Evaluating the electrochemical and photoelectrochemical production of hydroxyl radical during electrocoagulation process

Abstract

In this study, we evaluate for the first time the effect of ionic composition on the anodic production of hydroxyl radical (OHa) during electrocoagulation (EC) process in batch using carbon steel electrodes. Likewise, hydroxyl radical production from active chlorine (OHph) electrogenerated in EC photoassisted with UVA (λ = 365 nm) and UVC light (λ = 254 nm) was evaluated using car wash wastewater. Both, OHa and OHph, were analyzed by UV–Vis spectroscopy and fluorescence using coumarin as the probe. Under optimal conditions (j = 8 mA cm−2, 25 °C, 15 min, 6 rpm), turbidity, suspended solids and color were removed by 98.3%, 98.7% and 93.1%, respectively. However, total organic carbon (TOC) abatement only attained 27%. This can be related to the fact that OHa and OHph were not identified during EC, with or without UV irradiation. Hence, the organic matter is mainly removed by coagulation with Fe(OH)n species. Comparative treatment of the same wastewater by electrochemical oxidation (EO) with a Ti|IrO2-Ta2O5 anode in the presence of electrogenerated active chlorine and UVC light demonstrated the generation of OHph, thus encouraging the potential coupling of EC with EO.