Electrochemical treatment of the effluent of a fine chemical manufacturing plant

Abstract

In this work, the electrochemical oxidation of an actual industrial wastewater with conductive-diamond anodes has been studied. The wastewater is the effluent of a fine chemicals plant. This effluent consists of an aqueous solution of solvents (ketones and alcohols) with a high concentration of aromatic compounds coming from the raw materials, intermediates and products of the different processes of the plant and its COD is around 6000 mg dm −3. The electrolyses were carried out in a discontinuous operation mode under galvanostatic conditions, using a bench-scale plant equipped with a single compartment electrochemical flow cell. The conductive-diamond electrochemical oxidation (CDEO) allowed achieving the complete mineralization of the waste with high current efficiencies. These efficiencies seem to strongly depend on the concentration, pH and temperature but not on the current density (in the range studied). This confirms that besides the hydroxyl radicals mediated oxidation, CDEO combines other important oxidation processes such as the direct electrooxidation on the diamond surface and the oxidation mediated by other electrochemically formed compounds generated on this electrode. Other two advanced oxidation processes (ozonation and Fenton oxidation) have been also studied in this work for comparison purposes. Both technologies were able to treat the wastes, but they obtained very different results in terms of efficiency and mineralization. The efficiency of ozonation and electrochemical oxidation were very similar (especially during the first stages), although the energy consumption required by the electrochemical process to remove at fixed percentage of COD or TOC was significantly smaller than that of ozonation. The possible accumulation of carboxylic acid as final products excludes the use of Fenton oxidation as a sole treatment technology.