CHARACTERIZATION AND KINETIC STUDIES OF

FAT, OIL AND GREASE DEPOSITION IN SEWER

PIPELINES

BY

IMAN A.F HUSAIN

A thesis submitted in fulfillment of the requirement for the

degree of Doctor of Philosophy (Engineering)

Kulliyyah of Engineering

International Islamic University Malaysia

May 2017

ii

ABSTRACT

Fat, Oil and Grease (FOG) may cause blockages of the sewer system and are a serious

environmental problem. FOG is usually produced at food service establishments

(FSE) or any other food preparation facility. In Malaysia, the eating habits of people

are changing, people are eating outside home more often and thus the number of food

outlets is increasing, which results in more blockages due to FOG deposition. FOG

continuous build-up decreases the capacity of the sewer system as it solidifies and

deposits on the interior walls of the sewer, causing blockage in pipes and hence

restricting the wastewater flow. Over the time, sewers blocked by FOG will fail and

overflow out of the manholes, which eventually could make its way to state water

sources. This research aims to study the deposition of FOG in sewer systems, its

mechanism, rates and causes. The methodology for this research consists of

characterization of the physical and chemical constituents of the FOG deposits; a

study of the effects of oil, salt, mono sodium glutamate (MSG), and detergent to form

FOG particles; a kinetics study of palm oil saponification and FOG deposition; and

modeling and simulation of the FOG deposition in sewer pipes. A pilot scale model of

a gravity sewer was designed and setup in the lab. Synthetic wastewater was used for

simulating actual domestic sewage. Continuous monitoring of the FOG deposition on

the pipe wall was done for 20 days. For the computational modeling, multiphase

Eularian model with discrete element method (DEM) in ANSYS FLUENT 14.0 was

employed to simulate the wastewater-FOG particles flow and deposition in a sewer

pipe. The model uses the Eularian method for the wastewater continuous phase while

the Lagrangian method is used to solve the motion equations for the FOG particles.

The simulations were carried out using a transient solver due to the unsteady state

nature of the turbulent flows. The main salts found in the wastewater samples were

Sodium (27.56 mg/l) and calcium (25.42 mg/l). Characterization of the deposit

samples showed that the FOG deposits are made of metallic soaps that formed during

cooking, and deposit in grease traps and/or along the sewer pipes by the saponification

reaction of oil and free fatty acids with salts such as sodium (1.71 mg/l), calcium (1.96

mg/l) and potassium (0.77 mg/l). The laboratory scale experiments indicated that FOG

particles form at 26±2 °C within few days. Moreover, the factors contributing the most

to the formation of FOG particles were oil and salt concentrations. Sodium and

calcium were the main salts contributing to the saponification reaction and resulted

with 402.5 and 258.335 mg/l FOG as TSS. An oil concentration of 700 mg/L and

sodium concentration of 50 mg/l lead to the formation of 433.3 mg/L TSS FOG.

Moreover, MSG resulted with the formation of larger volumes of FOG particles (600

mg/l), which indicates that MSG is an important sodium source contributing to

deposition and pipe blockages. The pilot scale operation resulted in 5 cm deposition

on the pipe wall within 20 days. The kinetics showed that the FOG saponification is

an autocatalytic first order reaction exhibiting a sigmoidal kinetic curve. The reaction

was at its highest rate between 30 minutes to 240 minutes. Sodium concentration is

the limiting factor of the saponification reaction. The CFD Eularian-DEM multiphase

model has shown good potential for simulating the wastewater flow and demonstrates

the applicability of CFD to simulate and track the transport and deposition of FOG

particles onto the sewer pipe walls.

iii

خلاصة البحثABSTRACT IN ARABIC

دمات الغذائية تنتهي بالترسب في أنابيب الصرف فق الخالدهون والزيوت والشحوم التي يتم انتاجها في المطاعم ومرا إنالصحي مما يؤدي إلى انسدادها والتسبب بمشكلة بيئية خطيرة. ومما يزيد من تفاقم المشكلة زيادة عدد المطاعم بسبب

تاج تغير عادات الأكل لدى الناس، حيث أن أعدادًا أكثر من الناس أصبحت تفضل الأكل خارج المنزل. إن تزايد إنالدهون والزيوت والشحوم يؤدي إلى المزيد من حالات انسداد المصارف والتي بدورها تؤدي إلى ارتجاع تدفق ميا الصرف

ويشكل فيضان مياه الصرف الصحي مشكلة بيئية خطيرة المجاري من فتحة غرفة التفتيش.الصحي وبالتالي فيضان المطاف إلى مصادر المياه وتسبب تلوثها. حيث أن المياه العادمة قد تجد طريقها في نهاية

