Characterization of natural organic matter as major constituents in aquatic systems

Abstract

Natural organic matter (NOM) is ubiquitous in global aquatic systems, the mass concentrations ranging from 0.5 to 100 mg/l of organic carbon. The polydispersity of molar masses and the chemical structures comprising NOM give it a multifunctional role in natural environment and in water treatment processes. Important functions include serving as an electron donor in metal complexation, sorption of xenobiotics and adsorption onto mineral phases and onto activated carbon. NOM is partially oxidized during microbial utilization and during water treatment in which it may also become substituted with chlorine leading to a suite of products with toxic relevance. Meaningful methods of NOM characterization would be useful for the development of a predictive capacity for NOM behaviour in different water sources. Among analytical characterization methods, those directly applicable to aqueous samples are most useful and in addition to classical spectroscopic methods, more advanced methods have become available within the last decade. High pressure liquid chromatography using gels have proved useful in combination with UV/vis, fluorescence, light scattering and sensitive dissolved organic carbon detection techniques, yielding information on molecular absorbance, size distribution, molar mass and reactivity. Information on biodegradability of NOM can be deduced from experimental measurement of bacterial growth under defined conditions. The nature and amount of biologically assimilable organic carbon (AOC) in combination with the bacterial cell number and growth rate constants can provide a meaningful characterization of microbial stability in aquatic systems. In addition, determination of directly available and acid or enzymatically hydrolysable amino acids and carbohydrates can add to the understanding of NOM biodegradability over different time scales. The paper gives the results obtained by the application of the different methods for the characterization of aquatic NOM and its fractions of different origin. It can be shown that the availability of advanced characterization techniques offers the potential for predicting the functionality of aquatic NOM without precise knowledge of the chemical structures present in the macromolecular complex.