Bioprocess intensification in flow-through monolithic microbioreactors with immobilized bacteria

Microporous polymers (with porosity up to 90%) with a well-prescribed internal microstructure were prepared in monolithic form to construct a flow-through microbioreactor in which phenol-degrading bacteria, Pseudomonas syringae, was immobilized. Initially, bacteria was forced seeded within the pores and subsequently allowed to proliferate followed by acclimatization and phenol degradation at various initial substrate concentrations and flow rates. Two types of microporous polymer were used as the monolithic support. These polymers differ with respect to their pore and interconnect sizes, macroscopic surface area for bacterial support, and phase volume. Polymer with a nominal pore size of 100 microm with phase volume of 90% (with highly open pore structure) yielded reduced bacterial proliferation, while the polymer with nominal pore size of 25 microm with phase volume of 85% (with small interconnect size and large pore area for bacterial adhesion) yielded monolayer bacterial proliferation. Bacteria within the 25 microm polymer support remained monolayered, without any apparent production of extracellular matrix during the 30-day continuous experimental period. The microbioreactor performance was characterized in terms of volumetric utilization rate and compared with the published data, including the case where the same bacteria was immobilized on the surface of microporous polymer beads and used in a packed bed during continuous degradation of phenol. It is shown that at similar initial substrate concentration, the volumetric utilization in the microreactor is at least 20-fold more efficient than the packed bed, depending on the flow rate of the substrate solution. The concentration of the bacteria within the pores of the microreactor decreases from 2.25 cells per microm2 on the top surface to about 0.4 cells per microm2 within 3 mm reactor depth. If the bacteria-depleted part of the microreactor is disregarded, the volumetric utilization increases by a factor of 30-fold compared with the packed bed. This efficiency increase is attributed to the reduction of diffusion path for the substrate and nutrients and enhanced availability of the bacteria for bioconversion in the absence of biofilm formation as well as the presence of flow over the surface of the monolayer bacteria.