Iris Cherry Panorel
PULSED CORONA DISCHARGE AS
AN ADVANCED OXIDATION PROCESS
FOR THE DEGRADATION OF ORGANIC
COMPOUNDS IN WATER
Thesis for the Degree of Doctor of Science (Technology) to be presented
with due permission for public examination and criticism in Auditorium
1381 at Lappeenranta University of Technology, Lappeenranta, Finland,
on the 8th of November, 2013, at noon.
Acta Universitatis
Lappeenrantaensis 535
Supervisors Docent Sergei Preis, Associate Professor
Department of Chemical Technology
Lappeenranta University of Technology, Finland
Professor Marjatta Louhi-Kultanen
Department of Chemical Technology
Lappeenranta University of Technology, Finland
Professor Emeritus Juha Kallas
Department of Chemical Technology,
Lappeenranta University of Technology, Finland
Tallinn University of Technology, Estonia
Reviewers
Prof. Dr. Santiago Esplugas
Chemical Engineering Department
University of Barcelona
Marti i Franques, 1
08028 Barcelona, SPAIN
phone (+34) 93 402 1290
Email: santi.esplugas@ub.edu
Prof. Vasily Yakovlevich Ushakov
Electrical Power Engineering Systems Department
634050 Tomsk, Lenin Ave. 30
Tomsk Polytechnic University
Tomsk, Russia
Phone +73822 564410
E-mail: vyush@tpu.ru
Opponent
Prof. Dr. Santiago Esplugas
Chemical Engineering Department
University of Barcelona
Marti i Franques, 1
08028 Barcelona, SPAIN
Custos
Professor Marjatta Louhi-Kultanen
Department of Chemical Technology
Lappeenranta University of Technology
Finland
ISBN 978-952-265-477-9, ISBN 978-952-265-478-6 (PDF)
ISSN-L 1456-4491, ISSN 1456-4491
Lappeenrannan teknillinen yliopisto
Digipaino 2013
ABSTRACT
Iris Cherry Panorel
Pulsed corona discharge as an advanced oxidation process for degradation of organic
compounds in water
Lappeenranta 2013
48 p.
Acta Universitatis Lappeenrantaensis 535
Diss. Lappeenranta University of Technology
ISBN 978-952-265-477-9, ISBN 978-952-265-478-6 (PDF), ISSN-L 1456-4491, ISSN 1456-4491
Advanced oxidation processes (AOPs) have been studied and developed to suffice the effective
removal of refractory and toxic compounds in polluted water. The quality and cost of wastewater
treatment need improvements, and electric discharge technology has a potential to make a
significant difference compared to other established AOPs based on energy efficiency. The
generation of active oxidant species such as ozone and hydroxyl radicals by high voltage discharge
is a relatively new technology for water treatment. Gas-phase pulsed corona discharge (PCD),
where a treated aqueous solution is dispersed between corona-producing electrodes free of the
dielectric barriers, was developed as an alternative approach to the problem. The short living
radicals and ozone formed in the gas phase and at the gas-liquid interface react with dissolved
impurities. PCD equipment has a relatively simple configuration, and with the reactor in an
enclosed compartment, it is insensitive towards gas humidity and does not need the gas transport.
In this thesis, PCD was used to study and evaluate the energy efficiency for degrading various
organic compounds, as well as the chemistry of the oxidation products formed. The experiments
investigate the aqueous oxidation of phenol, humic substances, pharmaceutical compounds
(paracetamol, ibuprofen, indomethacin, salicylic acids, -estradiol), as well as lignin degradation
and transformation to aldehydes. The study aims to establish the influence of initial concentration
of the target pollutant, the pulsed discharge parameters, gas phase composition and the pH on the
oxidation kinetics and the efficiency. Analytical methods to measure the concentrations of the
target compounds and their by-products include HPLC, spectrophotometry, TOC and capillary
electrophoresis.
The results of the research included in this summary are presented in the attached publications
and manuscripts accepted for publication. Pulsed corona discharge proved to be highly effective in
oxidizing each of the target compounds, surpassing the closest competitor, conventional
ozonation. The increase in oxidation efficiencies for some compounds in oxygen media and at
lower pulse repetition frequencies shows a significant role of ozone. The role of the ·OH radicals
was established in the surface reactions. The main oxidation products, formation of nitrates, and
the lignin transformation were quantified.
A compound specific approach is suggested for optimization of the PCD parameters that have the
most significant impact on the oxidation energy efficiency because of the different characteristics
and responses of the target compound to the oxidants, as well as different admixtures that are
present in the wastewater. Further studies in the method’s safety (nitration and nitrosation of
organic compounds, nitrite and nitrate formation enhancement) are needed for promoting the
method.
Keywords: Water, advanced oxidation processes, electric discharge, ·OH radicals, ozone, energy
efficiency, phenol, paracetamol / acetaminophen, indomethacin, ibuprofen, -estradiol, salicylic
acid, humics, lignin, carboxylic acids, aldehydes, nitrates
UDC 628.16.087:537.52:66.094
PREFACE
This study was carried out in the Laboratory of Separation Technology, Lappeenranta University of
Technology, Finland.
I would like to acknowledge the generosity of the research foundation of LUT Tukisäätiö, the
Academy of Finland, the Fund of the Association of Finnish Steel and Metal Producers, KAUTE
säätiö (Lauri ja Niilo Santasalo rahasto), Centre for Separation Technology, Graduate School in
Chemical Engineering, and the Finnish Cultural Foundation for the financial supports that were
granted to sustain my research.
To my supervisor, Doctor Sergei Preis, your guidance, understanding and help to develop my
research abilities and your support in improving the content of my dissertation has been
invaluable and is highly appreciated. I am also indebted to my advisers, Professor Marjatta LouhiKultanen and Professor Emeritus Juha Kallas for being my mentors, giving me very useful insights
and support throughout these past four years.
My gratitude also goes to Dr. Iakov Kornev for his invaluable support through his expertise in high
voltage pulse generators and Dr. Henry Hatakka for helping me with the experimental set-ups, to
Jaana Ruokonen, Sanna Hellstén, and Laura Kaijanen for teaching me the necessary analytical
techniques, to my lovely students Anna Kreschik, Marion LeRoux, Pierre LePrince and Florianne
Lopez for helping me with the experiments and analyses. Your efforts made my tasks achievable.
I would also like to thank many friends, especially Jesse, Will, Sai, Verr, Bing, Marcelo, Piia, Matti,
Marju, Viki, Sini, Alex, Teemu, Tomomi, and Margie who were around physically and electronically
to share my joys and frustrations and cheer me up during stressful times.
I dedicate this thesis work to my parents, Alfonso & Pacita, and brother Eric for their love and
prayers, and their unconditional support and encouragement to pursue my interests.
All of you are His blessings in my life for which I am truly grateful for.
Lappeenranta, November 2013
Iris Cherry Panorel
Contents
Abstract
Preface
CONTENTS
LIST OF PUBLICATIONS ...................................................................................................................................... 9
Author’s contribution: ................................................................................................................................... 9
PART I: Overview of the Thesis ........................................................................................................................ 13
1.
2.
INTRODUCTION ....................................................................................................................................... 15
1.1
Research motivation ........................................................................................................................ 15
1.2
Objectives ........................................................................................................................................ 17
ADVANCED OXIDATION PROCESSES ........................................................................................................ 19
2.1
Oxidants ........................................................................................................................................... 19
2.1.1
Ozone ....................................................................................................................................... 20
2.1.2
Hydroxyl radical ....................................................................................................................... 21
2.2
Generation of Radicals .................................................................................................................... 21
2.3
Electrical Discharges ........................................................................................................................ 23
2.3.1
Dielectric barrier discharge ..................................................................................................... 24
2.3.2
Pulsed corona discharge .......................................................................................................... 24
2.4
Target compounds ........................................................................................................................... 25
2.4.1
Phenol ...................................................................................................................................... 25
2.4.2
Pharmaceuticals ...................................................................................................................... 25
2.4.3
Lignin........................................................................................................................................ 27
2.4.4
Humic Substances .................................................................................................................... 27
3.
EXPERIMENTAL PART............................................................................................................................... 29
4.
RESULTS AND DISCUSSIONS .................................................................................................................... 32
5.
4.1
Effect of pH .................................................................................................................................. 33
4.2
Effect of initial concentration ...................................................................................................... 34
4.3
Effect of oxygen content ............................................................................................................. 35
4.4
Effect of pulse repetition frequency ............................................................................................ 36
4.5
Reaction kinetics .......................................................................................................................... 37
4.6
Surface radical reaction ............................................................................................................... 39
4.7
Energy efficiency of PCD .............................................................................................................. 39
4.8
Effect of organic pollutants on nitrates formation ...................................................................... 40
CONCLUSIONS ......................................................................................................................................... 41
References ....................................................................................................................................................... 42
APPENDIX I....................................................................................................................................................... 47
PART II: Publications ........................................................................................................................................ 48
9
LIST OF PUBLICATIONS
This thesis is based on the following manuscripts which are referred to in the text as I-VI.
These journal articles are reproduced with permission from the publishers.
I.
Panorel, I., Kornev, I., Hatakka, H., Preis, S., 2011. Pulsed corona discharge for
degradation of aqueous humic substances. Water Science & Technology: Water
Supply 11(2), 238–245. doi:10.2166/ws.2011.045
II.
Panorel, I., Kornev, I., Hatakka, H., Preis, S., Louhi-Kultanen, M., 2013. Oxidation
of aqueous pharmaceuticals by pulsed corona discharge. Environmental
Technology 34(7), 923-930. doi:10.1080/09593330.2012.722691
III.
Panorel, I., Kornev, I., Hatakka, H., Preis, S., Louhi-Kultanen, M., 2013. Oxidation
of aqueous paracetamol by pulsed corona discharge. Ozone: Science &
Engineering 35(2), 116-124. doi:10.1080/01919512.2013.760415
IV.
