**5. Comparative study of the elimination of leachate pollution by different coagulants and flocculants**

The comparative study on the elimination of turbidity and COD by different coagulants and flocculants is shown in **Figure 19**.

These results show that FeCl3 gives a significant removal of COD and Turbidity with a high yield compared to other coagulants and flocculants. Aluminum sulphate allows elimination comparable to that obtained with FeCl3. With regard to the flocculants, the results showed that the Astral flocculant alone allowed a very interesting elimination of 53% and 75% respectively for the COD and the turbidity. No significant difference was observed for the removal efficiency of COD and turbidity by the flocculants Chimec supplied by the Italian company.

The effect of optimal concentrations of coagulant FeCl3 and flocculants (Astral, Supefloc, Alginate) alone or mixed on the production of sludge produced during the coagulation/flocculation process Coagulant type and dose volume of sludge is given in **Table 5**.

The addition of organic flocculants has been examined to improve the removal of organic matter.

FeCl3 + Superfloc showed a removal efficiency of 30 and 66% respectively of COD and turbidity (**Figure 20**). These values are lower than the results obtained for the FeCl3 + Astral or FeCl3 + Alginate mixture.

#### **Figure 19.**

*Comparative study of the elimination of COD and turbidity by different coagulants and flocculants.*


#### **Table 5.**

*Effect of optimal concentrations of coagulant and flocculants alone or mixed on the production of sludge.*

#### **Figure 20.**

*Effect of FeCl3 mixture, Superfloc flocculant, Astral flocculant using optimal doses on reduction of COD and turbidity.*

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

The combined action of ferric chloride-polyelectrolyte mixtures was investigated. Addition of flocculant at a coagulant: flocculant ratio (Astral 2.5: 0.5, Superfloc 2.5: 0.14 Alginate 2.5: 0.02) (g), gave removal capacities of COD and variable turbidity (**Figure 6**).

Similar results were observed, during the addition of polyelectrolyte K1370 and A321 to stabilized leachate samples without pH correction [26]. Addition of polyelectrolyte superfloc did not substantially affect organic matter removal, which did not exceed 30%, as compared with the results FeCl3 + Astral (62%), and FeCl3 + Alginate (50%). However, the removal of pollutants was enhanced during the addition of polyelectrolytes in the samples. It should be mentioned at this point that hydrolysis, precipitation and adsorption reactions of ferric cation in leachate samples are greatly affected by the presence of humic substances. Specific interactions may appear between the humic substances, the surface of flocculates and the dissolved ferric species, influencing the efficiency of coagulation–flocculation process.

### **6. Removal of heavy metals**

The removal of metallic elements by ferric chloride FeCl3 is given in **Table 6**. The concentration of heavy metals (Zn, Cu, Cd, Cr and Ni) in the leachate exceeds the maximum authorized values.

The flocculation coagulation made it possible to eliminate a yield varying between 80 and 99% (**Table 6**) for the various metallic elements studied (Cu, Zn, Cr, Cd, Ni, Pb and Sb). The results concerning the elimination of Chromium obtained during the present study are comparable with the results obtained for the treatment of leachate with FeCl3 [35] with a removal efficiency of 71% during the treatment with FeCl3 alone, whereas treatment with the latter in the presence of lime resulted in a yield of 90% of chromium [35, 36]. The same authors have shown that the aluminum sulphate allowed an elimination yield of 83% (**Table 7**).


**Table 6.**

*Analysis of metals in stabilized leachate before and after coagulation flocculation-using FeCl3 (concentration mg/l).*


#### **Table 7.**

*Comparative study of the removal of metals by coagulation flocculation [35].*

Lime has been used traditionally as a coagulant in the treatment of leachate for many years, requiring doses of around 1 to 15 g/l [35]. Amokrane et al. [37] have shown that the removal of heavy metals, such as Fe, Cd, Cr, reaches up to 90% efficiency during lime treatment. In fact, the removal of COD and heavy metals can be obtained at a pH of 10, which results in a yield of 28% and 86% respectively for COD and heavy metals, with the addition of 2,000 mg/l of ferric chloride [38–40]. In this study, the results indicate that iron (III) chloride [L5] coagulation-flocculation is very effective in reducing metallic elements; the reduction reaching 80 and 99.5% at optimal concentrations of 18.5 mmol/l Fe3+ achieved at a pH of 6.5. Similar results were obtained during the coagulation flocculation of leachate discharges from the city of Fez landfill by FeCl3 [37].

Previously, the low removal of heavy metals in the leachate landfill was observed by Silva et al. [41] during the coagulation/flocculation process.
