#1: Heat Generation in Batch Growth In the subsection on respiration (Section 5.

Question

#1: Heat Generation in Batch Growth In the subsection on respiration (Section 5.4), it is stated that the efficiency of energy conversion is 60% (eucaryotes, under aerobic conditions) when the microbe creates 36 moles of is not captured in ATP bonds, but is released as heat. The free energy change for complete oxidation of glucose is 686 kcal/mole. Use the above information to calculate the rate of energy removal (cooling) in kilo-Joules/hour that will be required to keep an industrial scale fermenter at a constant growth temperature during a batch culture of a eukaryotic microbe. Basis: 10,000 L of culture broth; Initial carbohydrate = 500 L of sugar molasses (75% weight percent di-and monosaccharides) added to the 10,000 L culture; . · remaining 50% goes to energy production.

Explanation / Answer

It is given that initial carbohydrate in 500L of sugar molasses which is 75% w/w of di- and monoscaccharides. Therefore, Wt of sugars in 500L of molasses = 0.75*(Volume of molasses) *(density of sugar molasses) = 0.75*500L*1.4kg/L = 525kg       (Here we have considered density of sugar molasses as 1.4kg/L).

Now 50% of these sugars go into cells as C source and 50% go into energy production of which 60% is captured as ATP bonds and 40% go as heat. This heat raises the temperature of the reactor.

Now we will first calculate the amount of sugar (at this point we will call all of the sugar as glucose) that generates heat. This will be calculated as 40% of 50% of 525 kg = 0.4*0.5*525 kg = 105 kg.

Now total heat generated by combution of 105 kg = 105kg *686kcal/mol*(1000/180)mols/kg*4.2 J/cal...(Note mol wt of glucose = 180, therefore, there are 1000/180 mols of glucose in 1 kg)

Calculating the above we get the total heat generated in the batch reactor due to microbial respiration, which is =1680700 kJ.

Now you see that the rate of growth of microbial cells or rate of consumption of glucose is not provided in the question (or you probably missed it in the post or this question is a part of another question where more data is given). Anyway, please note that you need to have a rate, which will tell you as to what rate this heat will be generated in the reactor (please check if any coefficients are given in the question, you can also calculate the rate of generation of heat using those coefficients).

I hope this will help you understand the problem.

Thanks

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