Efficient degradation of tannic acid in water by UV/H 2O 2 process

摘要

In this work, the degradation of tannic acid (TA) by UV/H 2 O 2 process has been investigated. UV/H 2 O 2 oxidation experiments were performed by UV irradiation at 254?nm of TA aqueous solutions in a photo-reactor. Firstly, the effects of certain parameters including pH, H 2 O 2 content, and temperature on the decomposition of H 2 O 2 during UV/H 2 O 2 process were evaluated. Results obtained showed that UV-irradiation of 1?g?H 2 O 2 ?L ?1 aqueous solution achieved almost complete decomposition of H 2 O 2 (> 98%) at pH?=?5 and 28?°C. H 2 O 2 decomposition follows pseudo-first-order kinetics with a rate constant of 0.0086?min ?1 under the optimal conditions. Secondly, the degradation of TA by UV/H 2 O 2 process was investigated. The effects of certain operating conditions including initial pH, temperature, H 2 O 2 concentration and initial total organic carbon (TOC) on the efficiency of degradation and mineralization of TA by UV/H 2 O 2 were evaluated. The results showed that UV/H 2 O 2 process achieved almost complete disappearance of the absorbance at 276?nm (> 96%) and high TOC removal (94%) from TA aqueous solutions containing 82?mg?C?L ?1 under pH?=?9 using 6?g?H 2 O 2 ?L ?1 at 28?°C. The results confirmed that the degradation and mineralization of TA molecules in water occur via chemical oxidation with hydroxyl radicals produced by photo-decomposition of H 2 O 2 by UV light. Chromatography analysis revealed that the mechanism of TA degradation involves several steps including the formation of gallic acid and pyrogallol. These aromatic intermediates undergo further oxidative ring opening to form carboxylic acids (oxalic and maleic acids) that end up to be completely mineralized. The electrical energy requirement consumed under the optimal conditions was 7.9?kWh?g ?1 TOC which is highly competitive with other advanced oxidation technologies such as ozonation and UV/O 3 processes. Based on these results, it can be concluded that UV/H 2 O 2 can be considered as a cost-effective method to treat wastewaters contaminated with natural organic matter.