Various configurations of vegetated bed systems with a variety of macrophytes have been tested experimentally in Cameroon, for the treatment of domestic wastewater. The aim of this work was to assess the growth and biomass production of Fuirena umbellata (Cyperaceae) and its potentials in the removal of faecal bacteria and nutrients from primarily treated domestic effluent. A wetland vegetated with this macrophyte and a non-vegetated wetland (control) were continuously fed with primarily treated domestic wastewater at an estimated loading rate of 205 Litres/day in dry and rainy seasons for two consecutive years. Physicochemical and microbiological parameters of the effluent were monitored at the inflow and outflows of the wetlands alongside with the growth and productivity attributes of the young plants during each season. The density of plants ranged in the wetland from 17 - 185 plants/m 2 and from 11 - 146 plants/m 2 respectively during the first and the second years. More biomasses were instead produced in the dry seasons than in the rainy seasons but with no significant differences observed. As for nutrients removal, higher efficiencies were observed in the vegetated wetland (45% - 73%) compared to the non-vegetated control (17% - 66%). Similar trends were observed for the faecal bacteria but with no significant differences between the seasons. However, the vegetated beds were significantly more efficient than the non-vegetated control in the reduction of many physicochemical parameters and faecal bacteria. This varied with the seasons.
Environmental pollution is one of the major constraints in developing countries. This is due to the lack of adequate services for the evacuation and treatment of wastewater, coupled with the rapidly expanding population and increasing industrialisation especially in the cities [
Vegetated bed systems (VBS) are used all over the world as cost effective alternative for wastewater treatment [
In improving the water quality in constructed wetlands, macrophytes degrade pathogens or help in their mitigation through the support that they offer to the naturally occurring micro-organisms in the substrate [
Therefore, this work focuses on the growth and biomass production of Fuirena umbellata (Cyperaceae) and its potentials in the removal of faecal bacteria and nutrients from domestic wastewater.
This study was conducted in a Yard-Scale constructed wetlands system (CWs) at the exit of an abandoned conventional treatment plant and constantly receiving domestic liquid wastes from students’ residence in Dschang University campus. Dschang is located between latitudes 5˚25'N and 5˚30'N and between longitudes 10˚00'E and 10˚5'E in the Western Highlands of Cameroon (
The climate in this region is of equatorial type with 4 months of dry season found between mid-November to mid-March, and 8 months of rainy season between mid-March to mid-November. Annual precipitations are estimated to range between 1433 mm and 2137 mm, while annual mean temperature is estimated at 20.8˚C with thermal amplitude of 2˚C. The wastewater used in the study was collected from a small primary treatment plant receiving domestic liquid wastes by simple gravitation from the students’ residence, situated at some 650 m from the treatment station all within the University campus. Part of the primarily treated wastewater was channelled into a 1.3 m3 gutter from where it was distributed to the experimental wetlands using polyvinyl chloride (PVC)
pipes.
Five wetlands (CW1, CW2, CW3, CW4 and CW5) of 3 × 1 × 0.6 m3 were constructed using cement blocks (
adjustable to enable the regulation of the water level in the substrate. Results presented in this paper are those of CW2 that was vegetated with Fuirena umbellata and CW3 that was used as the non-vegetated control wetlands. The adjustment of the inflow rate was estimated at 256.29 Litres/day. The bed capacity measured from the porosities of the gabion and the sand filter was estimated at 923 Litres. The hydraulic retention time (HRT) of 3.6 days was then calculated from the equation, as stated by [
Young shoots of Fuirena umbellata were collected from the natural wetland and washed in fresh water (
Parameters | Dry season | Rainy season |
---|---|---|
CND (μS/cm) | 3705 ± 383 | 2294 ± 354 |
Colour (PtCo) | 585 ± 91 | 616 ± 121 |
Turbidity (FTU) | 266 ± 3 | 311.3 ± 72 |
TSS (mg/L) | 697 ± 63 | 425 ± 58.7 |
8.7 ± 2 | 5.1 ± 1.2 | |
113 ± 18.7 | 94.3 ± 33 | |
14.5 ± 3 | 7.8 ± 3.5 | |
COD (mg/L) | 545 ± 11 | 582 ± 21.4 |
BOD5 (mg/L) | 229 ± 5 | 244.6 ± 9 |
Parameters | Dry season | Rainy season |
---|---|---|
TC | 7.36 ± 0.22 | 7.48 ± 0.27 |
FC | 7.27 ± 0.34 | 7.57 ± 0.35 |
FS | 7.76 ± 0.43 | 7.38 ± 0.56 |
which the shoots grew to a standing vegetation considered having good biological activity (
The height, number of leaves and density of plants were determined at intervals of two weeks throughout the experimental period. During each season of the year, the plants were harvested and weighed when at least 50% of them were observed to have flowered in the bed. Before harvest, the level of water in the wetland was reduced to the root zone (subsurface) to avoid rotting of the herbaceous stubs. This was reinstalled when the young shoots arose.