يهدف هذا البحث إلى دراسة المواصفات الكيميائية والفيزيائية للترسبات الدهنية في أنابيب الصرف الصحي. كما ويهدف إلى دراسة أسباب وآليات ومعدل الترسب الزمني للدهون والزيوت والشحوم. ومن ضمن العوامل المدروسة

الجلوتومات الدهون والزيوت والشحوم فقد تمت دراسة تأثير الزيت والملح والمنظفات وكذلك ملح والمؤدية إلى ترسبالأحادية الصوديوم والتي تستخدم عادة لتعزيز النكهة في الطعام. باللإضافة إلى دراسة معدل تكون الصابون من زيت

رفة. ولدراسة الآلية والمعدل لتكون الترسبات في النخيل وتكوين حبيبات الدهون والزيوت والشحوم في درجة حرارة الغأنابيب الصرف الصحي فقد تم تصميم وبناء نموذج لنظام الصرف الصحي يحاكي نظام الصرف الصحي المستخدم في

يوما لرصد الترسبات المتكونة. وفي النهاية فقد تم تصميم نموذج حاسوبي يحاكي 02ماليزيا وتمت مراقبته على مدى Ansysه الصرف الصحي وترسب الدهون والزيوت والشحوم في أنابيب الصرف الصحي باستخدام برنامج تدفق ميا

Fluent 14.0 .وذلك باختيار نموذج المحاكاة الذي يوظف نظريات لاغرانج ويولر المتعدد الوسائط

من الصابون الناشيء عن لقد أظهرت نتائج الفحص المخبري لعينات الترسب أن المادة المترسبة تتكون بشكل أساسي نفاعل الدهون والزيوت والشحوم أثناء القلي والطهي وفي مصيدة الشحوم وأثناء تدفق مياه الصرف الصحي في الأنابيب. وقد نتجت هذه الترسبات من تصبن الزيوت والشحوم بالتفاعل مع أملاح الصوديوم والكالسيوم والبوتاسيوم

قليلة. وعلاوة على ذلك فإن تركيز الزيوت والأملاح يعد العامل الأهم في تصبن على درجة حرارة الغرفة خلال أيام الشحوم والزيوت والدهون وتكون الترسبات. كما أن ملح الجلوتومات أحادية الصوديوم يعد مصدر مهم للصوديوم

ن الترسبات بسمك الذي يساهم في عملية التصبن. وقد أظهرت تجربة نموذج الصرف الصحي الذي تم إنشاؤه عن تكو يوما. وأظهرة الدراسة التي أجريت لقياس معدل تصبن الزيت أن تفاعل الزيت مع الصوديوم هو 02سم خلال 5

دقيقة. وقد 042دقيقة واستمر حتى 02تفاعل ذاتي التحفيز ويتبع منحنى سيني يظهر من خلاله أن التفاعل بدأ بعد ل التصبن. أما نموذج المحاكاة الحاسوبي فقد أظهر قدرة نموذج لاغرانج ويولر تبين أن الصوديوم هو العامل المحدد لتفاع

متعدد الوسائط على محاكاة تدفق مياه الصرف الصحي وترسب جزيئات الشحوم والزيوت والدهون على جدران أنابيب الصرف الصحي.

iv

APPROVAL PAGE

The thesis of Iman A.F Husain has been approved by the following:

_____________________________

Ma’an Fahmi Alkhatib

Supervisor

_____________________________

Mohammed Saedi Jami

Co-Supervisor

_____________________________

Mohamed Elwathig Saeed Mirghani

Co-Supervisor

_____________________________

Zahangir Alam

Internal Examiner

_____________________________

Abdul Latif Ahmad

External Examiner

_____________________________

Azni Idris

External Examiner

_____________________________

S.M Abdul Quddus

Chairman

v

DECLARATION

I hereby declare that this dissertation is the result of my own investigations, except

where otherwise stated. I also declare that it has not been previously or concurrently

submitted as a whole for any other degrees at IIUM or other institutions.

Iman A.F Husain

Signature ........................................................... Date .........................................

vi

COPYRIGHT PAGE

INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA

DECLARATION OF COPYRIGHT AND AFFIRMATION OF

FAIR USE OF UNPUBLISHED RESEARCH

CHARACTERIZATION AND KINETIC STUDIES OF FAT, OIL

AND GREASE DEPOSITION IN SEWER PIPELINES

I declare that the copyright holders of this dissertation are jointly owned by the student

and IIUM.

Copyright © 2017 Iman A.F Husain and International Islamic University Malaysia. All rights reserved.

No part of this unpublished research may be reproduced, stored in a retrieval system,

or transmitted, in any form or by any means, electronic, mechanical, photocopying,

recording or otherwise without prior written permission of the copyright holder

except as provided below

1. Any material contained in or derived from this unpublished research may

be used by others in their writing with due acknowledgement.

