Reduction of Chemical Oxygen Demand (COD) in wastewater by electrocoagulation using aluminum-aluminum, iron-iron, aluminum-iron electrode pair systems and three pair multi electrode system (iron-aluminum-titanium/iron-iron-iron)

Electrocoagulation (EC) has been performed with Al-Al, Fe-Fe, Al-Fe electrode pair systems and 3-pair multi-electrode system (Al-Fe-Ti as anodes and Fe-Fe-Fe as cathodes), for the reduction of chemical oxygen demand (COD) in water. The COD reduction of organic acids in water samples (in-situ) and real water samples (Rio Grande) has been performed. As model organic acids, oxalic and tartaric acids have been used for most part of the study. The estimation of COD consists of two steps, the oxidation step and the determination step. The oxidation step was performed by dichromate reflux method (macro method) and dichromate reactor digestion method (micro method using Hach COD reactor). The determination step was performed titrimetrically for macro method and colorimetrically for micro method. The COD removal efficiencies (%) of the above mentioned electrode pairs have been compared. EC has been performed for various organic acids with a theoretical oxygen demand (ThOD) of 1000 mg/L at different voltages (9V, 12V) and at different residence times (1-180 min). It has been found that 3-pair multi-electrode system has higher COD removal efficiencies (%) at lower EC residence times than the other electrode pairs. The order of COD removal efficiencies (%) for oxalic and tartaric acids was found to be 3-pair multi-electrode system>Fe-Fe>Al-Fe>Al-Al. The solid by-product of oxalic acid EC with 3 pair multi electrode system was characterized by FT-IR and XRD.