Electron donating capacities of DOM model compounds and their relationships with chlorine demand, byproduct formation, and other properties in chlorination.

Electron donating capacity (EDC) is a promising parameter to characterize the antioxidant properties and oxidant consumption of dissolved organic matter (DOM). To assess the potential of EDC in rapidly predicting the chlorine demand during chlorination, the EDC values were measured for ten DOM model compounds, including phenol, quinol, resorcinol, vanillin, tannic acid, l-phenylalanine, l-tryptophan, l-tyrosine, l-cysteine, and reduced glutathione. The EDC values varied according to the functional moieties present in the model compounds and the pH. At pH 7.0, the order of EDC values of the ten model compounds was (mol e-/mol C): 0.843 (cysteine) > 0.538 (tyrosine) > 0.522 (tannic acid) > 0.516 (resorcinol) > 0.452 (phenol) ≈ 0.450 (tryptophan) > 0.257 (vanillin) > 0.226 (reduced glutathione) > 0.160 (quinol) > 0.00035 (phenylalanine). The EDC values correlated well (R2 = 0.93) with the 24 h Cl2 demand of the model compounds (except for phenol and tannic acid). By contrast, there was poor correlation between the EDC values and the 24 h formation potentials of chlorination byproducts (trihalomethanes, haloacetic acids and haloacetonitriles). The levels and variation of the EDC values were not significantly correlated with the total organic carbon, specific UV absorbance at 254 nm, or assimilable organic carbon of the model compounds.