Effective degradation of cyclohexanecarboxylic acid by visible LED driven photo-Fenton

Abstract

This work explores the feasibility of visible LEDs (λ: 400–800 nm) used in photo-Fenton for the degradation of a 50 mg/L cyclohexanecarboxylic acid (CHA) as model naphthenic acid present in process wastewater from the oil sands industry. The influence of initial pH, catalyst concentration and iron oxidation state, H2O2 dose and radiant flux were studied. In all trials, an initial lag phase in both the H2O2 decomposition and TOC evolution was observed. This seems to be related to the generation of a complex between CHA, hydrogen peroxide and iron (CHA-H2O2-Fe). This iron scavenging decreases the H2O2 decomposition rate, leading to a lagged mineralization kinetics. Nonetheless, process intensification using visible radiation (λmax: 460 nm) favors the CHA-H2O2-Fe photoactivation and breakdown when using an H2O2 concentration higher than 33% of the stoichiometric dose for complete CHA mineralization. Under the optimum conditions pH0 3, Φ: 280 W/m2, Fe2+:20 mg/L and H2O2: 144 mg/L, which corresponds to 60% of the stoichiometric amount, 75% of TOC removal was achieved.