The objective of this study was to evaluate the potentials of beds vegetated with medicinal species ( Brillantaisia bauchiensis and Polygonum salicifolium) in a constructed wetland for domestic wastewater treatment in the Western Highlands of Cameroon. The study was carried out between March and September 2017 on plants collected from a natural wetland in Penka-Michel. The two plants species selected based on their ethnobotanical importance were transplanted and allowed to grow to maturity in a prepared natural wetland at Penka-Michel and a constructed wetland for domestic wastewater treatment on the campus of the University of Dschang. Growth parameters were followed for the two plants species in both wetlands. The physicochemical parameters and faecal bacteria concentrations were measured only for the vegetated and non-vegetated/control beds in the constructed wetland. Overall, the two plants species showed increased growth in height, diameter, leaf number and plants density. The change in diameter and density were very significantly influenced by species type in the constructed wetland than in the natural wetland. Generally, plant growth in height, diameter and density were higher with B. bauchiensis in the constructed wetland than with P. salicifolium in both wetlands. The mean faecal bacteria removal was higher in the vegetated beds for some bacteria than in the non-vegetated/control bed. There was a significant difference in the reduction efficiency of TSS, turbidity, BOD, Faecal streptococci and Total coliforms bacteria between the inflow and the outflow of some treatment beds especially the bed vegetated with Brillantaisia bauchiensis. There were correlations between the two plants species as concerns increased plants height, diameter, leave number, shoot number and nutrients uptake in the constructed wetland beds compared with the natural wetland.
The negative impact of the increase in world’s population from 6 billion in 2013 to over 7.5 billion people in 2018 with Africa having about 1.3 billion and 24.054 million people in Cameroon directly affects the environment. It causes various adverse efffects on living organisms and an imbalance on the ecosystem affecting drinking water sources, biodiversity, health and reproduction of species [
Aquatic macrophytes are large water tolerant vascular plants visible to the naked eye and have at least their vegetative parts growing permanently or periodically in an aquatic habitat [
To avoid causing constant and perpetual disequilibrium in ecosystems, wastewater needs to be properly treated before discharge and CW technologies are used nowadays to mimic the natural wetlands for wastewater treatment purposes. They are designed as surface flow (SF) or sub-Surface flow (SSF) systems using emergent macrophytes and floating macrophytes as used in lagoons systems to remediate wastewater with several hydrological, biogeochemical and biological benefits. Hence, from a biogeochemical viewpoint, the main function of a CW is the temporary storage and/or removal of chemical substances such as total suspended solids (TSS), Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD) as well as organic compounds (Phosphorus and Nitrogen) removal [
The high production and indiscriminate discharge of domestic wastewater from homes and agro-industries into natural wetlands without any treatment has contaminated wetlands and greatly affected the biodiversity in these important ecosystems and is a source of many diseases affecting humans [
It was in this light that this study was undertaken using the above mentioned wetland medicinal plants species to investigate their phytoremediation potentials of domestic wastewater in constructed wetlands.
The experimental setup was a Yard-Scale natural wetland in Penka―Michel located at latitude 5˚27'43.1"N and longitude 10˚14'09.3"E and the constructed wetland for domestic wastewater treatment located on the Dschang University campus on latitude 5˚26'39.9"N and longitude 10˚04'18.3"E. The climate in this region is of equatorial type with 4 months of dry season between mid-November and mid-March, and 8 months of rainy season between mid-March and 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 prepared natural wetland had a surface area of (4 × 2 m2) while the constructed wetland comprised of a 3 m3 digester, a distribution gutter (3 m3) and three wetland beds (WB1, WB2 and WB3) of volume (4 × 2 × 0.6 m3). All these, were constructed using cement blocks filled with concrete and the insides of the structures were plastered with a mixture of concrete, then smoothen with cement (CIMENCAM) mixed Sikalite® and ZUM AbdichtenTM was applied for water tightness. A slope of about 1% was respected at the bottom of each wetland bed to ease the flow of water from the inflow to the outflow. The constructed wetland beds were then connected to the distribution gutter by polyvinylchloride (PVC) pipes, each having a tap to control the flow rate and to ensure the continuous flow of wastewater into the wetland beds. The entire system was then linked by a PVC pipe to the deteriorated and abandoned conventional wastewater treatment system pre-existing, which served as the primary treatment system (
Gabions of 30 cm made up of stones of 5 - 8 cm in diameter were arranged at the inflow and outflow zones of the wetland beds. The outflow structures are fitted to enable the regulation of water level in the wetland. The main filter substrate is a 45 cm thick column of sand having particle size of about 2 mm in diameter (
Macrophytes used in constructed wetland beds are preferably annual herbs with erect stem. Hence, the chioce of the two macrophytes species was based on two broad criteria: physiology (Plant life form, plant lifecycle, stem type and cuticle thickness) and fedelity index (the citation of plant as medicinal by traditional practitioners) [
Life form | Lifecycle | Type of stem | Stem and leaf thickness (Cuticle) | Fidelity level |
---|---|---|---|---|
Herb = 4 Shrub= 1 Tree = 0 | Annual = 4 Biennal = 1 Perennal = 0 | Erect stem = 4 Criping stem = 2 Climbing stem = 0 | Hard stem/leaf = 3 Hard stem/soft leaf = 2 Soft stem/soft leaf = 0 | 40% - 49% = 5 30% - 39% = 4 20% - 29% = 3 10% - 19% = 2 0% - 9% = 1 |
erect stems, hard stem/leaf and high fidelity level (most cited as medicinal plants). Another criterion was very little material from Literature review about these plants.
