Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2020 Dec 18;8(12):2029.
doi: 10.3390/microorganisms8122029.

Uncoupling Foam Fractionation and Foam Adsorption for Enhanced Biosurfactant Synthesis and Recovery

Christian C Blesken  1 , Tessa Strümpfler  1 , Till Tiso  1 , Lars M Blank  1
Affiliations

Uncoupling Foam Fractionation and Foam Adsorption for Enhanced Biosurfactant Synthesis and Recovery

Christian C Blesken et al. Microorganisms. .

Abstract

The production of biosurfactants is often hampered by excessive foaming in the bioreactor, impacting system scale-up and downstream processing. Foam fractionation was proposed to tackle this challenge by combining in situ product removal with a pre-purification step. In previous studies, foam fractionation was coupled to bioreactor operation, hence it was operated at suboptimal parameters. Here, we use an external fractionation column to decouple biosurfactant production from foam fractionation, enabling continuous surfactant separation, which is especially suited for system scale-up. As a subsequent product recovery step, continuous foam adsorption was integrated into the process. The configuration is evaluated for rhamnolipid (RL) or 3-(3-hydroxyalkanoyloxy)alkanoic acid (HAA, i.e., RL precursor) production by recombinant non-pathogenic Pseudomonas putida KT2440. Surfactant concentrations of 7.5 gRL/L and 2.0 gHAA/L were obtained in the fractionated foam. 4.7 g RLs and 2.8 g HAAs could be separated in the 2-stage recovery process within 36 h from a 2 L culture volume. With a culture volume scale-up to 9 L, 16 g RLs were adsorbed, and the space-time yield (STY) increased by 31% to 0.21 gRL/L·h. We demonstrate a well-performing process design for biosurfactant production and recovery as a contribution to a vital bioeconomy.

