Assessment of VHG (Very High Gravity) ethanol fermentation in continuous multistage with cell recovery, reactivation and recycling using a blend of juice and molasses from sugarcane as raw material

The very high gravity (VHG) process can improve the production through high ethanol titer up to 15% (v/v), nearly doubling the productivity [9.8kg/(m3·h)], reducing vinasse to 5.4 L/L and minimizing the energy demand. The concept of this new process of high productivity and efficiency is based on the yeast kinetic model aimed to preserve cell activity at high ethanol content under high recycling. The process design is for continuous mode in multistage reactors with decreasing fermentation temperature profile in each stage (34 to 28°C), standardization of mash in microbiological and physicochemical terms, feeding mash distributed between the first and second reactors, and intracellular detoxification through a second centrifugation followed by yeast treatment promoting membrane recovery and enzymatic restoration. The basic parameters were developed at bench scale in fed-batch with cell recycle. An oxidation-reduction potential sensor was successfully used to determine the micro-aeration requirement for final stage of sugar exhaustion, to promote a respiratory environment able to support high ethanol content, and as a tool to monitoring the reactivation stage. The optimized set of parameters obtained in bench scale were used for scaling-up the process to a continuous fermentation pilot unit set to operate uninterruptedly.