Abstract

Treating fecal sludge prior its disposal in the environment remains a key point in ensuring the protection of the environment and public health. Raw fecal sludge from the town Bafoussam was treated using bio-digestors combined with maturation ponds and the removal efficiencies evaluated. The monitoring of physicochemical and bacteriological analysis at the inlet and outlet of the system showed that the system enables the reduction of pollutants with discharge values in conformity to the Cameroonian guidelines for wastewater effluent discharge. The following outlet concentrations and corresponding removal efficiencies were recorded; 25.63 mg/L (99.71%) for TSS, 5.46 mg/L (95.47%) for NH₄ -N, 3.31 mg/L (88.44%) for TP, 227 mg/L (97.85 %) for COD and 70 mg/L (95.4 %) for BOD5, 130 CFU/100 mL (99.99%) for fecal coliforms. The algal diversity in sampled wastewater revealed a richness of 43 species suggesting that such a system could also sustain algal production. Bio-digestors performed well in removing total suspended solids and ammonia with removal especially of 96% and 76.3% respectively, whereas stabilization ponds essentially enabled the elimination of fecal coliforms and fecal streptococci with 93.77% and 87.5% removal respectively.

Keywords

Bio-digester; Fecal sludge treatment; Waste stabilization ponds

Introduction

The global challenge that faces sustainable sanitation services in developing countries is the lack of fecal sludge (FS) management due to the rapid urbanization and population growth as it generates enormous quantities of FS [1,2]. Developing countries and emerging economies like Cameroon heavily depend on on-site sanitation systems (OSS) such as septic tanks or pit latrines for excreta disposal [3-5]. It was estimated that one-third of the world’s population relies on on-site sanitation systems producing a huge amount of sludge that requires safe disposal in-situ or transport and treatment offsite [6] and the solution for effective and sustainable FS management presents a global need [7-9]. The purpose of OSS is to protect and promote human health and environmental safety [10,11]. OSS are used daily by approximately 2.7 billion people in low-income communities globally and are being installed in huge numbers throughout subSaharan Africa [12]. This effectively means that sanitation targets for Sustainable Development Goal (SDG) 6 can only be met if FS among other wastes is properly managed [13]. The United Nation SDG6 aims to achieve universal access to “safely managed” sanitation by 2030 and the safely managed sanitation is described as the uses of improved facilities with safe disposal in situ or offsite transportation and treatment [14]. Uncontrolled disposal of untreated FS from such systems to local water bodies is detrimental to both the environment and public health. Compared to municipal wastewater, FS typically contains more than ten times the amount of organic and pathogenic contamination [6]. FS is a mixture of human excreta, which consists of water, organic, inorganic matter and harmful pathogens including nutrients, whereas FS management is a set of scientific practices that ensures safe collection, transportation, treatment, and disposal of onsite collected excreta without polluting the environment [15]. The entire world is racing to adopt a proper FS management service chain to ensure the safe disposal of FS after due treatment [16]. Most low-income countries like Cameroon do not have adequate FS management system.

Treatment is a crucial step for FS management to alleviate the associated environmental and health risks [17]. Thus, the treatment step is essential for the successful management of FS chain. A number of studies have looked at the treatment of FS in tropical areas [18-23]. However, most of these studies have been carried out on a pilot scale. Indeed, [6] presented an overview of potential, modest-cost treatment options for FS. These options were co-composting with organic solid waste, planted drying bed, unplanted drying bed, settling/thickening tank, settling pond, anaerobic digestion, co-treatment with sewage sludge, co-treatment with wastewater. Unfortunately, most FS treatment units in large scale in sub-Saharan Africa failed after construction due to a lack of monitoring and ongoing funding for operations [24]. The failures related to this mismanagement affect natural resources and pose health, environmental and socio-economic risks. The present research work is therefore an evaluation of a large-scale performance of combine bio-digestor and stabilization pond treating FS from OSS in the city of Bafoussam (Cameroon). The objective of this study was to assess the contribution of each component of the system to the removal of mineral, organic and bacteriological pollutants from the raw sludges while looking at the algal productivity as a key removal mechanism in the lagoon system.

