CBE 654 : BIOREACTOR ENGINEERING SEM 2 SESSION 2013/14ASSIGNMENT 1 : QUESTION

(SUBMISSION DATELINE 4pm FRIDAY 20/6/2014)

A production-scale fermenter with a liquid volume of 150m3 needs to be sterilized to 1:1000 probability of contamination (or one per 1000 batch will be contaminated).

The medium was found to have a viable microbial cell count of 5x105 cells per ml.

Steam is available at 1210C, and a thermocouple located in the fermenter gives the temperature-time data for the sterilization process is as in Table 1 below.

How long should the medium be held at the highest temperature so that the desired probability of sterility is achieved with minimum loss of nutrient quality? (3 Marks)

Table 1: Temperature-Time Data

TIME (minutes)TEMPERATURE (o C )

0 2510 7720 10230 11932 12160 12170 10680 9290 81100 71110 63120 56130 49150 39190 25

Given additional information

(a) Arrhenius equation is given as:

k=A . exp(−Ea

RT )

where A is Arrhenius constant Ea is activation Energy R is Universal Gas Constant T is temperature (K)

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(b) The activation energy and Arrhenius constant of B. stearothermophilus spores as follows:

Activation energy = 67.7 K cal. Mol-1 = 284.34 x 103 J. mol-1

Arrhenius constant = 1x1036.2 sec-1

(c) Universal gas constant R = 8.314472 J · K-1 · mol-1

(d) 0oC = 273.15 K

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