Impact of Domestic Solid Waste Management on Wet Land Water Quality: Case of Abomey-Calavi Municipality in Benin Republic ()
1. Introduction
The integrated management of water resources passes by its protection, its preservation and its treatment according to its diverse uses. The protection of water resources against the pollution is a global concern, on which depends the survival of the human kind [1]. Water resources quality and quantity stakes are closely associated with their cleaning up (treatment). The serious challenges about the quality and the quantity of water resources are closely linked to those of their purification [1] [2]. The lack of infrastructures of water purification, the inappropriate collection and treatment of the solid household waste contribute strongly to the degradation of the quality of ground and surface waters of the urban cities of countries with limited resources [3]. Being the most drinking fluid water is also a potential source of transmitting diseases especially in developing counties. According to World Health Organization (WHO) survey, 80% of all diseases in developing countries are water born [4].
According to [5], the management of the solid household waste has an impact on the environmental protection and on the health of the populations. In Benin Republic, the landfills are few; the practice of the embankment of wetlands by waste is the most common way for their management. This practice disturbs the functions assured by various elements of the ecosystems generating chemical, metallic and biological pollutions of surface and the groundwater [5] [6]; [7] noticed that about 80% of the solid household waste produced by Abomey-Calavi (CAC) municipality, the second biggest city of Benin are used to backfill the wetlands which, once filled in and stabilized, become residential areas where hand-dug wells are drilled for domestic water use. Hand-dug wells as the name implies are built manually and are little more than irregular holes in the ground, intersecting the water table [6]. The present study aims to assess the physico-chemical and microbiological characterization of waters from hand dug wells installed within 10 m circumference from wetlands in Abomey-Calavi Municipality to identify the various pollutions due to the embankment of these lands by the solid household waste.
2. Material and Methods
2.1. Study Area
The study was realized over a period of six months (March-August, 2009) in Abomey-Calavi city, the second urban community of Benin due to its population estimated to be about 1,000,000 habitants (RGPH3, 2008). The city’s geographical coordinates are 6˚26'46,8" latitude North and 2˚20'53" longitude East, it is surrounded by numerous water courses, such as the Ouémé river, the Nokoué lake and the Atlantic Ocean.
We have chosen three (3) points of water sampling which localization is summarized in Table 1. Sampling was done in the properly cleaned plastic jars. These plastic sampling jars were rinsed three times before the sampling of
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Table 1. Geographical coordinates of well and wet landss waters.
water. For every point of sampling, five samples are collected per month generating a total of 90 samples for six months. Sampled water was immediately analyzed just after the sampling.
2.2. Physico-Chemical Analysis of Sampled Water
Water analyzed are from unfilled wetlands, hand dug well on backfilled wetlands by domestic solid waste and witness well located approximately at 2 km from studied wetlands. The water samples takings, the preservation and their manipulation were made according to the rules of the International Standard Organization n˚ 5667/3 (1994). The pH, the conductivity, the dissolved oxygen and the turbidity were determined in situ. The pH was determined by a pH-meter WTW LF 340 Merck, the conductivity and the turbidity were respectively determined by the conductimeter WT 320 Merck, and the turbidimeter HACH on 2100 the YEAR ORCHIDIS. We have used the oximeter HANNA to assess the dissolved oxygen. Total Organic Carbon (TOC) was measured by an analyzer of Solid Module Shimadzu SSM 5000. Anions likes, nitrates, chlorides and nitrites, were measured by DIONEX ICS-3000 ionic chromatograph [8]. Heavy metals such as Lead (Pb), Cadmium (Cd), Chrome (Cr) and Nickel (Ni) were measured by ICP AES JY on 2000 sequential Ultrace [9].
2.3. Microbiological Analysis of Sampled Water
Microbiological examinations are practiced to look for protozoon in particular the cysts of Giardia and Amoeba. A total enumeration of bacteria was realized according to the method of the Center of Expertise of Quebec [10].
The bacteria indicating a faecal contamination such as Escherichia coli (E coli), Enterococcus and opportunist pathogen (Staphylococcus aureus, Staphylococcus scuiri,Pseudomonas aeruginosa) were identified by conventional method as described by [11].
The results obtained were processed and analyzed using the software SPSS 19.1. The different proportions were compared by x2 test or Fischer at significance level of 0.05.
3. Results and Discussion
3.1. Physico-Chemical Properties
Table 2 shows that backfilled wetlands sampled water was mineralized (898.32 ± 6.13 µs/cm) and rich in ions like chlorides, nitrates and nitrites. The turbidity of sampled water wetlands is 32.00 ± 2.83 NTU with 127.06 ± 3.20 mg/L of total organic carbon. Heavy metals such as Lead and Cadmium had respectively a concentration of 4.62 ± 1.19 µg/L and 0.38 ± 0.13 µg/L in sampled water of backedfilled wetlands.
