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Removal of Metaldehyde in Aqueous Solutions by Heterogeneous Photocatalysis and Adsorption Processes

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Removal of Metaldehyde in Aqueous Solutions by Heterogeneous Photocatalysis and Adsorption Processes Removal of metaldehyde in aqueous solutions by heterogeneous photocatalysis and adsorption processes A thesis submitted to University College London for the degree of Doctor of Philosophy by Zhuojun Li Department of Civil, Environmental & Geomatic Engineering University College London January 2020 1 Declaration I, Zhuojun Li confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. Name: Zhuojun Li Signature: Date: 2 Abstract Metaldehyde has been detected in surface water and drinking water in the UK, exceeding the EU and UK standard of 0.1 µg L-1. Conventional water treatment methods are not effective due to the physicochemical properties of metaldehyde while newly proposed methods are under research and cannot be applied at an industrial scale. This thesis investigated the removal of metaldehyde from aqueous solutions by heterogeneous photocatalysis using nanoparticle photocatalysts and adsorption processes using carbon materials, aiming to provide a feasible solution to the problem. Powdered activated carbon (PAC) proved to be the most effective material to remove metaldehyde from water. It has a relatively large specific surface area of 962.4 m2 g-1 and a pore size distribution in the micro-/meso-pores range that favours adsorption of metaldehyde. Adsorption of metaldehyde onto PAC was explained by the Langmuir -1 isotherm model, with a highest maximum adsorption capacity (qm) of 28.33 mg g , and by the pseudo-second order kinetic model, with highest adsorption rate (k2) of 0.16 g -1 -1 mg min . Low initial concentration of metaldehyde solution led to lower qm of PAC for metaldehyde due to low driving force for mass transfer and competition with water molecules. Humic acid, which represents natural organic matter in water, has little effect on adsorption of metaldehyde onto PAC. For water samples collected from various stages at Walton-on-Thames Water Treatment Works, the best treatment stage for dosing PAC to remove metaldehyde was apparently after the ‘static flocculation’ stage. Desorption of metaldehyde from used PAC was observed, suggesting that constant monitoring of metaldehyde is essential for adjusting dosage and recycling of PAC. Lastly, low temperature on-site regeneration of used PAC may be possible. 3 Impact Statement This thesis contributes to the knowledge of effectively removing a micropollutant from aqueous solutions. The impacts of this thesis are discussed as following: Inside academia: The modified method regarding the detection of metaldehyde by GC-MS described in Chapter 3 and the modified solid-phase extraction loading technique described in Chapter 5 can help other researchers set up their method to identify and quantify metaldehyde in aqueous solutions using GC-MS. Powdered activated carbon (PAC) used in this study can effectively and efficiently remove metaldehyde from water, regardless of the water quality, due to the distinctive pore size distribution of the PAC and the physicochemical properties of metaldehyde. It suggests that adsorption is the preferred removal mechanism for metaldehyde under the studied experimental condition. This discovery can provide insights to researchers that are interested in adsorption of other micropollutants which share similar properties with metaldehyde. And it is helpful for researchers that are interested in synthesizing adsorbents with customized pore size distribution to remove certain micropollutant, based on their properties. A slight increase in the percentage removal of metaldehyde was observed when UV-C light was applied in the adsorption system using PAC and granular activated carbon (GAC) under the studied experimental condition in Chapter 3. This suggests that the combination of possible adsorption and oxidation could enhance the removal of metaldehyde. This finding can help researchers further investigate 4 the possible adsorption-oxidation system in terms of removing micropollutants from water. Outside academia: Dosing PAC as slurry in the water collected after ‘static flocculation’ at Walton-on- Thames Water Treatment Works achieved the highest removal of metaldehyde under the studied experimental condition in Chapter 5. This discovery can be beneficial to water utility companies and drinking water treatment plants that share similar water sources, treatment processes, and daily output with Walton-on- Thames Water Treatment Works. Desorption of metaldehyde from used PAC back to water was observed under the studied experimental condition in Chapter 5. This result is informative for water utility companies and drinking water treatment plants. It also points out the importance of constant monitoring