Coagulation-based physicochemical removal of microfibers and microplastics in wastewater treatment plants /

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Student Theses

2025

Tariq, Khan Muhammad

Thesis

Wastewater treatment plant (WWTP) is a significant source of microfiber and microplastic (MF/MP) contamination in aquatic ecosystems. The level of exposure to these unregulated emerging contaminants defines the potential harm to the environment and public health. It is, therefore, critical to understand MF/MP contamination in terms of polymer type, number, shape, and size for devising an efficient removal process. Despite the growing literature on the subject, a knowledge gap exists due to the lack of removal technologies specifically designed for MFs/MPs. Accordingly, this PhD research contributes to the development of an environmentally friendly and cost-effective method for MF/MP removal from wastewater. Coagulation-based MF/MP removal from wastewater was carried out using a jar test experiment. In order to investigate the MF/MP removal mechanisms, the chemical composition and microstructural properties of MFs/MPs in the flocs were analyzed. At a chitosan-based coagulant dosage of 20 mg/L, the maximum removal rates of polypropylene (PP), polyethylene terephthalate (PET), and high-density polyethylene (HDPE) were 60.0±10.3%, 62.0±0.4%, and 57.5±1.5%, respectively. On the other hand, the highest removal efficacies of 91.0±1.0% for polyester (PEST) and 89.8±0.3% for nylon were obtained at a coagulant dosage of 10 mg/L. The removal efficiency of aluminium sulphate coagulation was 75.0±1.0 % for PP, 69.6±1.7% for PET, 57.5±1.3% for HDPE, 90.5±1.3% for PEST, and 92.0±0.9% for nylon at an optimum dosage of 30 mg/L and pH of 7. The removal efficiencies for MFs (PEST) and MPs (PP) at the optimum dosage of iron chloride (4.6 mg/L) and a pH of 7 were 95.0±1.1% and 61.5±1.3%, respectively. In a more alkaline medium (pH 9), the removal efficiency decreased to 80.0±1.3% for PEST and 36.6±0.4% for PP. The MFs/MPs tended to have a more negative charge at a high pH. As a result, the available positive charge from the coagulant was insufficient to neutralize the negatively charged particles, which resulted in decreased PEST and PP elimination.In this study, charge neutralization and adsorption were the main MF/MP removal mechanisms. The hydrolysis of iron and aluminium-based coagulants can produce Fe(OH)2+, Fe(OH)2+, and Fe(OH)3, and Al3+, Al(OH)2+, Fe(OH)4-, Al(OH)2+, Al(OH)2+, Al(OH)3, and Al(OH)4- respectively, which have the potential to combine with the negatively charged MFs/MPs to form flocs. These cationic coagulants electrostatically bind with anionic carboxyl groups in MFs/MPs. The presence of new functional groups, such as hydroxyl groups (OH), carboxyl groups (COOH), and C═C, on the surfaces of the MFs/MPs facilitated interactions between the flocs and MFs/MPs.Iron chloride and aluminium sulphate indicate their potential suitability for wastewater treatment. In addition, chitosan exhibits promising efficacy in removing MFs/MPs from effluent and provides new insights for future research in the field. The findings emphasize the significance of implementing these coagulants in actual WWTP contexts to combat the growing problem of MF/MP pollution. In addition to its scientific contribution, this research directly or indirectly aligns with the aims established by the United Nations (UN) Sustainable Development Goals (SDGs) by actively mitigating and minimizing marine pollution, enhancing water quality, and promoting the recycling and safe utilization of wastewater

LG51.H43 Dr 2025eb Tariqkm

https://educoll.lib.eduhk.hk/records/Ju3kRJ7m