Treatment of oil refinery wastewater by electrocoagulation–flocculation (Case Study: Shazand Oil Refinery of Arak)

In the present study, electrocoagulation–flocculation method was used to treat the wastewater from Shazand Oil Refinery in Arak, Iran. The wastewater contained 170,000 mg/L COD and 5.3 mg/L lead (Pb). In each step of the experiment, 2 L of the refinery wastewater was poured into a pilot made up of Plexiglas, and bipolar electrode arrangement was used. Optimum values of time, pH, and voltage parameters were determined for the aluminum electrodes. Results showed that time duration of 90 m, pH of 6, and voltage of 30 V was suitable for the removal of lead and COD. It should be noted that 48% of COD was removed and lead concentration decreased from 5.3 mg/L to lower than 0.05 mg/L. In addition, the COD removal efficiencies were 56 and 64% for eight and ten aluminum electrodes, respectively. The effect of iron electrodes on the removal of COD and lead was investigated under the same optimum conditions. Comparison between iron and aluminum electrodes indicated that iron electrodes demonstrate a better efficiency by removing 66.94% of COD from wastewater. It was also found that pH played a significant role in pollutants removal due to the formation of aluminum hydroxide gelatinous polymer.