Study On Comparison And Selection Mechanism Of Heterogeneous Catalysts In Ozone Catalytic Oxidation Of Petrochemical Wastewater

Petrochemical wastewater has a complex composition and poor biodegradability.It is a typical toxic and difficult-to-degrade industrial wastewater.Since 2017,the"Petrochemical Industry Pollutant Discharge Standards"?GB31571-2015?have been implemented.Petrochemical wastewater treatment plants in our country have ushered in a centralized treatment technology upgrade,mostly using ozone or ozone catalytic oxidation as the core of deep processing units.As the core of this process,the catalyst determines the treatment effect to a great extent.It is of great significance to select efficient catalysts and establish screening criteria based on wastewater quality.This article took the secondary effluent of a petrochemical wastewater treatment plant in the north as the research object and four commercially available heterogeneous catalysts called“A”,“B”,“C”,and“D”were used to study the catalytic performance of different catalysts.The differences and causes of organic removal by different catalysts were explored.Based on this,the comparison and selection mechanism of catalysts was established,which pointed out the direction for catalyst selection.In this study,the adsorption equilibrium time,saturation adsorption amount,and adsorption rate were taken into consideration to select and compare the catalyst adsorption performance.The test results showed that the saturated TOC adsorption capacity of the four catalysts“A”,“B”,“C”,and“D”after reaction for120 minutes was 4.86,1.80,5.76,and 7.57 mg/L,respectively,and the adsorption rate from high to low within 10 minutes was A>D>C>B,the adsorption equilibrium time was 30 min,90 min,60 min,90 min,respectively.Thus,“A”and“D”catalysts had good adsorption performance and each had its own advantages.“C”catalyst had a medium adsorption performance.The catalyst with the worst adsorption performance was“B”.The thresholds of influencing factors in the response surface test of ozone catalytic oxidation were determined by single-factor experiments.The dosages of ozone were 30-50 mg/?L·h?,the dosage of catalyst was 300-700 g/L,and the reaction time was 30-90 minutes.The temperature of the reaction water was determined to be 22?,and the initial p H of the water sample was 7.55.The theoretical calculations of the TOC removal rates of the four catalysts under their respective optimal operating conditions were 44.9%,24.6%,35.6%,and 47.0%,respectively.Through economic comparison and selection,it was found that the catalyst“A”had a low cost in the early stage of investment and the catalyst“D”had a better economy in the later stage of investment.A comparative test of“A”and“D”catalysts for ozone catalytic oxidation under actual operating conditions of the sewage plant found that although“D”catalyst had better treatment effect under its optimal conditions,it had a longer reaction time and higher catalyst usage than“A”.Therefore,“A”and“B”catalysts were selected as the two catalysts with the largest difference in treatment effect for subsequent research.The characterization test of the catalyst showed that“A”catalyst used Al₂O₃/activated carbon as the support and Cu O as the supported oxide,wherein the content of copper element was up to 91.91%.“B”catalyst used Si O₂/activated carbon as the support and Fe₂O₃as the supported oxide.The results showed that copper catalysts supported by Al₂O₃/activated carbon was suitable for the water used in this test.In addition,increasing the catalyst surface pore size and specific surface area properly can also effectively enhance the effect of the catalyst.Organic functional groups such as-C?CH,-C=C-and benzene ring were easily left on the catalyst surface,which had a negative impact on the reuse.From the distribution of hydrophilic and hydrophobic organics,it can be seen that the largest proportion of HOA components in raw water was 43.58%,and the smallest proportion of HON was 10.35%.The humic and fulvic acids in the catalyzed effluent could not be identified at the detection wavelength,and tyrosine and tryptophan proteins could be removed in large quantities.“A”catalyst had the best removal effect on the organic matter of the HOA component,with a TOC removal rate of 62.1%and the HIS component removal effect was only 6.5%.“B”catalyst had the best removal effect on the HOB component organic matter,with a TOC removal rate of 66.7%and it had no removal effect on HIS components.Therefore,the overall effect of the“A”catalyst was better.After the secondary catalytic oxidation test on the HIS components catalyzed by the two catalysts under the same test conditions,the removal rates were increased by 26.5%and14.3%,respectively,which indicated that prolonging the treatment time can effectively increase the removal.