Waste dairy whey is used to grow Kluyveromyces fragilis yeast in a continuous culture system operated at 30C and 1 atm pressure. Medium containing 4% w/w lactose (C12H22O11) and 0.15% w/w NH3 flows into a specially designed aerated bioreactor at a rate of 200 kg h21. The reactor is compartmentalised to facilitate gravity settling of the yeast; a suspension containing concentrated cells is drawn off continuously from the bottom of the reactor at a rate of 40 kg h21, while an aqueous waste stream containing 0.5 kg cells per 100 kg leaves from the top. All of the lactose provided is utilised by the culture. The biomass yield from lactose is known from preliminary experiments to be 0.25 g g21. The composition of the K. fragilis biomass is determined by elemental analysis to be CH1.63O0.54N0.16 1 7.5% ash.

(a) What is the RQ for this culture?

(b) It is proposed to supply the reactor with air at a maximum flow rate of 305 litres min21.

Will this provide sufficient oxygen? If not, what minimum level of oxygen enrichment

of the air is needed if the total gas flow rate is 305 litres min21?

(c) What is the concentration of residual NH3 in the aqueous waste stream?

(d) What is the concentration of cells in the cell concentrate?