Design and evaluation of photocatalytic reactors for water purification

[摘要] ENGLISH ABSTRACT:The photo-mineralization of organic compounds (in the combined presence of a Ti02based semiconductor catalyst, UV radiation and molecular oxygen) represents anadvanced oxidation technology with significant potential for environmental pollutionabatement. This oxidation process (generally known as photocatalytic oxidation - PCO) iscurrently the subject of extensive global research, with the main objective being theoxidative 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 aunique (and effective) configuration of catalyst, light source and reactor design needs toidentified. In terms of the water treatment scenario (which is the emphasis of this work) theneed exists to develop a practical and affordable PCO reactor for water treatment on alarge scale.The two laboratory-scale PCO reactors investigated in this work were based on a fallingfilm flow reactor design and were constructed with commercially available materials andcomponents. Degussa P-25 Ti02 was used as semiconductor catalyst and two types oflow-pressure mercury lamps as the UV light source. Three modes of operation wereinvestigated in order to determine the practical feasibility of the reactors. These includedthe recirculation, single pass and sequential single pass modes. The reactors wereoperated either as a Ti02 slurry-phase reactor (Reactor 1), or with Ti02 immobilized onstationary fiber glass and fibrous activated carbon sheet modules (Reactors 2A and 28respectively). Extensive parametric evaluations were done using conventional one-factorvariation and statistical methods according to optimal experimental design principles. ThePCO treatment of two model organic pollutants (para-Chlorophenol and cyanobacterialmicrocystin YA, YR, LR and RR) were investigated. These pollutants were spiked intovarious water matrices to the desired concentration level. The combined photocatalyticcarbonadsorption treatment of these two pollutants was also investigated in Reactor 28.The experimental results obtained through this work showed that both model pollutantswere successfully degraded in several water matrices by means of treatment in therespective PCO reactors. Moreover, this research was the first ever demonstration of theTi02 photocatalytic degradation of microcystin toxins in the aqueous phase. The largenumber of parametric and optimization studies yielded the relative contributions of thevarious process parameters (in terms of the defined photocatalytic efficiency parametersas responses) very effectively. Furthermore, statistical evaluation of the experimental dataprovided valuable insight into the scientific phenomena associated with Ti02 mediatedPCO processes.

[发布机构] Stellenbosch University