**3.2 Leachate settling**

The study of the elimination of leachate pollution by sedimentation is presented in **Table 3**. The settling time varies around 120 minutes. The supernatant was collected to analyze the COD after a stabilization time of 120 minutes.


**Table 3.**

*Study of leachate sedimentation for six sampling campaigns settling time 120 min.*

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

The COD removal rate varies between 5 and 34.5%, which is essentially a function of the quality of the leachate collected. Indeed, sedimentation remains essential to reduce leachate pollution at the lowest cost.

Settling is a process to reduce turbidity by allowing the water to stand for 2–24 hours for the particles to settle to the bottom of the basin. The advantage of settling is that it does not require any equipment other than settling tanks. However, the drawbacks of this method require several settling tanks when the polluting load and the flow rate are high.

The removal of suspended particles by sedimentation depends on the size and density of these particles. Settleable solids are measured as the visible volume accumulated at the bottom of an Imhoff cone after settling for one hour.

Unhindered settling is a process that removes discrete particles at a very low concentration without interference from nearby particles. The re-stabilization of the system by adding excess coagulant is not effective, since increasing the settling time promotes clarification of the supernatant beyond the critical coagulation concentration and the charge reversal point.
