Advanced oxidation processes (AOPs) using hydroxyl radicals and other oxidative radical species are being studied extensively for removal of organic compounds from various waste streams. However, large scale applications of these highly effective technologies in water and wastewater treatment are still very limited due to cost and inadequate information about the resultant water quality. This study focuses on the evaluation of the upstream processing and downstream post treatment analysis of selective AOPs. In the first stage of research, the performance of a proprietary catalyst (VN-TiO2) was compared with the industry standard P25 TiO2, for the use in a pilot-scale immobilized photocatalytic reactor. Using a dip coated fibreglass disk support in the VN-TiO2 solution and calcining, porous films with high surface area were produced. Although films formed by VN-TiO2 on fibreglass disks had a reaction rate 50% lower than that of P25, the VN-TiO2 disks were mechanically robust in the reactor, compared to those coated with P25. The addition of 15% P25 in the VN-TiO2 solution increased the reaction rate by 40%, while maintaining the mechanical stability. Reuse potential of both catalysts (VN-TiO2 and P25) was tested, and the rates of deactivation were comparable for both catalysts. Deactivation occurred possibly due to sustained adsorption of intermediates as well as loss of active sites due to heat treatment for reactivation. The low cost of the fibreglass, as compared to commonly used borosilicate glass, in combination with the VN-TiO2 catalyst is ideal for testing pilot scale reactor designs.
In the second stage of the study two bioassays were used to evaluate and compare the toxicity of bisphenol A, and its degradation intermediates formed in three AOPs, namely UV/H2O2, ozonation, and photocatalysis. Two assays were used in evaluating water quality, namely the Ames Test for mutagenicity and the YES assay for estrogencity. Both UV/H2O2 and ozonation removed less than 10% of the initial total organic carbon (TOC), whereas photocatalysis resulted in a 50% reduction of TOC indicating a significant difference in intermediate formation. No mutagenicity was found over the entire tested range of BPA degradation in any of the AOPs. Estrogenicity steadily decreased in accordance with BPA degradation, and was below the limit of detection for photocatalysis. UV/H2O2 and ozonation results indicated the possible formation of intermediates with slight estrogenic activity as estrogenicity reached a plateau with a constant value at 15% of initial estrogenicity, while BPA continued to degrade with time. The work demonstrated effective use of bioassay tools in determining performances of AOPs
