Wetlands have been used as a potentially cost-effective secondary waste
water treatment system to treat the waste water before discharge into the water bodies. The
aim of this study was to compare the pollution reduction ability of plant species at various
depths in a constructed wetland system. Two different grass species such as Eleucine indica
(Goose grass), Dactyloctenium aegyptium (Crowfoot grass) and a sedge namely Cyperus iria
(umbrella sedge) and the control without any plant species were introduced in the
constructed wetland system. The system was operated continuously by inlet valve from tank
filled with storm water. Physicochemical parameters such as pH, DO, BOD, TS, Nitrate and
Phosphate contents were measured in one week interval using standard procedures. The
results revealed that the pollution reduction ability was very high in Cyperus iria at one foot
depth whereas the nitrate and phosphate reduction ability was comparatively high in Cyperus
iria at their 1.5 feet depth

Kayanan, S.

Kishoran, S.

Nanthakumaran, A.

English

IR South Eastern University of Sri Lanka

181 
 
POLLUTION REDUCTION POTENTIAL OF SUBSURFACE FLOW 
CONSTRUCTED WETLAND SYSTEM  
A.Nanthakumaran
1
, S.Kayanan
2
 and S.Kishoran
3 
1, 2
Department of Bio - Science, Vavuniya Campus of the University  
of Jaffna, Sri Lanka 
3
Department of Zoology, Faculty of Science, Eastern University, Sri Lanka 
n_ananthi@hotmail.com 
 
ABSTRACT: Wetlands have been used as a potentially cost-effective secondary waste 
water treatment system to treat the waste water before discharge into the water bodies. The 
aim of this study was to compare the pollution reduction ability of plant species at various 
depths in a constructed wetland system. Two different grass species such as Eleucine indica 
(Goose grass), Dactyloctenium aegyptium (Crowfoot grass) and a sedge namely Cyperus iria 
(umbrella sedge) and the control without any plant species were introduced in the 
constructed wetland system. The system was operated continuously by inlet valve from tank 
filled with storm water. Physicochemical parameters such as pH, DO, BOD, TS, Nitrate and 
Phosphate contents were measured in one week interval using standard procedures. The 
results revealed that the pollution reduction ability was very high in Cyperus iria at one foot 
depth whereas the nitrate and phosphate reduction ability was comparatively high in Cyperus 
iria at their 1.5 feet depth. 
Keywords: wetland, secondary treatment, sedge, pollution reduction 
 
1. INTRODUCTION  
Wetlands provide water quality improvement by providing effective free treatment for 
many types of water pollution. Large quantities of pollutants from point sources and 
non-point sources have been removed by the process of natural filtration, sedimentation 
and phytoremediation in a cost effective manner (Doku et.al, 1993). These benefits had 
created a global interest in constructing wetlands for the main purpose of wastewater 
treatment (Kadlec and Wallace 2009). Sherwood and Reed (1993) reported that the 
emergent plants found in wastewater wetlands include cattails, reeds, rushes, bulrushes 
and sedges. They absorb their nutrients form sediment or directly from the water and 
some of them have highly developed root systems in the sediment layer.  
Vavuniya tank where the waste water from the Vavuniya town discharged without 
proper treatment causes pollution. It affects the crop productivity and the livelihood of 
fishermen who do fresh water fishing in this tank. Natural wetland system would be a 
most preferable secondary treatment system to treat the waste water before discharge 
into the water bodies. Mainly in dry zone area grasses are more suitable than the floating 
weeds. In dry season floating weeds are difficult to survive in considerably high 
temperature. 
This proposed project aims to compare pollution reduction potential of a constructed 
artificial wetland system using naturally available plant species such as Eleucine indica 
(Goose grass), Dactyloctenium aegyptium (Crowfoot grass) and a sedge namely Cyperus 
iria (umbrella sedge) and the control without any plant species.  
 
2. METHODOLOGY 
The subsurface flow constructed wetland systems were constructed with three plant 
species and one control (figure 2). The dimension of each system was 1.2m length, 0.6m 
width and 0.8m height. The bottom and around of wetlands were built with brick and 
182 
 
plastered with concrete. The inlet part was directly connected with waste water tank 
whereas each system has three outlets (figure 1) separately. 1
st
 outlet was in the 0.3m 
depth (1
st
 depth) whereas the 2
nd
 outlet in 0.5m (2
nd
 depth) and 3
rd
 outlet (3
rd
 depth) in 
0.6m depth installed in the constructed wetland system. The treatment and control 
systems were filled in the order of coarse gravels up to 0.1m height, then sand, fine 
gravel and fertile soil mixture (2:1:7) up to 0.4m height there after the fertile soil was 
filled up to 0.5m height. Then the storm water was filled up to 0.7m height.  
 
