CRANFIELD UNIVERSITY Rachel Louise Whitton Algae Reactors for Wastewater Treatment ...

240 Pages·2016·2.8 MB·English

by  Whitton, Rachel

CRANFIELD UNIVERSITY

Rachel Louise Whitton

Algae Reactors for Wastewater Treatment

School of Energy, Environment and Agrifood

EngD
Academic Year: 2015 - 2016

Supervisors: Prof. Bruce Jefferson & Dr Raffaella Villa
February 2016

CRANFIELD UNIVERSITY

School of Energy, Environment and Agrifood

EngD

Academic Year 2015 - 2016

Rachel Louise Whitton

Algae Reactors for Wastewater Treatment

Supervisors: Prof. Bruce Jefferson & Dr Raffaella Villa
February 2016

This thesis is submitted in partial fulfilment of the requirements for the
degree of EngD

© Cranfield University 2016. All rights reserved. No part of this
publication may be reproduced without the written permission of the
copyright owner.

Abstract
The onset of the Water Framework Directive (WFD) will challenge water utilities to
further reduce their wastewater phosphorus discharges to < 0.5 mg.L-1. Whilst
conventional treatments, such as chemical dosing, are able to meet these new discharge
consents, the strategies are representative of a linear economy model where resources are
unrecovered and disposed.
An alternative solution which can contribute to the aspiration of a circular economy is
microalgae. Microalgae are ubiquitous in wastewater environments and assimilate
phosphorus during their growth, to residual concentrations complementary of the WFD.
Furthermore, microalgal biomass can be anaerobically digested to produce biomethane
offering the potential for an energy neutral approach. However, uptake of microalgal
systems are lacking in the UK through limited knowledge of operation; and the belief that
such solutions are synonymous to large, shallow open ponds with extensive treatment
times. The development of alternative microalgal reactors are increasingly investigated
to overcome these implementation challenges. Of these, immobilised microalgae has
shown great potential; and whilst within its infancy demonstrates the greatest opportunity
for development and optimisation.
This thesis determines the critical operational parameters that influence the remediation
efficacy of immobilised microalgae for tertiary nutrient removal; including species
selection, biomass concentration, treatment period and lighting; with recommendations
for optimal performance. These recommendations are then applied to the design and
operation of an immobilised bioreactor (IBR) to understand the key design and operating
components that influence the overall economic viability. In doing so, the potential for an
IBR to be economically viable, within the next decade, in comparison to traditional
approaches are discussed.
Keywords: immobilisation, phosphate, nitrogen, circular economy

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Acknowledgments
My foremost thanks go to the members of the ‘algae team’. Headed, of course, by Prof.
Bruce Jefferson who pushed me to my intellectual limits and challenged me to achieve
my best. Not only have you supported me in achieving an EngD, but taught me to ‘man
up’ and ‘just do it!’ I appreciate all your encouragement and enthusiasm and the time you
committed to seeing me succeed (including your free time), I will be forever grateful.
I would like to especially thank Dr Raffaella Villa for her endless support and positivity.
You always managed to help me to step back from problems and issues, and realise that
they weren’t really problems at all. This is one of the many reasons why I couldn’t leave
you behind in Denmark!
To Dr Francesco Ometto, who taught me everything I know about microalgae! I really
enjoyed working with you and have many fond memories of our time together in the
microbiology lab. Your endless enthusiasm and ability to always put a smile on my face
contributed to ‘Whit-ton’ completing. I hope we always stay friends and wish you nothing
but the best.
I would like to thank Dr Marc Pidou for your friendship, support and technical assistance.
Your arrival in the ‘algae team’ reinvigorated the research, and your ability to think
outside the box allowed progress to be made at a point when I felt stuck in a rut. I’ll think
of you each and every time I drink a can of Coca Cola…!
Throughout the years, the ‘algae team’ have hosted a number of students whom I had the
pleasure in supporting and whose contribution helped progress themes of the research. I
thank Marie Chazaux, Amandine Le Mével, Vaiai Richmond, Marta San Juan Gomez and
especially Martina Santinelli for all your hard work and enthusiasm. I enjoyed getting to
know you all and learning about your home countries… which I am very much looking
forward to being invited to in the future..!
I express gratitude to David Inman and Adam Brookes of Anglian Water for making me
feel part of the AW team and providing guidance and support throughout the project. In
addition to Pete Vale of Severn Trent and Graeme Moore and Roi Otero of Scottish
Water, for your enthusiasm during the project and at the progress review meetings.
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I am extremely grateful for the technical support I received from my technician friends,
including Jane Hubble, Alan Nelson, Paul Barton, Rukshana Ormesher, Jan Bingham and
Maria Biskupska. Thank you for always being approachable, even when busy, and for
your guidance and the jokes we shared. I wonder if other students will find you can be
bribed with chocolate?
I am thankful to the STREAM administration; Paul Jeffrey, Ewan Mcadam and especially
Tania Rice for her support right up until the minute of my submission! Also, my fellow
Research Engineers in Cohort 2, in particular my Cranfield companions Catherine Rolph
and James Keeley. We did it!
To all my fellow PhD/EngD students in building 39/52a, especially Caroline Hepburn
and Frankie Hassard for your support and camaraderie even during the gloomiest days in
the ‘Room of Doom’ (with the help of the treat drawer!).
And of course to my Mum, Dad and sister Marie. Thank you for all your support and
encouragement through my entire studies. Thank you for always being there and your
constant belief in me. I’m very much looking forward to graduation and another set of
family air-brushed photos for us to display proudly within the family home.
Finally, I thank Michael Green (Dr!). We shared this experience together, through the
good and the bad, and I thank you for your support and understanding. I look forward to
the future and for us finally being able to sleep through the night without waking up with
the 3 am fear.
And as I always promised throughout the four/five years, I end my acknowledgements
with a quote from a boy band whom brightened up the gloomiest of writing up days…
‘All you people can't you see, can't you see? How your love's affecting our reality.
Every time we're down, you can make it right, and that makes you larger than life’
Backstreet Boys (1999)

