In the present study, suitable nanocomposites (based on low-cost clay minerals and organic molecules or polyelectrolytes) adapted to the charge of the effluent are shown to provide a very efficient pretreatment for the reduction of TSS and COD in a single step. Nanocomposites presented in this study are based on the clay mineral sepiolite and the cationic polymer poly-DADMAC. However, the general idea (as presented in [25]) behind the use of nanocomposites is to combine neutralization of the colloids (coagulation), achieved by the polymer’s charged sites, and bridging of the neutralized particles (flocculation), achieved by the fact that the polymer chains are connected to denser and heavier anchoring particles; this might yield very efficient pretreatment of wastewater and the reduction of TSS in one single treatment step.