**2.1 Coagulants-flocculants agents**

Polyelectrolytes of both natural and synthetic origin can flocculate colloids. Polyelectrolytes are polymers with a high molecular mass, which normally contain ionizable functional groups. Typical examples of polyelectrolytes are shown in **Table 1**.

In a simpler way, a polyelectrolyte (PE) can be defined as a polymer that dissociates into charged species in solution. Normally, the term polyelectrolyte is used for polymeric systems that consist of macroions, that is, macromolecules that carry charges or dissociable groups covalently bound to their structure, which in turn must be compensated for counter ions of opposite charges to guarantee the electroneutrality of the system [7].
