Infuence Of Mass Transfer Towards Pilot-Scale Semi-Continuous Cultivation Of Chlorella Vulgaris

Microalgae, well-known for their prominent photosynthetic efficiency and rapid growth rate emerge as a great feedstock for bio-energy production of third-generation biofuel. In this study, Chlorella vulgaris was chosen as the subject of investigation. The aim was to maximize the biomass production b...

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Main Author:	Gek, Khoo Choon
Format:	Thesis
Language:	English
Published:	2020
Subjects:	T Technology TP155-156 Chemical engineering
Online Access:	http://eprints.usm.my/50385/1/Infuence%20Of%20Mass%20Transfer%20Towards%20Pilot-Scale%20Semi-Continuous%20Cultivation%20Of%20Chlorella%20Vulgaris.pdf
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spelling	my-usm-ep.503852021-11-17T03:42:09Z Infuence Of Mass Transfer Towards Pilot-Scale Semi-Continuous Cultivation Of Chlorella Vulgaris 2020-06-01 Gek, Khoo Choon T Technology TP155-156 Chemical engineering Microalgae, well-known for their prominent photosynthetic efficiency and rapid growth rate emerge as a great feedstock for bio-energy production of third-generation biofuel. In this study, Chlorella vulgaris was chosen as the subject of investigation. The aim was to maximize the biomass production by investigating both the kinetic and mass transfer phenomena in a pilot-scale bubble column photobioreactor (BC-PBR) cultivation system. To account for the maximum microalgal biomass accumulation, the microalgae growth condition was optimized in the semi-continuous cultivation mode. Each cultivation cycle was carried out with 15 days of batch cultivation mode, followed by 3 cycles of 5 days each during semi-continuous cultivation mode. One-factor-at-a-time (OFAT) method was employed to investigate the effects of inoculum concentration of microalgae cells, photoperiod, and aeration rate towards microalgal growth performance, in the range of 0.1 – 0.35 g L-1, 12 and 24 h, and 0.12 – 0.19 vvm, respectively. The underlying mass transfer mechanism between gaseous CO2 and the culture medium were investigated under the optimized growth conditions. In addition, the reusability of the recycled water from the harvesting process was evaluated. To convert the microalgae into application biofuel, the harvested microalgal biomass was then converted into hydrochar via hydrothermal carbonization (HTC) reaction. The effects of hydrothermal temperature and retention time and the properties of hydrochar were studied at the range of 180 – 250 oC and 0.5 – 4 h, respectively. The research results showed that the optimum biomass accumulation was at 0.9819 g L-1, with cultivation conditions of: inoculum concentration of 0.3 g L-1, exposed under continuous (24 h) illumination with light intensity 60 – 70 μmol m-2 s-1, and supplied with compressed air at aeration rate of 0.16 vvm. The cultivation system underwent a bubble breakup mechanism during the transportation of gaseous CO2 into the culture medium with gas-liquid mass transfer coefficient, kLaL(CO2) of 0.45 s-1. Higher CO2 concentration environment did not affect the biomass accumulation due to the solubility limitation of CO2 in the microalgae culture. Based on optimized growth conditions for microalgae, a mathematical model for microalgae growth was developed. By incorporating the mass transfer parameter into the modified growth model, which was validated through an extended 120 days (21 cycles) of semi-continuous cultivation. In addition, the microalgae cells were proven to be able to grow in the recycled harvesting water. On the other hand, the highest energy yield of hydrochar was achieved at 76.59%, at the HTC under 210 oC for 0.5 h. Comparatively, higher heating value (HHV) of hydrochar produced was measured to be 24.51 kJ g-1, which is higher than that of raw biomass (12.58 kJ g-1). Moreover, the HTC process produced an aqueous phase that could be used as an alternative nutrient source for microalgae cultivation, yielding an average biomass accumulation of 0.8483 g L-1, demonstrating the feasibility of close loop cultivation. To conclude, mass transfer was a dominant factor affecting the kinetic growth of microalgae in pilot-scale semi-continuous BC-PBR cultivation system. It further affected the quality of produced biomass, and thus affected the downstream processing route chosen for optimal conversion of bioenergy. 2020-06 Thesis http://eprints.usm.my/50385/ http://eprints.usm.my/50385/1/Infuence%20Of%20Mass%20Transfer%20Towards%20Pilot-Scale%20Semi-Continuous%20Cultivation%20Of%20Chlorella%20Vulgaris.pdf application/pdf en public phd doctoral Universiti Sains Malaysia Pusat Pengajian Kejuruteraan Kimia
institution	Universiti Sains Malaysia
collection	USM Institutional Repository
language	English
topic	T Technology TP155-156 Chemical engineering
