An unpleasant smell can occur, among other locations, in waste water treatment plants, sludge treatment plants, composting plants, solar dryers…
However, the phenomenon is not limited to utility activities only – it can also occur in the food industry, the pharmaceuticals industry and other industries.
Systems for removal of unpleasant or undesirable odours:
- Washers/rinsers (also called scrubbers)
- Biofilters
- Zeolite filters
The differences among them are, in particular, the following:
- Washers: easy regulation during dosage of chemicals if necessary, and they can respond very quickly to very high concentrations of substances that cause unpleasant odours.
- Biofilters: they operate well at low and constant concentrations of pollutants, but acidification and clogging may occur if too much sulphide is present in the air.
- Zeolite filters: economical at low flows of polluted air, zeolite materials are replaced every two years.
The most versatile technique that has been used lately to remove unpleasant odours from the air are the so-called air washers.
There are several types of washer configurations:
- Dual-column washersThe first column is used to neutralise ammonia with sulphuric acid. The second column is used for oxidation of hydrogen sulphide and mercaptans with peroxide in an alkaline environment.
- One-column washers.The process is carried out at low pH and with ammonia neutralisation with sulphuric acid. Dosage of chlorous acid (HCLO2) and peroxide for oxidation of hydrogen sulphide and mercaptans.
- Semi-cross-flow washerIt can be used like washers with one or two columns
Example: Semi-cross-flow washer with one column.
