ABSTRACT
A lab-scale stirred-tank bioreactor was reversibly retrofitted to a packed-bed and a trickle-bed biofilm reactor to study and compare the conversion of CO2/H2 with immobilised Clostridiumaceticum. The biofilm reactors were characterised and their functionality confirmed. Up to 8.6â¯g of C. aceticum were immobilised onto 300â¯g sintered ceramic carrier material, proving biofilm formation to be a robust means for cell retention of C. aceticum. Continuous CO2/H2-fermentation studies were performed with both biofilm reactor configurations as function of dilution rates, partial gas pressures and gas flow rates. The experiments showed that in the packed-bed biofilm reactor, the acetate space-time yield was independent of the dilution rate, because of low H2 gas-liquid mass transfer rates (≤17â¯mmolâ¯H2â¯L-1â¯h-1). The continuous operation of the trickle-bed biofilm reactor increased the gas-liquid mass transfer rates to up to 56â¯mmolâ¯H2â¯L-1â¯h-1. Consequently, the acetate space-time yield of up to 14â¯mmolâ¯acetateâ¯L-1â¯h-1 was improved 3-fold at hydrogen conversions of up to 96%.