Water samples were collected at intervals of two weeks from November 2009 to October 2011 from the inflow and the outflow of the non-vegetated control and that vegetated with F. umbellata. Sterile laboratory glass bottles of 500 ml were used to collect water samples that were immediately transported in a cooler for analyses. 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.). A pipette was used for each sample and was always rinsed between dilutions to avoid contamination from one dilution to the other. The distilled water was sterilized by autoclaving in sealed sterile glass bottles for 15 minutes at 121˚C. Total coliforms, faecal coliforms and faecal streptococci were detected by membrane filtration following standard methods [
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 [
Samples for faecal streptococci and total coliforms were respectively incubated on BBLTM Bile Esculin and Tergitol® 7 Agars at 35˚C for 48 hrs [
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 [
where: Ci = inflow value; C0 = outflow value.
The treatment efficiency of the planted bed was compared with that of the control bed using the unpaired, one-tailed T-test. The Student’s T-test was performed at 0.05% probability level to compare the means of the parameters measured at the inflow and the outflows of the wetlands. As concerns microbial population density, data were log10 transformed to obtain the geometric means. The means as well as the standard error of mean (SEM) values were obtained from the column statistics of each raw data set using Prism. 4 software at 5% probability level.
Of the thirty-two young shoots of F. umbellata transplanted in CW2, 27 of them survived one month after transplanting, giving about 84.38% survival rate. These young shoots immediately entered into the leafy phase where they grew and multiplied rapidly presenting almost a linear growth relationship in trend. The growth and multiplication produced a population density of about 206 plants/m2 at the end of the dry season of the first year when more than 50% of the plants in the wetland flowered (
was lower compared to the previous year’s dry season. At the start of parameters measurement just one month after harvest, the wetland had a density of only 38 plants/m2. This density increased to 82 plants/m2 after three months of growth and then dropped again to 63 plants/m2 at the end of the dry season when the plants flowered. In the rainy season, the species had a very slow rate of increase in density but, by the end of the season the density in the wetland was by far more than that at the end of the dry season (146 plants/m2) as shown by
0.91 m high. In the dry season of the second year after harvesting F. umbellata at the end of the rainy season (first year), very few new shoots arose and grew very slowly. The plants grew almost linearly and after two months of the growth, the growth rate dropped to nearly constant (
Plants in the dry seasons flowered earlier than in the rainy seasons and by the end of the dry seasons almost all the plants in the bed had flowered. Moreover, some individuals especially those found near the inflow gabion of the wetland showed stunted growth. These flowered far earlier and at very low heights ranging from 16 - 30 cm only. However, this species in its natural environment rarely attends 0.6 m of height. Generally, all records of plant growth parameters including the number of leaves per plants, leaf length and width and plants density in bed were generally lower during the second year compared to data recorded during the first year in both seasons.