From the above criteria, these two wetland macrophytes were selected with high values of 17/20 to be tested in the CW for domestic wastewater treatment.
1) Brillantaisia cf. bauchiensis Hutch. & Dalz. (Acanthaceae) 17/20
2) Polygonum salicifolium Brouss ex Wild. (Polygonaceae) 17/20
The domestic wastewater used in the study was a mixture of the grey and black type chennelled from the abandoned conventional treatment plant receiving domestic liquid wastes from the students’ residence in campus of the University of Dschang at an inflow rate of about 3 m3 per day.
Young shoots of the two plants species were obtained from a natural wetland in Penka-Michel sub-division (Menoua Division). These were transplanted in the natural wetland in Penka-Michel and in the constructed wetland station on campus A of the University of Dschang. In the constructed wetland station, the plantlets were transplanted in WB1 and WB3 at a density of 6 plants/m2 as presented in
The primarily treated effluent from the conventional plant was channelled into a secondary digester and then into a 10 m by 0.5 m by 0.6 m gutter from where a constant flow of the wastewater into the wetland beds was assured at a loading rate of about 35 Lm−2 day−1 with the help of a tap. This wastewater was allowed at this rate for one month to ensure the proliferation of microorganisms and the adaptation of macrophytes in the wetland beds. This step was the domestication phase after which the survival rate for each species was obtained as follows:
Survival rate = Total number of shoots survived Total number of shoots planted × 100
If any macrophyte species had less than 50% survival it was replanted. The surviving young plants (
The efficiencies of the wetlands in the water quality improvement were evaluated by measuring the physicochemical characteristics of the wastewater at the inflow and from the outflow of the wetlands. 500 ml of water sample were collected from the inflow and from the outflow of each wetland. These were analysed at the Research Unit of Applied Botany at the University of Dschang for four consecutive months. The parameters measured included the true colour, turbidity, total suspended solids (TSS), nitrates ( NO 3 − ), phosphates ( PO 4 3 − ), chemical oxygen demand (COD) and five days biochemical oxygen demand (BOD5). However, parameters such as electrical conductivity (CND) and total dissolved solids (TDS) were measured directly in the field. All these parameters were measured following the standard methods for water and wastewater analyses described and published by [
The nutrient removal efficiency (%) of each wetland bed for each parameter was evaluated from the inflow concentration following the formula below:
Efficiency = C i − C 0 C i × 100
where, C i and C 0 respectively represent inflow and outflow concentration of each parameters.
The densities of plants growing in the natural wetland and those in the CW vegetated beds were evaluated following the formula below:
Density of plants in the bed = Number of shoots Surface Area
Wastewater samples were collected four times in four consercutive months from the inflow and outflow of WB1 (vegetated with B. bauchiensis), WB2 (non-vegetated control) and WB3 (vegetated with P. salicifolum), from May 2017 to August 2017. Sterile laboratory glass bottles of 500 ml volume each were used to collect water samples that were immediately transported in a cooler to the Research Unit of Applied Botany for analyses. In the laboratory, manipulations were carried out in strict conditions of sterility. In antiseptic 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 and a sterile new pipette was used for each sample to avoid contamination. 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 coliforms were incubated on DifcoTM m FC prepared Agar in Petri dishes at 44.5˚C for 24 hrs [
Samples for Faecal streptococci and Total coliforms were respectively incubated on BBLTM Bile Esculin and Tergitol® 7 Agars at 35˚C for 48 hrs [
Data were managed using Microsoft Excel and the software R, version 3.0.1 (R Core Team, 2013). Results at 95% probability level were considered significant. The plants height and diameter were examined for normality using the Shapiro-Wilk normality test. When they were found to be normally distributed, Analysis of variance (ANOVA) with the “summary.lm” function and two classificatory factors (species and wetland) were used to test whether there were significant differences between the means of parameters in the same site or between parameters in the same species in different sites. The distribution of counts of plant leaves (OR plant density) in relation to species (P. salicifolium and B. bauchiensis), wetland (constructed and natural) and the interaction between the two factors was modelled using log-linear Poisson, with time (every two weeks) serving as covariates.
