Electrocoagulation with Fe-SS Electrodes as a Fourth Stage of Tequila Vinasses Treatment for COD and Color Removal

Abstract

The tequila industry faces several environmental challenges due to its high yields of contaminants, especially tequila distillation stillage or tequila vinasses, with ten to twelve liters produced per liter of tequila. All treatments aim to shorten retention times to avoid the need for large equipment or new facilities and the saturation of residues within tequila distilleries. The complexity of tequila vinasses has led to treatments with several stages, whereby most of the organic matter content is reduced, but the treatment range results are insufficient. This study aimed to evaluate a fourth-stage tequila vinasse treatment using an electrocoagulation system that uses inexpensive electrodes (SS cathodes and iron anodes), has a low electrical consumption, and applies low voltages in order to meet safety, economic, and environmental criteria so as to comply with Mexican norm NOM-001-SEMARNAT-2021. Three sets of voltage–amperage controllable power source, a 4 mm cylindrical 304 stainless-steel cathode, and a 9 mm iron anode with 200 mL samples in 250 mL beakers were used; three replicas (R1, R2, and R3) underwent 2 h treatment at 1–6 volts to evaluate the voltage effect and 1–6 h of 5-volt treatment to assess the time effect. All samples were filtered with 8 μm and 0.25 μm meshes. Chemical oxygen demand, pH, electrical conductivity, turbidity, and color measurements (SAC for λ 436, 525, and 620 nm) were taken. The experiments determined the optimal voltage and time, considering a hydraulic retention time below 6 h. The results show that electrocoagulation of pretreated tequila vinasses effectively helps in the final removal of organic matter measured as COD, reaching values below 150 COD mg/L at 5–6 h with 5 V treatments and color reduction with 5 V, 1 h treatment. This leads to final polishing that complies with the Mexican wastewater discharge norm criteria.