**1. Introduction**

Leachate is the juice produced during the fermentation of household waste stored in public landfills, which can pose many problems during the design and maintenance of a landfill. Leachate from landfills has been identified as potential sources of contamination of soil, groundwater and surface water, as it can percolate through soils, causing pollution of waterways and groundwater, s' they are not properly collected, processed and safely disposed of [1–4].

The climate and landfill are the main factors influencing the production and composition of the leachate. Where the climate is prone to higher levels of precipitation, there will be no more water penetration into the landfill, and therefore no more leachate generated. Another factor is the topography of the site, which influences the runoff regimes and the water balance of the site.

The treatment of landfill leachate is a complicated process due to the type of contaminants it contains and the variation in volume. The percolation of rainwater through municipal landfill waste from leachate produced by the biological and chemical processes that occur in the waste increases the volume of leachate juice.

**Figure 1.**

*Diagram of landfill leachate treatment techniques, based on Abbas et al. [6]; Renou et al. [7], Shuokr et al. [8].*

#### *Reducing Pollution of Stabilized Landfill Leachate by Mixing of Coagulants and Flocculants… DOI: http://dx.doi.org/10.5772/intechopen.97253*

The combination of the above factors could generate an effluent whose properties also largely depend on the age of the landfill [2–5].

Solid waste from municipal landfills is considered a very important source of pollution since it contains enormous amounts of organic and mineral matter, some types of organic matter of which are biodegradable, where humic and fluvic acids represent a significant amount in old leachate. Optimizing the factors controlling the treatment of this liquid effluent can greatly increase the efficiency of the process. The physicochemical treatment process can be applied to landfill leachate without being affected by the toxicity of the leachate and could provide a simple, selective and economically acceptable alternative to traditional methods. The different treatment techniques often used to reduce pollution from leachate discharges are illustrated in **Figure 1** [6, 8].

The flocculation coagulation methods which are the most widely applied for the fight against pollution from leachate discharges [9–12]. State-of-the-art physico-chemical treatment processes have been developed [13, 14] and applied for the decontamination of leachate discharges. These different techniques depend on several parameters: leachate age, quality, cost and waste to be treated (household and industrial waste). Biological treatment processes such as activated sludge is problematic due to the low kinetics of degradation and foam production [15]. In the treatment of leachate many factors can influence the effectiveness of treatment by coagulation flocculation), such as the type and the optimal concentration of the coagulant/flocculant and the optimal pH [16–19]. The sanitary landfill method for final solid waste disposal continues to be widely accepted and used because of its economic benefits in developing countries [20].

The main objective of this study is the optimization of the conditions of the coagulation flocculation process in the treatment of landfill leachate, and the determination of the most appropriate dose for different coagulants and flocculants such as ferric chloride, sulphate aluminum, Alginate, ... at optimum pH which considerably reduces organic matter, suspended solids and metals present in leachate.

### **2. Materials and methods**

#### **2.1 Sampling techniques**

The leachate samples were collected from the Mohammedia town landfill in 50 L plastic bins, transported to the laboratory and stored at 4° C. The leachate samples were placed for 2 hours at room temperature before performing the flocculation coagulation tests. Then, the samples were thoroughly shaken to resuspend the deposited solids before further tests were performed.

#### **2.2 Coagulants/flocculant dosage**

Several coagulants and flocculants have been tested for the treatment of leachate discharges such as ferric chloride (FeCl3.6H2O), aluminum sulphate (Al2(SO4)3.18H2O), alginate, ... for destabilize suspended solids and colloids and eliminate pollution afterwards.

In addition, two flocculants such as the Astral flocculant and the cationic polyelectrolyte Superfloc supplied by companies in Casablanca, the flocculants Chemic1, Chemic2, Chemic3 supplied by an Italian company.

The experimental process consists of three steps: a rapid mixture of leachate containing coagulation reagents of the flocculation reagents at 160 rpm for 10 min, followed by slow agitation for 20 minutes and 30 rpm, then a step of final settling for 1 hour. The coagulation-flocculation was carried out with the optimized and previously determined operating parameters.

Furthermore, the treatment tests were carried out by the Jar test technique using six polyethylene beakers of volume equal to 1 liter to examine the different doses of coagulant with a well-defined initial pH (optimal pH). The tested samples were mixed thoroughly to resuspend the deposited solids, and the appropriate volume of the sample was transferred to the corresponding beakers. First, the optimum pH for FeCl3 activity was determined. A known volume of the solution of ferric chloride, aluminum sulfate or other coagulants and flocculants was added to 1 L of landfill leachate at various pH values adjusted with H2SO4 and NaOH. To study the optimum dose of coagulant, the pH of the leachate solution is maintained at the optimum value and variable doses of FeCl3 or Al2(SO4)3 were then added. After 60 minutes of decantation, the supernatant was taken for analysis. To evaluate the effectiveness of ferric chloride, aluminum sulphate or other coagulants and flocculants for the treatment of leachate, the following parameters were determined: turbidity, chemical oxygen demand (COD)… settled sludge and metallic elements not eliminated.

#### **2.3 Analytical techniques**

The turbidity was determined by a HI 93703 microprocessor turbidimeter. The Chemical Oxygen Demand (COD) and the other physicochemical parameters (NTK, total phosphate, etc.) for the characterization of the leachate were determined according to standard methods [21].

The pH of the solutions was measured using an "Accumet Basic AB15 pH-meter" from the Fisher Scientific brand with a combined Ag/AgCl glass electrode according to standard NF T 90-008 February 2001 (T90-008). The conductivity was measured using a conductivity meter brand "YK-2001PH intelligent conductivity pH-meter" according to standard NF EN 27888 January 1994 (T90-031). The COD was carried out according to the AFNOR standard in force [NF T90-101 February 2001 (T90-101)]. The measurement of the biological oxygen demand after five days (BOD5) was facilitated by the use of the gauge method [(EN 1899 May 1998) (T90- 103)] using the BOD5 meter of the VELP brand. The absorbance measurements were carried out using a UV-visible spectrophotometer.

