【正文】 Co. Ltd. Halifax England) high pressure Hg lamp, was used in order to stimulate day light, which is congenital for such photooxidation studies. All the measurements were performed at room temperature. The color and decolorization ratios were measured with spectrophotometric technique and calculated according to the literature [20].This was done by monitoring the absorbance change at ? max of maximum peak for dye. The estimation of decolorization degree (DD%)was done according to the relation (12). Effect of the H2O2 concentration To determine the desired conditions of Fenton and Fentonlike processes for the decolorization of RR 12 dye, important variable such as effect dosage of H2O2 concentration on color removal efficiency was investigated. In order to investigate the effect of H2O2 concentration on the decolorization efficiency, experiments were conducted at different H2O2 concentrations from 2 mM to 50 mM with 2X10?5M Fe2+ or Fe3+ solutions and pH . Fig.(1a,b) shows the relationship between the color removal % of dye and the initial concentration of H2O2 in the photoFenton and photoFentonlike processes. The objective of this evaluation is to select the effective operational concentration of H2O2 in photoFenton and photoFentonlike processes. The existing results as in Fig. (2a,b) show the relationship between the degradation degree (DD%) of dye and time in the photoFenton and photoFentonlike processes, the addition of H2O2 from 2 mM to 30 mM increases the decolorization of the dye from % to % at 55 increase in the decolorization is due to the increase in hydroxyl radical concentration by addition of further increasing of H2O2 concentration to 50 mM,degradation efficiency is decreasing due to the fact that at a higher H2O2 concentration scavenging of hydroxyl radicals will occur eq.( 7 )[21]. In the photoFentonlike process, the addition of H2O2 between 2 mM to 50 mM increases decolorization from % to 98% at 55min. Further increase causes no significant change in decolorization for photoFentonlike processes. As demonstrated from the results, the better color removal efficiency for RR 12 dye was obtained at concentration of 10mM in photoFenton process and 20 mM H2O2 in photoFenton process see (Table 1 ). The effect of H2O2 concentration on the degradation rates of RR12 is shown in Fig.(3a,b). The degradation rates were increased by increasing the concentration of H2O2. This can be explained by the effect of additionally produced hydroxyl radicals. With increasing H2O2 concentration from 2mM to 10mM for photoFenton processes, the rate constant increased but above this range the improvement was not obvious. This may be due to rebination of hydroxyl radicals and also hydroxyl radicals reaction with H2O2contributing to the OH scavenging capacity [18, 22]. It can be postulated that H2O2 should be added at an optimum concentration to achieve the best degradation. Hence 10mM of H2O2 appears as an optimal dosage for photoFenton process and 20mM of H2O2 for photoFentonlike process as in Fig (1a,b). Effect of pH The reactive dye wastewaters have an alkaline pH, which leads to the precipitation of iron hydroxide, requiring preneutralisation. The redox potential of the system is also lower in an alkaline pH. Studies showed that the oxidation is rapid at the pH range 24, and the acidification of the waste water is necessary [23]. Therefore, in this work the best results were achieved at pH . Fenton oxidation is known as a highly pH dependent process since pH plays an important role in the mechanism of OH production in the Fenton’s reaction [24]. At high pH (pH 4), the generation of OH gets slower because of the formation of the ferric hydroxo plexes. The plexes would further form [Fe(OH)4] when the pH value is higher than [25]. On the other hand, at very low pH values () hydrogen ions acts as OH radicalscavengers. The reaction is slowed down due to the formation of plex species [Fe (H2O)6]2+, which reacts more slowly with peroxide pared to that of [Fe(OH)(H2O)5]2+. In this study, optimum pH value was determined for reactive dye ( RR 12 ) . During this determination, pH was adjusted between 2 and 6 and efficiencies of color removal (decolorization degree % )were observed . Maxiumum color removal efficiencies were obtained at pH , for the dye in case photoFenton and photoFentonlike processes. At pH , [dye]=1X105M,[Fe+2]= [Fe+3] = 2X105 M , [H2O2]=10mM in photoFenton and 20mM in photoFentonlike , the color removal gives the best results pared with pH , as shown in Fig. ( 4 ) .The efficiencies of color removal (decolorization degree % ) enhanced from % at pH to % at pH at the same time ( 55min ) in photoFenton process , while in photoFenton – like process , color removal % increases from % at pH to % at pH at the same time ( 55min). In highly acidic solutions (pH ) the decolorization rates bee significantly slower with decreasing pH while a similar behavior is also found in highly alkaline solutions[25]. Effect of initial dye concentration The effect of the initial concentration of dye (RR 12 ) introduced in the reaction mixture on color removal for the dye was studied in both photoFenton and photoFenton – like processes. This was conducted at pH , 10mM H2O2 and[Fe+2 ]= 2X 10–5 M in photo Fenton process and at pH , 20mM H2O2, [ Fe+3]= 2X 10–5 M in photoFentonlike process . Dye concentrations were varied from 1 x 10–5 to 9X10–5M. The optimum dye concentrations were 1 x 10–5 M as shown in Fig.(5a,b). The color removal in photo Fenton process reached % at 30 minute and further reached % at 55 min, while in photoFentonlike process the color removal reached % at 55 minute and increased to % at 80 minute . The Fig.(5a,b) shows that with the increase in dye concentration, the time required for deg