 
 
 
 
 
The waste water in the Vavuniya town area discharges to the Vavuniya tank. This waste 
water went through the grid to remove the large particle then reach to the oxidation pond 
which was not in working condition and directly discharge to the tank. For this research, 
the inlet waste water was collected in between the grid and oxidation pond. Two grass 
species such as Eleucine indica (Goose grass), Dactyloctenium aegyptium (Crowfoot 
grass) and a sedge namely Cyperus iria (umbrella sedge) were selected for the wetland 
system. Forty plants were planted in each treatment. The sample collection was started 
after three weeks of establishment of the plant species at each three depths. Three 
samples was collected in each outlets. The system was operated by inlet valve from tank 
filled with storm water while the retention time was three days. During this time, the 
invasive plants were removed and cut the wetland plants before the flowering time. 
The physicochemical parameters such as pH, Dissolved Oxygen (DO), Biological 
Oxygen Demand (BOD), Total solids (TS), concentration of phosphate and nitrate of 
water were measured (Reeta Kori, S. P., 2007) for the inlet wastewater and the outlet 
water after passing through the wetland system collected at three different depths in one 
week interval sstarting after three weeks of grass and sedge establishment from mid of 
August to end of November 2014.  
The statistical analysis especially mean comparison was used to compare the pollution 
reduction ability of plant species at various depths in a constructed wetland system. 
Three replicates was used for each cases indicated by “N” whereas the grouping 
information showed by the letters explained the mean comparison.  
3. RESULTS AND DISCUSSION 
Analysis of physicochemical parameters 
I. pH 
The average pH level in inlet was 8. According to the Sri Lankan standard accepted pH 
level should be in between 6.5 – 8. Results revealed that plant species had the ability to 
reduce the pH within the acceptable limit. The pH reduction efficiencies of Eleucine 
indica, Dactyloctenium aegyptium and Cyperus iria were nearly 8%, 6% and 10% 
respectively at their first depth.  
Figure 1: Introduced plant species in wetland 
system 
Figure 2: outlets of the wetland 
system 
183 
 
A. Tukey Pairwise Comparisons among the plant species  
(Grouping Information Using the Tukey Method and 95% Confidence)  
Table 4: Tukey Pairwise Comparisons for pH among plant species 
Plant_spp & control N Mean Grouping 
Cyperus iria 3 0.708889 A 
Eleucine indica 3 0.518889 B 
Dactyloctenium aegyptium 3 0.425556 C 
Control 3 0.156667 D 
 
 
B. Tukey Pairwise Comparisons among the depths 
(Grouping Information Using the Tukey Method and 95% Confidence) 
Table 5: Tukey Pairwise Comparisons for pH among the depths 
Depth N Mean Grouping 
1 4 0.5350 A 
2 4 0.4375 B 
3 4 0.3850 B 
Mean comparison for every plant species and control showed that the mean of Cyperus 
iria> Eleucine indica > Dactyloctenium aegyptium > control for depths, mean of depth1 
> depth2 = depth3. Hence Cyperus iria has high pH reduction ability at 1
st
 depth. 
II. Total Solids (TS) 
The inlet water consisted nearly 1265ppm of total solids. The accepted level for TS in 
the waste water must be below 50ppm before discharge into the inland water bodies. In 
this study no plant species had the ability to reduce the TS level below the standard. The 
TS reduction efficiencies of Eleucine indica, Dactyloctenium aegyptium and Cyperus 
iria were nearly 84%, 75% and 92% respectively at 3
rd
 depth. This may be due to the 
inadequate retention time and the depth  
A. Tukey Pairwise Comparisons among plant species  
(Grouping Information Using the Tukey Method and 95% Confidence) 
Table3: Tukey Pairwise Comparisons for TS among the plant species 
Plant_spp & control N Mean Grouping 
Cyperus iria 3 1098.56 A 
Eleucine indica 3 994.00 B 
Dactyloctenium aegyptium 3 855.67 C 
Control 3 503.78 D 
 
