3-01: Development of Tumbling Pretreatment Reactor and Hydrolyser System for Producing Sterile Hydrolysate

One of the biggest challenges to effective microbial fermentation of cellulosic biomass is the sterility of the hydrolysate. To avoid any microbial contamination during fermentation, either antibiotics are added to hydrolysate or pasteurization methods are followed. However, these methods increase the cost of biofuels production.  Also, adding antibiotics can impact the environment and will increase the population of antibiotic resistant microbes over time. To overcome this problem, we have developed a 5 gallon high pressure tumbling reactor for AFEX^TM pretreatment and a low pressure 50 gallon tumbling hydrolyser with the necessary controllers to perform enzymatic hydrolysis (> 18% solid loadings or higher) under sterile conditions. About 6 batches (1 kg from each batch) of corn stover was pretreated and transferred to a sterile tumbling vessel without exposing the biomass to air.  Residual ammonia is stripped from the biomass by passing steam through the reactor.  After most of the ammonia is stripped, commercial enzymes and sterile water are added to the pretreated biomass and hydrolysis is carried out at 50 ^oC for 3 days. The liquid hydrolysate was heated at 100 ^oC (for 10 minutes) to deactivate the enzymes and then transferred to sterile bottles while passing through a sintered stainless steel frit. Sterile, bottled hydrolysate was then stored (room temperature and 4^oC) for several months to evaluate both sterility and stability.  The mass balance for the entire operation including details describing how the biomass is loaded, pretreated, hydrolyzed, transferred to sterile bottles will be provided.