Panorel, I., Kaijanen, L., Kornev, I., Preis, S., Louhi-Kultanen, M., Sirén, H., 2013.
Pulsed corona discharge oxidation of aqueous lignin: decomposition and
aldehydes formation. Environmental Technology.
doi:10.1080/09593330.2013.821144
V.
Preis, S., Panorel, I., Kornev, I., Hatakka, H., Kallas, J. 2013. Pulsed corona
discharge: The role of ozone and hydroxyl radical in aqueous pollutants oxidation.
Water Science and Technology. (accepted for publication on May 28, 2013)
VI.
Preis, S., Panorel, I., Llauger Coll, S., Kornev, I., 2013. Formation of nitrates in
aqueous solutions treated with pulsed corona discharge: the impact of organic
pollutants. Ozone: Science and Engineering. (accepted for publication on August
19, 2013)
Author’s contribution:
Publication I: the author planned and carried out the PCD experiments, conducted the
quantitative analyses of the main compounds and the oxidation products in the samples,
carried out the literature search, analysed the results and wrote the manuscript. The results
were presented by the author during the international conference on sustainable water
resource management & treatment technologies, Nagpur, India, on January 2011.
Publications II and III: the author planned and carried out the experiments, conducted the
quantitative analyses of the main compounds and the oxidation products in the samples
10
using HPLC, carried out the literature search, analysed the results and wrote the manuscript.
The work also included the supervision of the BSc students, Floriane Lopez (Claude Bernard
University, IUT Lyon I) in the task of estradiol and salicylic acid oxidation, and Anna Kreschik
(Tomsk Polytechnic University) and Marion LeRoux for ibuprofen and indomethacin
oxidation. The results of Publication II were presented by the author during the international
conference on materials and technologies for green chemistry, Tallinn, Estonia, on
September 2011.
Publication III: the author planned and carried out the experiments, conducted the
quantitative analyses of the main compounds and the oxidation products in the samples
using HPLC and IC, carried out the literature search, analysed the results and wrote the
manuscript.
Publication IV: the author carried out the literature search, performed the initial
experiments with the cooperation of a BSc student under supervision, analysed and
compiled the results, and wrote the publication. The author presented the results of the
paper during the COST action FP1105 workshop, Edinburgh Napier University, on May 2013.
Publications V and VI: the author was responsible for the quantitative analyses of the
experimental samples.
11
LIST OF SYMBOLS AND ABBREVIATIONS
Symbols
C
concentration of reactant (mol m-3), defined in Eq. 13
E
delivered energy dose (kWh m-3), defined in Eq. 14
energy efficiency (g kW-1h-1), defined in Eq. 15
hv
light
k2
second-order reaction rate constant (m3 J-1), defined in Eq. 13
P
pulsed power delivered to reactor (W), defined in Eq. 13
pKa
logarithmic acid dissociation constant
R
polyphenolic compound (represented in Eq. 2)
t
reaction time (h), defined in Eq. 13
V
volume of the discharge zone (m3), defined in Eq. 13
Acronyms
AOP
Advanced Oxidation Process
IC
Ion Chromatography
HPLC
High Performance Liquid Chromatography
HS
Humic Substance
NTP
Non Thermal Plasma
PCD
Pulsed Corona Discharge
PDBD
Pulsed Dielectric Barrier Discharge
STP
Sewage Treatment Plant
TBA
tert Butyl Alcohol
TOC
Total Organic Carbon
VOC
Volatile Organic Compound
12
13
PART I: Overview of the Thesis
14
15
1. INTRODUCTION
1.1 Research motivation
Fresh water sources are rapidly depleting or becoming unfit for human consumption or
inadequate to meet requirements of certain industries. The extensive industrialization, as
well as rapid increase in population, consequently increases the discharge of pollutants to
the environment. This scenario is emphasized especially in developing countries where
pollution control is not strongly enforced just yet (Wu, 2009).
The range of pollutants from different industries or human activities and the yet unknown
toxic contribution that these chemicals make to water sources is one of the bigger concerns.
Depending on the nature of the pollutants and the desired level of water quality, certain
combinations of well-established water treatment methods (i.e. mechanical, biological and
chemical, including ozone application) have been proven to be effective and are widely in
use in most domestic and industrial sources. However, the challenge lies in the removal of
toxic and refractory compounds that are potent in low concentrations, as is the case of
pharmaceuticals. The methods mentioned above would be either ineffective or
unaffordable. The drawback in most biological treatment methods is the reduced
effectiveness when pollutants are of toxic nature.
Recent advances in technology focus on advanced oxidation technologies to address this
issue. The most evident solution would be chemical reaction between organic pollutants and
oxidants with a high ability to initiate chemical reactions, i.e. having high oxidation-reduction
potential. The reagents with high oxidation potential are hydroxyl radicals (·OH), ozone (O3),
and hydrogen peroxide (H2O2), which make these active species very important in reactions
involving organic pollutants. In the present study, more focus was given to hydroxyl radicals
(·OH) because not only is it the most reactive among the three, it is less selective in
abstraction from the C-H bonds of organic matter present in the waste water (Buxton, et al.,
1988). Oxidation involving ozone and hydrogen peroxide is generally considered to proceed
through formation of hydroxyl radical. It is theoretically able to oxidize the majority of
organic compounds until their mineralization.
Advanced oxidation processes (AOPs) rely on the highly reactive hydroxyl radicals for
oxidizing the pollutant molecules. These AOPs have been studied and developed to suffice
the effective removal of refractory and toxic organic compounds in polluted water. As these
processes are almost non-selective, higher chemical dosages or increased energy might be
necessary to compensate for interfering reactions apart from that of the target compound.
Ozonation in large scale water treatment, for instance, consumes substantial amounts of
energy due to the synthesis of ozone and its application. In aqueous media, ozone
16
decomposes into hydroxyl radicals, although it requires three molecules of ozone to produce
two molecules of ·OH radical. When ozone is delivered to the water, it reacts with impurities
or mineral ions along the path, or part of the radicals recombine, contributing to the energy
loss (Hoigné & Bader, 1976). For AOPs to be economically feasible, their energy consumption
must be reduced. Implementation of high voltage discharge technology for water
purification results in the formation of the radical in-situ with immediate utilization in
reaction with pollutants.
The effectiveness of high voltage electric discharges for degrading pollutants has been cited
already in several studies (Sun, et al., 1999). Some other recent studies involving ultra-short,
50-300 ns, gas-phase PCD and pulsed dielectric barrier discharge (PDBD) (Shin, et al., 2000),
(Oda, 2003), (Tochikubo, et al., 2004), effectively showed the generation of ·OH radicals in
humid gas (Ono & Oda, 2000) and conclude that these processes are viable means for
oxidation of air pollutants (Roland, et al., 2002).
Single pulse discharge creates a concentration of ·OH radicals within the range between 1014
and 1015 cm-3 in 30-50 s after the pulse, which gives a substantial yield with the discharge
frequency of a few hundred pulses per second (pps). This makes it possible to bring ·OH
radicals and other short-living oxidants into contact with water. But with ·OH radicals’
lifetime in gas only being a few tens of microseconds (Ono & Oda, 2003), the discharge zone
must coincide with the gas-liquid contact zone. The alignment of zones became possible due
to the PDBD and PCD technique invented and applied by the scientists in Russia, Netherlands
and Israel (Boev & Yavorovsky, 1999) (Yavorovsky, et al., 2000), (Hoeben, et al., 2000),
(Ryazanova & Ryazanov, 2004), (Pokryvailo, et al., 2006).
The PDBD techniques, although proven to be viable in purification of groundwater from
ferrous and manganese ions (Boev & Yavorovsky, 1999), showed low efficiency in oxidation
of phenol in experiments conducted by the author. To increase the energy efficiency, the
PCD has to be applied: this discharge takes place in the gas space between non-insulated
electrodes, which increases the inter-electrode distance from 2-3 mm in PDBD to 15-40 mm
in PCD. The absence of insulation makes voltage applied to the electrodes work on
formation of active oxidative species in the inter-electrode gap instead of charging the
insulation. This makes the PCD method a very competitive technique among the AOPs for
water treatment.
Regardless promising energy efficiency known for the PCD applications (Hoeben, et al.,
2000), (Pokryvailo, et al., 2006), little is still known concerning PCD economic
competitiveness with other AOPs in respect of specific pollutants, its potential in
mineralization of pollutants and the safety of the method.
17
1.2 Objectives
The application of gas-phase PCD to water/waste water treatment remains largely unknown
due to its novelty. The circumstance dictates the necessity to accumulate knowledge in
treatment regularities, kinetics, energy efficiency and chemistry of oxidation of aqueous
organic pollutants of eco-toxicity concern. While high voltage discharge techniques have
already proven to be effective for degradation of organic pollutants (Lukes, et al., 2005),
(Tomizawa & Tezuka, 2007), the efficiencies of these AOPs still need improvement if it is to
be a technical and economical answer to environmental pollution. This approach will
potentially increase the applications of the aforementioned technique in the area of water
treatment, by establishing its ability to safely oxidize refractory organic compounds at a
lower processing cost.
The objective is to be achieved by further reduction in the energy consumption through
established optimum treatment conditions. The study is based on model compounds of
environmental concern, humic substances (Publication I), paracetamol (Publication III), lignin
(Publication IV), phenol (Publication V), and other medical compounds including
indomethacin, ibuprofen, -estradiol, and salicylic acid (Publication II). The main focus is the
degradation efficiency and kinetics, degree of mineralization, and identification and
quantification of oxidation products.
