2. Coagulation

2.1 Basic principles

The difficulty in separating colloids present in water by simple decantation or filtration stems from the fact that these particles, which are of mineral (clay), plant (humic or fulvic acids, algae), animal (zooplankton), human (fatty suspensions, ERU discharges) or industrial (various types of wastewater) origin, are found in water in the form of very fine electrically charged particles (always negatively charged in natural waters). The mutual repulsion exerted by these particles prevents them from agglutinating under the effect of natural attractive forces (called "van der Waals forces" at this scale) and thus acquiring a sufficient size to become settleable or filterable (figure