





























1 

 

In ternationa l
Scholars
Journa ls

 

African Journal of Environmental Economics and Management ISSN 2375-0707 Vol. 9 (2), pp. 001-009, 
February, 2021. Available online at www.internationalscholarsjournals.org © International Scholars Journals 

 

Author(s) retain the copyright of this article. 

 

 

Full Length Research Paper 

 

Removal of faecal bacteria and nutrients from domestic 
wastewater in a horizontal surface flow wetland 

vegetated with Echinochloa pyramidalis 

 
Lekeufack Martin1, Fonkou Théophile1*, Pamo Tedonkeng Etienne2 and Amougou Akoa3

 
 

1
Laboratory of Applied Botany, University of Dschang, Cameroon. 

2
Department of Animal Production, Faculty of Agronomy, University of Dschang, Cameroon. 
3
Department of Plant Biology, Faculty of Science, University of Yaoundé I, Cameroon. 

 
Accepted 24 July, 2020 

 
The aim of this study was to evaluate the removal of faecal bacteria and nutrients from domestic 
wastewater, in surface flow wetlands vegetated with Echinochloa pyramidalis. Horizontal surface flow 
(HSF) wetlands were fed with primarily treated domestic wastewater at organic loading rates varying 

from 20.74 to 27.15 g BOD/m
2
/day for two consecutive years. Water samples were collected at two 

weeks interval from the inflow and the outflow of the treatment wetlands for physicochemical and faecal 
bacteria analyses. Physicochemical parameters with highest removal rates were total suspended solids 

(TSS, 62-80%), Nitrates (57-73 %) and PO4
-3

 (57-84 %). Faecal indicators reductions of 1.4 and 0.3 log 

units (1
st

 year) and 1.15 and 0.65 log units (2
nd

 year) were respectively recorded in the vegetated and 
the control wetlands. Reductions of total coliforms, faecal coliforms and faecal streptococci were 
significantly higher in the vegetated wetland than in the non-vegetated control in both seasons of the 
first year. In the contrary, there was no significant difference in the removal rates of faecal indicators 
between vegetated wetland and the non-vegetated control during the dry season of the second year. 
Wetlands vegetated with E. pyramidalis was proven to be continuously efficient in the removal of faecal 
indicators for the two years of study, with no significant differences between the seasons of the year 
and between the years. 

 
Key words: Wastewater, wetlands, Echinochloa pyramidalis, faecal bacteria removal, nutrients removal. 

 
 
INTRODUCTION 

 
Constructed wetlands (CWs) have been used as 
promising wastewater treatment alternatives to the more 
expensive conventional systems, especially in developing 
countries (Kivaisi, 2001; Song et al., 2006). They produce 
high quality effluent at low investment cost, simple 
operation and with very low energy dissipation (Ayaz and 
Akca, 2001). They therefore help greatly to reduce the 
health hazards associated with the waste disposal 
methods in most developing countries (Gilbert et al., 
1976; Mburu et al., 2008). Studies on constructed  
 
 
 
*Corresponding author. E-mail: tfonkou@yahoo.fr. Tel: +237 
77570991. 

 
 
 
 

 
wetland systems vegetated with macrophytes have 
shown that the percentage reductions of physicochemical 
parameters are generally high especially in tropical 
zones, where climatic conditions are able to sustain 
vegetation all the year round. Research works in the 
recent years have been focused on the ability of 
macrophytes based constructed wetlands to reduce 
oxygen demands and nutrients such as nitrates and 
phosphates (Kengne et al., 2009a; Fonkou et al., 2010). 
Meanwhile, the removal of faecal contaminants indicators 
from domestic wastewater has not gained much concern. 
Several studies reporting on microbial water quality 
improvement have shown that constructed wetlands 
reduce microorganism populations in wastewater at 
varying but significant degree of effectiveness (Paluszak 



2 

 

  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
Figure 1. The yard-scale setup of the experiment station. 

 
 

 

et al., 2003; Keffala and Ghrabi, 2005; Song et al., 2006; 
Mburu et al., 2008; Reinoso et al., 2008). Song et al., 
(2006) reported 99.7% reduction of faecal coliforms in 
Asia, Paluszak et al. (2003) and Reinoso et al. (2008) 
respectively reported the removals of 99 and 96% for 
Escherichia coli and faecal streptococci in Europe while 
Keffala and Ghrabi (2005) and Mburu et al. (2008) also 
respectively reported removals of 90 and 99.9 for faecal 
coliforms in Africa.  

