Physical processes such as sedimentation, flotation and filtration remain at the heart of most process trains for the treatment of water and wastewater flows. 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 determined by 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 (< 1000 µm), surface forces play a vital role in controlling the removal characteristics of the system.