Design and development of a novel textile based bioreactor: : Ethanol and biogas production as case studies

Abstract: Bioreactors are designed to provide enabling conditions for the controlled growth of microorganisms, such as good heat and mass transfer, aeration, hydrodynamics, geometry for adequate gas holdup, pH and foaming control, conditions for optimal substrate consumption and product formation, as well as mechanisms for monitoring microbial conditions. Additionally, bioreactors are designed to handle stress that would be exerted on them by the weight of the fermenting media and by the high pressure used for sterilisation. Bioreactors are usually constructed with materials such as stainless steel, carbon steel and borosilicate glass, which must be suitable for growing the fermenting microbes, be inert and corrosion proof. In this thesis, a textile-based bioreactor was designed and developed for aerobic and anaerobic fermentation based production processes with emphasis on mixing, mass transfer, temperature control, rheology, hydrodynamics and stress containment in the bioreactor.Temperature control was carried out using a heat control tubing either at the bottom of the bioreactor or as a heating jacket around its vertical height. The developed temperature control system was tested anaerobically and aerobically. Under anaerobic conditions with yeast it resulted in 200 % increase in ethanol productivity in comparison with the prototype without temperature control.A mixing system was developed for flocculating microbes and tested for anaerobic fermentation processes such as ethanol and biogas production. The developed mixing system led to the elimination of mass transfer limitation even at 30 times less bulk flow conditions. The mixing system also favoured stable bed formation, and the possibility of operating the bioreactor at a dilution rate above 1/h for ethanol production using flocculating yeast. A mixing system was also developed for aerobic fermentation and it led to improved media rheological and hydrodynamic performance of the bioreactor for fungi fermentation. The improved performance could be seen from minimised foam formation and stabilisation at an aeration rate of 1.4 VVMon a viscous, integrated first- and second-generation ethanol substrate with an initial viscosity of 93 cP.The stress that would be exerted on the bioreactor when used for large-scale applications was simulated and validated at laboratory scale. For 100–1000 m3 bioreactor, the tension per unit length that would be exerted on it would be between 300–20000 N/m.In this thesis, it was found that the use of the developed textile bioreactor was effective in reducing the fermentation-associated investment cost by 21 % or more, introducing flexibility and addressing several technical problems associated with both anaerobic and aerobic fermentation-based production processes.