These results presented here show that Fuirena umbellata has tolerance potential to the variability and potential toxic effects of the primarily treated domestic wastewater used, since with its dense root system, it grows and multiplies rapidly in an artificial constructed wetland supplied with domestic wastewater [
Parameters | Dry season | Rainy season | ||||||
---|---|---|---|---|---|---|---|---|
Inflow | Outflow Vegetated | Removal (%) | Outflow Control | Inflow | Outflow Vegetated | Removal (%) | Outflow Control | |
T.C | 7.7 ± 0.44 | 6.13 ± 0.22 | 94.67 | 7.1 ± 0.26 | 7.6 ± 0.27 | 6.20 ± 0.36 | 93.58 | 7.1 ± 0.38 |
F.C | 7.5 ± 0.65 | 6.25 ± 0.54 | 79.92 | 6.9 ± 0.54 | 7.5 ± 0.65 | 6.27 ± 0.24 | 84.38 | 6.8 ± 0.99 |
F.S | 8.0 ± 0.38 | 6.61 ± 0.31 | 98.37 | 7.6 ± 0.45 | 8.2 ± 0.35 | 5.96 ± 0.52 | 94.62 | 7.4 ± 0.67 |
During the second year, the removal efficiencies varied from 80% to 89% in the vegetated wetland and from 55% to 63% in the control were recorded in the dry season. The most reduced faecal bacteria indicators were faecal streptococci (89%) followed by faecal coliforms (81%) in the vegetated wetland and faecal coliforms (63%) followed by total coliforms (59%) in the non-vegetated control. However, there were no significant differences (P > 0.05) as concerns the removal of the different parameters within the vegetated wetland during the dry season of the second year. But the vegetated wetland significantly reduced all the three parameters (P < 0.05) compared with the non vegetated control during this dry season of the second year (
In the rainy season, the removal efficiencies varied from 81% to 92% in the vegetated wetland and from 55% to 73% in the non vegetated control. During this season, the removal of parameters in the vegetated wetland presented the same trend as in the dry season. Contrarily in the non vegetated control, the faecal streptococci (73%) were the most reduced parameter followed by faecal coliforms (71%). However, no significant difference (P > 0.05) existed between
the vegetated wetland and the non-vegetated control as concerns the faecal coliforms removal in the rainy season of the second year (
The role of the substrate-root matrix is depicted by the variance of faecal indicators counts observed at the outflow of the wetlands during the different seasons. The significant performances of the wetland vegetated (P < 0.05) compared with the control in during the experimental period could be explained by the interaction between the sand/gravel-root matrixes in the vegetated wetland coupled with the difference in substrate’s microbial composition due to the presence of Fuirena umbellata. [
The reductions of 1.5 and 0.3 log units were observed at the outflow of the vegetated and control wetlands respectively during the first year. These results are similar to those of [
In the vegetated wetland, no significant differences were observed in the count of faecal indicators between the different seasons throughout the two years period. This is an indication of the stability of the system throughout the years regardless of the season. These results are however different from those of [
in the rainy season, the BOD5 followed the TSS with a percentage reduction of 69%. However, there were no significant differences (P > 0.05) between the removal efficiencies of the different parameters in the vegetated wetland during the dry season. Also, the no significant differences existed (P > 0.05) between the vegetated and the non vegetated control wetlands as concerns the removal of TSS, nitrates and COD. Nevertheless, the vegetated wetland was significantly more efficient (P < 0.05) than the non vegetated control in the reduction of phosphates and BOD5. During the rainy season, the vegetated wetland again was significantly more efficient (P < 0.05) in the reduction of COD and BOD5. There were no significant differences between the two wetlands (P > 0.05) as concerns the reduction of the other parameters.
During the second year, the nutrients with the highest removal rates (71%) in
Parameters | Dry season | Rainy season | ||||
---|---|---|---|---|---|---|
Inflow | Outflow vegetated | Outflow control | Inflow | Outflow vegetated | Outflow control | |
CND (μS/cm) | 3815 ± 288 | 2772 ± 212.7 | 3344 ± 295 | 1880 ± 322 | 1984.6 ± 304 | 1467 ± 221 |
Colour (PtCo) | 1533 ± 186 | 579.3 ± 33.69 | 803 ± 93 | 1049 ± 184 | 287.1 ± 59.6 | 348 ± 68 |
Turbidity (FTU) | 437 ± 71 | 122.7 ± 5.31 | 176 ± 26 | 464 ± 89 | 63.18 ± 17.29 | 105 ± 30 |
TSS (mg/L) | 399 ± 72 | 42.75 ± 5.31 | 104 ± 15 | 1513 ± 676 | 47.82 ± 6.1 | 100 ± 19 |