The removal mechanisms of these bacteria are 
numerous. These include predation, natural die off, ultra 
violet radiations on the cell wall of bacteria, oxygen 
leakages from the roots of macrophytes, bactericidal 
substances secreted by roots as well as the antibiotic 
properties of some bacteria living in the rhizosphere 
(Green et al., 1997; Song et al., 2008). In Cameroon, 
many studies have been published on Echinochloa 
pyramidalis as concerns its biomass production in 
constructed wetlands, its ability in faecal sludge 
dewatering improvement and biosolids recovery, its 
response to salinity stress, its nutritional potentials and 
also its presence in natural wetlands especially the 
polluted ones (Kengne et al., 2009a, b; Fonkou et al., 
2010; Pare et al., 2011a, b; Lekeufack et al., 2011). But 
there has been no concern on its ability to reduce bio-
indicators of faecal contamination from wastewater, 
despite the continuous report of a water related diseases 
in developing countries.  

The aim of this study was to evaluate domestic 
wastewater quality improvement in a horizontal surface 
flow (HSF) wetland configuration vegetated with E. 
pyramidalis. The removal efficiencies of faecal coliforms, 

 
 
 

 

faecal streptococci and total coliforms as well as some 
physicochemical parameters were measured in the 
wetland vegetated with E. pyramidalis and in the non 
vegetated control wetland for two consecutive years. 
 
 
MATERIAL AND METHODS 
 
This study was conducted in a constructed wetland system in the 
campus of the University of Dschang, located between latitudes 
5°25’ and 5°30’ North and between longitudes 10°00’ and 10°5’ 
East in the Western Highlands of Cameroon. The climate in this 
region is of equatorial type with two seasons: 4 months of dry 
season from mid-November to mid-March, and 8 months of rainy 
season from mid-March to mid-November. Annual precipitations 
range between 1433 and 2137 mm, while annual mean temperature 
is estimated at 20.8°C with thermal amplitude of 2°C (Anonymous 
data from the local meteorological station, 1978-2008). Wastewater 
used in the study was collected from a small primary treatment 
plant receiving domestic liquid wastes from the students’ residence 

at an inflow rate of 3 m
3
 per day. Part of the primarily treated 

wastewater was channelled into a 1.3 m
3
 gutter from where it was 

distributed to the experimental wetlands using PVC pipes. 
 

 
Design of the experimental wetlands 
 

Five wetlands of 3 × 1 × 0.6 m
3
 were constructed using cement 

blocks (Figure 1). The inside of the structures were plastered with 

concrete, then Cement and Lankofuge
TM

 for water tightness. A 1% 
slope was constructed on the bottom of each wetland bed to ease 
the movement of water from the inlet to the outlet. Gabions of 30 
cm with stones of 5-8 cm in diameter were arranged at the inlet and 
outlet zones of the wetlands, while a drainage layer of about 10 cm 
was arranged at the bottom. The outlet structures were adjustable 
to enable the regulation of the water level in the substrate. 



3 

 

   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
Figure 2. Longitudinal section of the experimental wetland.  

 
 
 
 
 
 
 

 

CW3 
 

CW1 

 
 
 
 
 
 
 
 

 
Figure 3. Aspect of the vegetation in the wetland at the start of the 
analysis in the first year. 

 
 

 
The main filter substrate was a 40 cm column of sand having 
particles size < 2 mm (Figure 2). Results presented on this paper 
are those of CW1, that was vegetated with E. pyramidalis and CW3 
that was used as the non vegetated control wetlands. The inflow 
rate was estimated at 205 litres/day. The bed capacity measured 
from the porosities of the gabion and the sand filter was 923 litres. 
The hydraulic retention time (HRT) of 4.5 days was then calculated 
from the equation: 

= 
 

 

  
 

   
 

 
as stated by Lorion et al. (2001). The constructed wetlands serve as 
a secondary treatment associated to the existing primary treatment 
in which only the particle filter and the digester were still functioning. 
 

