Study of Coagulation Process with Lime in Treatment of Landfill Leachate from Fkih Ben Salah City (Morocco)

The leachates are the seat of complex processes which give them a heterogeneous character. Their compositions vary according to several factors: nature of the waste, conditions of their deposition, climatic conditions, their durations of stay, etc. They contain important quantities of organic, mineral matters even of bacteria, which require their treatment in order to safeguard the environment. To do this, several methods are used, such as membrane techniques (reverse osmosis, nanofiltration, etc.), biological techniques (activated sludge, SBR, etc.) and physicochemical techniques (Coagulation-flocculation, adsorption on activated carbon, etc.). Among these techniques, the leachate treatment by coagulation process with the lime showed interesting reduction of the various pollutants: 92.95% of turbidity, 88.23% of suspended matter, 89.89% of COD, 90.83% of BOD5, 78.39% of Fe, 77.78% of Mo, 38.29% of Cd, 48.75% of Al, 50.24% of S, 20.57% of K, 27.24% of phosphorus and 19.53% of Cl. Based on these results, the coagulation with the lime reveals interesting because it allows to reduce at a lesser cost the pollutants present in leachates.


Introduction
The Fkih Ben Salah landfill generates leachates with a high polluting load (COD Journal of Geoscience and Environment Protection = 74,530 mg O 2 /L and Conductivity = 24.90 ms/cm). They are a source of contamination for groundwater and superficial water, Idlahcen, Souabi, Taleb et al. (2014) and Chtioui, Khalil, Souabi et al. (2008). They must be imperatively treated before being rejected in the natural environment, Renou, Poulain, Givaudan et al. (2009), by using simple and little expensive technologies, Berradi, Chabab, Arroub et al. (2014).
The main objective of this work is to study the coagulation with the lime of young leachates. It aims to determining the optimal conditions of this treatment for a significant reduction of TSS, the organic and mineral load, Merzouki, Hanine, Lekhlif et al. (2016). The use of the lime is opportune, because it plays the coagulant role (Ca 2+ ), and at the same time it allows the neutralization of the leachate (acid pH of the young leachate) thanks to its ions OH − . Its effectiveness compared with other coagulants (Fe 3+ , Al 3+ ) has been shown by several authors, Merzouki, Hanine, Lekhlif et al. (2016), Hamidi, Salina, Mohd Nordin et al. (2007), Benradi, El Yahyaoui, Bouhlassa et al. (2013), El Bada, Assobhei, Kebbabi et al. (2010), .
In this study, we present the results of the coagulation tests using the following parameters: pH, turbidity, COD, BOD5, conductivity, quantity of the generated sludge, mineral and metallic elements (Al, Fe, Cd, Mg, Ca, Cl, Mo, P, K, Si, S), as well as abatement rates of present pollutants in the leachate.

Sampling Zone
The landfill of Fkih Ben Salah city covers an area of 20 ha. It is located in 12 km north of the city on the R11 national road (Figure 1). It receives more than 85.51 tons per day of waste and generates 2730.72 L/day of leachate, Merzouki, Hanine, Lekhlif et al. (2016), corresponding to rate of 3.49% liter of leachate by ton of waste. The leachate samples were collected directly at the level of collection trucks bringing household waste to the landfill. Volumes of leachate (5 L) were collected and mixed to form a homogeneous sample. The pH, the electrical conductivity and the temperature were measured in situ. In order to determine the other parameters, the samples were kept at a temperature below 4˚C and transmitted to 4˚C and transmitted to the laboratory within 24 hours.

Preparation of Coagulant
For coagulation, a stock solution of coagulant was prepared by adding in one liter of distilled water 60 g of the hydrated lime in powder form of Ca(OH) 2 . From this solution, increasing volumes are taken and added to six beakers, each containing a volume of 500 ml of leachate. The concentration of Ca(OH) 2 obtained ranges from 2 to 12 g/L.

Procedure Jar Test
The coagulation tests were accomplished in a Jar test apparatus ( Figure 2). The mixture was agitated quickly at a speed of 250 rpm for 5 minutes and then to a speed of 25 rpm for 20 minutes. After 120 min of decantation, supernatant fraction samples are then recovered to analyze the following parameters: pH, DCO, total suspended solids (TSS), quantity of sludge and concentrations of mineral and metallic elements.

