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Optimizing Vortex Separation for Microplastic Removal from Freeway Runoff: Performance and Efficiency Analysis - Microplastic pollution is an emerging environmental problem that has been widely found in many environmental compartments. Microplastics are typically defined as particulate pollutants with a size smaller than 5mm, but larger than 1 nm. The pervasive nature of microplastic pollution warrants a critical investigation of the many different potential sources of this widespread contaminant. While a large amount of microplastics is removed in the domestic water reclamation system, its existence in our vast network of roadways and freeways is a potential source of microplastics pollution to our soil and water environments and deteriorate the existing stormwater runoff treatment systems. Due to lack of appropriate engineered microplastic removal applications, many microplastics from the transportation sector are released to the rivers and oceans.
A vortex separator applies centrifugal and gravitational forces created by liquid flow to separate solids from liquid matrix. A vortex is created by the tangential flow entering the vortex chamber at the top boundary. When centrifugal and gravitational forces are exerted differently on particles and water, particles with a density >> 1.0 g/cm3 will settle down, and water exits on the top. The critical condition appears during the presence of high flow rate, which lowers treatment time in the unit, and results in system failures. On the other hand, the vortex chamber approach gains advantages during high flow due to flow velocity and momentum increase in the conduits. This maximally differentiates angular momentum between particles and water in the cyclone, which leads to high effectiveness in solids separation from water via a combination of gravitational and centrifugal forces during the wet season.
Our designed vortex separator for microplastic removal from the freeway debris had a capacity of 0.9 ft3. The engineered vortex separator was tested at 3-, 6-, 12-, and 24- gpm at 30 ppm and 60 ppm of sweeping materials concentrations for each size range of 45-100 µm, 100-300 µm, 300-1000 µm, and 1000-4750µm. The mass balance of fed sweeping materials was investigated for each run to warrant the balance of input and output. All particle sizes, except 45-100 µm, yielded mass conservation at a ~71%-100%, while the 45-100 µm had lower recovery of ~66%-68%. The data show the higher flow rate results in higher sweeping materials removal. The removal efficacy increases as the fraction size range increases at 47.9%-60.8%, 89.6%, 94.8%-97.9%, 99.5% for 45-100 µm, 100-300 µm, 300-1000 µm and 1000-4750µm size range, respectively.
Our study is an ongoing study and the microplastic qualification is continuing.
