4. Wash. Spin. Pressing

After the actual filtration phase, the cake must be washed to remove as much filtrate as possible from its pores, either to recover most of the filtrate or to obtain a cake that is substantially free of filtrate.

As removing the last traces of filtrate from the cake interstices requires the passage of large volumes of washing liquid, it is sometimes more advantageous to repeat one or more filtrations after resuspending the cake in washing liquid.

Often, the aim is also to obtain a cake with as little moisture as possible, in order to reduce the subsequent costs of transport, drying, etc. In such cases, after filtration and washing operations, the cake is dewatered, either mechanically (by crushing the cake with a compressed air-filled cushion or by significantly increasing filtration pressure), or by passing steam or air through it....