Methodology

Study area

The Fecal Sludge Treatment Plant (FSTP) for the management of FS in the city of Bafoussam is located at about 20 km of City of Bafoussam (West Region of Cameroon). This city covers an urban area of about 402 km² limited by latitude 05°28’ and 11°20’ longitude (Figure 1). The city is located at about 1,521 m above sea level and has an estimated population of 347,517 inhabitant in 2019. The city has a tropical climate with one dry season (November to March) and one rainy season (April to October). The average rainfall is 1,871 mm with an average temperature of 20°C. A large part of the city consists of informal settlements with very basic water supply, sanitation and waste disposal [25]. On-site sanitation systems for excreta collection are the main sanitation disposal facilities in the city. Before 2016, the city does not have any FS treatment plant and the estimated FS production was 1,440 m³ per week. This amount of FS was collected and discharged in the peri-urban areas of the city as well as in the Noun River [25].

Figure 1: Thematic map showing the localization of the city of Bafoussam in Cameroon as well as the FS treatment plant.

Description of the Bafoussam FS treatment plant

The Bafoussam FS treatment plant occupies an overall land area of 1,200 m² on an elevation topography which allows the flow of liquid through gravity and consists of the following stages (Figure 2):

Figure 2: Picture showing the aerial view of the Bafoussam FS treatment plant (A: Biodigester units; B: Waste stabilization pond units).

• A pre-treatment stage consisting of a screening grid system (2.5 cm mesh diameter; length 39 cm; width 35 cm) placed at the entrance of the sludge reception chamber for sorting out the refusals of the FSTP.

• A primary treatment consisting in three (03) anaerobic biodigesters, each biodigester measures of size 5 × 2 × 1.5 m (length × width × depth) in series. They serve for the thickening and separation of the solid-liquid fraction of the sludge;

• A secondary treatment made up of ten (10) consecutive maturation ponds (22 × 2.4 × 1) m for length, width and height respectively for the hygienization of the leachate from biodigesters;

• The tertiary treatment consisting of a filtration basin of 5 × 2 × 1 for length, width and depth containing pozzolan.

Experimental procedure

Sampling frequency and procedure: Five sampling points were retained in this study. The first sample (P1) was taken at the entrance of the FSTP, more precisely downstream of the bar screen, and consisted mainly of sludge samples in order to have its characteristics before the beginning of the treatment. The second sampling (P2) was done at the level of the first pond, directly at the exit of the anaerobic biodigester, in order to appreciate the purification performances of the biodigesters in the treatment process. The third sampling point (P3) was located at the level of the fifth pond, because this pond constitutes the mid- stage of the treatment process and it is important to know how the system evolves in terms of pollutant reduction. The fourth point (P4) located in the tenth pond was chosen to assess the degree of treatment of the system in the last pond and the fifth point (P5) is the outlet of the treatment plant and therefore corresponds to the end of the treatment. Sampling was done monthly over a period of three months for physico-chemical analyses and determination of algal diversity.

Physico-chemical and bacteriological characterization of samples: pH, Total Suspended Solids (TSS) and Electrical Conductivity (EC) were measured in situ using the HACH pH meter model HQ14d. Chemical Oxygen Demand (COD) was quantified with the closereflux dichromate reduction method at 150°C for 2 hours followed by a spectrophotometric quantification with a spectrophotometer model HACH DR 3900. Biological oxygen demand for five days (DBO₅) was quantified after five days of incubation in the darkness at 20°C with Oxytop head gas sensors after inhibition of nitrification. NH₄-N was quantified with the Nessler method, NO₃-N with the cadmium reduction (NitraVer 5) method and Total Phosphorus (TP) with the molybdovanadate method for extraction and quantification with a HACH DR 3900 spectrophotometer after acid digestion. These methods were carried out as described in Standard Methods for the Examination of Water and Wastewater [26]. Fecal coliforms and fecal streptococci were quantified using the membrane filtration method [27].

