Contribution of dissolved organic matter to chemical oxygen demand in three Chinese lakes and in treated sewage

Dissolved organic matter plays a significant role in determining chemical oxygen demand. Resin fractionation is the most widely used technique which isolates fractions based on their hydrophobicity and hydrophilicity. In this study, DAX-8 and XAD-4 resins were used to investigate the relationship between hydrophobic and hydrophilic organic matters and their contributions to chemical oxygen demand in three Chinese lakes and in treated sewage. In Chenghai Lake, the average chemical oxygen demand attributable to hydrophobic organic matter was 10.20 mg/L and that from hydrophilic organic matter was 3.08 mg/L. As a proportion of the total chemical oxygen demand, they were 27 and 8%, respectively. In Yangzonghai Lake, the hydrophilic organic matter contributed 42% of the total chemical oxygen demand, while the hydrophobic organic matter contributed only about 18%. In Dianchi Lake, the hydrophobic and hydrophilic organic matters adsorbed by the resins were comparable. In treated sewage, on average, about 21% of the TCOD was from hydrophobic organic matter and 13% was from hydrophilic organic matter. The ratios of hydrophobic and hydrophilic organic matters to total chemical oxygen demand in the three lakes and in the treated sewage were different, indicating the differences among the three typical major plateau lakes in chemical oxygen demand contribution origin and in pollution process.