Answer Happy

(a) When considering aeration of chemostats, describe the different steps that contribute to the overall oxygen transfer process. In each case, identify the parameters and / or factors that determine the transfer rate for that step. [8 marks] (b) A simple dynamic test was carried out to determine the oxygen mass transfer characteristics of a chemostat. Once the chemostat was at steady state, the air flow was switched off for a known amount of time, and then restarted. The dissolved oxygen concentration after restarting the air flow is given in Table Q4-1 below. Table Q4-1 Dissolved O2 concentration upon restarting air flow Time [min] Dissolved O2 Concentration [gm-?] 1.50 1 3 3.62 5 7 9 11 5.47 6.34 6.77 7.33 7.66 7.70 8.00 13 15 o 1 Given that: roverall = k_ a' (Coz - Coz) -rx Yx/02 where roverall is in g m-3 min-, determine the value of kla'. [8 marks] (c) When working at laboratory scale, the oxygen transfer within a Miniature Stirred Bioreactor is said to be better than that within a standard Erlenmeyer flask. Why is this the case? [4 marks]