2. IIUM or its library will have the right to make and transmit copies (print

or electronic) for institutional and academic purposes.

3. The IIUM library will have the right to make, store in a retrieved system

and supply copies of this unpublished research if requested by other

universities and research libraries.

By signing this form, I acknowledged that I have read and understand the IIUM

Intellectual Property Right and Commercialization policy.

Affirmed by Iman A.F Husain

……..…………………….. ………………………..

Signature Date

vii

ACKNOWLEDGEMENTS

All glory is due to Allah, the Almighty, whose Grace and Mercies have been with me

throughout the duration of my programme. Although, it has been a herculean task, His

Mercies and Blessings have given me ease and helped me complete this thesis.

I would like to express my deepest appreciation to Associate Prof. Dr. Ma’an

Alkhatib for his continuous support, encouragement and leadership, and for that, I will

be forever grateful. I put on record and appreciate his detailed comments, useful

suggestions and inspiring queries, which have considerably improved this thesis.

I wish to express my appreciation to and thanks to the co-supervisors

committee who provided time, effort and support for this project: thank you for

sticking with me.

It is my utmost pleasure to dedicate this work to my beloved husband

Mohamed Saleh, who granted me the gift of his unwavering belief in my ability to

accomplish this goal: thank you for your endless support and patience.

Finally, I would also like to express my gratitude to my dear parents and my

family for their support and love, which has always been my drive for pursuing my

goals in life.

viii

TABLE OF CONTENTS

ABSTRACT .................................................................................................................. II ABSTRACT IN ARABIC ........................................................................................... III APPROVAL PAGE ..................................................................................................... IV

DECLARATION .......................................................................................................... V COPYRIGHT PAGE ................................................................................................... VI ACKNOWLEDGEMENTS ........................................................................................ VII LIST OF TABLES ...................................................................................................... XII LIST OF FIGURES .................................................................................................. XIV

LIST OF ABBREVIATIONS ................................................................................ XVIII

LIST OF SYMBOLS ................................................................................................... III

CHAPTER ONE:INTRODUCTION ......................................................................... 1 1.1 Background .................................................................................................. 1 1.2 Problem statement ....................................................................................... 4 1.3 Significance of the study ............................................................................. 5

1.4 Research philosophy .................................................................................... 6 1.5 Research objectives ..................................................................................... 6

1.6 Research scope............................................................................................. 7 1.7 Thesis organization ........................................................................................... 7

CHAPTER TWO: LITERATURE REVIEW ........................................................... 9 2.1 Overview........................................................................................................... 9 2.2 wastewater: figures and facts .......................................................................... 10 2.3 Characteristics and typology of wastewater ................................................... 11

2.4 Wastewater network: historical development of the collection system in

Malaysia ................................................................................................................ 15

2.5 Sewer pipe system in Malaysia.................................................................. 19 2.5.1 Pipe Material ...................................................................................... 20

2.5.2 Pipe size .............................................................................................. 20 2.5.3 Design of the gravity sewer line ......................................................... 20

2.6 Issues related to municipal wastewater sewer systems.............................. 25

2.7 FOG ................................................................................................................ 26 2.7.1 Definition of FOG .............................................................................. 26

2.7.2 Chemical composition of FOG .......................................................... 26

2.7.3 Physical properties of FOG ................................................................ 28

2.7.4 Sources of FOG in the Sewer System ................................................ 29 2.7.5 Chemical and biological reactions related to FOG ............................ 30 2.7.6 Kinetics of FOG saponification .......................................................... 31 2.7.7 Effects of FOG deposition .................................................................. 32 2.7.8 Current control methods of FOG deposition ...................................... 33

2.7.9 Treatment of FOG .............................................................................. 34 2.7.10 Re-using FOG ................................................................................. 35 2.7.11 Studies on FOG Deposition in sewer pipes .................................... 37

2.8 Computational Fluid Dynamics (CFD) ..................................................... 39 2.8.1 An overview of CFD applications in sewer system and wastewater . 41

ix

2.8.2 Fundamentals of CFD modeling ........................................................ 44

2.8.2.1 Governing equations ..................................................................... 46 2.8.2.2 Turbulence modeling ..................................................................... 46

2.8.2.3 Multiphase modeling ..................................................................... 48 2.8.2.4 Numerical analysis ........................................................................ 50 2.8.2.5 Commercial CFD software packages ............................................ 51 2.8.2.6 Simulation of FOG deposition using ANSYS FLUENT .............. 52

