Characterisation of pollutants in stormwater treatment facilities

Sammanfattning: The overall objective of this thesis is to increase the knowledge of both the pollutants within stormwater treatment facilities and the maintenance of these facilities. This objective has been achieved by studying water and sediment with respect to metal concentrations, fractionation, and toxicity from ponds, sedimentation tanks, and gully pots with different catchment characteristics as well as from the sediment removal process.The results showed that, in all facilities, the metals in the standing water were predominantly attached to particles. In the sediment, the ponds showed the highest concentrations of metals and percentages of fine particles followed by sedimentation tanks and gully pots. Two of the ponds and one sedimentation tank had elevated concentrations of Cu, Ni, and Zn in the sediment compared to the other studied facilities, concentrations that are consistent with these facilities being influenced by the highest traffic loads. In general, the metal fractionation between the facilities differs where the ponds have more metals in the mobile fraction than the sedimentation tanks and gully pots. All facilities showed that Cr was the least available while Cd was the most available in the ponds, Zn in the sedimentation tanks, and Cu in the gully pots. The results showed that for most metals, the oxidizing and reducing conditions would be most critical with respect to the release of metals from sediments. However, the results from the metal fractionation showed that, for all treatment facilities, between 45-96% of the metals (except Cr and Ni) were in potentially mobile form and could, therefore, be a threat to the environment if the facilities are not maintained properly. The results showed that facilities with similar catchment areas have similar metal concentrations, particle-size distributions, and fractionation in the sediment. The toxicity test showed that of all the facilities, the standing water in only one gully pot in the residential area showed a toxic response to the bacteria, Vibrio fischeri. The sediment showed toxic response in all facilities where the ponds had the highest toxicity followed by the sedimentation tanks and gully pots. Both water and sediment from all of the studied facilities exceed one or more of the compared guidelines. In general, the metal concentrations and guidelines for water and sediments were not consistent with the results from the toxicity test. Therefore, to accurately evaluate the environmental impact of pollutants trapped in stormwater treatment facilities, it is important to carry out both chemical analyses and toxicity test. These stormwater treatment facilities need to be maintained in order to function properly; therefore, the sediment must be removed. During the sediment removal from the gully pots and the pond, the concentration in the water phase increased and became more hazardous after the sediment removal compared to before. The gully pots in the residential area had higher metal concentrations in the water phase than the gully pots receiving only road runoff. The sediment phase, however, did not show a large difference in concentrations between before and after the sediment was removed. Due to the high metal and PAH concentration in the removed water, the water should not be poured back to the gully pot and based on the results, an annual cleaning of the gully pot is recommended. The identification of sources in gully pot water and sediment shows that the metals Cu, Pb, Zn, Ni, Cd and Hg and PAHs were enriched in the gully pots, which indicates that they probably come from anthropogenic sources.