Modeling of microalgal shear‐induced flocculation and sedimentation using a coupled CFD‐population balance approach

Abstract

In this study, shear-induced flocculation modeling of Chlorella sp. microalgae was conducted by combination of population balance modeling and CFD. The inhomogeneous Multiple Size Group (MUSIG) and the Euler-Euler two fluid models were coupled via Ansys-CFX-15 software package to achieve both fluid and particle dynamics during the flocculation. For the first time, a detailed model was proposed to calculate the collision frequency and breakage rate during the microalgae flocculation by means of the response surface methodology as a tool for optimization. The particle size distribution resulted from the model was in good agreement with that of the jar test experiment. Furthermore, the subsequent sedimentation step was also examined by removing the shear rate in both simulations and experiments. Consequently, variation in the shear rate and its effects on the flocculation behavior, sedimentation rate and recovery efficiency were evaluated. Results indicate that flocculation of Chlorella sp. microalgae under shear rates of 37, 182, and 387 s is a promising method of pre-concentration which guarantees the cost efficiency of the subsequent harvesting process by recovering more than 90% of the biomass. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:160-174, 2018.

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

“…Actually, few works have been so far presented in the literature dealing with the use of PBEs for simulating microalgae flocculation. Some of them focus on the quantitative description of flocs size overshoot during prolonged microalgae flocculation [99] , [100] , while some others deal with the interactive effects of fluid dynamics with the process when not-ideal force fields are acting inside the flocculation device [101] . PBEs have also been proposed to optimize and design a process where flocculation and sedimentation occur simultaneously .…”

“…In PBEs describing microalgae flocculation, the physicochemical effects are determined by the surface properties of colliding cells and specifically by the charge distribution as well as by the colloidal characteristics of particles [100] . However, in some works [102] the collision efficiency is represented by an adjustable parameter, while in some others [22] , [101] it is set equal to 1, thus assuming that all collisions lead to the formation of new flocs (aggregates). This is typically the case when flocculants are employed.…”

Numerical Analysis of Convective Heat Transfer Characteristics in Microalgae Slurries in Tube Flow

“…Golzarijalal et al [12] have combined computational fluid dynamics (CFD) and population balance modeling techniques to study the shear-induced flocculation of microalgae. Ranganathan and Savithri [13] have used the CFD technique to simulate the hydrothermal liquefaction (HTL) of Nannochlor-opsis sp.…”

Modeling of Flocculation and Sedimentation Using Population Balance Equation

“…A standard k − ε turbulence model was employed because it reduces the computational effort and increases the reasonable accuracy of the model [23,24].…”

“…Based on the previous experiment, the boundary conditions of the inlet were defined as the velocity inlet, and other parts were defined as the wall. All procedures explained were conducted by using the Ansys Fluent 15.0 software package [24].…”