Gold, silver or other metals can be recovered from wastewater (see:


For example, chromium used in metal-plating industries or leather tanning can be recovered thanks to specific filters and technology. Chromium-6 (hexavalent chromium) bath can be re-used/re-cycled for few cycles of plating or dyes by filtering iron and other contents. This also enhances the quality of plating. The sludge that comes out after filtration can then be valorized safely into clean water and/or biogas and/or other outputs.