 

Setting up the experiment 
 
Young shoots of E. pyramidalis were collected from a natural 
wetland and washed in fresh water. After weighing, shoots were 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

planted in CW1 at a density of 14 shoots/m
2
. Primarily treated 

effluent from a conventional treatment plant was collected in a 
gutter and allowed to directly flow into the wetlands at organic 

loading rates varying from 20.74 to 27.15 g BOD/m
2
/day in dry 

season and the rainy season of two consecutive years. Macrophyte 
shoots were domesticated in the wetland for one month during 
which they grew and had standing vegetation considered to have 
good biological activity (Figure 3). The wastewater was then 
allowed to flow constantly into each bed at a loading rate of 85.43 L 

m
-2

day
-1

 in a horizontal surface flow (HSF) configuration for two 
consecutive years. At the end of every season, the plants were 
harvested after they have flowered. 

 

Sample collection and microbiological analyses 

 
Water samples were collected at two weeks interval throughout the 
research period at the inflow and the outflow of the treatment 
wetlands, from December 2009 to October 2011. 500 ml of each 
were kept in sterile laboratory glass bottles and transported in a 
cooler to the laboratory where they were immediately analyzed.  

In the laboratory, manipulations were carried out in strict 
conditions of sterility. In aseptic conditions, 1 ml of homogenous 
raw sample was measured and added into 9 ml of sterile distilled 
water to have 1:10 dilution. This same operation was repeated from 
the first dilution until the desired dilution was obtained (1:10, 1:100, 
1:1000, 1:10 000, etc). The pipette was always rinsed between 
dilutions to avoid contamination. The distilled water was sterilized 
by autoclaving in sealed sterile glass bottles for 15 min at 121°C.  

Total coliforms, faecal coliforms and faecal streptococci were 
detected by the membrane filtration following standard methods 

(APHA, 1998; CEAE, 2005). AC Cellulose Membranes Filters
TM

 
with pore-size 0.45 µm were used on a WHEATON filtering 

Funnel
TM

 attached to a CM 1500 vacuum pump
TM

.  
Appropriate sample volumes, in three different dilutions (10

-2
, 10

-

3
 and 10

-4
) for effluent or (10

-3
, 10

-4
 and 10

-5
) for influent were 

filtered and incubated for each parameter. This was to ensure 
having at least a plate with colony counts ranging between 20 to 
100 CFU (Hench et al., 2003). Samples for faecal coliforms were 

incubated on Difco
TM

 mFC prepared Agar in Petri dishes at 44.5°C 
for 24 h (Karathanasis et al., 2003). Thereafter, all characteristically 
blue and central white hollowed blue colonies were counted as 
faecal coliforms.  

Samples for faecal streptococci and total coliforms were 

respectively incubated on BBL
TM

 Bile Esculin and Tergitol
®

 7 Agars 
at 35°C for 48 h (Karathanasis et al., 2003). Thereafter all 
characteristically black and yellow colonies were respectively 



4 

 

 
 
 

 
Table 1. Average counts (log10 units CFU/100 ml) of faecal contaminant indicators (Total coliforms, TC; Faecal coliforms, FC; 
and Faecal streptococci, FS) in the inflow and outflow of the vegetated and the control wetlands during the dry and rainy seasons 
of the first year.  

 
  Dry season   Rainy season  

 

Parameter 
Inflow 

Outflow Outflow 
Inflow 

Outflow Outflow 
 

 Vegetated Control Vegetated Control  

   
 

T.C. 7,36±0,22 6,10±0,43 7,18±0,39 7,48±0,27 6,36±0,28 7,10±0,25 
 

F.C. 7,27±0,34 5,21±1,55 6,77±0,41 7,57±0,35 6,25±0,73 7,34±0,47 
 

F.S. 7,76±0,43 6,32±1,60 7,51±0,45 7,38±0,56 6,37±0,76 7,25±0,62 
  

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
Figure 4. Percentage removals of faecal indicators in the vegetated and in the control wetlands in the dry season (A) and rainy season (B) 
of the first year. 

 
 

 
counted for faecal streptococci and total coliforms. Each result was 
expressed as number of Colony Forming Units per 100 ml 
(CFU/100ml) of sample. 

