Dissolved Organic Matter increase and its impact on Polarity and aromaticity

The objective of this study was to assess whether the increase of NOM (natural organic matter) reported for natural waters in various countries could be observed for Suezenvironment water resources. Long term data for TOC, oxidability, colour, turbidity and other physico-chemical parameters were retrieved from 23 sites mostly in France (18), UK (3), Germany (1) and North America (1). Evolution curves were plotted for the available parameters. 13 out the 23 sites studied revealed an increase of NOM measured as total organic carbon. Sites showing a NOM increase were located in North America, UK and France, suggesting a worldwide phenomenon. This increase was often accompanied by an increase in water temperatures, a likely consequence of global warming. Permanganate oxidability did not always follow the same trend as TOC or UV absorbance, suggesting a change in the character of NOM. For these sites, TOC increased at a rate of 0.1 to 0.4 mgL/year. When extrapolated over the next 20 years, this would imply an increase of NOM by 15 to 100%. In an attempt to mimic possible changes of NOM character with NOM increase, waters showing a wide range of NOM levels, spanning from 1 to 23 mg/L of DOC, were characterized using the recently developed Polarity Rapid Assessment Method (PRAM), UV absorbance and 3D-fluorescence spectroscopy. No trend could be found between polarity/hydrophobicity-anionic character as a function of NOM level, suggesting that an increase of NOM should not imply a higher difficulty of treatment other than a requirement for higher reagent doses. The UK waters consistently showed an unusual and yet unexplained behavior with respect to their retention on weak and strong ion-exchange resins. On the other hand UV and fluorescence spectroscopy revealed a higher aromatic character and a higher degree of humification for waters with high DOC levels. This higher proportion of humic substances needs to be removed by the treatment process prior to disinfection to avoid forming excessive levels of disinfection-by-products. NOM increase in water resources seems to be a worldwide phenomenon that will have a drastic effect on water treatment in the next two decades and hence deserves further monitoring.