Compacted Silage Fermentation on Whole Sweet Sorghum Plant for Distributed Bioethanol Production

The development of the bioethanol industry is facinga bottleneckdue to challenges in the collection and storage of biomass. In thisstudy, we explored the use of compacted silage fermentation to preservewhole pulverized sweet sorghum. To sterilize native and contaminantbacteria, we employed sulfur dioxide and inoculated SO2-tolerant Saccharomyces cerevisiae TSH4 for long-term preservation in an ethanol atmosphere. Baggedsilage experiments present the most effective preservation dosage,which was 2000 ppm SO2 concentration and 2% TSH4 yeastinoculation. Based on these conditions, we found that compacted silagewith different compaction densities enabled all fermentations to becompleted within 60 days. The highest ethanol concentration is achievedat a compaction density of 600, at which ethanol conversion rate reachesto 93.4%. Higher compaction densities produce more leachate, whichresults in ethanol loss up to 9.7%. During the 240 days of long-termstorage, there was no significant change in ethanol content despitean increase in acetic acid concentration. Additionally, distilledvinasse was found to be comparable to whole silage maize in termsof nutrients, thus proving the feasibility of constructing distributedbiofuel plants. Compactedsilage fermentation on whole sweet sorghum plantyielding both green ethanol and high-quality feed is promising fordistributed biofuel industrialization.