**8. Effect of the order of introduction of coagulants and flocculants**

The effect of the order of introduction of the flocculant FeCl3 and Astral on the removal of organic matter (COD), turbidity and sludge production are shown in (**Figure 21**).

Beyond the type of tests we performed in coagulation, we tested the influence of the method of adding the coagulant and flocculant on the properties of the leachate destabilized by coagulation/flocculation. In practice, in addition to the procedure described above where the reagents were added separately (coagulant + flocculant, flocculant + coagulant), we carried out a simultaneous addition of the coagulant and the flocculant. The protocol is then similar to that of coagulation on Jar test, but instead of the coagulant alone, the flocculant is added after the coagulant.

The results obtained show that when ferric chloride (FeCl3) is introduced first, followed by the flocculant, the yield of COD and turbidity varies around 81% and 79% respectively. When FeCl3 is introduced at the same time as the flocculant, the turbidity is considerably reduced (56%), while the COD is around 78% which does not show a significant difference between when FeCl3 is introduced first, followed by by the flocculating agent. In addition, the results obtained when the flocculant is introduced before FeCl3 showed a significant decrease in COD (59%) and turbidity (58%). However, the reduction in organic matter (COD) during the addition of coagulant-polyelectrolyte mixtures is greater than the results obtained by the addition of similar and single doses of FeCl3. In addition to the removal of pollutants, sludge production was considered in this work, as it may affect the economic feasibility of the proposed treatment method. The sludge produced during the physicochemical treatment of landfill leachate (**Table 9**) is composed by the amount of colloidal organic matter and suspended solids, as well as by the compounds formed due to the possible addition of chemical reagents.

The quantity of sludge produced by the introduction of FeCl3 followed by the flocculant is 200 ml/l (compacted sludge) which remains low compared to the results obtained by introducing the Astral flocculant the first followed by FeCl3

#### **Figure 21.**

*Effect of the order of introduction of the dose dose of coagulant and flocculant FeCl3 and Astral on the elimination of organic matter (COD) and turbidity.*


**Table 9.**

*Effects of the order of introduction of the dose of FeCl3 and Astral flocculant on sludge production. Optimal concentrations: FeCl3: 2500 mg/l, Flocculant: 500 mg/l and pH = 7.*

(300 ml/l). In addition, the study of the coagulation of the mixture (flocculant + FeCl3) showed a large quantity of uncompacted sludge (750 ml/l). In conclusion, the addition of FeCl3 first, followed by the flocculant results in a small amount of compacted sludge volume.

#### **9. Discussion**

Knowing the composition of the waste (household waste + industrial waste) makes it possible to assess the risks of percolation through the soil (leaching). During the solubilization by rainwater, metal oxides and chemicals, often highly toxic contained in the waste, pass into the leachate water. Ecologically, the alarm bells have already been sounded, because in addition to the air pollution, the waters of the Oued Al Maleh which is close to the landfill (10 m) are heavily polluted due to the leachate produced by the old public dump of Mohammedia [1, 4].

To assess the impact 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 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 carried away by runoff and reach surface water, or infiltrate through the substratum of the landfill and contaminate the water of the water table which is not deep (case of the city of Mohammedia). The results of **Tables 1** and **2** have shown that the leachate is characterized by high concentrations of organic matter, ammonium and nitrogen compounds..... The leachate from these separate stages contains different constituents and therefore different characteristics.

In the coagulation - flocculation process [4]. It is very important to adjust the pH since coagulation occurs within a specific pH range for each coagulant and flocculant and depending on the type and characteristic of the raw effluent to be treated.

Coagulation/flocculation is a commonly used process for wastewater treatment in which reagents such as ferric chloride and/or ferric polymer are added to landfill leachate in order to destabilize colloidal materials. This causes the agglomeration of the small particles into easily settling flocs. Several studies have reported the examination of this process for the treatment of landfill leachate, in particular in relation to the optimization of the performance of coagulant/flocculant, the determination of the experimental conditions, the evaluation of the pH, and the search for the addition of flocculant [4, 24].

To improve the coagulation/locculation process, the addition of some commercial polyelectrolytes has been investigated, including two cationics (Astral and Superfloc). The treatment of the leachate by coagulation flocculation using several coagulants has shown that the percentage of elimination of various pollution parameters such as COD, BOD5, turbidity and sludge formed during the treatment vary with the type of coagulant or flocculant chosen for study.