B. Tukey Pairwise Comparisons among the depths 
(Grouping Information Using the Tukey Method and 95% Confidence) 
Table4: Tukey Pairwise Comparisons for TS among the depths 
Depth N Mean Grouping 
3 4 928.417 A 
2 4 868.250 A 
1 4 792.333 B 
 
Mean comparison showed that the mean of Cyperus iria > Eleucine indica > 
Dactyloctenium aegyptium > control and according to mean comparison for depths, 
mean of depth3 = depth2 >depth1. Hence Cyperus iria had high TS reduction ability at 
3
rd
 and 2
nd
 depth. 
184 
 
III. Dissolved Oxygen (DO) 
DO of inlet waste water was around 1.2 ppm. Regarding the surface water bodies’ 
standard for DO level must be above 5ppm. Here Dactyloctenium aegyptium did not 
have the ability to increase the DO level above 5ppm at their 2
nd
 and 3
rd
 depth. The 
ability of increasing DO level was gradually increasing with increasing depth. The DO 
increasing efficiencies of Eleucine indica, Dactyloctenium aegyptium and Cyperus iria 
were nearly 10, 6 and 13 times respectively at 1
st
 depth.  
A. Tukey Pairwise Comparisons among plant species  
(Grouping Information Using the Tukey Method and 95% Confidence) 
Table5: Tukey Pairwise Comparisons for DO among the plant species 
Plant_spp & control N Mean Grouping 
Cyperus iria 3 11.0642 A 
Eleucine indica 3 7.8597 A 
Dactyloctenium aegyptium 3 4.0927 B 
Control 3 3.1556 B 
 
B. Tukey Pairwise Comparisons among the depths 
(Grouping Information Using the Tukey Method and 95% Confidence)  
Table6: Tukey Pairwise Comparisons for DO among the depths 
Depth N Mean Grouping 
1 4 9.5925 A 
2 4 6.0020 B 
3 4 4.0346 B 
 
The mean comparison for plant species and control revealed that mean of Cyperus iria = 
Eleucine indica > Dactyloctenium aegyptium = control and according to mean 
comparison for depths, mean of depth1> depth2 =depth1. Hence Cyperus iria has high 
DO improving ability at 1
st
 depth.  
IV. Biological Oxygen Demand (BOD) 
BOD level of inlet waste water was nearly 15 ppm. Cyperus iria had the greater ability 
to reduce the BOD level whereas the BOD reduction was very less in Dactyloctenium 
aegyptium, but in all plant species BOD level was gradually increased with the 
increasing depth. BOD standard for surface water bodies are 30ppm. Here all three plant 
species reduce the BOD below standard in all depths. The BOD level decreasing 
efficiencies of Eleucine indica,     Dactyloctenium aegyptium and Cyperus iria were 
nearly 66%, 64% and 69% respectively at first depth. 
A. Tukey Pairwise Comparisons among plant species  
(Grouping Information Using the Tukey Method and 95% Confidence)  
Table7: Tukey Pairwise Comparisons for BOD among the plant species 
Plant_spp & control N Mean Grouping 
Cyperus iria 3 9.896 A 
Eleucine indica 3 9.379 A 
Dactyloctenium aegyptium 3 9.060 A 
Control 3 2.250 B 
 
B. Tukey Pairwise Comparisons among the depths 
(Grouping Information Using the Tukey Method and 95% Confidence) 
185 
 
Table8: Tukey Pairwise Comparisons for BOD among the depths 
Depth N Mean Grouping 
1 4 7.83750 A 
2 4 7.64625 A 
3 4 7.45500 A 
 
According to mean comparison for plant species and control explained that the mean of 
Cyperus iria = Eleucine indica = Dactyloctenium aegyptium > control and according to 
mean comparison for depths, mean of depth1 = depth2 = depth3. Hence all three grasses 
had BOD reduction ability for at any of three depths.  
V. Nitrate 
Nitrate concentration at inlet waste water was nearly 22.7ppm. Cyperus iria had greater 
ability to reduce the nitrate level whereas it was very less in Dactyloctenium aegyptium, 
but in the three plant species nitrate level was gradually reduced with the increasing 
depth up to second depth then the nitrate level suddenly increased in third depth. 
Acceptable nitrate level for inland water bodies is 5ppm.results showed that no plants 
had the ability to reduce the nitrate level below the acceptable limit at all depths. The 
nitrate reduction efficiency of Eleucine indica, Dactyloctenium aegyptium and Cyperus 
iria were nearly 47%, 39% and 64% respectively at 2nd depth. 
A. Tukey Pairwise Comparisons among plant species  
(Grouping Information Using the Tukey Method and 95% Confidence) 
Table9: Tukey Pairwise Comparisons for Nitrate among the plant species 
Plant_spp & control N Mean Grouping 
Cyperus iria 3 13.4809 A 
Eleucine indica 3 9.6684 B 
Dactyloctenium aegyptium 3 7.9314 C 
Control 3 5.1731 D 
 
