| Dyeing wastewaters has been one of the hotspots in the field of environment attributed to its difficult treatment. Pulsed discharge technology which can degrade the organic pollutes into either nontoxic or low toxicity compounds, is in the nature of convenient, high energy efficiency and without secondary pollution. Therefore, there has been growing interest in the degradation of dyeing wastewater. The present work investigated the degradation of two typical acid dyes (Methyl Orange and Eosin Yellowish) as well as two basic dyes (Basic Orange and Methylene Blue) in a gas-liquid series plate-plate type high-voltage pulsed discharge reactor. In this article, both decolourisation efficiency and the total organic carbon (TOC) removal were discussed, not only about monocomponent solutions, but also about two-component mixtures with different molecular structures. Various operating factors were investigated as well.The conclusions after comprehensive analyses are summarized as followings.(1) All of the single dyes studied presented high color removal efficiency by pulsed discharge treatment, which was above90%at9min. The reaction kinetics followed a pseudo first-order model for all monocomponent dyes. The decolourisation of acid dyes behaves a little bit faster than basic ones of the same class. Comparing to decolourisation efficiency, the TOC removal dropped to19.9%～32.6%at21min. And the mineralization of acid dyes was more efficient than basic dyes.(2) The degradation efficiency of each dye clearly declined in the mixures. However, comparing with the single dyes, the energy yield significantly increased when this reactor was used to treat the mixed dyes. The energy yield at a discharge time of21min for acid and basic mixtures were7.16g/(kWh) and3.44g/(kWh), respectively. In agreement with the consequences for single component system, the degradation efficiency of mixed acid dyes was higher than the basic mixture. (3) The initial concentration of the dyes played an important role on its degrading. As the initial concentration increasing, the degradation efficiency of dyes decreased while the energy yield of the reactor increased. The mineralization of two-component mixtures was related to their constituents’ratio. It achieved the maximum value while their concentrations were equal. And the one with higher concentration was predominant on the degradation efficiency of mixtures.(4) The initial pH and electrical conductivity of the solution played an important role on the degrading of dyes. Generally, the individual dyes and the mixtures of the same type behaved in the same way toward degradation. As the initial pH of the system increasing, the degradation efficiency of acid dyes rose, and the opposite was true for basic dyes. The augment of initial conductivity played passive effect on the decomposition efficiency of all the dyes studied.(5) The decolorization efficiency and TOC removal of dyes decreased, while adding more trapping agent of hydroxyl radical to the solution. On the opposite, the addition of hydrogen peroxide promoted the degradation of dyes before its concentration was saturated.(6) According to the change of solution pH and conductivity, and the analysis of UV-Vis spectra and HPLC, the possible degradation pathway of dyes was concluded. The chromophore of dyestuff was cracked firstly, and then the benzene rings decomposed into small molecule organic acids with the effect of many active species. And it would be further mineralized into some inorganic ions in the light of the augment of the solutions conductivity. |
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