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

The optimal process variables for landfill leachate coagulation using Fe (III) and Al (III) were found at pH 6.5 for Fe (III) and 5.3 for Al (III) at coagulant doses of 18.5 mmol/l Fe (III) and 5.82 mmol/l Al (III). Although the doses required were identical (0.035 mol/l of Fe3+ or Al3+), with an initial COD concentration of 4100 mg/l, FeCl3 led to a higher elimination of organic compounds (55%) than 'aluminum (42%). Indeed, the results obtained during our study made it possible to show that FeCl3 is more interesting in terms of reducing pollution, in particular the elimination of COD and turbidity with a yield of 95 and 67% respectively and the COD. In addition, the results showed that the pH considerably affects the coagulation and flocculation by the different coagulants and flocculants tested. The decrease in pH due to Fe + Al cations which present acidic characteristics; therefore, hydrolysis took place under acidic conditions caused by precipitation of metal hydroxides. Several studies have examined coagulation-flocculation for the treatment of landfill leachate, aimed at optimizing performance, namely selection of the most suitable coagulant, determination of experimental conditions, evaluation of the effect of pH, and the choice of flocculant [42]. In addition, during the precipitation process, coagulation, flocculation and adsorption appear to contribute to the removal of organic matter from the leachate [43, 44].

As for other coagulants and flocculants the results showed the yield of COD and turbidity varies from one reagent to another. The Astral and Lesieur flocculants in a mixture with FeCl3 were able to improve the reduction of leachate pollution. No significant difference was observed in the reduction of COD and turbidity by the flocculants supplied by the Italian company (Chimic 1, 2, 3) during flocculation coagulation. In addition, the order of introduction of FeCl3 and Astral flocculant showed that the reduction of pollution (COD and Turbidity) is better when introducing FeCl3 first (elimination of 81% of COD and 79% of turbidity) while the introduction of the flocculant before the FeCl3 resulted in a yield of 59%of the COD and 58% of the turbidity.

It was shown by Hamzeh et al. [45] that at an initial concentration of 5690 mg/L and at a pH of 4.8, a maximum COD removal of 56% was obtained with 0.8 g/l of FeCl3, compared to 39% with 0.4 g/l of Al2(SO4)3. In addition, Ez Zoubi et al. [46] showed during the treatment of leachate produced by the public landfill of the city of Fez with FeCl3 that the COD content goes from 53199.6 mg/l to 41933 mg/l with a yield of 21% while Bakraouy et al. [25] showed that FeCl3 could remove a yield of 65% of COD. This shows that the pollution removal efficiency varies with the coagulant used, the age and the quality of the leachate.

The treatment of leachate is a difficult and expensive process [25]. Although, the leachate can be treated biologically, the COD removal efficiency is generally low due to the high ammonium ion content and the presence of toxic compounds such as metal ions. The results suggest that FeCl3 may be a viable coagulant in managing COD problems associated with landfill leachate. In addition, the treatment of the leachate by coagulation-flocculation has led to a reduction in the physicochemical (COD, BOD5, ...) and suitable microbiological parameters while the coagulation flocculation combined with a biological treatment of SBR type has allowed eliminate 99% of the COD from leachate produced by the public landfill in the city of Fez [47].

As regards the study of the elimination of metals by coagulation flocculation with FeCl3, the results have shown that the efficiency of elimination of the metallic elements by the various coagulants and flocculants varies between 80 and 99.6. This proves that the flocs formed during coagulation flocculation allow most of the metal elements to be adsorbed in the leachate.

Khalill et al. [35] have shown that flocculation coagulation is a very effective technique for reducing metal pollution from leachate produced at the landfill in the city of Fez. However, the efficiency of removing the metallic elements varies from one coagulant to another and the combination of lime on the one hand with ferric chloride and on the other hand with Alumina Sulfate improves the efficiency of elimination of the elements Cr (90%), Fe (96%) and Mn (99%) [35].

