Over the past three decades, increasing concentrations of dissolved natural organic matter (DNOM) have been observed in Nordic surface waters. This increase has an effect on the natural environment because DNOM impacts the water chemistry in surface waters through its chemical characteristics and ecosystems through being a source of food for organisms. Moreover, surface waters are used for drinking water and therefore this increase in DNOM has a negative effect for waterworks. It is important to investigate DNOM in the environment to understand its environmental effects and to predict future impacts from DNOM.
This study had two main objectives: to create an absorbent material that will selectively absorb DNOM from water and to improve methods for studying the biodegradability of DNOM. An already developed absorbent material, swellable-organically modified silica (SOMS), was modified with polyethyleneimine (PEI) so that it was selective toward DNOM. After several absorption experiments, it was determined that the material was able to selectively bind humic substances (high molecular weight part of DNOM with more aromaticity) but did not absorb the fulvic substances (lower molecular weight DNOM with more aliphatic character). This material could be further improved to become an effective absorbent for removing DNOM from water.
The amount of nutrients used in studying the biodegradation of DNOM was examined. Nutrients with a ratio of 2N: 1P were compared with 3.54N: 1P to look at different amounts of nitrogen to phosphorous and how it affects respiration rate. It was determined that using 3.54N: 1P ratio nutrients in the biodegradation experiments significantly lowers the biodegradability in the samples and therefore gives a lower signal. The use of 2N: 1P should be used in future biodegradation experiments to have better signal in the experiments. This method improvement is important for accurately characterizing DNOM.