*3.2.1 Effects of Fe3+ and Al3+ on the removal of leachate pollution*

The coagulation results for the FeCl3 and Al2(SO4)3 leachate are shown in **Figures 2** and **3**.

The comparative study of coagulation-flocculation by Fe3+ and Al3+ is given in the **Table 4**.

### *3.2.2 Effect of pH on FeCl3 leachate coagulation*

In the coagulation-flocculation process [29, 30]. It is very important to adjust the pH since coagulation occurs within a specific pH range for each coagulant and depending on the type and characteristic of the raw effluent to be treated.

The COD removal efficiency tests, using FeCl3 were performed for pH values between 2 and 12 (**Figure 4**). The optimum pH of the raw leachate, before the addition of the coagulant is 6.5. At this pH, the COD and the turbidity dropped by 84% and 96% respectively. This conclusion is in agreement with that of [27].

#### **Figure 2.**

*Effect of FeCl3 on the elimination of leachate pollution. Experimental conditions: initial COD of the leachate = 3175 mg/l and initial turbidity = 128 NTU, pH = 7.8.*

#### **Figure 3.**

*Effect of Al2(SO4)3 on COD removal, turbidity and settled sludge. Experimental conditions: initial COD of leachate = 2400 mg/l, initial turbidity = 140 NTU, pH = 7.8.*


#### **Table 4.**

*Comparative study of coagulation-flocculation by Fe3+ and Al3+.*

**Figure 4.**

*Effect of pH on leachate coagulation using FeCl3. Experimental conditions: (optimal FeCl3 concentration: 3500 mg/l), initial leachate COD = 3168 mg/l, initial turbidity = 110 NTU and pH 7.8.*

*3.2.3 Effect of pH on leachate coagulation using Al2(SO4)3*

**Figure 5** shows the effect of pH on leachate coagulation using aluminum sulfate. The results show a removal of turbidity which varies around 84% at pH 5.3. The maximum sludge volume, generated at optimum pH, is 240 ml/l. Partial dissolution of aluminum oxide and the appearance of a net positive charge on the surface should be considered.

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

**Figure 5.**

*Effect of pH on leachate coagulation using Al2(SO4)3. Experimental conditions: (optimal concentration of Al2(SO4)3: 1000 mg/l), initial leachate COD = 2.400 mg/l, initial turbidity = 140 NTU and pH 7.8.*

Flocs generated under strongly acidic or basic conditions were significant, but in very small numbers, especially in an acidic environment. The reduction in pH is due to the acidic character of Al3+ from Al2(SO4)3. For the other coagulant doses tested, the flocs were microscopic and similar in size.

## **4. The effect of coagulants and flocculants on the removal of COD and turbidity**

#### **4.1 Effect of the mixture: Astral Flocculant + FeCl3**

To improve the elimination of leachate pollution, we tested a flocculant supplied by the company. This flocculant is currently used at the wastewater treatment plant which treats the wastewater of company by coagulation flocculation. The effect of Astral flocculant on turbidity and COD removal is shown in **Figure 6**.

**Figure 6.** *Reduction of turbidity and COD by the Astral Flocculant alone.*

The results show that the COD and turbidity parameters decrease with the increase in the concentration of Astral flocculant. The optimum concentration of the flocculant varies around 200 mg/l. From this value optimal, the concentration of COD and turbidity increases with the increase in the concentration of flocculant. The COD goes from 3300 mg/l to 1600 mg/l and the turbidity goes from 140 to 40 NTU with a removal efficiency of 53% and 71% respectively for the COD and the turbidity.

Indeed, the mode of action of polymers is however very different and depends mainly on their electrical charge properties and the concentration of flocculant. The stabilized leachate may contain too much organic matter (biodegradable, but also refractory to biodegradation) consisting mainly of humic substances [31, 32] as well as ammoniacal nitrogen, heavy metals, organochlorines and inorganic salts [33].

The pH is an essential parameter to be taken into account for the physicochemical treatment of liquid discharges by coagulation flculation. Indeed, we have studied the effect of pH on coagulation flocculation by the flocculant Astral. The results are shown in **Figure 7**. The effect of pH on the elimination of pollution from leachate discharges by coagulation flocculation has shown that there is no variation in turbidity and COD in the field. With a pH of between 2.5 and 12. The quantity of sludge formed during treatment remains lower. In addition, the results showed that the turbidity of raw leachate increases from 115 NTU to 40 NTU starting from acidic pH 2.5 while the COD goes from 3300 mg/l to 1550 mg/l with a yield of 65% and 53% respectively for turbidity and COD.

The study of coagulation flocculation by FeCl3 (2500 mg/l) in the presence of variable concentrations of Astral flocculant is illustrated in **Figure 8** while monitoring the performance by measuring the parameters of COD, Turbidity and sludge production. These results showed that the increase in the concentration of Astral Flocculant made it possible to considerably reduce the COD and turbidity parameters while increasing the production of sludge. The turbidity value stabilizes around 15 NTU while it appears that the COD is around 1150 mg/l for a flocculant concentration of 600 mg/l with a yield of 62% and 89% respectively for the COD and the turbidity. The volume of sludge produced is around 800 ml/l with complete elimination of the coloring. at pH 6,5.

Furthermore, the study of the reduction in the pollution of leachate discharges by FeCl3 in the presence of a constant concentration of Astral flocculant (200 mg/l) is given in **Figure 9**. The results have shown that the increase in

**Figure 7.** *Effect of pH on the reduction of turbidity and COD by the Astral Flocculant alone (200 mg/l).*

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

**Figure 8.**

*Study of the mixture: FeCl3 (2500 mg/l FeCl3) + Astral flocculant variable flocculant COD = 3056 mg/l, pH = 6.5.*

**Figure 9.** *Study of the mixture: FeCl3 + ASTRAL flocculant (200 mg/l) variable FeCl3. COD = 3100 mg/l, pH = 6.5.*

addition of FeCl3 increases the removal of COD and turbidity while increasing the production of sludge that requires treatment. It appears that the optimum concentration varies around 5000 mg/l of FeCl3 for a pH of 6.5. Indeed, in our study, the elimination of leachate pollutants was improved by the addition of cationic polyelectrolytes (Astral and Lesieur Flocculant). It should be noted that at this stage hydrolysis, precipitation and adsorption reactions of leachate pollutants are greatly affected by the presence of humic and fulvic substances. Indeed, specific interactions can appear between humic substances, the surface of flocculates and dissolved ferric species, influencing the efficiency of the coagulation-flocculation process. The effect of a coagulant and flocculant mixture addition on the removal of COD and partially stabilized leachate turbidity could improve leachate remediation efficiency.
