Study of a coupled adsorption/electro-oxidation process as a tertiary treatment for tequila industry wastewater

Vinasse wastewater from tequila industry that has been conventionally treated is usually characterized by a chemical oxygen demand (COD) above 150 mg L^-1, which is the maximum content permitted for discharge by Mexican Regulation. In order to increase the wastewater quality, different processes were applied, and from the experimental results, the advantages and limitations were analyzed. In this way, although Fenton experiments showed acceptable COD removal efficiencies (79-90%), operation as well as cost limit its adoption as a viable technology. Therefore, additional experiments explored electro-Fenton (EF) as well as adsorption coupled to EF in a tubular reactor. The corresponding data revealed that there was no additional increase in COD removal performance probably due to the low oxygen solubility in the electrolytic solution and the high pH that prevents the existence of Fe²⁺ ions necessary for the Fenton mixture. In view of these results, when an activated carbon (AC) filter was coupled to polarization at current densities between 0.5 and 2 mA cm^-2, removal efficiencies from 71 to 81%, corresponding to final COD of 78 to 33 mg L^-1, were achieved. Also, the adsorbent surface was continuously regenerated, promoting a more efficient adsorption and a longer service life for the AC filter. In this case, by using a current density of 0.5 mA cm^-2, COD was reduced to sufficiently small values for discharge into natural water bodies, maintaining low energy consumption and therefore acceptable operation costs.