| With the development of industry,the demand for aniline has been on the rise and more and more aniline-containing wastewater was discharged into the environment.The treatment of aniline wastewater aroused more and more attention of the relevant departments.Ozone has been widely used in a variety of wastewater treatment due to its strong oxidizing ability and without the production of secondary pollutant.However,the practical application of ozonation for wastewater treatment is limited by its low solubility and mass transfer efficiency.As a process intensification method,high-gravity technology is realized by using a rotating packed bed?RPB?.Liquids are spread into the thinner liquid film by the huge shearing force under the high gravity environment,which strongly increases the gas-liquid interfacial area and decreases the transfer resistance of gas into the liquid phase.Compared with the stirred tank reactor?STR?,the mass transfer coefficient of the liquid phase can be increased by 2-8times.Therefore,the high-gravity technology can effectively enhance the mass transfer of the ozone from the interface into the liquid phase and finally improve the efficiency of oxidative degradation.In this paper,an RPB was employed to intensify the mass transfer of ozone and improve the mineralization efficiency of aniline in ozone-based advanced oxidation processes.The influencing factors,synergetic effects,degradation mechanism and coexisting substances in its decomposition were investigated in the RPB-O3/Fe?II?and RPB-O3/Fenton processes.The conclusions are shown as follows:Under the RPB-O3/Fe?II?system,effects of operating parameters on removal efficiency of total organic carbon?TOC?and aniline,and the behavior of Fe?II?were studied.The increase of high gravity factor was beneficial to the deep degradation of aniline-containing wastewater.The percentages between direct and indirect reactions of ozonation and the behavior of Fe?II?were deeply affected by initial pH of wastewater,and the RPB-O3/Fe?II?system has broadened the pH range of ozonation process.Aniline mineralization efficiency increased with the increase of ozone concentration,but ozone utilization efficiency decreased.The optimal operation conditions were determined with high gravity factor of 100,Fe?II?concentration of 0.8 mmol·L-1,O3 concentration of 36 mg·L-1and initial pH of 3.In this case,a fast decay of aniline was conducted and the aniline removal efficiency reached 100%in 12min,and TOC removal efficiency was 73%in 60 min.Under the RPB-O3/Fenton system,the addition of hydrogen peroxide reduces oxidant residues and increases the utilization of Fe?II?.RPB-O3/Fenton system was compared with conventional O3/Fenton in stirred tank reactor?STR-O3/Fenton?or single ozonation in RPB?RPB-O3?,and the results indicated a synergistic effect between the RPB and Fenton processes for the degradation of aniline.The optimum operational conditions were obtained at the initial concentration of aniline of 200 mg·L-1,high gravity factor of 100,O3 concentration of 36 mg·L-1,initial pH of 5,with 0.8 mmol/L Fe?II?and 2.5 mL H2O2 for RPB-O3/Fenton system.Under the optimized conditions,the removal efficiency of AN was 100%in 10 min.The TOC removal efficiency reached 89%,and the COD removal efficiency was 85%.The ratio of BOD5/COD was 0.54 in 60 min.The formation of nitrobenzene,p-benzoquinone,maleic acid and oxalic acid were detected by liquid chromatograph-mass spectrometer?LC-MS?,and the degradation pathway for aniline was proposed based on experimental evidence.The effects of coexisting substances of real wastewater on oxidation efficiency of RPB-O3/Fe?II?and RPB-O3/Fenton system were investigated.For RPB-O3/Fe?II?system,sodium phosphate and sodium nitrate were promoting coexisting substances,while sodium hydroxide,sodium carbonate,sodium nitrite,sodium chloride,tap water,and sodium bicarbonate were inhibitory coexisting substances.For RPB-O3/Fenton system,the order of the effects of promoting coexisting substances on TOC removal rate was in the following order:Na3PO4>NaNO3>NaOH.The order of the effects of inhibitory coexisting substances on TOC removal rate was shown as:NaCl>NaNO2>tap water.The Na2CO3 and NaHCO3 in RPB-O3/Fenton system could promote the oxidation efficiency at low concentrations,but inhibit it at high concentration.The effect of coexisting substances on the RPB-O3/Fenton system was always less than that in the RPB-O3/Fe?II?system.Thus,the RPB-O3/Fenton system was more adaptable to complex water quality. |
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