Wastewater and sludge are usually mixtures of solid components and
liquids. The liquid phases almost always also contain solute substances.Whereas the solute components cannot be removed, at least not right
away (see heading Adsorbents), small particles are also frequently
difficult to remove to a sufficient degree.
This problem is addressed on the one hand by means of suitable technical equipment such as
- Chamber presses
- Belt presses
- Revolving screens and belt filters
but in most cases a chemical conditioning of the medium to be dewatered
is necessary to achieve more rapid and effective separation.
The chemical conditioning process functions according to the principle
of the mutual attraction of particles with opposing charges. The
surfaces of all solids in suspensions carry either a positive or a
negative charge. The conditioning agents (usually high-molecular, i.e.
polymers or coagulants) must optimize the polarized charge effect by
creating a balance of charges within the system (isoelectric point).