Due to their heterogeneity and polydispersity, refractory organic substances (ROS) play a multifunctional role in the natural environment and in water treatment processes. Those properties also complicate an authentic analytical characterization. Since ROS are ubiquitous in natural waters and as they have the potential to form toxic disinfection by-products research aims at the characterization of their behavior in water treatment processes. Gel chromatography in combination with UV/Vis and sensitive dissolved organic carbon detection is shown to be useful, yielding information on molecular absorbance, molecular mass distribution, and reactivity. Additional experiments under defined conditions lead to information about the fate of ROS during biological, oxidation and adsorption processes. It is shown that ozonation, peroxonation, and chlorination result in partial decomposition of high molecular mass structures to low molecular hydrophilic compounds which are more bioavailable for microorganisms. In contrast to this, adsorption using activated carbon removes organic fractions of lower molecular mass, whereas the high molecular mass compounds of ROS showing relative high UV absorbance remain in solution. Based on this partial decomposition to smaller and therefore better bioavailable compounds oxidative processes can be used to improve the efficiency of waste water treatment.

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