A pilot study of BTEX removal from highly saline water by an advanced electrochemical process

Results are reported of a systematic study on the performance of an advanced oxidation treatment that couples anodic oxidation (AO) and in situ generation of strong oxidants (Cl₂, S₂O₈²⁻) in the electrolytic cell, for removing benzene, toluene, ethyl benzene, and xylenes (i.e. BTEX) from high salinity waters. A batch-mode pilot electrochemical unit equipped with a boron-doped diamond (BDD) anode and a carbon-PTFE electrode as cathode was employed. Contrary to most published work, special focus was placed on the treatment efficiency, individually for benzene, toluene, ethyl benzene and xylene compounds (m&p-xylene, o-xylene) in a real water matrix (seawater), aiming to evaluate the oxidation mechanisms and to optimize the experimental conditions (such as current density, feed water flow rate, concentration of BTEX) for electrochemical decomposition, using an experimental design based on Face Centered Composite design coupled with Response Surface Methodology. The response surface plots verify the results of the statistical analysis, since electric current is the most detrimental factor to benzene removal, whereas feed flow rate and BTEX initial concentration are the two most significant factors, affecting negatively the removal efficiency of the other four hydrocarbons. Under the optimum conditions (current density ∼74 mA/cm², feed recirculation flow rate 0.2 m³/h and BTEX initial concentration 2.5 mg/L) xylenes and ethyl benzene were completely (100%) removed within 30 min of electrolysis, more than 90 % of toluene was removed within 60 min, while 70–80 % of benzene was eliminated within 120 min. The study demonstrated the efficiency of electrochemical process for treating recalcitrant organics in concentrated brines.