Characterization of isolated fractions of dissolved organic matter from natural waters and a wastewater effluent

Dissolved organic matter (DOM) was concentrated from natural waters and the effluent of a wastewater treatment plant using a portable reverse osmosis (RO) system. The humic acid (HA), fulvic acid (FA) and hydrophilic (HyI) fr actions were isolated and purified by the XAD-8 resin combined with the cat ion exchange resin method. The FA fractions predominated in natural waters and accounted for 54-68% of the total amount of dissolved organic carbon (D OC), whereas the HA and HyI fractions constituted, respectively, 13-29 and 9-30% of the total DOG. The effluent of wastewater was almost devoid of HA and the HyI fraction exceeded FA. The elemental compositions of HA and FA w ere in the ranges typical for natural humic materials, but the HyI fraction s did nor exhibit humic character. H-1 NMR spectra revealed that the HyI fr actions were almost devoid of aromatic protons and the aliphatic region fea tured more sharp signals than HA and FA fractions, indicating that HyI frac tions were consisted of more simple compounds and less complex mixtures. Th e aliphatic functional groups in these fractions of DOM samples followed th e order HA < FA < HyI. Proton titrations indicated that HA, FA and HyI frac tions of DOM samples from different sources had similar total acidity whose range was 9.0-11.6 meq/g C. This similarity may be due to the sample fract ionation method. The copper titration results showed that the number of tot al Cu binding sites for the three fractions of different DOM samples were g uile similar (1.46-1.60 mmol/gC), which was consistent with the similarity in total acidity from proton titrations. The affinity of copper with each i solated fraction followed the order HA approximate to FA > HyI. The rate of Cu complexation with the HyI fraction was faster than the rate with the HA or FA fraction of the Suwannee River DOM, implying that copper reacted wit h relatively weak ligands faster than with strong ligands. (C) 2001 Elsevie r Science Ltd. All rights reserved.