The research objectives include:
- Establishing of the oxidation process efficiency, dependent on the controlled process
conditions – the gas phase composition, the initial pollutant concentration, pH, salt content
(conductivity), the pulse parameters and its repetition frequency;
The energy efficiency of oxidation presents the key parameter of the process economy and
competitiveness. Technical conditions such as the content of oxygen in the gas phase
present an additional factor affecting economy and technical feasibility (Publications I-IV).
- The study of the nature of oxidation process, the character and the role of oxidants;
The role of ozone and ·OH radicals has to be established to understand the chemistry of the
process. The hypothesis of surface character of the ·OH radical attack needs special
attention (Publication V).
- The study of the impact of mass transfer to the treatment efficiency.
Being a key issue in the majority of heterogeneous gas-liquid processes, the mass transfer
needs thorough investigation for proper choice of treatment conditions.
- The study of the process safety concerning nitrous oxides formation.
18
The use of air as the gas phase in PCD inevitably results in the formation of nitrous oxides,
which may present a special issue in terms of treatment safety (Publication VI).
The research objectives were studied using the target pollutants and the model compounds
of fast and slow oxidation rate, disclosing the role of long- and short-living oxidants. The
products and the intermediates formed in oxidation, establishing reaction pathways,
dependent on the discharge parameters were identified to the extent available for the
author. The practical significance of the expected research results should be the
improvement of process efficiency. The disclosure of physical aspects of the surface
phenomena in the PCD action is the major objective of the proposed research.
19
2. ADVANCED OXIDATION PROCESSES
The term advanced oxidation processes (AOPs) was introduced by Glaze et al. (1987) and
since then have garnered a lot of interest in the scientific community and promoted
development for its application. AOPs are defined as processes where hydroxyl radicals are
generated in sufficient amount to chemically oxidize organic and inorganic pollutants and
purify water under ambient conditions (Glaze, et al., 1987). Appropriate application of AOPs
is the degradation of refractory or toxic compounds found in segregated effluents or
polluted waters wherein physical, biological or chemical methods would be inadequate.
Two stages of oxidation are involved in this process. The first stage is the generation of
hydroxyl radicals, wherein electrons are transferred from a reductant to an oxidant, thus
creating radical species with extra electrons. These radicals are unstable, and as such, are
highly reactive because of the unpaired electron. This tends to be followed by the
consumption of the radicals in additional reaction with the target compounds. The oxidants
produced from these AOPs oxidize organic and inorganic materials until oxidation products
that are thermodynamically stable are formed. In the case of reactions with organic
compounds, the BOD and COD levels in the waste water are reduced significantly, with the
final product being carbon dioxide and water after complete oxidation or mineralization.
Electric discharges (i.e. dielectric barrier discharge, pulsed corona discharge) result in
conditions not often achieved by chemical methods, thus producing hydroxyl radicals (·OH),
ozone (O3), hydrogen peroxide (H2O2), atomic oxygen (O), and hydroperoxyl radicals (HO2)
(Eliasson, et al., 1987).
2.1 Oxidants
There are several oxidants that are able to react with other compounds by removing one or
more electrons, thereby changing the target compound’s chemical properties (i.e. reducing
its toxicity or increasing its biodegradability). While there exists many of these oxidants, only
a select few have been widely studied for applications in the field of environmental
technology. A comparison of the oxidation potentials of some of these oxidants is shown in
Table 1. In wastewater treatment systems, this value is a measurement of the ability or
potential of wastewater to permit the occurrence of specific oxidation-reduction reactions. A
higher value signifies stronger oxidizing capability.
Table 1 Oxidizing potentials of reagents commonly used for wastewater treatment at 25 °C
Oxidant
Oxidizing potential (V)
Fluoride
F2 + 2e- = 2F2.87
Hydroxyl radical
·OH + H+ + e- = H2O
2.33
Ozone
O3 + 2H+ + 2e- = O2 + H2O
2.07
Singlet oxygen
O(1D) + 2H+ + 2e- = H2O
1.78
Hydrogen peroxide
H2O2 + 2H+ + 2e- = 2H2O (acid)
1.76
20
The oxidants that are of interest in this study are those that can be generated by an electric
discharge at atmospheric pressure, particularly ozone and hydroxyl radicals.
2.1.1 Ozone
Ozone was discovered and named by Christian Freidrich Schönbein in 1839 for its strong
smell (derived from the Greek word ózein: to smell) (von Sonntag & von Gunten, 2012). It is
a strong oxidant and a highly reactive gas owing to its electronic configuration as a hybrid of
four molecular resonance structures. As a molecule, it can react directly with the target
compound. With organic matter, some of the pathways can be electrophilic reaction,
nucleophilic reaction, and dipolar cyclo-addition (Criegee mechanism) when it reacts with an
unsaturated bond. Indirectly, ozone forms radical species when it decomposes in water,
which then reacts with the target compounds or the contaminants. It is also able to oxidize
inorganic constituents such as arsenic, manganese and iron to form insoluble oxides.
A radical-type chain reaction scheme describes the kinetics of aqueous ozone decomposition
in the presence of organic and inorganic solutes (Staehelin & Hoigné, 1985). The
decomposition of ozone is accelerated by initiators, i.e. hydroxyl ion OH-, leading to a radical
chain reaction carried out by substances called promoters. The presence of some organic or
inorganic compounds (scavengers) which reacts with ·OH radicals but not producing the
superoxide radicals terminates the chain reaction and inhibits further ozone decay. This
decomposition is usually a first-order process with the rate constant being dependent on the
concentrations of initiators, promoters, and inhibitors (Staehelin & Hoigné, 1982). Equation
(1) below is a combination of the chain reactions from initiation to termination, showing that
three ozone molecules are necessary to produce two ·OH radicals.
3O3 + OH- + H+ → 2·OH + 4O2
(1)
Some of the more common promoters maintaining the chain reaction include formic or
glyoxylic acids and some primary alcohols. Inhibitors which do not react with ozone, but
scavenge the ·OH radicals include tertiary alcohols such as tert-butanol, carbonates and
bicarbonates.
Above a critical value of pH 5 – 6, aqueous ozone decomposes faster and the ·OH radicals
become the dominating oxidants. The decomposition of ozone to ·OH radicals can be
accelerated further by combining it with UV light, H2O2, active carbon and metallic ions of
variable valence catalysts.
Ozone still remains to be the most practical oxidizing agent in potable and special water
treatment applications despite of its high cost. In terms of economic aspects, the often slow
direct chemical reaction of ozone that is desired with the dissolved solute causes a
significant loss of the ozone dosed in the water.
21
2.1.2 Hydroxyl radical
For oxidizing refractory organics, indirect ozonation involving free radicals such as ·OH
radicals would be the more effective mechanism because of the higher oxidation-reduction
potential of these species than ozone. Being one of the strongest oxidants, ·OH radicals react
quickly with most organic compounds. It is more reactive approaching the diffusion control
rates for solutes such as aromatic hydrocarbons, unsaturated compounds, aliphatic alcohols,
and formic acid (Hoigné & Bader, 1976). With a short half-life in water in the order of
microseconds, concentrations of free hydroxyl radicals can never reach levels above 10-12 M
(Glaze & Kang, 1988), therefore it must be generated in situ. Whereas ozone is highly
selective with its direct reaction to specific solutes, ·OH radicals react fast and show minimal
selectivity with organic and inorganic solutes (von Gunten, 2003).
Hydroxyl radical is the neutral form of hydroxide ion generated by dissociation of H2O2 or
ozone, or via reaction of atomic oxygen with water. Depending on the intermediates, several
ways have been studied for generating these radicals and are generally grouped as ozonebased, UV-based, photocatalysis, and Fenton reactions.
Possible reaction pathways of ·OH radicals with polyphenolic organic compounds can be
abstraction of H atom subsequently forming H2O, or the addition of ·OH radical to the
organic compound (eq. 2, 3). The ·OH radical could also react with another ·OH radical
forming a stable product H2O2 (Bishop, et al., 1968) (eq. 4).
RH + ·OH → R· + H2O
(2)
R + ·OH → R(OH)·
(3)
·OH + ·OH → H2O2
(4)
But despite of the oxidizing capabilities of these reagents, their fate in the wastewater is as
complex as the composition of the waste water itself, significantly affected primarily by the
characteristics of the solution (i.e. temperature, pH, concentration, conductivity).
2.2 Generation of Radicals
Having emphasized that ·OH radicals and ozone are the oxidants of interest in this study,
some of the established technologies for generating these reagents are briefly presented,
with more focus on the high voltage discharge technologies.
Ozone / Hydrogen Peroxide (O3/H2O2)
The complex mechanism of the spontaneous decomposition of ozone in water producing
·OH radicals was demonstrated by Hoigné & Bader (1983a) and Hoigné & Bader (1983b).
Considering the short half-life of hydroxyl radicals, the addition of hydrogen peroxide
22
(peroxone), could accelerate the decomposition rate of ozone. Hydrogen peroxide in its
undissociated form barely reacts with ozone. In water however, being a weak acid (pKa =
11.75), it partially dissociates into hydroperoxide ion (HO2-). This anion reacts readily with
ozone to form the ·OH radicals, thus elevating the hydroxyl radicals concentration, and
consequently increasing the oxidation rate. This technology has been well established
already (Paillard, et al., 1988) (Duguet, et al., 1990), (Trancart, 1990).
Ozone / UV
Combination of ozone and UV (photolysis of aqueous ozone) can yield hydrogen peroxide,
which as described earlier, with ozone promotes the formation of hydroxyl radicals.
hv
O3 + H2O → O2 + H2O2
(5)
hv
O3 + H2O → O2 + 2 ·OH
(6)
Gottschalk, et al. (2000) recommended for ultraviolet lamps to have a maximum radiation
output at 254 nm for an efficient ozone photolysis. The study by Peyton & Glaze (1988)
described the hydroxyl radical being the principal active species in photolytic oxidation. This
was also supported by the degradation study of 4-chlorophenol by Esplugas, et al. (1994),
which led to mineralization of the target compound.
