Two-Phase Flow Modeling of Solid Dissolution in Liquid for Nutrient Mixing Improvement in Algal Raceway Ponds

Haider Ali,Cheol Park,Dongda Zhang,Jonathan Wagner

doi:10.3390/en11040899

Haider Ali, Cheol Park + Show 2 more

Open Access

https://doi.org/10.3390/en11040899

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Abstract

Achieving optimal nutrient concentrations is essential to increasing the biomass productivity of algal raceway ponds. Nutrient mixing or distribution in raceway ponds is significantly affected by hydrodynamic and geometric properties. The nutrient mixing in algal raceway ponds under the influence of hydrodynamic and geometric properties of ponds is yet to be explored. Such a study is required to ensure optimal nutrient concentrations in algal raceway ponds. A novel computational fluid dynamics (CFD) model based on the Euler–Euler numerical scheme was developed to investigate nutrient mixing in raceway ponds under the effects of hydrodynamic and geometric properties. Nutrient mixing was investigated by estimating the dissolution of nutrients in raceway pond water. Experimental and CFD results were compared and verified using solid–liquid mass transfer coefficient and nutrient concentrations. Solid–liquid mass transfer coefficient, solid holdup, and nutrient concentrations in algal pond were estimated with the effects of pond aspect ratios, water depths, paddle wheel speeds, and particle sizes of nutrients. From the results, it was found that the proposed CFD model effectively simulated nutrient mixing in raceway ponds. Nutrient mixing increased in narrow and shallow raceway ponds due to effective solid–liquid mass transfer. High paddle wheel speeds increased the dissolution rate of nutrients in raceway ponds.

Highlights

Microalgae cultivation in outdoor raceway ponds largely depends on sunlight, turbulent mixing, CO2, and nutrient distributions
The experimental and computational fluid dynamics (CFD) results were verified by comparing the results of solid–liquid mass transfer coefficient and nutrient concentrations
Various pond aspect ratio (AR), water depths, paddle wheel speeds, and nutrient particle sizes were considered to ascertain their effects on solid–liquid mass transfer coefficient, solid holdup, and nutrient concentrations in a commercial raceway pond

Summary

Introduction

Microalgae cultivation in outdoor raceway ponds largely depends on sunlight, turbulent mixing, CO2 , and nutrient distributions. 45% carbon, 10% nitrogen, and 1.5% phosphorous. CO2 serves as the major carbon source, whereas different nutrients (i.e., nitrate, nitrite, ammonium, and phosphate) are introduced to supply other necessary chemical elements (i.e., nitrogen, phosphorous, and potassium) to algae cells. Optimal concentrations of 0.02 mol/m3 to 16.1 mol/m3 for nitrogen and 0.007 mol/m3 to 1.3 mol/m3 for phosphorous have been reported for maximum algal productivity [1]. Algal growth and nutrient uptake depend on various factors, including nutrient concentrations in ponds, boundary layer thickness, and different types of nutrients used [3]. A sufficient supply of nutrients is an effective approach to increase algal productivity of raceway ponds, but the necessary optimal nutrient concentration requirements are often ignored [4,5].

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