Study On Treatment Of Chemical Organic Wastewater By Ozone-based Advanced Oxidation Processes In A Rotating Packed Bed

With the increase in the discharge of chemical wastewater,organic pollutants in the wastewater pose an increasing threat to the environment.The composition of chemical organic wastewater is complex;the organic pollutants are not easily decomposed and some are toxic,and it is difficult to degrade those pollutants completely by traditional methods.Therefore,the innovation and improvement of chemical organic wastewater treatments are of significant importance for the environmental protection in China.Ozone-based advanced oxidation process(AOP)is one of the cutting-edge technologies with potential applications in the field of water treatment.However,the ozone absorption efficiency in traditional reactors is low,which leads to an increase in treatment costs.The application of ozone in industrial wastewater treatment is limited,and an efficient ozone-based reactor is desired.In this study,a rotating packed bed(RPB)was employed to intensify the ozone-based AOPs.Different kinds of chemical organic wastewater were targeted to study ozone mass transfer and the degradation kinetics of organic compounds.According to the mass transfer theory,an overall volumetric mass-transfer coefficient model of ozone absorption into organic solution in an RPB was established,and a novel approach for establishing the empirical models of organic degradation and COD removal was proposed.Two kinds of actual chemical wastewater were treated in RPB with ozone-based AOPs,and the models exhibited good predictability for the wastewater treatment.The main research contents and conclusions are as listed below.(1)The hydroquinone wastewater was treated by RPB-O3 and RPB-O3/H2O2 processes,and hydroquinone degradation,COD removal,and ozone absorption were studied.In the acidic conditions,the results indicate that these two processes had similar results.The removal percentage and Y in RPB-O3/H2O2 process were higher than in RPB-O3 process.With the increase of pH from 7 to 11,the removal percentages of hydroquinone(?HQ)and COD(?COD)increased,and the treatment effect of RPB-O3/H2O2 was better than RPB-O3.When RPB-O3/H2O2 was used to treat hydroquinone wastewater,?HQ,?COD,?O3 and Y reached 90%,43%,90%and 0.5,respectively,at rotational speed of 800 rpm,gas flow rate of 60 L·h-1,liquid flow rate of 30 L·h-1,pH of 10.0,ozone concentration of 75 mg·L-1,r(H2O2/O3)of 0.25 and temperature of 298 K.Under similar conditions,?HQ,?COD,?O3 and Y were 83%,33%,80%and 0.45,respectively with the RPB-O3 process.1,4-benzoquinone is the main intermediates in hydroquinone degradation by O3 and O3/H2O2 processes.(2)An overall volumetric mass-transfer coefficient(KGa)model of ozone absorption into two kinds of organic wastewater in RPB was established.The effects of different factors on experimental and model KGa values were investigated.The predictability of the model was investigated by comparing the predicted and the experimental KGa values.The predicted and experimental KGa agreed well with the deviations within 10%and 15%for hydroquinone wastewater and phenol wastewater,respectively,suggesting that this model has good predictability for the mass transfer process of ozone absorption into organic wastewater with different reaction rates in RPB.This model can be used to predict the ozone mass transfer process in not only single organic wastewater,but actual coking wastewater.(3)The phenol,catechol,hydroquinone and aniline wastewaters were treated by RPB-O3 processes,and the kinetics of organic compounds degradation and COD removal were investigated.According to the treatment of hydroquinone wastewater,empirical models of organic degradation and COD removal rate were established.The predicted and experimental degradation rate agreed well with the deviations within 25%,suggesting that the empirical models have good predictability.The model also can be used for the prediction of the actual wastewater treatment.(4)Hydroquinone wastewater was treated by RPB-O3/H2O2 process.It is necessary to consider both the direct oxidation reaction between O3 with hydroquinone,and the reaction between O3 with HO2 when pH>5.0.With the increase of pH,kapp-HQ and kapp-COD engaged in reactions increased,and it is favorable for hydroquinone treatment by RPB-O3/H2O2 process in alkaline condition.kapp-HQ and kapp-COD increased with rising r(H2O2/O3),rotational speed,ozone concentration,gas flow rate and liquid flow rate.Under the same conditions,kapp-HQ in RPB-O3/H2O2 and STR-O3/H2O2 were 2.341 s-1 and 0.00159 s-1,respectively,and kapp-COD in RPB-O3/H2O2 and STR-O3/H2O2 were 0.536 s-1 and 3.820×10-4 s-1,respectively.(5)RPB-O3 and RPB-O3/H2O2 processes were used to treat the actual polyformaldehyde(POM)wastewater.The reaction rate constant between ozone and COD of POM wastewater was about 280-285 L·mol-1·s-1,and the activation energy was 31.5 kJ·mol-1.The COD removal effects in RPB-O3 and RPB-O3/H2O2 processes were compared and it was found that O3/H2O2 is more suitable for POM wastewater treatment in RPB.The COD removal percentage of POM wastewater by RPB-O3/H2O2 was 55%at the gas flow rate of 60 L·h-1,liquid flow rate of 30 L·h-1,pH of 8.5,ozone concentration of 70 mg·L-1,r(H2O2/O3)of 0.4,temperature of 290 K and initial COD of 110-120 mg·L-1.Under the similar conditions,the COD removal percentage by RPB-O3 was only 26%.The RPB-O3/H2O2 process has advantages on the COD removal and ozone utilization over RPB-O3,STR-O3 and STR-O3/H2O2 processes.(6)RPB-O3 process was used to treat effluents from regulating tank and secondary sedimentation tank in actual coking wastewater treatment.The ozone utilization coefficients of Y in the treatment of effluent from the secondary sedimentation tank were 0.1-0.5.The deviation of predicted and experimental KGa in coking wastewater treatment was within 25%,and the removal percentage of volatile phenol in effluents from the secondary sedimentation tank and regulation tank reached 100%and 61%respectively.The empirical correlation model of RPB-O3 process can be used to predict the treatment of COD and volatile phenol in effluent from the regulation tank.The biodegradability of effluent from the secondary sedimentation tank improved after the effluent was treated by the RPB-O3 process,and the value of BOD5/COD of the treated effluent increased for about three times compared to the untreated wastewater.On the contrary,the biodegradability of effluent from the regulation tank decreased after the effluent was treated by the RPB-O3 process.The RPB multistage treatment of coking wastewater was superior to the RPB circulation treatment.