Pseudomonas putida is used for fermentation of lactose present in cheese whey in

Question

Pseudomonas putida is used for fermentation of lactose present in cheese whey in a con- tinuously operating aeration tank at a dilution rate of D = 0.28 h-1. The lactose con- centration in the feed and the effluent are S,-2 g/L and Se = 0.1 g/l. The growth rate and lactose removal is limited by oxygen transfer. The following information is available: XuM = 0.45 gX7g S, Yvo,-0.25 gX7g2 and C* = 8 mg/l (saturation DO). a. Determine the steady-state biomass concentration (X) and the specific rate of oxygen consumption (go2) b. What should be the oxygen transfer coefficient (Kia) to overcome oxygen transfer limitations if the desired DO concentration in the fermentation medium is 2 mg/l?

Explanation / Answer

a) steady-state biomass concentration can be calculated by using the following expression

x=Yx/s(S0-Se)

data has given Yx/s =0.45gX/gS S0= 2g/L and Se=0.1g/l

therefore biomass X= 0.45x(2-0.1) g/L = 0.855g/L

now we know that OUR(oxygen uptake rate) = qo2x=ux/Yx/o2 or

qo2 = u/Yx/o2   in steady state condition u=D(dilution rate)

hence we can write in steady state

qo2 = D/Yx/o2

now given data are, D= 0.28 h-1 and Yx/o2 =0.25gX/g O2

Therefore, qo2 =0.28/0.25 =1.12 h-1

b) we know that when o2 transfer is rate limiting step then

OTR(oxygen transfer rate)= OUR(Oxygen uptake rate)

Now OTR= KLa(C*-CL) ,where KLa is coefficient of oxygen transfer and C* is saturation DO and CL is DO in media

so we can arrage this equation as

KLa(C*-CL)= qo2 x

now C*=8mg/L CL=2mg/L we have already estimated the value of qo2=1.12h-1and x=0.855g/L= 855mg/L in problem 1

so putting all together in above equation we will get

KLa =159.6 h-1

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