mitigation of carbon dioxide from synthetic flue gas using indigenous microalgae

258 Pages·2017·4.79 MB·English

TITLE PAGE
MITIGATION OF CARBON DIOXIDE FROM
SYNTHETIC FLUE GAS USING INDIGENOUS
MICROALGAE

Submitted in fulfilment of the requirements
of the degree of
Doctor of Philosophy: Biotechnology
In the Faculty of Applied Sciences at
The Durban University of Technology

Virthie Bhola
2017

Supervisor: Professor Faizal Bux
Co-supervisor: Professor Feroz Mahomed Swalaha
MITIGATION OF CARBON DIOXIDE
FROM SYNTHETIC FLUE GAS USING
INDIGENOUS MICROALGAE
DECLARATION
VIRTHIE BHOLA

I hereby declare that this thesis, submitted for Doctor of Philosophy in
Biotechnology at the Durban University of Technology represents my own work.
It has not been submitted before for any diploma/degree or examination at any
other Technikon/University. Where use is made of any author’s work, it has been
duly acknowledged.
2017

Reference Declaration in Respect of a Doctor of Philosophy Thesis

I, Virthie Bhola (full name of student), Professor Faizal Bux, and Professor Feroz Mahomed
Swalaha (full name of supervisors) do hereby declare that in respect of the following thesis:
Mitigation of carbon dioxide from synthetic flue gas using indigenous microalgae

1. As far as we know and can ascertain:
(a) no other similar dissertation/thesis exists;
(b) the only similar dissertation/thesis(s) that exist(s) is/are referenced in this thesis

2. All references as detailed in the thesis are complete in terms of all personal
communications engaged in and published works consulted
APPROVAL

We hereby approve the final submission of the following thesis:
Mitigation of carbon dioxide from synthetic flue gas using indigenous microalgae
ABSTRACT

Fossil carbon dioxide emissions can be biologically fixed which could lead to the development
of technologies that are both economically and environmentally friendly. Carbon dioxide, which
is the basis for the formation of complex sugars by green plants and microalgae through
photosynthesis, has been shown to significantly increase the growth rates of certain microalgal
species. Microalgae possess a greater capacity to fix CO compared to terrestrial plants. Selection
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of appropriate microalgal strains is based on the CO fixation and tolerance capability, both of
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which are a function of biomass productivity. Microalgal biomass could thus represent a natural
sink for carbon. Furthermore, such systems could minimise capital and operating costs,
complexity, and energy required to transport CO to other places.
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Prior to the development of an effective CO mitigation process, an essential step should be to
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identify the most CO -tolerant indigenous strains. The first phase of this study therefore focused
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on the isolation, identification and screening of carboxyphilic microalgal strains (indigenous to
the KwaZulu-Natal province in South Africa). In order to identify a high carbon-sequestering
microalgal strain, the physiological effect of different concentrations of carbon sources on
microalgae growth was investigated. Five indigenous strains (I-1, I-2, I-3, I-4 and I-5) and a
reference strain (I-0: Coccolithus pelagicus 913/3) were subjected to CO concentrations of 0.03
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- 15% and NaHCO of 0.05 - 2 g/1. The logistic model was applied for data fitting, as well as for
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estimation of the maximum growth rate (µ ) and the biomass carrying capacity (B ). Amongst
max max
the five indigenous strains, I-3 was similar to the reference strain with regards to biomass
production values. The B of I-3 significantly increased from 0.214 to 0.828 g/l when the CO
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concentration was increased from 0.03 to 15% (r = 0.955, p = 0.012). Additionally, the B of
max
I-3 increased with increasing NaHCO concentrations (r = 0.885, p = 0.046) and was recorded at
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0.153 g/l (at 0.05 g/l) and 0.774 g/l (at 2 g/l). Relative electron transport rate (rETR) and
maximum quantum yield (F /F ) were also applied to assess the impact of elevated carbon
v m
sources on the microalgal cells at the physiological level. Isolate I-3 displayed the highest rETR
confirming its tolerance to higher quantities of carbon. Additionally, the decline in F /F with
v m
increasing carbon was similar for strains I-3 and the reference strain (I-0). Based on partial 28S
ribosomal DNA gene sequencing, strain I-3 was found to be homologous to the ribosomal genes
of Chlorella sp.