A one-way ANOVA with the “summary.lm” function was used to verify the existence of significant differences in the means of physico-chemical parameters (electrical conductivity, TDS, TSS, turbidity, colour, BOD, COD, NO 3 − and PO 4 3 − ) and bacteriological parameters (Faecal coliforms, Faecal streptococci, Total coliforms and E. coli) between the inflow and the outflow wetland beds and between the outflows of the wetland beds.
Model1: Leaf number ~ Species ∗ Site + Time Model 2 : Bactria counts ( log units ) ~ treatment bed ∗ Time
After one month of adaptation in the natural wetland, all the 45 plantlets of both plants species survived in the natural wetland while all 45 survived for Polygonum salicifolium and 43 for Brillantaisia bauchiensis survived after one month of domestication in the constructed wetland for wastewater treatment.
In the natural wetland, both plants gradually adapted in their new site and steadily grew from an average height of 30.58 cm to 99.49 cm at the end of the experiment with a relative growth rate of 0.055 cm/cm/day for Polygonum salicifolium. The tallest plant here was 140 cm. Brillantaisia bauchiensis also grew from an average height of 15.07 cm to 60.03 cm with a relative growth rate of 0.034 cm/cm/day, the tallest plant here measuring 79 cm. In the CW, both plants gradually acclimatized in their new environment and Polygonum salicifolium steadily grew from an average height of 28.55 cm to 99.53 cm with a relative growth rate of 0.055 cm/cm/day and the tallest plant being 203 cm. Brillantaisia bauchiensis as well grew from an average height of 11.6 cm to 114.53 cm with a relative growth rate of 0.064 cm/cm/day and the tallest plants here being 165 cm. These results show that the two plants species grew taller in the constructed wetland than in the natural wetland. These are comparable to those of [
The growth in height of P. salicifolium in the natural wetland was significantly different from that of Brillantaisia bauchiensis as indicated by the intercept effect in
The diameter of Polygonum salicifolium in the natural wetland increased from an average of 3.063 to 7.1 mm giving a relative increase of 0.004 mm/mm/day with the largest plant having a diameter of 15.78 mm. Brillantaisia bauchiensis increased from 3.82 to 11.51 mm with a relative increase of 0.0064 mm/mm/day and the thickest plant having a diameter of 17.76 mm. The diameter of Polygonum
Model effects | Estimates | Standard errors | t-values |
---|---|---|---|
Intercept | 7.286 | 1.292 | 5.641*** |
Natural wetland | −2.790 | 1.827 | −0.195 |
Constructed wetland | −0.356 | 1.827 | −0.195 |
B. bauchiensis vs Treatment site | 6.121 | 2.583 | 2.369* |
* shows the level of significance at probability level of 5%. The intercept is the effect of P. salicifolium and natural wetland combined.
salicifolium in the CW increased from 4.22 to 9.1 mm with a relative increase of 0.0051 mm/mm/day and the thickest plant having a diameter of 12.01 mm. Brillantaisia bauchiensis averagely increased from 3.34 to 20.15 mm with a relative increase of 0.011 mm/mm/day and the thickest plant having a diameter of 29.61 mm. These results equally show that the two plants species grew thicker in the constructed wetland than in the natural wetland. The changes in the diameter of a plant in the different habitats are summarised in
The increase in diameter of Brillantaisia bauchiensis in the Constructed wetland was significantly different from that P. salicifolium in the constructed wetland as indicated by the intercept effect in
Model effects | Estimates | Standard errors | t-values |
---|---|---|---|
Intercept | 0.469 | 0.135 | 3.484** |
Natural Wetland | 0.295 | 0.190 | 1.550 |
Constructed Wetland | 0.019 | 0.190 | 0.100 |
B. bauchiensis vs Constructed Wetland | 0.894 | 0.269 | 3.321** |
** shows significance at probability level of 1%. The intercept is the effect of P. salicifolium and natural wetland combined.
