Research On The Decolorization Effect And Oxidation Mechanis Of Ozone Oxidation Method Treating Acrylonitrile Wasterwater

Acrylonitrile wastewater has poor biodegradability and high toxicity which is hard todispose. Its composition is complicated including nitrile, cyanide, pyridine, lipids, organicacid and a large number of oligomer and polymer. When treated by biological methods, thecontaminants cannot be completely degraded and the effluent chroma is high.Ozone oxidation was used as a decolorization method for the effluent of acrylonitrilewastewater biological treatment. The impact of different gas-liquid mixing modes （differentreactor forms） on the decolorization effect was studied, the operating parameters wereoptimized, the O₃oxidation mechanism was determined and the oxidation kinetics of the maincontaminants were analyzed.The investigation of the effect of ozone oxidation treating the acrylonitrile productwastewater showed that ozone oxidation was capable to be used as the advanced treatmentprocess of the effluent of the acrylonitrile wastewater biological treatment. After reacted for9h, the chroma removal rate reached93.7%and NO₂^-N removal rate was100%. As B/Cincreased from0.2to0.37, water biodegradability has increased. The concentrations of CODand NH₄⁺-N were not significantly changed，but the concentration of NO₃^--N was increased.The reaction selectivity between ozone and pollutants was strong and the degradation speedwas slow.The optimum operating condition was determined through the investigation of five mainfactors which had obvious influence on the effluent chroma and COD. Under the condition ofusing O2as the gas source of the O₃generator, adopting gas-liquid mixing plate reactor, platerotating speed50r/min, initial pH7⁸and gas flow rate600ml/min, after reacted for60min,the chroma removal rate reached87%and COD removal rate was40%. Calculation showedthat removing one time of chroma needed to consume O₃1.7mg, and removing one mg ofCOD needed to consume O₃2.6mg in each liter of water.The mechanism of O₃oxidation was determined through the investigation of theoxidation effect when OH inhibitor was added into the system. The experimental resultsshowed that the direct reactions between O₃and the contaminants played a dominant role inthe process of O₃treating acrylonitrile wastewater. The degradation and transformation law ofnicotinamide, acrylic，3-cryanopyridine and other major contaminants were further identified. The oxidation kinetics of the main contaminants was analyzed and the degrading speedsof several contaminants were compared. The experimental results showed that the oxidationdegrading speeds of the main contaminants in a descending order were: nicotinamideacrylonitrile> nicotinamide>3-cyanopyridine.