Energy recovery from biomethanation of vinasse and its potential application in ozonation post-treatment for removal of biorecalcitrant organic compounds

Abstract

Vinasse is characterized by a high chemical oxygen demand (COD) and dark brown colour, which requires abatement before disposal to prevent the pollution of receiving streams. Anaerobic digestion (AD) usually applied for vinasse treatment can only reduce the COD with the colour remaining unabated. This study investigated the feasibility of combining AD and ozonation for vinasse treatment. The AD process alone achieved high COD removal of 95 %, at a best organic loading rate of 15 kgCOD/m3/d. However, the anaerobic effluent still had an intense dark brown colour caused by a considerable amount of residual biorecalcitrant COD of 4.5 g/L. The ozonation post-treatment of the anaerobic effluent removed 80 % of the colour with up to 92 % ozone transfer at optimal parameters of pH 4, substrate dilution factor of 2, and 90 mg/L/min ozone dosage. Kinetic analysis showed that for a constant feed flow combined system, the ratio of the anaerobic reactor unit to the ozonation reactor unit is recommended to be 20:1. Also, from energy analysis, application of the bioenergy produced from AD to supplement the total energy requirement of the combined system could lead to 50 % savings on energy, and a carbon dioxide emission reduction of 122 kg CO2/m3 of vinasse treated. The combined system is thus a promising technology for vinasse treatment and can contribute to combating greenhouse gas emissions.