Biological processing in oscillatory baffled reactors (OBRs)

Abstract

Bioprocessing involves using complete cells or any of their components for the manufacture of products such as pharmaceuticals, fuel, health products and precursor compounds for plastics. Bioprocessing can provide sustainable routes for the manufacture of products which are traditionally manufactured from fossil-derived chemicals. The stirred tank reactor (STR) is the prevalent fermenter/reaction vessel in industry due to its simplicity and cost. However; the basic design has not changed for centuries. This thesis describes the use of oscillatory baffled reactors (OBRs) for bioprocessing. Generally, the “niche application” of OBRs is in performing ‘long’ processes in plug flow conditions, so they should be suitable for many bioprocesses. In this thesis, four research projects using OBRs are presented: modelling of plug flow and OBR design; enzymatic saccharification; microalgae culture; and anaerobic digestion (AD). A robust method to maximise plug flow in various OBR designs is described. Second order, polynomial models (R2=92.1% and 97.3%) were used to maximise plug flow at Ψ=1.9. The net flow rate (Q) was shown to affect the quality of plug flow which has implications for OBR design. Enzymatic saccharification was conducted in reactors based on OBR and STR technology. The OBR required 94-99% less power to achieve the necessary mixing intensities to maximise glucose production. Chlamydomonas reinhardtii was cultured in a modified OBR for use as a photobioreactor (PBR). Maximum growth rates were increased by 95% in the OBR compared to cultures conducted in T-flasks. A flotation effect was observed that suggests that a dual culture and harvest device for microalgae is possible. Anaerobic digestion of dairy slurry and co-digestion with glycerol was conducted in digesters based on OBR and STR technology. The OBR achieved a maximum specific methane yield 28% higher than the STR. However, blockages occurred in the OBR and 89% less power was required for temperature control in the STR, predominantly due to differences in surface areas to volume ratios. Overall, OBR technology was successfully used in three bioprocesses, with improvements demonstrated over traditional technologies such as STR and/or T- flasks. Commercial systems based on OBR technology could be designed, provided that sufficient data is generated to overcome the risks associated with adoption of a novel technology such as OBRs.