Biomethane potential test for rapid assessment of anaerobic digestion of sewage sludge

158 Pages·2015·2.68 MB·English

University of Wollongong
Research Online
University of Wollongong Thesis Collection University of Wollongong Thesis Collections
2014
Biomethane potential test for rapid assessment of
anaerobic digestion of sewage sludge: co-digestion
with glycerol and trace organic removal
Thanh Nguyen
University of Wollongong
Recommended Citation
Nguyen, Thanh, Biomethane potential test for rapid assessment of anaerobic digestion of sewage sludge: co-digestion with glycerol and
trace organic removal, Master of Philosophy thesis, School of Civil, Mining and Environmental Engineering - Faculty of Engineering
and Information Sciences, University of Wollongong, 2014. http://ro.uow.edu.au/theses/4398
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Faculty of Engineering and Information Sciences
School of Civil, Mining and Environmental Engineering

Biomethane potential test for rapid assessment of anaerobic
digestion of sewage sludge: co-digestion with glycerol and trace
organic removal

Thanh Nguyen

This thesis is presented as part of the requirements for the
award of the Degree of Master of Philosophy
from the University of Wollongong

March 2014
CERTIFICATION
I, Thanh Nguyen, hereby declare that this thesis, submitted in partial fulfilment of the
requirements for the award of Master of Engineering by Research Degree, to the
school of Civil, Mining and Environmental Engineering, Faculty of Engineering,
University of Wollongong is wholly my own work unless otherwise referred or
acknowledged. The document has not been submitted for qualification at any other
academic institution.

