Treatment train

A treatment train is a sequence of stormwater treatments, designed to meet the needs of a particular environment in order to maximise results.

Treatment trains are important when a treatment measure needs pre-treatments to remove pollutants, such as nutrients and fine sediment, that would otherwise impact its performance.

For example, wetlands are designed to remove heavy metals and nutrients, like fertilisers, from stormwater. However, they will perform poorly if gross pollutants (litter) and coarse sediments (gravel and sand) are not removed by a sediment pond upstream.

Typical treatment combinations

The following treatments combinations depicted use arrows to indicate the direction of stormwater flow. Treatment measures should be appropriately selected and ordered to protect wetlands and raingardens from gross pollutants and coarse sediments.

Rainwater tanks and raingardens

Rainwater tanks icon

Raingardens icon

Rainwater tanks collect run-off from impervious surfaces like roofs, reducing the amount entering waterways.

Raingardens are specially-designed garden beds that filter run-off from surrounding areas or stormwater pipes.

Gross pollutant traps and swales

Gross pollutant trap icon

Swales icon

Gross pollutants traps use physical processes to trap solid waste such as litter and coarse sediment.

Swales are linear, depressed channels that collect and transfer stormwater. They can be lined with grass or more densely vegetated and landscaped.

Sediment ponds and wetlands

Sediment ponds icon

Wetlands icon

Sediment basins are ponds with open water that capture coarse sediment and litter carried by stormwater.

Constructed wetlands are a series of shallow, densely-planted ponds that filter water.

Stages of the treatment train

Process: step 1
 

Primary treatment

Processes
  • physical screening
  • rapid sedimentation​
Pollutants
  • gross pollutants
  • coarse sediment​
Typical application
  • grassed swales
  • litter traps
  • sediment ponds​
Process: step 2
 

Secondary treatment

Processes
  • fine particle sedimentation
  • filtration techniques​
Pollutants
  • fine sediment
  • attached pollutants​
Typical application
  • swales
  • infiltration trenches
  • porous paving
  • bio-retention systems
Process: step 3
 

Tertiary treatment

Processes
  • enhanced sedimentation and filtration
  • biological uptake
  • absorption onto sediments​
Pollutants
  • nutrients
  • dissolved heavy metals​
Typical application
  • bio-retention/bio-infiltration systems and wetlands
Last updated:
17 September 2021