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Table of Contents
Abstract ....................................................................................................................... i
Acknowledgments .................................................................................................... iii
List of Figures ......................................................................................................... viii
List of Tables ............................................................................................................ xi
List of Equations ..................................................................................................... xiii
Abbreviations ......................................................................................................... xiv
Introduction ........................................................................................1
1.1 Background .......................................................................................................1
1.1.1 Microalgae for wastewater nutrient remediation .......................................2
1.1.2 Understanding the route to implementation ..............................................3
1.2 Research Development .....................................................................................6
1.3 Aims and Objectives .........................................................................................7
1.4 Thesis Plan ........................................................................................................9
1.5 References ......................................................................................................13
Microalgae for Municipal Wastewater Nutrient Remediation:
Mechanisms, Reactors and Outlook for Tertiary Treatment ....................................17
2.1 Introduction ....................................................................................................18
2.1.1 Overview of Microalgal Nutrient Remediation Mechanisms .................19
2.2 Microalgal Bioreactor Configurations for Wastewater Nutrient
Remediation ..........................................................................................................28
2.2.1 High Rate Algal Pond (HRAP) ...............................................................32
2.2.2 Photobioreactor (PBR) ............................................................................32
2.2.3 Microalgal Biofilms .................................................................................33
2.2.4 Matrix-immobilisation .............................................................................33
2.3 Influence of Operational Parameters and Bioreactor Design on Remediation
Performance ..........................................................................................................34
2.3.1 Influent Nutrient Concentration and Treatment Period ...........................34
2.3.2 Light, Temperature and Biomass Productivity ........................................38
2.4 Conclusions and Key Remaining Challenges .................................................41
2.5 Acknowledgements ........................................................................................42
2.6 References ......................................................................................................42
Influence of Microalgal N and P Composition on Wastewater Nutrient
Remediation 53
3.1 Introduction ....................................................................................................54
3.2 Materials and Methods ...................................................................................57
3.2.1 Microalgal biomass culture and immobilisation .....................................57
3.2.2 Freshwater species characterisation - nutrient remediation and internal N
and P composition ............................................................................................57
3.2.3 Wastewater nutrient remediation trials for S.obliquus and C.vulgaris ....58
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3.2.4 Calculations for optimal biomass concentration for wastewater treatment
by S.obliquus and C.vulgaris – suspended and immobilised cultures ..............59
3.3 Results ............................................................................................................60
3.3.1 Freshwater species characterisation - nutrient remediation and internal N
and P composition ............................................................................................60
3.3.2 Wastewater nutrient remediation by S.obliquus and C.vulgaris .............64
3.3.3 Discussion: implications for an immobilised microalgal reactor for tertiary
wastewater nutrient remediation .......................................................................67
3.4 Conclusions ....................................................................................................72
3.5 Acknowledgements ........................................................................................72
3.6 References ......................................................................................................72
Tertiary Nutrient Removal from Wastewater by Immobilised
Microalgae: Impact of N:P Ratio and Hydraulic Retention Time (HRT) ................77
4.1 Introduction ....................................................................................................78
4.2 Materials and Methods ...................................................................................80
4.2.1 Wastewater ..............................................................................................80
4.2.2 Microalgae cultivation and immobilisation procedure ............................81
4.2.3 Experimental setup for continuous treatment ..........................................82
4.2.4 Sample analysis and biomass growth ......................................................84
4.3 Results and Discussion ...................................................................................85
4.3.1 Phosphate remediation .............................................................................85
4.3.2 Nitrogen remediation and pH ..................................................................88
4.3.3 Bead remediation characteristics .............................................................92
4.4 Conclusions ....................................................................................................94
4.5 Acknowledgements ........................................................................................94
4.6 References ......................................................................................................95
The Effect of Light on Wastewater Nutrient Remediation by
Immobilised Microalgae ...........................................................................................99
5.1 Introduction ..................................................................................................100
5.2 Materials and Methods .................................................................................102
5.2.1 Microalgal cultivation and immobilisation procedure...........................102
5.2.2 Wastewater ............................................................................................103
5.2.3 Experimental set up and light regime ....................................................103
5.2.4 Batch nutrient remediation sample analysis and biomass growth and yield
on light energy ................................................................................................105
5.2.5 Light transmittance ................................................................................106
5.3 Results ..........................................................................................................106
5.3.1 Impact of wavelength and PFD on nutrient remediation and growth ...106
5.3.2 Light attenuation ....................................................................................109
5.3.3 Light regimes .........................................................................................111
5.4 Discussion: Implications for lighting microalgae for wastewater nutrient
remediation .........................................................................................................119
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