Evaluation of the Quality of Household Waste Leachate Treated by Settling Ponds at the Ouagadougou Waste Treatment and Valorization Center

In African cities, today’s patterns of consumption are increasingly generating solid and liquid waste. This waste requires adequate management as it poses significant risks to public health and the environment. To meet the challenge in Ouagadougou, a waste treatment and recycling center has been implemented. The leachates from household refuse evacuated in this center are treated by two series settling ponds whose performances have been evaluated throughout the present study. For this purpose, samples were taken from the basins and analyzed weekly for two months. On these samples, the physical parameters (pH, temperature, conductivity), organic pollution indicators (BOD5, COD, SS), nitrogen pollution (nitrate, nitrite) and phosphorus pollution (ortho-phosphates) were evaluated according to AFNOR standards. The average of suspended-matter contents above 13,000 mg/L and this particulate pollution abatement recorded is 2.04%, whereas the Chemical Oxygen Demand reached respective maximum values of 660 and 480 mg/L for both basins. Nutrients such as nitrates were well eliminated whereas orthophosphates are released. PH values varied between 8.62 and 9.51, while electrical conductivity values varied between 482 and 625 μS/cm. The Fecal Coliforms reached maximum concentrations of 10,000 and 12,800 UFC/100mL.


Introduction
In the context of sustainable development, African towns are confronted with major challenges to be taken up as far as the environment preservation and the way of life improvement are concerned, looking at the lack of suitable infrastructures to ensure the management of waste water and solid waste.  [2]. This study aims at estimating the purification performance of the treatment basins of leachate derived from household rubbish evacuated in this Center.

Main Objective
This study aims at evaluating the treatment efficiency of leachate derived from household refuse through a device of two aerobic basins in series.

Specific Objectives
To establish the typology of leachate produced in the Waste Treatment and Valorization Center to evaluate the purification performance in BOD 5 , COD, and mineral elements such as nitrogen and phosphorus.

Household Leachate Treatment Technologies
Leachate from urban dump is one of the major constraints for the management of refuse dump. Their composition varies from one discharge to another depending on the nature and age of the waste. It evolves according to the state of degradation of the waste. The different types of leachate due to their variable composition must undergo specific treatments before they are discharged into the receiving environment. We therefore distinguish: Biological processes: these are the oldest processes used for the treatment of leachates, because of their efficiency to reduce polluting loads in organic matter.
Biodegradation is provided by microorganisms (bacteria) in aerobic or anaerobic environments. Biological processes such as activated sludge or lagoon used in the case of this study.
Physico-chemical processes: they are based on coagulation-flocculation, adsorption and precipitation. These processes are used as pre-treatment or finishing step to complete the treatment process, or to eliminate specific pollutants. This process makes it possible to eliminate the colloidal organic matter. Thermal processes: these are old processes based on the evapo-concentration that is commonly used for the treatment of leachates and the recovery of waste in biogas.
Membrane processes: This is a combination of processes such as microfiltration, ultrafiltration or nanofiltration. The latter make it possible to pretreat the leachate before a reverse osmosis finishing treatment and making it possible to obtain an effluent whose quality meets the rejection standards.

Presentation of the Waste Treatment and Valorization
Center (WTVC) One composting and maturing unit; One valorization unit of plastic waste; Three wells for observing the quality of ground water; Two observation wells of biogas underground migration.
This work concerns the treatment basins ( Figure 2 and Figure 3) of the household rubbish leachate which characteristics are written down in Table 1. It can be noticed that the basins are oversized. This is done in anticipation of an increase in the waste capacity of the center. Due to oversizing, the nominal residence time of 44 days remains lower than the actual residence time of the water in the basins.

Material
The sampling material is composed of plastic, small bottles with one-liter capacity containing the samples meant for physico-chemical analyses and 250 ml glass sterilized vials for bacteriological analyses. Each sampling small bottle has the

Methods of Samples Analysis
The analyses carried out on our samples are in conformity with the norms indicated in Table 2. Analyses have been carried out in ONEA laboratories, in the Environment quality analyses laboratory (LNEA) and in the laboratory of the natural substances department of IRSAT. The main analyses carried out are the physico-chemical and bacteriological analyses. The samples were taken each Monday for two months (September and October 2016) for analyses. The sample is made at more than 150 cm from the bank of the basin. The samples (leachate) analysis in laboratory consists in determining the physico-chemical, biological and microbiological parameters. The following table shows the different parameters, the units as well as the analysis methods used in laboratory.

