Electrochemical degradation of polycyclic aromatic hydrocarbons in creosote solution using ruthenium oxide on titanium expanded mesh anode

In this study, expanded titanium (Ti) covered with ruthenium oxide (RuO2) electrode was used to anodically oxidize polycyclic aromatic hydrocarbons (PAH) in creosote solution. Synthetic creosote-oily solution (COS) was prepared with distilled water and a commercial creosote solution in the presence of an amphoteric surfactant; Cocamidopropylhydroxysultaine (CAS). Electrolysis was carried out using a parallelepipedic electrolytic 1.5-L cell containing five anodes (Ti/RuO2) and five cathodes (stainless steel, 316L) alternated in the electrode pack. The effects of initial pH, temperature, retention time, supporting electrolyte, current density and initial PAH concentration on the process performance were examined. Experimental results revealed that a current density of 9.23 mA cm-2 was beneficial for PAH oxidation. The sum of PAH concentrations for 16 PAHs could be optimally diminished up to 80-82% while imposing a residence time in the electrolysis cell of 90 min. There was not a significant effect of the electrolyte (Na2SO4) concentration on oxidation efficiency in the investigated range of 500-4000 mg/L. However, an addition of 500 mg Na2SO4 L-1 was required to reduce the energy consumption and the treatment cost. Besides, there was no effect of initial PAH concentration on oxidation efficiency in the investigated range of 270-540 mg PAH L-1. Alkaline media was not favourable for PAH oxidation, whereas high performance of PAH degradation could be recorded without initial pH adjustment (original pH around 6.0). Likewise, under optimal conditions, 84% of petroleum hydrocarbon (C10-C50) was removed, whereas removal yields of 69% and 62% have been measured for O and G and COD, respectively. Microtox and Daphnia biotests showed that electrochemical oxidation using Ti/RuO2 could be efficiently used to reduce more than 90% of the COS toxicity.