| The coal chemical industry has an important strategic position in the national economy,but the wastewater generated from the coal chemical production process contains a large number of toxic and hazardous N-heterocyclic organic compounds.Quinoline,pyridine and indole are typical N-heterocyclic organic compounds in the secondary biochemical effluent of coal chemical industry,which are difficult to be degraded effectively by conventional wastewater treatment technologies.Based on the above background,this study selected quinoline as the main target pollutant,which was degraded by TiO2photocatalytic system with different electron capture agents(H2O2/PS)to improve its reaction efficiency.Finally,a comparative analysis of the degradation of typical N-heterocyclic organic compounds in coal chemical wastewater was carried out in the defined reaction system,with the following results:(1)UV/TiO2 photocatalytic reaction system degraded quinoline with 64.52%and40.28%of quinoline and TOC removal rate,respectively.The optimum TiO2dosage is 1.2g/L,the optimum p H is 6.5 due to isoelectric point of TiO2and dissociation constant of quinoline.The contribution of free radicals to the degradation of quinoline was:O2-ˇ>h+>ˇOH,and it was inferred that the degradation of quinoline was mainly achieved by the attack of O2-ˇon the pyridine ring.The reaction system was effective in degrading typical N-heterocyclic organic compounds in coal chemical wastewater,with 42.24%and 69.58%of pyridine and indole degradation,respectively.(2)UV/TiO2/H2O2 photocatalytic reaction system degraded quinoline,the optimum dosage of H2O2was 0.05 mol/L and the optimum p H was 6.5,at which the removal and mineralisation rates of quinoline were 93.16%and 65.84%respectively.TheˇOH produced by fixed concentration of H2O2was not sufficient to remove high concentrations of quinoline and its intermediate products,and the degradation of quinoline was inhibited by both air aeration and nitrogen aeration,and the inhibitory effect of air aeration was stronger.Based on the results of the free radical quenching experiments,it was inferred that the degradation of quinoline was accomplished by a combination ofˇOH and O2-ˇ.TheˇOH attacks the 5-and 8-positions on the benzene ring and the O2-ˇattacks the 2-,3-and 4-positions on the pyridine ring.Quinoline and indole can be effectively degraded in this reaction system,but pyridine cannot be effectively degraded.(3)UV/TiO2/PS photocatalytic reaction system can effectively degrade medium to high concentrations of quinoline.97.07%of quinoline and 72.32%of TOC were removed at 20 mg/L under optimal experimental conditions.0.012 mo/L was the optimal dosage of PS.This reaction system can effectively degrade quinoline in a wide p H range,and the degradation rate of quinoline under air aeration is lower than that of nitrogen aeration,but its The degradation rate of quinoline under air aeration was lower than that of nitrogen aeration,but the reaction rate constant was higher.The contribution of different free radicals to the degradation of quinoline:SO4-ˇ>O2-ˇ>ˇOH>h+.It is inferred that the degradation of quinoline in this reaction system is mainly by SO4-ˇattacking the electrons at the 5-and 8-positions on the benzene ring.The reaction system is applicable to the degradation of typical N-heterocyclic organic compounds in coal chemical wastewater,and the degradation process is consistent with quasi primary reaction kinetics.(4)By comparing the degradation effects of quinoline in three reaction systems and the degradation results of other N-heterocyclic organic compounds(pyridine and indole)under different experimental factors,it is concluded that the UV/TiO2/PS photocatalytic reaction system is the most stable and efficient for the degradation of typical N-heterocyclic organic compounds in coal chemical wastewater. |
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