chemical dosing system

What is a chemical dosing system?

A chemical dosing system is a facility for automated injection of reagents into a wastewater network for the control of septicity and odour emissions.

These systems are typically used at pump stations, sewer manholes, and rising mains. However, they can be installed any place where odour containment is required.


In sewers, bio-reactions regularly occur. These reactions produce Hydrogen Sulphide (H₂S). This is the gas commonly identified by its ‘bad egg’ smell.

Ferrous dosing units reduce the impact of H₂S odours by initialising an alternative chemical reaction. They use ferrous chloride to bind with sulphides in the wastewater to form a stable, insoluble precipitate.

In this way, they are able to eliminate the formation of H₂S odours.

Key system benefits:

  • Reduces the emission of H₂S gas by up to 95%
  • Lessens corrosion of wastewater system facilities by H₂S gas
  • Ensures compliance with Work Health Safety (WHS) Regulations

2. How magnesium hydroxide dosing units work

The chemical reaction which causes H₂S emissions functions its best at pH levels between 6.8 and 7.2. Any higher or any lower and conditions are no longer ideal.

Magnesium dosing units work by elevating the pH level of sewerage to level 8 or higher. And, as this puts conditions out of the 6.8 to 7.2 pH level range, less odorous gas is produced.

This reduction in odorous gases by extension reduces odours.

Key system benefits:

  • H₂S levels are regulated downstream from dosing point
  • Lowers the emission of H₂S gas by up to 80%
  • Ensures compliance with Work Health Safety (WHS) Regulations

3. How calcium nitrate dosing units work

In untreated wastewater, bacteria initiates a biological process which develops free-ranging sulphides. And these sulphides bond with hydrogen molecules to form highly toxic H₂S gas.

Adding nitrates to the wastewater offers an alternative oxygen source and this creates a new reaction pathway to reduce H₂S production.

The reduction of H₂S production thereby decreases the presence of odours.

Key system benefits:

  • Reduces the emission of H₂S gas by up to 90%
  • Lessens corrosion of wastewater system facilities by H₂S gas
  • Ensures compliance with Work Health and Safety (WHS) Regulations

Difference between chemical dosing systems

Different chemical dosing systems use different reagents. And each reagent works in alternative ways.

However, extensively, they work to achieve the same outcome. They all condition sewage to prevent the biological or chemical formation of odorous emissions.

Which reagent and system will be suitable for your organisation will depend on your wastewater network.

Regulation of chemical dosing systems

Odours are off-putting, intrusive, and in some cases dangerous.

To protect communities and environments, regulatory authorities and Work Health and Safety (WHS) legislation monitors odour emissions.

If an organisation does not implement a chemical dosing system or if their system is insufficient then they can be fined or faced with litigation.

Additionally, should organisations neglect their responsibilities regarding odour management, they can experience a community backlash due to odour emissions and their impact on the environment.

Testing and monitoring of wastewater networks

Testing and monitoring of your organisation’s wastewater network should take place regularly.

This needs to be done for data collection prior to designing your chemical dosing regime. It is also important for optimising the effectiveness of your system.

Thinking chemical dosing systems? Think OdourPro.

At OdourPro, we are Australia’s leader in complete odour control technologies. We have more than 25 years of experience. Over which time we’ve built our reputation on innovative and reliable products.

We can diagnose your odour problem quickly and accurately, before providing you with an odour reduction system which stops up to 99.9% of odours.



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