| Abstract | Istraživanje koje je provedeno u sklopu ove disertacije temelji se na uklanjanju dvaju
mikrozagađivala iz vode naprednim oksidacijskim postupcima (NOP), primjenom ultrazvuka
visoke snage te ozona. Odabrana mikrozagađivala imaju različite namjene i pripadaju različitim
skupinama spojeva – gemfibrozil je farmaceutik koji služi za regulaciju lipida u krvi, dok je
epoksikonazol pesticid koji se koristi u preventivne i kurativne svrhe za zaštitu biljaka. Oba
spoja su, prema Istraživačkom centru Europske komisije, kandidati za ulazak na buduće popise
štetnih tvari za praćenje zbog pojavnosti u okolišu i nedovoljne istraženosti potencijalnih štetnih
učinaka.
Istraživanje je provedeno u laboratorijskim uvjetima i daje uvid u učinkovitost primjene
ultrazvuka visoke snage i ozona na uklanjanje odabranih mikrozagađivala iz vode. U
ispitivanjima su korištene modelne otopine odabranih mikrozagađivala pri kontroliranim pHvrijednostima
primjenom fosfatnog pufera (pH = 7) te prirodna jezerska voda u koju je dodana
ona količina mikrozagađivala da se postigne ukupna koncentracija 10 μmol L-1. Eksperimenti
u kojima se koristila prirodna voda pokazuju uspješnost postupka razgradnje u uvjetima u
kojima prirodan sastav vode znatno utječe na njegovo odvijanje. Također je ispitivana
učinkovitost razgradnje uz prisutnost hvatača hidroksilnih radikala (t-BuOH). Eksperimenti s
ciljem određivanja kinetičkog modela i numeričkog dobivanja vrijednosti konstanti brzina
razgradnje provedeni su za svaki pojedini postupak. Koncentracije mikrozagađivala određivale
su se primjenom tekućinske kromatografije visoke djelotvornosti (HPLC) upotrebom PDA
(epoksikonazol) ili fluorescencijskog detektora (gemfibrozil).
U istraživanju je obuhvaćeno i utvrđivanje produkata razgradnje mikrozagađivala koji su nastali
primjenom odabranih naprednih oksidacijskih postupaka. Za njihovo određivanje koristio se
sustav tekućinske kromatografije ultravisoke djelotvornosti (UHPLC) sa spektrometrom masa
visokog razlučivanja (Q-TOF). Na temelju toga dan je prijedlog mogućih putova razgradnje za
svaki primijenjeni napredni oksidacijski postupak.
Toksični učinci odabranih mikrozagađivala i razgradnih produkata određivani su in silico
(pomoću računala) analizom uz pomoć matematičkog modeliranja kvantitativnog odnosa
strukture i aktivnosti (QSAR). Odabrani parametar za predviđanje toksičnih učinaka bio je LC50
- koncentracija koja je smrtonosna za 50% testnih organizama. |
| Abstract (english) | The research carried out as part of this doctoral dissertation aims to investigate the removal of
two micropollutants from water by advanced oxidation processes (AOPs), using high power
ultrasound and ozone. The selected micropollutants serve different purposes and belong to
distinct groups of compounds – gemfibrozil is a pharmaceutical used as a lipid regulator, while
epoxiconazole is a pesticide with both preventative and curative action used for plant protection.
According to the Joint Research Centre (JRC), the European Commission’s science and
knowledge service, both compounds are considered as contaminants of emerging concern and
are identified as potential candidates for the Watch list under the Water Framework Directive
for future monitoring due to their occurrence in the environment and lack of data concerning
potential harmful effects.
Conventional water treatment processes are usually inefficient in removing emerging
contaminants. Therefore, AOPs represent a promising alternative in water treatment. They are
characterized by the generation of highly reactive hydroxyl radicals (•OH), which are almost
non-selective in their reactions with organic compounds and have high reaction rate constants.
The use of high power ultrasound as an AOP has been reported to be a highly efficient process
for the removal of micropollutants and is considered to be an environmentally-friendly
technology since it does not require the addition of chemicals and does not generate waste.
