EFFECT OF AMBIENT-TEMPERATURE ON THE HEATING-COOLING REQUIREMENT OF A SINGLE CELL PROTEIN BATCH REACTOR OPERATING ON CHEESE WHEY

A 4.81 fermenter was used for batch production of single cell protein from cheese whey using the yeast Kluyveromyces fragilis. The reactor was operated at an air flow rate of 9.6 1 min-1 a mixing speed of 300 rpm and a pH of 4.5 +/- 0.2. A maximum yeast population of 820 million cell ml-1 and a lactose removal of 96% were achieved after 12 h giving a yield of 0.78 g cell g-1 lactose utilized. The maximum temperature observed in this study was 33-degrees-C indicating that a cooling system for batch production of Single Cell Protein (SCP) at room temperature is not needed. A heat balance was performed on the entire system and the temperature of the medium was calculated at various ambient temperatures (10-30-degrees-C). The results showed that in order to maintain the reactor temperature within the optimum temperature range (30-35-degrees-C) required for the growth of K.fragilis, supplementary heat will be required if the ambient temperature is below 22-degrees-C whereas a period of heating followed by a period of cooling will be required if the ambient temperature is above 22-degrees-C. By providing supplementary heat, a maximum yeast population can be reached rapidly and the length of the batch operation can be substantially reduced. The cooling requirement at the end of the operation can be accomplished by running cooling water. The economy of SCP production can be improved by operating several batch reactors in a series in which the heat removed from one unit (during the cooling phase) is used to heat the next unit (during the heating phase).