Hydrogen Peroxide and Ferrous/Ferric Oxidation with UV
Hydrogen peroxide can react with ferrous ions (Fenton reaction) to also generate hydroxyl
radicals. The formed Fe(III) ions further react with the hydroxide ions to regenerate the Fe(II)
ions in a reversible reaction, which when exposed to UV at a wavelength of 350 nm,
indirectly contributes to further generation of hydroxyl radicals.
Fe2+ + H2O2 → ·OH + OH- + Fe3+
(7)
Fe3+ + OH- ↔ Fe(OH)2+
(8)
Fe(OH)2+ + hν → ·OH + Fe2+
(9)
Complete mineralization was achieved during the oxidation of chlorophenoxy herbicides
with Fe3+/H2O2, in acidic and aerated conditions (Pignatello, 1992). Similar results were
achieved by Sedlak & Andren (1991) for the oxidation of chlorobenzene in acidic medium.
Other techniques for producing ·OH radicals for the oxidation of other substances include
gamma radiolysis of water (Goldstone, et al., 2002), ultrasonic irradiation (Milne, et al.,
2013), or wet oxidation (with or without catalysts) at critical conditions for enabling
dissolution of oxygen in water.
23
2.3 Electric Discharges
Electric discharge describes the passage of an electric charge through a material which does
not normally conduct electricity. The dielectric medium could either be gas, liquid, or solid.
Electric discharge is often accompanied with the formation of plasma which is an electrically
neutral ionized gas. Perhaps the most common occurrences of plasma in nature are lightning
and auroras. Lightning is the most frequently observed form of a spark discharge occurring
at near-atmospheric pressure accompanied by an acoustic phenomenon, thunder. This kind
of discharge, together with arc discharge, is called thermal plasma because all the energy
density is solely in the discharge channel, thus resulting in very high temperatures.
Non-equilibrium or non-thermal plasma (NTP) on the other hand results from the application
of a short-duration pulsed power to a gaseous gap at atmospheric pressure. The surrounding
gas is kept at room temperature because the ionization degree is low and the electrons do
not heat up the heavy particles (molecules and ions) efficiently. When an intense electric
field is applied, a discharge is formed which causes the formation of self-propagating
electron avalanches (known as streamers) within the gas volume. The plasma chemistry is
driven by electrons causing ionization, molecule excitation, and production of radicals. It is
for this reason that the application of NTP for chemical reactions in environmental
applications has been continuously developed. From a practical point of view, plasmas that
can be generated and maintained at atmospheric pressure rather than low pressure are
more desirable.
The effectiveness of electrical discharges generated by high voltage has been proven to
degrade pollutants in wastewater (Sun, et al., 1999), and also for the disinfection of
microbially contaminated liquids (Anpilov, et al., 2001). The use of electrical discharge in gas
has also been widely used for pollution control such as NO and SOx removal from
combustion gases or cleaning up of dust particles from particular industries (paper, steel)
(Urashima, et al., 1997), (Rosocha, et al., 1993), (Dinelli, et al., 1990).
In water, high voltage discharge induces a non-thermal plasma method for generating ozone
and ·OH radicals from oxygen and water (Ono & Oda, 2003). The energy input is small such
that the temperature in the reactor does not increase significantly.
The following oxidation reactions produce the highly reactive oxidants:
e- + H2O → e- + ·H + ·OH
(10)
e- + 3O2 → e- + 2O3
(11)
O + H2O → 2OH
(12)
The dissolved ozone in water can in turn decompose to form ·OH radicals or react directly
with the pollutants (von Sonntag & von Gunten, 2012).
24
Non-thermal plasma is a viable technology for large scale industrial application. By producing
highly reactive species, the technique is able to degrade pollutants non-selectively, without
needing high temperatures or low pressures. The most known wastewater treatment
techniques allowing operation at NTP conditions are dielectric barrier discharge (DBD) and
pulsed corona discharge (PCD).
2.3.1 Dielectric barrier discharge
Dielectric barrier discharge (DBD) is typically generated between two electrodes with at least
one covered in a dielectric layer. It consists of a number of single micro-discharges,
uniformly distributed in the interelectrode gap due to the presence of dielectric barriers
(Eliasson, et al., 1987), (Kornev, 2003). The dielectric layer stabilizes the discharge and
prevents the formation of an arc between the electrodes and maintains an even distribution
of microdischarges over the electrode surface by limiting the amount of charge (Kogelschatz,
et al., 1997). Previous studies described dielectric barrier discharge as silent discharge since
it does not blare as loud as the spark discharge in the air. Only alternating current (AC) or
pulsed power supply can be applied to this system of electrodes. At gas pressures of one
atmosphere, gap spacing (in millimetres) and the application of alternating high voltage
(pulse repetition frequency range in tens of Hz to several kHz), a large number of microdischarges spread in space and time over the electrode area and are created in the gas. The
humidity in air increases the strength of the microdischarge.
Still widely used in ozone generators, the filamentary type of DBD was firstly applied in 1857
by Werner von Siemens for generating ozone to rid water of bacterial contaminants. It has
however found a wide range of applications in the industry such as lamps or plasma TV
displays. Environmental applications such as decomposition of dilute VOC’s in air (Oda, 2003)
have also been reported. An example of the author’s experience in tests of other practical
applications of DBD is supplied in Appendix 1.
2.3.2 Pulsed corona discharge
Pulsed corona discharge is another technique to produce non thermal discharges utilizing
high voltage pulses. Streamer properties in PCD are almost similar to those in DBD but the
interelectrode distance is bigger in PCD. It uses an asymmetric electrode pair, where the
discharge develops in the high field region near the sharp electrode and spreads out towards
the cathode.
The characteristics of the ions producing the plasma depend on the polarity of the discharge
and the characteristics of the gas mixture, specifically on the electron attaching species
(Chang, 1991). When the electrode with the strongest curvature is connected to the positive
output of the power supply, the discharge that develops is a positive corona. In a wire-plate
configuration, this may appear as a tight sheath around the electrode or as a streamer
moving away from the electrode. A negative corona develops when this electrode is
25
connected to the negative terminal of the power supply. This may seem as a rapidly moving
glow or as small active spots called “beads” (van Veldhuizen & Rutgers, n.d.), (Chang, 1991).
Initially used for electrostatic precipitators, the applications for corona discharge have
expanded to a wide range of disciplines from decontamination of high volume air streams,
destruction of toxic compounds and pollution abatement, generation of ozone, or in
semiconductor manufacturing. In cases such as application of the technology for military
wastes (chemical and biological) or microbial inactivation, toxicological and eco-toxicological
studies are still needed.
The PCD configuration used in this study utilizes high voltage electrode wires and concluded
by grounded electrode plates. The pulsed streamer discharge ends in the grounded plate so
that high voltage terminates in time and no spark discharge is produced.
2.4 Target compounds
The second stage of oxidation following the formation of hydroxyl radicals involved in AOPs
is the reaction of these formed species with the target compounds in water. The choice of
the target compounds was motivated by the efficient capability of this technology to
degrade refractory compounds that are ubiquitous in the environment and may pose danger
to aquatic life.
2.4.1 Phenol
Phenol is considered to be a reference compound for evaluating the effectiveness of an AOP
as it is among the most widespread toxic water-soluble persistent chemicals that has acute
environmental impact. Effluents from many industries such as petroleum refineries, coke
plants, chemical plants, explosive producers and phenolic resin manufacturers are generally
known to contain high levels of phenolic compounds. These substances are prevalent, and
the fact that they are known as hazardous and toxic to aquatic life means that they would
have to be removed from concentrated wastewaters prior to release in the aquatic
environment. Thus this chemical has been intensely studied for decades, accumulating a
substantial amount of publicly available data for reference. Phenol is also in general a rapidly
oxidizable substance allowing studies of fast reaction under various operating conditions of
treatment, for example, pulse repetition frequency.
2.4.2 Pharmaceuticals
The increasing number of analytical techniques developed for detecting minute levels of
compounds in water samples have led to a whole new perspective of how we deal with the
disposal and use of medical drugs. The presence of prescription and non-prescription drugs
and their metabolites in surface water streams studied in North America and Europe are
drawing attention not only for the unknown effects of these compounds to human and
aquatic life when ingested, but also for the apparent inefficiency of the wastewater
26
treatment methods being used in the sewage treatment plants (STPs). Some of the
pharmaceuticals in this study are among the highly consumed drugs in the households
today. Genotoxic as well as immunotoxic effects to fishes have been reported after exposure
to wastewater containing estrogenic and alkylphenolic chemicals (Liney, et al., 2006).
-Estradiol
An estrogen or a female hormone, estradiol is used for hormone replacement therapies to
treat postmenopausal symptoms. Another derivative of estradiol, ethinyestradiol, is one of
the main ingredients of hormonal contraceptives. The occurence of these compounds
(Huang & Sedlak, 2001) in sewage treatment plant effluents are at levels that could cause
feminization of wild fish such as perch or trout (Kavanagh, et al., 2004), (Bjerregaard, et al.,
2006). Constant exposure to these hormonally active chemicals would affect the sexual
behaviour and immune function of fish. The detectable presence of estradiol in receiving
bodies of water near STPs is a concern that needs to be addressed by the applied
wastewater treatment technique. The presence of highly potent hormones in surface waters
could be one of the inevitably growing challenges in environmental science and technology.
Paracetamol
A widely used over-the-counter pain killer and fever reducer, paracetamol (acetaminophen
in North America) is also one of the main active pharmaceutical ingredients in flu
medications, making it a very common household drug. Consumed in high amounts, it is not
surprising that the presence of this compound in surface waters is of highest concentration
relative to other pharmaceutical compounds (Vulliet, et al., 2011).
