Alcohol distillation is mainly employed for the purification of alcohol from aqueous blends. Although, there are several applications of the process; three main areas of use are: distillation of alcohol following molasses fermentation; distillation of wine; and distillation for the industrial production of alcohol from agricultural raw materials. The main pollutants of vinasse are organic matter, suspended solids, and nitrogen. However, vinasse also contains in high concentrations of potassium, calcium, chloride and sulphate. The organic matter content is variable depending on the feed material and the distillation application.
Although, a great part of the organic content of vinasse is biodegradable, there are recalcitrant organic compounds such as polyaromatic compounds, polyphenols mainly lignins, tannins, and humic acids. Thermal degradation of reducing sugars and amino compounds is mainly the source of the melanoidins giving the dark colour of vinasse. These compounds exert negative effects on the microorganisms and inhibit biological treatment processes.
The wastewater, although a great part of it biodegradable, contains an inert fraction which poses several problems in both aerobic and anaerobic treatment. A pretreatment is necessary before biological treatment.
Chemical oxidation seems to be the most suitable alternative for the modification of the characteristics of organic matter. The ozonation has been the most widely tested process for vinasse pretreatment to enhance the biodegradability. Fenton’s oxidation and other advanced oxidation processes have also proved their worth in achieving the desired results.