Introduction Access to clean water and sanitation on the one hand and water use in agriculture and industry on the other hand to meet diverse needs of human societies in the coming decades is still a challenging issue. There is a growing concern about the presence of non-biodegradable materials and organic contaminants in water supplies as important limiting factors of the exploitation of water resources. In large numbers of developing countries, leather industry is one of the most active sections. Most of the produced leathers are hides of cattle and sheep changing from degradable material to non-degradable ones by experiencing physical and chemical processes. Leather industries produce large amounts of saline wastewater due to their plenty use of water in each section of the tanning process. Saline wastewaters are kinds of wastewater such as the tannery, petroleum refinery and oil extraction that contain more than 10 gram per liter mineral salts. The saline tannery wastewater also contains the high concentration of organic materials and various chemical compounds like lime, sodium sulfite, sulfate ammonium, sodium chloride, disinfections, vegetable tannins, salts of chromium and chloride. In recent years, different applications of advanced oxidation processes (AOPs) are applied to remove organic loading (COD) from wastewater. Advanced oxidation processes produce Hydroxyl radicals that among them HO• is the most powerful one after Fluoride in oxidization of organic compounds. This radical is also favorable because of its high efficiency in oxidation beside non-selective reactivity that makes it able to take the electron from all organic compounds. Fenton as one of the (AOPs) has a broad-spectrum in contamination elimination. Fenton has the simplicity of the technology, with low operation expenses and can be applied at the low temperature and atmospheric pressure. Fenton reagents are Fe2+ and H2O2. The consumption rate of Fe2+ is higher than its regeneration. To solve this problem electrochemical advanced oxidation processes (EAOPs) are introduced. (EAOPs) are based on the combination of Fenton reagents and electrochemical process. Compared to the conventional Fenton process, the electro-Fenton process has the benefit of allowing better control of the process, more efficacy in less hydraulic retention time, less excess sludge and avoiding the storing and transport of the H2O2. The Electro-Fenton process has two different types. In the first one so-called Fered-Fenton, Fenton reagents are added to the reactor from outside and inert electrodes regenerate ferrous ions while in the second type, only hydrogen peroxide is added from outside and Fe2+ is provided from sacrificial cast iron anodes. The main purpose of this study was effective investigation on Fered-Fenton advanced oxidation process for removal of organic loading (COD) from saline tannery wastewater under optimized conditions including the effect of initial pH, [Fe2+]/[H2O2], H2O2 concentration, current and hydraulic retention time in the presence of high concentration of CI" ions. 2. Materials and Methods Pilot studies and investigations were carried out in laboratory scale. Saline tannery wastewater samples were taken from the wastewater treatment plant of Varamin, Iran. The examined Fered-Fenton reactor depicted on Figure 1 consists of four graphite electrodes, two anodes and two cathodes, due to chemical inert and decomposable characteristic of graphite. The electrodes dimensions were 140inm∗ 60mm∗ lmm, and the distance between them was 1.5 cm. The reactor volume that is made of Plexiglas was 1 L, equipped with an electrical mixer and digital power to adjust amperage. Chemicals including ferrous sulfate, hydrogen peroxide, and concentrated sulfuric acid (Merk Chemical Co. Inc., Germany) and filter paper #42 (Whatman Co. Inc., United Kingdom) were analytical grade and used without further purification. The pH values of wastewater samples were adjusted using sulfuric acid and soda before ferrous sulfate and hydrogen peroxide were added to the system. At first, ferrous sulfate was added and mixed vigorously, then hydrogen peroxide was injected into the reactor. After connecting electrodes to the power supply and putting them in the reactor, amperage and voltage were set. All tests were done according to the standard methods (APHA) and each part of experiments was repeated three times. (Figure presented) 3. Discussion and Results pH is one of the most impressive factors in Fenton reactions. Adjustment of pH is necessary for precipitation of iron, hydrogen peroxide decomposition, complex and recalcitrant iron compounds and overall efficacy of the process. Based on the own results at the laboratory scale (Fered-Fenton reactor) observed the maximum efficiency of COD removal at pH between 2.5 and 3.5. Oxidation efficiency essentially reduces at pH values lower than 3 because of resulting stable complexes from Fe2+ and H2O2 that leads to deactivation of Fe2+ as a catalyst. While pH value increases from 3 to 5, the process efficiency declines continuously. At higher pH values than 5, Iron species begin to precipitate as ferric hydroxides and cause a reduction in efficiency of the process. During the process continuous detection of pH in order to keep optimized pH value constant is really essential. Generally, water hydrolysis and formation of Carboxylic acids make the pH decay in the system. Since high concentrations of CI" ions available in tannery wastewater, Hypochlorous acids (HC10) and Hydrochloric acid (HCl) are formed that they would also drop the pH. Hence, lack of continuous detection of pH results in the inadequacy of Fered-Fenton process for COD removal from saline tannery wastewater at pH optimized. In the Fenton and Electro-Fenton processes, the mass ratio of ferrous iron and hydrogen peroxide is very crucial in terms of overall cost and efficacy of the process in COD removal. Excess or shortage of any of these two reagents would make the process insufficient either by scavenging of hydroxyl radicals or by stopping the process. In the absence of Fe2+ efficiency of the process is limited to only 14% that is because a few number of iron ions were available as the catalyst to generate enough OH•. Besides, water electrolysis could not provide so many hydroxyl radicals to oxidize organic compound more effectively. The maximum efficiency of the system was achieved by [Fe2+]/[H2O2]=0.6. More addition of Fe2+ causes both OH• scavenging and more iron sludge. Hydrogen peroxide is the main source of hydroxyl radicals in Fenton related processes. An inadequate dosage of H2O2 does not generate enough hydroxyl radicals to achieve complete mineralization. Although an increase in the amount of H202 raises the efficacy of the process, the overdose of it let the side reactions initiate i.e. all of the generated OH• would not be utilized to oxidize organic matters. New radical species generated from side reactions are not as strong as OH• so they reduce the efficacy of the process. Furthermore, COD is defined as the amount of a specified oxidant that reacts with the sample under controlled conditions. Therefore, the determination of Fenton reagent's dosages should be made on the basis of initial COD for an efficient treatment. By increasing the initial COD, the required dosage of H2O2 would raise and consequently expand the amount of Fe2+. By considering the fact that samples are real saline tannery wastewater, all of the samples do not show the same initial COD and oscillate in a range of 900 to 1500 mg/lit. Further increase in the ratio of [H202]/[CODi] would lead to the adverse effect of scavenging reactions and finally to the ineffectiveness of the process. Therefore, the [H2O2]/[CODi]=2 would be considered as the optimum ratio. When no current was applied to the reactor Fenton process was predominant. With the increase in current, the electro-regeneration of Fe2+ from Fe3+would be improved.