Electrochemical treatment of a synthetic wastewater containing a sulphonated azo dye. Determination of naphthalenesulphonic compunds produced as main by-products

The electrochemical treatment of wastewaters from textile industry is a promising technique for substances which are resistant to biodegradation. This paper deals with the electrochemical decolourisation/degradation of synthetic solutions containing a reactive dye, C.I. Reactive Orange 4. Oxidation, reduction and oxido-reduction processes were evaluated using Ti/SnO 2-Sb-Pt and stainless steel electrodes as anode and cathode, respectively. Electrolyses were performed at galvanostatic conditions in a filter press reactor. Decolourisation and degradation were followed by means of total organic carbon (TOC), chemical oxygen demand (COD) measurements and high performance liquid chromatography (HPLC). A higher mineralisation rate for oxidation was found whilst oxido-reduction process gave more oxidised species. The kinetics of decolourisation was of pseudo-first order in all cases. The reduction process was the slowest process to decolourise. Gas chromatography-mass spectrometry (GC-MS) was employed to investigate the main intermediate compounds, confirming the presence of 2-amino-1, 5-naphthalenedisulphonic acid (2A15NDS) in solution. When this compound was generated, it was gradually degraded during the oxidation and oxido-reduction processes indicating the feasibility and durability of Ti/SnO 2-Sb-Pt electrodes. However, during the electrochemical reduction process, this compound was continuously generated but it was not degraded. © 2011 Elsevier B.V.
The authors would like to acknowledge the Spanish Ministry of Science and Innovation (MICINN) and European Union (FEDER funds) for the financial support (CTM2007-66570-C02-02 and CTM2010-18842-C02-02). A. I. del Rio thanks the Spanish Ministry of Science and Innovation (MICINN) for her F.P.I. grant awarding. J. Molina is grateful to the Conselleria d'Educacio (Generalitat Valenciana) for his FPI grant awarding.