Experimental Study Of Treating Dye Wastewater By Non-Equilibrium Plasma Combined With Activated Carbon Fiber

Non-equilibrium plasma water treatment is an advanced oxidation technology, which integrates the effectiveness of many active species including hydroxyl radical, hydrogen peroxide, ozone, etc., and bears preferable future application and large market potential because of its advantages of low energy consumption, high treatment efficiency, rapid and non-selective reactivity, and free of secondary pollution, etc.. The current difficulties for widely application of this technology exist mainly in selection of appropriate adsorbents and catalysts. In this work, the original electrical discharge reactor was improved for degrading methyl orange as the model pollutant in water. The infiuence of technological parameters on degradation efficiency was investigated and the best technical parameters were confirmed. The degradation mechanism of organic pollutants by non-equilibrium plasma was discussed. Two kinds of modified activated carbon fiber were prepared by dipping method. One was ACF modified by H₂O₂, and the other was ACF modified by Fe(NO₃)₃. The modified ACF were added for degrading methyl orange combined with non-equilibrium plasma. The adsorption of pollutants and the catalytic effect of ACF were evaluated. And the synergistic mechanism of modified activated carbon fiber with non-equilibrium plasma was discussed.With pulsed voltage supplied between the high voltage needle electrode in the aqueous phase and the ground electrode in gas phase, activate species of hydroxyl radical and hydrogen peroxide were produced in liquid phase and ozone in gas phase, some of which dissolved into the liquid phase. Both the efficiency and the degradation rate of methyl orange were obviously improved with the addition of H₂O₂, Fe²⁺ to the reactor, while it may lead to secondary pollution. Methyl orange was easy to break down into small-molecules, such as carboxylic acid and aniline in the gas-liguid discharge reaction. The small-molecules could be mineralized into carbon dioxide and water by·OH eventually.The combined treatment by pulse discharge with modified ACF showed good synergistic effect due to the adsorption and catalysis of modified ACF. A high concentration of pollutants on ACF surfaces was achieved by adsorption, and the surfaces performed as conversion and decompose centers of pollutants. The surface acidic functional groups of H₂O₂ modified ACF could reacts with the activate species in the discharge reaction, which could generate·OH and increase degradation efficiency. The active surface area of Fe(NO₃)₃ modified ACF increased. After heat treatment Fe(NO₃)₃ was converted to Fe₂O₃, which could generate Fe²⁺ and O₂ in the discharge reaction. The methyl orange can be degraded by·OH and O₃, which were generated from Fe²⁺ and O₂ by fenton reaction and free-radical reaction.