Determination of the Structural Characteristics of Microalgal Cells Walls under the Influence of Turbulent Mixing Energy in Open Raceway Ponds

Haider Ali,Cheol Park,Taqi Cheema

doi:10.3390/en11020388

Abstract

Turbulent flow mixing is essential in optimizing microalgal cultivation in raceway ponds. Microalgal cells are however highly sensitive to hydrodynamic stresses produced by turbulent mixing because of their small size. The mechanical properties (wall deformation and von Misses stress) of the microalgal cell wall structure under the influence of turbulent mixing are yet to be explored. High turbulence magnitudes damage microalgal cell walls by adversely affecting their mechanical properties which consequently destroy the microalgal cells and reduce the biofuel production. Therefore, such a study is required to improve the biofuel productivity of microalgal cells before their cell wall damage in raceway pond. This study developed a novel fluid–structure interaction (FSI)-based numerical model to investigate the effects of turbulent mixing on the cell wall damage of microalgal cells in raceway ponds. The study investigated microalgal cell wall damage at four different locations in a raceway pond in consideration of the effects of pond’s hydrodynamic and geometric properties. An experiment was conducted with a laboratory-scale raceway pond to compare and validate the numerical results by using time-dependent water velocities. Microalgal cell wall shear stress, cell wall deformation, and von Misses stress in the raceway pond were investigated by considering the effects of aspect ratios, water depths, and paddle wheel rotational speeds. Results showed that the proposed numerical model can be used as a prerequisite method for the selection of appropriate turbulent mixing. Microalgal cell wall damage is high in shallow and narrow raceway ponds with high paddle rotational speeds.

Highlights

Turbulent flow mixing prevents the sedimentation of microalgal cells in raceway ponds, facilitates removal of the oxygen, and increases the interaction of microalgal cells with sunlight and carbon dioxide
Water depths, and paddle wheel rotational speeds were investigated to examine their effects on cell wall shear stress, wall deformation, and von Misses stress at different locations in the raceway pond
An experiment was conducted in another laboratory-scale raceway pond to compare and validate the proposed numerical arbitrary Lagrangian–Eulerian (ALE) methodology based on water velocity (Figure 3)

Summary

Introduction

Turbulent flow mixing prevents the sedimentation of microalgal cells in raceway ponds, facilitates removal of the oxygen, and increases the interaction of microalgal cells with sunlight and carbon dioxide. Turbulence reduces the boundary layer around microalgal cells, and this reduction increases the diffusion rate of nutrients to the cell surface [1,2,3,4]. An increase in the water depth increases the water volume of the raceway pond which in return reduces the water circulation velocity. This reduction in the water velocity results in an ineffective turbulent mixing that reduces the interaction of microalgal cells with sunlight, carbon dioxide, and nutrients [9].

Objectives

Methods

Results

Conclusion