2.9 Summary .................................................................................................... 55

CHAPTER THREE:METHODOLOGY: .............................................................. 56 3.1 Overview.................................................................................................... 56 3.2 Materials and Equipment ........................................................................... 57

3.2.1 FOG deposit and wastewater samples ................................................ 57

3.2.2 Vitrified clay pipe ............................................................................... 58 3.2.3 Oil as FOG source .............................................................................. 58

3.2.4 Synthetic wastewater .......................................................................... 59 3.2.5 Glassware ........................................................................................... 59 3.2.6 Filter papers ........................................................................................ 59 3.2.7 Equipment .......................................................................................... 60

3.3 Experimental Methods ............................................................................... 61 3.3.1 Characterization of the samples ......................................................... 62

3.3.1.1 Physical Characterization .............................................................. 62 3.3.1.2 Chemical Characterization ............................................................ 63

3.3.3 Screening of the metal salts that contribute to FOG formation .......... 64

3.3.4 Tests of oil and sodium effect on FOG particles formation ............... 66 3.3.5 Sodium dissociation monitoring ......................................................... 67

3.3.6 Tests of detergent effect on FOG particles formation ........................ 68 3.3.7 Tests of MSG effect on FOG particles formation .............................. 68

3.3.8 Kinetic study of palm oil saponification ............................................ 69 3.3.8.1 Kinetic experiment ........................................................................ 69 3.3.8.2 FTIR spectroscopy tests for detecting sodium soap ........................ 69

3.3.8.3 Data fitting and calculation of kinetic model constants ................ 70

3.3.9 Pilot scale study of FOG deposition ................................................... 71 3.3.9.1 Design of pilot scale sewer system................................................ 71 3.3.9.2 Pilot scale set up and operation ..................................................... 75 3.3.9.3 Calculation of the deposition rate .................................................. 78

3.4 CFD modeling and simulation ................................................................... 78

3.4.1 Bench marking and validation ............................................................ 79 3.4.2 CFD modeling and simulation of FOG deposition ............................ 80

3.4.2.1 Case description ............................................................................ 80 3.4.3 Mesh independency study .................................................................. 81

3.4.3.1 Creating Geometry ........................................................................ 81 3.4.3.2 Mesh generation ............................................................................ 82 3.4.3.3 Physics and solver set-up ................................................................. 82

3.4.3.4 Post processing of the simulation results ...................................... 83 3.4.4 Set up of the FOG deposition simulation model ................................ 83

3.4.4.1 General set-up of the solver and physics ....................................... 84 3.4.4.2 Models selection ............................................................................ 84 3.4.4.3 Materials list .................................................................................. 86

x

3.4.4.4 Phases interaction .......................................................................... 87

3.4.4.5 Setting the boundary conditions .................................................... 87 3.4.4.6 Solution Methods .......................................................................... 88

3.4.4.7 Solution controls ........................................................................... 88 3.4.4.8 Solution initialization and calculation activities ........................... 89 3.4.4.10 Post processing of the results ......................................................... 89

3.5 Summary .................................................................................................... 90

CHAPTER FOUR: RESULTS AND DISCUSSION .............................................. 91 4.1 Introduction................................................................................................ 91 4.2 Samples characterization and screening .................................................... 92

4.2.1 Sample Characterization .................................................................... 93 4.2.2 Screening of salts ............................................................................... 99

4.2.3 Summary of the first objective ......................................................... 101 4.4 Factors affecting FOG deposit formation ................................................ 102

4.4.1 Effect of Sodium and Oil concentrations ......................................... 102 4.4.1.1 Experimental results of FOG optimization experiment .............. 102 4.4.1.2 Anova analysis and model fitting................................................... 105

4.4.2 Monitoring of Conductivity, pH and TDS ....................................... 108

4.4.3 Effect of LiQuid detergent ............................................................... 111 4.4.4 Effect of MSG .................................................................................. 112

4.4.5 Summary of the second objective .................................................... 115 4.5 Mechanisms of FOG deposit formation .................................................. 115

4.5.1 Pilot scale operation ......................................................................... 116

4.5.2 Understanding the saponification of FOG inside the sewer pipe ......... 121 4.5.3 Mechanistic Model of FOG Particles Deposition on the Sewer Pipe ... 122

4.5.4 Characterization of FOG Deposits Samples Collected from the Pilot

Scale Operation .............................................................................................. 123

4.5.5 Summary of third Objective .................................................................. 124 4.6 Kinetic study of the cold saponification of palm oil..................................... 125

4.6.1 Kinetics of Palm Oil Saponification using FTIR Absorbance .............. 127

4.6.2 Data Fitting and Saponification Kinetic Parameters ............................. 128

4.6.3 Summary of the fourth Objective ......................................................... 131 4.7 CFD simulation ............................................................................................. 131

