Ethanol is produced by anaerobic fermentation of glucose by Saccharomyces cerevisiae. For the particular strain of S. cerevisiae employed, the maintenance coefficient is 0.18 kg kg^{- 1} h^{- 1}, Yxs is 0.11 kg kg^-1, Y_PX is 3.9 kg kg^-1 and µ_max is 0.4 h^-1.  It is decided to investigate the possibility of using Zymomonas mobilis bacteria instead of yeast for making ethanol. Z. mobilis is known to produce ethanol under anaerobic conditions using a different metabolic pathway to that employed by yeast. Typical values of Yxs are lower than for yeast at about 0.06 kg kg^-1; on the other hand, the maintenance coefficient is higher at 2.2 kg kg ^-1 h ^-1. Ypx for Z. mobilis is 7.7 kg kg^-l; µ_max is 0.3 h- 1.  From stoichiometry, what is the maximum theoretical yield of ethanol from glucose                 

#Question id: 14333

#Section 5: Bioprocess Engineering and Process Biotechnology

A cylindrical bioreactor of diameter 3 m has four baffles. A Rushton turbine mounted in the reactor has a diameter one third the tank diameter and is operated at a speed of 90 rpm. The density of the fluid is approximately I g cm^-3. The reactor is used to culture an anaerobic organism that does not require gas sparging. The broth can be assumed Newtonian. As the cells grow, the viscosity of the broth increases. when the viscosity is 1000 times greater than water, estimate the power required to achieve turbulence.

#Question id: 14334

#Section 5: Bioprocess Engineering and Process Biotechnology

Laboratory-scale fermenters are usually mixed using small stirrers with electric motors rated between 100 and 500 W. One such motor is used to drive a 7cm turbine impeller in a small reactor containing fluid with the properties of water. The stirrer speed is 900 rpm. Estimate the power requirements for this process.

#Question id: 14336

#Section 5: Bioprocess Engineering and Process Biotechnology

A cylindrical stirred bioreactor of diameter and height 2 m has a Rushton turbine one-third the tank diameter in size. The bioreactor contains Newtonian culture broth with the same density as water and with viscosity 4 cP. The tank is now aerated. In the presence of gas bubbles, the approximate relationship between ungassed power number (N_P)₀ and gassed power number (N_P)g is: (N_P)g =0.5 (N_P)₀. What maximum stirrer speed is now possible in the sparged reactor? Estimate the mixing time.

#Question id: 14337

#Section 5: Bioprocess Engineering and Process Biotechnology

#Question id: 14338

#Section 5: Bioprocess Engineering and Process Biotechnology

Quasi steady state condition is