 

Measurement of physicochemical parameters 
 
The physicochemical parameters including total suspended solids 
(TSS), Nitrates, Orthophosphates, Chemical Oxygen Demand 
(COD), and 5-days Biochemical Oxygen Demand (BOD5) were 
measured according to procedures described by Hach (2004). 

 

Statistical analyses 
 
The analysis of variance ANOVA in Prism.4 software at 0.05% 
probability level was used to test parameter differences between 
the inlet and the oulets of the wetlands. Means were then separated 
using Newman-Keuls Multiple Comparison Test under windows 
(Fonkou et al., 2010). As concerns microbial population density, 
data were log10 transformed to obtain the geometric means. 
 

 

RESULTS 

 

Removal of faecal bacteria 

 

Table 1 presents mean microbial densities in the inflow 
and outflows of the wetland during the first year of 

 
 
 

 

monitoring. The mean concentrations of faecal indicators 
varied generally from 7.3 to 7.8 log units at the inflow, 6.8 
to 7.5 and 5.2 to 6.4 log units respectively at the outflows 
of the control and vegetated wetlands. Compared with the 
inlet, average reductions of 1.6 and 0.35 log units were 
respectively observed at the outlets of the vegetated and 
non vegetated control wetlands during the dry season 
and 1.2 and 0.27 log units during the rainy season. These 
corresponded to percentage removals ranging from 87 to 
95% and from 24 to 71% respectively. From statistical 
analyses, the concentrations of faecal bacteria at the 
outflow of the vegetated wetland were in general 
significantly different (P˂0.05) from the outflow in both 
seasons.  

The most reduced parameter in the vegetated wetland 
was faecal coliforms in both seasons, while least reduced 
was faecal streptococci. In the control wetland, the most 
reduced parameter in both seasons was total coliforms 
and faecal streptococci were still the least reduced. 
Figure 4 presents the mean removal rates of faecal 
contaminant indicators in the wetlands during the first 
year. Removal efficiencies ranging from 88 to 95% in the 
vegetated wetland and from 26 to 71% in the control were 
recorded in the dry season. During the rainy season, 86 
to 92% and 24 to 51% removal rates were recorded in the 
vegetated and control wetlands 



5 

 

  
 
 

 
Table 2. Average counts (log10 units CFU/100 ml) of faecal contaminant indicators (Total coliforms, TC; Faecal coliforms, 
FC; and Faecal streptococci, FS) in the inflow and outflow of the vegetated and the control wetlands during the dry and rainy 
seasons of the second year.  

 
  Dry season   Rainy season  

 

Parameter 
Inflow 

Outflow Outflow 
Inflow 

Outflow Outflow 
 

 Vegetated Control Vegetated Control  

   
 

T.C 7,65±0,44 6,59±0,55 7,05±0,26 7,60±0,27 7,08±0,31 7,14±0,38 
 

F.C 7,50±0,65 6,35±0,44 6,94±0,54 7,50±0,65 6,32±0,90 6,81±0,99 
 

F.S 8,00±0,38 6,89±0,77 7,59±0,45 8,19±0,35 6,74±0,55 7,41±0,67 
  

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Figure 5. Percentage removals of faecal indicators in the vegetated and control wetlands in the dry season (A) and 
rainy season (B) of the second year. 

 
 
 

respectively. The wetlands were all more efficient in the 
dry season than in the rainy season, but there was no 
significant difference between the seasons. In this year, 
the outflow of all the wetlands were significantly different 
from the inflow for all the parameters, but the outflow of 
the vegetated wetland was significantly more efficient 
(P˂0.05) than that of the control in the removal of total 
coliforms in the dry season, and all the three parameters 
in the rainy season. The outflow of the control wetland 
was not different from the inflow (P˃0.05) in the rainy 
season for faecal coliforms and faecal streptococci.  

In the second year, the mean concentrations of faecal 
indicators at the outflows of the wetlands ranged 
generally from 5.6 to 7.1 and 6.0 to 7.6 log units in the 
vegetated and non vegetated control wetlands respec-
tively (Table 2). This gives average removal efficiencies 
of 1.2 and 0.6 log units at outflows of planted and non 
vegetated control wetlands respectively in the dry 
season, and 1.09 and 0.69 log units respectively in the 
rainy season.  

