An investigation of fluorescent organic matter in water during springtime at Borgunda water treatment plant
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Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Infrastructure and environmental engineering (MPIEE), MSc
Publicerad
2023
Författare
KARLSSON, EIRA
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
An analysis of fluorescent organic matter was performed at Borgunda drinking water
treatment plant. The plant draws water from the lake Vättern and provides about
100 000 consumers with drinking water. Previous spring seasons, the plant experienced
problems with their sand filters being clogged and occasionally complaints have been
made about an unpleasant taste and odour from the water. It is likely that these problems
are caused by organic matter such as algae bloom. The objective of the thesis was to
investigate how the composition of the water changed over time, how it changed over
sand filters and if the sand filters gave different results.
The aim of the thesis was to investigate the composition of dissolved organic matter
(DOM) at the intake of the raw water, before and after sand filtration at Borgunda
treatment plant, using fluorescence spectroscopy. In addition to this, three hypotheses
were formulated such as; the fluorophore signal will increase with warmer
temperature, with eastern wind direction and the presence of algae can be linked to
operational problems in the sand filter.
To investigate, a sampling campaign was performed at seven occasions during the
spring season at the raw water, incoming water to the plant, outflow of each sand filter,
after UV radiation and of the outgoing water. The samples were analysed in the
laboratory by using fluorescence, absorbance, and dissolved organic matter
measurements. The PARAFAC model was applied and showed that chlorophyll was
found in the raw water, incoming and outgoing water. Two components above
wavelengths of 550 nm were found that likely correspond to more than one algae
species. During a visible pollution event on the surface in one of the sand filters,
samples were also analysed in microscope and found diatoms and green algae. The
removal performance of the sand filters was analysed, and results indicate that there are
biofilms in the sand filters that during the sample period sometimes produce material
that increases the fluorescence signal. Sand filer 2 most frequently had worse removal
or was producing stronger signals when compared to the other sand filters. Sand filter
3 overall had the best removal performance over the sampling period.
No clear connection could be found between the increasing temperature and increased
signal in fluorescence components. The eastern wind direction could however be linked
to increased signals and is a possible explanation for increased organic material, causing
problems in sand filters. Future studies are recommended to investigate the impact of
snowmelt and increased flow in runoff streams, that bring nutrient and enables
phytoplankton growth in, on surface waters used as drinking water sources.
Beskrivning
Ämne/nyckelord
Organic matter Drinking water Vättern Fluorescence Algae Phytoplankton