Modeling the Separation of Microorganisms in Bioprocesses by Flotation

Abstract

Bioprocesses for the production of renewable energies and materials lack efficient separation processes for the utilized microorganisms such as algae and yeasts. Dissolved air flotation (DAF) and microflotation are promising approaches to overcome this problem. The efficiency of these processes depends on the ability of microorganisms to aggregate with microbubbles in the flotation tank. In this study, different new or adapted aggregation models for microbubbles and microorganisms are compared and investigated for their range of suitability to predict the separation efficiency of microorganisms from fermentation broths. The complexity of the heteroaggregation models range from an algebraic model to a 2D population balance model (PBM) including the formation of clusters containing several bubbles and microorganisms. The effect of bubble and cell size distributions on the flotation efficiency is considered by applying PBMs, as well. To determine the sensitivity of the results on the model assumptions, the modeling approaches are compared, and suggestions for their range of applicability are given. Evaluating the computational fluid dynamics (CFD) of a dissolved air flotation (DAF) system shows the heterogeneity of the fluid dynamics in the flotation tank. Since analysis of the streamlines of the tank show negligible back mixing, the proposed aggregation models are coupled to the CFD data by applying a Lagrangian approach.

Structured population balances to support microalgae-based processes: Review of the state-of-art and perspectives analysis

“…The collision efficiency can be seen as the probability that two colliding cells do aggregate. To better distinguish among the factors influencing the collision efficiency, Schmideder [106] separated the physicochemical and the hydrodynamic effects.…”

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“…Next, they validated their model using a compartmental model. Schmideder et al [4] presented a study on dissolved air flotation and microflotation, which are primary purification steps in a range of bioprocesses utilizing microorganisms (e.g., algae and yeast). However, since the efficiency of these separation processes depends on the aggregation of microorganisms with microbubbles, they compared new or used existing aggregation models to investigate the suitability range of these models to predict separation efficiency in fermentation broths.…”

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