Trihalomethane formation potential of organic fractions in secondary effluent

Organic matter is known to be the precursor of numerous chlorination by-products. Organic matter in the secondary effluent from the Wenchang Wastewater Treatment Plant (Harbin, China) was physically separated into the following fractions: particulate organic carbon (1.2-0.45 mu m), colloidal organic carbon (0.45-0.1 mu m), fine colloidal organic carbon (0.1-0.025 mu m), and dissolved organic carbon (DOC) (< 0.025 mu m). Moreover, < 0.45 mu m fraction was chemically separated into hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N), and hydrophilic fraction (HPI). The chlorine reactivity of these organic fractions obtained from both size and XAD fractionations were evaluated. The structural and chemical compositions of the HPO-A, HPO-N, TPI-A, and TPI-N isolates were characterized using elemental analysis (C, H, O, and N), Fourier transform infrared spectroscopy (FT-IR), and proton nuclear magnetic resonance spectroscopy (H-1-NMR). Results showed that DOC was dominant in terms of total concentration and trihalomethane formation potential (THMFP), and there was no statistical difference in both specific THMFP (STHMFP) and specific ultraviolet light absorbance among the 0.45, 0.1, and 0.025 mu m filtrates. HPO-A had the highest STHMFP compared to other chemical fractions. HPO-A, HPO-N, TPI-A, and TPI-N contained 3.02%-3.52% of nitrogen. The molar ratio of H/C increased in the order of HPO-A < HPO-N < TPI-A < TPI-N. The O/C ratio was relatively high for TPI-N as compared to those for the other fractions. H-1-NMR analysis of the four fractions indicated that the relative content of aromatic protons in HPO-A was significantly higher than those in the others. The ratio of aliphatic to aromatic protons increased in the order of HPO-A < HPO-N. < TPI-A < TPI-N. FT-IR analysis of the four fractions showed that HPO-A had greater aromatic C=C content whereas HPO-N, TPI-A, and TPI-N had greater aliphatic C-H content. TPI-N contained more oxygen-containing functional groups than the other fractions.