Effects of CeO2 and ZnO Nanoparticles on Anaerobic Digestion and Toxicity of Digested Sludge

85 Pages·2013·8.15 MB·English

Effects of CeO and ZnO Nanoparticles on Anaerobic Digestion
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and Toxicity of Digested Sludge

by

Nguyen Minh Duc

A thesis submitted in partial fulfillment of the requirements for the
degree of Master of Science in
Environmental Engineering and Management

Examination Committee: Prof. Chettiyappan Visvanathan(Chairperson)
Dr. Oleg Shipin
Dr. Gabor Hornyak
Title Page

Nationality: Vietnamese
Previous Degree: Bachelor of Science in Biotechnology
University of Dalat, Vietnam

Scholarship Donor: Deutscher Akademischer Austausch Dienst
(DAAD), Germany – AIT Fellowship

Asian Institute of Technology
School of Environment, Resources and Development
Thailand
May 2013
i
Acknowledgements

I would like to express my deepestand profound gratitude to my advisor, Prof.C.
Visvanathan for his valuable guidance and supports and also his constant encouragement
that help me to complete this thesis. Working with him not just only develops my scientific
working method, but also greatly boosts my confidence and passion to continue this
profession.

I also would like to express my gratefulness to the examination committee members,Dr.
Oleg Shipin and Prof. Louis Hornyak,for their valuable advices and suggestions.

I like to express my special thank to Dr. Jega Jegatheesan of Deakin University, Australia
for providing nanoparticles and experimental supports for this research work.

I am grateful for the DAAD Scholarship that financially supports me to complete my
master degree here.

My special thanks give to all Professor Visu’s Research Team members, Mr. Le Minh
Truong, Mr. Nguyen Hong Phuc, and Mr. Paul Jacob for their constant assistances,
encouragement and above all, for being my friends.

I am thankful to all the administrative and laboratorial staffs of the Environmental
Engineering and Management Program for their support. Many thanks are also extended to
staffs and researchers in the Center of Excellent in Nanotechnology and Biotechnology
Laboratory for their guidance.

Finally, I would like to send my deepest gratitude to my grandmother, my parents, my
brother and everyone in my family for their love and care that give me inspiration and
encouragement to complete my master program in AIT.

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Abstract
With the rapid growth of nanotechnology in past decade, nanoparticles, such as CeO and
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ZnO, are now widely commercialized in many products. The industrialization and
commercialization of NPs have made the release of these compounds to the environment
and wastewater treatment plants become inevitable. However, many researchers have
found that conventional WWTPs can effectively remove NPs from the wastewater.It means
that the higher the removal efficiency of NPs, the higher NPs exist in the waste sludge.
Therefore, NPs can accumulate to a very high concentration in the waste sludge. However,
information about impact and toxicity of NPs on sludge treatment stream is still very
restricted. As a result, this research aimed to study abouteffects of CeO and ZnO NPs on
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sludge anaerobic digestion process, sludge dewatering process, and toxicity of sludge to
bacteria and plants.
The result showed that CeO and ZnO NPs could cause inhibition to the biogas production
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of anaerobic digestion system. The exposure concentration of ZnO at 1,000 mg/L caused
greatest inhibition to the biogas volume (65.3%) and the methane composition (40.7%), as
compared with controlled sample. In addition, at tolerable exposure concentration of ZnO,
the system could overcome the inhibition effect after 14 days of incubation. In the other
hand, CeO at low concentration of 10 mg/L could increase the generated biogas volume by
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11%. The positive effect of CeO at low concentration was also observed on bacterial
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toxicity test. The ZnO NPs was more toxic to bacteria than CeO NPs at same exposure
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concentration. However, the bacterial toxicity of both nanoparticles were reduced when
they were applied on the sludge. Moreover, after went through anaerobic digestion process,
the bacterial toxicity was again lessen. Additionally, required time to dewater the digested
sludge was increased proportionally with the exposure concentration of nanoparticles.
Finally, the accumulation of CeO and ZnO NPs on sludge made the digested sludge
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become unsuitable to be used as biosolid, since the contaminated digested sludge caused
great inhibition on root growth and seed germination of plants.
In conclusion, CeO and ZnO nanoparticles greatly impactedthe anaerobic digestion
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system by inhibiting the biogas production process. Moreover, they made digested sludge
become difficult to dewater. Besides, the toxicity of nanoparticles still remained even
afteranaerobic digestion process that could inhibit the bacterial viability and seed
germination and root growth of plants.

