4. Filtration in Water and Used Water Purification

The following chapter shall provide an overview about granular media filtration. Within this framework, key insights into construction, operation, and modeling are provided. Nevertheless, membrane and cake filtration are also briefly discussed. Filtration is one of the oldest water treatment technologies and is based on the retention of solids by a filter media letting the water pass through while holding the suspended particles back. Filtration has experienced much development and has found widespread applications in many areas of water treatment. The great popularity is a result of its extensive customizability and simplicity, thus achieving good treatment results with an uncomplicated operation. Due to the different choices of filter media, operation modes, and construction, filtration units can be tailored to each application. This is exemplified in four cases studies from different water treatment fields, ranging from drinking water production to treatment and reuse of effluents. Regeneration of the media and regular backwashing procedures are essential insuring long lifetimes and optimal treatment results. Filtration performance and operation can be modeled with the basic and very general Darcy law, with the empirical Kozeny equation, which considers the effects of the pore structure of the medium on flow, or with the Ergun equation, which is an extension of Darcy’s law and additionally takes into account the effects of particle inertia and the frictional behavior of the fluid in porous media.