A Study On The Process Of Pre-Ozonation Of Refractory Aromatic Compounds

Chemical industry waste water is typical refractory acidic waste water for biochemical degradation, which often contain some aromatic compounds. Therefore, effective pretreatment of aromatic compounds is necessary. In the reported literatures, ozonation is a common pretreatment method, and is usually applied under alkaline condition. Considering the facts, A ozone-based advanced oxidation process (Ti(Ⅳ)-catalyzed H2O2/O3(Ti(Ⅳ)/O3/H2O2) system) was used to pretreat aromatic compounds under acidic conditions. Furthermore, a conception of the oxidative degree (4TOC-COD/4TOC) was proposed to Rapid determination of the biodegradability of wastewater.In the third chapter,the degradation efficiencies of dimethyl phthalate (DMP) by O3, O3/H2O2, Ti(Ⅳ)/O3and Ti(TV)/O3/H2O2were investigated under acid conditions. The results indicated that Ti(Ⅳ)/O3/H2O2was the best process according to the results of the degradation efficiency of DMP and the utilization rate of ozone at pH2.8. The apparent rate constants of DMP degradation by O3, O3/H2O2, Ti(Ⅳ)/O3and Ti(Ⅳ)/O3/H2O2under the same conditions were3.96×10-4s-1、9.54×10-4s-1、1.07×10-3s-1and 6.41×10-3s1, respectively. The ozone utilization rate of Ti(Ⅳ)/O3/H2O2was increased by6.51%compared with that of ozonation alone. The experimental results showed that the optimized concentrations of Ti(Ⅳ) and H2O2were1.4mg·L-1and10mg·L-1, respectively. According to the results of gas chromatography-mass spectrometry (GC/MS) and ion chromatography analysis, the possible reaction pathway of DMP degradation by Ti(Ⅳ)/O3/H2O2was proposed and discussed.In the forth chapter, he changes of biodegradability (BOD/COD) of several refractory aromatic compounds in pre-ozonation were investigated, and a conception of the oxidative degree (i.e., the oxidative degree of an organic compound, defined as was put forward to quantify the optimal ozone dose. The results showed that the oxidative degrees and biodegradability of nitrobenzene,1,2-dimethyl phthalate and sulfosalicylic acid solutions all increased in the process of pre-ozonation, and they had a positive correlation. The values of BOD/COD of the samples could be more than0.25when their oxidative degrees were greater than0.65, showing that the samples could be directly treated by biological treatment. The above results indicate that the value of oxidative degree can probably be used to rapidly evaluate the biodegradability of wastewater. Considering determination of the oxidative degree is simple and speedy, it will be of significance to promote application of ozonation technology in the pre-treatment of refractory wastewater.m the fifth chapter, the pretreatment efficiency of Ti(Ⅳ)-catalyzed ozonation for a pharmaceutical wastewater and the correlation between the oxidative degree and biodegradability (BOD/COD) were investigated in acid mediums. The results indicated that the optimized concentrations of Ti(Ⅳ) and H2O2were10mg·L-1and200mg·L-1, respectively. The value of pH also affected the degradation efficiency of Ti(Ⅳ)/O3/H2O2, the removal rates of chemical oxygen demand (COD) and total organic carbon (TOC) were56.13%and31.49%after120min at pH5, respectively, and that the oxidative degree and BOD/COD value of the pharmaceutical wastewater increased from the original0.388and0.019to0.608and0.297, respectively. The oxidative degrees of the samples had positive correlation with their biodegradability, and could be used to quickly judge biodegradability of samples in wastewater treatment.