are characterized by a distinct different main function or product.
The main function of the rotary kiln incinerator is the destruction
of hazardous and otherwise difficult waste (not the production of
steam and electricity); the main function of the cement kiln is
the production of clinker. Due to these activities pollutants are
emitted, by-products and wastes are generated. By-products are
considered as a secondary outcome of a process, not its main aim
(e.g. steam and electricity); they can be applied into the process itself or used in other applications. Following the definition, solid
residues can only be seen as by-products if they can be usefully applied; when being landfilled they should rather be denominated as
waste.