Zeta Potential in Water Treatment Process Control

Physical processes such as sedimentation, flotation and filtration remain at the heart of most process trains for the treatment of water and wastewater. All these processes depend on the principles relating the size, density and the charge of the particles to be removed. The relative importance of the particle charge on the process efficiency is strongly dependent on the size of the particles under investigation.
Once the particles reach a certain size their mass causes a rate of sedimentation due to gravity that is sufficiently large to outweigh any effects due to the surface chemistry of the particles. However, within the range of sizes normally encountered within water and waste water processes (less than 1000 µm), there will be a fraction of fine material, less than a few tens of microns, where understanding charge interactions between the particles will assist in determining the optimum treatment regime.
The surface charge, or more strictly speaking, the zeta potential (z), is determined by measuring the particle velocity induced when a potential difference is applied across a capillary cell containing the sample (Zetasizer, Malvern Instruments Ltd.).
Zeta potential is known to be a key determinant in understanding physical processes such as flocculation and sedimentation.