ESEL Paper Review_201307 24
By Hong Guo
Phone: (+82) (0)10 82276568
1, Title and Author
Title: Discrete Phase Model Representation of Particulate Matter (PM) for Simulating PM separation by Hydrodynamic Unit opeartions
Journal: Environ. Sci. Technol
Josua A. Dickeson * and John J. Sansalone
Environmental Engineering and Sciences, University of Florida, 217 Black Hall, P.O. BOX 116450, Gainesville, Florida 32611
2. Summary of Paper
? In this study, PM discrete phase modeling (DPM) and computational fluid dynamics (CFD) are applied to model PM fate as a function of particle size and flow rate in two common types of hydrodynamic separator (HS) units
? PSDs are categorized based on granulometric indices.
? Results focus on ensuring modeling accuracy while examining the role of size dispersivity and overall PM fineness on DN requirements.
? Model validation was performed and results illustrated in Figure 1. The screened HS model had an overall mean absolute RPD of 6.5%, a maximum absolute RPD of 11.7% (at 2.3 L/s) and a over prediction bias error of 5.0%. The baffled HS had an overall mean absolute RPD of 4.6% (100 mg/L) and 4.1% (300 mg/L), a maximum absolute RPD of 9.2% (100 mg/L at 1.8 L/s) and 7.3% (300 mg/L at 18.1 L/s), and an over prediction bias error of 1.1%. 100 mg/L) and 0.7% (300 mg/L). The low bias likely indicates that a majority of the error is likely from physical data collection. The CFD-modeled HS units satisfy the requirements for model validation.
? Of primary importance is the DN required for acceptable convergence of the ΔEMC for a given DPM. For the six gradations centered on 66.7 and 100 μmthe maximum modeled RPD is less than 2.1% at a DN of 8. For a DN of 8 and the three gradations centered on 33.3 μm, the maximum modeled RPD is 7.5%. However, at a DN of 16 the maximum modeled RPD is 1.1%.
? High resolution, per-particle size removal data sets offer a fundamental perspective on the behavior of any unit operation, in this study, two similar HS units.
? Currently, regulatory requirements for approval of unit operations such as these HS units rely on the physical modeling of a given unit, under specific flow conditions, for a specific PM influent gradation.
? A disadvantage in such disparate regulations is the required physical modeling needed for diverse regulatory frameworks. One solution is for regulators to allow full-scale testing of a unit operation to physically model the per-particle size behavior with a heterodisperse PSD with high resolution PSD monitoring, such as a laser diffraction analysis given a demonstration of mass and volume balances.
? Only monodisperse gradations are reasonably measured and modeled by a DN) 1; the d50m. Given a constant density across the PSD and a given flow field, this result matches the expectation driven by particle fluid dynamic theory.
? As the PSD becomes heterodisperse or dense, particles will no longer reside in the same flow regime and the nonlinear relationship between particle size and particle drag force greatly impacts the accuracy of using the singular gravimetric median as the sole representative particle.
? For these fine PSDs a significant portion of the gradation is below the effective separation potential of both HS units for a majority of the studied flow rates. This results in a largely suspended PM with more opportunity for variability in modeled behavior because of poorly represented gradations and low separation potential by both units.
? Gradation uniformity and fineness impact the discretization error at DNs in the range 1-8.
? As DNs increase beyond 16, the effect of gradation uniformity and overall fineness are essentially negligible for all tested gradations
? For the gradations centered on 66.7 and 100 μm model convergence is achieved at a DN of 8 regardless of gradation uniformity. Based on the results, a discretization at a DN of 8-16 generally provides a discretization error that for many applications can provide acceptable results for coarser gradations to the gradations centered on 33.3 μm, a DN of 16-32 is recommended.
This research studies the behavior of activated sludge and the obtained profiles are very appropriate date for future studies.
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