Li, Chaoran;
(2023)
Coagulation-flocculation-sedimentation for the removal of microplastics from surface water.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Microplastics (MPs), mainly of size 10-150 μm, have been found in surface freshwater systems such as tap water, suggesting that water treatment plants are not effectively removing MPs. Furthermore, limited information is available on the removal of MPs in the surface drinking water treatment process. However, the widespread presence of MPs in surface freshwater systems indicates that surface drinking water sources are polluted with MPs. This research aims to investigate the removal of MPs by conventional surface water treatment using approaches traditionally designed to remove particulate matter from water: coagulation-flocculation and sedimentation. To measure and understand the mechanism of the MP removal, a new method for overcoming the limitations of visual counting of MPs was developed. During the coagulation-flocculation-sedimentation experiments, the jar testers were used. Total organic carbon (TOC), Zeta potential, Photometric Dispersion Analyser (PDA), Fourier transform infrared (FTIR), turbidity meter, and scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDS) were also used for MP characterization. In order to preliminarily investigate the effects of coagulant-flocculation and sedimentation in surface freshwater, polystyrene beads with a density of 1.04–1.06 g/cm3 (similar to the water) were selected, resulting in removals as high as 98.9 ± 0.94 %. Microplastics with different sizes (10-1000 μm), densities (0.89-1.38 g/cm3), and materials were also studied. The study found that higher density (like PVC) or larger size (over 150 μm) MPs were easier to settle. The optimal removal was achieved when PAC was 0.4 mmol/L, and polyacrylamide (PAM) was 3 mg/L, with the optimal conditions of pH=8 (before adding PAC), mixing at 240 rpm for 1 min, flocculation at 35 rpm for 13 min and sedimentation for 25 min. The removal of mixture MPs in natural freshwater reached 97.1 % with economic considerations. A proposed flocculation model was successfully applied to the data and the proportionality constant, by fitting the data and using the least-squares method to determine the stoichiometric coefficient and equilibrium adsorption constant for floc formation. In terms of model parameters such as Zeta potential, and plastic content in the flocs, PAC was the most effective flocculant. In conclusion, this research demonstrated a widely used process as a high-efficient method for removing and monitoring MPs from surface water treatment plants. Future research should focus on combining granular activated carbon (GAC), sand filtration, biodegradation, and other means to develop a systematic method for MP removal in treatment plants.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Coagulation-flocculation-sedimentation for the removal of microplastics from surface water |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Civil, Environ and Geomatic Eng |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10175052 |
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