Dissolved organic matter from treated effluent of a major wastewater treatment plant: characterization and influence on copper toxicity.

A combination of reverse osmosis (RO) concentration and DAX-8/XAD-4 resin adsorption techniques is used to isolate the various constituents of urban dissolved organic matter (DOM) from inorganic salts. Three fractions: hydrophobic (HPO), transphilic (TPI) and hydrophilic (HPI) accounting respectively for 35%, 20% and 45% of extracted carbon, are isolated from effluents of a major French wastewater treatment plant. This atypical DOC distribution, in comparison with natural water where the HPO fraction dominates, shows the significance of HPI fraction which often gets neglected because of extraction difficulties. A number of analytical techniques (elemental, spectroscopic: UV, FTIR) allow highlighting the weak aromaticity of wastewater effluent DOM (EfOM) due to fewer degradation and condensation processes and the strong presence of proteinaceous structures indicative of intense microbial activity. Copper toxicity in the presence of DOM is estimated using an acute toxicity test on Daphnia Magna (Strauss). Results reveal the similar protective role of each EfOM fraction compared to reference Suwannee river fulvic acid despite lower EfOM aromaticity (i.e. specific UV absorbance). The environmental implications of these results are discussed with respect to the development of site-specific water quality criteria.