Indometacin
Indometacin is another non-steroidal anti-inflammatory medication prescribed for fever,
swelling and pain, although considered to be more potent than paracetamol. Another
clinical use of indomethacin is to delay premature labour by reducing uterine contractions.
Ibuprofen
Another popular over-the-counter pain reliever, ibuprofen is among the most popular drugs
in the world, and the second most consumed drug for the musco-skeletal subgroup in
Finland as of 2012 (FIMEA, 2012) despite being intended for short-term use and temporary
treatment. The presence of ibuprofen in rivers and surface waters has been detected
(Ternes, 1998) along with other pharmaceuticals, suggesting its high mobility in aquatic
environment (Buser, et al., 1999).
Salicylic acid
Salicylic acid is another anti-inflammatory drug known for relieving fever and easing aches. It
is also typically a constituent of topical liniments for soothing muscle pains, and can be
found in many skin-care products for treating acne or dermatitis, and in shampoos for
27
minimizing dandruff. Due to wide usage of products containing salicylic acid, it is most likely
that this compound is highly present in the wastewater streams.
2.4.3 Lignin
Lignin is an organic compound mostly derived from wood, and most plants such as straw. It
is commonly found in pulp and paper manufacturing wastewater as a dissolved compound
when it is separated during the pulping process. Lignin contains various phenolic and nonphenolic aromatic structural elements formed during its biosynthesis by dehydrogenative
polymerization of coniferyl and synapyl alcohols. It comprises about 10-15% by weight of
black liquor which is the major pulp and paper side stream. In waste water streams, its
presence causes high concentration of dissolved organic matter, dark brown colour, and
odour. Conventional treatment processes are not effective in destroying lignin: coagulation
can only remove large molecules of lignosulfonates (Dilek & Gokçay, 1994); increased
chlorination for the treatment of potable water containing lignin can lead to formation of
hazardous chlorinated substances (Chang, et al., 2004). With increasingly stringent
requirements for discharges, it is important to have cost effective methods capable of
degrading lignin.
Lignin also presents an interest as a bulk source of valuable organic raw material that is able
to substitute fossil based raw materials for plastics, carbon fibres or for certain chemical
products. For instance, a study by Gooselink, et al. (2011) on lignin valorisation shows a
potential of lignin oil as a replacement for phenol in a PF-wood resins.
2.4.4 Humic Substances
Humic substances (HS) comprise a major portion of dissolved natural organic matter such as
microbially degraded plant tissues including lignin. They are evident in the brown coloration
of surface waters and some water supply systems as they are inherently difficult for
microbes to mineralize. Their inherent recalcitrance makes biodegradation under natural
conditions insufficient for mineralization, and as such, HS remain in the surface waters or in
water supply systems if not removed by physical methods (filtration, coagulation,
adsorption). During treatment, disinfection by chlorination of water containing these
substances can lead to the formation of trihalomethanes (THMs) which is a hazardous byproduct that increases adverse birth risks (Gallagher, et al., 1998).
A summary of the target compounds used in this study and the analytical techniques used to
measure the parent compound is demonstrated in table 2 below. The analyses of
intermediate products are described in more detail in Publications I-IV.
28
Table 2. Analytical methods for measurement of parent compound.
Compound
CAS name
Formula
MW
Phenol
C6 H6 O
94.11
100
Salicylic Acid
C7 H6 O3
100
(2-Hydroxybenzoic
acid)
138.12
Paracetamol
C8 H9NO2
151.17
100
C13 H18 O2
206.29
100
C19 H16 Cl NO4
357.79
100
C18 H24 O2
272.38
10
(N-(4hydroxyphenyl)
acetamide)
Ibuprofen
2-(4Isobutylphenyl)
propanoic acid
Indomethacin
1-(4chlorobenzoyl)-5methoxy-2-methyl1H-Indole-3-acetic
acid
β-estradiol
(17β)- Estra1,3,5(10)-triene3,17-diol
Humic Acids
Lignin
--
--
Structure
C0,
mg L-1
Method
Spectrophotometer
4-nitroaniline method
at 540 nm
UV-VIS
297 nm
HPLC (210 nm)
50/50 of water/
acetonitrile
HPLC (220 nm)
40/60 of 0.1% acetic
acid/ acetonitrile
HPLC (320 nm)
40/60 of 0.2% H3PO4
/acetonitrile
HPLC (210 nm)
55/45 of 20mM
CH3COONH4/ MeOH
--
--
3, 7, 14,
23
Spectrophotometer
80 - 600
Spectrophotometer
455 nm (colour)
tannin/lignin method
at 630 nm
29
3. EXPERIMENTAL PART
The PCD system has been described extensively in the published papers (Publications I-VI).
The main advantage of this concept is the simplicity of the design and operation, ease of
maintenance, and its highly optimizable conditions for oxidation process.
The geometry of the system allows for a dispersion of the treated solution from the top of
the reactor to form droplets and streams, passing through the electrodes where it then
reacts with the active oxidants being generated in the plasma zone. Hydroxyl radicals and
atomic oxygen are formed directly on the surface of water, allowing for the reaction with the
impurities in water (Figure 1).
Figure 1. PCD water treatment scheme
The luminescence of the corona is most intense near the electrode wires with a non-uniform
distribution over the cross-section of the channel (Figure 2).
Figure 2. PCD glow as seen from the side of the reactor
30
The overall experimental system consisting mainly of the PCD reactor and the high voltage
pulse generator is illustrated in Figure 3, with a brief description of the other components.
Figure 3. PCD reactor layout
1 – Water reservoir with a volume of 100 L
2 – Water circulation pump that is controlled by a frequency regulator (3). A flow meter (not
shown) confirms the actual water flow rate.
3 – Frequency regulator (not shown in the diagram)
4 – Perforated plate for dispersing the water, producing droplets and films
5 – High voltage electrodes of 0.5 mm stainless steel wire diameter, distanced 30 mm in
between and positioned 17 mm from vertical grounded plate electrodes (not shown)
6 – PCD chamber, 0.034 m3
7 – Sampling port for taking out water samples after reaction
8 – Manual feed port for adding chemical solutions
9 – Oscilloscope (Agilent 54622D) for monitoring voltage and current
10 – Gas cylinders
11 – Drain port
12 – Pulse generator consisting of a thyristor power switch circuit, pulse step-up transformer,
high-voltage magnetic compression stages, and a pulse compression block
31
The pulse voltage and current were measured with the Agilent 54622D oscilloscope, the
peaks (Figure 4) of which when calculated as an integral product, give the amount of energy
delivered to the reactor at 0.30 to 0.33 J per pulse (Publication V).
Figure 4. Voltage and current oscillograms of the pulse
The working water solutions were all prepared by dissolving the compound in 1 L of
Millipore water and diluted with tap water at ambient temperature in the reactor tank to
the desired volume and concentration. Depending on the solubility of the compound, it was
sometimes necessary to pre-dissolve the compound by increasing pH using NaOH or heating
the stock solution. Details are described in Publications I-VI. Unless otherwise stated, the
reaction time applied for all experiments was 30 minutes with sampling time increment of 2
to 5 minutes; circulation time of 3 minutes was applied prior to each sampling. Phenol
experiments were conducted for longer time because the volume used was 100 L (twice as
much as with the other compounds).
32
4. RESULTS AND DISCUSSIONS
The PCD oxidation of the target compounds has been described in (Publications I-VI). The
oxidation of these compounds was studied in different matrices of experimental parameters
(Table 3) to evaluate the optimum conditions for achieving high energy efficiency,
consequently reducing costs.
Table 3. Experimental plan
Compound
Pulse repetition
rate, pps
Phenol*
Paracetamol
Indometacin
Ibuprofen
Salicylic acid
Humic acid
Lignin
-estradiol**
200, 400, 600,
840
400
Initial concentration, pH
mg L-1
100
pH 4, pH 6,
pH 10
100
pH 6, pH 10
100
(monitored)
100
(monitored)
50, 75, 100
pH 7, pH
10.5
3, 7, 14, 23
(monitored)
80, 90, 140, 300, 600 (monitored)
0.2, 2.7
(monitored)
Oxygen content
air, 90% oxygen
air, 90% oxygen
air, 90% oxygen
air, 90% oxygen
air
air, 90% oxygen
5% O2, air, 90% O2
air
*The presence of different concentrations (0, 0.1 mmol L-1, 1 mmol L-1) of the surfactant igepal C-630
for the oxidation of 1 mM of phenol at 600 pps in air was evaluated.
**Urine, urea & sucrose were added to evaluate the effect of these admixtures on the degradation
of -estradiol
The environmental concern over the increasing presence of active pharmaceutical
ingredients (API) in wastewaters and surface waters instigated this research on the
degradation of analgesics which are among the most commonly used over-the-counter
drugs. Resistant to conventional biological water treatment in STPs, these chemicals
eventually end up in the environment. AOPs are prospective methods for the degradation of
such substances especially in the effluents of pharmaceutical plants or hospitals (Esplugas, et
al., 2007). While Klavarioti, et al. (2009) reported effective removal efficiencies, large-scale
implementation would be very energy consuming. Of another particular concern is the
recalcitrance of humic substances to biological degradation. Also, the ubiquitous presence of
lignin surrounding pulp and paper mills waste water streams and cardboard landfill
leachates is also a challenge because of its poor biodegradability and the toxic phenolic
substances that result from its decomposition.
An overall pH reduction was observed for all experiments conducted. This is most likely
attributed to the low molecular weight carboxylic acids formed from the cleavage of the
benzene ring. Depending on the degradation pathway and the contribution of ·OH radicals
and ozone during oxidation, there are several oxidation products identified in the previous
33
studies. Most commonly reported are polyphenols (catechol, resorcinol, hydroquinone),
unsaturated carboxylic acids (acrylic, maleic and fumaric acids), and saturated carboxylic
acids (formic, oxalic and glyoxylic acids) (Beltrán, et al., 2005). The identified carboxylic acids
in the degradation of pharmaceutical compounds in this study included acetic, formic and
oxalic acid. Vanillin and syringaldehyde were measured for lignin, as well as the general
aldehydes formed.