Determination of the system’s physico-chemical and bacteriological removal efficiency: The effect of pollutant loads on the treatment performance of the plant was evaluated after determining the concentrations of physicochemical and bacteriological parameters at the inlet and outlet according to [28] method of calculation (Equation 1). Parameters considered for the removal efficiency were EC, COD, BOD₅, TP, NH₄-N, NO₃-N, fecal coliforms and fecal streptococci. (Eq. 1)

Determination of algal diversity:

Sample collection and conditioning: Water samples for algal analysis were taken from the ponds where the physico-chemical parameters were determined, in order to better appreciate the contribution of algae in the wastewater treatment process. Samples were taken in each pond at different depths (10 cm; 40 cm and 70 cm) to allow access to all points of the lagoons. For each lagoon pond units investigated, three (03) composite samples were taken. Per composite sample, 500 mL was collected in bottles and fixed in situ with iodine solution (0.5mL/100mL of sample). These samples were transported in dark conditions to the laboratory using cooler boxes at 04°C for observation.

Biological analysis: The biological analysis of water samples consisted of the algal biomass and densities determination following the method described by [29]. Algae observations and counting were performed using a light microscope, model Olympus CH-2. The determination of algal diversity was done following identification keys [30-33].

Data analysis: An Analysis Of Variance (ANOVA) with p=0.05 was carried out to compare the physico-chemical and bacteriological qualities of the FS at the inlet to that of the leachate at the outlets of the system. Descriptive statistics of samples were undertaken to express the parameters’ dispersion. Before the ANOVA test, normality and variance homogeneity were tested using the Levene tests. Algal density and diversity in wastewater samples were examined. Due to the nonnormal distribution in the prevalence and diversity of algal population in this study, Pearson correlation test was computed to assess the relationship between the algal dominance and the physico-chemical parameters of wastewater (pH, EC, NH₄-N, TP, BOD₅). The software Excel of Microsoft Office for Window 2016 was used to compute all the data.

Results and Discussion

Physico-chemical and bacteriological characteristic of FS .

FS received at the treatment plant exhibits high physico-chemical and bacteriological concentrations (Table 1). These values enable the classification of raw FS produced in Bafoussam in the category of “high strength sludge “according to the classification of [34]. However, a high variability was noted between raw FS samples (n=3). The variability observed in the concentration of FS parameters was also noted by several authors [34,35,24]. This variability in FS quality could be attributed to household habits and local environmental conditions such as storage duration, toilet usage, inflow and water infiltration into the latrine pits [36,9]. Organic matter (BOD₅ and COD) contents in samples were high? contrasting those obtained by [3] in the city Yaounde (Cameroon). This could be explained by the high prevalence of dry pit toilet which allows less dilution of the sludge added to a slow degradation process as compared to septic tanks or flushing toilets which are more common amongst OSS emptied by trucks in Yaounde. However, values recorded by [24] are generally of the same range with those obtained in this study.

Sludge parameters	Mean value and standard deviation	Literature values
		*Kengne IM, et al. [3]	**Bassan M, et al. [24]	*Nzouebet WAL, et al. [35]
pH	7.070 ± 0.310	6.5-9.3	/	5.9-8.9
EC (mS/cm)	1.960 ± 0.980	/	/	0.2-17.2
TSS (g/L)	8.740 ± 6.890	/	/	/
NO3-N (g/L)	0.440 ± 0.130	//	/	/
NH4-N (g/L)	0.120 ± 0.070	0.4	/	0.01-2.5
TP (g/L)	0.028 ± 0.006	/	/	/
COD (gO2/L)	10.550 ± 3.990	30.5	12.4	0.4-124.2
BOD5 (gO2/L)	1.790 ± 0.140	/	2.1	0.1-18.5
Fecal coliforms (Log CFU/100 mL)	21,000 ± 10,830	/	/	/
Fecal streptococci (Log CFU/100 mL)	15,900 ± 13,830	/	/	/

Table 1: Physico-chemical and bacteriological characteristics of FS recorded in this study alongside that of other cities (n=3).
*Physico-chemical characteristics of FS recorded in the city of Yaounde (Cameroon)
**Physico-chemical characteristics of FS recorded in the city of Ouagadougou (Burkina Faso)

Evolution of physico-chemical and bacteriological parameters along the treatment system

Longitudinal profile of the physico-chemical and bacteriological pollutants in FS along the FSTP is shown on figure 3 and 4. A decrease of the pollution parameters from inlet to outlet of the system was observed. pH values ranged from 7.07 ± 0.31 (inlet) to 7.52 ± 0.11 (outlet), with very little variation between treatment stages. These pH values ranging between 6 and 9 and are compatible with the growth of microorganisms in wastewater systems [7]. For other parameters the longitudinal profile showed a reduction trend from the inlet to the outlet whatever the parameter.