Keywords: 3-(3-hydroxyalkanoyloxy)alkanoic acid (HAA); biosurfactant; foam adsorption; foam fractionation; integrated product recovery; metabolic engineering; rhamnolipid; scale-up.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Graphical explanation of foam fractionation and foam stability as well as the molecular structures of RLs and HAAs. (A) Rising gas bubbles (white, black arrows indicate flow directions) and draining interstitial liquid (light blue, blue arrows indicate flow directions). The foam lamella marked with a green frame is enlarged in (B) with surfactants (black line: hydrophobic moiety; blue points: hydrophilic moiety) either adsorbed on the gas-liquid interface, agglomerated as micelles, or dissolved in the liquid. Pseudomonads (yellow) are suspended in the liquid or adsorbed on the gas-liquid interphase by hydrophobic cell surface structures. The molecular structure of the produced surfactants is shown in (C), for (1) HAA and (2) mono-RL, considering that the hydrocarbon chain length varies between C8 and C12 for the applied whole-cell biocatalysts.
Figure 2
Figure 2
Fermentation setup with the two stages in the growth phase, and the harvest phase. Growth phase: 1st stage: no gassing into the stirred bioreactor. 2nd stage: activated gassing; discharging foam through the exhaust into the foam centrifuge; foamate reflux into the reactor (bypass in blue). Harvest phase: introduced by stopping the reflux and guiding the foamate into the fractionation column, equipped with an aeration and a separation of drained liquid back into the bioreactor. Fractionated foam left the upper opening of the fractionation column into the automated adsorption unit with two alternating adsorption columns. Permeate was collected and weighed, the eluate was collected separately. Bioreactor working volume was maintained by weight-controlled refill. Sampling points are marked as ① reactor, ② drainage reflux, ③ fractionated foam, ④ permeate inlet.
Figure 3
Figure 3
Cultivation of P. putida KT2440 Δflag_RL (A,B) and P. putida KT2440 ΔlapF_HAA (C,D) in a bioreactor with 2 L working volume. Growth phase (yellow background) and a subsequent continuous product separation during the harvest phase (t = 4 h to t = 36 h). (A,C) Biomass concentration in the reactor (blue) and in the fractionated foam (black) and the biomass enrichment (EX, gray). (B,D) Surfactant concentrations were measured in the fermentation broth of the reactor (blue) and in the fractionated foam (black), depicted together with the surfactant enrichment (EP, gray). The error bars indicate the deviation from the mean of two biological replicates.
Figure 4
Figure 4
Pictures of the operating foam fractionation column at RL enrichment after 9.7 h of cultivation. (A) General view of the column with (1) the upper outlet of the fractionated foam, the connectors for (2) the inlet of the foamate from the bioreactor, and (3) the outlet for the drainage reflux and to maintain the liquid level of the pool (indicated by green line), (4) the sparger positioned at the column bottom. (B) Polyhedral foam structure at the upper outlet of the fractionation column. (C) Spherical foam formation just above the pool.
Figure 5
Figure 5
Foam fractionation performance for RL (A,B) and HAA (C,D) separation in the external foam fractionation column. (A,C) Separated mass flow of surfactant for every 2 h (gray columns) and the total mass of separated product (blue) during harvest phase. (B,D) Product recovery RP for every 2 h during harvest phase, with the mean value as blue line. The error bars indicate the deviation from the mean of two biological replicates.
Figure 6
Figure 6
Product harvest ((A): RLs; (B): HAAs) after foam adsorption and subsequent desorption, first with ethanol (blue) and then with methanol (gray) for each elution. Two adsorption columns alternated every 8 h, for 32 h, resulting in 4 desorption procedures. The error bars indicate the deviation from the mean of two biological replicates.
Figure 7
Figure 7
Cultivation of P. putida KT2440 Δflag_RL in a bioreactor with 9 L working volume. Growth phase (yellow background) and a subsequent continuous product separation during the harvest phase (t = 12 h to t= 46 h). (A) Biomass concentration in the reactor (blue) and in the fractionated foam (black) and the biomass enrichment (EX, gray). (B) Surfactant concentrations were measured in the fermentation broth of the reactor (blue) and in the fractionated foam (black), depicted together with the RL enrichment (EP, gray).
Figure 8
Figure 8
RL harvest after foam adsorption and a subsequent desorption, with ethanol as eluent for the regular elution during cultivation (blue, desorption 1 to 4). Two adsorption columns alternated every 8.5 h, for 34 h, resulting in 4 desorption procedures. Final desorption with methanol was executed at the end of the cultivation (gray, desorption 5).
Figure 9
Figure 9
Weight of permeate collected after the adsorption column over the course of the harvest phase. Permeate trends in a 2 L working volume for the RL synthesis (black), and HAA synthesis (blue). The error bars indicate the deviation from the mean of two biological replicates. The permeate trend for RL synthesis in a 9 L working volume is plotted in gray.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

References

    1. Henkel M., Geissler M., Weggenmann F., Hausmann R. Production of microbial biosurfactants: Status quo of rhamnolipid and surfactin towards large-scale production. Biotechnol. J. 2017;12 doi: 10.1002/biot.201600561. - DOI - PubMed
    1. Mulligan C.N. Environmental applications for biosurfactants. Environ. Pollut. 2005;133:183–198. doi: 10.1016/j.envpol.2004.06.009. - DOI - PubMed
    1. Fenibo E.O., Ijoma G.N., Selvarajan R., Chikere C.B. Microbial Surfactants: The next generation multifunctional biomolecules for applications in the petroleum industry and Its associated environmental remediation. Microorganisms. 2019;7:581. doi: 10.3390/microorganisms7110581. - DOI - PMC - PubMed
    1. Kosaric N., Vardar-Sukan F. Biosurfactants. CRC Press Taylor & Francis Group; Boca Raton, FL, USA: 2015.
    1. Ines M., Dhouha G. Glycolipid biosurfactants: Potential related biomedical and biotechnological applications. Carbohydr. Res. 2015;416:59–69. doi: 10.1016/j.carres.2015.07.016. - DOI - PubMed