Under what conditions does the trp repressor block transcription of the trp operon?

TLS Online TPP Program

#Question id: 14220

#Section 5: Bioprocess Engineering and Process Biotechnology

A value of kLa = 30 h^-1 has been determined for a fermenter at its maximum practical agitator rotational speed and with air being sparged at 0.5 l gas/l reactor volume-min. E. coli with a qO2 of 10 mmol O2/g-dry wt-h are to be cultured. The critical dissolved oxygen concentration is 0.2 mg/l. The solubility of oxygen from air in the fermentation broth is 7.3 mg/l at 30⁰C.

What maximum concentration of E. coli can be sustained in this fermenter under aerobic conditions?

TLS Online TPP Program

#Question id: 14221

#Section 5: Bioprocess Engineering and Process Biotechnology

E. coli have a maximum respiration rate, qO2max, of about 240-mg O2/g-dry wt-h. It is desired to achieve a cell mass of 20 g dry wt/l. The kLa is 120 h-1 in a 1000-l reactor (800 l working volume). A gas stream enriched in oxygen is used (i.e., 80% O2) which gives a value of C* = 28 mg/L. If oxygen becomes limiting, growth and respiration slow; for example,

                                     

   where CL is the dissolved oxygen concentration in the fermenter. What is CL when the cell mass is  at 20 g/l?

TLS Online TPP Program

#Question id: 14222

#Section 5: Bioprocess Engineering and Process Biotechnology

A stirred-tank reactor is to be scaled down from 10 m3 to 0.1 m3. The dimensions of the large tank are: Dt = 2 m; Di = 0.5 m; N = 100 rpm.Determine the dimensions of the small tank (Dt , Di , H) by using geometric similarity?

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TLS Online TPP Program

#Question id: 14223

#Section 5: Bioprocess Engineering and Process Biotechnology

A furnace wall is constructed of firebrick 15-cm thick. The temperature inside the wall is 700⁰C the temperature outside is 80⁰C. If the thermal conductivity of the brick under these conditions is 0.3 W m-1 K^-1, what is the rate of heat loss through 1.5 m2 of wall surface?

TLS Online TPP Program

#Question id: 14224

#Section 5: Bioprocess Engineering and Process Biotechnology

Heat is transferred from one fluid to a second fluid across a metal wall. The film coefficients are 1.2 and 1.7kW m^-2 K^- 1. The metal is 6-mm thick and has a thermal conductivity of 19 W m^-1 K^-1. On one side of the wall there is a scale deposit with a fouling factor estimated at 19 W m^-1 K^-1. What is the overall heat-transfer coefficient?

TLS Online TPP Program

#Question id: 14225

#Section 5: Bioprocess Engineering and Process Biotechnology

A fermenter is maintained at 35⁰C by water circulating at a rate of 0.5 kg s^-1 in a cooling coil inside the vessel. The inlet and outlet temperatures of the water are 8⁰C and 15⁰C respectively. The length of the cooling coil is increased by 50%. In order to maintain the same fermentation temperature, the rate of heat removal must be kept the same. Determine the new cooling-water flow rate and outlet temperature by carrying out the following calculations. The heat capacity of the cooling water can be taken as 4.18 kJ kg^- 1 o C^- 1. From a steady-state energy balance on the cooling water, calculate the rate of cooling with the original coil ___________________.