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Table of Contents

Chapter Title Page

Title Page i
Acknowledgements ii
Abstract iii
Table of Contents iv
List of Tables vi
List of Figures vii
List of Abbreviations viii
1 Introduction 1
1.1 Background 1
1.2 Objectives of Study 2
1.3 Scope of Study 2
2 Literature Review 3
2.1Nanoparticles 3
2.1.1 Definition 3
2.1.2 Classification of nanoparticles 4
2.1.3 Application of nanoparticles 5
2.1.4 Manufacture of nanoparticles 5
2.1.5 Cerium oxide nanoparticles 7
2.1.6 Zinc oxide nanoparticles 8
2.2 Nanoparticles in Environment 9
2.3 Nanoparticles in Wastewater Treatment Plants 10
2.3.1 Release of nanoparticles in wastewater treatment plants 10
2.3.2 Removal of nanoparticles in wastewater treatment plants 10
2.4 Toxicity of Nanoparticles 12
2.4.1 Toxicity of nanoparticles on various organisms 12
2.4.2 Toxicity mechanism of nanoparticles 14
2.5 Anaerobic Digestion 15
2.5.1 Introduction 15
2.5.2 Anaerobic digestion process 15
2.5.3 Factors influence anaerobic digestion process 16
2.5.4 Parameters indicate performance of anaerobic digestion 17
2.6 Sludge Dewatering 18
2.7 Effect of Nanoparticles on Anaerobic Digestion 19
2.8 Future Outlook of Nanotoxicity 19
3 Materials and Methods 22
3.1 Introduction 22
3.2 Preparation and Characterization of Nanoparticles 23
3.3 Preparation and Characterization of Sludge 23
3.4 Preparation of Substrate 23
3.5 Biochemical Methane Potential Test 23
3.5.1Experimental procedure 23
3.5.2 Analytical method and calculation 25
3.6 Capillary Suction Time 27
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3.7 Microbial Toxicity Test 27
3.7.1Culture of bacteria 27
3.7.2 Toxicity test procedure 28
3.7.3 Calculations of microbial toxicity test 29
3.8 Phytotoxicity Test 29
4 Results and Discussions 31
4.1 Nanoparticles Characteristics 31
4.2 Effects of Nanoparticles on Anaerobic Digestion 32
4.2.1Optimization of BMP test 32
4.2.2Effects of nanoparticles on biogas production 35
4.2.3Effects of nanoparticles on methane production 37
4.2.4Effects of nanoparticles on sludge characteristics 39
4.3 Effects of Nanoparticles on Sludge Dewatering 41
4.4 Effects of Nanoparticles on Bacterial Viability 42
4.4.1Bacterial toxicity of nanoparticles 42
4.4.2Bacterial toxicity of sludge containing nanoparticles 44
4.5 Effects of Nanoparticles on Plants 48
5 Conclusions and Recommendations 51
5.1 Conclusions 51
5.2 Recommendations for Future Study 52

References 53

Appendix A 57
Appendix B 59
Appendix C 65
Appendix D 67
Appendix E 70
Appendix F 73
Appendix G 75

v
List of Tables

Table Title Page
2.1 Nanomaterials in Nanotechnology 3
2.2 Nanoparticles Classification Groups 4
2.3 Applications of Nanoparticles in Various Fields 6
2.4 Sources of Nanoparticles in Environment 9
2.5 Fates of NPs in Various Unit Operations in WWTPs 11
2.6 Toxic Effects of Nanomaterials on Different Organisms 13
2.7 Advantages and Disadvantages of Anaerobic Digestion 15
2.8 Dewatering Performances of Various Techniques 18
2.9 Effects of CeO and ZnO NPs on Anaerobic Digestion 20
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2.10 Future Outlooks on Nanotoxicity 21
3.1 Analytical Parameters and Testing Methods 26
4.1 Particles Size of CeO and ZnO Nanoparticles 31
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4.2 Characteristics of Sludge Mixture Before and After AD 34
4.3 Characteristics of Digested Sludge at Various NPs Exposure 40
4.4 Inhibitions of NPs to Seed Germination and Root Growth 48

