Effect of the process conditions on the anaerobic fermentation of glucose for the production of chemicals

In the context of biorefinery for the production of chemicals, this study optimised the processes to enhance the anaerobic production of ethanol and short chain organic acids from glucose. The optimised variables included (with a total of 49 runs) residence time (2-100 h), temperature (25-35 OC), type of inoculum (soil or anaerobic digester), presence or absence of pre-acclimation of the inoculum, glucose concentration (5-50 g/L), continuous or batch mode and composition of the mineral media (mineral solution with or without trace elements, with deionised or tap water). In continuous experiments the residence time was the most important parameter that affected glucose conversion (over 80 % glucose conversion for residence time longer than 30 h) and product yields (ethanol was the main product in the range of residence times 20-50 h, with yields in the range 0.30-0.40 g/g glucose removed). Temperature, type of inoculum and pre-acclimation had little effect on glucose conversion and products yield. The addition of trace elements had an important beneficial effect on the removal of glucose when it was fed at the highest concentration (50 g/L) in both continuous and batch experiments. In batch runs acetate was generally the main fermentation product rather than ethanol and ethanol conversion into acetate was favoured by nitrogen sparging, probably due to the reduced hydrogen partial pressure.