Abstract:
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The occurrence of metals and organic compounds such as phthalates, nonylphenols
(NPs) and its ethoxylates (NPEs) in urban stormwater runoff makes it a large
contributor of pollutants to receiving waters, the pollutants’ toxicity can severely
affect the aquatic life.
This study focuses on the analysis of stormwater from an urban catchment area of 25
ha in Kärra, northern Göteborg. An automatic sampler, controlled by a flow meter,
was installed in the separate sewer system pipe that conveys the stormwater from the
catchment area to the river Göta Älv without any pre-treatment. Flow-proportional
stormwater samples were collected during four rain events. Sediments from the side
of the road and from a ditch draining of the catchment area were also collected. The
stormwater samples were analyzed to find the total metal concentrations and eight
conventional water quality parameter, whereas the sediments were screened for
organic compounds.
The substance flow model SEWSYS (Sewer System), developed in
MATLAB/Simulink, was used for simulating stormwater volumes, finding pollutant
concentrations in runoff and identifying the main pollutant sources. Two versions of
SEWSYS were used, the second being an adaptation including organic compounds in
the simulation. The simulated site mean concentrations (SMCs) were compared with
the concentrations found in the analysis of stormwater. It was seen that the main
sources were roofs for zinc (Zn) and atmospheric deposition and pollution from
diverse areas for lead (Pb) and copper (Cu), SEWSYS tends to underestimate the
loads of Zn and Cu but overestimates Pb.
The metal concentrations and organic compounds in sediments were compared with
results from other studies. It was found that in Kärra concentrations were comparably
lower than those found in Gårda and Järnbrott stormwater treatment facilities.
The organic substance fluxes from the sources to the sampling catchment were
calculated using the SFA methodology. The loads of organic substances were
calculated using factors describing the emission of phthalates and nonylphenols from
different sources in urban areas together with results from the detailed classification
and quantification of sources in the area. The flow analysis showed that annual fluxes
in stormwater of the phthalates DEHP and DINP were ~ 2000 g respectively. The
annual loads of Nonylphenols were ~100 g. The comparison with the SEWSYS
simulation for the month of November and the calculated fluxes for a month showed
lower values for the simulation of phthalates but extremely higher results for the
simulation of Nonylphenols. Sediment samples verified the occurrence of these compounds and a comparison with results from other studies showed that
concentration levels are low. The sediments from the detention dike were found to be
more polluted than the sediments collected from the side of the road. |