Haegyun Lee

Modeling and experiment for removal of algae and nutrient using a DAF system installed on a ferryboat

AbstractMany lakes or irrigative reservoirs in Korea are rapidly polluted with algae because of the increasing amounts of pollutants discharged from nonpoint sources. Though dissolved air flotation (DAF) is one of the most efficient processes for removing algae, there are limitations associated with conveying polluted water to a plant located on the lakeside. In this study, a reaction tube was optimized to enhance collision between microbubbles and pollutants. The length, diameter, and space of the reaction tube were modified and tested in the laboratory. A numerical model using three-dimensional Navier–Stokes equations was set up for the analysis of flow around the reaction tube. The laboratory tests showed that the efficiency of phosphorus removal is improved as the reaction tube length is reduced. Phosphorus removal efficiency was improved, as the tube diameter was larger and the reaction space was reduced. A pilot test was performed to verify these results and modeling results. A ferryboat installed w...

Development of a hybrid treatment system for combined sewer overflows using a hydrocyclone and a dissolved air flotation system

AbstractCombined sewer overflows (CSOs) contain a mixture of untreated, contaminated sanitary, and storm water. CSOs include both precipitated and suspended matters. In this study, a novel system is proposed to treat CSOs using a combined hydrocyclone and dissolved air flotation (DAF) system for removal of both precipitated and suspended matter. The optimum operating conditions were determined by changing the internal flow rate and the split ratio (Rf) in the hydrocyclone and by changing the angle of the nozzle to determine the floc size, flow rate, and recycle ratio in the DAF system. The types of organic matter contained in prepared synthetic water samples are categorized as soluble CODcr (SCOD) and particulated CODcr (PCOD) in the characterization of the removal rate of the precipitated and suspended matter. The suspended solids (SS) were classified by their specific gravity to determine the removal rate of both precipitated and suspended matter. In a pretreatment process, the system employed a cationi...

Application of DGFEM to 1D High-Order Boussinesq Equation

The Runge-Kutta DGFEM (Discontinuous Galerkin Finite Element Method) is applied to the discretization of 1D high-order Boussinesq equation of Madsen et al. (2002). Discontinuous Galerkin method is used, which allows discontinuities at the element interfaces, for the spatial discretization and explicit high-order Runge-Kutta method is adopted in time integration. The connection between interfaces is set as an approximate Riemann problem and Lax-Friedrichs numerical fluxes are employed. To remove the unnecessary oscillations, Savitzky-Golay filter is applied to the solution at each time step. When necessary, a numerical sponge layer is set to mimic the open boundary condition and relaxation zone is set for the internal wave generation. As benchmark case studies, the propagation of sine (linear) wave and nonlinear wave over a submerged breakwater are simulated with the developed numerical model. For the latter case study, the results are compared with experimental data and good agreement is observed.

Simulation of One-Dimensional Transcritical Flow with Discontinuous Galerkin Finite Element Method

With the increase of the frequency in large-scale floods and natural disasters, the demands for highly accurate numerical river models are also rapidly growing. Generally, flows in rivers are modeled with previously developed and well-established numerical models based on shallow water equations. However, the so-far-developed models reveal a lot of limitations in the analysis of discontinuous flow or flow which needs accurate modeling. In this study, the numerical shallow water model based on the discontinuous Galerkin method was applied to the simulation of one-dimensional transcritical flow, including dam break flows and a flow over a hump. The favorable agreement was observed between numerical solutions and analytical solutions.

Flow Simulation in a Meandering Channel using a 2-dimensional Numerical Model

The point sand bars of Hahoi Village on Nakdong River have undergone considerable changes including fluvial and vegetation characteristics due to flood regulation by the dams constructed upstream. In this study, the numerical fluvial/sediment and water quality model, KU-RLMS, is applied to the aquatic area near Hahoi Village (middle/upper region of the Nakdong River) for clarifying the mechanisms of changes in hydraulic and aquatic characteristics. The fixed-bed hydraulic experiment was carried out for horizontal two-dimensional numerical model. The numerical simulation reveals that flow is accelerated near the left bank of Booyongdae downstream of the Hahoi Village area. Circulatory flow pattern was observed at the right bank downstream of Hahoi Village. The simulation was in good agreement with the hydraulic/physical experiment. For the discharge of design flood, at the area of circulatory flow pattern, the superelevation of about 1.0 m at the right bank was predicted compared to the left bank of high flow velocity, which is also in good agreement with hydraulic experiment.