Understanding Odour Control

This short paper looks at the human sense of smell, and in particular the process of odour control. It considers why odour control is required, how odours work, their constituent parts, how we detect them and what odour control measures are available. Commercial odour control is required in lots of situations, for example where an industrial process creates an unpleasant odour that affects the surrounding area. How many times have you visited an industrial

site, for example, an animal rendering plant, chicken factory, landfill site, or effluent plant and thought that it was about time they found out how to control that distasteful odour?

Well, by understanding the problem you can start to identify what odour control products may be helpful in overcoming this problem.

It’s even rumoured that the Queen of England has the local Windsor effluent plant close when she’s in residence at Windsor Castle due to the foul smelling odour!

Nitrogen, oxygen and sulphur

Three Elements to understand odour control you first need to understand the make-up of odours. There are basically three elements that cause most foul odours; nitrogen, oxygen and sulphur, and all of them can be found everywhere. Fortunately, not all odours are bad, those containing oxygen are usually sweet whilst those with nitrogen and sulphur usually foul.

Smelling airborne nitrogen, oxygen and sulphur compounds

The parent compound of the nitrogen is normally ammonia, found in all manner of household and industrial compounds such as glass cleaners and smelling salts. Whilst pungent, ammonia is not normally considered foul unlike organic derivatives of ammonia. Amines such as dimethylamine and trimethylamine give rise to fishy odours, and higher amines; tetra and penta-methylenes arise from the putrifaction of flesh. Ammonia derivatives are also associated with pet urine.

Sulphurous odours are normally associated with rotten eggs and organic derivatives such as butyl mercaptan with animals such as the skunk.

Detecting odours

In order to detect odours, the responsible compound needs to be volatile and therefore be dispersed in the air we breathe. Once airborne the compound can stimulate the olfactory glands in the nose and cause a number of complex reactions resulting in what we know as smell. With some compounds, only a few molecules may be needed to cause this reaction, whilst others are capable of blocking odours when in high concentrations and become no longer detectable above certain levels. This, in fact, is very dangerous as it may be a lethal compound such as Hydrogen Sulphide.

Many foul smells are formed by dead and decaying matter and during the process of decay the organic material breaks down into other, volatile, compounds giving rise to the smell.

Chemical masking and neutralisation

Chemical masking and neutralising products odour control can be achieved in two different ways, by masking or neutralising.

Masking is the concept behind air fresheners in that a pleasant smell is introduced in high enough concentrations to mask the unpleasant smell. The nose then only detects the pleasant smell that gives rise to a fresh smell. The only downside to this approach is that the bad smell is not removed but stays in the background and any masking may need to be continually repeated to hide the smell.

Neutralisation is the process that nullifies the odour-producing chemical, including those persistently produced. During this process, the specially formulated agent is atomised and absorbs the odour-producing compound, neutralising the compound. The result is not just the elimination of the unpleasant smell but a light and fresh aroma to the location.