On the design and simulation of an airlift loop bioreactor with microbubble generation by fluidic oscillation

Abstract

Microbubble generation by a novel fluidic oscillator driven approach is analyzed, with a view to identifying the key design elements and their differences from standard approaches to airlift loop bioreactor design. The microbubble generation mechanism has been shown to achieve high mass transfer rates by the decrease of the bubble diameter, by hydrodynamic stabilization that avoids coalescence increasing the bubble diameter, and by longer residence times offsetting slower convection. The fluidic oscillator approach also decreases the friction losses in pipe networks and in nozzles / diffusers due to boundary layer disruption, so there is actually an energetic consumption savings in using this approach over steady flow. These dual advantages make the microbubble generation approach a promising component of a novel airlift loop bioreactor whose design is presented here. The equipment, control system for flow and temperature, and the optimization of the nozzle bank for the gas distribution system are presented. §1 Introduction Airlift reactors are perceived to have performance advantages over bubble columns and stirred tank bioreactors for many applications, biorenewables production in particular.Where the product is a commodity biochemical or biofuel, energy efficiency is the primary concern. There are multiple objectives for the optimization of energy efficiency, however. The hydrodynamics of stirring is an important consideration, as are the phase transfer of nutrient influx and the efflux of inhibitor products and byproducts. Finally, the metabolism of cells or microbes engaged in the biochemical production are a major constraining factormass transfer from the bulk liquid to the bioculture must be maintained. There are two important reasons to use airlift loop bioreactors (ALB) that arise from the airlift effects: flotation and flocculation. Small bubbles attached to particles or droplets significantly lower the density of the aggregrate. Grammatika and Zimmerman (2001) describe these generalized flotation effects. Such aggregates are susceptible to floc formation. Typically, microbes or cells that sediment out of the suspension accumulate in stagnation zones at the bottom expire.Given the importance of energy usage in the operation of ALBs, it is surprising that the sparging system, which is the central power consumption feature of the ALB, has not received more attention. Jones (2007) gives a good review of the major features of ALB, including the conventional types of sparger design. Chisti and Moo-Young (1987) classify the spargers used in the ALB as dynamic and static. Dynamic spargers use injection through nozzles to disperse the gas introduced. Static spargers are typically less reliant on the momentum of the jet, and the gas is introduced typically through a perforated plate (see Deshpande and Zimmerman, 2005a,b) or less commonly, through a porous baffle (Heijnen and Van't Riet, 1984). This study was motivated by the development of a novel microbubble generation technique based on fluidic oscil...

Intensification of yeast production with microbubbles

“…Compared to microbubbles, the diffusive mass transfer from coarse bubbles is low (Zimmerman et al, 2009;Al-Mashhadani et al, 2011), resulting in a metabolic switch -from an oxidative state (only several minutes following pitching) to an oxido-reductive metabolism (during lag phase) (Sonnleitner and Hahnemann 1994;. At this stage, cell viability and growth rate is low, hence the relatively low biomass yield .…”

“…Because ALBs undergo pneumatic agitation, they are referred to and imagined as a type of bubble column (Zimmerman et al, 2009). The pressure-driven circulatory motion owing to the design is the key reason for their inclusion in many new reactor designs in contrast to stirred tank reactors, A c c e p t e d M a n u s c r i p t where the introduction of energy via impellers limit reactor yield.…”

“…In spite of the sparger type employed, conventional ALBs suffer from production of large bubbles (mm-range) and, as a consequence, due to their low residence time and low surface area to volume ratio, are inefficient in gas transfer into reactors. Zimmerman et al, (2009) proposed an improved design of the ALB, by fitting with an energy efficient microbubble generator unit. Microbubbles can rapidly improve the gaseous nutrient concentration with proper mixing, another advantage of the microbubble (Al-Mashhadani et al 2015).…”

Proposal for an electro/fluidic no-moving-part transducer based on wall-jet separation from a heated curved surface

“…The latter limitation is obvious if the task the fluidic system performs is an analysis of a fluid sample. Another obvious example is the case of operating the fluidic oscillator with CO 2 in an algae growing bioreactor [3] where, of course, no electrically active fluids can replace the role of CO 2 in algal photosynthesis.…”

“…(b) The other reason is the recent increasing use of fluidic oscillators as means for improving efficiency of various processes such as, e.g., heat and mass transfer, which benefits from the agitation [2], or the generation of microbubbles [3] where the oscillation avoids bubble growth by conjunctions [18]. Although the key selling factor of the fluidic oscillators is their autonomy and simplicity (for reliability and low cost), even there is now often requested a control by electronics.…”