The most reduced parameter in the planted bed during 
the second year was faecal coliforms in the dry season 
and total coliforms in the rainy season. The least reduced 
parameter was faecal streptococci in both seasons. In the 
non vegetated control the most reduced parameter was 
faecal coliforms in both seasons and the least reduced 
was faecal streptococci. 

 
 
 
 

Figure 5 presents the average percentage removals of 
faecal contaminants indicators in the wetlands during the 
second year. Removal efficiencies ranging from 81 to 
91% in the vegetated wetland and from 55 to 63% at in 
the control were recorded in the dry season. In the rainy 
season, 66 to 92% and 55 to 71% were recorded in the 
vegetated and non vegetated control wetlands 
respectively. Statistical analysis revealed no significant 
differences between the two wetlands, although the 
outflows were always significantly different from the 
inflows. The removals of faecal coliforms and faecal 
streptococci in the vegetated wetland during the dry 
season were significantly higher than those recorded in 
the non vegetated control. The wetlands seemed more 
efficient in the dry season than in the rainy season but the 
difference between the two seasons was not significant 
(P˃0.05). The vegetated and the control wetlands also 
seemed more efficient in the removal of faecal indicators 
in the first year than in the second year, even though 
there was statistically no significant difference (P˃0.05) 
between the two years. 
 

 

Reduction rates of physicochemical parameters 

 

Figure 6 presents the removal efficiencies of the 
treatment beds during the first year as calculated from 



6 

 

  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Figure 6. Percentage reductions of physicochemical parameters in the vegetated and control wetlands in the dry 
season (A) and rainy season (B) during the first year (Cnd, conductivity; TSS, Total Suspended Solids). 

 

 
Table 3. Average physicochemical characteristics of water at the inflow and outflow of the wetlands during the dry and the rainy 
seasons of the first year  

 
   Dry season   Rainy season  

 

 Parameter 
Inflow 

Outflow Outflow 
Inflow 

Outflow Outflow 
 

  
Vegetated Control Vegetated Control  

    
 

 CND (µs/cm) 3815±288 3440±239 3344±295 1880±322 1694±309 1467±221 
 

 TSS (mg/l) 399±72 103±14 104±15 1513±676 56±11 100±19 
 

 Turbidity (FTU) 437±71 198±17 176±26 464±89 80±22 105±30 
 

 Colour (PtCo) 1533±186 911±85 803±93 1049±184 386±107 348±68 
 

 NO3
-
 (mg/l) 55±24 35±18 48±18 5±1 1.8±0.39 2.26±0.64 

 

 PO4
-3

 (mg/l) 186±43 133±49 150±31 69±22 31±15 34±11 
 

 COD (mg/l) 702±63 360±42 376±44 788±97 288±37 496±59 
 

 BOD (Mg/l) 219±38 112±16 130±20 317±28 120±9 206±23 
  

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Figure 7. Percentage removals of physicochemical parameters in the vegetated and control wetlands in the dry 
season (A) and rainy season (B) of the second year (Cnd, conductivity; TSS, Total Suspended Solids). 

 

 

the data presented in Table 3. The TSS was the para-
meter with the highest reduction rate in the vegetated 
wetland during the dry season (62%) and during the rainy 
season (92%). Percentage reduction of 58% was 
recorded for nitrates during the dry season and 57% for 
phosphates in the rainy season. Throughout this first 
year, conductivity and TSS had higher reduction rates in 
the non vegetated control than in the vegetated wetland, 
but there was no significant difference between the two 

 
 

 

wetlands (P˃0.05). The vegetated wetland had higher 
removal efficiencies for nitrates and phosphates than the 
non vegetated control in both seasons.  

During the second year, nutrients with the highest 
removal rate (84%) in the vegetated wetland were phos-
phates, while nitrates were reduced at 73% in the rainy 
season. TSS in this bed was respectively reduced at 68 
and 80% in the dry season and rainy season (Figure 7). 
The highest reduction rates in the control wetland were 



7 

 

  
 
 

 
Table 4. Average physicochemical characteristics of water at the inflow and outflow of the wetlands during the dry and the rainy 
seasons of the second year.  

