Fluidization of fungal pellets in a 3D-printed micro-fluidized bed

Yi Zhang^a, Yuen Ling Ng^b, Kheng-Lim Goh^b, Yvonne Chow^c, Steven Wang^d, Vladimir Zivkovic^a

School of Engineering, Newcastle University, Newcastle Upon Tyne NE1 7RU, UK.

Abstract

Micro-fluidized bed (MFB) can be used as a fast screening tool for preliminary testing of engineering designs, but the applications of MFB for bioprocessing research such as microorganism cultivation is still deficient. This paper reports the unique fluidization performance of fungal pellets in a 3D-printed micro-fluidized bed, thus giving insights to the hydrodynamic study of pellets and broadening the potential of MFB in the bioprocessing and bioproduction fields. The results indicated that the static bed voidage were substantially larger (around 0.6) than the conventionally used value of 0.4. The observed decrease in packed bed voidage with increasing pellet mass was attributed to the increased compaction of pellets. A novel extended bed regime was observed prior to partially and fully fluidized bed regimes for liquid-solid fluidization. Due to the wall effect and surface forces, higher values of the minimum fluidization velocity and Richardson-Zaki empirical constants (n and K) were determined. In liquid-solid-gas fluidization system, fluidization regimes including packed-bed regime, fluidization regime and elutriation regimes were mapped. The effects on gas flow and pellet weight on fluidization performance were also investigated. It was noticed that pellets were fully fluidized at low biomass weight (i.e. 0.5 g) but the increase of pellet mass led to partially fluidization where the packed bed height increased with increasing pellet mass but decreased with increasing gas flowrate. Pellet fluidization velocity including axial velocity and radial velocity were measured by PIVlab analysis. The results indicated that pellet axial velocity was mainly affected by vertical gas flow while radial velocity was dominated by vortexes and surface forces.

Keywords: Micro-fluidized bed, 3D-printing, Fluidization, Fungal fermentation, Bioreactor.