4.7.1 Mesh Independence Study ............................................................... 132 4.7.2 Simulation of FOG Deposition ........................................................ 136

4.7.2.1 Velocity profiles .......................................................................... 140

4.7.2.2 Volume fraction ........................................................................... 145 4.7.2.3 Particle tracking .......................................................................... 146

4.7.3 Summary of the fifth objective ......................................................... 147 4.8 General summary ..................................................................................... 147

CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS ................ 149 5.1 Conclusions ............................................................................................. 149

5.2 Recommendations.................................................................................... 151 REFERENCES ....................................................................................................... 153

LIST OF PUBLICATIONS .................................................................................... 174 APPENDIX A ........................................................................................................... 176

xi

Terms for Multiphase CFD .................................................................................... 176

APPENDIX B ........................................................................................................... 178 Methods for improving modeling accuracy ........................................................... 178

APPENDIX C ........................................................................................................... 181 Generating the dependent and independent pi’s .................................................... 181

APPENDIX D ........................................................................................................... 183 Bench mark case for validation .............................................................................. 183

B.1 Case description ....................................................................................... 183 B.2 Creating the Geometry ............................................................................. 185 B.3 Creating the mesh .................................................................................... 186

B.4 General set up .......................................................................................... 187 B.5 Models selection ...................................................................................... 187

B.6 Setting the boundary conditions .............................................................. 187 B.7 Solution controls ...................................................................................... 188 B.8 Measurements .......................................................................................... 188 B.9 Results ..................................................................................................... 188

xii

LIST OF TABLES

Table No. Page No.

2.1 Typical composition of untreated domestic wastewater 13

2.2 EPA's conventional and nonconventional pollutants category 14

2.3 Average characteristics of selected industrial wastewaters 14

2.4 Major development of the sewerage sector in Malaysia 17

2.5 Population equivalent (PE) 21

2.6 Normal pipe roughness for gravity sewer 22

2.7 Typical roughness coefficient, ks 23

2.8 Typical Manning coefficient, n 24

2.9 Typical values for Hazen-Williams Coefficient, C 24

2.10 Most common FFAs 27

2.11 Most popular commercial CFD packages 52

3.1 Composition of synthetic wastewater 59

3.2 List of equipment employed in the experiments 60

3.3 Fixed conditions of the lab experiments 66

3.4 Selected options for the optimization model 66

3.5 Design of the optimization runs using RSM 67

3.6 The repeating parameter of the dimensional analysis 72

3.7 The Dimensionless parameters obtained from the Bukingham method 72

3.8 Calculated dimensions of the scaled down pilot model 74

3.9 The general specs of the computational workstation 78

3.10 Statistics and sizes of the generated grids 82

3.11 Characteristics of wastewater and FOG 86

xiii

3.12 Phase interaction models for DPM-wastewater 87

3.13 Boundary conditions for all phases 88

3.14 Under-relaxation factors for the solution controls 89

4.1 Characterization results for FOG and Waste water samples 94

4.2 FOG and TSS analyzed by Wong et al (2007) 96

4. 3 Screening experiment with used oil 100

4.4 FOG concentrations with different oil and NaCl Concentrations 103

4.5 Lack of fit tests for each of the fitting models 105

4.6 Analysis of variance for the selected model 106

4.7 Experiments of effect of oil and sodium concentrations on FOG

particles formation 109

4.8 Mean values for FOG particle formations 113

4.9 Characterization of FOG deposits and wastewater samples collected

from pilot scale experiment 124

4.10 Absorbance between 1750-1735 cm-1 129

4. 11 Goodness of the sigmoidal fit 130

4.12 Comparison of the convergence of the coarse, medium and fine mesh 133

D.1 Under relaxation factors for the validation case 182

xiv

LIST OF FIGURES

Figure No. Page No.

2.1 Institutional framework for sewerage management in Malaysia

(Hamid and Narendan, 2004) 17

2.2 Regulatory bodies of IWK services and effluent discharge 19

2.3 Design of grease trap 30

2.4 Iterative general modeling procedure (ANSYS, Fluent user's guide:

Version 6.3, 2007) 42

2.5 Steps for performing grid-independence study ( LEAP CFD Team, 2012) 51

3. 1 The Identified manhole with FOG deposition 58

3.2 Flow chart showing the summary of the research methodology 61

3.3 Experimental setup of salts screening runs 65

3.4 A schematic of the sewer pipe problem 71

3.5 Schematic diagram of the gravity sewer model 76

3.6 Schematic of the bench mark case of U bend pipe 80

3.7 Description of the simulated pipe 81

4.1 Collected wastewater and FOG samples 93

4.2 FOG deposit samples after drying in oven 94

4.3 Screening experiments with used palm oil 101

4.4 Effect of oil and sodium concentration on FOG particles formation 103

4.5 Effect of oil concentration (mg/L) on FOG particles (mg/L) 104

4.6 Effect of sodium concentration (mg/L) on FOG (mg/L) 105

4.7 Comparison of actual and predicted FOG (mg/L) 107

4. 8 Effect of FOG and initial Na concentrations on the final Na concentration 108

