“WATEQ” Debye-Hückel Equation

87 Pages·2011·8.49 MB·English

FACULTY OF BIOSCIENCE ENGINEERING
CENTRE FOR ENVIRONMENTAL SANITATION
Academic Year 2010 – 2011

ANAEROBIC DIGESTION OF MANURE: IMPROVED MODELLING
BY TAKING INTO ACCOUNT PHYSICOCHEMICAL EFFECTS

Kimberly Solon

Promotor: Prof. dr. ir. Eveline Volcke

Master Dissertation to obtain the degree of
M.Sc. in ENVIRONMENTAL SANITATION
Deze pagina is niet beschikbaar omdat ze persoonsgegevens bevat.
Universiteitsbibliotheek Gent, 2021.
This page is not available because it contains personal information.
Ghent University, Library, 2021.
ACKNOWLEDGEMENTS

ACKNOWLEDGEMENTS

First and foremost, I would like to express my deepest gratitude to my promotor Prof. dr. ir.
Eveline Volcke. She has been very supportive, guiding, and motivating throughout the
completion of this work. Her contributions of time and ideas are greatly valued. Her advices
were not only essential to this work but also helped me gain insights into the workings of
academic research in general.
I am also thankful to the staff at the Centre for Environmental Sanitation: Prof. van den
Heede, Veerle, Sylvie, and Isabel. They have all, in one way or another, helped make my
studying in Ghent University and staying in Belgium a wonderful experience.
My sincerest thanks also goes to VLIR-UOS for the wonderful opportunity provided to me,
without which, this study would not have been possible.
And lastly, I would also like to thank my family for being supportive of me during my time
away from them. Living far from them has taught me to appreciate and love them more. I
dedicate this work to them.

Kimberly Solon
Ghent, Belgium
August 2011
i
SUMMARY

SUMMARY

Anaerobic digestion is an old waste stabilization technology which is becoming widely-used
and studied because of its additional advantage of energy production, thus considered as a
sustainable technology. One of the advances in the field of anaerobic digestion is the
development of the Anaerobic Digestion Model 1 (ADM1), a structured model with the
biochemical processes categorized into five steps of disintegration, hydrolysis, acidogenesis,
acetogenesis, and methanogenesis, and with the physicochemical processes classified as
liquid-liquid, gas-liquid, and liquid-solid processes.
In the ADM1, several processes are omitted which are considered as the limitations of the
model. One of those limitations is the exclusion of ion activity corrections because it was
assumed that anaerobic systems, in general, are dilute systems containing insignificant
amount of ions. However, there are particular anaerobic systems with high levels of ions,
such as those used for anaerobic digestion of cattle manure, that it is essential to include
corrections for non-ideality. This study assessed the effects of taking into account ion
activities on anaerobic digestion modelling.
The first part of the study is the comparison between the Debye-Hückel, Extended Debye-
Hückel, Güntelberg, Davies, and “WATEQ” Debye-Hückel ion activity correction
expressions considering the ions which are commonly present in cattle manure. A larger
difference in the calculated ion activity correction factors were obtained among the five
expressions at higher ionic strengths even within their ionic strength validity range.
In the second part of the study, a system involving thermophilic anaerobic digestion of cattle
manure was considered according to the study of Batstone et al. (2003). The ADM1 model in
the AQUASIM simulation environment was implemented in the MATLAB platform. The
Debye-Hückel, Güntelberg, and Davies expressions were then included in the model
implemented in the MATLAB simulation environment to account for the ion activity
corrections. The extended Debye-Hückel and WATEQ Debye-Hückel expressions were not
used because of the absence of literature values for the ion-dependent constants included in
those expressions.
Steady-state conditions were set in the ADM1 model in the MATLAB simulation
environment and the results of the simulation were compared to the results obtained in a
ii
SUMMARY

similar model with ion activity corrections. No significant difference were found for the ionic
concentrations of valerate, butyrate, propionate, acetate, carbonate, and ammonium ions
between the simulations with and without ion activity corrections. However, significant
difference was obtained in the concentration of the hydrogen ions, which consequently means
a significant difference in the pH. There is also a significant difference in the pH obtained
among the three ion activity correction expressions.
Next, pulsed conditions were set in the ADM1 model in the MATLAB simulation
environment and the results of the simulation were compared to the results obtained in a
similar model with ion activity corrections. Similarly, no significant difference were found
for the ionic concentrations of valerate, butyrate, propionate, acetate, carbonate, and
ammonium ions between the simulations with and without ion activity corrections. However,
significant difference was obtained in the concentration of the hydrogen ions, and therefore,
pH. There is also a significant difference in the pH obtained among the three ion activity
correction expressions. A pH decrease as a response to each of the pulses was also observed.
The largest decrease in pH as a response to a pulse is observed in the simulation with activity
correction using the Debye-Hückel expression, followed by the simulation with the
Güntelberg expression, then by the simulation with the Davies expression. The least decrease,
on the other hand, is observed in the simulation without the ion activity correction.
The significant difference between the obtained ion activity coefficients using the three ion
activity correction expressions suggests that in running simulations with an input different
from that used in this study, the appropriate ion activity correction expression should be used
depending on the ionic strength. It is recommended that laboratory corroboration should be
done to validate the use of each of the ion activity correction expressions.

