Model-Based Prediction of Perceived Light Flashing in Recirculated Inclined Wavy-Bottomed Photobioreactors

Giuseppe Olivieri,Daniela Mezza,Monica Moroni,Luca Piersanti,Marco Bravi,Marcel Janssen

doi:10.3390/pr9071158

Giuseppe Olivieri, Daniela Mezza + Show 4 more

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https://doi.org/10.3390/pr9071158

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Abstract

Microalgae biomass production rate in short light-path photobioreactors potentially can be improved by mixing-induced flashing light regimes. A cascade photobioreactor features a thin liquid layer flowing down a sloping, wavy-bottomed surface where liquid flow exhibits peculiar local recirculation hydrodynamics, potentially conducive to an ordered flashing light regime. This article presents a model-based analysis of the frequency distribution of perceived irradiance in said wavy-bottomed photobioreactor. The model combines a Lagrangian description of the motion of individual cells, in turn derived from the hydrodynamic parameters of the photobioreactor extracted from an experimentally validated Computational Fluid Dynamic model, with a simplified description of the irradiance field across the culture thickness, down to the spectral analysis of perceived irradiance. The main finding of the work is that the wavy bottomed photobioreactor provides a ‘robust’ spectral excitation to the circulating microalgae up to 3 Hz frequency, while in flat panels and bubble columns excitation decays evenly at a 24 db/octave rate. This analysis paves the way to improving the light flashing performance of the wavy-bottomed photobioreactor with respect to geometry (cavity size and installation inclination) and operation (flow rate).

Highlights

The current market of microalgae is growing fast in recent years and the microalgae culture systems require improved microorganisms and significant improvements in process and equipment to support the increased microalgal biomass demand.The core of the microalgal metabolism is the photosynthesis process converting light and carbon dioxide to chemical energy and new biomass
We postulate that an intermediate quantity could be considered in assessing the relationship between process design and existing and ongoing experimental research on the flashing light effect, and that this quantity is the frequency spectrum of the variation of perceived irradiance with time. This method of characterizing flashing performance of photobioreactor hydrodynamics has never been used in the literature. To calculate this time-varying quantity, we developed and utilized a model that couples a radiation transport model and hydrodynamic transport; thereafter we analyzed spectrally the calculated quantity
The wavy-bottomed photobioreactor light regime was simulated for 1800 s to ensure that each zone of it had been reached by microalgae

Summary

Introduction

The current market of microalgae is growing fast in recent years and the microalgae culture systems require improved microorganisms and significant improvements in process and equipment to support the increased microalgal biomass demand.The core of the microalgal metabolism is the photosynthesis process converting light and carbon dioxide to chemical energy and new biomass. With the aim of producing hydrodynamically induced light/dark cycles and improving mass transfer, Torzillo et al [10] proposed a novel cascade photobioreactor featuring a thin liquid layer flowing along a sloping, wavy bottomed surface. This system was characterized both experimentally and computationally [11,12] and for some operating conditions, it seems to be characterized by a particular fluid dynamics structure that can provide the flashing light regime by rapid mixing of microalgal suspension

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