 
   Dry season   Rainy season  

 

 Parameter 
Inflow 

Outflow Outflow 
Inflow 

Outflow Outflow 
 

  Vegetated Control Vegetated Control  

    
 

 CND (µs/cm) 3705±383 3311±427 3183±383 2293±354 1936±316 1414±259 
 

 TSS (mg/l) 584±90 151±21 117±38 616±120 83±6.2 86±15 
 

 Turbidity (FTU) 265±29 100±14 60±12 311±71 58±4.02 65±21 
 

 Colour (PtCo) 696±62 372±73 232±47 424±58 213±22 149±21 
 

 NO3
-
 (mg/l) 8±1.95 4±0.6 4,19±0.64 5±1 1,33±0.39 2,52±0.42 

 

 PO4
-3

 (mg/l) 112±18 17±3 33±4 94±32 30±5 29±6 
 

 COD (mg/l) 545±10 278±15 429±30 582±21 213±27 426±43 
 

 BOD (Mg/l) 229±4 117±6 164±22 244±9 90±11 173±20 
 

 

 

recorded for TSS (76%) and (78%) in the dry and rainy 
seasons respectively. Conductivity had the least reduction 
(11%) in the dry season while nitrates had the least 
reduction (26%) in the rainy season. The vegetated 
wetland was significantly more efficient (P˂0.05) than the 
non-vegetated control in the removal of nitrates in this 
rainy season. BOD and COD removals rates during the 
dry season of the first year (44 and 42% respectively) 
were lower but not significantly different from those 
recorded in the rainy season (55 and 57%). This trend 
was not respected in the second year, since the reduction 
rate of 49% recorded for COD and BOD during the dry 
season was low and significantly different from the 64% 
(BOD) and 63% (COD) obtained in the rainy season. It is 
noticed that the reduction of oxygen demands was always  
˂ 50% in the dry seasons and always ˃ 50% in the rainy 
seasons. As indicated in Tables 3 and 4, the quality of the 
water in the outflow of the wetlands was still very poor, 
even though high percentage reductions of several 
parameters were observed. 
 

 

DISCUSSION 

 

The reductions of 1.4 and 0.3 log units observed in the 
vegetated and control wetlands respectively in the first 
year are similar to those observed by Karathanasis et al. 
(2003) and Torrens et al. (2009) in polycultured systems. 
These results are also found within the range of removals 
reported for constructed wetlands treating domestic 
wastewater in similar conditions (Greenway, 2005; Morsy 
et al., 2007; Reinoso et al., 2008).  

The wetland vegetated with E. pyramidalis was signi-
ficantly more efficient (P˂0.05) than the non vegetated 
control in the reduction of parameters such as total 
coliforms in the dry season and all the three parameters 
in the rainy season. These differences may explain the 
role played by plants roots in the substratum-root matrix, 
and the difference in substrate’s microbial composition 
due to presence of plants as the wastewater passes 
through. Kaseva (2004) emitted a similar reasoning when 

 

 

he found that his vegetated systems were more efficient 
than the non vegetated control. The results of the present 
research are different from those reported by Mburu et al. 
(2008) where the non vegetated control bed was in the 
average more efficient than the vegetated wetland in a 
subsurface horizontal flow system.  

The high but non significant removals of faecal indica-
tors in the non vegetated control in the dry season of the 
first year could also be attributed to the various physical, 
chemical and biological mechanisms for bacterial removal 
in constructed wetlands (Williams et al., 1995; Green et 
al., 1997; Stevik et al., 2004). Photolysis (due to ultra-
violet radiations) is surely the predominant mechanism 
because in the rainy season the vegetated wetland was 
more efficient in the removal of bacteria than the non 
vegetated control.  

The second year presented a similar variability of 
bacteria concentrations as in the first year. Although no 
significant differences existed between the two years, the 
first year appeared to be more efficient in faecal bacteria 
removal than the second. This can be attributed to the 
high plant density observed in the vegetated wetland in 
the second year, which may block the U.V radiations from 
having effect on the bacteria. This observation is contrary 
to the observations found in literature where the age of 
the wetlands is suppose to have greater efficiency in the 
second year as the plants are well established in their 
roots network with a stable symbiotic relationship with the 
substrate microorganisms, thus promoting the different 
removal mechanisms in the wetlands (Tchobanoglous, 
1987; Lee et al., 2009). Other mechanisms involved 
include filtration, sedimentation, adsorption, oxidation, 
antibiosis, predation and die-off from exposure to toxins of 
plants and other bacteria (Green et al., 1997; Kaseva, 
2004). The differences between the non vegetated control 
and the vegetated wetlands may be attributed to the 
influence of plants. The multiplication of substrate 
microorganisms and their coordination in the removal 
processes in the second year is not to be also neglected. 
The better performances of the vegetated wetland could 
also be attributed to tropical climate conditions that are 