vi
List of Figures

Figure Title Page
2.1 Nanoscale materials 3
2.2 Nanoparticles manufacturing methods 7
2.3 Wastewater and sludge treatment processes in WWTPs 11
2.4 Sedimentation of nanoparticles into the sludge of WWTPs 12
2.5 Toxicity mechanisms of nanoparticles 14
2.6 Steps of anaerobic digestion process 16
3.1 Overall research methodology 22
3.2 Modified bottle for BMP test 24
3.3 CST apparatus 27
3.4 Overall microbial toxicity test procedure 28
4.1 Size distribution of CeO nanoparticles 31
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4.2 Size distribution of ZnOnanoparticles 32
4.3 Biogas production of BMP test at various I/S ratios 33
4.4 Methane gas compositions of various I/S ratio samples 35
4.5 Effects of CeO and ZnO nanoparticles on biogas production 35
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4.6 Total volume of biogas production 36
4.7 Possible mechanisms to overcome nanoparticles toxicity 37
4.8 Methane composition of various samples 38
4.9 Total volume of methane production of various samples 39
4.10 Effects of NPs on sludge dewatering 41
4.11 Protective mechanism of bacteria to overcome NPs toxicity 42
4.12 Bacterial toxicity of CeO nanoparticles dispersion 43
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4.13 Bacterial toxicity of ZnO nanoparticles dispersion 43
4.14 Cytoprotective mechanism of CeO NPs 44
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4.15 Bacterial toxicity of CeO NPs on sludge supernatant 45
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4.16 Bacterial toxicity of ZnONPs on sludge supernatant 46
4.17 Comparison of CeO NPs toxicity of different samples 47
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4.18 Comparison of ZnO NPs toxicity of different samples 47
4.19 Germination index of different samples 49
4.20 Toxicity of digested sludge on bacteria and plant 50

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List of Abbreviations

AD Anaerobic Digestion
BMP Biochemical Methane Potential
CFU Colony Forming Unit
CNTs Carbon Nanotubes
CODs Chemical Oxygen Demand soluble
CST Capillary Suction Time
DI Deionized
DLS Dynamic Light Scattering
DNA Deoxyribonucleic Acid
ENMs Engineered Nanomaterials
ENPs Engineered Nanoparticles
EPS Extracellular Polymeric Substance
GC Gas Chromatography
GI Germination Index
I/S Inoculum/Sludge
LB Luria-Bertani or Lysogeny Broth
NMs Nanomaterials
NOM Natural Organic Matter
NPs Nanoparticles
QDs Quantum Dots
ROS Reactive Oxygen Species
RPM Rounds Per Minutes
STP Standard Temperature and Pressure
TS Total Solid
UASB Upflow Anaerobic Sludge Blanket
UV Ultraviolet
VFA Volatile Fatty Acid
VS Volatile Solid
WWTPs Wastewater Treatment Plants