B. Tukey Pairwise Comparisons among the depths 
(Grouping Information Using the Tukey Method and 95% Confidence) 
Table10: Tukey Pairwise Comparisons for Nitrate among the depths 
Depth N Mean Grouping 
2 4 10.0027 A 
1 4 8.9228 B 
3 4 8.2648 C 
 
Regarding to mean comparison for grass species and control showed that the mean of 
Cyperus iria > Eleucine indica > Dactyloctenium aegyptium > control and according to 
mean comparison for depths, mean of depth2 > depth1 > depth3. Nitrogen undergoes its 
various transformation and some are taken up by aquatic plants some is leached to the 
subsoil (Kadlec and Knight, 1996). Hence Cyperus iria had high pollution reduction 
ability at depth2. 
 
VI. Phosphate 
Phosphate concentration at inlet waste water was 7.4 ppm. The results indicated that 
Cyperus iria had the greater ability to reduce the phosphate level whereas it was very 
less in Dactyloctenium aegyptium, Acceptable phosphate level for inland water bodies is 
5ppm. Eleucine indica, and Cyperus iria had the ability to reduce the phosphate level 
below the acceptable limit at all depths. The efficiency of phosphate level reduction of 
Eleucine indica, Cyperus iria and Dactyloctenium aegyptium were nearly 38%, 42% and 
186 
 
24% respectively. Phosphate level in outlet water was varied among plant species as well 
as depths. 
A. Tukey Pairwise Comparisons among plant species  
(Grouping Information Using the Tukey Method and 95% Confidence)  
Table11: Tukey Pairwise Comparisons for Phosphate among the plant species 
Plant_spp & control N Mean Grouping 
Cyperus iria 3 2.88600 A 
Eleucine indica 3 2.60233 A 
Dactyloctenium aegyptium 3 1.44300 B 
Control 3 0.80783 C 
 
B. Tukey Pairwise Comparisons among the depths 
(Grouping Information Using the Tukey Method and 95% Confidence) 
Table12: Tukey Pairwise Comparisons for Phosphate among the depths 
Depth N Mean Grouping 
2 4 2.23850 A 
1 4 2.01650 A 
3 4 1.54938 B 
 
According to mean comparison for plant species and control revealed that the mean of 
Cyperus iria = Eleucine indica > Dactyloctenium aegyptium > control and according to 
mean comparison for depths, mean of depth1 = depth2 > depth3. Hence both Cyperus 
iria and Eleucine indica had a significant high phosphate reduction ability at depth1 and 
depth2. 
4. CONCLUSION 
Results of the physicochemical parameters showed that the plant species reduced the pH, 
BOD, TS and the concentrations of Phosphate and Nitrate and increased the DO.  
Further the results revealed that among the three species tested the sedge Cyperus iria 
was more effective in reducing the pollution level. The pollution reduction ability of pH, 
DO, BOD and TS were very high in Cyperus iria at 0.3m depth whereas the Nitrate and 
Phosphate reduction ability were comparatively high in Cyperus iria at 0.5m depth. 
5. REFERENCES 
Doku, I. A., and G.W. Heinke. 1993. "The Potential for Use of Wetlands for Wastewater 
in the Northwest Territories". Report to the Department of Municipal and Community 
Affairs, Government of the Northwest Territories. 
Kadlec, R.H. (2009). Wastewater treatment at the Houghton Lake wetland: hydrology 
and water quality. Ecol. Eng. 35, 1287–1311. 
Sherwood, C. & Reed, P., 1993. Constructed Wetlands For Wastewater Treatment, 
Washington: EPA. 
Reeta Kori, S. P. (2007). Guide Manual: water and waste water analysis. India: Central 
pollution control board. 
Kadlec,R.H. and Knight, R.L. (1996). Treatment Wetlands. CRC Press/Lewis Publishes, 
Boca Raton, Florida. 


Pollution reduction potential of subsurface flow constructed wetland system

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Pollution reduction potential of subsurface flow constructed wetland system

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