Mixing, mass transfer and energy analysis across bioreactor types in microalgal cultivation and lipid production
type: CreativeWork
description: Microalgae are recognised as a source of lipids for bioenergy, nutrients and pharmaceuticals. Photobioreactors, closed vessels for microalgal cultivation, are known to have high energy consumption due to mixing and aeration. Sparging is commonly used for mixing and gas-liquid mass transfer in photobioreactors, but is energy intensive. The aim of this work was to reduce these energy requirements by optimising conventional sparging and considering surface aeration coupled with mechanical agitation as an alternative. An airlift photobioreactor was used as a base for comparison with two novel, surface aerated reactors: oscillatory baffled and wave photobioreactors. The three bioreactors were compared in terms of power input, mixing, CO2 mass transfer, algal growth and lipid production. Prior to comparison, each photobioreactor was optimised based on these parameters. To calculate power input, isothermal gas expansion equations were used for sparged systems and calorimetry was used for mechanically agitation systems. Mixing was investigated using a salt tracer and phenolphthalein indicator and mass transfer was measured using the gassing-in method. Scenedesmus sp., a high lipid-producer, was cultivated in low nitrate media across a range of mixing rates in each photobioreactor.In the airlift photobioreactor a critical minimum CO2 supply rate (of 2.7×10-5 m s-1) was found, below which carbon was limiting and above which energy was spent on sparging without increased productivity (0.20 g L-1 d-1 biomass; 0.03 g L-1 d-1 lipid). In the oscillatory baffled reactor, insufficient mass transfer limited algal productivity (0.11 g L-1 d-1 biomass; 0.02 g L-1 d-1 lipid). The wave reactor had high CO2 mass transfer coefficients (10 – 140 h-1) in comparison to the airlift (2.7 – 40 h-1) and oscillatory baffled reactors (6.3 – 37 h-1). Sufficient biomass productivity (0.18 g L- -1 d-1) and higher lipid productivity (0.045 g L-1 d-1) at lower power input in the wave reactor resulted in…
abstract: Microalgae are recognised as a source of lipids for bioenergy, nutrients and pharmaceuticals. Photobioreactors, closed vessels for microalgal cultivation, are known to have high energy consumption due to mixing and aeration. Sparging is commonly used for mixing and gas-liquid mass transfer in photobioreactors, but is energy intensive. The aim of this work was to reduce these energy requirements by optimising conventional sparging and considering surface aeration coupled with mechanical agitation as an alternative. An airlift photobioreactor was used as a base for comparison with two novel, surface aerated reactors: oscillatory baffled and wave photobioreactors. The three bioreactors were compared in terms of power input, mixing, CO2 mass transfer, algal growth and lipid production. Prior to comparison, each photobioreactor was optimised based on these parameters. To calculate power input, isothermal gas expansion equations were used for sparged systems and calorimetry was used for mechanically agitation systems. Mixing was investigated using a salt tracer and phenolphthalein indicator and mass transfer was measured using the gassing-in method. Scenedesmus sp., a high lipid-producer, was cultivated in low nitrate media across a range of mixing rates in each photobioreactor.In the airlift photobioreactor a critical minimum CO2 supply rate (of 2.7×10-5 m s-1) was found, below which carbon was limiting and above which energy was spent on sparging without increased productivity (0.20 g L-1 d-1 biomass; 0.03 g L-1 d-1 lipid). In the oscillatory baffled reactor, insufficient mass transfer limited algal productivity (0.11 g L-1 d-1 biomass; 0.02 g L-1 d-1 lipid). The wave reactor had high CO2 mass transfer coefficients (10 – 140 h-1) in comparison to the airlift (2.7 – 40 h-1) and oscillatory baffled reactors (6.3 – 37 h-1). Sufficient biomass productivity (0.18 g L- -1 d-1) and higher lipid productivity (0.045 g L-1 d-1) at lower power input in the wave reactor resulted in…
author: Jones, Sarah Melissa Jane
language: eng
keywords: Bioprocess Engineering
date published: 2015
date modified: 2026-07-22T22:23:46Z
provider: University of Cape Town
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Centre for Bioprocess Engineering Research

PropertyValue
property ID: Handle
value: http://hdl.handle.net/11427/20064