Study On Degradation Of Lignin Derivatives By Ozonation Catalyzed By Metal Oxides Loaded On Activated Carbon

Due to its complex compositions,high concentration of organic matters,deep color and the presence of toxic pollutants,pulp and papermaking wastewater was difficult to biodegrade.The lignin and their derivatives were the main organic pollutants during the pulping and bleaching process,which leaded to the high chemical oxygen demand and deep color of effluent after secondary biological treatments,and this made wastewater unable to meet water quality standards for emission.In this study,the effects of activated carbon supported metal oxides on the degradation of lignin derivatives?eugenol,guaiacol,veratryl alcohol?during catalytic ozonation were systematically investigated and the influence mechanisms were discussed.It provided important scientific data for the practical use of catalytic ozone-biological treatment combined process and catalytic ozone technology in the degradation of lignin derivatives and other refractory organic pollutants in pulp and papermaking wastewater.Firstly,activated carbon supported metal oxides catalysts?Fe/AC,Cu/AC,Ni/AC?were prepared and characterized.The results showed that the active components Fe₂O₃,CuO,Cu₂O and NiO were successfully supported on the surface of activated carbon.The lignin derivatives were degraded by catalytic ozonation with the prepared catalysts.The effects of catalyst type,catalyst loading amount,catalyst dosage and initial pH on the COD_Cr removal efficiency and the reaction kinetics of COD_Cr removal were investigated in the catalytic ozonation of degrading lignin derivatives,The results showed that the characteristics of the active components supported on catalyst had significant influence on the ozonation degradation of lignin derivatives.Different active components had different catalytic activities for the degradation of different lignin derivatives by ozonation.Fe/AC catalyst had the highest catalytic activity for eugenol,and.under the condition of pH 11,loading amount3%and Fe/AC dosage of 0.3 g/L,the COD_Cr removal efficiency reached 91.2%after 60min;Cu/AC catalyst had the highest catalytic activity for guaiacol,and under the condition of pH 11,loading amount 3%and Cu/AC dosage of 1.0 g/L,the COD_Crr removal efficiency reached 90.21%after 60 min;Ni/AC catalyst had the highest catalytic activity for veratryl alcohol,and under the condition of pH 11,loading amount 5%and Ni/AC dosage 1.5 g/L,the COD_Crr removal efficiency reached 92.95%after 60 min.It indicated that different catalysts had different effects on COD_Cr removal efficiency in the catalytic ozonation and degradation of different lignin derivatives.The kinetic analysis showed that the degradation process of COD_Cr accorded with the apparent second-order kinetics in the catalytic ozonation degradation of lignin derivatives The active components supported on the AC effectively increased the kinetic rate constant and accelerated degradation rate of lignin derivatives.Secondly,biodegradability analysis showed that catalytic ozonation by Fe/AC,Cu/AC and Ni/AC catalysts significantly improved the biodegradability of lignin derivatives.At 60min of catalytic oxidation,the BOD₅/COD_Cr of eugenol,guaiacol and veratryl alcohol reached 0.59,0.46 and 0.61,respectively.Experiment of adding radical scavenger showed that the degradation of lignin derivatives in the catalytic ozonation by Fe/AC,Cu/AC and Ni/AC catalysts followed the hydroxyl radical reaction mechanism,and·OH played a key role in the degradation of lignin derivatives.UV-Vis absorption spectra and GC-MS analysis showed that the structure of lignin derivatives were destroyed in the catalytic ozonation by Fe/AC,Cu/AC and Ni/AC catalysts,and intermediate products were generated and then were degraded after a series of reactions,which made the refractory organic matters in the simulated wastewater of lignin derivatives gradually reduce.This had positive effects on the treatment of simulated wastewater from lignin derivatives and might be the main reason for the improvement of biodegradability of lignin derivatives.Finally,the results showed that the lignin derivatives and other pollutants in the pulp and papermaking wastewater were degraded and removed gradually in catalytic ozonation treatment by prepared catalysts.The order of COD_Cr removal efficiency was Ni/AC>Fe/AC>Cu/AC in catalytic ozonation treatment of pulp and papermaking wastewater by prepared catalysts.The degradation of pollutants in wastewater followed the hydroxyl radical reaction mechanism.The removal of COD_Cr accorded with the apparent second-order kinetics and the active components supported on the AC effectively increased the kinetic rate of the reaction.Catalytic ozonation significantly improved the biodegradability of pulp and papermaking wastewater.The BOD₅/COD_Cr reached a maximum of 0.61 after 60 min,which were 35 times higher than that at 0 min.It indicated that the catalytic ozonation technology was a promising pretreatment method for biological treatment,which could effectively improve the efficiency of subsequent biological treatment.