Effect of operating conditions on biomass growth during citric acid production by solid-state fermentation

Abstract

AbstractThe effect of aeration, agitation, and bed loading on biomass and product concentration during citric acid biosynthesis by solid-state fermentation was investigated. For this purpose, Aspergillus niger S was cultivated on sugar beet pulp in a 4.5 dm3 horizontal rotating drum bioreactor. The results suggest that the parameters examined have a remarkable effect on the quantity of biomass being formed and on the product concentration. The maximum citric acid production (about 150 g per kg of the substrate dry matter) was obtained under the following conditions: aeration rate 0.2 dm3 kg−1 min−1, mixing (periodical) 1 min once an hour, and bed loading 30 % of the bioreactor working volume. However, these values did not favour biomass formation. Moreover, it was found that accumulation of the product reached its maximum when the amount of biomass was minimal (approximately 252-29 g per kg of the substrate dry matter) under the conditions involved.