Hybrid Clay-Polymer Nanocomposites for the Clarification of Water and Effluents

Background: Freshwater resources will not be able to meet all requirements and water should not be considered a self-renewable, low cost resource. Thus, the needs for increased amount of water imply adopting several approaches that include intercepting and transferring water, desalination and water re-use. In all three approaches removal of turbidity and total suspended solids (TSS) is a crucial step, as one of the essential parameters limiting water quality. This paper reviews a series of patents focusing on the use of clay-polymer nanocomposites to obtain very fast and efficient turbidity and suspended solids removal in water and effluents. Method: The rational beyond the use of nanoparticles based on an anchoring denser core (for example a clay mineral) to which chains of a polyelectrolyte with charge that opposes the colloidal charges, is that it induces fast formation of neutralized flocs, that are denser than organic colloids. In such a way all three colloidal stability factors (size, charge and density) are addressed achieving very fast clarification. Results: This paper summarizes several applications and examples of the procedure: removal of algae or microbes in surface water, clarification of saline effluents or sea water before desalination, and almost complete removal of turbidity and suspended solids in several industrial very turbid effluents. In all cases, clarification is obtained in seconds by the formation of 20-500 μm flocs, and their further separation by sedimentation or filtration, within a very wide pH range (3-11). Conclusion: Clay polymer nanocomposites can offer very effective clarification yielding reduction of more than 90% of the turbidity and the suspended solids in water or effluents, including in some cases deactivation of microorganisms that could offer an environmentally oriented alternative to chlorination. The good performance observed is presumably due to the broad versatility that stems from the use of different polymers and clays, and even different clay-polymer ratios yielding a wide range of charges.