Removal of geosmin and 2-methylisoborneol from drinking water by UV/Tio2 treatment

Research Doctorate - Doctor of Philosophy (PhD)Geosmin and 2-methylisoborneol (MIB) are taste and odour compounds commonly present in drinking water. Their presence can be detected even at the nanogram-per-litre level, and at such low concentrations they are not readily removed by conventional water treatment processes. Consequently, alternative treatment processes are needed that add significant cost to the water treatment option. Recently, it has been found that UV/TiO2 photocatalysis is capable of degrading geosmin and MIB, and because TiO2 is relatively cheap UV/TiO2 photocatalysis is a possible commercial treatment option. However, the reaction kinetics and mechanisms are not well understood, which limits current development. This study was aimed at gaining a better understanding of kinetics and mechanisms of the photocatalytic degradation of geosmin and MIB by UV/TiO2. It sought to undertake an extensive experimental investigation to quantify the influence of TiO2 type, TiO2 loading, geosmin and MIB concentration, UV intensity, mixing condition, pH and presence of additives (bicarbonate, alcohols and humic acid) on the removal of geosmin and MIB. Before embarking on the experiments, however, a rapid and cost-effective methodology for the quantification of geosmin and MIB at the nanogram-per-litre level was required. Consequently, a solid phase micro-extraction technique coupled with gas chromatography/mass spectrometry (GC/MS) analysis was developed. Briefly, accurate and reproducible measurements were achieved with biphenyl-d10 as the internal standard and preconditioning the fibre prior to the adsorption stage. Optimum extraction temperature and duration were found to be 270oC and 30 minutes, respectively. Once the quantitative detection process was in place geosmin and MIB degradation experiments were carried out using various commercial TiO2 photocatalysts, including Degussa P25 and Millennium PCs with different specific surface areas. All these photocatalyst were found to be effective to remove geosmin and MIB, with Degussa P25 giving the best performance. Interestingly, there was no apparent correlation between the specific surface area of the photocatalyst particle and the degradation rate. A reason for this is possibly related to the agglomeration occurring when the material is suspended in water. The experiments examining the degradation rate of geosmin and MIB involved both suspended and immobilised TiO2 systems. Dark adsorption studies showed that there was negligible adsorption of either geosmin or MIB onto the TiO2 surface. This observation was supported by zeta potential measurements which identified repulsion between the different surfaces. The degradation rate of both geosmin and MIB involving the activation of TiO2 photocatalyst with UV light followed a first-order kinetic processes with respect to TiO2 loading, geosmin and MIB concentration, pH, UV intensity and mixing condition. The degradation rates for the suspended Degussa P25 photocatalyst exhibited energy efficiencies comparable to those of existing treatment processes such as hydrogen peroxide/UV. The mechanistic studies focused on understanding the generation process for hydroxyl radicals. It was found that the presence of bicarbonate and alcohols, that are known hydroxyl radical scavengers, resulted in a decrease in the degradation rates of both geosmin and MIB. The increased negative effect bicarbonate<methanol