Abstract
Tannic acid (TA) is a major pollutant present in the wastewater generated from vegetable tanneries process and food processing. This work studied TA degradation by two advanced oxidation processes (APOs): UV irradiation at the wavelength of 254 nm in the presence of hydrogen peroxide (H2O2) and ferrous iron (photo-Fenton) and in the presence of potassium persulfate. The influence of certain experimental parameters such as K2S2O8, H2O2, Fe2+, and TA concentrations, initial pH and temperature was evaluated in order to obtain the highest efficiency in terms of aromatics (decay in UV absorbance at 276 nm) and TOC removals. Chemical oxidation of TA (0.1 mM) by UV/persulfate achieved 96.32% of aromatics removal and 54.41% of TOC removal under optimized conditions of pH = 9 and 53.10 mM of K2S2O8 after 60 min. The treatment of TA by photo-Fenton process successfully led to almost complete aromatics removal (99.32%) and high TOC removal (94.27%) from aqueous solutions containing 0.1 mM of TA at natural pH = 3 using 29.4 mM of H2O2 and 0.18 mM of Fe2+ at 25 °C after 120 min. More efficient degradation of TA by photo-Fenton process than UV/persulfate was obtained, which confirms that hydroxyl radicals are more powerful oxidants than sulfate radicals. The complete removal of organic pollution from natural waters can be accomplished by direct chemical oxidation via hydroxyl radicals generated from photocatalytic decomposition of H2O2.
Highlights
Tannic acid (TA) is the simplest principal member of a specific group of hydrolysable tannins [1,2,3]
The efficiency of UV/persulfate (UV/PS) and photo-Fenton (UV/PF) methods was evaluated by following monitoring UV absorbance at 276 nm and total organic carbon (TOC)
The results from this study showed that the performance of photo-Fenton process is significantly superior to that of UV/persulfate process in the degradation of TA aqueous solutions
Summary
Tannic acid (penta-m-digallolyl glucose) (TA) is the simplest principal member of a specific group of hydrolysable tannins [1,2,3]. The formula of commercial TA, C76 H52 O46 (Figure 1), involves a large number of reactive functional groups, such as hydroxyl and phenolic hydroxyl. It is a water-soluble polyphenolic material with high molecular weights, between 500 and 3000 Da [4,5]. TA is a natural compound found in bananas, sorghum, coffee, and tea [6,7] It is found in industrial wastewaters, which is an emerging problem because of their harmful influence on natural ecosystems [5,8]. Kidney, and central nervous system problems due to its high toxicity [9,10,11]
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