Question

9.10. A completely mixed bioreactor is used for ethanol fermentation of hydrolyzed starch solution containing 30 g/l total sugar. The following data are available: ?_m = 0.15 h^–1, K_S = 0.5 g/l, F = 10 l/h, Y_X/S = 0.1 g X/g S, Y_P/S = 0.5 gP/gS, k_S = 0.1 d^–1.

a. For 95% conversion of substrate to product, determine the required reactor volume and ethanol productivity when the system was operated without cell recycle.

b. For the same degree of conversion, determine the required reactor volume and ethanol productivity when the system was operated with cell recycle. r = 0.4, C = X_r/X = 3, ? = 0.1.

Answer 1

Ethanol Fermentation is done in a completely mixed bioreactor, here the starch solution has 30 g/l sugar.

(a) Here, m is the mass fraction fed per hour , m= 0.15 h^-1, and K_s = 0.5 g/l, and the feed rate is 10 l/h.

The required reactor volume is based on the feed rate and mass fraction, hence:

Here conversion of substrate to product is taken as 0.95. Hence the required reactor volume = 62.76 L

Ethanol productivity is dependent on the amount of sugar in the sugar solution, conversion and the production rate, hence:

Without recycle the produtivity will be 0.285 P/S.d.

(b) For the same degree of conversion, The required reactor volume will be given as:

Here the

For the same degree of conversion, The required reactor volume with recycle will become 188.28 L.

And the productivity with cell recycle of recycle ratio 0.4, will change as:

Without recycle the produtivity will be 0.285 P/S.d.