Organic and inorganic matter removal from tannery wastewater using the electrocoagulation process

In this study, the effect of current density and stirring speed on treatment of tannery wastewaters by the electrocoagulation process using aluminum electrodes was investigated. In the studies, it was determined that the stirring speed did not have much effect on the removal efficiency, but increased the reaction rate. While the second degree reaction rate constant is k2 = 0.0444 L g−1 min−1 at 100 rpm stirring speed, this value increases to k2 = 0.1261 L g−1 min−1 when the stirring speed is increased to 400 rpm. Although the COD removal efficiencies at 0.6 and 1.2 mA cm−2 current densities were almost the same, the COD removal efficiencies decreased at 1.8 and 2.4 mA cm−2 current densities. However, while the treatment time was approximately 50 min at 0.6 mA cm−2 current density, this time decreased to 25 min at 1.2 mA cm−2 current density. At the end of 60 min of retention time under the determined optimum conditions, 84% COD, 98% turbidity, 97% oil-grease, 98% chromium, 68% total nitrogen, 100% phosphate and 79% sulfate removal efficiencies were obtained. The energy consumption of the system was calculated as 2.37 kWh m−3. In the cost analysis studies, it was concluded that the increase in current intensity did not have much effect on the treatment efficiency, but increased the treatment cost. While the electricity and electrode cost of the system at 0.6 A current intensity was 0.239 $ m−3, this cost was obtained as 0.8817 $ m−3 for 2.4 A.