Importance of Hydrodynamic Conditions on the Electrochemical Incineration of Cresols, Indigo Textile Dye and Vinasses Present in Industrial Wastewater Using a Filter-press- Type Fm01-lc Reactor with Bdd Electrodes

This paper deals with the role of hydrodynamic conditions using a filter-press-type FM01-LC electrochemical reactor equipped with 2D (plate) and 3D (mesh) boron doped diamond (BDD) electrodes for the incineration of recalcitrant organic matter. A strategy for the electrochemical incineration of different organics, such as p-cresol, o-cresol, indigo textile dye and vinasses, is shown. The current density limits, where the electrochemical incineration occurred via hydroxyl radicals (OH) formed by water oxidation at the BDD-H2O-media interface, were determined by microelectrolysis tests through Tafel analysis. Based on these data, the electrochemical incineration at different Reynolds numbers and current densities in the filter-press-type FM01-LC electrochemical cell, for each pollutant, was characterized. The performance of the FM01-LC cell, during the degradation of organic compounds, was discussed in terms of current efficiency and energy consumption, and these were compared to those reported in other cells. The convenience of using the FM01-LC electrolyzer is discussed. *Corresponding author Email: [email protected] INTRODUCTION Recently, synthetic electrodes of boron-doped diamonds (BDD), manufactured by chemical vapor deposition (CVD), have been used for degradation of recalcitrant organic compounds. This degradation occurs via hydroxyl radicals (•OH) formed by water oxidation at the BDD-H2O-pollutant interface. These hydroxyl radicals have unique properties that promote the oxidation of several organic compounds to CO2 [1-6]. The previous studies on incineration in reactors employing BDD electrodes have been carried out in flow-by cells, whose working (BDD) and auxiliary electrodes have circular geometry [1,5-10], and in an impinging jet cell [11,12]. Panizza et al. [9] and Polcaro et al. [11] included the study of the hydrodynamic conditions in incineration, finding that incineration is increased as a function of flow rate. These authors concluded that total incineration of organics is due to the formation of hydroxyl radicals from the water discharge and the oxidation was mass-transport controlled. On the other hand, the electrochemical incineration of organics has been performed in batch cells with parallel plate electrodes, where convection is supplied by magnetic stirrer [4]. Recent studies by our research group [13,14], refer to electrochemical incineration of organic compounds in a FM01-LC reactor equipped with 2D BDD electrodes. This reactor is a filter-press in which hydrodynamic flow enhances hydroxyl-organic contact at the BDD surface, a phenomenon that increases organic mineralization efficiency. However, even though it is known that 3D electrodes improves spacetime yield, this electrode configuration has not been used for electrochemical incineration. The objective of this paper is to define the role of hydrodynamic conditions using a filter-press-type FM01-LC electrochemical reactor using 2D (plate) and 3D (mesh) BDD electrodes for the incineration of some model organic pollutants, such as p-cresol, ocresol, indigo textile dye and vinasses in aqueous me222 J. Environ. Eng. Manage., 18(3), 221-230 (2008) Table 1. BDD electrode dimensions, experimental details of the FM01-LC electrolyzer Electrode length, L 16 cm Electrode height, B 4 cm Electrode spacing, S 0.55 cm Electrode Area, 2D BDD, A2D BDD 64 cm 2 Electrode Area, 3D BDD (3 mesh), Amesh-BDD 444 cm 2 Overall voidage, ε (using 2D BDD and turbulence promoter) 0.83 (using mesh-BDD (3 mesh)) 0.62 Hydraulic (equivalent) diameter, de = 2BS/(B+S) 0.97 cm Particle size, dp (mesh-BDD) 0.2 cm Turbulence promoter Plastic mesh type D CD and LD = 11 mm. Mean fluid velocity, u 0.4 to 400 cm s Kinematics viscosity, υ 0.01 cm s