The ejector loop reactor: Application for microbial fermentation and comparison with a stirred‐tank bioreactor

Abstract

Ejector loop reactors (ELR) are successfully used in industrial chemical processes for gas/liquid reactions. They achieve higher mass transfer rates compared to the stirred‐tank reactor (STR) at comparable specific power input. Insufficient oxygen transport and shear stress induced growth inhibition are limiting parameters during microbial fermentation. Due to its better mass transfer characteristics, the ELR was expected to have beneficial effects on biomass and recombinant protein production. One concern, however, was whether the ELR's shear stress characteristics would have a negative effect. This study evaluated the suitability of using the Buss‐Loop® Reactor (BLR), one of the most advanced ELR technologies, as a bioreactor. The well‐studied STR was used as a reference. A lab scale BLR was adapted for microbial fermentation. Mass transfer rates and specific power inputs were within the same order of magnitude in the ELR and the reference STR. Maximum kLa values of 207 and 205 h−1 at power inputs of 6.9 and 9.7 W/L were measured in the ELR and STR, respectively. During batch fermentation of Escherichia coli K12 MG1655, maximum cell densities were higher in the ELR (OD600 of 22) than in the STR (OD600 of 18). Green fluorescence protein (GFP) production with pGS1 was comparable; however, more GFP was released into the media in the ELR. This indicates higher cell disruption compared to the STR. Despite this drawback of the first prototype, our work clearly demonstrates the potential of the ELR as a system for microbial fermentations.

Development and Research of New Media Jet Aeration Scheme in a Loop Bioreactor Producing Microbiological Products

“…To ensure this range, a compressor pressure of 1 bar is quite sufficient, which allows the use of low-pressure compressors with a rated power of less than 100 watts, which is 8 times less than the compressor power used in experiments. It should be emphasized that these large energy expenditures for the compressor operation were one of the reasons for the development of loop reactors with jet aeration, as an alternative to the bubble columns and apparatus with a stirrer (certain tank bioreactors) (Ughetti et al, 2018;Weber et al, 2018b;Meyer and Charles, 1982).…”

“…The development of such pressure by pump is associated with a high rotation speed of impeller. This, in its turn, leads to a significant increase in slice loads on cells, leading to inhibition of the biomass growth (Ughetti et al, 2018;Weber et al, 2018a;Moresi et al, 1983). The situation is complicated by a need to ensure aseptic conditions: before entering the ejector, air must be cleaned from mechanical impurities and disinfected (Stanbury et al, 2016;Soderberg, 2014; The aeration rate values (up to 0.26 vvm) obtained in experiments are sufficient for the cultivation of a number of biopesticides based on the bacteria Bacillus thuringiensis (Rahbani et al, 2015;Silva et al, 2011).…”

“…The most frequent jet mixing scheme (Fig. 1a) proposes a method by mixing the liquid and gaseous media in an ejector and feeding the finished mixture into a bioreactor (Ughetti et al, 2018;Moresi et al, 1983). In addition, the fermentation medium in loop is conveyed to the ejector nozzle, performing the function of a motive fluid, but the air is sucked in.…”

“…The mixture, saturated with air, can be either sprayed onto the medium surface in reactor or supplied in doses (Warmeling et al, 2016;Meyer and Charles, 1982). The aeration rate in jet loop bioreactors may vary over a wide range from 0.25... to 2.0 vvm (Ughetti et al, 2018;Weber et al, 2018a;Moresi et al, 1983). Furthermore, due to the mixing of media in ejector (and not in apparatus), a more uniform distribution of air in medium and its greater oxygen saturation are ensured (Weber et al, 2018b).…”

Monitoring gradient formation in a jet aerated bioreactor

“…In recent studies, an increase in mass transfer up to ∼200% and therefore higher productivities were achieved in jet loop Abbreviations: CMC, Carboxy methyl cellulose; JLR, Jet aerated loop reactor; OTR, Oxygen transfer rate; STR, Stirred tank reactor reactors (JLRs) compared to stirred tank reactors (STRs) [7,8]. Surprisingly in some cases the concentration of the anaerobic and overflow metabolite acetate was already increasing for cultivation at strictly aerobic conditions [9].…”