in plant diameter was highest with B. bauchiensis in the constructed wetland ( 1.677 ± 0.269 , N = 45 ) compared to other species-habitat interactions, as evidenced in
There was no interaction between species and wetland type in predicting leaf production. P. salicifolium in the CW showed a constant trend in leaf production, the natural wetland witnessed rather a fall in leaf production. Overall, B. bauchiensis had the minimum leaf production irrespective of the wetland where it was grown ( β ^ = − 0.669 ± 0.120 , P < 0.001 ) as shown in
Model effects | Estimates | Standard errors | Z-values |
---|---|---|---|
Intercept | 2.943 | 0.113 | 26.491*** |
Natural wetland | −0.669 | 0.120 | −5.575*** |
Constructed wetland | −0.000 | 0.988 | 0.000 |
Time | −0.005 | 0.006 | −0.705 |
B. bauchiensis vs Treatment site | −0.112 | 0.173 | −0.640 |
*** shows significance at probability level of 0.1%. The intercept is the effect of P. salicifolium and natural wetland combined.
In the natural wetland, the density of Polygonum salicifolium increased from 6 plants/m2 at the start of the experiment in March to 7 plants/m2 during the domestication phase, to 21 plants/m2 at the end of the experiment while that of Brillantaisia bauchiensis increased from 6 plants/m2 to 9 plants/m2 during the domestication phase, to 62 plants/m2 at the end of the experiment. The plant density of Polygonum salicifolium in the CW increased from 6 plants/m2 at the start of the experiment to 15 plants/m2 during the domestication phase, to 49 plants/m2 at the end of the experiment. As for Brillantaisia bauchiensis, its density increased from 6 plants/m2 to 20 plants/m2 during the domestication phase, and finally to 214 plants/m2 at the end of the experiment in the month of September. The young shoots which arose from both plants species in the wastewater treatment beds grew rapidly without any inconveniency and covered the entire respective beds with time.
Shoot production by the two plants species in response to natural and artificial habitats is summarised in
The growth parameters increased very slowly during the domestication phase as the plants were still struggling to adapt in their new but more polluted environment
Model effects | Estimates | Standard errors | Z-values |
---|---|---|---|
Intercept | 0.916 | 0.119 | 7.652*** |
Natural wetland | 1.061 | 0.116 | 9.147*** |
Constructed wetland | 0.875 | 0.119 | 7.355*** |
B. bauchiensis vs Constructed | 0.678 | 0.136 | 5.000*** |
Time (Weeks) | 0.083 | 0.004 | 21.583*** |
*** shows significance at probability level of 1%. The intercept is the effect of P. salicifolium and natural wetland combined.
at the start of the experiments in March (during the dry.season). This slow growth might have been due to the fact that the experiment was started in the dry season with the plants receiving more concentrated wastewater with mineralized pollution. The plants grew rapidly with the coming of the rainy season with the highest growth registered within the last weeks of the study when the wastewater was more diluted with constant rain fall [
Wastewater is rich in nutrients that enrich and nourish the soil. Plants growing in wastewater constructed environment make use of these nutrients for their growth and development [
The total suspended solids (TSS) at the outflows of the treatment beds varied between 133 and 153.5 mg/l compared to the inflow (243.3 mg/l). Total suspended solids were significantly reduced in the outflows of the treatment beds
compared to the inflow. However, the reduction was higher (46%) in filter bed vegetated with Brillantaisia bauchiensis ( β ^ = − 208.50 ± 72.77 , P < 0.01 ) followed by that vegetated with Polygonum salicifolium 43.08%. Although the TSS concentration at the ouflow of the control bed was significantly lower than the inflow (
The turbidity values at the outflow of all the beds ranged between 232 and 283.3 FTU but were not significantly lower than the inflow value of 440.5 FTU except for the bed vegetated with Brillantaisia bauchiensis ( β ^ = − 110.25 ± 42.97 , P < 0.02 ) with turbidity value of 232 FTU corresponding to reduction efficiency of 44.46% (
The COD of the non vegetated control bed was lower (87 mg/l) than those of the vegetated beds (193.3 and 273.5 mg/l) which were still lower than the COD value at the inflow (297.8 mg/l). The percentage reduction efficiency was however higher in the control bed (70.64%) than in the vegetated beds (22.92% and 41.92%). However, the outflow of the vegetated beds had higher COD than the inflow so that the efficiency of reduction was negative rather. The BOD values of the outflow of the treatment beds ranging between 63.75 mg/l and 102.4 mg/l generally lower than the mean BOD at the inflow of the beds. The non-vegetated/control bed had the lowest mean BOD value of 63.75 mg/l corresponding to 72.79% reduction efficiency ( β ^ = − 153.5 ± 52.78 , P < 0.01 ) while the bed vegetated with Brillantaisia bauchiensis followed with a mean BOD value of 98.3 mg/l with a reduction efficiency of 58.37% ( β ^ = − 118.95 ± 52.78 , P < 0.04 ) lower than the guideline value of 100 mg/l [