iii
TABLE OF CONTENTS

TABLE OF CONTENTS

Page

Acknowledgements ……………..…………..…………………………..……….. i

Summary ….……………………..…………………………..…………………... ii
Table of Contents ……..…………………..…………………………..…………. iv
List of Abbreviations .………………………..…………………………..……… v
I. Introduction ….……………………..…………………………..……………... 1
I.1. Anaerobic digestion ….……………………..……………………………. 1

I.2. Animal manure 2
……..…………………..…………………………………
I.3. Physicochemical effects …..……………………..……………………….. 4

I.4. Objectives of the study 5
……..…………………..…………………………
II. Literature Review ..………………………..…………………………..……… 6

II.1. Anaerobic digestion and the anaerobic digestion model .....…………….. 6

II.1.1. Biochemical processes ……..……………………………….......... 7

II.1.2. Physicochemical processes .....……………………..…………….. 11

II.2. Ion activity and its relation to ion concentration .....…………………….. 15
II.2.1. Electrostatic interaction and specific interaction ……………….... 16
II.2.2. Ionic strength ……..…………………..…………………………... 16
II.2.3. Ion activity coefficient .………………………..…………………. 17

II.2.3.1. Debye-Hückel equation .………………………..……….. 18
II.2.3.2. Extended Debye-Hückel e quation .……………………… 19
II.2.3.3. Güntelberg equation …………….…………..…………... 20
II.2.3.4. Davies Equation …..…… ………………..………………. 21
II.2.3.5. “WATEQ” Debye-Hücke l equation .……………………. 21
II.2.4. Application of activity corrections ………………………..……… 22
III. Comparison between activity correction methods …………………………... 24
IV. Simulation Study ...……………………..…………………………………… 32
IV.1. Comparison of steady-state simulation of ADM1 in AQUASIM and
MATLAB .…..……………..…………………………..……....……… 32
IV.2. Effect of activity correction on steady-state ADM1 behaviour ……….. 36
IV.3 Comparison of dynamic simulation of ADM1 in AQUASIM and
MATLAB .…..……………..…………………………..……....……… 40
IV.4. Effect of activity correction on dynamic ADM1 behaviour ..………… 44
V. Conclusions ...………………..………..…………………..………………….. 47
VI. Perspectives ..…………………..………………………….………………… 49
References …...………..…………..…………………………..…………………. 50
Appendix ...………………………..…………………………..…………………. 55

iv
LIST OF ABBREVIATIONS

LIST OF ABBREVIATIONS

Symbol Description
ADM1 Anaerobic Digestion Model 1
C/N carbon to nitrogen ratio
C/N/P carbon to nitrogen to phosphorus ratio
IWA International Water Association
MS/su monosaccharides
AA/aa amino acids
LCFA/fa long chain fatty acids
VFA volatile fatty acids
va valerate
bu butyrate
pro propionate
ac acetate
ch carbohydrates
pr proteins
li lipids
I inerts
IC inorganic carbon
IN inorganic nitrogen
cat cations
an anions
C carbon content of component i
i
N nitrogen content of component i
i
v rate coefficients for component i on process j
i,j
f yield of product on substrate
product,substrate
K acid-base equilibria coefficient
a,acid
K Henry’s law coefficient
H
v
LIST OF ABBREVIATIONS