Ozonation, on the other hand, is a well-established technology often employed for water
disinfection and can be applied as an AOP for the removal of micropollutants under certain
conditions where •OH radicals are generated through ozone decomposition.
Extensive lab-scale research was conducted with the following objectives:
• to determine the efficiency of both AOPs in the removal of selected micropollutants
from water by experimentally obtaining the value of reaction rate constant,
• to identify the degradation by-products formed,
• to propose the reaction pathways of selected micropollutants,
• to predict the toxicity of selected micropollutants and their degradation by-products.
The dissertation is organized as follows.
Chapter 1 provides an introduction outlining the problem statement and the overview of the
previous research with the focus on several key areas: detection, identification and occurrence
of emerging contaminants in natural and drinking water and wastewater; their fate and transport
in natural aquatic environment and the knowledge on their reaction pathways and by-products;
identification of potential toxicological effects; mechanisms for the removal of emerging
contaminants and treatment technologies that can be effectively used for their removal. Two
selected micropollutants, gemfibrozil and epoxiconazole, are presented with details on their
specific properties, occurrence in water environment and toxicity data. At the end of the chapter,
objectives of the study are stated, the hypothesis is given, and scientific contribution is outlined.
Chapter 2 presents the theoretical background for the thesis. It describes advanced oxidation
processes with emphasis on the application of high power ultrasound and the phenomenon of
acoustic cavitation, responsible for the emergence of sonochemical processes. All parameters
that affect the sonochemical degradation of micropollutants are presented in detail. The
concepts of chemical dosimetry used for the quantification of OH radicals are described and a
model for the determination of OH radicals steady-state concentration is provided. The kinetics
of sonochemical degradation is described using mathematical models which consider the
complexity of sonochemical process in heterogeneous conditions. The theory on application of
ozone as an AOP is presented with the main mechanisms of ozone reactions in water. Its
instability in water results in fast decay followed by numerous chain reactions. The most widely
accepted decay mechanism of ozone in water is described.
Chapter 3 describes the experimental setup for the removal of emerging contaminants using
high power ultrasound. It explores the ultrasound performance under different input parameters
to optimize experimental conditions for micropollutants degradation (acoustic power
determination using calorimetric method, steady-state •OH radicals estimation conducted using
terephthalic dosimetry system). It also includes the determination of the optimum concentration
of radical scavenger (t-BuOH) which is assumed to scavenge the vast majority of •OH radicals
to get the information on the part of the degradation associated with very high temperature
pyrolysis. Regarding the application of ozone as an AOP, this chapter describes the
experimental setup for preparing the ozone stock solution and the materials and methodologies
used for measuring the ozone concentrations, either by direct UV measurement (stock solution)
or indigo method.
Chapters 4 and 5 present the results of application of high power ultrasound in the degradation
of gemfibrozil and epoxiconazole, respectively, in both model and natural water. The results of
kinetic experiments were obtained to estimate the observed reaction rate constant. Chapters also
include relevant information on the identified degradation by-products and their proposed
structures which were used to propose the relevant reaction pathways of gemfibrozil and
epoxiconazole degradation upon ultrasonic sonication. The results of toxicity assessments of
both micropollutants and their by-products using in silico analyses and mathematical modeling
based on the qualitative structure-activity relationship (QSAR) are also presented.
Chapters 6 and 7 present the results of using ozone as an AOP in degradation of selected
micropollutants. The materials, methods and experimental procedures are based on two
degradation mechanisms – the reaction with molecular ozone and the reaction with OH radicals
generated through ozone decomposition. The results obtained from separate kinetic
experiments provided the degradation rate constants for the reaction of O3 and OH radicals
with gemfibrozil and epoxiconazole, respectively. The experiments also showed that
gemfibrozil reacts readily with both oxidant species, as opposed to epoxiconazole which
showed minimal reactivity towards ozone.
Chapter 8 contains a brief discussion on the results of this research and the final conclusions of
this thesis. |
