Heavy metal removal from motorway stormwater using zeolites

The possibility of using zeolites to reduce the levels of heavy metals present in motorway stormwater has been investigated. Currently, the primary pollutant removal mechanism used in treating stormwater is retaining the large volume of stormwater in detention ponds to allow time for the contaminants (mainly those associated with particulate matter) to separate out. There is also a need to reduce the levels of heavy metals in the dissolved phase, possibly by introducing some kind of ion exchange material into the treatment facility. Batch experiments have been conducted on two zeolites (synthetic MAP and natural mordenite) to test their ability to remove dissolved heavy metals from simulated and spiked motorway stormwater. Synthetic zeolite MAP showed almost complete removal (>91%) of the studied heavy metals (Zn, Cu, Pb, Cd) from both solutions. However, the use of such synthetic zeolites could have serious environmental implications as it was found to increase sodium levels to 295 mg/l, remove calcium and increase the pH of the spiked motorway stormwater to 8.5. Mordenite was less effective at reducing the levels of heavy metals (42-89% in synthetic solution, 6-44% in motorway stormwater) and exhibited a preference for Pb>Cu>Zn approximately Cd. It is proposed that the uptake of heavy metals is partially inhibited by the other dissolved contaminants present in motorway stormwater.