Abstract
The current living standards are letting our surface water and groundwater be filled with micropollutants since the traditional wastewater treatment plants are not able to eliminate them completely. This thesis is focused on the functionality of photocatalytic membranes for the degradation of micropollutants in water. The combination of photocatalytic oxidation and membrane filtration in a single system is promising as an additional step in water treatment.
𝛼-Alumina supports were used for the membrane fabrication by dip-coating them with a layer of 𝛾-alumina and subsequently a TiO2 layer. A photocatalytic membrane reactor operated in single-pass dead-end mode was designed and fabricated to test the membranes.
The effect of the illumination distribution and intensity on the membrane surface was studied. 20 % more degradation was obtained for the most homogeneous light distributions at the same average irradiation and filtration rate (210 W.m-2 and 9.7 L.m-2.h-1). Moreover, a linear relationship between the surface reaction rate constant and the photon flux was obtained for the most homogeneous distribution ranging between 50 to 550 W.m-2.
The catalyst load was also analyzed, by fabricating nine membranes with catalyst thicknesses from 0.26 to 21.9 μm. An optimum thickness of ~3 μm was reported for the single-layer membranes as the degradation slightly improved beyond this thickness. However, an increase in degradation for membranes with multiple catalytic layers was still possible, indicating a direct connection between the material morphology and the optimal catalyst thickness.
We propose two simple models to elucidate the synergy between photocatalytic oxidation (reaction) and membrane filtration (rejection). The first model describes the transport phenomena and the photocatalytic reaction on the membrane surface, where the membrane is treated as a boundary condition. In the second model, the membrane function is included by considering the light intensity decay with thickness as a result of the light absorption. Both models have been used to describe the experimental results, obtaining unique photocatalytic reaction parameters.
The discoloration of methylene blue in an aqueous solution was used as a model compound to fit the two models. Other pharmaceuticals were also degraded in our reactor to further investigate the applicability of these membranes. Here, we emphasized the importance of the water matrix in the photocatalytic degradation of micropollutants since it can hinder or help the process.
𝛼-Alumina supports were used for the membrane fabrication by dip-coating them with a layer of 𝛾-alumina and subsequently a TiO2 layer. A photocatalytic membrane reactor operated in single-pass dead-end mode was designed and fabricated to test the membranes.
The effect of the illumination distribution and intensity on the membrane surface was studied. 20 % more degradation was obtained for the most homogeneous light distributions at the same average irradiation and filtration rate (210 W.m-2 and 9.7 L.m-2.h-1). Moreover, a linear relationship between the surface reaction rate constant and the photon flux was obtained for the most homogeneous distribution ranging between 50 to 550 W.m-2.
The catalyst load was also analyzed, by fabricating nine membranes with catalyst thicknesses from 0.26 to 21.9 μm. An optimum thickness of ~3 μm was reported for the single-layer membranes as the degradation slightly improved beyond this thickness. However, an increase in degradation for membranes with multiple catalytic layers was still possible, indicating a direct connection between the material morphology and the optimal catalyst thickness.
We propose two simple models to elucidate the synergy between photocatalytic oxidation (reaction) and membrane filtration (rejection). The first model describes the transport phenomena and the photocatalytic reaction on the membrane surface, where the membrane is treated as a boundary condition. In the second model, the membrane function is included by considering the light intensity decay with thickness as a result of the light absorption. Both models have been used to describe the experimental results, obtaining unique photocatalytic reaction parameters.
The discoloration of methylene blue in an aqueous solution was used as a model compound to fit the two models. Other pharmaceuticals were also degraded in our reactor to further investigate the applicability of these membranes. Here, we emphasized the importance of the water matrix in the photocatalytic degradation of micropollutants since it can hinder or help the process.
| Original language | English |
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| Qualification | Doctor of Philosophy |
| Awarding Institution |
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| Supervisors/Advisors |
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| Award date | 10 Mar 2023 |
| Place of Publication | Enschede |
| Publisher | |
| Print ISBNs | 978-90-365-5553-1 |
| DOIs | |
| Publication status | Published - 10 Mar 2023 |