Figure 3: Longitudinal profile of physico-chemical parameters along the treatment system (A:pH; B:EC; C:TSS; D:NO3-N; E:NH4-N; F:TP).

Figure 4: Longitudinal profile of organic and bacteriological pollutions along the FS treatment plant (A:COD; B:BOD5; C:FC; D:FS).

The quality of the leachate at the outlet of the treatment plant, complies with the WHO and MINEPDED discharge standards (Table 2).

Leachate quality at the outlet of FSTP (n=3)	Mean value and standard deviation	Guidelines for discharge of effluent
			WHO**
pH	7.520 ± 0.110	6-9	6-8.5
EC (mS/cm)	0.970 ± 0.590	NA	NA
TSS (g/L)	4.040 ± 1.950	NA	NA
NO3-N (g/L)	0.0130 ± 0.007	<0.030	<0.030
NH4-N (g/L)	0.015 ± 0.090
TP (g/L)	0.0032 ± 0.001	<0.010	<0.010
COD (gO2/L)	0.178 ± 0.400	<0.200	NA
BOD5 (gO2/L)	0.042 ± 0.015	<0.050	NA
Fecal coliforms (CFU/100 mL)	130 ± 90	<2,000	1,000
Fecal streptococci (CFU/100 mL)	64 ± 40	<1,000	NA

Table 2: Mean value for physico-chemical and bacteriological parameters of leachates (n=3) from FS treatment plant. Cameroon and WHO Guidelines are presented as a reference.
*Cameroon guidelines for wastewater effluent discharge from the Ministry of Environment, Nature Protection and Sustainable Development in Cameroon [37].
**[38] guidelines for the safe use of wastewater, greywater and excreta in Agriculture.

Removal efficiency

The removal efficiency of the system was evaluated at different level in order to see the contribution of each component of the system. Table 3 summarizes the removal efficiencies throughout the system. The biodigester stage showed good removal efficiencies were obtained for the pollution parameters such as TSS, FS, FC, NH₄-N, COD BOD₅ with respective removal efficiency of 96.1%, 91.20%, 77.86%, 76.32%, 65.49% and 62.93%. However, negative removal efficiencies were recorded for the parameters EC and TP. Anaerobic digestion technologies have been used as primary treatment for FS. Indeed, Ruhela M, et al. [39] by assessing the efficiency of FS treatment in India pointed a complex biochemical process in biodigesters where organic matter decomposes in the absence of oxygen to produce biogas (methane and carbon dioxide) and residual digestate (stabilized organic matter). In their study they obtained comparable average removal efficiencies of 83.64% for BOD₅, 79.96% for COD, 64.78% for TSS. Arthur PMA, et al. [40] pointed out the anaerobic reactions occurring in ponds to be responsible for wastewater pollutant reduction (namely fermentation, denitrification and ammonification). The overall removal performances are higher than 85% except for the electrical conductivity (59.84%). We noted a strong reduction (p<0.05) of FC and FS. This largest decrease in fecal indicators would be due to thermophilic conditions occurring in aerobic digestion processes as well as the and also interactions with heterotrophic organisms (algae), which have a bactericidal effect on pathogenic germs. Indeed, Gantzer C, et al. [41] by monitoring of bacterial and parasitological contamination during various treatment of sludge have found the most important decrease of E. coli observed in anaerobic mesophilic digestion. Zacharia A, et al. [42] by evaluating the occurrence, concentration, and removal of pathogenic parasites and fecal coliforms in three waste stabilization pond systems in Tanzania pointed out the highest fecal coliform reduction in wastewater (3.8 log units/100 mL)