It was shown by Hamzeh et al. [45] that at an initial concentration of 5690 mg/l and at a pH of 4.8, a maximum COD removal of 56% was obtained with 0.8 g/l of FeCl3, compared to 39% with 0.4 g/l of Al2(SO4)3. In addition, Ez Zoubi et al. [46] showed during the treatment of leachate produced by the public landfill of the city of Fez with FeCl3 that the COD content goes from 53199.6 mg/l to 41933 mg/l with a yield of 21% while Bakraouy et al. [25] showed that FeCl3 could remove a yield of 65% of COD. This shows that the pollution removal efficiency varies with the coagulant used, the age and the quality of the leachate.

Although, the leachate can be treated biologically, the COD removal efficiency is generally low due to the high ammonium ion content and the presence of toxic compounds such as metal ions. The results suggest that FeCl3 may be a viable coagulant in managing COD problems associated with landfill leachate. In addition, the treatment of the leachate by coagulation-flocculation has led to a reduction in the physicochemical (COD, BOD5, ...) and suitable microbiological parameters while the coagulation flocculation combined with a biological treatment of SBR type has allowed eliminate 99% of the COD from leachate produced by the public landfill in the city of Fez [47].

However, it should be noted that the precipitation and adsorption of ions in leachate samples is strongly affected by the amount of humic compounds present, which impairs the efficiency of coagulation.

Tatsi et al. [26] in a study of coagulation flocculation for the removal of COD, showed that the addition of Aluminum to fresh leachate resulted in a 25–38% reduction in COD using a dose of 3 g/l d 'Aluminum. Amokrane et al. [37] have shown that ferric chloride is more effective than Aluminum Sulphate with a yield of 94 and 87%, respectively, in removing turbidity from landfill leachate. The removal rates of COD and color are 41% and 70% respectively by adding 2.5 g/l of ferric chloride as Fe3+ [45].

The addition of Superfloc polyelectrolytes did not significantly affect the elimination of organic matter, which does not exceed 30%, compared with the results obtained with the mixture FeCl3 + Astral (62%), and FeCl3 + alginate (50%) Similar results were observed during the addition of polyelectrolytes K1370 and A321 for the treatment of stabilized leachate without pH correction [25]. However, the removal of pollutants was improved by the addition of polyelectrolytes to the samples. It should be noted that at this stage the hydrolysis, ferric cation precipitation and adsorption reactions in the leachate are greatly affected by the presence of humic and fulvic substances. Indeed, specific interactions can appear between humic substances, the surface of flocculants and dissolved ferric species, influencing the efficiency of the coagulation-flocculation process. The effect of addition of coagulant and flocculant mixture on COD removal and partially stabilized leachate turbidity could improve leachate remediation performance.

#### **10. Conclusion**

The establishment of landfills in sites that are not suitable or not specifically designed for this purpose increases the risk of contamination of surface and groundwater, and consequently human health, knowing that water is the source of life. Following a bio-physico-chemical evolution of this piled up waste and the action of the rains, a juice called leachate is generated. This juice constitutes a source of pollution for the environment.

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

In this study, the treatment of leachate from the public landfill in the city of Mohammedia by a flocculation coagulation process was evaluated. Landfill leachate was characterized by a low pH value and a high concentration of pollutants. Organic matter varies between 2153 and 2707 mg/l of COD, and from 1080 to 1405 mg/l of total nitrogen. As for turbidity, however, the elimination of turbidity remains dependent on the efficiency of the coagulation, ie the coagulant used for the study.

In addition, the results obtained showed that ferric chloride is more effective than aluminum sulphate in removing COD, especially when the pH is above 9. Hydrated iron hydroxides precipitate more easily than flocs formed. by aluminum, which results in a more efficient removal of pollutants than that obtained at lower pH values. The optimal doses of the various coagulants and flocculants chosen for the study vary from one reagent to another. However, the reduction in pollution by the flocculants alone does not show an efficiency of elimination whereas the coagulant and flocculant mixture allows a good elimination of the pollution. FeCl3 remains the most suitable coagulant to further eliminate organic and metal pollution. In addition, flocculation coagulation has significantly reduced metal pollution.

It can be concluded that the physicochemical treatment by coagulation flocculation proposed for the treatment of leachate is effective. The technique has several advantages:


It can be concluded that FeCl3 could have a considerable impact on reducing pollution compared to other results obtained with other coagulants and flocculants.
