Electroremediation of Naphthalene in Aqueous Solution Using Alternating and Direct Currents

The key objectives of this study were to evaluate the use of an alternating current (AC) for the degradation of naphthalene in spiked aqueous solutions and to investigate the effect of current density on the degradation rates of naphthalene. Direct current (DC) was also used to compare the rates of degradation. Sodium chloride $\left(\mathrm{NaCl}\right)$ and anhydrous sodium sulfate $\left({\mathrm{Na}}_2{\mathrm{SO}}_4\right)$ were used as the supporting electrolytes. Degradation rates and byproducts formed were investigated when DC and AC were separately passed through naphthalene solutions. A square wave AC, having a frequency equal to $0.1\mathrm{Hz}$ was used. Naphthalene solutions having an initial concentration of about $20\mathrm{mg}∕\mathrm{L}$ $(\sim 0.15\mathrm{mM})$ were subjected to an AC peak current density and DC density of $6\mathrm{mA}∕{\mathrm{cm}}^2$ , using $\mathrm{NaCl}$ as the supporting electrolyte. An approximate 65% reduction in the concentration of naphthalene was observed after a period of 48 h when DC was applied. Degradation was almost 100% when the AC was applied during the 48-h period. The effect of current density on the electrochemical degradation rate of naphthalene in aqueous solution was also investigated at alternating and direct current densities of 1, 3, and $6\mathrm{mA}∕{\mathrm{cm}}^2$ using ${\mathrm{Na}}_2{\mathrm{SO}}_4$ as the supporting electrolyte. AC peak current densities of 1, 3, and $6\mathrm{mA}∕{\mathrm{cm}}^2$ resulted in overall conversions of 77, 87, and 95%, respectively, of naphthalene in solution. The corresponding values for DC application were 95% for all current densities while the initial degradation rates were greater at higher DC densities. Based on the degradation products formed, hydroxylation is believed to be the key mechanism for the degradation of naphthalene.