Parameters	Raw fecal sludge	Outlet of bio digester units	Outlet of the system
EC (mS/cm)	1.960 ± 0.980b	3.116 ± 0.123bc (-58.97%)	0.791 ± 0.610a (59.64%)
TSS (g/L)	8.740 ± 6,890bc	0.343 ± 0.084b (96.07%)	0.026 ± 0.013a (99.99%)
NO3-N (g/L)	0.440 ± 0.130bc	0.366 ± 0.075b (16.81%)	0.003 ± 0.001a (99.31%)
NH4-N (g/L)	0.120 ± 0.070bc	0.029 ± 0.008b (75.83%)	0.006 ± 0.007a (95.33%)
TP (g/L)	0.028 ± 0.006b	0.026 ± 0.005b (71.42%)	0.003 ± 0.002a (88.21%)
COD (gO2/L)	10.550 ± 3.990bc	3.227 ± 0.029b (69.41%)	0.227 ± 0.058a (97.84%)
BOD5 (gO2/L)	1.790 ± 0.140bc	0.565 ± 0.018b (68.43%)	0.070 ± 0.010a (96.08%)
FC (CFU/100 mL)	7 × 106 ± 3 × 106bc	2 × 106 ± 9 × 105b (71.42%)	130 ± 90a (99.99%)
FS (CFU/100 mL)	5.5 × 106 ± 1.8 × 106bc	1.01 × 106 ± 9 × 105b (81.81%)	64 ± 40a (99.99%)

Table 3: Mean value and standard deviation of physico-chemical and bacteriological characteristic of FS and leachate at different levels of the system associated to their removal efficiency in brackets.
Note: Values followed by the same letter are not significantly different from each other following one-ways ANOVA test, p<0.05.

Lagoon systems are known for their economical treatment of municipal wastewater, especially if low-cost land is available [43]. The evolution of physico-chemical and bacteriological parameters along this part of the FSTP was monitored and showed a regression of these pollutant parameters in the outlet leachates. The removal efficiency of pond used as secondary treatment in this study revealed high removal efficiency (Table 3). Reduction of 59.64%, 99.99%, 99.31%, 95.33%, 88.21%, 97.84% and 96.08%, 99.99% and 99.99% was recorded respectively for the parameters EC, TSS, NO₃-N, NH₄-N, TP, DCO, DBO₅, fecal coliforms and fecal streptococci. The highly significant (p<0.05) reduction in physicochemical and bacteriological parameter concentrations along the treatment systems could be related to the predominance of physicochemical pollutant removal processes, including sedimentation, adsorption, sorption, predation, volatilization, photodegradation and the effect of UV radiation [43,5]. Indeed, Coleman et, al. (2010) pointed complex reciprocal biological interactions occurring between resident bacteria, algae and other microbial communities in waste stabilization pond systems and these biological interactions and microbial communities may also play a part in the fate of pollutants. Several authors mentioned the reduction of wastewater pollutants using waste stabilization ponds in Cameroon [44,5]. The great elimination of phosphorus could be partly due to algal intake and sedimentation of dead algae. Indeed, algae are able to metabolize and accumulate high levels of phosphorus in the form of polyphosphates beyond what is necessary for their growth and energy transfer [45]. Besides the algal role in the removal process, predation and the effect UV radiation killing of microorganisms could be mentioned as other removal processes especially in tropical climate with much sunlight..

Algal density and diversity along the pond part of the FSTP

Microscopic observations of the 12 wastewater samples from the pond part of the systems enable the identification of 44 algal species distributed in 4 phyla, six classes, 19 families and 26 genera (Figure 5). The phylum Bacillariophyta is the most represented with 14 species followed by Chlorophyta and Euglenophyta with 12 species each. The Cyanophyta are the least represented with 5 species. The variation of the algal density in the different lagoons is shown in table 4. At the first pond the algal density is about 451,830 algae/mL. This density increases considerably at the fifth pond with a value of 1,611,750 algae/ mL of sample and drops at the tenth pond to a density of 1,536,220 algae/mL. At the outlet of the plant this density is 77,460 algae/mL.

Figure 5: Variation of the algal density (in Log10 unit) and number of species at each sampled lagoon.

