Eligio P. Rivero

Electrochemical oxidation of bio-refractory dye in a simulated textile industry effluent using DSA electrodes in a filter-press type FM01-LC reactor

This work presents a study on degradation of indigo carmine dye in a filter-press type FM01-LC reactor using Sb2O5-doped Ti/IrO2-SnO2 dimensionally stable anode (DSA) electrodes. Micro- and macroelectrolysis studies were carried out using solutions of 0.8 mM indigo carmine in 0.05 M NaCl, which resemble blue denim laundry industrial wastewater. Microelectrolysis results show the behaviour of DSA electrodes in comparison with the behaviour of boron-doped diamond (BDD) electrodes. In general, dye degradation reactions are carried out indirectly through active chlorine generated on DSA, whereas in the case of BDD electrodes more oxidizing species are formed, mainly OH radicals, on the electrode surface. The well-characterized geometry, flow pattern and mass transport of the FM01-LC reactor used in macroelectrolysis experiments allowed the evaluation of the effect of hydrodynamic conditions on the chlorine-mediated degradation rate. Four values of Reynolds number (Re) (93, 371, 464 and 557) at four current densities (50, 100, 150 and 200 A/m2) were tested. The results show that the degradation rate is independent of Re at low current density (50 A/m2) but becomes dependent on the Re at high current density (200 A/m2). This behaviour shows the central role of mass transport and the reactor parameters and design. The low energy consumption (2.02 and 9.04 kWh/m3 for complete discolouration and chemical oxygen demand elimination at 50 A/m2, respectively) and the low cost of DSA electrodes compared to BDD make DSA electrodes promising for practical application in treating industrial textile effluents. In the present study, chlorinated organic compounds were not detected.

Electrogeneration of Active Chlorine in a Filter-Press-Type Reactor Using a New Sb2O5 Doped Ti/RuO2-ZrO2 Electrode: Indirect Indigoid Dye Oxidation

Abstract This paper presents the study on active chlorine mediated electrochemical oxidation of model solutions that simulate textile effluents containing an indigoid dye (indigo carmine) and sodium chloride (0.05 M) using a new Sb2O5-doped Ti/RuO2-ZrO2 electrode. The study was carried out in a filter-press electrochemical reactor specially designed to minimize flow deviations and provide homogeneous mass transfer flux over the electrode surface. Firstly, the mass-transfer-limited chloride oxidation reaction was studied in the absence of dye in order to understand the active chlorine formation process. Changes in pH, chloride concentration and UV-visible absorption spectra during electrolysis reveal the formation of active chlorine (mainly hypochlorite) with current efficiencies for chloride oxidation of 0.558 and 0.503 at 10 and 20 mA cm−2, respectively. Secondly, chloride oxidation was investigated in the presence of indigo carmine dye (0.5 mM) where in-situ generated active chlorine was responsible for -C=C- bond breaking and dye degradation. The solution discoloration followed a pseudo-first order kinetics where kinetic coefficient was inversely proportional to dye concentration. The oxidation with active chlorine had an average efficiency of 0.7 and a very competitive energy consumption between 49.2 and 128.5 kW h (kg COD removed)−1 depending on current density and flow rate.

Parametric Mathematical Modelling of Cristal Violet Dye Electrochemical Oxidation Using a Flow Electrochemical Reactor with BDD and DSA Anodes in Sulfate Media

Abstract An important issue in electrochemical oxidations of pollutant compounds, like organic dyes, is identifying a suitable correlation between operational conditions and electrochemical process performance. In such sense, this work deals with the parametric modelling of direct electrochemical incineration of crystal violet (CV) dye in a FM01-LC flow electrochemical reactor with a plastic spacer configuration using boron doped diamond (BDD) and dimensionally stable (IrO2 and IrO2-SnO2-Sb2O5) anode plates. Mathematical model takes into account the fluid dynamics effects by the use of FM01-LC reactor considering mass transport rate of organic compound (R) from bulk solution to electrode surface, characterized by a dispersion coefficient and Pe number. The effect of strong oxidants produced in the electrode surface can be neglected since the characteristic time constant reaction of pollutants with such oxidants is lower than those describing the diffusion of organic compound to the electrode surface. Model parameters were estimated throughout a fitting method of the experimental data. The model proposed here predicted a 99.7 removal percentage of CV with boron doped diamond and IrO2-SnO2-Sb2O5 anodes obtained experimentally, meanwhile a 79 % removal with the IrO2 anode was reached at Re = 2204 during an electrolysis time of 7200 s for both cases. In the case of IrO2 anodes, complex interactions between hydroxyl-radical and electrode surface provokes an intermediate kinetic process, with an effectiveness factor of 0.59. When BDD and IrO2-SnO2-Sb2O5 anodes were used, the removal process mediated by hydroxyl-radicals absorbed in electrode surface was fully limited by mass transport.