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Modeling BOD removal in free watersurface constructed wetlands with variable residence time-based methods

Sebro, Degefu Yohannes LU (2021) In TVVR21/5004 VVR820 20192
Division of Water Resources Engineering
Abstract
Constructed wetlands (CWs) have been applied for several years in the removal process pollutants
from secondary treatment plants and stormwater. In this paper, the Variable Residence Time
(VART) model for solute transport in streams was extended to simulate the BOD removal process
in free water surface flow constructed wetlands (FWS CWs). The double layer concept of the basic
VART model was extended to FWS CWs, contemplating the wetland as a similar layer system
with water column (WC) and root zone (RZ). The RZ was further divided into advection dominated
upper root layer, and diffusion dominated the lower root zone. Two distinctive models were
developed based on this, namely VART-BOD-F model that incorporates the first-order decay... (More)
Constructed wetlands (CWs) have been applied for several years in the removal process pollutants
from secondary treatment plants and stormwater. In this paper, the Variable Residence Time
(VART) model for solute transport in streams was extended to simulate the BOD removal process
in free water surface flow constructed wetlands (FWS CWs). The double layer concept of the basic
VART model was extended to FWS CWs, contemplating the wetland as a similar layer system
with water column (WC) and root zone (RZ). The RZ was further divided into advection dominated
upper root layer, and diffusion dominated the lower root zone. Two distinctive models were
developed based on this, namely VART-BOD-F model that incorporates the first-order decay of
BOD and VART-BOD-M model that combines multiple Monod kinetics in the wetland system.
Unlike conventional wetland methods, both models involve dynamic root zone concept with
changing reactive depth. The application of mass exchange between the water column and
dynamic diffusion root zone was the distinct feature of the models. From time series data based
simulation test results, coefficient of determination (r2) and root mean square error (RMSE) values
for the VART-BOD-F model ranges from 0.79 to 0.91 and 0.69 to 1.84, respectively, while for
VART-BOD-M model varies from 0.83 to 0.96 and 0.63 to 1.77 respectively. Furthermore, the
performance of the second model (VART-BOD-M model) was tested later with another data
obtained from Manzala Wetland, Egypt (Deng et al., 2016). When the two models compared,
including with the exiting DND model, the VART-BOD-M model, which involved various
mechanisms showed better values of r2 and RMSE, and capable of following reasonably best fit
concerning observed effluent concentration. Although the VART-BOD-M model has better
efficiency than the VART-BOD-F model, it involved several parameters and certain assumptions
that might have compromised the results and analysis. Hence, the VART-BOD-M model can be a
better tool for simulating the BOD removal process in FWS CWs when there is data available for
defined parameters (Less)
Popular Abstract
BOD and other pollutants from effluent of waste water treatment can be removed using constructed wetland by the help of bacterial activities and other processes in the wetlands. In this paper I presented two numerical models that simulate the BOD removal process in Free Water Constructed Wetlands namely, VART-BOD-F and VART-BOD-M. The performance of the models was evaluated using one-year time series BOD concentration data of Gustine wetland in CA, USA and also compared with the exiting model developed previously based different criteria. The coefficient of determination (r2) and root mean square error RMSE values indicates, the two models can be a good tool to simulate BOD removal in Free Water Surface Constructed Wetlands.
Please use this url to cite or link to this publication:
author
Sebro, Degefu Yohannes LU
supervisor
organization
course
VVR820 20192
year
type
H2 - Master's Degree (Two Years)
subject
keywords
BOD removal, Free water-surface constructed wetlands, VART-BOD, models, dynamic diffusion zone
publication/series
TVVR21/5004
report number
21/5004
ISSN
1101-9824
language
English
additional info
Examiner: Magnus Larson
id
9041478
date added to LUP
2021-03-08 18:54:14
date last changed
2021-03-31 13:01:27
@misc{9041478,
  abstract     = {{Constructed wetlands (CWs) have been applied for several years in the removal process pollutants
from secondary treatment plants and stormwater. In this paper, the Variable Residence Time
(VART) model for solute transport in streams was extended to simulate the BOD removal process
in free water surface flow constructed wetlands (FWS CWs). The double layer concept of the basic
VART model was extended to FWS CWs, contemplating the wetland as a similar layer system
with water column (WC) and root zone (RZ). The RZ was further divided into advection dominated
upper root layer, and diffusion dominated the lower root zone. Two distinctive models were
developed based on this, namely VART-BOD-F model that incorporates the first-order decay of
BOD and VART-BOD-M model that combines multiple Monod kinetics in the wetland system.
Unlike conventional wetland methods, both models involve dynamic root zone concept with
changing reactive depth. The application of mass exchange between the water column and
dynamic diffusion root zone was the distinct feature of the models. From time series data based
simulation test results, coefficient of determination (r2) and root mean square error (RMSE) values
for the VART-BOD-F model ranges from 0.79 to 0.91 and 0.69 to 1.84, respectively, while for
VART-BOD-M model varies from 0.83 to 0.96 and 0.63 to 1.77 respectively. Furthermore, the
performance of the second model (VART-BOD-M model) was tested later with another data
obtained from Manzala Wetland, Egypt (Deng et al., 2016). When the two models compared,
including with the exiting DND model, the VART-BOD-M model, which involved various
mechanisms showed better values of r2 and RMSE, and capable of following reasonably best fit
concerning observed effluent concentration. Although the VART-BOD-M model has better
efficiency than the VART-BOD-F model, it involved several parameters and certain assumptions
that might have compromised the results and analysis. Hence, the VART-BOD-M model can be a
better tool for simulating the BOD removal process in FWS CWs when there is data available for
defined parameters}},
  author       = {{Sebro, Degefu Yohannes}},
  issn         = {{1101-9824}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{TVVR21/5004}},
  title        = {{Modeling BOD removal in free watersurface constructed wetlands with variable residence time-based methods}},
  year         = {{2021}},
}