R gas law constant (0.0083145 bar M-1 K-1)
ΔG free energy
k acid base kinetic parameter
A/Bi
I inhibition function
inhibitor,process
k first order parameter
process
k a gas-liquid transfer coefficient
L
k 50% inhibitory concentration
m,process
K half saturation value
S,process
K inhibitory parameter
I
S inhibitor concentration
I
ρ kinetic rate of process j
j
Y yield of biomass on substrate
substrate
μ Monod maximum specific growth rate
max
p pressure of gas i
gas,i
P total gas pressure
gas
S soluble component i
i
T temperature
V volume
X particulate component i
i
dis disintegration
hyd hydrolysis
dec decay

vi
CHAPTER ONE: INTRODUCTION

CHAPTER ONE: INTRODUCTION

During the past 25 years, anaerobic digestion has been considered as the main development
in the field of waste treatment of organic municipal waste, wherein a large percentage of the
installations are located in Europe, with an increasing number of anaerobic digestion plants
installed per year. However, not all installed plants were successful mainly due to poor
planning, design, or operation (De Baere, 2005). The Anaerobic Digestion Model 1 (ADM1),
a structured model consisting of biochemical and physicochemical processes, aims to help in
the design, operation, and optimization of anaerobic digestion plants (Batstone et al., 2002).
In addition to organic municipal waste treatment, another application of the anaerobic
digestion process is the treatment of animal manure, usually in small farmscale plants (1-20
m3 substrate/day) (Escobar & Heikkilä, 1999). Since manure, in general, contains higher
concentrations of ions than other types of wastes such as organic municipal, crop, and
slaughterhouse wastes, it is expected that ion activity or ionic strength effects will occur. One
of the limitations of the ADM1 is the absence of ionic strength effects correction which leads
to a difference between the ADM1 simulation results and the actual output of an animal
manure anaerobic digestion plant.

I.1. Anaerobic digestion
Anaerobic digestion is one of the oldest biological wastewater treatment processes (Cloete &
Muyima, 1997), mainly used for the stabilization of solids (Grady & Lim, 1980). It consists
of biological reactions in which microorganisms break down biodegradable material in the
absence of oxygen (Metcalf & Eddy, 2003). Anecdotal evidence points out that biogas from
anaerobic digestion was used as early as the 10th century to heat bath water in Assyria (He,
2010) and during the 16th century in Persia (Sabonnadiére, 2009). Volta recognized the
presence of methane in marsh gas while Sir Humphrey Davy determined the presence of
methane in gases produced from cattle manure (Tietjen, 1975). One of the first practical
applications of the anaerobic digestion process was in Exeter, England in 1897, when Donald
Cameron built a sewage treatment facility designed to recover biogas to be used as fuel for
heating and street lighting (Deublein & Steinhauser, 2011). Furthermore, another digestion
plant was reported to be built in 1897 at the Matunga Leper Asylum in Bombay, India
utilizing human wastes to obtain biogas for their lighting needs (Chawla, 1986). It was in the
1
C HAPTER ONE: INTRODUCTION
second half of the 19th century that the important discovery of the anaerobic bacteria occurred
(Popoff, 1875). More studies related to anaerobic digestion were conducted during and after
the Second World War driven by a reduction of energy supplies (Sims, 2004).
The interest in the anaerobic treatment process results from its advantages, such as less
energy requirement, biological sludge production, and reactor volume requirement compared
to aerobic treatment systems. An additional and very important advantage is the production of
methane which is a potential energy source. Disadvantages of the process include sensitivity
to the adverse effects of low temperatures to the reaction rates, liability when toxic
substances are introduced, and possible production of odours (Metcalf & Eddy, 2003). It is
viewed that anaerobic digestion is a renewable energy-producing technology that protects the
environment, thus realizing the main goals of sustainable development. It is believed that the
process will continue to improve and be widely-implemented within the next decade (Yu &
Schanbacher, 2010).

Anaerobic digestion can be divided into two kinds of processes: biochemical processes and
physicochemical processes. Through the biochemical processes, the raw composites are
converted to methane, carbon dioxide, biomass, inerts, etc. The physicochemical processes,
on the other hand, mainly describe the physical phenomena and chemical reactions that
occur. These processes occurring during anaerobic digestion are adapted in the ADM1
through a set of parameters, stoichiometries, and equations. A detailed description of the
ADM1 is provided in the next chapter.

I.2. Animal manure
Not all types of waste are suitable for anaerobic digestion. The process can only degrade
organics, and it is important to note that some organics require longer retention times than
others. Important characteristics of feedstock for anaerobic digestion that must be considered
are the total solids content, moisture content, nutrient content, and C/N ratio of the feedstock.
There is a wide variety of feedstock that can be used for anaerobic digestion such as
agricultural waste, sewage sludge, organic municipal solid waste, slaughterhouse waste, scrap
and spoilage from fruits and vegetables processing, and manure (Rilling, 2005).
According to the US Environmental Protection Agency, manure is defined as dung and urine
of animals that can be used as a form of organic fertilizer. Animal manure considered is
classified as dairy cattle manure, beef cattle manure, swine manure, and poultry manure.
2