Table 4. Common oxidation products of phenolic compounds
Attack of
·OH radical
on the
benzene
ring
Cleavage of
benzene
ring
catechol
hydroquinone
resorcinol
acrylic acid
maleic acid*
fumaric acid*
formic acid
oxalic acid
glyoxylic acid
* Z = cis isomer of butenedioic acid,
E = trans isomer of butenedioic acid
4.1 Effect of pH
Phenol (Publication V)
Sample solutions with initial pH of 6 rapidly stabilized to pH 3 to 4. The pH of the samples
that started in alkaline condition of pH 10 decreased to pH 6 when the sufficient energy dose
is delivered. In controlled pH experiments, the tendency to decrease still occurred slightly
(from pH 10 to pH 8). However, it is of importance to mention that maintaining the pH at a
constant alkaline level did not improve phenol degradation as compared to the pH variable
within alkaline-neutral diapason, i.e. maintaining the pH just above neutral is important. In
initial acidic condition of pH 4, the decrease to about pH 2.5 was fast but did not decrease
any further. The phenol degradation for this condition was slow achieving about 50% less
than that of the alkaline. This was an expected result for phenol for its susceptibility to
oxidation in dissociated phenolate form.
Salicylic acid (Publication II)
Neutral solutions of salicylic acid started with pH of about 7 to 7.5, and after the maximum
energy dose of 2.5 kWh m-3 was delivered, pH decreased to 4. The degradation achieved at
34
this point (maximum) was 65% while mineralization determined as TOC reduction was at
15%. In alkaline conditions starting at pH 10.5, the increment of decrease was about the
same, levelling off to pH 6.5 at maximum energy dose. However, contrary to the beneficial
effect of alkaline condition on phenol degradation, the degree of salicylic acid oxidized was
only 60%, with a slightly improved mineralization of 20%.
Paracetamol (Publication III)
Dissolution of paracetamol yields an acidic solution with pH 6 at the onset of the
experiment. During the course of oxidation, the solution further became acidic reaching pH 3
after a maximum energy dose of 3.125 kWh m-3. The paracetamol degradation achieved at
this point was 67%, while mineralization was 11% at best. Alkaline conditions with initial pH
of about 10 - 10.5 resulted in a drastic pH reduction to 4, with improved paracetamol
degradation of 90% and improved mineralization of 18.5%. This is a similar trend to that of
phenol as expected for paracetamol containing phenolic moiety.
4.2 Effect of initial concentration
Humic acid (Publication I)
Humic acid was effectively oxidized by PCD achieving almost complete degradation at the
maximum tested energy dose of 1.25 kWh m-3. At higher initial concentration of 23 mg L-1,
the rate of degradation proceeded slightly slower than that of an initial 7 mg L -1 in the
beginning, but eventually equalized as more energy was delivered to the system. A higher
initial concentration however increased the oxidation efficiencies due to the increased
probability of radicals reacting with the pollutant. The degree of mineralization however was
higher when the initial concentration was low achieving 75% mineralization, while only 40%
mineralized for the solution that started at 23 mg L-1. The relatively high mineralization of
humic acid showed that there was minimal formation of carboxylic acids because despite of
the different parameters applied, the pH only decreased slightly from an initial value of
about 8 - 8.5 to pH 7 - 7.5. Certain buffering of humics was expected due to the release of
free ammonia from the amino groups present in the molecules.
Lignin (Publication IV)
Initial lignin concentration was varied from 80 mg L-1 to 600 mg L-1. At the lowest starting
concentration, the achieved lignin degradation was over 80% at an energy dose of
2.5 kWh m-3 in air. With the same energy delivered, sample solutions with initial
concentrations of 300 and 600 mg L-1 achieved lower degradation of 53% and 30%
respectively. In diminished oxygen conditions (5-7% O2), an expected similar trend was
observed, although lignin degradation was much smaller, from 45% to 10%. Mineralization
data were not of interest, but instead, the degree of formation of aldehydes was measured
35
for purposes of lignin transformation valorisation. With increasing initial concentration, the
yield of aldehydes formed relative to the oxidized lignin showed a decreasing trend in air,
but the opposite increasing trend in diminished oxygen conditions (refer to effect of oxygen
content).
Salicylic acid (Publication II)
Dilute solutions of salicylic acid resulted in a faster degradation. With an energy dose of
1.6 kWh m-3, complete degradation was achieved for solutions starting at 50 mg L -1, whereas
this corresponded to about 50% degradation only for samples with an initial 100 mg L -1
concentration. For the lower initial concentration solution, mineralization was also higher at
34% when 2.5 kWh m-3 of energy was delivered, compared to 14% mineralization when
100 mg L-1 of solution was oxidized.
4.3 Effect of oxygen content
Paracetamol
In increased oxygen atmosphere, it is certain that higher ozone concentration is formed,
although the formation rate of ·OH radicals could also be increased in proportions; however,
such measurements are beyond the scope of this study. Increasing the oxygen content
during paracetamol oxidation doubled the degree of removal compared to air. At an energy
dose of 2 kWh m-3, paracetamol was completely degraded, with mineralization of 21%. After
the maximum energy dose of 3.125 kWh m-3, mineralization was 27.6%. In air, only 50% of
the original paracetamol content was removed at an energy dose of 2 kWh m-3 and 6.5%
mineralized which further increased to 11% after the maximum energy dose. This indicates
equally significant roles of both ozone and ·OH radicals in paracetamol degradation. In
alkaline solutions, the difference between air and 89% oxygen conditions was less
pronounced maybe due to the dissociation of paracetamol which already increased its
reactivity even in air. However, increasing the oxygen level still improved the degradation in
about the same rate as in neutral solution.
Ibuprofen
For the degradation of ibuprofen, the addition of oxygen did not have the same outcome as
that of paracetamol. Despite the faster initial degradation for the first 10 minutes in oxygen,
the overall degradation after delivering a maximum 3.125 kWh m-3 of energy was almost the
same; 83% in air and 86% in oxygen. Mineralization of ibuprofen in air reached 25%, while in
oxygen it achieved a slightly higher 32% mineralization. The relatively slow reacting nature of
this compound suggests that ozone did not play a significant role in its oxidation.
36
Indomethacin
The oxidation of indomethacin occurred rapidly with air showing complete degradation after
only 1 kWh m-3 of energy was delivered. With the addition of oxygen in the reactor, an even
faster reaction occurred, requiring only half of the energy dose in air for complete
degradation of the compound. This indicates a strong influence of both ozone and ·OH
radicals in the oxidation process. Mineralization for both conditions was rapid at the onset of
the reaction reaching about 33% both in air and oxygen media with the energy dose
required to complete the degradation. However, even with additional energy dose up to the
maximum 3.125 kWh m-3, the mineralization only slightly improved to 35 – 40%. This
indicates that after the consumption of the parent compound and its mineralization, the
remaining by products are those which are very difficult to mineralize at the final stage of
the process, most likely the short-chain carboxylic acids.
Humic Acid
For the oxidation of humic substances, the increased oxygen concentration slightly increased
the degradation rate achieving a 90% oxidation after a minimal energy dose of 0.5 kWh m-3,
whereas in air only 77% was oxidized with the same energy. This slight improvement in
oxidation shows the moderate role of ozone. The mineralization, however, doubled in
oxygen media achieving almost 50% compared to the 25% obtained in air.
Lignin
Comparing the results with initial concentration of about 300 mg L -1, the achieved
degradation at 5-7% oxygen was only 20%, in air at 35%, and was 60% at increased 89%
oxygen content. For the case of lignin however, rather than trying to enhance its
degradation, the interest was more on obtaining potential valuable aldehyde by-products,
and the most practical way to see this was to optimize conditions such that more aldehyde
was formed for every lignin oxidized. In the case of experiments in air, the maximum ratio
was obtained with most dilute solution (137 mg aldehydes/g lignin oxidized at initial
concentration of 80 mg L-1). This would not be favourable for industrial applications because
potential typical lignin concentrations would be higher. Decreasing the oxygen content to
about 5 - 7% reduces the ·OH radicals and ozone forming a milder oxidation environment for
lignin. In this condition, an opposite trend was observed: an increasing lignin concentration
corresponded to an increasing aldehyde to lignin formation ratio.
4.4 Effect of pulse repetition frequency
Pulse repetition frequency is a very significant parameter affecting the degradation of the
target compounds. The differing frequencies show the interaction between the ·OH radicals
and ozone with respect to the target compound. The pulse repetition frequency is able to
37
indirectly confirm the role of ozone and ·OH radical in oxidation. The substances refractory
towards oxidation with ozone show minor dependence on the frequency since the majority
of work is made by the radicals formed at the treated solution surface. The substances
exhibiting instant reaction with ozone also should show little dependence on frequency
since all the oxidants are consumed regardless the time between the pulses. The reactions
having the rate at intermediate scale, i.e. substances oxidizible with both ·OH radical and
ozone, however, should benefit from longer pauses between pulses giving more time for
relatively stable ozone to participate in oxidation. In the present work the author observed
reactions, where the pulse repetition frequency played a role, for example oxidation of
phenol and humic substances, as well as reactions independent of the frequency. Other
variable parameters such as water temperature, water flow rate and gas-liquid contact
surface area showed minor effect on PCD oxidation and were thus disregarded.
