(1). Consider a 1000L CSTR in which biomass is being produced with glucose as the substrate. The microbial system follows a Monod relationship with; 
µmax = 0.4 h-1, Ks = 1.5 g/L, and yield factor Y X/S = 0.5 g biomass/g substrate consumed.

If the normal operation is with a sterile feed containing 10 g/L glucose at a rate of 100 l/h.

(a) What is the specific biomass production rate (g/L-h)

(b) If the recycle is used with a recycle stream of 10 L/h and a recycle biomass concentration five times as large as that in the reactor exit, what would be the new specific biomass production rate?

(c) Explain any difference between the volumes found in part a and b.


(2) In a two stage chemostat system, the volumes of the first and second reactors are V1 = 500L and V2 = 300L, respectively.

The first reactor is used for biomass production and the second is used for a secondary metabolite formation. 
•The feed flow rate to the first is F = 100L/h and 
•the glucose concentration in the feed is So= 5.0 g/L, 
•µmax = 0.3 h-1, 
•Ks = 0.1 g/l and 
•YX/S = 0.4 gdw cells /g glucose.

(a) Determine cell and glucose concentration in the effluent of the first stage.

(b) Assume that growth is negligible in the second stage and the specific rate of product formation is q_P = 0.02g P/g cell h, and Y_(P/s)= 0.6 g P/g S. Determine the product and substrate concentration in the effluent of the second reactor.

(3) Penicillin is produced by P. chrysogenum in fed-batch culture with the intermittent addition of glucose solution to the culture medium.

The initial culture volume at quasi-steady state is Vo = 500L, and glucose- containing nutrient solution is added with a flow rate of F= 50L/h. Glucose concentration in the feed solution and initial cell concentration are So = 300 g/L and Xo = 20 g/L, respectively. The kinetic and yield coefficients of the organism are µmax = 0.2 h-1, Ks = 0.5 g/Land Yx/s = 0.3 g dw/g glucose.

(a) Determine culture volume at t = 10 h

(b) Determine concentration of glucose at t = 10 h

(c) Determine the concentration and total amount of cells at t = 10 h

(d) If qP = 0.05 g product.g cells h and P0 = 0.1 g/L, determine the product concentration at t = 10 h

(4) An industrial wastewater stream is fed to a stirred-tank reactor continuously and cells are recycled back to the reactor from the bottom of the sedimentation tank placed after the reactor. The following are given for the system;
F= 100L/h; So = 5000mg/L; µmax = 0.25 h-1; Ks = 200mg/L; a= (recycle ratio) =0.6; C (cell concentration factor) = 2; Ymx/s = 0.4.

The effluent concentration is desired to be 100mg/L.

(a) Determine the required reactor volume

(b) Determine the cell concentration in the reactor and in the recycle stream.






(c) If the residence time is 2h in the sedimentation tank, determine the volume of the sedimentation tank and cell concentration in the effluent of the sedimentation tank.

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