Spectrophotometer 9,200 RAYLEIGH 2-beam 1 nm bandwidth. Turbidity was measured using a turbidimeter according to NF EN ISO 7027 March 2000 (T 90-033). The determination of the materials in suspension was carried out by the centrifugation method of the standard [NF T 90-105 January 1997 (T 90-105)]. The phenolic compounds were determined by the colorimetric method using the Folin–Ciocalteu reagent [22]. The nitrate assay was carried out by the spectrometric method in the presence of sulfosalicylic acid according to standard EN ISO 78-90 January 1997 (T 90–045). The determination of the total phosphorus was carried out by spectrometric method according to NF T 90–023 January 1997. The determination of ammoniacal nitrogen NH4 was carried out by the spectrophotometric method with indophenol blue according to AFNOR NF T 90–015 January 1997. The method of heavy metal analysis is atomic absorption spectrophotometry with a graphite furnace (VARIAN AA 20 model).

### **3. Results and discussions**

#### **3.1 Leachate characteristics**

To assess the impacts of a landfill on the environment, it is necessary to characterize the effluents it generates. Indeed, whatever the mode of operation of a landfill, the leachate constitutes, if it is not treated before its discharge, a source of *Reducing Pollution of Stabilized Landfill Leachate by Mixing of Coagulants and Flocculants… DOI: http://dx.doi.org/10.5772/intechopen.97253*


#### **Table 1.**

*Physico-chemical parameters of leachate (mg/l) from Mohammedia landfill.*

nuisance which is added to the numerous problems of contamination of the surrounding environment. These liquids loaded with mineral and organic substances resulting from the decomposition of waste can be entrained by runoff and reach surface water, or infiltrate through the bedrock of the landfill and contaminate the water of the water table which is not deep.

The different physicochemical parameters analyzed in the landfill leachate are presented in **Table 1**. In addition, the results of the analysis of metals (Cu, Zn, Cr, Ni, Pb, Sb and Sn) in the three sampling companies were carried out (**Table 2**).

The characteristics of a leachate can generally be represented in terms of basic parameters such as COD, BOD, BOD5/COD ratio, color, pH, content of metallic elements [4]. These results showed that the leachate is characterized by high concentrations of organic matter and high concentrations of ammonium and nitrogen compound (**Table 1**). The organic matter, in terms of COD varies between 2153 and 2707 mg/l (stabilized leachate), while high concentrations of ammoniacal nitrogen (587 to 1410 mg/l) and NTK (1080 to 1405 mg/l) have been detected. The main concentrations of heavy metals are between 0.1 to 4.2 mg/l for Cr, 0.04–0.005 mg/l for cadmium and 0.8 to 0.3 mg/l for Pb. The characterization of the average leachate showed that the BOD5/COD ratio varies between 0.2 to 0.13, which shows that the leachate is rich in organic matter and not biodegradable (humic and fulvic substances).

In addition, turbidity and conductivity are very high values, far exceeding the standards for treated wastewater. This shows that decision-makers in Morocco must make an effort to save the current situation of public landfills in order to protect the


**Table 2.** *Analysis of the metallic elements of leachate from the Mohammedia landfill.* health of the population. The low values of the BOD5/COD ratio (0.2–0.13) thus show that the leachate is rich in non-biodegradable organic matter, which can cause several impacts on surface water and groundwater [2]. Souabi et al. [1], showed that for leachate discharges from Mohammedia (main collector), the BOD5/COD ratio varies between 0.2 and 0.13, showing that the leachate is not easily biodegradable and can therefore cause several impacts on surface water. (Oued El Maleh). The same authors have shown that the COD values obtained vary between 2301 and 2750 mg/l and remain much lower than the content detected by [23] discharged into the sea. The variation in the characteristics of the leachate has been attributed to many factors, such as variations in the composition of the solid waste, the age of the landfill, the hydrogeology of the landfill, precipitation and specific weather conditions. and waste moisture [7, 24, 25]. From 5 to 10 years, the landfill is known as "middle age" and its leachate has a COD of between about 3000 to 15000 mg/l [20]. After 10 years, a landfill contains less biodegradable material and the leachate has a COD value of less than 2000 mg/l [4, 11].

For a given leachate, fluctuations in pH, flow, COD and BOD5 contents, etc. have been observed over time [4, 11]. This can influence the efficiency of the elimination by different treatment techniques and disturb the receiving environment if the leachate is rejected without treatment, which justifies the installation of a homogenization basin. The age of the landfill is one of the main factors that also influences the characteristics of the leachate.

Landfill leachate contains chemicals, including metal ions such as iron. Indeed, efficient and cost-effective leachate treatment techniques are difficult to implement [26]. Rivas and Gimento [27] pointed out that old landfills produce stabilized leachate with a relatively low COD content ranging from 500 to 5000 ppm, a slightly basic pH of 7.5 to 8.5, low biodegradability (BOD5/COD less than 0.1) and a significant amount of heavy metals and high molecular weight compounds (humic and fulvic substances). Leachate exhibits considerable variation in composition [11]. The concentration of contaminants are mainly influenced by the age of the landfill, as well as by the type of waste deposited at the landfill and other hydrogeological factors [11, 17].

The characterization of the average leachate has shown that the BOD5/COD ratio varies between 0.2 to 0.13, which shows that the leachate is rich in organic matter and not biodegradable (humic and fulvic substances) which can cause several impacts on the water surface and groundwater [28].
