Thesis (PhD)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The photo-mineralization of organic compounds (in the combined presence of a Ti02
based semiconductor catalyst, UV radiation and molecular oxygen) represents an
advanced oxidation technology with significant potential for environmental pollution
abatement. This oxidation process (generally known as photocatalytic oxidation - PCO) is
currently the subject of extensive global research, with the main objective being the
oxidative removal of organic and inorganic pollutants from water, air and soil. Presently,
many barriers still block the way to commercial implementation of this technology, hence a
unique (and effective) configuration of catalyst, light source and reactor design needs to
identified. In terms of the water treatment scenario (which is the emphasis of this work) the
need exists to develop a practical and affordable PCO reactor for water treatment on a
large scale.
The two laboratory-scale PCO reactors investigated in this work were based on a "falling
film" flow reactor design and were constructed with commercially available materials and
components. Degussa P-25 Ti02 was used as semiconductor catalyst and two types of
low-pressure mercury lamps as the UV light source. Three modes of operation were
investigated in order to determine the practical feasibility of the reactors. These included
the recirculation, single pass and sequential single pass modes. The reactors were
operated either as a Ti02 slurry-phase reactor (Reactor 1), or with Ti02 immobilized on
stationary fiber glass and fibrous activated carbon sheet modules (Reactors 2A and 28
respectively). Extensive parametric evaluations were done using conventional one-factor
variation and statistical methods according to optimal experimental design principles. The
PCO treatment of two model organic pollutants (para-Chlorophenol and cyanobacterial
microcystin YA, YR, LR and RR) were investigated. These pollutants were spiked into
various water matrices to the desired concentration level. The combined photocatalyticcarbon
adsorption treatment of these two pollutants was also investigated in Reactor 28.
The experimental results obtained through this work showed that both model pollutants
were successfully degraded in several water matrices by means of treatment in the
respective PCO reactors. Moreover, this research was the first ever demonstration of the
Ti02 photocatalytic degradation of microcystin toxins in the aqueous phase. The large
number of parametric and optimization studies yielded the relative contributions of the
various process parameters (in terms of the defined photocatalytic efficiency parameters
as responses) very effectively. Furthermore, statistical evaluation of the experimental data
provided valuable insight into the scientific phenomena associated with Ti02 mediated
PCO processes. / AFRIKAANSE OPSOMMING: Die foto-mineralisasie van organiese verbindings (in die gekombineerde teenwoordigheid
van 'n Ti02 gebaseerde halfgeleier katalisator, UV straling en molekulêre suurstof)
verteenwoordig 'n gevorderde oksidasie-tegnologie met beduidende potensiaal vir
bekamping van omgewingsbesoedeling. Hierdie oksidasie-proses (algemeen bekend as
fotokatalitiese oksidasie - FKO) is tans wêreldwyd die onderwerp van ekstensiewe
navorsing, met hoofdoel die oksidatiewe verwydering van organiese en anorganiese
besoedelingstowwe uit water, lug en grond. Huidiglik bestaan daar nog vele struikelblokke
wat die weg na kommersiële implementering van hierdie tegnologie blokkeer, gevolglik
moet 'n unieke (en effektiewe) konfigurasie van katalisator, ligbron en reaktor-ontwerp nog
identifiseer word. In terme van die waterbehandeling situasie (wat die klem van hierdie
werk is) bestaan die nodigheid om 'n praktiese en bekostigbare FKO reaktor te ontwikkel
vir watersuiwering op 'n groot skaal.
Die twee laboratorium-skaal FKO reaktore in hierdie studie was gebaseer op 'n "vallende
film" vloeireaktor ontwerp en is gekonstrueer met kommersieël beskikbare materiale en
komponente. Degussa P-25 Ti02 is aangewend as halfgeleier katalisator en twee tipes
lae-druk kwik lampe as die UV ligbron. Drie bedryfsmodes is ondersoek met die doel om
die praktiese haalbaarheid van die reaktore te bepaal. Hierdie het ingesluit die
resirkulasie, enkeldeurvloei en enkeldeurvloei-sekwensie modes. Die reaktore is bedryf as
óf 'n Ti02 flodder-fase reaktor (Reaktor 1) óf met Ti02 ge-immobiliseer op 'n stasionêre
veselglas en veselagtige ge-aktiveerde koolstof blad-modules (Reaktor 2A en 28
onderskeidelik). Omvattende parametriese evaluasies is gedoen deur gebruik te maak
van konvensionele een-faktor variasie en statistiese metodes na aanleiding van optimale
eksperimentele ontwerp beginsels. Die FKO behandeling van twee modelorganiese
besoedelingstowwe (para-Chlorofenol en siano-bakteriese mikrosistien YA, YR, LR en
RR) is ondersoek. Hierdie besoedelingstowwe is ge-ent in verskeie watermatrikse tot die
verlangde konsentrasievlak. Die gekombineerde fotokatalitiese - aktiveerde koolstof
behandeling van die twee besoedelingstowwe is ook ondersoek in Reaktor 28.
Die eksperimentele resultate verkry deur hierdie werk het getoon dat beide die modelbesoedelingstowwe
suksesvol gedegradeer is in verskeie watermatrikse deur behandeling
in die onderskeie FKO reaktore. Trouens, hierdie navorsing was die eerste demonstrasie
ooit van die Ti02 fotokatalitiese degradasie van mikrosistien toksiene in die waterige fase.
Die groot aantal parametriese en optimiseringstudies het die bydraes van die verskeie
proses-parameters (in terme van die gedefinieerde fotokatalitiese effektiwiteitsparameters
as response) baie effektief verskaf. Verder, statistiese evaluasie van die eksperimentele
data het waardevolle insig verskaf tot die wetenskaplike verskynsels te assosieer met Ti02
gemedieërde FKO prosesse.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52178 |
| Date | 12 1900 |
| Creators | De Villiers, David |
| Contributors | Engelbrecht, W. J., Wessels, G. F. S., Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 259 p. |
| Rights | Stellenbosch University |
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