Hydrodynamic characterization of a new small-scale reactor mixed by a magnetic bar

Novel external-loop-airlift milliliter scale bioreactors for cell growth studies: Low cost design, CFD analysis and experimental characterization

Many researchers have limited access to fully equipped laboratory-scale batch bioreactors and chemostats due to their relatively high cost. This becomes particularly prohibitive when multiple replicas of the same experiment are required, but not enough bioreactors are available to operate simultaneously. Additionally, experiments using shaken flasks are common but show significant limitations in terms of maintaining homogeneous conditions in liquid cultures or installing instrumentation for monitoring. Here, we proposed to tackle this significant hurdle by providing a route to make available the manufacture of low-cost, milliliter-scale bioreactors. This approach seems plausible for enabling proof-of-concept experiments before moving to a larger scale without significant investments. The conceptually designed systems were based on external-loop bioreactors due to their flexibility, simplicity, and ease of assembling and testing. Designs were initially evaluated in silico with the aid of COMSOL Multiphysics. The successfully evaluated systems were then constructed via additive manufacturing and assembled for hydrodynamics testing via tracer methods. This was enabled by a newly home-made optical absorbance sensor (OAS) for in-line and real-time measurements. Both the in silico and experimental results indicated close to ideal mixing conditions and low shear stress. Cell growth curves were prepared by culturing Escherichia coli and following its cell density in real-time. Our cell growth rate and maximum cell density were similar to those previously obtained in closely related systems. Therefore, the proposed bioreactors are an affordable alternative for batch and continuous cell growth studies rapidly and inexpensively.

Comparison Between Fluorescent Probe and Ion-Selective Electrode Methods for Intracellular pH Determination in Leuconostoc mesenteroides

The intracellular pH (pH_in) of Leuconostoc mesenteroides subsp. mesenteroides 19D was evaluated by two different methods, fluorescent probe and ion-selective electrode. Two fluorescent probes 5 (and-6)-carboxyfluorescein diacetate succinimidyl ester (cFDASE) and 5 (and-6)-carboxy-2',7'-dichlorofluorescein diacetate succinimidyl ester (cDCFDASE) were tested to evaluate the intracellular pH (pH_in) of living cells at a medium pH (pH_ex) ranged from 5.0 to 6.5. Salicylic acid was used as a probe for the ion-selective electrode method. Cells kept 60-80% of cFDASE probe at all pH_ex values against 5-10% of cDCFDASE probe at pH_ex ≤ 6.0. The pH_in values measured by the ion-selective electrode were higher by 0.1-0.6 pH units at pH_ex ranged from 5.0 to 6.5 than those determinated by fluorescent probe method. The possibility to study the intracellular pH at a wide external pH range using a single probe, and the simplicity of the material and experimental protocol may make the ion-selective electrode method most useful and easy to measure the intracellular pH of lactic acid bacteria compared with the other techniques like fluorescent probes.

Impact of shear stress and impeller design on the production of biogas in anaerobic digesters

Today, intensification of anaerobic digestion is still a scientific and technical challenge. The present study proposed combined experimental and computational fluid dynamics simulations to characterize the impact of shear stress and impeller design on the biogas production after sequential additions of substrate. Liquid phase (cattle manure digestate) rheological law was experimentally determined and input in numerical simulations. The results showed that the original use of a double helical ribbon in digester allowed a significantly faster dispersion of fresh substrate than the use of a classical Rushton turbine, leading to a 50% higher methane production rate. However, with both impellers, too high agitation rates entailed a clear slow-down of production rate and a decrease in CH₄ content. To avoid this loss of productivity, it was shown that the maximal value of shear stress, determined by numerical simulations, was a consistent parameter to set the upper agitation conditions in digesters.