The role of saline-related species in the electrochemical treatment of produced water using Ti/IrO2-Ta2O5 anode

Large volumes of produced water (PW) are daily generated at oil and gas exploration plants, and it has to be efficiently treated before final disposal, avoiding the sending of recalcitrant organic and inorganic constituents to the ecosystem. Anodic oxidation (AO) was employed in the treatment of a PW using a Ti/IrO2-Ta2O5 dimensionally stable anode (DSA). The role of the high concentration of chloride (13 g L-1) and sulfate (0.8 g L-1) in the effluent was investigated regarding the quantification of oxidizing species, chemical oxygen demand (COD) removal, different applied current densities (j), total current efficiency (TCE), and a partial costs analysis. The better efficiency, in terms of organic removal (79% of COD elimination), was achieved by applying 30 mA cm−2 during 240 min of electrolysis, at room temperature, without pH adjustment before or after the treatment. Under these conditions, lower concentrations of undesirable chlorinated species were produced, as well as lower energy requirements were also achieved regarding those achieved at 60 and 90 mA cm−2, and consequently, reduced costs were estimated. It seems that no significant influence on the oxidation of the organic matter was observed due to the higher dissolved sulfate concentration in the effluent. Conversely, the high concentration of chloride in the effluent plays an important role to favor the electrochemical production of oxidant species which act in the bulk of the solution to remove the organic matter as well as the chloride ions help in the maintenance of the conductivity.