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Surface waters in Scotland, as well as in southern Norway and southern Sweden have experienced a significant increase in NOM-concentrations and fluctuations over the last decades, likely due to the combined effects of climate variation and reduced acid rain.
NOM concentration levels and physiochemical properties vary significantly in space and time. Especially the seasonal fluctuations are site specific and therefore unique to any raw water source.
Surface waters are commonly used as raw water sources by waterworks for tap-water production in these countries. NOM in the water affect colour, taste and odour. Increasing concentrations of NOM, thus, causes increased demand for coagulant and disinfectant doses. NOM influences, furthermore, the stability and thereby the removal of inorganic particles and pathogens and increase the mobility of micro-pollutants. It fouls membranes, block filtration pores and compete for adsorption sites. In the water distribution networks, NOM influences on corrosion and leads to regrowth and biofilm formation during distribution, including house installations (e.g. problems with biofilm-amoebae-Legionella).
The increasing amount and variability of NOM concentrations and characteristics, thus, represents severe challenges for process control in water treatment and distribution systems.