Parameters	Algal density (Cells/mL)	Number of species recorded	NH4-N (g/L)	TP (g/L)	BOD5 (gO2/L)	EC (mS/cm)	pH
Algal density (Cells/mL)	1	0.968	-0.727	-0.711	-0.947	-0.984	0.399
Number of species recorded	0.968	1	-0.532	-0.512	-0.835	-0.907	0.616
NH4-N (g/L)	-0.727	-0.532	1	1.000*	0.910	0.839	0.399
TP (g/L)	-0.711	-0.512	1.000**	1	0.900	0.827	0.361
BOD5 (gO2/L)	-0.947	-0.835	0.910	0.900	1	0.989*	-0.082
EC (mS/cm)	-0.984	-0.907	0.839	0.827	0989*	1	-0.227
pH	0.399	0.616	0.339	0.361	-0.082	-0.227	1

Table 4: Pearson correlation test (95% confidence interval) between physicochemical parameters and algal density and diversity.
**Correlation is significant at the 0.01 level (1-tailed)
*Correlation is significant at the 0.05 level (1-tailed)

There is an algal density increase from the first to the tenth ponds. This increase can be explained by the fact that in the first pond the nutrients necessary for algal growth are not well mineralized thus are not yet available. Also, there is a high content of ammonia which may be detrimental to algal growth as [46] and [47] reported ammonia to inhibit algal growth. In the fifth basin, the high density observed can be due to the bioavailability of nutrients, especially nitrogen and phosphorus. In the tenth pond there is a decrease in nutrients and consequently a decrease in algal density although not significant. At the outlet, the decrease in algae may be due to the filtration in the filtration unit made up of pouzzolan which retains a large part of the algae. The algal density recorded in this study is low as compared to those obtained by Kengne ES, et al. [20]. Indeed, these authors counted 8.74 × 10⁷; 10.78 × 10⁷; 13.93 × 10⁷ cells/mL and 7.4 × 10⁷; 6.92 × 10⁷; 7.94 × 10⁷ cells/mL for hydraulic holding times 4,7 and 10 days respectively for the first and second maturation basins treating leachate from FS dewatering in Cameroon. The difference observed between these results could be explained by the experimental conditions and the configuration of the pond system as this study is carried out at large scale compared to [20] who conducted a pilot-scale study. Indeed, at the pilot scale, the wastewater volumes, i.e., the size of the ponds in the pilots is very small. In contrast, full-scale ponds are larger in volume with potential dilution effects. The algal density and diversity observed in this study could be explained by the fact that NO₃-N, NH₄-N and available phosphorus are mineral nutrient ions, highly soluble in water, which are directly taken up by algae. Brix H, et al. [48] pointed out the favorable conditions for microbial degradation and nutrient uptake by algae to be the main mechanisms responsible for the elimination of pollutants in waste stabilization. In addition, Dahiya S, et al. [49] pointed the effects of light intensity and phototactic movement of algae to affect the prevalence and diversity of algal population in waste stabilization pond ecosystem. The development of algae is at the expense of organic matter and pathogenic microorganisms. In addition, the development of Oscillatoria sp. found in this study is characteristic of eutrophic environments, this is confirmed by the COD and BOD₅ which are high in the first basin. Its presence in the first basin gives information on the richness in organic matter (Figure 5). Its absence in the fifth and tenth basin shows that the organic matter content has considerably decreased. Navicula sp. is present in large quantities in the tenth basin; it is known for its oligotrophic environment’s preference, thus confirming that these points have low organic matter contents. The species Nitzschia spp, Phacus spp, Euglena spp, are present in the fifth basin but not in large quantities. This can be explained by the fact that these species develop well in eutrophic environments, and their low presence is because of the decrease in organic matter in the pond environment and this is justified with the values of COD and BOD₅ which have decreased in these basins.

