Abstract
This paper offers a novel application of our model worked out in Maple environment to help understand the very complex transport processes in horizontal subsurface flow constructed wetland with coarse gravel (HSFCW-C). We made tracer measurements: Inside a constructed wetland, we had 9 sample points, and samples were taken from each point at two depths. Our model is a divided convective-dispersive transport (D-CDT) model which makes a fitted response curve from the sum of two separate CDT curves showing the contributions of the main and side streams. Analytical solutions of CDT curves are inverse Gaussian distribution functions. This model was fitted onto inner points of the measurements to demonstrate that the model gives better fitting to the inner points than the commonly used convective-dispersive transport model. The importance of this new application of the model is that it can resemble transport processes in these constructed wetlands more precisely than the regularly used convective-dispersive transport (CDT) model. The model allows for calculations of velocity and dispersion coefficients. The results showed that this model gave differences of 4–99% (of velocity) and 2–474% (of dispersion coefficient) compared with the CDT model and values were closer to actual hydraulic behavior. The results also demonstrated the main flow path in the system.
Highlights
Constructed wetlands (CWs)— known as treatment wetlands—are engineered systems for wastewater treatment
We developed an accurate process with the aim to fit the Fréchet distribution function onto effluent tracer test results from HSFCW-C (Dittrich and Klincsik 2015a)
Our results provide a deeper understanding of transport processes inside the system and give us a more detailed insight into hydrodynamics of CWs
Summary
Constructed wetlands (CWs)— known as treatment wetlands—are engineered systems for wastewater treatment. Constructed wetlands have a very low or zero energy demand; operation and maintenance costs are significantly reduced compared to conventional treatment systems (Almuktar et al 2018). There are two main types of constructed wetland: freesurface flow systems (FSF-CW) and subsurface flow systems (SSF-CW). SSF-CWs can be further divided according to the direction of the wastewater flow. Wastewater in SSF-CWs runs either horizontally (in HSSF-CWs) or vertically (in VSSF-CWs) towards the filter media. In VSFCWs, there is an unsaturated, non-permanent flow, and in HFSFCWs there is a saturated, non-permanent flow (Wu et al 2015; Valipour and Ahn 2016). We investigated HFSFCWs using coarse gravel as filter medium (HFSCW-C). Constructed wetlands can treat a wide variety of polluted water, including municipal, domestic, agricultural, or industrial wastewaters (Vymazal 2009)
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