4.9 Monitoring electrical conductivity of the six prepared flasks and blanks 110

xv

4.10 FTIR spectra of FOG particles with addition of NaCl as sodium source 111

4.11 FTIR spectra of FOG particles with addition of detergent 112

4.12 Comparison between the FOG particles formed by additions of

a) MSG b) MSG+NaCl c) NaCl 113

4.13 FTIR spectra of FOG particles with MSG as the sodium source 114

4.14 Monosodium glutamate chemical structure 114

4.15 FOG deposition thickness onto the sewer pipe wall 116

4.16 FOG deposition in pipe after 5 days 118

4.17 FOG deposition in pipe after 10 days 119

4.18 FOG deposition in the pipe at day 20 120

4.19 Saponified FOG curd collected from the pipe at day 20 121

4.20 Soap forms micelles in wastewater with the carboxylate groups

on the surface and the nonpolar tails in the interior (Smith M., 2001) 122

4.21 A mechanistic model representing the mechanism of soap particles

deposition on the pipe wall 123

4.22 Saponification reaction of oil under basic conditions (NsB notes, 2011) 125

4.23 Saponification reaction experiment at time 0, 2, and 8 hours 126

4.24 Sigmoidal plot of the saponified oil along the 8 hours reaction 128

4.25 Plot of the actual and calculated absorbance values by the sigmoidal fit 130

4. 26 Velocity development along the center line of the pipe 133

4.27 Velocity profile at the outlet horizontal centerline 134

4.28 Velocity contours for the fully developed wastewater flow in

coarse (a), medium (b), and fine(c) mesh 134

4.29 Wall Y+ for coarse (red), medium (black) and fine (green) mesh 135

4.30 Mesh independency study: comparison of the average velocity at

the outlet 136

4.31 Geometry of the computational domain of the flow in the sewer pipe 137

xvi

4.32 Inflation layers of the medium quality tetrhedral mesh 138

4.33 Tetrahedral mesh of the wastewater fluid domain inside the sewer pipe 138

4.34 FOG particles diameter distribution along the centerline of the pipe 140

4.35 Contours of the velocity magnitude of FOG particles at the inlet 141

4.36 Contours of FOG particles velocity at the outlet 142

4.37 FOG particles velocity at the center line 142

4.38 Wastewater velocity distribution at the center line 143

4.39 Wastewater velocity distribution at the outlet horizontal line 144

4.40 FOG particles velocity at the outlet center line 144

4.41 Contours of the FOG particles volume fraction 145

4.42 FOG particles concentration at the outlet horizontal line 146

5.1 Suggested model for the control of FOG at the source 152

C.1 Ten iterative steps for CFD model development and evaluation 180

D.1 Schematic diagram of the U bend pipe 183

D.2 Locations at which the measurements were recorded 184

D.3 Pipe Geometry using Ansys Design Modeler 186

D.4 Structured mesh of the curved pipe 187

D.5 Axial velocity contours 189

D.6 Axial velocity contours obtained by (Azore Technologies, LCC) 189

D. 7 Vertical plane S/D= -1 (inlet side) 190

D. 8 Axial velocity magnitude (m/s) versus the radius of the pipe at

vertical plane, S/D= +1 (outlet side) 191

D. 9 Axial velocity at vertical plane S/D =18 (at the outlet) 191

D.10 Axial velocity at the bend at θ=157.5° 192

D.11 Axial velocity at the bend at θ= 67.5° 192

xvii

D.12 Axial velocity at the bend at θ= 112.5° 193

D.13 Contours of the Reynolds stress 193

D.14 Reynolds stresses at the bend at 157.5° 194

D.15 Reynolds stresses at the bend at 67.5° 194

D.16 Reynolds stresses at the bend at 122.5° 195

xviii

LIST OF ABBREVIATIONS

Ca Calcium

CFD Computational fluid

dynamics

CST Communal septic tank

DEM Discrete element

method

DPM Discrete phase model

EFM Environmental fluid

mechanics

EPA Environmental

protection agency

FFA Free fatty acids

FOG Fat, oil, and grease

FSEs Food service

establishments

GI Grease interceptor

GT Grease trap

IST Individual septic tank

IT Imhoff tank

IWK Indah water konsortium

K Potassium

MSG Monosodium glutamate

Na Sodium

PE Population equivalent

POME Palm oil mill effluent

PVC Polyvinyl chloride

RC Reinforced concrete

Re Reynolds number

RSM Response surface model

SSA Sewerage service act

SSOs Sanitary sewer

overflows

TAGs Triacylglycerides

TSS Total suspended solids

VCP Vitrified clay pipe

iii

LIST OF SYMBOLS

µ Viscosity (kg/m.s)

