Electrocoagulation treatment of sugarcane vinasse: Operating parameters and cost analysis by response surface methodology

The production of ethanol biofuel using sugarcane as substrate generates vinasse as the main wastewater from the fermentation-distillation process. The Brazilian legislation allows the use of vinasse for fertigation in limited volumes, and the remaining effluent must be treated prior to its reuse or discharge into the environment. The study aimed to evaluate the electrocoagulation (EC) technique as an alternative treatment process for raw sugarcane vinasse. The effects of the electrode gap (1-3 cm), applied electric charge (0-39000 C/L), current density (2.2-20 mA/cm(2)), and stirrer speed (0-680 rpm) were evaluated in a batch electrolytic reactor with aluminum electrodes. The evaluation results revealed that dissolved solids were removed and the pH increased during electrolysis in all experimental conditions, which suggested that EC was suitable for the pH neutralization of vinasse without the requirement of salt addition. An electrode gap of 1 cm and a current density of 2.2 mA/cm(2) resulted in the lowest electric energy consumption (11.0 kW h/m(3)) and the lowest increment in the electrolyte temperature (9.5 degrees C). High vinasse clarification was achieved under the optimal operating conditions of 1 cm electrode gap, 31,000 C/L applied electric charge, 6.1 mA/cm(2) current density, and 430 rpm stirrer speed, with 13.5 kW h/m(3) and 2.88 kg Al/m(3) of consumption. The treatment cost was calculated to be 6.95 US$/m(3), from which the electrode dissolution was determined to be 75%. The sludge settling velocity was 0.14 cm/min, which suggested poor sedimentability, possibly due to bubble gas adsorption on the surface of the formed flocs. Results of the proposed operational parameters indicate that EC can be used as a pre-treatment of vinasse, adapting the main sugarcane processing wastewater biotechnological use.