spellingShingle	T Technology TP155-156 Chemical engineering Gek, Khoo Choon Infuence Of Mass Transfer Towards Pilot-Scale Semi-Continuous Cultivation Of Chlorella Vulgaris
description	Microalgae, well-known for their prominent photosynthetic efficiency and rapid growth rate emerge as a great feedstock for bio-energy production of third-generation biofuel. In this study, Chlorella vulgaris was chosen as the subject of investigation. The aim was to maximize the biomass production by investigating both the kinetic and mass transfer phenomena in a pilot-scale bubble column photobioreactor (BC-PBR) cultivation system. To account for the maximum microalgal biomass accumulation, the microalgae growth condition was optimized in the semi-continuous cultivation mode. Each cultivation cycle was carried out with 15 days of batch cultivation mode, followed by 3 cycles of 5 days each during semi-continuous cultivation mode. One-factor-at-a-time (OFAT) method was employed to investigate the effects of inoculum concentration of microalgae cells, photoperiod, and aeration rate towards microalgal growth performance, in the range of 0.1 – 0.35 g L-1, 12 and 24 h, and 0.12 – 0.19 vvm, respectively. The underlying mass transfer mechanism between gaseous CO2 and the culture medium were investigated under the optimized growth conditions. In addition, the reusability of the recycled water from the harvesting process was evaluated. To convert the microalgae into application biofuel, the harvested microalgal biomass was then converted into hydrochar via hydrothermal carbonization (HTC) reaction. The effects of hydrothermal temperature and retention time and the properties of hydrochar were studied at the range of 180 – 250 oC and 0.5 – 4 h, respectively. The research results showed that the optimum biomass accumulation was at 0.9819 g L-1, with cultivation conditions of: inoculum concentration of 0.3 g L-1, exposed under continuous (24 h) illumination with light intensity 60 – 70 μmol m-2 s-1, and supplied with compressed air at aeration rate of 0.16 vvm. The cultivation system underwent a bubble breakup mechanism during the transportation of gaseous CO2 into the culture medium with gas-liquid mass transfer coefficient, kLaL(CO2) of 0.45 s-1. Higher CO2 concentration environment did not affect the biomass accumulation due to the solubility limitation of CO2 in the microalgae culture. Based on optimized growth conditions for microalgae, a mathematical model for microalgae growth was developed. By incorporating the mass transfer parameter into the modified growth model, which was validated through an extended 120 days (21 cycles) of semi-continuous cultivation. In addition, the microalgae cells were proven to be able to grow in the recycled harvesting water. On the other hand, the highest energy yield of hydrochar was achieved at 76.59%, at the HTC under 210 oC for 0.5 h. Comparatively, higher heating value (HHV) of hydrochar produced was measured to be 24.51 kJ g-1, which is higher than that of raw biomass (12.58 kJ g-1). Moreover, the HTC process produced an aqueous phase that could be used as an alternative nutrient source for microalgae cultivation, yielding an average biomass accumulation of 0.8483 g L-1, demonstrating the feasibility of close loop cultivation. To conclude, mass transfer was a dominant factor affecting the kinetic growth of microalgae in pilot-scale semi-continuous BC-PBR cultivation system. It further affected the quality of produced biomass, and thus affected the downstream processing route chosen for optimal conversion of bioenergy.
format	Thesis
qualification_name	Doctor of Philosophy (PhD.)
qualification_level	Doctorate
author	Gek, Khoo Choon
author_facet	Gek, Khoo Choon
author_sort	Gek, Khoo Choon
title	Infuence Of Mass Transfer Towards Pilot-Scale Semi-Continuous Cultivation Of Chlorella Vulgaris
title_short	Infuence Of Mass Transfer Towards Pilot-Scale Semi-Continuous Cultivation Of Chlorella Vulgaris
title_full	Infuence Of Mass Transfer Towards Pilot-Scale Semi-Continuous Cultivation Of Chlorella Vulgaris
title_fullStr	Infuence Of Mass Transfer Towards Pilot-Scale Semi-Continuous Cultivation Of Chlorella Vulgaris
title_full_unstemmed	Infuence Of Mass Transfer Towards Pilot-Scale Semi-Continuous Cultivation Of Chlorella Vulgaris
title_sort	infuence of mass transfer towards pilot-scale semi-continuous cultivation of chlorella vulgaris
granting_institution	Universiti Sains Malaysia
granting_department	Pusat Pengajian Kejuruteraan Kimia
publishDate	2020
url	http://eprints.usm.my/50385/1/Infuence%20Of%20Mass%20Transfer%20Towards%20Pilot-Scale%20Semi-Continuous%20Cultivation%20Of%20Chlorella%20Vulgaris.pdf
_version_	1747822033680465920

Infuence Of Mass Transfer Towards Pilot-Scale Semi-Continuous Cultivation Of Chlorella Vulgaris

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