of micropollutants during the treatment processes, which helps to identify the appropriate time frame needed for adjusting the treatment methods. Low temperature on-site regeneration of used PAC may be possible. This aspect can be further looked into by water utility companies and drinking water treatment plants to develop an energy-saving and waste-reducing method to recycle and regenerate the used PAC. 5 Acknowledgements Undertaking this PhD has been a great experience and a spectacular journey for me. I am thankful for all the help and care I have received from the academic/research staff, family, friends, and strangers during my study. Firstly, I would like to express my greatest appreciation to my supervisor, Dr Luiza Cintra Campos, for her patient guidance, vital encouragement, continuous support and feedback on the experimental designs, manuscript preparations, and thesis write-up. Luiza is passionate about research and truly cares for me, not only for my research but also my life as an international student in London. I am often inspired by her enthusiasm and creative ideas. Many thanks to my second supervisor, Prof Zhengxiao Guo, and members of his research group, Dr Yuchen Yang, Juntao Li, Dr Jian Guo, and Dr Zhuangnan Li. With the guidance from them, I have gained a brand new perspective to my research. I also extremely appreciate that they have helped me with the material characterization techniques in this thesis and that I have had the opportunity to have access to the analytical instruments in the Chemistry Department at UCL. And thanks to Dr Steve Firth for his instructions on performing EDX analysis. Special thanks to Dr Judith Zhou for her technical support with the analytical instruments in the Environmental Engineering Laboratory of the Department of Civil, Environmental, and Geomatic Engineering at UCL, and her feedbacks on my methodology. 6 My thanks extend to the laboratory technicians of the Environmental Engineering Laboratory, Dr Utku Solpuker, Mrs Catherine Unsworth, and Dr Francis O'Shea for helping me with experimental settings and demonstrating lab classes. Many thanks to Dr Suseeladevi Mayadevi, Dr Jong Kyu Kim, Dr Bharat Kale, Dr Ulises Jáuregui-Haza, Dr Jenny O’Reilly, and Dr Michael Chipps for their collaborations and advices on my research. I would like to thank Dr Melisa Canales and Dr Anna Bogush for their support of my research as well. My appreciation also goes to my friends in London, especially Like Xu, Fan Huang, Yu Shen, Vega Wang, Yuting Huang, and Dr Dong Ding, for all your help and support when I needed it most. Also thanks to my friends in China and around the world, especially Wenting Huang, Yidong Chen, Wenjia Fan, Qimiao Shen, Xian Jiang, Junyan Li, Haoyang Sun, Xiafeng Xu, Yang Yang, Yang Li, Chen Su, Shida Wang, and Yifan Wang for the happy memories we created together. I would like to give my greatest appreciation to my parents and grandparents for believing in me and for their unconditional support throughout my study. Lastly, I am grateful for the love and support of Petri and his family. Petri, you are the best thing that ever happened to me. Jag älskar dig så mycket. 7 List of Publications The experimental investigations presented in this thesis have been published in the following peer-reviewed journals respectively: Li, Z., et al., Degradation of metaldehyde in water by nanoparticle catalysts and powdered activated carbon. Environmental Science and Pollution Research, 2017. 24(21): p. 17861-17873. Li, Z., et al., The impact of humic acid on metaldehyde adsorption onto powdered activated carbon in aqueous solution. RSC Advances, 2019. 9(1): p. 11-22. Li, Z., et al., Investigation of metaldehyde removal by powdered activated carbon from different water samples. Environmental Science: Water Research & Technology, 2020. The researcher has co-authored the paper published in the following peer-reviewed journal: Ferino-Pérez, A., et al., Explaining the interactions between metaldehyde and acidic surface groups of activated carbon under different pH conditions. Journal of Molecular Graphics and Modelling, 2019. 90: p. 94-103. 8 Table of Contents Abstract ...................................................................................................................... 3 Impact Statement ....................................................................................................... 4 Acknowledgements .................................................................................................... 6 List of Publications ..................................................................................................... 8 Table of Contents ....................................................................................................... 9 List of Tables ...........................................................................................................
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