Continuous photocatalytic, electrocatalytic and photo-electrocatalytic degradation of a reactive textile dye for wastewater-treatment processes: Batch, microreactor and scaled-up operation

Reactive Red 106, a synthetic azo dye, was degraded by means of photocatalysis, electrocatalysis and photo-electrocatalysis with an immobilized titanium dioxide nanotube catalyst. The planned first part of the experiments was carried out inside a photo-electrocatalytic continuous-flow microreactor unit, which was used for the evaluation of the effective decomposition mechanisms, the assessment of the investigated degradation kinetics and the transport. The processes were described with a convection diffusion-reaction mathematical model. Full degradation was achieved under photo-electrocatalytic operation. The second half of the tests was executed inside a batch-vessel system, consisting of two separate compartments. In the anode device partition, an electrode, made of a nanometer-scaled TiO2 tube film, was placed, whereas a Ti foil was positioned in the cathode's electrical section. The separation of the electrolytes made it possible to analyze the conversion individually, monitoring the disintegration of the textile pigment compound in each structural component separately, and studying the changing environmental phenomena for either the polarized positive or negative function. Water-based produced chemicals were determined with ultra-high-performance liquid chromatography (UHPLC), coupled with ultraviolet-visible (UV-vis) or mass (MS) spectroscopy detectors. The solution was successfully discolored (100%) either under engineered microfluidic operation or inside a beaker's enclosed volume. However, the rate inside the latter was faster, while there were unlike intermediate species formed in either the anodic or cathodic electrochemical cell. The maximum conversion achieved on the anode side was 80% of the initial concentration of the dye, whereas 63% of the dye was degraded on the cathode side. Finally, a scaled-up input configuration was designed for treating larger feedstock capacities. (C) 2018 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.