Christopher Jon Wigoda
Thesis (12/02): Influence of root culture morphology on liquid holdup and trickle-bed bioreactor design
ABSTRACT
In this thesis, a quantifiable assessment of the influence of root hairs in trickle-bed systems was presented by comparing drainage characteristics of hairy and hairless Hyoscyamus muticus root cultures.
This was accomplished using the previously developed root hair removal technique for H. muticus roots [2], whereby PBA (1-pyrene butyric acid) is added to the typical B5 nutrient medium.
Liquid holdup results were analyzed for simple draining conditions by drainage of liquid media from submerged root cultures upon inversion of the 150 mL Ehrlenmeyer flasks.
Static holdups in root beds were found to be an order of magnitude greater than maximum correlated holdups for conventional packed beds.
Static holdup in root beds is thus unable to be accurately modeled by the literature correlations studied due to the vastly non-ideal nature of the root beds.
The absence of roots hairs was found to reduce the fractional retained liquid by approximately one-half.
In support of interpretation of experimental Eotvos numbers, regressed effective diameters were determined for H. muticus roots to quantify their restriction of fluid flow according to pressure drop data.
Dynamic holdup was measured as the fractional volume of drained liquid per reactor void volume.
Due to the lack of inlet superficial velocities, single drainage profiles were analyzed to obtain dynamic holdup relative to the instantaneous drainage velocity.
Dynamic holdup was shown to have an exponential dependence on drainage velocity similar to correlated dynamic holdups in hairless root beds and the presence of root hairs diminished this volume.
Finally, qualitative reasoning was presented to indicate that greater dynamic holdup induces enhanced mass transfer effects within the root bed, which is a vital parameter for root reactors considering the significant oxygen uptake demands at the root tips.