4.5 Reaction kinetics
The description of the reaction kinetics is complicated due to the unknown concentrations of
the ·OH radicals and ozone, as well as their individual contribution to the reaction. At the
initial stages of reaction, the degradation of parent compound followed a linear pattern. The
minimal impact of water flow rate and contact surface observed in the previous study
(Publication I) indicates the transitory presence of a constant amount of oxidants available in
the discharge zone. The reaction rate constants were determined assuming that the
combined effect of the oxidants result in a second-order reaction rate: first order relative to
the target pollutant and first order relative towards the oxidant.
For practical applications, the total concentration of the oxidants involved in the reaction
could be characterized by the power delivered to the volume of the discharge zone, with the
second-order reaction rate constant (Publications II, III & V):
dC/dt = k2·C·PV-1
(13)
where C is the concentration of the pollutant, mol m-3; k2 is the second-order reaction rate
constant, m3J-1; P is the pulsed power delivered to the reactor, W; V is the volume of the
discharge zone, 0.034 m3 in the experimental device.
The second-order reaction rate coefficients calculated for the initial period of treatment are
given in Table 5. Among the target compounds studied, fastest oxidation was obtained for
indomethacin; however, the oxidation of its intermediate products was slow. Indomethacin,
which has the highest number of unsaturated bonds among the studied pharmaceutical
compounds, has the highest reaction rate coefficient. The strong electrophilic nature of ·OH
radicals (Marusawa, et al., 2002) readily attracts it to the unsaturated bonds, thereby
increasing the reaction rate.
38
Table 5. The 2nd order reaction rate coefficients for different oxidation media
Media
Compound
Degree of Unsaturation
Reaction rate coefficient, k2, m3J-1
Acidic, air
Paracetamol
5
9.3 ± 1.0 · 10-8
Ibuprofen
5
9.6 ± 2.0 · 10-8
Salicylic acid
5
9.7 ± 2.0 · 10-8
Indometacin
12
7.8 ± 0.7 · 10-7
Phenol
4
1.5 ± 0.3 · 10-7
Paracetamol
5
2.2 ± 0.5 · 10-7
Ibuprofen
5
2.5 ± 0.1 · 10-7
Indometacin
12
2.1 ± 0.2 · 10-6
Paracetamol
5
1.6 ± 0.3 · 10-7
Salicylic acid
5
8.2 ± 1.0 · 10-8
Phenol
4
3.0 ± 0.3 · 10-7
Phenol
4
5.4 ± 0.4 · 10-7
Acidic, oxygen
Alkaline, air
Alkaline, oxygen
It can be seen from Table 5 that the oxidation rate was higher in oxygen-enriched media due
to a higher ozone equilibrium concentration. The improved degradation rate in alkaline
conditions for paracetamol and phenol might be attributed to the dissociation of phenol,
thereby increasing reactivity towards oxidation.
The dependence of the reaction rate coefficient on oxygen concentration in the gas phase
indicates the necessity to draw together the data to possibly develop the third-order
equation taking into account three parameters together, substrate and oxygen
concentrations and the applied pulsed power. Under current data set conditions such
description is difficult to verify (needs full-factorial experimental plan for power or
frequency, and substrate and oxygen concentrations).
Moderate reactions were observed for humic acid and paracetamol in oxygen media. Slow
reacting compounds in air and oxygen media are ibuprofen, lignin, salicylic acid and estradiol. Humics and paracetamol had slow reactions in air. The pulse repetition greatly
affects the degradation rate as the increasing frequency corresponds to a faster oxidation.
The kinetics for the combined effect of ·OH radicals and ozone on humic acids was described
39
in Publication I in terms of pseudo-first order reaction rate coefficients. The decreasing rate
coefficient with increased frequencies indicates that the 30% contribution of ozone takes
place between pulses. This interdependence between the pulse frequency and the initial
concentrations emphasizes the influence of at least two different oxidants with different
reaction rates and yields.
4.6 Surface radical reaction
The addition of ·OH radical scavenger, the surfactant igepal C-630 in equimolar amount to
that of phenol concentration in the solution hindered the surface reaction of the radicals
with the target pollutant; whereas the addition of tert-butyl alcohol (TBA) did not show its
scavenging properties even in concentrations exceeding the ones of phenol by a factor of
ten. This supports the hypothesis of surface formation of oxidant species and surface
reaction. Addition of compounds typically present in domestic sewage such as urea and
sucrose in -estradiol oxidation considerably slowed down the reaction. Of even bigger
interference in the oxidation process was the presence of urine in the sample known to
contain fragments of amino-acids with surfactant properties. The ratio of admixtures,
however, was remarkably bigger than in phenol oxidation with TBA.
4.7 Energy efficiency of PCD
The energy efficiencies of the oxidation of the target compounds with varying parameters
were described in Publications I-VI. Considering that the approximate energy of a single
pulse is about 0.3 J as mentioned earlier, at the maximum pulse repetition frequency of 840
pps, the power dissipated in the discharge is 250 W. A pulse repetition frequency of 200 pps
corresponds to 60 W of delivered power.
The delivered energy dose E, kWh m-3 is calculated by:
(14)
where P is the pulse integral power delivered to the reactor, kW; t is the oxidation time, h;
and V is the volume of the treated solution, m3.
Knowing the delivered energy dose, the energy efficiency , g kW-1h-1 is calculated according
to the equation:
(15)
40
The common point in these reactions was the beneficial effect of increased oxygen
concentrations towards higher energy efficiency for degrading the target compound. As seen
in Table 6, the results, however, showed the differences in their interaction with the ozone
generated as a result of introducing oxygen.
Table 6. The energy consumption efficiency in target compounds oxidation in 100 ppm solutions
Oxidation efficiency, g kW-1h-1
Substance /
media
Air, acidic
Air, alkaline
Oxygen, acidic
Oxygen, alkaline
55
88
120
140
Paracetamol
20 - 28
31 - 52
50 – 70
-
Ibuprofen
24 - 41
-
58 – 65
-
Indomethacin
120 - 150
-
158 – 172
-
Salicylic acid
20 - 35
17 - 20
-
-estradiol
(3 ppm)
-
3.8
-
-estradiol with
urea, sucrose and
urine
-
1.5 -1.9
-
Phenol
The oxygen in the reactor is mainly consumed for the synthesis of ozone which when
increased, contributes further to the degradation of the target compound. In the presence of
nitrogen from air, PCD results in the formation of nitrogen oxides which upon contact with
water, are transformed to nitrates (Kornev, et al., 2012).
4.8 Effect of organic pollutants on nitrates formation
The presence of the studied target organic compounds (paracetamol, ibuprofen, and
indomethacin) reduced the formation of nitrates in the PCD as seen in Publication VI.
However, oxalate and formate, substantially improved the nitrates formation. The presence
of these carboxylic ions may have improved the aqueous ozone decomposition and hydroxyl
radical formation, thus enhancing the nitrate formation. Once the parent compound is
completely oxidized, as evident in the case for indomethacin, oxidation products
dramatically promote nitrate formation. Although there is a need of establishing the
products responsible for the promotion, oxalate and formate concentrations observed in
this experiment were low.
41
5. CONCLUSIONS
This study confirms the effectiveness of pulsed corona discharge for the oxidation of
phenolic and aromatic compounds of various types. The efficiency of the oxidation process
increases with the reduced pulse repetition frequency when fast reacting compounds are
treated allowing for a higher contribution of ozone in oxidation between pulses. For slow
reacting refractory pollutants however, it is more beneficial to use higher pulse repetition
frequencies to significantly increase the oxidation rate since the role of ozone in slow
reactions occurred to be minor.
Enriching the gas phase with oxygen shows a significant increase in oxidation efficiency of
the target compound due to the abundant formation of oxidants, ozone and ·OH radicals.
Subsequently, depleting oxygen in the gas phase lowers the oxidation rate as well as the
oxidation efficiency. Higher initial concentration of the pollutant improves the oxidation
efficiency accordingly. The improved oxidation efficiency observed in alkaline media
indicates the increased ozone absorption and secondary ·OH radicals formation, both of
which readily react with the dissociated phenolic moieties.
The effectiveness in oxidizing the parent compound has been shown by the extent of
mineralization achieved which is mainly due to the action of non-selective ·OH radicals
formed at the water surface combined with the ozone formed at higher oxygen
concentrations. With decreasing oxygen concentrations, the role of ·OH radicals during
oxidation substantially increases.
The rate is being controlled mostly by the discharge pulse parameters, with the mass
transfer showing minimal influence on the oxidation efficiency. The oxidation of the target
pollutants is brought about by the reaction of the hydroxyl radicals and atomic oxygen which
are formed on the interface of the water.
The energy efficiencies achieved in PCD oxidation surpass those of ozone, which is the
closest competitor of the technology or that of other AOPs where reported data is available.
This makes the process more advantageous especially with the simple configuration. The
advantage of PCD equipment in terms of oxygen usage for improved oxidation reaction is
that the gas is simply replenished, eliminating the need for gas transport.
The data obtained in this study give some additional knowledge that the pulsed corona
discharge oxidation technique is energy and cost efficient relative to competing available
technologies for plasma-based environmental applications.
42
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47
APPENDIX I
DBD in medical and agricultural applications
Several applications on the use of microsecond-pulsed DBD have been investigated in Drexel
Plasma Institute. One of the studies conducted by the author makes use of DBD treated
water to decontaminate pig skin laden with E. Coli. The objective was to compare its
effectiveness to that of commercial sanitizers. With the parameters used, the results showed
that plasma water, when applied immediately to the surface of pig skin, eliminated as much
bacteria as a hand sanitizer, reducing the E. Coli concentration from 1 x 106 to 1 x 105.
Plasma water on pig skin with E. Coli
1E+08
E. Coli concentration, cfu mL-1
2.85E+07
1E+07
2500 Hz
1E+06
9.90E+05
3000 Hz
Stock
Control
1E+05
8.13E+04
Sanitizer
1E+04
15
30
60
Plasma water treatment time, sec
Figure 5. Performance of plasma treated water in comparison with commercial hand sanitizer
Further application of the DBD treated water to C. sporogenes was initiated, and as
preliminary data showed potential, more verification was necessary. Another study involves
the use of the plasma for inducing cell differentiation, but at a very early stage, no
conclusions could still be drawn.
