integration of biological wastewater treatment and algal growth for biofuels

250 Pages·2014·4.85 MB·English

INTEGRATION OF BIOLOGICAL
WASTEWATER TREATMENT AND ALGAL
GROWTH FOR BIOFUELS

A thesis submitted to The University of Sheffield by
Philippa Jane Uttley

For the degree of
Doctor of Philosophy

APRIL 2014

Department of Chemical and Biological Engineering
Sir Robert Hadfield Building
Mappin Street
Sheffield S1 3JD
UK

For Graham and Jennie,
with love

ABSTRACT
This thesis is concerned with the production of biofuels from microalgae that can be
grown in wastewater on marginal land. Algal-derived biodiesel is a promising
alternative to both the finite reserves of fossil fuels and also the current biofuel
crops that take up agricultural land. The case for coupling biological wastewater
treatment to the production of algal biodiesel is a compelling one that is explored in
this research using a combination of mathematical modelling and laboratory
experiments.
Algae utilise by-products of the wastewater treatment process such as carbon
dioxide, nitrate and ammonia. In this work, a mathematical model of an integrated
wastewater treatment and algal cultivation system is presented. The model
contains two units: an activated sludge unit for secondary wastewater treatment
and a pond for the cultivation of algae. These units have both liquid phase and gas
phase integration. For the liquid phase, the treated effluent from the activated
sludge unit is transferred to the algal pond to provide nutrients for algal growth.
The model also incorporates gas-phase integration whereby the CO rich off-gas
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from the activated sludge unit is captured and used to enhance the algal growth. In
addition, the O enriched off-gas from the algal pond is recycled back to improve
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dissolved oxygen levels in the activated sludge unit.
The mathematical model uses equations for algal growth that were developed using
laboratory experiments to measure the effect of dissolved CO , nitrate and
2
ammonia on the growth kinetics of a typical strain of freshwater alga: Chlorella sp..
The model includes the industry standard Activated Sludge Model No. 3 for
wastewater treatment. An economic profit function is used in the model to find the
optimal pattern of gas phase integration to maximise Net Present Value over a
specified project lifetime. For the case considered, the model predicts that
integration using the gas and liquid exchange described above is necessary for a
profitable outcome. This is a general approach that can be used to retrofit biofuel
production onto an existing wastewater site, or design a new integrated system
from first principles.
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ACKNOWLEDGEMENTS
I would like to take this opportunity to extend my gratitude to my primary
supervisor, Dr Stephen Wilkinson, whose encouragement and guidance made this
work possible. His enthusiasm in explaining concepts that were completely new to
me has been very much appreciated. Steve’s innovative approach to problem-
solving and experimentation always kept things interesting; I feel lucky to have had
such an imaginative supervisor throughout the course of this research.
I am very grateful to my secondary supervisor, Dr Jim Gilmour, from the
Department of Molecular Biology and Biotechnology for advising me on all things
algal. Jim has shown great patience in explaining fundamental biology to a chemist,
even when I’ve asked for clarification on the most basic of concepts. I very much
appreciate the time and knowledge afforded to me, as well as the space to work in
a very busy laboratory.
I would further like to thank: Dr Stephen Palmer and MWH, for funding; The E-
Futures Doctoral Training Centre, its Director, Prof Geraint Jewell, Programme
Manager, Dr Neil Lowrie, and former Director, Prof Tony West; The Engineering and
Physical Sciences Research Council (EPSRC) and the RCUK Energy Programme.
Thanks also to my E-Futures colleagues for advising me on subjects outside my own
expertise, and to the members of Jim’s group who helped me in the lab with
equipment and algae.
Last but not least, my husband and daughter – thanks for making me smile at the
end of each day.

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TABLE OF CONTENTS
ABSTRACT ..................................................................................................................... 5
ACKNOWLEDGEMENTS ................................................................................................ 7
TABLE OF CONTENTS .................................................................................................... 9
LIST OF FIGURES ......................................................................................................... 13
LIST OF TABLES ........................................................................................................... 15
NOMENCLATURE ........................................................................................................ 17
CHAPTER 1 - INTRODUCTION ..................................................................................... 21
1.1 Background .................................................................................................. 21
1.1.1 The fuels crisis and climate change...................................................... 21
1.1.2 Biofuels ................................................................................................. 24
1.2 Project Aims ................................................................................................. 26
1.3 Contributions and Thesis Structure ............................................................. 29
CHAPTER 2 - LITERATURE REVIEW ............................................................................. 30
2.1 Microalgae ................................................................................................... 30
2.1.1 Characteristics and requirements for growth ...................................... 30
2.1.2 Algal biofuels ........................................................................................ 34
2.2 Biological Wastewater Treatment ............................................................... 36
2.2.1 Overview .............................................................................................. 36
2.2.2 The Activated Sludge Process .............................................................. 37
2.3 Process Integration and Energy from Waste .............................................. 40
2.3.1 History and use of process integration methods ................................. 41
2.3.2 Energy from waste ............................................................................... 43
2.3.3 Algae and industrial wastewater treatment ........................................ 46
2.4 Modelling and Optimisation of Biological Processes .................................. 47
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2.4.1 Mathematical Modelling ...................................................................... 47
2.4.2 Mathematical Optimisation ................................................................. 51
CHAPTER 3 - MODELLING METHODS ......................................................................... 56
3.1 Introduction ................................................................................................. 56
3.2 Modelling Software ..................................................................................... 56
3.2.1 CellDesigner .......................................................................................... 56
3.2.2 Sentero ................................................................................................. 57
3.2.3 Biological models.................................................................................. 58
3.2.4 Plant synthesis and design ................................................................... 58
3.3 Modelling Wastewater Treatment and Algal Growth ................................. 58
3.4 Modelling Continuous Processes................................................................. 62
3.5 Modelling Units Using Separate Gas and Liquid Compartments ................ 66
3.6 Process Economics ....................................................................................... 70
3.7 Optimisation ................................................................................................ 74
CHAPTER 4 - MATERIALS AND METHODS: MICROALGAE .......................................... 80
4.1 Materials ...................................................................................................... 80
4.1.1 Chemicals ............................................................................................. 80
4.1.2 Algal species ......................................................................................... 80
4.1.3 Algal culture medium ........................................................................... 80
4.1.4 Growth conditions ................................................................................ 81
4.1.5 Spectroscopy ........................................................................................ 82
4.1.6 Data processing .................................................................................... 83
4.2 Methods ....................................................................................................... 83
4.2.1 Cultivation of Chlorella sp. with varying concentration of NaNO ...... 83
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4.2.2 Cultivation of Chlorella sp. with varying concentration of NH Cl ........ 85
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4.2.3 Cultivation of Chlorella sp. with varying concentration of CO ........... 87
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