Efficiency And Mechanism Of Calcium Peroxide Enhanced Fenton Oxidation Treatment Of Phenol Wastewater

Although the Fenton oxidation technology can achieve better results in the treatment of industrial wastewater,the technology generally requires the pH of the reaction to be around 3,resulting in the need to adjust the pH before and after the wastewater treatment.This not only limits the scope of application of Fenton oxidation technology,but also causes corrosion to the reactor and increases economic losses.In addition,the slower conversion rate of Fe³⁺to Fe²⁺and the self-decomposition of H₂O₂lead to lower utilization of Fenton’s reagent and reduce the Fenton oxidation effect.In order to strengthen the Fenton oxidation effect,this paper uses the strong oxidizing properties of calcium peroxide（CaO₂）to enhance the wastewater treatment capacity of Fenton oxidation technology.The chemical oxygen demand（COD）removal rate was used as the main indicator,the effect of CaO₂enhanced Fenton oxidation system on phenol wastewater treatment was investigated,and the mechanism of CaO₂enhanced Fenton oxidation was discussed.Finally,a possible phenol degradation pathwas proposed.The main research contents and conclusions of this paper are as follows:（1）The treatment effects of CaO₂enhanced Fenton oxidation system on phenol was compared.The results show that the CaO₂can effectively strengthen the degradation effect of phenol wastewater by Fenton oxidation system,the phenol removal rate reaches 100%and the COD removal rate reaches 95.59%within 15 min.At the same time,the influencing factors were analyzed during the degradation of phenol by the CaO₂enhanced Fenton oxidation system,and the following optimal conditions were obtained:Fe²⁺dosage was 4 m M,H₂O₂dosage was 8 m M,CaO₂dosage was 4 m M,The initial concentration of phenol was 100 mg/L.The effect of the initial pH value of the solution experiments showed that in the range of pH 3–11,the COD removal rate of the system for phenol wastewater was all above 90%.Coexisting anions influence experiments showed that within the concentration of 500mg/L,the influence of different coexisting anions follows the following order:Cl^->SO₄^2-≈HCO₃^->NO₃^-.According to TOC analysis,most of the organic matter was mineralized when the CaO₂enhanced Fenton oxidation system degrades phenol wastewater,the TOC removal rate can reach 89.41%when the treatment time is 30min.（2）The content changes of iron ions,H₂O₂and active species in the CaO₂enhanced Fenton oxidation system and the contribution of the active species to phenol degradation were discussed and analyzed.The results show that the strengthening of CaO₂to Fenton oxidation is mainly to convert Fe³⁺to a transtion state such as[Fe（OH）²⁺-CaO₂]（Fe（Ⅲ））,and then reduce[Fe（OH）²⁺]（Fe（Ⅲ））to[Fe（OH）⁺]（Fe（Ⅱ））through internal electron transfer,and generate·O₂^-at the same time,thereby improving the effevtive utilization of iron ions and H₂O₂in the system,increasing the generation of·OH and·O₂^-,enhancing the performance of Fenton oxidation technology.（3）Through ultraviolet scanning spectrum analysis and three-dimensional fluorescence spectrum analysis,it is known that phenol was rapidly degraded in the CaO₂enhanced Fenton oxidation system,and intermediate products with benzene rings were formed.Through the analysis species of intermediate products,it was found,the intermediate products of phenol degradation mainly include benzene ring-containing substances（ethylbenzene,2,5-dimethylbenzaldehyde and9-methylidenefluorene）,2-ethyl-1-hexanol,4,4-dimethyl-1-pentene and a variety of alkanes（mainly alkanes with a carbon chain length of 5-12 carbon numbers）.（4）According to the analysis results of intermediate products,three degradation paths of phenol in the CaO₂enhanced Fenton oxidation system are proposed:path one is that phenol is directly ring-opened under the action of active species to generate unstable chain products such as pentene,pentane,hexane and hexanol,which are then degraded into H₂O and CO₂;path two is that a part of phenol is degraded into small molecular chain products,and these small molecular chain products are combined with undegraded phenol by dehydration and dehydrogenation to form monocyclic products such as ethylbenzene and 2,5-dimethylbenzaldehyde,then the ring is opened to generate unstable chain products such as heptane and octane,which are finally degraded into H₂O and CO₂;the third route is the dehydrogenation of phenol to form a phenoxy group,then the phenoxy group combined with phenol to form 9-methylene fluorene by dehydrated,and then the 9-methylene fluorene is ring-opened to form long-chain alkanes（mainly alkanes with 10 or more carbon atoms）,which are then Degraded into H₂O and CO₂.