Study On Process Intensification Of Ozonation Of Dye Wastewater

The dye wastewater has the characteristics of large amount of water,complex change of water quality,deep color,and some dyes have toxic,carcinogenic and even genotoxic effects on the humans.It will adversely influence not only the environment but also human health,if it is discharged without adequate treatment.In the treatment of dye wastewater,ozone oxidation technology has been widely studied because of its high efficiency and harmlessness without secondary pollution.However,the industrial application of ozonation has been limited by high production cost of ozone and the low ozone utilization due to poor mass transfer rate of ozone.In this study,the process intensification of ozonation of acid red 18?AR18?wastewater was investigated using a newly-developed micro bubble gas-liquid reactor,and the VOF model was used to simulate the variation of the gas liquid interface in the bubble reactor.The effects of the ozone mass transfer on decolorization and mineralization efficiency in the micro bubble gas-liquid reactor,and the intensification effect of the micro bubble reactor on O₃/Ca?OH?₂ process in the degradation of dye wastewater and the mechanism of enhancement were investigated.The main results are as follows:The micro bubble reactor can improve the gas-liquid mass transfer efficiency,the ozone concentration in the liquid phase can reach a stable state rapidly,and the ozone concentration in the liquid phase is about 11.7 mg/L,which is about 10% higher than that of the bubbling system.The concentration of hydroxyl radicals in the bubble reactor was higher than that of the traditional bubbling system.After 5 minutes of ozonation,the hydroxyl radical concentration in the micro bubble system was as high as 121.45 ?M,which was about 11 times higher than that of the bubbling system.The concentrations of ozone and hydroxyl radicals produced in liquid phase were less affected by pressure,but affected by liquid phase temperature.The concentration of ozone in water decreased with the increase of temperature,and the hydroxyl radical production increased with the increase of temperature,as well as an increasing ozone inlet flow and ozone concentration.The decolorization and mineralization efficiency of the microbubble reaction system were higher than that of the bubbling system.In the micro bubble system,the decolorization of dye wastewater takes 8 minutes,and the removal rate of TOC is more than 70% in the ozone oxidation treatment for about 35 minutes.It was found that the first order reaction rate constant of the mineralization is 0.0343 min-1,which is one order of magnitude higher than that of the bubbling system.The decolorization and mineralizationof AR 18 wastewater were increased with decreasing initial AR 18 concentration,as well as an increasing ozone concentration.The intermediates formed during ozonation were detected by GC/MS.Eight organic intermediates were found and then the possible ozonation mechanism of AR 18 in aqueous solution was proposed.The ozonation of acid red 18?AR18?wastewater was investigated in an integrated process consisting of O₃/Ca?OH?₂ system and a newly-developed micro bubble gas-liquid reactor.The effects of operating parameters such as Ca?OH?₂ dosage,reactor pressure,liquid phase temperature,initial dye concentration and inlet ozone concentration on decolorization and mineralization?TOC removal?were studied in order to know the ozonation performance of this new integrated process.The decolorization and TOC removal efficiency increased with increasing inlet ozone concentration and increasing Ca?OH?₂ dosage before 2 g/L,as well as decreasing initial dye concentration.The reactor pressure and liquid phase temperature have little effects on the decolorization and TOC removal efficiency.The intensification mechanism of Ca?OH?₂ assisted ozonation was Ca?OH?₂ ionization produces OH-and Ca²⁺,under the condition of OH-/O₃,it is beneficial to the formation of hydroxyl radical.The mechanism for Ca?OH?₂ intensified mineralization of dye solution is the simultaneous removal of CO₃2-ions,as hydroxyl radical scavengers,due to the presence of Ca²⁺ions.Results indicated that the proposed new integrated process is a high efficient ozonation process for persistent organic wastewater treatment.