Any place or process in which wastewater is collected, conveyed or treated has
the potential to generate and release nuisance odours. Early stages of processing
tends to produce smelly gases like Hydrogen Sulphide (H2S), Sulphur Dioxide (SO2),
Bromine and Oxides of Nitrogen, Chlorine (Cl2) etc., which can be toxic or even
corrosive in higher concentrations. In most water pumping stations, filtration plants,
and waste water treatment plants, control of odour is of prime importance.
Malodorous gases undergo a gas phase filtration prior to exhausting from irrigation tanks
and pumping stations.

Importance of odour control during sewage treatment

Majority of odour problems occur in the collection system, primary treatment facilities
and in solids’ holding facilities. This condition occurs when oxygen transfer to the
wastewater is limited. In the anaerobic state, the microbes present in the wastewater
have very little dissolved oxygen available for respiration. This allows microbes known as
“sulfate-reducing bacteria” to thrive. These bacteria utilize the sulfate ion that is naturally
abundant in most waters as an oxygen source for respiration. The byproduct of this activity
is hydrogen sulfide. This byproduct has a strong, offensive and rotten-egg like odour. In addition
to its odour, hydrogen sulfide can cause severe corrosion problems as well.

The main odour generating areas are:

• Waste water and sewage collection/processing facilities
• Clarifiers
• Digesters
• Aeration basins
• Lagoons
• Pumping stations
• Headworks
• Sludge handling areas etc.
• Chemical cleaning compounds, solid waste, and other accumulated human garbage increases the natural contamination of sewage water.

Nuisance odours and gases evade the best preventative efforts of modern waste water treatment plants.
Industrial odour control is complex and difficult task. Even the waste disposal workers are now beginning
to understand the importance for odour control.