Biomethane Potential and Physicochemical Characterization of Vinasse: A Case-Study for the Waste Stream from Cassava-Based Ethanol Distillery

Abstract

Vinasse is a highly polluting by-product waste from bioethanol production processes. In this work, the biochemical methane potential (BMP), biodegradability index (BI), competitiveness index (CI) and physicochemical properties of cassava vinasse (CV) obtained from an ethanol distillery were studied to gain a better understanding of its characteristics and suggest alternative treatment routes and usage. At 28 o C, the CV used had a moisture content, specific gravity, refractive index and Brix value of 93%, 1.03, 1.34 and 5.88% sucrose, respectively. It exhibited relatively high Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD) of 62000-736500 and 21620-25000 mg/L, respectively. These, coupled with its acidic pH of 4.2–4.8 and cyanuric acid content of 386–450 mg/L, emphasized its potential as a pollutant both on land and water. The high volatile solids content of 71580-72250 mg/L and BOD-to-COD ratio of 0.3:1–0.4:1 both point to the presence of biodegradable organic matter. The CV contained macro and micro-nutrients in addition to salts of phosphates, nitrates and sulphates. At standard temperature and pressure, a BMP of 247.10 NmL/gVS points to the potential of the CV as a bioenergy resource. Also, while a BI of 0.82 indicated that 82% of organic matter in CV is degradable, a CI above 10 means no competition between the methanogens and the sulphate-reducing bacteria (SRB) if the CV is subjected to anaerobic digestion (AD). Based on these results, the CV could be treated via AD with simultaneous biogas production and, to some extent, used as a nutrient source for microbial-driven bioprocesses.