55 ± 24 | 2.03 ± 0.44 | 48 ± 18 | 5 ± 1 | 1.76 ± 0.32 | 2.26 ± 0.64 | |
186 ± 43 | 120 ± 24.1 | 150 ± 31 | 69 ± 22 | 29.95 ± 13.21 | 34 ± 11 | |
COD (mg/L) | 702 ± 63 | 310 ± 44 | 376 ± 44 | 788 ± 97 | 210.4 ± 35.8 | 496 ± 59 |
BOD5 (mg/L) | 219 ± 38 | 64.5 ± 4.41 | 130 ± 28 | 317 ± 28 | 74.7 ± 4.45 | 206 ± 23 |
BOD5/COD | 0.312 ± 0.56 | 0.208 ± 0.10 | 0.346 ± 0.64 | 0.402 ± 0.29 | 0.356 ± 0.12 | 0.415 ± 0.39 |
the vegetated wetland were phosphates, while nitrates were reduced at 60% in the rainy season. TSS in this bed were respectively reduced at 73% and 88% in the dry season and rainy season (
From
wetland in both seasons (
Concerning this removal of nutrients, the significant reduction of COD and BOD5 in the wetland during the first year in the vegetated wetland, as well as the decrease in the BOD5/COD ratio in the wetland with respect to the inflow is an indication that the degradable organic matter in the wastewater was removed in the wetland [
Parameters | Dry season | Rainy season | ||||
---|---|---|---|---|---|---|
Inflow | Outflow vegetated | Outflow control | Inflow | Outflow vegetated | Outflow control | |
CND (μS/cm) | 3705 ± 383 | 3263 ± 341 | 3183 ± 383 | 2293 ± 354 | 1357 ± 294 | 1414 ± 259 |
Colour (PtCo) | 696 ± 62 | 280 ± 35 | 232 ± 47 | 424 ± 58 | 142 ± 2 | 149 ± 21 |
Turbidity (FTU) | 265 ± 29 | 82 ± 12 | 60 ± 12 | 311 ± 71 | 37 ± 4 | 65 ± 21 |
TSS (mg/L) | 584 ± 90 | 127 ± 22 | 117 ± 38 | 616 ± 120 | 52 ± 6.1 | 86 ± 15 |
8 ± 1.95 | 3.6 ± 0.6 | 4.19 ± 0.64 | 5 ± 1 | 2.2 ± 0.7 | 2.52 ± 0.42 | |
112 ± 18 | 28.7 ± 4 | 33 ± 4 | 94 ± 32 | 24.9 ± 3.2 | 29 ± 6 | |
COD (mg/L) | 545 ± 10 | 172 ± 8.7 | 429 ± 30 | 582 ± 21 | 159 ± 18.3 | 426 ± 43 |
BOD5 (mg/L) | 229 ± 4 | 72.4 ± 3.6 | 164 ± 22 | 244 ± 9 | 67 ± 7.7 | 173 ± 20 |
BOD5/COD | 0.42 ± 0.4 | 0.42 ± 0.41 | 0.382 ± 0.73 | 0.419 ± 0.43 | 0.42 ± 0.42 | 0.406 ± 0.47 |
enhanced by the root exudates [
The removal of nutrients (nitrates and phosphates) in the vegetated wetland was always more than that of the non vegetated control throughout the experimental period. However, significant differences between the two wetlands existed (P < 0.05) only in the removal of phosphates in the dry season of the first year and nitrates in the rainy season of the second year. In constructed wetlands, these parameters are removed by macrophytes, microphytes and other microbial uptake where, the inorganic nutrients are converted to organic biomass and stored as tissues [
The removal of TSS was highest and non significant in the vegetated wetland compared with the non vegetated control throughout the two years period. This parameter in constructed wetlands is mainly removed through filtration by the substrate, sedimentation and adsorption to the substrate and may be to the vegetation in the wetland [
This work had an objective to study the growth and biomass production of Fuirena umbellata (Cyperaceae) and its potentials in the removal of faecal bacteria and nutrients from domestic wastewater. At the end of this study we can say that, the rapid growth and high biomass yield of Fuirena umbellata in wastewater water make it a potential species for use in wastewater treatment in tropical regions. It is found to grow more densely in rainy season but produces more biomass instead in the dry season. The wetland vegetated by Fuirena umbellata was significantly more efficient in the removal of total coliforms and faecal streptococci in the first year, faecal coliforms and faecal streptococci in the second year with no significant differences between the seasons and between the years. Its presence in the wetland also influenced the removal of physicochemical parameters and significantly, the reduction of BOD5 and COD in the wastewater throughout the two years period. This suggests the recommendation of this macrophyte for use in constructed wetland technologies for domestic wastewater treatment in tropical climates. From the quality of the effluent produced and discussed in this paper, the wetland vegetated with Fuirena umbellata could be strongly recommended for use in domestic wastewater reclamation and reuse in developing countries.
The authors thank the International Foundation for Science (IFS) for the financial support to Dr. FONKOU Théophile through the grants N˚W/3782-1 and N˚W/3782-2.
Lekeufack, M., Fonkou, T. and Pamo Tedonkeng, E. (2017) Growth Characteristics of Fuirena umbellata in a Surface Flow Constructed Wetland and Its Influence in Nutrients and Faecal Bacteria Removal from Domestic Wastewater in Cameroon. Journal of Environmental Protection, 8, 171-193. https://doi.org/10.4236/jep.2017.82014