Thanh Nguyen
March 2014

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ABSTRACT
Anaerobic digestion (AD) is the most widely used treatment process for sewage
sludge stabilisation over concerns of public health. In addition, the production of
methane (CH ), a renewable fuel, has also shaped the prospective of AD within the
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context of energy security and global warming. This dissertation thus aimed to
evaluate two main aspects of the AD process of sewage sludge. First, the potential of
enhancing biogas production was assessed when co-digesting sewage sludge with
glycerol. Glycerol is a by-product of biodiesel production and then rich in organic
carbon. Second, the capacity of removing trace organic compounds (TrOCs) was
examined.
Results reported here suggest the stability of anaerobic conversion determined the
ultimate CH yield, greatly affecting the assessment of CH potential. Alkalinity
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buffer and inoculum over substrate (I/S) ratio were demonstrated to be important
factors in maintaining steady state of the AD process. The addition of NaHCO
3
resulted in an increase of CH production of sewage sludge that could be ascribed to
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well-buffered conditions for methanogens. A significant enhancement in CH yield
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from sewage sludge was achieved with an increase of I/S ratio from 1/9 to 1/1.
Adequate quantity of inoculum for degrading substrate was responsible for such
improvement. Moreover, no disruption of CH production was found since only
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0.25% and 0.5% glycerol of digested sludge (by volume) was applied. The obtained
ultimate CH yields of three types of glycerol were comparable, indicating that any
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glycerol was possibly used as a potential co-substrate of sewage sludge.
Additionally, the identification of appropriate values of alkalinity and I/S ratio for an
optimal CH production was dependent on key characteristics (i.e. pH and alkalinity)
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of sewage sludge and glycerol.
Experimental results from anaerobic co-digestion of raw primary sludge and glycerol
show that the addition of 0.5% and 1.0% of glycerol to raw primary sludge (by
volume) could improve the anaerobic sludge conversion in terms of the daily and
cumulative CH production. Carbon-rich content and high solubility of glycerol led
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to an increase only within the first seven days. Despite the buffer supplementation,
the instability of the AD process was clearly observed in this batch test through
characteristics of the feeds and digestates (acidic pH and low alkalinity for example),
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suggesting a shock of organic loading due to insufficient inoculum and extra organic
matter from glycerol. The feasibility of glycerol as a co-substrate of raw primary
sludge was satisfactory to give rise to CH generation. On the other hand, excessive
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addition of glycerol as a co-substrate may destabilise the AD process, and thus be
counter-productive.
The removal of TrOCs by AD was evaluated. The evolution of pH and alkalinity as
well as CH yields obtained from experiment data and kinetic analysis indicated a
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steady state of methanogenesis in TrOC-spiked bottles after 1.6 days. In a two-phase
matrix (i.e. sludge and water), TrOCs could partition (adsorb) to the solid phase as
well as the water phase. Their distribution in these phases was examined using a two-
phase fate model, which considers mass transfer (i.e. sorption and desorption). In this
study, the removal of the investigated TrOCs is defined as anaerobic biodegradation.
Their various removal efficiencies were consistently related to their molecular
properties in terms of functional groups rather than other physicochemical properties.
Compounds with the inclusion of halogen, methoxy and amine/amide groups
exhibited an effective removal while low or no removal efficiencies were observed in
compounds possessing alkyl functional groups. Regarding compounds possessing
high biodegradability (k > 0.001 L/gVS.d), water-solid partition coefficient (k )
b p
determined from the proposed two-phase fate model could describe their distribution
in the sludge phase better than their hydrophobicity (in terms of log D). For
biologically persistent compounds (k < 0.001L/gVS.d), sorption properties, which
b
can be predicted by log D values, were responsible for the fate of organic
contaminants in sludge matrix.
An economic design at laboratory scale of biomethane potential testing could rapidly
assess the AD of sewage sludge. Results also demonstrated increased methane yields
when using glycerol as a co-substrate of sewage sludge and trace organic removal
efficiency under anaerobic conditions. These findings are of great importance for
scaling up AD facilities in real wastewater treatment plants.
Keywords: anaerobic digestion, anaerobic co-digestion, biomethane potential,
sewage sludge, glycerol, trace organic compounds, sorption.
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ACKNOWLEDGEMENTS
Completion of my Master by Research at the University of Wollongong has not been
achieved by my efforts alone, but memorably contributed by many wonderful people
to whom I must express my honest thanks.
My sincere gratitude is offered to Professor Long Duc Nghiem who gave me a
precious opportunity to carry out my research in his Strategic Water Infrastructure
Laboratory along with his enthusiastic guidance and support, which led to significant
improvement in my academic writing and research skills. I must also sincerely thank
Associate Professor Muttucumaru Sivakumar, my co-supervisor for his insightful
comments and suggestions throughout my course.
A word of thanks must be also recorded to other team members associated with the
Strategic Water Infrastructure Laboratory for their commitment and companionship
throughout my study. I would also like to offer special thanks to Dr. Jinguo Kang for
his help regarding trace organic analyses and gratitude to Kaushalya Wijekoon for
her suggestions and assistance in some of the laboratory analyses and system
operations.
I would also express my thanks to our laboratory technicians, Mr. Robert Rowlan,
Mr. Frank Crabtree and our laboratory manager Dr. Ling Tie for their whole-hearted
assistance from the very first days of setting up my experiment system.
Thanh Hoa Province Government, Vietnam and the University of Wollongong are
greatly thanked for offering me the Master scholarship.
To my family, my heartfelt thanks are expressed for their unconditional love and
belief.
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TABLE OF CONTENTS
CERTIFICATION ........................................................................................................ i
ABSTRACT ................................................................................................................. ii
ACKNOWLEDGEMENTS ........................................................................................ iv
TABLE OF CONTENTS ............................................................................................. v
LIST OF FIGURES .................................................................................................. viii
