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Assessment of Suspended Solid Removal in a Surface Flow Constructed Wetland Using a Three-Dimensional Numerical Model

Abstract

Surface flow constructed wetlands (SFCWs) have been widely used to treat various types of wastewater and stormwater due to the advantages such as low costs for operating and maintenance compared with conventional treatment systems. In SFCW, the flow pattern, which is determined by the geometric features including bed morphology and vegetation distribution, significantly influences the removal processes of suspended solids and other pollutants. In this study, a three-dimensional computational fluid dynamics model, that integrates hydrodynamic model and the Lagrangian particle tracking model, is applied to determine the effectiveness of a SFCW in removing suspended solids based on the predicted flow characteristics and distribution of suspended solids in the wetland. After the validation, the three-dimensional numerical model is applied to illustrate the three-dimensional internal flow pattern in the wetland. The predicted concentrations of suspended solids at several cross-sections in downstream direction are compared with the field sampling data and also the results from a traditional first-order decay model. The results show that the 3D model performs reasonably well predicting complex flow fields associated with complex wetland geometry. This study indicates that the 3D model is an effective tool to support the management and operation of field SFCWs. Also, it can help to improve the design of SFCWs providing better understanding of interactions among the geometric features, the flow characteristics and the contaminants behaviors.

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Abbreviations

A i :

Surface area of a CSTR [m2]

C :

Concentration of the water quality parameter [mg/L]

C D :

Drag coefficient [−]

C in i and C out i :

TSS concentrations entering and leaving a CSTR, respectively [mg/L]

C L :

Time scale constant [−]

C s :

Surface friction coefficient [−]

C μ :

Cunningham correction slip factor constant [−]

C*:

Background concentration of the water quality parameter [mg/L]

d p :

Particle diameter [m]

F D :

Drag force per unit mass [N/kg]

k :

Areal decay rate constant [m/year]

L e :

Eddy length [m]

p :

Pressure [Pa]

q :

Hydraulic loading time [m/year]

Q :

Flow rate [m3/s]

Re p :

Particle Reynolds number [−]

S ij :

Strain rate tensor [−]

t :

Time [sec]

u :

Fluid phase velocity [m/s]

u i :

Average flow velocity [m/s]

u p :

Particle velocity [m/s]

u surf i :

Water surface flow velocity [m/s]

u′, v′, and w′:

Gaussian distributed random velocity fluctuation [m/s]

W i and W j :

Sind speeds in x and y direction [m/s]

x :

Fraction of distance from in inlet to the outlet [m]

x j :

Global Cartesian coordinates [m]

ε :

Turbulence dissipation rate [m2 s−3]

ζ:

Normally distributed random number]

ν :

Kinematic viscosity [m2/s]

ρ :

Water density [kg/m3]

ρ p :

Density of the particle [kg/m3]

τ e :

Eddy lifetime [sec]

τ ij :

Reynolds-stress tensor [−]

μ :

Molecular viscosity [Pa∙s]

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Correspondence to Zhi Chen.

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Han, S., Chen, Z., Zhou, F. et al. Assessment of Suspended Solid Removal in a Surface Flow Constructed Wetland Using a Three-Dimensional Numerical Model. Water Resour Manage 28, 3111–3125 (2014). https://doi.org/10.1007/s11269-014-0658-3

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Keywords

  • Hydrodynamic modeling
  • Removal efficiency
  • Surface flow constructed wetland
  • Suspended solids