Physico-Chemical Parameters
1) Temperature, pH, electrical conductivity and dissolved oxygen. Temperature, pH, electrical conductivity and dissolved oxygen have been recorded in situ using a WTW 3401/SET multimeter disposing of three sounds for these measurements.
The display of the temperature is coupled in. The reading is made after the display stabilization.
2) Suspended Solid (SS) Suspended Solid (SS) constitute the whole of mineral and/or organic particles present in natural or polluted water. They correspond to the concentration of non-dissolved elements of a sample. The abundance of SS in water causes a re-Journal of Environmental Protection duction of the sunlight penetration into water and therefore a reduction of the biological production particularly because of a fall in dissolved oxygen by reduction of photosynthesis phenomena. In the purification stations, the SS can be eliminated through a simple decantation or through decantation caused with the addition of a coagulant. In the lagoon basins, these ones are eliminated through sedimentation followed by their digestion in the mudzone.
In this study, the determination of SS has been made the day of sampling, using the weighing method after filtering on GFC filter and drying at 105˚C. The concentration in SS is obtained by the following formula (1) Cr O − ) consumed by oxidation through chemical way of matters liable to rust. Oxidation was done for 2 hours at the temperature of 150˚C and this in acid milieu, in presence of silver sulfate (catalyst) and mercuric sulfate (used to eliminate the interferences caused by chlorides ions).
The reading is made using a DR 2400 HACH spectrophotometer. It permits to appreciate the concentration in organic and mineral matters, dissolved or in suspension in water, through the quantity of oxygen requested for their total oxidation by chemical way.

Fecal Coliforms
The analysis of fecal coliforms starts the day of the sampling. The counting of fecal coliforms has been carried out using the filtering technique on membrane.
The principle is mentioned in the French norm NF in ISO 9308-1. The essay consists in a filtering on membrane which pores have a size of 0.45 µm, followed by a culture in a differentiation agar-agar (Chromocult Agar ES) and then incubated at 36˚C (±2˚C) during 48 h. After confirmation, the number of formative units of colonies is expressed as follows (2).
With: C, number of colonies per 100 mL; A, number of characteristic/or controlled colonies; B, number of colonies sub-cultured for control; N, number of presumed colonies; Vt, volume of the sample or the dilution of this one, expressed in millimeter; Vs, volume which must be reported by the result (100 mL).

Results of Physico-Chemical Analysis
The results of leachate analysis through samplings for two months (September and October 2016) are written down in the Table 3. When comparing the parameters average values with the waste water throwing out norms in the nature, we notice that parameters such as pH, temperature, conductivity, nitrites ( PO − ) respect this norm fixed by Burkina Faso. As for Suspended Solids, the Chemical Oxygen Demand, the 5-day Biochemical Oxygen Demand and fecal coliforms (FC) present very high values, given the national standard. Leachate presents a low content in nitrates and ortho-phosphates which are undesirable substances and source of eutrophication.
Concerning the standard deviation, we have observed that some parameters

1) Temperature
The average temperatures registered during the period of the study are respectively 30.82˚C and 30.62˚C for basin 1 and basin 2. These values comply with the standard fixed in Burkina Faso, since these ones are included between 18 and 40˚C. Some authors have recorded an average temperature of 29.8˚C [3], close to the average of this study results. The temperature depends on climate conditions [4]. To evaluate the characteristics of a treatment, temperature is an important parameter as far as the kinetic of bacteria and biological activity is dependent on climatic conditions. Since the temperature varies according to seasons, indirectly the basins purification performance varies according to the period of the year. In that way, we observe that during the dry season, the biological activity is more important than during the rainy season. It can be noted that in the study area, the maximum temperature can reach 45˚C in dry season [5], with the dry wind.   . This is acceptable considering the national regulation included between 6.5 and 9. The pH recorded in basin 2 during this study is higher than the pH recorded in basin 1 as shown in Figure 4 due to development of algae and good oxygenation condition [4]. Some authors have recorded an average pH of 8.44 for a value widely below those obtained in the framework of this study [7]. It is important to note that pH is function of the effluents ageing [8]. The pH is a de-  This could confirm that the basins are well-aerated due to the shallow depth of water in the basins. Some authors have recorded a low average value in dissolved oxygenlike Toklo and collaborator who indicated an average of 1.07 mg/L, which is below the average values recorded during this study [10]. The content of oxygen is a very important parameter for the survival of microorganisms. The lack of dissolved oxygen in the waste waters induces a process of anaerobia degradation with a smell emanation as consequence. Purifying waste water, means to reduce considerably organic and microbiological pollution in order to increase its concentration in dissolved oxygen. Therefore, we can say that effluents derived from the leachate treatment are oxygenated in a quite important way to ensure the survival of the purifier microorganisms.