3.2. Microbiological Characteristics of Water Samples
The microscopic examinations revealed the presence of protozoons and particularly cysts of Giardia lamblia and Entomoeba hystolitica in all of the sampled water, except those of the witness well. A summary of the different microorganisms isolated during the study period are presented in Table 3. Microorganisms such as Enterococcus, Staphylococcus aureus Pseudomonas aeruginos and Staphylococcus scuiri were present in 78 water sampled and constituted86.4%. Escherichia coli arepresentmorethan 50 per 100 ml for total coli forms and 2.5 per 100 ml for E.coli.
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Table 2. Physico-Chemical characteristics of well and wetlands waters.
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Table 3. Enumeration of coliform and pathogen bacteria in different water samples.
4. Discussion
The present study was focused on the physico-chemical and microbiological characterization of water sample from the wetlands to identify the various pollutions due to the embankment of wetlands by solid household waste. The results of this study revealed that sampled water from backedfill wetlands is more turbid (62.5 NTU) than those of wetlands (32 NTU). The water we analyzed is rich in organic substances with concentrations more important for water from backedfilled wetlands. This would be explained probably by the degradation of the organic substance contained in waste used to backfill the site of our study. According to [12] the degradation of the fermentable fractions of waste requires an important consumption of oxygen. Yet in countries with limited resources, the fermentable fraction of the solid household waste is about 50% [5] [7]. As a consequence, the concentrations of oxygen dissolved by the water samples from backfilled wetlands by waste are low than those of wetlands. Water is said to be polluted when its quality is degraded as a result of man’s activities to an extent that it becomes less suitable for its intended use [13]. Our result corroborated this finding.
Fecal coliforms were frequent in the sampled water and were more important in sampled water from backfilled wetlands. [14] made a correlation (r = 0.59; p = 0.001) between the presence of Enterococcus, E.coli and the degree of water pollution. These results confirmed those of [15] who underlined that a high value of the turbidity would foster the [16] proliferation of certain bacteria (440,000 CFU/ml of E coli. and 456,000 of Enterococcus). The values of E.coli identified in water of backfilled wetlands and wetlands are confirmed by the concentrations in nitrates and nitrites. Indeed, the concentrations of nitrites are higher in water from backfilled wetlands than in those of wetlands. This has shown a nitrogenous pollution of water from backedfill wetlands by the domestic solid waste [16]. The presence of nitrates in water from the backfilled wetlands would be due to a diffuse accumulation at the bottom of water column followed by a vertical transfer [17]. As the wetlands are shallow, the ions and the microorganisms of water from the polluted bottom infiltrate easily into the ground and contaminate the groundwater. Nitrites concentration is also a good indicator of the water pollution by the anthropological activities. This is probably the result of the nitrification, by the bacteria, of the ammonium ion obtained from the decomposition by ammonification of animals and the biodegradation of the household and agricultural waste [18]. The high value of nitrites in water from backedfilled wetlands confirms the important microbial flora. The concentrations of backfilled wetlands water in chlorides are higher than those from wetlands. As the chlorides ions are an indicator agent of water pollution by the solid household waste [16] [19], we would deduct that embankment of the wetlands by waste would be a cause of chemical and bacteriological pollution. The degree of mineralization (conductivity and pH) also gives an indication on the level of water pollution [2]. The samples of analyzed water are weakly acid, this high
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Table 4. Metallic elements concentrations in water samples.
acidity on the water from backfilled wetlands (pH = 5.37 ± 0.11) create an environment convenient to the proliferation of the pathogenic microorganisms, the source of pollution. An encouraging note in this study is the low concentration of metallic elements in the sampled water, particular heavy metals such as the Lead, the Cadnium and the Chromium (Table 4). Indeed, the sector of recycling of the metallic objects of waste is very developed in Abomey-Calavi city and would justify the low concentrations of heavy metals in backedfilled wetlands water.
Moreover hand pumps must be installed at least twenty meters away from the backfill land in order to minimize the seepage impact on the pumped water used for domestic used.
5. Conclusions
In summary, this study shows that the backfilled wetland water used for domestic purpose use is highly polluted and not suitable for human consumption. Therefore, alternate sources of drinking water must be explored especially the pumping of good quality drinking water.
This contamination finds its origins in the lack of the infrastructures of wastewater system and management of domestic solid waste. To sort different components of the waste, to store those on the landfills would be progress for the improvement of their management. Finally the efforts of raising awareness of the various actors on the protection of the ecosystems to discourage the practice of embankment have to be continued.