Removal Characteristics of Fibrous and Particulate Microplastics : A Study of the Effectiveness of Coagulation-Flocculation- Sedimentation

Sammanfattning: The rapid proliferation of microplastics (MPs) over the last few decades have raised alarms about the major environmental and health impacts posed by this anthropogenic source. The widespread propagation and transport of MP particles in water sources have accelerated the need to study the eco- toxicological impacts as well as the efficacy of various removal mechanisms from these critical water sources. This study focused on the removal mechanism of coagulation, flocculation and sedimentation (CFS) and the effect of microplastic morphologies and densities on removal efficiency. Lab scale jar tests were performed on raw water from the Fyris river, and two common metal-based coagulants aluminum chloride (PAX-215), and iron chloride (PIX-111) were used. Water quality parameters evaluated were total suspended solids, turbidity, pH, electrical conductivity, and chemical oxygen demand. The metal coagulants were used in the presence of polyethylene terephthalate fiber (PET-F), polypropylene fiber (PP-F), polyamide particles (PA-P), and a mixture of all three MPs respectively. MP removal efficiency was determined via filtration of the top 700 mL of water remaining after CFS and mechanical weighing of filtered particles. PET-F had the most favorable removal efficiency with an average of 99.3% and 98.8% for PIX-111 and PAX-215 respectively. The mixed MPs also showed good removal efficiencies of 97.9% and 95.6% for PIX-111 and PAX-215 respectively. The PA-P had the lowest removal efficiency of 92.4% and 84.6% for PIX-111 and PAX-215 respectively. It was found that fibrous based MPs had greater removal efficiencies than particulate-based MPs and this was confirmed in the Fourier Transform Infrared (FTIR) analysis. However, some errors related to the extraction of the supernatant water after CFS may have contributed to cross contamination of MPs observed in all analyzed samples. Furthermore, the hydrophobicity of MPs prevented extraction of all MPs from the supernatant water which may have contributed to the high removal efficiencies that were observed. Therefore, more investigations would be needed in order to prove the findings of this study.