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Chapter 1

Introduction

1.1 Background
With the rapid growth of nanotechnology in past decade, nanoparticles (NPs) are now
widely commercialized in many products. NPs have been used in paint, coatings, catalysts,
biomedicine, cosmetics, skin creams, toothpastes and many other applications. Unique
physicochemical characteristics (e.g. magnetic, optical and electrical features) make the
use of NPs ideal in manufacture industries. Cerium oxide (CeO ) and Zinc oxide (ZnO)
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nanoparticles have been popular in recent years and they have been applied widely in many
fields. CeO NPs have been used as fuel catalyst to reduce harmful emission from engine
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combustion. Moreover, these have been used as fuel cell electrolyte, antioxidant,
semiconductor, UV absorber, coating and polishing chemical. ZnO NPs have been widely
commercialized in consumer products, such as antibactericide coating, sunscreen and other
industrial, medical and military applications.
The industrialization and commercialization of NPs have made the release of these
compounds to the environment becomes inevitable. NPs could be released either from the
production process or consumption of products to industrial and municipal wastewater
treatment plants (WWTPs). Recently, fate and transport of NPs in WWTPs and the toxicity
of NPs with biological activities of various treatment processes have been investigated.
These researches showed that NPs cause inhibition effects on biodegradation, nitrification
and anaerobic digestion process (Liu et al., 2011; García et al., 2012). However, many
researchers have found that conventional WWTPs can effectively remove NPs from
wastewater. Agglomeration and adsorption of nanoparticles play a major role in the
sedimentation of NPs in the sewage sludge, which resulted in low concentration of NPs in
effluent (Brar et al., 2010). It means that the higher the removal efficiency of NPs in
biological treatment, the higher NPs exist in the sludge. Therefore, NPs can accumulate to
a very high concentration in the waste sludge. However, impact and toxicity of NPs on
sludge treatment stream is still an abandoned area of research.
Settled sludge from sedimentation tank is collected and treated in various steps before
being sent to landfills or reused in other applications. Anaerobic digestion of waste sludge
from biological process is a popular technique because of its economic and environmental
benefits. The production of biogas from anaerobic digestion process is the main advantages
of this technique. However, it has been reported that nanoparticles in sludge can cause
adverse effects to the biogas generation of anaerobic digestion (García et al., 2012).
Therefore, the inhibition effect of nanoparticles on performance of anaerobic digestion
needs to be investigated. Moreover, the digested sludge after anaerobic digestion is usually
dewatered and then applied as soil conditioner, compost and other applications. However,
nanoparticles accumulated in sludge can make the sludge become toxic and inappropriate
to apply as biosolid. Therefore, information about phytotoxicity and bacterial toxicity of
digested sludge contaminated with nanoparticles is essential to have insights about the
reusability of waste sludge. In addition, the effect of nanoparticles to the dewaterability of
digested sludge is still unknown. So whether or not nanoparticles in sludge can hinder the
sludge dewatering process, toxicity of nanoparticles in sludge is eliminated during
anaerobic digestion or it causes inhibition effect on bacteria and plants, these are still
questions that need to be answered.
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The biochemical methane potential (BMP) test is a standard method to determine the
methane yield of anaerobic digestion process and to monitoring anaerobic toxicity. This is
a cheap, simple and reliable technique to estimate the rate and amount of methane
production in the process (Chynoweth et al., 1993). By using the conventional capillary
suction time (CST) test, dewaterability of digested sludge can be investigated. In addition,
microbial toxicity test is the common method to assess and monitor the environmental
pollution and toxic chemicals. Escherichia coli (E. coli) has been widely used as model
organism to test the toxicity of chemical and sludge. Phytotoxicity of nanoparticles is
commonly tested by studying the inhibition on seed germination and root growth. Tomato
(Solanum lycopersicum) and mung bean (Vigna radiata) have been popularly used as test
species and were recommended by US EPA(EPA, 1996).
In this study, effects of CeO and ZnO NPs on the methane gas production of sludge in
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anaerobic digestion process were investigated. Impacts of these nanoparticles on sludge
dewatering process were also studied. The toxicity of sludge before and after anaerobic
digestion were estimated, in order to know whether the toxicity of NPs could be eliminated
by anaerobic digestion or not. Phytotoxicity of digested sludge contaminated with
nanoparticles was studied to have conclusion on the reusability of digested sludge.
Therefore, results obtained from this study helped us to understand fate and effects of
CeO and ZnO NPs on the whole sludge treatment process.
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1.2 Objectives of Study
The main objectives of this study are:
1. To evaluate the effect of CeO and ZnO nanoparticles on biogas production from
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anaerobic digestion of sludge.
2. To evaluate the effect of CeO and ZnO nanoparticles on dewaterability of
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digested sludge.
3. To evaluate the bacterial toxicity and phytotoxicity of digested sludge containing
CeO and ZnO nanoparticles.
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1.3 Scope of Study
To achieve above objectives, the scope of this study is set as follow:
1. Biochemical Methane Potential (BMP) test was conducted in laboratory scale at
30oC to imitate the mesophilic anaerobic digestion process. The sludge wastaken
from UASB reactor of Singha Beer Factory.
2. E. coli was used as indicator bacteria to assess the bacterial toxicity of the sludge.
3. Seeds of tomato (Solanum lycopersicum) and mung bean (Vigna radiata) were
used in phytotoxicity test.
4. CeO and ZnO NPs concentration of 10; 100; 500 and 1,000 mg/L were used in
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this study.

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