Petroleum refinery wastewater treatment through the successive process of electrocoagulation and electrooxidation

Water pollution and scarcity are problems of the current time due to the industrial and biological wastes that are thrown into the aquatic environment, especially the water produced from petroleum refineries, because it contains organic and inorganic pollutants. In this study, work was done to reduce the chemical oxygen demand (COD), which represents some major pollutants such as organic materials in real wastewater collected from the Najaf refinery in Iraq, using successive electrocoagulation (EC) and electrooxidation (EO) processes. Graphite and aluminum (Al) electrodes were used as the anode, and a stainless-steel electrode (SS) as the cathode. The Box-Behnken design (BBD) of experiments was used. Starting from COD (1250 ppm), the effect of current density, time, NaCl concentration, and pH on the removal efficiency was studied. The results indicate that the removal efficiency is directly proportional to the increase in current density, time, and NaCl conc, whereas it is inversely proportional to the increase in pH, as the optimal conditions for removal were at current density, time, NaCl concentration, and pH in this case. Conditions: About 97.5% COD removal was achieved. Through the results of the ANOVA analysis, it was found that current density and time have a high effect on removal, while NaCl concentration and pH have a lower effect on removal.