Removal of Metals from Stormwater in Rain Gardens with Different Sorption Materials
Ladda ner
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Infrastructure and environmental engineering (MPIEE), MSc
Publicerad
2023
Författare
JARDEBY, ANDERS
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Polluted stormwater is a common problem in urban environments. With large parts of
cities made up of impermeable areas and an expected increase of heavy rain, this is an
issue that likely will get more attention in the coming years. In order to relieve pollution
effects on the aquatic ecosystems’ stormwater treatment alternatives must be
developed. One possible treatment system is rain gardens, where polluted stormwater
can be treated by both infiltration and retention techniques. This project was carried
through at a pilot rain garden located in Gårda where stormwater from the catchment is
treated in bioretention filters with different sorption materials such as ash, biochar, peat,
and a control filter with compost. Three types of sampling were done, one after that
different amounts of water volumes were added and then the effluents were sampled,
the second at different depths in the filter beds through soil-water samplers under
vacuum, and the third through passive sampling from a pipe inserted in the filter bed at
the corresponding depths as the soil-water samplers. Sampling was carried out during
winter conditions when the plants in filter beds were believed to be inactive. Three
sampling occasions were done of treated stormwater per sampling method and the
untreated stormwater, i.e., the influent The concentrations of eight metals, As, Pb, Cd,
Co, Cu, Cr, Ni, and Zn, both dissolved and total metal concentrations, were analysed in
all samples and additional analysis of TSS, VSS, IC, TOC, and TN were conducted in
the laboratory. The results showed high removal capacities of the metals mostly
occurring in high concentrations in urban stormwater such as Co, Cu, Ni, and total Pb
and Cu. Arsenic in general and dissolved Pb, Cd, and Cr were not effectively removed,
instead, these metals leached from all filters. Three metals, Cu, Cr, and Zn had
concentrations exceeding the guideline values of the Gothenburg municipality for
discharge of polluted water to recipients from all filters. The removal efficiency of total
suspended solids (TSS) and volatile suspended solids (VSS) was high in all filters
whereas the removal efficiency of cations, anions, dissolved organic carbon (DOC),
and dissolved total nitrogen (TN) varied among the different filters. Of the four filters
studied, biochar was the most efficient for the removal of metals and organic matter,
and the remaining three filters performed quite similarly. The conclusion of this thesis
work is that biochar filters are recommended for the removal of TSS, VSS, and metals
emitted in urban environments. Further research is recommended to clarify why some
metals,such as Asleach from the soil and sorption materials. The results for the removal
efficiency of anions, cations DOC, and TN were inconclusive and further studies are
recommended.
Beskrivning
Ämne/nyckelord
Stormwater treatment, bioretention filters, toxic trace metals, winter conditions, biochar, peat and ash