Assimilable organic carbon in molecular weight fractions of natural organic matter.

Assimilable organic carbon (AOC) in natural organic matter (NOM) has been measured in three Norwegian waters. The AOC measurement has been done on unfiltered and membrane-filtered (molecular weight (MW) cut-off of 1000 and 10,000) samples. While the colour in the waters is mainly related to the NOM with MW > 10,000, the AOC was mainly related to the NOM with MW < 1000. The fraction of the NOM with MW < 1000 corresponds to 16-38% of the total organic carbon (TOC), and 4-9% of the colour. This shows that a water treatment process removing the colour and a large part of the TOC in the water will not necessarily result in a reduction in the biofilm formation potential.