5) Suspended Solids (SS)
The average concentration of Suspended Solids (SS) measured in the leachate is 14,000 mg/L for basin 1 and 13,714 mg/L for basin 2 as indicated in Figure 6 below  In other contexts, some authors have recorded average less important contents in Suspended Solids. It is the case of leachates from the landfill in the city Essaouira in Marocco [7].
The determination of content in Suspended Solids is important in the characterization of effluents and the choice of technology to be implemented, since it permits to assess the breakdown of pollution between the dissolved phase and the particle phase. On examining the contents which are too important in Suspended Solids at the exit of the system, it is obvious from this, that the treatment is less efficient on the Suspended Solidsreduction, so that effluents derived from the treatment by the two basins in series require an additional quantity of water regarding the size of basins and it needs an additional treatment to make them in accordance with the throwing norms in the natural milieu.

6) Nitrogen
Ammonium ( The degradation of organic nitrogen in ammonium is an integral part of the nitrogen cycle in the production of nutriments. Ammonium nitrogen is toxic for aquatic life. In natural water, ammonium nitrogen comes mainly from the leachingof farming wateras well as waste water from the cities and industries in an anaerobia milieu. In the framework of this study ammonium pollution is nearly absent in the two basins. This confirms the basins fair oxygenation which ensures an aerobic treatment. On the contrary, some authors have recorded important average values in ammonium [3]. The more or less high presencein ammonium nitrogen could be connected to the origin of waste but also to an anaerobic process within the treatment system. Nitrates

The Presence of Microbiological Pollution
The bacteriological analysis was related to the determination of concentrations in fecal coliforms within the leachate derived from household rubbish ( Figure   8). Fecal coliforms are a group of bacteria being a part of total coliforms. Their presence in the treatment basins indicates that these last ones could also contain pathogen microorganisms. In fact, fecal coliforms constitute a group of bacteria of which the detection in the environment generally gives evidence for fecal pollution. The average content of fecal coliforms is 3700 UFC/100mL for B1 and 5825 UFC/100mL for B2. These values are not acceptable considering the limit value admitted by the national standard which imposes 2000 UFC/100 mL. The extreme values are 200 UFC/100mL and 10,000 UFC/100mL for B1 and 700 UFC/100mL and 12,800 UFC/100mL for B2. Since fecal coliforms derive from fecal matters their presence could be explained by the presence of animal feces and excreta contained in the rubbish; but it also could be favored by defecationin the open air near the basins. As far as the increase of the concentrations in basin B2 is concerned, this could be related to a phenomenon of resetting in suspension of decanted muds through an important arrival of water. This is particularly plausible since we have noticed an increase of ortho-phosphates concentrations in the same time as pointed out above. The treatment by the two successive   [13]. They generally noted as we did that microbiological quality of leachates is not satisfactory.

Conclusion
The evaluation of the purifying performance related to the treatment basins of the leachate derived from household rubbish of the Waste Treatment and Valorization Center of Ouagadougou has permitted to point up the effluents characteristics. It results from the physico-chemical analysis that if nitrates and nitrites are well-eliminated, these leachates are subject toless satisfactory reductions on the important parameters such as COD with only yields of about 17.20%. This undeniable fact could be related to a bad measurement for too short stay times regarding the high charge of pollution admitted in the system. Concerning the bacteriological pollution, we can note a recontamination of basins by the fecal coliforms, considering the anthropogenic activities near the site. On the whole, in the light of this study, to get better performances of the system, an additional treatment is proved to be necessary through the adding of new basins in series to those already existing, in order to preserve environment and human being health.