Ozonation Of Acid Red14Wastewater In A Microporous Tube-in-tube Microchannel Reactor

Ozonation is a very effective technology in treating wastewatercontaining recalcitrant compounds and regarded as one of the mostpromising alternative for solving the problem of color in textile effluents.The ozonation of compounds in wastewater depends not only on thereaction kinetics but also on the transfer between phases. It has beenreported that the rate limiting step in the ozonation of dye containingwastewater is the mass transfer of ozone from the gas phase to the liquidphase due to its low solubility in water. As one of the most importantmeans to intensify mass transfer, microscale devices such asmicrocontactors and microreactors have exhibited great potentialopportunities in many areas in recent years. In this study, ahigh throughput microporous tube in tube microchannel reactor(MTMCR) with better mass transfer efficiency has been developed as anovel gas liquid contactor and applied to ozonation process. Theozonation of synthetic wastewater containing azo dye Acid Red14(AR14) was investigated in the MTMCR. The main findings are summarized as follows.1. In the O3H2O physical absorption system, the ozone liquidvolumetric mass transfer coefficient in the MTMCR was derived and theeffects of operating parameters were studied. It can be seen that the ozoneliquid volumetric mass transfer coefficient in the MTMCR increased withthe increase of gas or liquid volumetric flow rate. It was found that theozone liquid volumetric mass transfer coefficient in the MTMCR is atleast one order of magnitude higher when compared with conventionalgas liquid contactors.2. It is found that reducing the micropore size and the annularchannel width led to a higher mass transfer rate and was beneficial todecolorization and ozone utilization. Decolorization efficiency increasedand ozone utilization efficiency decreased with an increasingozone containing gas volumetric flow rate, as well as a decreasing liquidvolumetric flow rate and initial AR14concentration. The highestdecolorization efficiency for AR14was obtained at the initial pH of9.0.The degradation kinetics was observed to be a pseudo first orderreaction with respect to AR14concentration and the pseudo first orderrate constant for the degradation of AR14was0.228min1. The lowerCOD removal compared with the decolorization can be explained byincomplete oxidation of organic material and that many intermediatesexisted in AR14ozonation. 3. The formation of six intermediates during AR14ozonation wasdetected by GC/MS and the probable degradation pathway of AR14inaqueous solution was proposed. It can be concluded that the splitting ofthe N=N bonds in AR14is attributed to the attacks by ozone andhydroxyl radicals, and the subsequent degradation of the intermediates isascribed mainly to the oxidation of hydroxyl radicals. During theozonation, most of the nitrogen atoms in AR14were converted intonitrogen and all the sulfur atoms were transformed into sulfate ions.4. The effect of inorganic salts on ozonation of AR14wasinvestigated. The experimental results reveal that at any given pH, thepresence of NaCl Na2SO4NaNO3Na2CO3and NaHCO3are beneficialfor decolorization. The decolorization and ozone utilization efficiency ofAR14increased with the increase of inorganic salt concentration in thesolution.