Degradation of organics in real oil sands process water by electro-oxidation using graphite and dimensionally stable anodes

Abstract

The effectiveness of electro-oxidation (EO) using graphite anode and dimensional stable anode (DSA) for the degradation of organics in real oil sands process water (OSPW) was investigated and the performances of the two anodes were compared. EO by graphite anode was able to reduce the chemical oxygen demand (COD), acid extractable fractions (AEF), classical and oxidized naphthenic acids (NAs) and aromatics in OSPW even at current density as low as 0.5 mA/cm2. The removal of organics by DSA started when the current density reached 2 mA/cm2. The removal of classical NAs by both anodes increased with the increase in the applied current density and was always higher than the removal of AEF. Graphite anode showed higher NA and AEF removals than DSA at current densities below 20 mA/cm2. The reactivity of NAs in OSPW toward oxidation on both anodes increased with the increase in the cyclicity and carbon number. EO by DSA generated low-carbon number NAs as byproducts of the oxidation of high-carbon NAs. Graphite anode maintained higher current efficiency at all applied current densities. Both anodes were able to remove the aromatic compounds, with DSA being more selective toward aromatics especially those with multiple aromatic rings, which were removed completely at 20 mA/cm2 after 90 min. The results indicated that graphite anode is more effective for OSPW treatment at lower current densities, while DSA shows better performance at higher current densities.