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The influence of abiotic parameters (light intensity and light:dark cycles) and varying nutrient
concentrations on the growth of the highly CO tolerant Chlorella sp. was thereafter investigated.
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It was found that an increase in light intensity from 40 to 175 umol m2 s-1 resulted in an
enhancement of B from 0.594 to 1.762 g/l, respectively (r = 0.9921, p = 0.0079). Furthermore,
max
the highest B of 2.514 g/l was detected at a light:dark cycle of 16:8. Media components were
max
optimised using fractional factorial experiments which eventually culminated in a central
composite optimisation experiment. An eight-factor resolution IV fractional factorial had a
biomass production of 2.99 g/l. The largest positive responses (favourable effects on biomass
production) were observed for individual factors X (NaNO ), X (NaH PO ) and X (Fe-EDTA).
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Thereafter, a three-factor (NaNO , NaH PO and Fe-EDTA) central composite experimental
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design predicted a maximum biomass production of 3.051 g/l, which was 134.65% higher when
compared to cultivation using the original ASW medium (1.290 g/l).

A pilot scale flat panel photobioreactor was designed and constructed to demonstrate the process
viability of utilising a synthetic flue gas mixture for the growth of microalgae. The novelty of
this aspect of the study lies in the fact that a very high CO concentration (30%) formed part of
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the synthetic flue gas mixture. Overall, results demonstrated that the Chlorella sp. was able to
grow well in a closed flat panel reactor under conditions of flue gas aeration. Biomass yield,
however, was greatly dependent on culture conditions and the mode of flue gas supply. In
comparison to the other batch runs, run B yielded the highest biomass value (3.415 g/l) and CO
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uptake rate (0.7971 g/day). During this run, not only was the Chlorella strain grown under
optimised nutrient and environmental conditions, but the culture was also intermittently exposed
to the flue gas mixture. Results from this study demonstrate that flue gas from industrial sources
could be directly introduced to the indigenous Chlorella strain to potentially produce algal
biomass while efficiently capturing and utilising CO from the flue gas.
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DEDICATION

For my dad, Mr Kemraj Bhola

For your endless love, support and encouragement. All of my achievements I owe to your
unwavering devotion.

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ACKNOWLEDGMENTS

I would like to acknowledge the following:

(cid:1) God Almighty without whom none of this would have been possible.

(cid:1) My dad, Mr Kemraj Bhola, for his steadfast strength, wisdom and faith.

(cid:1) My amazing husband, Mr Rakesh Bhana, for his help with multiple aspects of this thesis,
for his moral support and for always believing in me. Without your constant support and
encouragement this would not have been possible.

(cid:1) My brother, Mr Kamith Bhola, for been my constant pillar of strength and for always
been someone I could depend on.

(cid:1) Prof F. M. Swalaha, for his devoted efforts in assisting me throughout my research and
for all his guidance and encouragement in overcoming the various obstacles encountered
during my study. I cannot thank you enough for the time you have dedicated to assist me.

(cid:1) Prof F. Bux, for his advice, assistance and encouragement during the course of this
research project. His commitment to research excellence ensured that my project
conformed to the highest standards.

(cid:1) Mrs Trisha Mogany, for her dependable friendship and ever obliging advice and
assistance. I cannot thank you enough for your patience, support and understanding.

(cid:1) Dr S. Kumari, for her valuable contribution towards the successful submission of my
research article as well as supervision with molecular aspects of my study.

(cid:1) Dr M. Nasr, for his insightful knowledge and experience, especially towards the
submission of research publications.

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(cid:1) Dr K. Ramluckan, for assistance with gas chromatography studies and always going the
extra mile to ensure that all my academic endeavours were successful.

(cid:1) Miss Karen Reddy, a friend I could always rely on for her encouragement and support.

(cid:1) Mr Ismail Rawat, for his invaluable efforts and aid throughout my research project.

(cid:1) Staff and students at the Institute for Water and Wastewater Technology, Durban
University of Technology for their analytical support and guidance.

(cid:1) The National Research Foundation and Durban University of Technology for funding.

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PREFACE

Aspects of the work covered in the following thesis can be found in the following
publications:

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