Foam Formation and Control in Bioreactors

Abstract

The generation of foam during the course of a bioprocess remains a major technological challenge to be resolved and needs further investigation. The foaming tendency of the cultivation media used in bioreactors induces various direct,that is microbial cells stripping and contamination, as well as indirect adverse effects, that is modification of the properties of the medium subsequent to the addition of chemical antifoam leading to toxic effects at the level of the microbial metabolism and fouling of the downstream processing equipment. In this work, the mechanisms leading to foam formation are described at the molecular level (adsorption of surface‐active molecule at the gas–liquid interface), and also at the process level. In view of the potential foam‐associated problems, special attention is given to the level of the compatibility of the intensification of the gas–liquid operation in bioreactors. Due to these considerations, both the chemical and mechanical antifoam techniques have been evolved. Numerous new antifoam formulations and original combinations of chemical antifoams have been especially designed in order to meet the specific requirements of bioprocesses. Original mechanical techniques to prevent foam formation in bioreactors have been elaborated from combined knowledge involving the fluid dynamics of gas–liquid dispersion and interfacial processes (e.g. the “stirring as foam disruption” concept).

Scale-down assessment of the sensitivity of Yarrowia lipolytica to oxygen transfer and foam management in bioreactors: investigation of the underlying physiological mechanisms

“…The differences of the use of nitrogen and fatty acids during the cultures in the bioreactor could explain the significant drop of foam formation between the well-mixed intensive bioreactor and the bioreactor exhibiting oxygen deficiencies. Indeed, proteins tend to stabilize the foam, whereas fatty acids act as antifoam [4,7,20]. Accordingly, in the pilot-scale bioreactor exhibiting strong mixing and oxygen transfer deficiencies, the rate of consumption of fatty acids is very low compared with the test performed in well-mixed conditions.…”

Physical and physiological impacts of different foam control strategies during a process involving hydrophobic substrate for the lipase production by Yarrowia lipolytica

“…On the opposite, K L a decreases to a value of 0.0169 ± 0.0004 s -1 when 43 mL of antifoam agent is added to the broth (this quantity is equivalent to the one added during a cultivation run). This reduction of the global mass transfer efficiency is well described in the literature and can be related to greater bubble coalescence in the bulk liquid or adsorption of antifoam to the interfaces of bubbles and cells [14,21]. The following section involves the use of a DO-stat strategy to optimize the air flow rate and the foam formation intensity.…”

“…Of course, this conclusion does not mean that conventional chemical defoamer comprising a dedicated motor/shaft assembly separated from the bioreactor mixing system could not be efficient in the context of this process. However, conventional mechanical defoamer presents the drawbacks associated with additional operational costs that have to be attributed to the use of a second motor and mechanical system [14]. Even if some correlation involving the onset of foaming can be found in the literature [23], it is not easy to predict foaming issues during a microbial culture since physico-chemical properties of the broth continuously change and the induction of the synthesis of foaming agent by microbial cells is related to these complex modifications [24,25].…”

“…Foam formation is a big challenge for process engineer, especially when intensive aeration is required. Adverse effects of foam are multiple [12][13][14], i.e. decrease of the working volume of the reactor, removal of microbial cells and metabolites, increased risk of contamination, decrease of the oxygen transfer rate after the addition of chemical antifoam.…”

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

“…As a generally higher foaming capability for RLs was determined previously [ 20 , 47 ], it is assumed that other components in the culture broth promote foam formation. Mainly cells, lysed cells, and secreted proteins are known to increase the foaming of a culture broth [ 34 , 73 ]. This statement is supported by the observed HAA-free foam after the adsorption column, containing the same biomass concentration as the foam that is entering the adsorption column.…”