Coproduction Of Hydrogen And Volatile Fatty Acid By Thermophilic Fermentation Of Sweet Sorghum Stalk

Hydrogen is one of the most important energy sources in future considering the energy security,increasing the demand of renewable energy and its environmental and unique high energy properties.Renewable resources,lignocellulosic biomass for fuel and chemicals production are environment-friendly due to the less emission of carbon dioxide to the atmosphere and to replace the fossil source to meet the demand.Among the biological way,this thesis focuses anaerobic fermentation for hydrogen and volatile fatty acid(VFA)production from high soluble sugar containing lignocelluloses,sweet sorghum stalk.The structural carbohydrate(cellulose and hemicellulose)is still under-utilized in the process of microbial fermentation and need to further studies to improve the production performance and being more compatible.In order to achieve the aims,potential of hydrogen and VFA coproduction was investigated from sweet sorghum stalk using Clostridium thermocellum and Clostridium thermosaccharolyticum as production microbes.The optimum conditions for the highest yield of products found as 1:1 inoculation ratio of both strains,24 h of time gap between C.thermosaccharolyticum followed by C.thermocellum after the first inoculation and 5 g/L of substrate concentration.The maximum hydrogen yield was 5.1 mmol/g-substrate and co-products were acetic acid(1.27 g/L)and butyric acid(1.05 g/L)at optimum conditions.Experimental data showed that co-culture increased 55%hydrogen,9%acetic acid and 10%of butyric acid production from single-culture.Improved hydrogen and VFA coproduction was studied from two step fermentation withdilute acid treatments of the residual slurry after 1st step using C.thermosaccharolyticum strain in both step.The optimum severity conditions for the highest yield of products found from the treatment acid concentration of 1.5%(w/v)at 120 ? for 10 g/L of substrate concentration.Experimental data showed that two-steps fermentation increased 76%hydrogen,84%acetic acid and 113%of butyric acid production from single step.Maximum hydrogen yield was 5.77 mmol/g-substrate and co-products acetic acid and butyric acid were 2.17 g/L and 2.07 g/L respectively.Efficient co-production of hydrogen and VFA from sweet sorghum stalk was developed successfully in two-steps dark fermentation process involving alkali and enzyme treatment of the residual slurry after 1st step.The whole slurry was used without washing after alkali treatment.The optimum severity of treatment for highest yield of products was 2%(w/v)of alkali at 120 ? along with enzyme loading for 10 g/L of substrate.The two-step fermentation using C.thermosaccharolyticum increased production by 95%of hydrogen,97%of acetic acid and 143%of butyric acid yields higher than those obtained in single step fermentation.Highest hydrogen yield was 6.37 mmol/g-substrate and co-products acetic acid and butyric acid were 2.33 g/L and 2.36 g/L respectively.Together these results,two-step hydrogen and VFA fermentation with integrated alkali and enzyme treatment in between can be a useful strategy to improve the overall energy recovery.This process would be competitive,promising and add more value to the process of sweet sorghum biorefinery.