Measurement of Biological and Physicochemical Parameters
The potential of Hydrogen (pH), the electrical conductivity (CE), the tempera- The estimation of the sludge produced after treatment by the lime coagulation technique was realized by measuring its volume and weight after decantation, filtration and drying in an oven at 105˚C until constant weight.

Characterization of the Studied Leachate
The leachates studied have a brownish color and a fecal odor. Their contents are presented in Table 1.

Visual Observations
During coagulation, it is observed that the sludge separates progressively depending on the coagulant dose. During decantation, the leachate color changes.
It gradually changes from brown to light brown (Figure 3). This change of color by coagulation has also been observed by several authors, El Bada, Assobhei,

Evolution of the pH
The pH of the young leachate is acid character (4.05). This denotes the installation of the anaerobic process, in particular in its acidogenesis phase producing the AGV. When the lime concentration increases, the supernatant pH value increases ( Figure 4). This can be explained by the release of the OH − ions in solution. Journal of Geoscience and Environment Protection

Evolution of the Quantity of Sludge Generated by Coagulation
As shown in Figure 5 and Figure

Evolution of Electrical Conductivity
According to the figure (Figure 7), we note a slight decrease of the electrical conductivity, it passes from 24.08 mS/cm to 21.91 mS/cm to 6 g/L of Ca(OH) 2 , then an increase to 24.16 mS/cm from 10 g/L. At the beginning, the added lime eliminates the ions and molecules, contributing to the conductivity of leachate,

Evolution of Turbidity and Suspended Matter
The results of turbidity ( Figure 8) show a decrease in the addition of lime. It passes from 8031.67 NTU to 566.27 NTU in a concentration of 10 g/L, which corresponds to a removal efficiency of about 92%. This value is similar to that found by Renou, Poulain, Givaudan et al. (2009) for an initial turbidity of 5190 NTU and by Slater, Uchrin, & Ahlert (1983), and it is very high than that found by El Bada, Assobhei, Kebbabi et al. (2010) who carried out tests on an initial leachate turbidity of 130 NTU during methanation (65%). As for Shabiimam & Anil (2011), having studied a leachate presenting an initial turbidity of 317 NTU, they were able to obtain a 99.9% removal of the turbidity at pH = 8 with a coagulant dose of 25 g/L.
According to Figure 9, the suspended matter abatement rate reaches 88.23% at 10 g/L of lime. This rate is in the range of values found by numerous authors, Melike & Kadir (2007). Merzouki, Hanine, Lekhlif et al. (2016) have found successively a reduction of 82% and 71.6% of the suspended matter on the raw leachate.

Evolution of the Organic Matte
The addition of the lime has reduced the COD of the leachate (Figure 10). The abatement rate is 89.76%. It is comparable to that obtained by Merzouki, Hanine, Lekhlif et al. (2016)  The addition of the lime allowed to reducing also the BOD5 of the leachate ( Figure 11). The removal is 83.48%.
The elimination of COD and BOD5 of the leachate is due to the coagulation by the lime. It is also probably due to the adsorption on metal precipitates, including those of Ca 2+ , which are formed in the basic pH range, such as hydroxides, phosphates, carbonates, etc., or by entrainment during the coagulation of Figure 10. Evolution of COD reduction as a function of the lime concentration (g/L). COD and BOD5 decrease with lime increase simultaneously, giving a biodegradability ratio ranging between 1.21 and 3.27 with an average of 2.17 (Table   2), which denoting the biodegradability of the studied leachate, Kouassia, Ahoussik, Koffiy et al. (2014). We note that at the first addition of 2 g/L of lime, the ratio COD/DBO5 increases and then decreases (Table 2, Figure 12). The increase is probably due to hydrolysis reactions or reactions leading to the release of entities more or less biodegradable. The decrease afterwards can be explained by the coagulation, precipitation and adsorption reactions which may occur as a result of the increase in the lime quantity; the mineral and refractory fractions tend to decrease also.

Evolution of Mineral and Metallic Elements
The concentration of the main heavy metals presents in the leachate decreases.
The elimination rates are 77.14% for the iron (Figure 13

Conclusion
The physicochemical study of the leachate characterization of the public landfill