Aluminium is the most common metallic element in the earth's crust, with most of it occurring in complex forms in the ground. Aluminium salts, which are a by-product of the production of aluminium products such as aluminium profiles, can also be used as raw materials. For applications requiring very pure products, alumina is produced from bauxite. When dissolved with sulphuric or hydrochloric acid, aluminium sulphate and aluminium chloride are produced. If the aluminium hydroxide is dissolved in caustic soda, sodium aluminate is produced. The main applications of aluminium salts are described in the section Metal salts in wastewater treatment plants .

Aluminium salts are often dosed in order to combat bulking sludge or filamentous bacteria (e.g. M. parvicella). For this purpose, higher concentrations are dosed than necessary for pure phosphate elimination. Sewage treatment plants, which previously had to dose expensive aluminium products for this purpose, could permanently dispense with this dosing after the introduction of the S::Select^® process and use more cost-effective precipitants.



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