were used to study the degradation efficiency of V?IV?and V?V?activated H₂O₂ in soil.The effects of Fenton on soil properties and microbial community were evaluated,andthe main contents and conclusions are as follows:1 Degradation of DEP by V₂O₃ activationof H₂O₂in aqueous solution was studied.V₂O₃ can rapidly and effectively activate H₂O₂,and there is a result about 65%of DEP is degraded in the first 60 minutes of the reaction.The degradation of DEP significantly affected the degradation of DEP at pH 3.0,but the degradation rate was70%at pH 5.0,7.0 and 9.0,which is indicated that can effectively degrade DEP was in a wide pH range of in the V₂O₃/H₂O₂ system.The qualitative and quantitative analysis of the free radicals of the system was realized by EPR and benzoic acid?BA?.It is demonstrated that^·OH was the main motive force for the degradation of DEP,and meanwhile the influence of anions on the degradation of DEP in the reaction system was investigated.It was found that high concentrations of chloride?Cl^-?and Nitrate ions?NO₃^-?inhibit the degradation of DEP.The addition of small molecular acids such as gallic acid and caffeic acid significantly inhibits the degradation of DEP by the system,while oxalic acid and citric acid contribute significantly to DEP.When the concentration of oxalic acid was 0.5mM and the degradation rate of DEP was get to 94%.The intermediate product of DEP process was determined by GC-MS,it was found that monoester,phthalic acid and 2-OHBA were the main products.2 Degradation of DEP by activation of H₂O₂ in aqueous solution was studied.The degradation rate of DEP was 60%in the VO₂/H₂O₂ system,while that of the VO₂ and H₂O₂ alone did not degraded,which also indicated that the VO₂/H₂O₂ system could also produce^·OH for DEP degradation.The degradation rate of DEP was lower than that of V₂O₃/H₂O₂ system,but when H₂O₂ was 2.0 mM,the degradation rate of DEP was also get to 60%.According to the results,the excessive concentration of H₂O₂ was not conducive to DEP degradation.The ability of generation of^·OH in the VO₂/H₂O₂system is weaker than that of the V₂O₃/H₂O₂system,the reason for the transmission of electrons to H₂O₂ in VO₂ is weaker than V₂O₃.3 Degradation of DEP by V₂O₅ activation of H₂O₂in aqueous solutionwas studied.When the dosage of V₂O₅ is 0.1 g/L,the degradation efficiency of DEP is the best.While the reaction time is extended to 24 h,the degradation rate of DEP is up to61.1%.Under the same conditions,the degradation rate of DEP in the V₂O₅ or H₂O₂system is less than 5%.Oxalic acid is a reducing small molecule acid that is can reduce V?V?to V?IV?,even V?III?,and the effect of low valent vanadium?V?on the degradation of DEP is more significant.The results showed that there was no obvious EPR signal in the DMPO,DMPO/H₂O₂,H₂O₂ and V₂O₅ systems,and it was proved that V₂O₅/H₂O₂ could produce^·OH,and that can be generated within the range at a wide pH.4 The effects of H₂O₂ on soil microbes were investigated under the experimental conditions with soil and water ratio of 2:1.The results showed that the microbial diversity of the treated group was significantly lower than that of the control.It was suggested that the oxidant inhibited the growth of microorganisms.In addition,the diversity of microbes on the 1st and 28th day of the control are also significant differences,probably because the first day of treatment did not activate the microorganisms,resulting in diversity and abundance are far less than the 28d.At the classification level of the door,the H₂O₂ treatment was similar to the microbial community in the control soil,and the soil of the control group changed greatly with the incubation time.In general,the PCoA and cluster clustering analysis showed that the structure of the bacteria was significantly different from that of the control group.At the level of the genus,three H₂O₂ treatment groups had a high similarity,especially the H₂O₂ treatment and the citrate/H₂O₂ treatment group.