Presenter: Ryan LaRue
Supervisor(s): Dr. David Latulippe
Project Description: The presence of anthropogenic plastic waste in aquatic environments is widespread and poses significant environmental, human, and economic consequences. Microplastics (MPs) are of particular concern due to their small size (e.g. micron-to-millimeter range), irregular shapes, and wide-ranging ecological effects. A significant source of aquatic MPs originates from the effluents of wastewater treatment plants (WWTPs). Membrane technologies already used in some WWTPs for wastewater polishing are well-positioned to mitigate this efflux of MPs. However, little is known about how membrane parameters (e.g. pore size, etc.) and MP properties (e.g. size, etc.) affect filtration performance (e.g. productivity, MP/ solids removal, etc.). In particular, it is critical to characterize the effect of MPs on membrane fouling, and the ability of membranes to reject the MPs. To this end, MPs for filtration research were created by ball-milling polyethylene powder which was then sieved to yield irregular, non-spherical MPs (~10 µm). These particles are representative of the irregular MPs found in WWTP effluents. To examine the effect of the presence of MPs on membrane fouling, MPs were suspended in municipal wastewater (WW; 0.1-10 mg/L) and filtered at constant pressure through a selection of poly(vinylidene fluoride) ultra- and microfiltration membranes. Results indicate that filtering suspensions of WW containing MPs produce greater fouling-induced permeate flux declines than filtering WW alone; this effect is membrane-dependent and more pronounced at higher MP concentrations. Subsequently, constant-flux filtration experiments were performed to quantify MP transmission through 5 µm-rated microfiltration membranes using MPs milled and sieved from a fluorescent polyethylene feedstock. Even though ~99% of MPs were rejected, particles were still detected in permeate samples via a fluorescent assay. Particle size measurements indicate that the permeated MPs could be as large as the membrane's stated pore size. These observations highlight the need to optimize membrane processes for improved filtration performance.
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