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.