Some well known inorganic compounds have been subject to treatment for a century and to recent improvements and innovations. The occurrence, the environmental behaviour and the removal techniques of inorganic substances depend primarily on their aquatic chemistry, involving various reactions. The knowledge on speciation and its alteration is essential for process selection. Out of the more recent problems of some inorganic substances, natural, geogenic arsenic plays obviously a major role in a large number of countries. The relatively high chronic toxicity induced lower drinking water standards and activities on improved arsenic removal. Arsenic is a good example to demonstrate the chemistry principles and to derive new treatment techniques at affordable costs. A full-scale process comparison in Germany is presented, indicating the superior efficiency of a newly developed fixed-bed adsorption with a commercial granular ferric hydroxide, developed in the early 1990s. It is especially suitable for small-scale water supplies, for well-head treatment and even for decentralised removal of arsenic with low maintenance requirements.

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