Design and evaluation of photocatalytic reactors for water purification

De Villiers, David (2001-12)

Thesis (PhD)--Stellenbosch University, 2001.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/52178
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