Electro-Fenton mineralization of diazo dye Black NT2 using a pre-pilot flow plant

Abstract

This project assessed the mineralization of Black NT2 (BNT2), a diazo dye frequently used in tanneries, using electrochemical technologies based on boron-doped diamond electrodes (BDD). The experimental trials included adding an Fe2+-catalyzed process known as the electro-Fenton (EF) reaction. The process was carried out in a recirculating pre-pilot plant that used a filter-press electrochemical reactor connected to a reservoir. The pre-pilot reactor was equipped with a BDD plate anode coupled with a BDD cathode to electrogenerate hydrogen peroxide (H2O2) in situ. The effects of experimental variables such as current density (j) and initial BNT2 concentration were tested. The best conditions to mineralize an initial BNT2 concentration equivalent to 250 mg L−1 of total organic carbon (TOC) in a 50 mM Na2SO4 solution using the EF process were 0.3 mM Fe2+, pH 3.0, j = 30 mA cm2, and Q = 12 L min−1. After 90 min of treatment, 100% TOC abatement was achieved. In all cases, TOC decreased following a pseudo-first-order kinetics. For the highest initial dye concentration, 100% TOC was achieved after 120 min, with 70% average current efficiency and 0.01088 KWh (g TOC)−1 energy consumption at the end of the process. For experiments without complete mineralization, the evolution of some nontoxic, short-chain carboxylic acids—such as oxalic, maleic, succinic, acetic, and formic—were quantified using high performance liquid chromatography (HPLC) analysis. These findings suggest that the EF reaction is an interesting, feasible alternative for enhanced dye degradation in tannery water treatment processes.