The reduction of nitrate in the effluent at the outflow of treatment beds was between 1.85 mg/l and 2.45 mg/l, lower than the inflow value of 4.1 mg/l. The wetland bed vegetated with Polygonum salicifolum had the best removal percentage of 65.66% followed by the wetland bed vegetated with Brilantaisia bauchiensis (49.85%) while the non vegetated bed was the least (36.53%). There
were no significant differences in the mean phosphate concentration between the inflow 6.218 mg/l and the outflows of the treatment beds were not significantly different with each other: Brillantasia bauchiensis (7.618 mg/l), non-vegetated/control bed (6.023 mg/l) and Polygonum salicifolium (5.243 mg/l). The control bed had the highest reduction efficiency (−1.16%) followed by the bed with Polygonum salicifolium (−4.45%) and then the bed vegetated with Brillantaisia bauchiensis (−20.16%). These results differ from those of [
(69.82% - 73.3%) than the control bed (61.14%). Generally, there was reduction of faecal bacteria from the effluent in the outflow of the treatment beds compared to the log concentration number in the inflow effluent. There was a significant difference in the log units of faecal bacteria concentrations between the inflow and outflow of the treatment bed vegetated with Polygonum salicifolium in bed 3 ( β ^ = − 2.15 ± 84 , P < 0.01 ) in Faecal streptococci removal (
were significant for Faecal streptococci and total coliforms compared to the inflow. There was no significant difference for the other treatment beds in Faecal coliforms bacteria. The bed vegetated with Brillantaisia bauchiensis was more efficient in E. coli removal (85%) and in Total coliforms (73.3%) than the other beds. These results corroborate those of [
The objective of this study was to evaluate the growth and wastewater treatment potentials of Brillantaisia bauchiensis and Polygonum salicifolium in vegetated beds. Overall, it was shown that both plants species increased in growth parameters in both wetlands but B. bauchiensis in the constructed wetland was significantly higher than B. bauchiensis in the natural wetland and P. salicifolium from both wetlands. Moreover, B. bauchiensis from the constructed wetland was more proficient in shoot/biomass production than P. salicifolium and there was a correlation between increased height, diameter, leave and shoot production by the plants species in the constructed wetland treatment station with respect to nutrient uptake. Even though the plants grew rapidly after the domestication period, there was not relationship between plant growth rate and its purification efficiency.
As concerns the phytoremediation potentials of the two plant species, the mean faecal bacterial removal was higher in the vegetated (treatment) beds for some faecal bacteria than in the non-vegetated control bed. There was a significant difference in the mean reduction efficiency of TSS and BOD at the outflow in all the beds compared to the inflow but the percentage reduction was higher in the vegetated beds. The bed vegetated with Brillantaisia bauchiensis performed better than the bed with Polygonum salicifolium in faecal bacterial reduction. Despite the variability of the characteristics of the primarily treated water, the plants grow best in the CW showing its great potentials in domestic wastewater remediation.
Nevertheless, the two plants species are suitable in domestic wastewater management. There was evidently high biomass production in the constructed wetland species than those of the natural wetland. We recommend that tissue culture and examination for the presence of faecal bacteria and heavy metals be conducted in case of conservation of the two plant species in wastewater treatment station and productivity in high quantity for other advantages.
The authors thank the traditional practitioners in Batcham, Bassap, Foumban and Penka-Michel for their collaboration to identify wetland medicinal plants.
The authors declare no conflicts of interest regarding the publication of this paper.
Boyah, J.K., Fonkou, T., Nguelefack, T.B., Nguetsop, V.F. and Lekeufack, M. (2019) Wastewater Treatment Potentials of Vegetated Beds with Brillantaisia cf. bauchiensis Hutch & Dalz and Polygonum salicifolium Brouss ex Wild in the Western Highlands of Cameroon. Journal of Environmental Protection, 10, 389-412. https://doi.org/10.4236/jep.2019.103023