Gross pollutant traps are not able to perform any form of chemical or biological filtration processes. This means that more complex dissolved pollutants arent able to be removed. The physical filtration methods that exist in the gross pollutant traps are not able to remove particles dissociated within the stormwater, and hence pollutants such as hydrocarbons and oils as well as heavy metals, nutrients and attached pollutants cannot be removed by gross pollutant traps. Gross pollutant traps are usually used as a precursor to tertiary and secondary systems that are designed to remove these pollutants. Treatment trains are common uses of stormwater management systems and hence these combined systems are able to remove oils and hydrocarbons, whereas gross pollutant traps cannot on their own. Check out our Gross pollutant trap here, the ECOPROTECTOR

They are able to use gravity separation processes to capture oil if it is present as a dissolved pollutant. Using the simple process of gravity separation, once the stormwater enters the silt chamber and settles, the oil rises to the top of the stormwater and separates due to the density differences. Due to the placement of the outlet riser, the oil is unable to rise out of the outlet and is trapped. This oil can be removed through vacuum truck maintenance removal.

If there is a need to remove hydrocarbons and oils from the stormwater being treated, coalescing systems and oil separators are recommended to be used. Common examples and further information on oil separators and coalescing systems can be found here.