One other interesting study was evaluating the effect of plasma treated water on the growth
rate and sugar content of some plants. It is based on a premise that the change in the
properties and composition of plasma treated water might affect plant growth and quality.
The observed increased levels of reactive nitrogen species and oxidizing species and the
change of pH are properties that could play a vital part in the growing plants. Preliminary
data showed remarkable effect on the growth rate of plants stressing the need for further
evaluation.
PART II: Publications
Publication 1
Pulsed corona discharge for degradation of aqueous humic substances.
corona
Technology:
Water Supply 11(2), 238 245 doi:10.2166/ws.2011.045, with permission from the copyright
holders, IWA Publishing.
Reprinted by permission of IWA Publishing
© IWA Publishing
Publication 5
Pulsed Corona Discharge: The Role of Ozone and Hydroxyl Radical in Aqueous Pollutants
Oxidation.
Reproduced from the paper accepted for publication on May 28, 2013 by Preis, S., Panorel,
I., Kornev, I., Hatakka, H., Kallas, J.,(2013)
corona discharge: the role of ozone and
Technology, with
hydroxyl radicals in aqueous pollutants oxidation
permission from the copyright holders, IWA Publishing.
Reprinted by permission of IWA Publishing
© IWA Publishing
Pulsed Corona Discharge: The Role of Ozone and Hydroxyl
Radical in Aqueous Pollutants Oxidation
sergei.preis@lut.fi; iris.panorel@lut.fi; henry.hatakka@lut.fi; juha.kallas@lut.fi)
j.kornev@mail.ru
Abstract
Keywords
INTRODUCTION
MATERIALS AND METHODS
Water
Perforated plate
System of
electrodes
Electric discharge
reactor
Sample feed
port
Voltage pulse
generator
Input
ports
Voltage and current
monitoring
O2
N2
Storage tank
Pump
Voltage, kV
15
10
5
0
-5
0 .5
1.0
Time, µs
1 .5
0.5
1 .0
Time, µs
1 .5
Current, A
400
200
0
Figure 2
Gas
cylinders
RESULTS AND DISCUSSION
Energy efficiency in oxidation
Figure 3:
Figure 4:
Contact surface and efficiency correlation
Surface reaction
tert
Figure 5:
Figure 6:
The role of ozone and OH-radical in oxidation
Phenol oxidation
Oxalate oxidation
Phenol oxidation kinetics practical description
et al
P
V
k2
dC/dt = k2·C·PV-1
k2
P
CONCLUSIONS
Acknowledgements
C
V
References
J. Phys. D: Appl.
Phys. 34
Russian J. Appl. Chem 75
Int. Journ. Environ. Waste Management
11
J. Physics D: Appl.
Physics 41
Appl. Microbiol. Biotechnol 52
Ind. Eng. Chem 15
Plasma Chem.
Plasma Proc 26
Wat. Res., 37
. J. Phys. D: Appl.
Phys 32
Ozone: Science and Engineering, 1
Ozone: Sci. Eng
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Ozone: Sci. Eng 35
Ozone: Sci. Eng
Die Analyse der Organischen Verunreinigungen in Trink-, Brauch- und
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IEEE
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Publication 6
Formation of nitrates in aqueous solutions treated with pulsed corona discharge: the
impact of organic pollutants.
This is a version of the paper that has been accepted for publication in Ozone: Science and
Engineering on August 19, 2013.
Reprinted by permission of the International Ozone Association
© International Ozone Association
sergei.preis@lut.fi
Abstract
Keywords:
1. Introduction
1
2. Materials and Methods
Experimental device and materials
2
(
Water
Perforated plate
System of
electrodes
Voltage pulse
generator
Electric discharge
reactor
Sample feed
port
Input
ports
Voltage and current
monitoring
O2
N2
Storage tank
Pump
3
Gas
cylinders
VS1
Capacitor
charger
C1
T1
Ls1
C2
Ls2
C3
Analytical methods
4
Ls3
C4
3. Results
Effect of frequency
5
Effect of pH and conductivity
6
7
4. Discussion
8
Nitrate yield, g kW-1 h-1
16
14
12
10
8
6
Parent compound
4
Oxidation products
2
0
9
Conclusions
10
Acknowledgements
References
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Water Quality Research Journal of Canada
Applied Microbiology & Biotechnology
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IEEE Transactions on Plasma
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Technology
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Plasma
Sources Science and Technology
Russian Federation Patent
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496.
VAUTERIN, JOHANNA JULIA. The demand for global student talent: Capitalizing on the value of
university-industry collaboration. 2012. Diss.
497.
RILLA, MARKO. Design of salient pole PM synchronous machines for a vehicle traction application.
2012. Diss.
498.
FEDOROVA, ELENA. Interdependence of emerging Eastern European stock markets. 2012. Diss.
499.
SHAH, SRUJAL. Analysis and validation of space averaged drag model for numerical simulations of
gas-solid flows in fluidized beds. 2012. Diss.
500.
WANG, YONGBO. Novel methods for error modeling and parameter identification of redundant
hybrid serial-parallel robot. 2012. Diss.
501.
MAXIMOV, ALEXANDER. Theoretical analysis and numerical simulation of spectral radiative
properties of combustion gases in oxy/air-fired combustion systems. 2012. Diss.
502.
KUTVONEN, ANTERO. Strategic external deployment of intellectual assets. 2012. Diss.
503.
VÄISÄNEN, VESA. Performance and scalability of isolated DC-DC converter topologies in low
voltage, high current applications. 2012. Diss.
504.
IKONEN, MIKA. Power cycling lifetime estimation of IGBT power modules based on chip
temperature modeling. 2012. Diss.
505.
LEIVO, TIMO. Pricing anomalies in the Finnish stock market. 2012. Diss.
506.
NISKANEN, ANTTI. Landfill gas management as engineered landfills
environmental aspects. 2012. Diss.
507.
QIU, FENG. Surface transformation hardening of carbon steel with high power fiber laser. 2012.
Diss.
508.
SMIRNOV, ALEXANDER. AMB system for high-speed motors using automatic commissioning.
2012. Diss.
509.
ESKELINEN, HARRI, ed. Advanced approaches to analytical and systematic DFMA analysis. 2013.
510.
RYYNÄNEN, HARRI. From network pictures to network insight in solution business
internal communication. 2013. Diss.
511.
JÄRVI, KATI. Ecosystem architecture design: endogenous and exogenous structural properties.
2013. Diss.
512.
PIILI, HEIDI. Characterisation of laser beam and paper material interaction. 2013. Diss.
513.
MONTO, SARI. Towards inter-organizational working capital management. 2013. Diss.
Estimation and mitigation of
the role of
514.
PIRINEN, MARKKU. The effects of welding heat input usability of high strength steels in welded
structures. 2013. Diss.
515.
SARKKINEN, MINNA. Strategic innovation management based on three dimensions diagnosing
innovation development needs in a peripheral region. 2013. Diss.
516.
MAGLYAS, ANDREY. Overcoming the complexity of software product management. 2013. Diss.
517.
MOISIO, SAMI. A soft contact collision method for real-time simulation of triangularized geometries
in multibody dynamics. 2013. Diss.
518.
IMMONEN, PAULA. Energy efficiency of a diesel-electric mobile working machine. 2013. Diss.
519.
ELORANTA, LEENA. Innovation in a non-formal adult education organisation
four education centres. 2013. Diss.
520.
ZAKHARCHUK, IVAN. Manifestation of the pairing symmetry in the vortex core structure in ironbased superconductors. 2013. Diss.
521.
KÄÄRIÄINEN, MARJA-LEENA. Atomic layer deposited titanium and zinc oxides; structure and
doping effects on their photoactivity, photocatalytic activity and bioactivity. 2013. Diss.
522.
KURONEN, JUHANI. Jatkuvan äänitehojakautuman algoritmi pitkien käytävien äänikenttien
mallintamiseen. 2013. Diss.
523.
HÄMÄLÄINEN, HENRY. Identification of some additional loss components in high-power lowvoltage permanent magnet generators. 2013. Diss.
524.
SÄRKKÄ, HEIKKI. Electro-oxidation treatment of pulp and paper mill circulating waters and
wastewaters. 2013. Diss.
525.
HEIKKINEN, JANI. Virtual technology and haptic interface solutions for design and control of
mobile working machines. 2013. Diss.
526.
SOININEN, JUHA. Entrepreneurial orientation in small and medium-sized enterprises during
economic crisis. 2013. Diss.
527.
JÄPPINEN, EERO. The effects of location, feedstock availability, and supply-chain logistics on the
greenhouse gas emissions of forest-biomass energy utilization in Finland. 2013. Diss.
528.
SÖDERHOLM, KRISTIINA. Licensing model development for small modular reactors (SMRs)
focusing on the Finnish regulatory framework. 2013. Diss.
529.
LAISI, MILLA.
Sea region. 2013. Diss.
530.
VORONIN, SERGEY. Price spike forecasting in a competitive day-ahead energy market. 2013.
Diss.
531.
PONOMAREV, PAVEL. Tooth-coil permanent magnet synchronous machine design for special
applications. 2013. Diss.
532.
HIETANEN, TOMI. Magnesium hydroxide-based peroxide bleaching of high-brightness
mechanical pulps. 2013. Diss.
533.
TYKKÄLÄ, TOMMI M. Real-time image-based RGB-D camera motion tracking and environment
mapping. 2013. Diss.
534.
PEKKOLA, SANNA. Performance measurement and management in a collaborative network.
2013. Diss.
multi-case study in