LIST OF TABLES ..................................................................................................... xii
LIST OF ABBREVIATION ..................................................................................... xiv
1 INTRODUCTION .................................................................................................... 1
1.1 Background of the study ................................................................................. 1
1.2 Scope of study ................................................................................................. 3
1.3 Research objectives ......................................................................................... 3
1.4 Expected outcomes.......................................................................................... 4
1.5 Thesis outline .................................................................................................. 4
2 LITERATURE REVIEW.......................................................................................... 6
2.1 Sewage sludge ................................................................................................. 6
2.1.1 Types of sewage sludge ........................................................................... 6
2.1.2 Constituents of sewage sludge ................................................................. 9
2.2 Anaerobic sludge digestion ........................................................................... 11
2.2.1 Fundamentals of anaerobic digestion ..................................................... 11
2.2.2 Current status of the anaerobic digestion process .................................. 11
2.2.3 Factors influencing the anaerobic digestion process .............................. 14
2.2.4 Anaerobic digestion in sewage sludge treatment ................................... 18
2.3 Anaerobic co-digestion of sewage sludge with other substrates ................... 20
2.3.1 Advantages of anaerobic co-digestion in treating sewage sludge .......... 20
2.3.2 Current status of anaerobic co-digestion of sewage sludge and other
organic materials ................................................................................................ 21
2.4 The behaviour of trace organic contaminants during the anaerobic digestion
process .................................................................................................................... 29
2.4.1 Trace organic compounds and their effects ........................................... 29
2.4.2 Occurrence of emerging contaminants in sludge ................................... 30
2.4.3 Anaerobic digestion in the removal of trace organic compounds .......... 31
2.5 Summary ....................................................................................................... 34
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3 MATERIALS AND METHODS ............................................................................ 35
3.1 Materials ........................................................................................................ 35
3.1.1 Inoculum ................................................................................................ 35
3.1.2 Substrates ............................................................................................... 35
3.2 Experimental methods ................................................................................... 35
3.2.1 Biomethane potential test equipment ..................................................... 35
3.2.2 Experimental protocols .......................................................................... 36
3.2.3 Experimental description ....................................................................... 38
3.3 Analytical methods........................................................................................ 42
3.3.1 Basic parameters .................................................................................... 42
3.3.2 Chemical oxygen demand ...................................................................... 43
3.3.3 Methane yield calculation ...................................................................... 43
3.3.4 Trace organic analysis ............................................................................ 45
3.3.5 Viscosity of glycerol .............................................................................. 46
4 BIOMETHANE POTENTIALOF SEWAGE SLUDGE AND GLYCEROL ........ 48
4.1 Sewage sludge ............................................................................................... 48
4.1.1 Characteristics of sewage sludge ........................................................... 48
4.1.2 Effects of buffer supplement on the anaerobic treatment of sewage
sludge ................................................................................................................ 50
4.1.3 Methane production of sewage sludge ................................................... 56
4.2 Glycerol as a co-substrate ............................................................................. 62
4.2.1 Characteristics of pure and crude glycerol ............................................. 62
4.2.2 Variations of control parameters in the study of methanogenesis of
glycerol ............................................................................................................... 64
4.2.3 Methanogenic conversion of glycerol .................................................... 68
4.3 Summary ....................................................................................................... 74
5 ANAEROBIC CO-DIGESTION OF SEWAGE SLUDGE AND GLYCEROL .... 75
5.1 Characteristics of mixtures of sewage sludge and glycerol .......................... 75
5.2 Removal of volatile solids and chemical oxygen demand ............................ 79
5.3 Methane potential of co-digestion mixture of sewage sludge and glycerol .. 82
5.4 Summary ....................................................................................................... 90
6 FATE OF TRACE ORGANIC COMPOUNDS DURING ANAEROBIC
DIGESTION OF SEWAGE SLUDGE ...................................................................... 91
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6.1 Overall performance of AD of trace organics ............................................... 91
6.1.1 The variation of control parameters during over the digestion time ...... 91
6.1.2 Anaerobic conversion of trace organic compounds ............................... 94
6.2 Dynamics of trace organics under anaerobic sludge treatment ..................... 97
6.3 Removal performance of trace organic compounds under anaerobic sludge
treatment ............................................................................................................... 108
6.3.1 Overall removal of trace organic compounds ...................................... 108
6.3.2 Role of chemical structures .................................................................. 111
6.4 Fate of trace organic compounds in sludge matrix under anaerobic condition.
..................................................................................................................... 115
6.5 Summary ..................................................................................................... 120
7 CONCLUSIONS AND RECOMMENDATIONS ............................................... 121
7.1 Conclusions ................................................................................................. 121
7.2 Recommendations for future studies ........................................................... 123
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