A Sewer pipe cross

sectional-area

C Oil concentration

C Hazen-Williams

coefficient

D Internal diameter (m)

Dh Hydraulic diameter

DP FOG particle diameter

Ɛ Roughness height

ɛ Turbulent dissipation

Ɛp Surface roughness of

particles

g Acceleration due to

gravity (m/s2)

hL, minor Minor head losses

hL,major Major head losses

K Kinetic energy

KL Head losses coefficient

Ks Roughness coefficient

Lc Characteristic length of

the pipe

Lh,turbulent Hydrodynamic entry

length for turbulent flow

n Manning coefficient

N Number of FOG particle

Patm Atmospheric pressure

Q Wastewater flow rate

R Hydraulic radius (m)

S Hydraulic gradient

SG4°C Specific gravity at 4 °C

t Time

Tc Thickness of the

deposition layer

U Wastewater flow

velocity

V Velocity (m/s)

Vp Particles velocity

ꝭ Friction factor

ρ Density (kg/m3)

ρ Wastewater density

ρp FOG particles density

τW Shear stress

Ѳ Pipe slope

ѵ Kinematic viscosity of

water (m2/s)

CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND

Throughout history, wastewater has evolved to be a serious environmental concern for

industrialized societies trying to cope with the explosion in human population

numbers. One of the greatest challenges of wastewater is sanitary sewers blockages

due to accumulation of fat, oil, and grease (FOG). Sanitary sewer overflows (SSOs)

have a great impact on the public health and the environment. SSOs can spill raw

untreated sewage out of manholes and onto city streets, playgrounds, streams, rivers

and lakes before it can reach a treatment facility.

There are several causes of SSOs, including failing, outdated infrastructure and

poor sewer management. When sewage collection systems are inadequate the impacts

on the health of the community and on the environment can be extremely serious.

Sewage pollutes our waters with pathogens, excess nutrients, heavy metals and other

contaminants. Sewage carries pathogens that can possibly contaminate our drinking

water supplies causing diarrhea, vomiting, respiratory and other infections, hepatitis,

dysentery and other diseases (American rivers, 2014). It is reported that 1.6-2.5

million deaths occur annually due to diarrhea in children under the age of 15 (Mara et

al., 2010).

SSOs occur because of too much rain or snowmelt infiltration through the

ground into leaking sanitary systems. It can also happen if the sewers and pumps are

too small to carry sewage from newly developed subdivisions or commercial areas.

Blocked pipes and other equipment are one of the major reasons that cause

SSOs all over the world. It is estimated that 23,000 to 75,000 SSOs occur every year

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in the United states, approximately 48% are due to line blockages, of which 47% are

related to fat, oil and grease (FOG) (He et al., 2011). Over 25,000 flooding incidents

are happening in the UK every year with FOG contributing to over 50% of these

incidents (Williams et al., 2012). Moreover, there are numerous blockages throughout

Malaysia every year, in the years 2011-2013 the number of service complaint due to

sewer blockages has increased from 19,245 to 21,578 which makes 58% of the overall

service complaint received by IWK to be related to public sewer blockages while in

the years 2015- June 2016, 50-55% of the complaints received were public sewer

blockage, out of which 45% is due to FOG, the remaining is due to dumping large

solid waste, growth of tree roots into the pipes,..etc. (IWK, 2013).

Fat, oil and grease that may cause blockage of the sewer system is a serious

environmental problem. FOG is usually produced at food service establishments

(FSE) or any other food preparation facility. The by-products and wastes from these

FSE include meat, sauces, gravy, dressings, deep-fried food, baked goods, cheeses and

butter (GARZA, 2004). All of the aforementioned waste products are considered FOG

and may build up in the sewer system when discharged directly into the facility’s

plumbing system. Other sources of FOG might be from the industrial activities such as

palm oil mill effluent (POME) and automobile workshop discharges.

In Malaysia, the eating habits of people are changing. People are eating more

frequently outside the home and thus, the numbers of food outlets are increasing (Tan

and Yeap, 2012). According to a global analysis report, the number of consumer food

service outlets has increased from 8,358.8 in 2008 to 11,064.4 in 2014 (Agriculture

and Agri-food Canda, 2014). With more food service outlets opening, the

consumption of FOG will increase and therefore, the issue of SSOs due to FOG will

become worse if no measures were taken to control the deposition incidents.

