Gross pollutants traps are structures that use physical processes to trap solid waste such as litter and coarse sediment. They are commonly used as the primary treatment because they mostly remove large, non-biodegradable pollutants.
Treatments and contaminants
Primary treatment includes:
Typical retained contaminants include:
How gross pollutant traps work
There are many different types of gross pollutant traps. All of them perform a similar function: trapping litter and sediment above 5 millimetres in size so that they can be removed from the water system. By removing large pollutants, downstream treatment of stormwater can occur more effectively.
Since gross pollutant traps tend not to be effective in removing nutrient, they are most often used as part of a treatment train with other stormwater treatment measures such as wetlands or bio-retention systems.
Selecting a gross pollutant trap
Selecting a gross pollutant trap for stormwater installations can be confusing, with many vendor claims and issues to consider. Ideally, every system should be independently verified.
We take a conservative approach when considering gross pollutant trap systems. When assessing a system, we require validation of manufacturer claims such as nutrient removal.
Advantages and limitations
Advantages of gross pollutant traps are that they:
have a relatively small lateral footprint
are hidden from view
Limitations of gross pollutant traps are that they:
provide limited removal of fine sediment and dissolved pollutants
have a high cost of build
are complex to install
require regular cleaning
Tips and advice
Most off-the-shelf gross pollutant traps are suited to pre-treatment of small to medium sized systems, so are not meant for treating large areas of catchment like wetlands. Sediment ponds are usually the preferred option for larger systems.
For more information on the design of gross pollutant traps, refer to Chapter 14 “Other Measures" in the WSUD Engineering Procedures available for purchase from CSIRO publishing.