**7. Effects of coagulation flocculation on sludge production**

In general, the amount and characteristics of the sludge produced during the coagulation flocculation process are highly dependent on the specific coagulating and flocculating agent used and the operating conditions. The volume of wet sludge settled after the coagulation flocculation process is an interesting parameter to take into account when choosing the coagulant used for the treatment. The volume (ml/l) of the settled sludge can be is represented as a function of the dose of the coagulant.

The effect of the optimal concentrations of FeCl3 coagulant and flocculants (Astral, Supefloc, Alginate) alone or in mixture in the production of sludge is given in **Table 6**.

The addition of organic flocculants has been investigated for improving the removal of organic material. The FeCl3 + Superfloc mixture showed a removal efficiency of 30 and 66% respectively of COD and turbidity. These values are higher than those obtained in the case of the FeCl3 + Astral or FeCl3 + alginate mixture.

From **Table 8**, it is observed that the volume of sludge produced was considerably reduced with increasing dose of polyelectrolyte in the coagulation process. This may be due to the cationic nature of the polyelectrolyte used in this study. In fact, the high molecular weight of the polyelectrolyte allowed an improvement in the growth of the particles, which facilitates the settling. The cationic flocculant also has the ability to attract and retain colloidal particles at the polar sites of the molecule. In general, organic polymers generate less sludge than inorganic salts since it does not add weight or combine chemically with other ions in the water to form a precipitate. Thus, the sludge produced by the use of ferric chloride in combination with a polyelectrolyte is greatly reduced.


#### **Table 8.**

*Effect of optimal concentrations of coagulants and flocculants alone or in mixture on sludge production.*

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

The combination of Ferric Chloride, Alginate and Superfloc produces less sludge (ml/l) than when Ferric Chloride is used with Astral Flocculant.
