Studies On Sugarcane Bagasse Degradation And Biohydrogen Production By Thermophilic Anaerobic Fermentation

Depletion of fossil fuels and environmental concern have attracted widespread attention,and thus the development of alternative energy sources has become a matter of urgency. Sug-arcane bagasse (SCB) is an abundant renewable resource that can be transformed into biofuel.Effective bioconversion of SCB is of great significance. C. thermocellum, an anaerobic ther-mophilic strain, can synthesize cellulosome which is capable of degrading cellulose effective-ly, and produce hydrogen, ethanol and organic acids. This study investigated the SCB degra-dation and hydrogen production by Clostridium thermocellum from several aspects:1) thecharacteristics of SCB biodegradation and hydrogen production in CBP using C. thermocel-lum;2) establishment of co-culture system and its applicationin SCB pretreatment and hy-drogen production;3) evaluation on the enhancement of non-ionic surfactants in SCB degra-dation induced by C. thermocellum.Cellulose and hemicellulose of SCB pretreated with NH4OH-H2O2are41.36±0.24%and18.10±0.16%, respectively. C. thermocellum can directly degrade Avicel, filter paper and SCBwith hydrogen, ethanol and organic acids as the main metabolic products. Due to recalcitranceof lignocellulose, both substrate utilization and hydrogen production of SCB are lower thanthose of Avicel and filter paper. The substrate utilization and hydrogen production of SCBreaches81%and89.77%of those in filter paper, indicating SCB as a feasible substrate forhydrogen production. Optimization of inoculum size, substrate concentration, particle sizeand yeast extracts concentration can improve hydrogen production, but on the whole,SCB-hydrogen production is not high in the monoculture of C. thermocellum.Suitable pretreatment method can modify the structure of SCB, leading to a commenda-ble performance in hydrogen production and SCB degradation. Compared to milling pre-treatment and NH4OH-H2O2pretreatment, sodium hydroxide pretreatment exhibits higher del-ignification (60.07%) and hemicellulose removal ratio (18%). The co-culture of cellu-lose-degrading bacterium, C. thermocellum, and the hemicellulose-degrading bacterium,Thermoanaerobacterium aotearoense, shows its synergistic advantages over theirmono-culture in hydrogen production. The hydrogen production by co-culture was35.79mmol/L, which increased by13.7%and25.05%compared to the mono-cultures of C. ther-mocellum and T. aotearoense, respectively. The optimized pretreatment conditions for SCBwere3%sodium hydroxide loading,25:1LSR and80oC for3h. Simultaneous inoculation ofthe strains, a thermophilic fermentation (55oC,150r/min) of168h, and4%pretreated SCB,the highest hydrogen production (50.05mmol/L) was reached. Biodegradation of SCB accompanied with accumulation of reducing sugar was remarka-bly improved with the addition of non-ionic surfactant in CBP system using C. thermocellum.Addition of0.25%Triton X-100resulted in an accumulation of3.65g/L reducing sugars anda substrate degradation of46.6%, which increased by approximately36-fold and1.2-fold, re-spectively, compared with control. Furthermore, the addition of Triton X-100has little nega-tive effect on hydrogen production in CBP using C. thermocellum. The result suggests thatTriton X-100is a most promising enhancer in improving the biodegradation of lignocellulose.