Mass Transfer Features of Wavy-Bottomed Cascade Photobioreactors

Monica Moroni,Agnese Cicci,Giorgia Sed,Marco Bravi,Giuseppe Torzillo,Barbara Mazzarotta,Nicola Verdone

doi:10.3390/chemengineering5040086

Monica Moroni, Agnese Cicci + Show 5 more

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https://doi.org/10.3390/chemengineering5040086

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Abstract

It has been suggested that the energy-efficient production of microalgae biomass can be more easily obtained in short light path photobioreactors that can be operated at high biomass concentration. On the downside, however, high biomass concentrations also require an efficient gas exchange rate to avoid metabolic growth limitation or inhibition. A cascade photobioreactor featuring a thin liquid layer flowing down a sloping, wavy-bottomed surface can be operated at a biomass concentration that is much higher compared to most usual open-type equipment. Liquid flow, upon investigation, proved to exhibit peculiar “local recirculation” hydrodynamics, potentially conducive to the mixing of superficial and deep zones of the photobioreactor. Mass transfer coefficient represents a useful parameter to optimize the performance of a microalgal photobioreactor and its scale-up. The aim of the present article is to discuss the experimental mass transfer features of this novel type of photobioreactor and highlight expected opportunities and issues entailed by different ways of installing and operating such novel types of photobioreactors.

Highlights

Microalgae are currently used as food and sources of food fractions and are touted to be a potential feedstock for green biochemicals and biofuels
The variation in the mass transfer coefficient can possibly be related with the observed The variation in the mass transfer coefficient can possibly be related with the macroscopic hydrodynamic features of the wavy-bottomed photobioreactor geometry
The local recirculation frequency relevant to the very same published in [15,16] could explain the behavior of mass transfer coefficients obtained by the photobioreactor geometry published in [15,16] could explain the behavior of mass transfer smaller test unit and could provide hints about those obtained with the larger one

Summary

Introduction

Microalgae are currently used as food and sources of food fractions and are touted to be a potential feedstock for green biochemicals and biofuels. Several hindrances prevent the adoption of microalgae as a low-value feedstock, among which are the scarce scalability of both open (ponds) and closed photobioreactors (PBRs), the significant cost (both capital and operational) to run them, plus a downstream processing cost that is generally higher than that affecting traditional storage biomass [1]. All these hindrances are being actively scavenged to make large-scale production and deployment of microalgal biomass possible at a lower cost and to make microalgal biomass a viable alternative to other biomass sources beyond current niche high value markets. An adequate CO2 supply is required to avoid biomass growth limitation, but a symmetric buildup of waste and toxic

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