title: Segmented flow is controlling growth of catalytic biofilms in continuous multiphase microreactors.
abstract: Biofilm reactors are often mass transfer limited due to excessive biofilm growth, impeding reactor performance. Fluidic conditions play a key role for biofilm structural development and subsequently for overall reactor performance. Continuous interfacial forces generated by aqueous-air segmented flow are controlling biofilm structure and diminish mass transfer limitations in biofilm microreactors. A simple three step method allows the formation of robust biofilms under aqueous-air segmented flow conditions: a first-generation biofilm is developing during single phase flow, followed by the introduction of air segments discarding most of the established biofilm. Finally, a second-generation, mature biofilm is formed in the presence of aqueous-air segments. Confocal laser scanning microscopy experiments revealed that the segmented flow supports the development of a robust biofilm. This mature biofilm is characterized by a three to fourfold increase in growth rate, calculated from an increase in thickness, a faster spatial distribution (95% surface coverage in 24 h), and a significantly more compact structure (roughness coefficient <1), as compared to biofilms grown under single phase flow conditions. The applicability of the concept in a segmented flow biofilm microreactor was demonstrated using the epoxidation of styrene to (S)-styrene oxide (ee > 99.8%) catalyzed by Pseudomonas sp. strain VLB120ΔC cells in the mono-species biofilm. The limiting factor affecting reactor performance was oxygen transfer as the volumetric productivity rose from 11 to 46 g L tube (-1) day(-1) after increasing the air flow rate. In summary, different interfacial forces can be applied for separating cell attachment and adaptation resulting in the development of a robust catalytic biofilm in continuous microreactors.
authors.affiliation: Laboratory of Chemical Biotechnology, Department of Biochemical and Chemical Engineering, TU Dortmund University, Emil-Figge-Str. 66, Dortmund, 44227, Germany.
authors.forename: Rohan
authors.initials: R
authors.lastname: Karande
authors.forename: Babu
authors.initials: B
authors.lastname: Halan
authors.forename: Andreas
authors.initials: A
authors.lastname: Schmid
authors.forename: Katja
authors.initials: K
authors.lastname: Buehler
mesh_terms: D018441:Biofilms / Q000254:growth & development*; D019149:Bioreactors / Q000382:microbiology*; D003470:Culture Media; D004852:Epoxy Compounds / Q000378:metabolism; D011549:Pseudomonas / Q000254:growth & development* / Q000378:metabolism*; D012212:Rheology; D020058:Styrene / Q000378:metabolism
chemical_list: D003470:Culture Media; D004852:Epoxy Compounds; D020058:Styrene; C013690:styrene oxide
keywords: Pseudomonas; catalytic biofilms; continuous bioprocess; microreactors; multiphasic biocatalysis; segmented flow