NOVELTY - Anaerobic fermentation of a feedstock to produce a product comprises: (a) fermenting the feedstock in a fermenter with a heat tolerant microorganism capable of producing the product under conditions suitable for the bioconversion of the feedstock by the microorganism and forming a fermented liquid; (b) removing at least a portion of the fermented liquid; (c) degassing the fermented liquid to at least partially remove byproduct gasses from the fermented liquid; and (d) vaporizing at least a portion of the product contained in the fermentation liquid in the vacuum evaporation apparatus.    USE - The method is useful for anaerobic fermentation of feedstock, preferably glycerol to produce ethanol (claimed), and for improving the efficiency and productivity of biofermentation process.    ADVANTAGE - The method is highly efficient and cost effective. The method shows recycling and reuse of expensive reagents.    DETAILED DESCRIPTION - Anaerobic fermentation of a feedstock to produce a product comprises: (a) fermenting the feedstock in a fermenter with a heat tolerant microorganism capable of producing the product from the feedstock under conditions suitable for the bioconversion of the feedstock by the microorganism and forming a fermented liquid; (b) removing at least a portion of the fermented liquid comprising the product from the fermenter and conducting the fermentation liquid to a vacuum assisted purification zone, where the vacuum assisted purification zone includes at least one degassing apparatus and at least one vacuum evaporation apparatus; (c) degassing the fermented liquid to at least partially remove byproduct gasses from the fermented liquid in the degassing apparatus to the fermentation liquid entering the vacuum evaporation apparatus; and (d) vaporizing at least a portion of the product contained in the fermentation liquid in the vacuum evaporation apparatus operated under vacuum and at elevated temperatures, where the elevated temperatures are tolerated by the heat tolerant microorganisms present in the fermentation broth, and the vapor produced in the vacuum evaporator is product-enriched vapor. An INDEPENDENT CLAIM is included for anaerobic fermentation of glycerol to produce ethanol comprising (a1) fermenting glycerol in a fermenter with a heat tolerant microorganism capable of producing ethanol from glycerol under conditions suitable for the bioconversion of glycerol to ethanol and forming a fermented liquid, (b1) removing at least a portion of the fermented liquid comprising ethanol from the fermenter and conducting the fermentation liquid to a vacuum assisted purification zone, where the vacuum assisted purification zone includes at least one degassing apparatus and at least one vacuum evaporation apparatus, (c1) degassing the fermented liquid in the degassing apparatus to the fermentation liquid entering the vacuum evaporation apparatus, where by-product gasses are at least partially removed from the fermentation liquid, and (d1) vaporizing at least a portion of the ethanol contained in the fermentation liquid in the vacuum evaporation apparatus operated under vacuum and at elevated temperatures, where the elevated temperatures are tolerated by the heat tolerant microorganisms present in the fermentation broth, and the vapor produced in the vacuum evaporator is ethanol-enriched vapor.