## 1 Introduction  
Tannic acid (penta-m-digallolyI glucose) (TA) is the simplest principal member of a specific group of hydrolysate tannins [1; 2; 3]. The formula of commercial TA, C\({}_{76}\)H\({}_{52}\)O\({}_{46}\) (Figure 1), involves a large number of reactive functional groups, such as hydroxyl and phenolic hydroxyl. It is a water-soluble polyphenic 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 also found in industrial wastewaters, which is an emerging problem because of their harmful influence on natural ecosystems [5; 8]. It causes liver, kidney, and central nervous system problems due to its high toxicity [9; 10; 11]. TA is recalcitrant to conventional biological treatments and other methods [8; 12; 13; 14; 15; 16]. In our laboratory, electrocoagulation process has been successfully used as a method for treating wastewaters contaminated with TA, but large amounts of precipitates were discharged at the end of the treatment [17]. Recently, advanced oxidation processes (AOPs) based on the generation of hydroxyl radicals (HO\({}^{\bullet}\)) from H\({}_{2}\)O\({}_{2}\) have been suggested to eliminate TA [18]. The photochemical system UV/H\({}_{2}\)O\({}_{2}\) has also been recently used for TA degradation. This process generates good quality of treated water in comparison with other AOPs, but the amounts of hydroxyl radicals are obtained mainly by H\({}_{2}\)O\({}_{2}\) decomposition with UV irradiation, which is a high-energy consumption process. Therefore, it is essential to find more efficient and low-cost alternative technology processes to eliminate TA from water. To achieve this goal, AOPs such as UV/persulfate and photo-Fenton processes have been considered as useful options. AOPs, based on the formation of sulfate radical SO\({}_{4}\)\({}^{\bullet-}\) and hydroxyl radical HO\({}^{\bullet}\), have been used in in the treatment of wastewater containing bio-recalcitrant organic pollutants/toxicants recalcitrant compounds to convert them into biodegradable products [18; 19; 20; 21]. Persulfate (K\({}_{2}\)S\({}_{2}\)O\({}_{8}\)) salts decompose in water into persulfate anion (S\({}_{2}\)O\({}_{8}\)\({}^{2-}\)). It is a very strong oxidant (E\({}^{\circ}\) = 2.05 V/NHE), which is not selectively reactive and is relatively stable at room temperature [22; 23]. However, it is kinetically slow in reacting with many organics at ambient temperatures [24; 25]. The photochemical activated degradation of S\({}_{2}\)O\({}_{8}\)\({}^{2-}\) ion to sulfate radical (SO\({}_{4}\)\({}^{\bullet-}\)) has been used as a technique to accelerate the procedure [24; 26; 27]. Sulfate radical (SO\({}_{4}\)\({}^{\bullet-}\)) is a very strong oxidant for its high standard redox potential (2.5-3.1 V) with a kinetically fast reacting tendency [20; 28]. In general, SO\({}_{4}\)\({}^{\bullet-}\) can be generated via photolysis, ultrasonic thermolysis, or activation by transition metals of persulfate or peroxymonosulfate for the oxidation of various organic pollutants [29; 30; 31; 32; 33; 34]. UV/S\({}_{2}\)O\({}_{8}\)\({}^{2-}\) has been considered as a highly efficient method to destruct different organic pollutants [35; 36]. The peroxdisulfate chemistry can be demonstrated by the following equations [24; 37; 38]:  
\[\mathrm{S_{2}O_{8}}^{2-}+\mathrm{hv}\to 2\mathrm{SO_{4}}^{\bullet-} \tag{1}\]  
\[\mathrm{SO_{4}}^{\bullet-}+\mathrm{H_{2}O}\to\mathrm{H^{+}}+\mathrm{SO_{4}}^{2 -}+\mathrm{OH^{-}} \tag{2}\]  
\[\mathrm{SO_{4}}^{\bullet-}+\mathrm{OH^{-}}\to\mathrm{HO^{\bullet}}+\mathrm{ SO_{4}}^{2-} \tag{3}\]  
\[\mathrm{SO_{4}}^{\bullet-}\mathrm{\ or\ HO^{\bullet}}+\mathrm{pollutant}\to \mathrm{degradation\ of\ pollutant} \tag{4}\]  
Figure 1: Structure and properties of Tannic Acid. HO\({}^{\bullet}\) are powerful oxidants (E\({}^{\circ}\) = 2.80 V/NHE), which react immediately and non-selectively with organic pollutants in water.