8 

 

 
 
 

 

known to be suitable all year-round for rapid biological 
growth, which influence the treatment processes (Kaseva, 
2004). The wetland vegetated with E. pyramidalis had 
more effect on the removal of faecal coliforms and was 
least efficient on faecal streptococci removal. This is 
thought that, the bactericidal substances which may be 
produced by this species roots, mixed with the toxic 
effects of substrate microorganisms have less effect on 
faecal streptococci, but more on faecal and total 
coliforms.  

The passage of wastewater through the non vegetated 
control wetland resulted in the reduction of several 
contaminants to considerable levels in different seasons; 
however, the presence of vegetation further improved the 
treatment efficiencies except in few cases. The significant 
removal of most physicochemical parameters was 
regardless of the presence of vegetation in the treatment 
wetland as earlier observed by Hench et al. (2003). This 
may be attributed to the shallow depth of the treatment 
wetlands which may have minimal effect on the treatment 
processes (Coleman et al., 2001). The reduction of 

BOD5, COD and PO4
-3

 was regardless of the presence of 

vegetation; however there were significant differences 
(P˂0.05) between their removals in the vegetated wetland 
and the control in the second year and not in the first. 
Their concentrations in both the vegetated and the non 
vegetated control were significantly different from the 
inflow in both years. The efficiencies of the wetlands in 
the removal of physicochemical parameters compared to 
the microbial parameters were higher in the second year 
than those of the first year. It can be understood that the 
removal mechanisms for bacteria and those of 
physicochemical parameters are not the same. In the 
second year, the massive treatment is richer in substrate 
bacteria for biodegradation and the root network of the 
macrophyte is well established in the wetland. Secondly, 
since in the first year, plant roots had not yet reached 
maximum depth, the treatment processes will likely 
become higher during the second year of study as the 
roots would have reached sufficient depth (Kern and Idler, 
1999).  

In all, the vegetated wetland was generally more effi-
cient in the reduction of parameters. This, in addition to 
uptake, may also be thanks to their additional aeration at 
the root zone to facilitate the processes of degradation 
and detoxification by aerobic microorganisms (Lin et al., 
2002). In this study the macrophyte bed repeatedly 
reduced nitrates more than the non vegetated control. 
This may be due to the functions of plants in constructed 
wetlands which include uptake of nitrates, supplying 
organic carbon for denitrification and providing attach-
ment sites for denitrifying bacteria (Kadlec and Knight, 
1995; Lin et al., 2002; Thullen et al., 2002; Lee et al., 
2009). COD reductions that were consistently higher in 
the vegetated wetland could be attributed to the fact that 
macrophytes and microorganisms depend on nutrients in 
wastewater for survival. In contrast, their metabolites 

 
 
 
 

 

provide important N and P sources for micro-organisms 
which are very important mechanisms (Ji et al., 2002). 
 

 

Conclusion 

 

The constructed wetland vegetated with E. pyramidalis in 
a horizontal surface flow configuration (HSF) was 
continuously efficient in the removal of faecal indicator 
bacteria from domestic wastewater for the two years, with 
no significant differences existing between the seasons of 
the year and between the years. The age of the wetland 
generally had a negative influence in the removal of 
faecal indictors; but this difference was not significant. 
The constructed wetland vegetated with E. pyramidalis 
was most efficient in the removal of faecal coliforms 
followed by total coliforms, but was least efficient in the 
removal of faecal streptococci as compared to the non 
vegetated control. The contribution of E. pyramidalis in 
the removal of faecal indicators and physicochemical 
parameters was quite high, suggesting this macrophyte to 
be recommended in wetland technology for domestic 
wastewater treatment. 
 
 
ACKNOWLEDGEMENT 

 

The authors thank the International Foundation for 
Science (IFS) for financial support to the corresponding 
author through grants N° W/3782-1 and N° W/3782-2. 
 
 
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