Application of electrochemical processes for tannery wastewater treatment

Abstract

Tannery wastewater (real and synthetic) was treated by an electrochemical method with the principal aim of eliminating ammonium. Of various materials tested as electrodes graphite proved the best anode and steel the best cathode. Ammonium elimination was negatively influenced by the presence of organic pollutants and sulphides. The best results were obtained using electroxidation as a polishing step for the final effluents of a biological treatment plant. Ammonium elimination efficiency after 30 min of electrolysis at a current density of 0.44 A/dm2 was equal to 99%. For these conditions energy consumption for the elimination of 1 kg of NH4 + was 132 kwh. The process was less efficient when applied to raw and partially treated wastewater: to achieve the same result, electroxidation time had to be doubled and current density to be increased about threefold. COD removal was satisfactory when the initial values were relatively low (less than 300 mg/l) and only partial (about 70%) while treating wastewater with initial COD above 1200 mg/l. In conclusion the process can be used as a polishing step for the final effluent from a biological treatment plant for tannery wastewater. In some extreme situations it can also replace biological nitrification.