Recycling plants and materials recovery facilities (MRFs) are full to the brim with different materials from domestic and industrial sources that produce plenty of powder and dust. Solid waste for recycling can include metals, glass, cardboard, plastics and wood. In single-stream enclosed MRFs, multiple waste sources, both organic and inorganic, co-mingle and must be separated. 

These processes generate odours from sources like hydrogen sulphide, dimethyl sulphide and mercaptans. The human nose can detect these smells at levels in the parts per billion, so even low concentrations can result in foul odours. 



And because nearly any solid, including metal, can explode when in dust form, recycling plants are highly prone not only to odours, but to dust explosions and fires.

In some facilities, the mixed residual waste is combusted and used as a fuel for energy production. These incineration plants can also provide an odour control function. However, it is likely that there is an annual shutdown for several weeks every year for re-lining and other maintenance. To prevent an odour nuisance during this time, a stand-by molecular filter fitted in a by-pass loop makes a good option. 

Instead of collection by truck, some modern residential developments provide for pneumatic conveyance of domestic waste from individual homes to a central collection point through underground pipes. These cases require dust and odour filtration on the exhaust of the system at the collection building to avoid nuisances in heavily populated areas.