Correlation between physicochemical parameters and algal density and diversity

Performing the Pearson correlation tests at 95% confidence interval showed negative correlation between density and specific diversity and the physicochemical parameters considered. We obtained the correlations of r² =-0.727 (NH₄-N), r² =-0.711 (PO₄-P), r² =-0.947 (BOD₅), r² =-0.984 (EC), r² =0.399 (pH) and r² =-0.532 (NH₄-N), r² =- 0.512 (PO₄-P), r² =-0.835 (BOD₅), r² =-0. 907 (EC), r² =0.616 (pH) respectively between algal density and physicochemical parameters on the one hand and between specific diversity and physicochemical parameters on the other hand (Table 4). However, a positive correlation was recorded between these biological parameters and pH. This explains that the pH was compatible for the development and proliferation of algal species (Figure 6). In addition, a positive correlation was recorded between the different physicochemical parameters, the most significant of which were recorded between the parameters PO₄-P and NH₄ -N (r² =1, at the 0.01 level) and DBO₅ and EC (r²0.89, at the 0.05 level). Also, a positive correlation was recorded between the biological parameters (r²=0.968). The negative correlation recorded between biological and physicochemical parameters confirms the hypothesis that algal development occurs at the expense of organic matter, i.e., that a decrease in organic matters in wastewater is followed by the proliferation of algal species. Indeed, Sun X, et al. [50] pointed algae-bacterial symbiosis and interactions as mechanisms responsible for the elimination of purification processes in pond systems. For these authors, microalgae utilize CO₂ for photosynthesis, assimilate nutrients, and release oxygen into the effluent stream. The oxygen released by microalgae can be used for the metabolism by heterotrophic microorganisms (bacteria) for oxidizing organic matter and ammonia. For [51] algal-bacterial symbiosis to occur in waste stabilization ponds, oxidation ponds, and high-rate algal ponds. The algal-bacterial symbiotic relationship was proven to be enhancing the removal efficiency [50-52] mentioned algal-bacterial symbiosis to be responsible for carbon sequestration in wastewater treatment using waste stabilization pond. For these authors, biological sequestration of CO₂ by algae is gaining importance, as it makes use of the photosynthetic capability of these aquatic species to efficiently capture CO₂ emitted from various industries and converting it into algal biomass as well as a wide range of metabolites such as polysaccharides, amino acids, fatty acids, pigments, and vitamins. The positive correlation observe between only the pH and biological parameters in this study could be explained by the fact that pH has acted as key feature that determines the algal growth. Indeed, different species have different pH requirements, though most of them are reasonably adapted to pH variations [52]. The high metabolic rates during active growth phase of algae result in the liberation of OH− ions into the media that contributes to its pH increase. Many studies pointed the pH between 7.5 and 9.5 to be associated with higher growth and biomass yields of algae [53,54]. The mean pH recorded at each sampled ponds in this study ranged between 7.49 and 7.69 (Figure 3).

Figure 6: Photos of some algae found in samples from the lagoons of the Bafoussam fecal sludge treatment plant (A: Closterium sp., B: Dictyocha sp., C: Scenedesmus quadricauda, D: Microspora sp., E: Oscillatoria sp., F: Phacus orbicularis, G: Rhopalodia rupestris, H: Nitzschia solita, I: Cosmarium sp., J: Phacus tortus, K: Eremosphaera gigas, L: Fragilaria capucina, M: Rhopalodia sp., N: Aulacoseira sp., O: Nitzschia ocula).

Conclusion

FS produced in Bafoussam was shown to present a high strength and variability at the entry of the treatment plant. Biodigester was proven to treat the organic fraction of the sludge while the series of maturation ponds refined the quality of the leachate coupled to the algal uptake of nutrients in combination with the die-off action of solar UV-rays, as the study was carried out in a tropical climate. High algal population and diversity as recorded in this study suggests such a combination of biodigesters to maturation ponds could be considered as an algal-based productivity system. This study could give indications to the algologists, i.e., that algae can be multiplied from wastewater, which could be a potential axis of wastewater valorization for the production of algae. An evaluation of biogaz yield of the biodigester units for energy supply of the city could be recommended for further researches.

Acknowledgements

Special thanks are due to Professor Guetsop Victor François, Applied Botany Laboratory, University of Dschang for biological analysis of wastewater samples. We dedicate this paper to Professor Ives Magloire Kengne Noumsi who passed away on June 14, 2020 for his valuable contribution in Fecal Sludge Management (FSM) in Cameroon and abroad.

Funding

This work received a support from the liquid sanitation project in the city of Bafoussam, Cameroon (Cameroon Sanitation-CAMSAN-, 2017) founded by the International Association for Development (IAD).

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Article Type: RESEARCH ARTICLE

Citation: Kengne ES, Tekamdjo SLT, Nzouebet WAL, Wanda C, Nbendah P, et al. (2024) Treatment of Fecal Sludge (FS) Using Combine BioDigestor and Stabilization Pond in a Tropical Urban Area. Int J Water Wastewater Treat 10(2): dx.doi.org/10.16966/2381-5299.194

Copyright: © 2024 Kengne ES, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Publication history: 

Received date: 24 Apr, 2024

Accepted date: 27 May, 2024

Published date: 31 May, 2024