A set of technological devices for mechanical and biological or mechanical, chemical and biological treatment of wastewater. The function of biological wastewater treatment plants is removal of solids, easily and hard subsiding suspensions, colloids and organic substances from wastewater.

In the biological treatment process take part micro-organisms in aerobic, anaerobic and changing (aerobic - anaerobic) conditions, The main technical devices in a biological wastewater treatment plant include: biofilters, active deposit devices and fermentation chambers.

• Wastewater treatment plant