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Despite the fact that SSOs due to FOG is an ongoing problem, only a few

studies have been conducted in the US, the UK and Korea to understand the causes of

FOG deposition and its composition (He et al., 2011; Williams et al., 2012; Shin et al.,

2015). However, it is thought that the composition and the characteristics of FOG

deposits could vary with differences in the culture, climate, type of sewer system, and

eating habits of people. However, in the Malaysian case there is a lack of scientific

understanding of FOG deposits and its mechanisms. In fact, no comprehensive study

of the issue in Malaysia has been undertaken, until now.

Whilst the above-mentioned researches provided an insight into the

composition of the deposits, elude to some factors which influence the deposit

formation, pertain to the regions in which the studies were conducted, a more

sophisticated approach is needed in order to provide a tool for analyzing all the

potential factors and conditions that may contribute to the formation of the FOG

deposition.

The developments within the last decades of both numerical techniques and

the increase in computational power has enabled the wide application of

computational fluid dynamics (CFD) methods, in many areas of fluid dynamics,

including environmental fluid mechanics (EFM). Cushman-Rosin & Gualtieri (2008)

defined environmental fluid mechanics as the scientific study of naturally occurring

fluid flows or air and water on our planet Earth, especially those that affect the

environmental quality of air and water. Within EFM, for many years, CFD methods

have found a wide application in the analysis of natural water systems, such as rivers,

lakes, estuaries and coastal waters. Examples of such applications include the study of

the flow, transport and mixing of contaminants and sediments within those systems.

Also, CFD methods have been applied in wastewater engineering. Some of the

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applications include analysis of combined sewer systems overflows (Dufrense et al.,

2009), evaluation of the efficiency of activated sludge reactor (Karama et al., 1999),

design of channel hydraulic flocculation (Liu et al., 2004), evaluation of disinfection

calculation methods (Wols et al., 2010), municipal sewer system design (Chen et al.,

2013) and modeling of solid transport (Torres et al., 2008). Therefore, CFD could be

used in the study of FOG deposit formation in the sewer pipelines.

This research aims at studying the deposition of FOG in sewer systems, in

terms of its mechanism, causes and rate. The methodology for this research consists of

characterization of the physical and chemical constituents of the FOG deposits, the

study of the kinetics of FOG deposition using an experimental system specially

designed and fabricated for this study, and computational modeling and analysis of the

factors influencing FOG deposition. It is foreseen that this study will provide a

comprehensive understanding of FOG deposition for Malaysia.

1.2 PROBLEM STATEMENT

Sullage or greywater sources (primarily kitchen waste and those from restaurants)

typically contain elevated oil and grease levels. In the past (and even present) these

sources were channelled to public drains. This is a practice that contravenes the Street,

Drainage and Building Act, 1974 (Ujang and Henze, 2006). As a consequence,

streams and rivers become polluted, and aquatic life is threatened due to

contamination from untreated sullage. To mitigate the problem, the Malaysian

Government started adopting the policy of combined and centralized sewage systems

as part of the National Sewerage Development Plan. The strategy is to basically

channelize both sullage and sewage sources to sewage treatment plants (STPs) to

undergo further treatment. The operational consequence of the policy is that waste

5

high in concentration of oil and grease will also enter the sewage network. This

inadvertently causes blockages due to deposition/accumulation and subsequently,

result in sanitary sewer overflows (SSOs). The maintenance cost has also increased

and has become burdensome to the national sewage operator, Indah Water

Konsortium (IWK). The study, therefore, will add value to the adopted method of

sullage treatment for environmental preservation.

Wastewater treatment plants in Malaysia are not capable of handling a high

load of FOG which has subsequently increased the level of FOG in Malaysian rivers.

In the other hand, the wastewater municipalities, whom are responsible for

maintaining the collection systems, give little guidance on the effective control and

prevention methods for FOG deposition. Most of the previous studies focused on the

treatment and reuse of FOG while there is a substantial lack of scientifically-based

information regarding the causes and mechanism of FOG deposit formation.

1.3 SIGNIFICANCE OF THE STUDY

FOG has been identified as an emerging pollutant of concern (EPC) in Malaysian

wastewater streams. FOG is increasing in volume due to the expansion in oil

processing industries and food service establishments (Alade et al., 2011).

Understanding the mechanism in which FOG deposits form and the factors

influencing its formation will greatly help in setting the best management practices for

handling FOG at the source. Moreover, the research outcomes will benefit the

wastewater utilities in controlling, predicting and treatment of FOG deposition by

providing a better understanding of the chemical and physical constituents of the

deposition.