Scale-up of a high productivity continuous biofilm reactor to produce butanol by adsorbed cells of Clostridium beijerinckii

An immobilized cell reactor for producing acetone butanol ethanol (ABE or solvents) when using Clostridium beijerinckii BA101 demonstrated reactor productivities of 3.49, 5.99 and 16.13 g l^-1 h^-1 at dilution rates of 0.29, 1.00 and 2.00 h^-1, respectively. These dilution rates are based on the total volume of the reactor. The reactor was scaled up successfully as these productivities are close to those achieved in small reactor. Dilution rate based on the void volume increased reactor productivity from 16.13 to 34.76 g l^-1 h^-1. The packed bed reactor blocked after a period of 2302 h of continuous operation due to excessive cell growth. Nutrient limitation was applied as a means of reducing cell growth while keeping the reactor productive; however, this approach was not successful. It was found that most of the cell growth in adsorbed cell bioreactors occurs on the surface of the cell support. The free cell continuous reactor demonstrated much lower reactor productivity. In the immobilized cell reactor only a fraction of the biomass was in the solventogenic state. A significant amount of biomass was present as inactive biomass (spores). It is suggested that sporulation be blocked in C. beijerinckii BA101 in order for reactors to be more productive. It is postulated that once such a culture is developed nutrient limitation should be attempted to avoid reactor blockage due to excessive cell growth.