Electrocoagulation Treatment for Reverse Electrodialysis Wastewater from Petroleum Refinery

The present study investigated an evaluation efficiency of electrocoagulation (EC) for the pretreatment of a saline concentrated effluent from the reverse electrodialysis (RED-C) stage from an oil refinery, aiming at water reuse in the industrial process. In this approach, an electrocoagulation system with 1 L capacity was set up for batch treatment using aluminum electrodes. Initially, experiments with a semi-synthetic RED-C effluent were assessed for contaminants removal using fixed current density of 8.30 mA/cm2 and 1 cm distance between electrodes. The influence of initial pH (5 and 7), controlled temperature (20, 30 and 40°C) and operation time (60 and 120 min) on removal efficiency was investigated and solid residue were measured. The results showed that the optimum conditions were at pH 7 and 20-30°C with removal rates around 70%, 57%, 10% and 44% for Ca, Sr, Na and COD, respectively. Thereafter, experiments were conducted with a real RED-C using the best condition founded in preliminary tests, this time applying a current density of 5 and 10 mA/cm2 and 0.5 cm distance at room temperature (approximately 23°C). Regarding the tests with real RED-C, for both current densities the removals were greater due to decrease in distance between electrodes and larger temperature range that improved electrocoagulation. In general, the use of current density of 10 mA/cm2 and reduction of inter-electrode distance increased EC efficiency which exhibited removal rates of 88%, 77%, 26% and 24% for Ca, Sr, Na and COD, respectively. Although, it was observed a decrease in COD removal from real RED-C due to the addition of inorganic ions in the semisynthetic effluent that precipitated as salts, removing more organic as a coadjuvant compound. The solid slugde production for this same condition were 5.65 g/L.