Treatment of Tannery Wastewater by Chemical Coagulation and Electrocoagulation Feride Ulu 1 , Mehmet Kobya 1, 2 Abstract The purpose of this study was to research the chemical coagulation on wastewater of primary sedimentation basin which belongs to Tanning Industry Wastewater Treatment Plant by using various type chemical substances. Besides, electrocoagulation process was applied on wastewater of primary sedimentation basin and final sedimentation basin. For this purpose, during chemical coagulation experiments, Al-base coagulants (alum and AlCl3) and Fe-base coagulants (Fe2(SO4)3 and FeCl3) were used as coagulated materials. The coagulate dosage and pH range effects to the efficiency of treatment was researched. During these experiment more efficiency has observed when the coagulate materials including ferric salt were used. The best result was obtained when pH 7.5. An electrocoagulation (EC) reactor using iron plate electrodes were designed. The effect of parameters such as pH, current density and operating time on COD, total S, total Cr, NH3-N and SS removal were investigated. At the end of EC process 30% COD and 60% SS disposal were obtained in the primary sedimentation basin of wastewater. In the same condition, 35% COD and 85% SS disposal were obtained in the final sedimentation basin of wastewater. Disposal of NH3-N was calculated 20% for both wastewaters. However, due to the results were not quite satisfactory, for application of disposal of NH3-N another system improvement has started. Keywords: Chemical coagulation, Electrocoagulation, Tannery wastewater. 1. INTRODUCTION In order to sustain our global water supply, many environmental action programmes have been established to address pollution issues and numerous Environmental Directives, regulations and legislation have been issued in order to define quality standards for water, set emission standards for discharges to water and to control emissions of dangerous pollutants [1]. The leather industry is well known as a high consumer of water. Therefore, this industry belongs to one of the most polluting industrial sectors [2]. It can result in heavy pollution from effluents containing high levels of salinity, organic loading, inorganic matter, dissolved and suspended solids, ammonia, organic nitrogen and specific pollutants (sulphide, chromium and other toxic metal salt residues) [3]. Tannery wastewater owes its pollution load to a massive presence of chloride, ammonia and various organic substances. The characteristics of tannery wastewater vary widely depending on: the nature of the adopted tanning process, the amount of water used, the process of hide preservation, the hide processing capacity and the in-plant measures followed to reduce pollution. Various physico-chemical techniques have been studied for their applicability to the treatment of tannery wastewater. Among these are coagulation, membrane processes, biological oxidation, membrane bioreactors, ozonation, Fenton, UV oxidation, ion exchange and activated carbon adsorption [4-7]. Coagulation process widely used as coagulants inorganic aluminium and ferric salts is by far the most widely used process to 1 Gebze Technical University, Department of Environmental Engineering, 41400 Gebze, Turkey 2 Kyrgyz-Turkish Manas University, Department of Environmental Engineering, Bishkek, Kyrgyzstan