Electrochemical degradation of Azo-dye Acid Violet 7 using BDD anode: effect of flow reactor configuration on cell hydrodynamics and dye removal efficiency

Abstract

Abstract: The electrochemical oxidation of synthetic textile effluent containing Azo-dye Acid Violet 7 (200 mg L−1) was investigated using planar disk electrodes placed in a one inlet–outlet (I–O) cylindrical reaction chamber. Two different I–O configurations were studied, one parallel and the other perpendicular to the electrodes. Both reactors were equipped with boron-doped diamond (BDD) anodes and titanium cathodes. The effect of cell design on the hydrodynamic characteristics and efficiency of the reactors in terms of colour and chemical oxygen demand (COD) removal was studied. Mass transfer coefficient (Km) values of 1.86 × 10−5 m s−1 and 2.56 × 10−5 m s−1 were obtained for the parallel and perpendicular I–O flow reactors, respectively, using the limiting current technique. The degradation results indicated that the colour elimination was quite efficient regardless of the type of reactor used and that complete colour removal could be reached in less than 80 min at applied current density of 30 mA cm−2 and above. However, higher COD removal efficiency was always achieved in the parallel I–O flow cell compared to perpendicular I–O flow reactor at all of the current densities studied, which can be attributed to the possibility of some stagnation in the lateral regions of the electrodes. These favour a longer contact time between the pollutants and the anode, also favouring its removal. Besides, similar electric energy consumption per g COD removal was observed during the treatment with either reactors; thus demonstrating the suitability of the parallel I–O flow cell for the efficient and economic treatment of textile effluent. Graphical abstract: [Figure not available: see fulltext.].