Influence of Humic Substance in Solids on the Measurement of Oxygen-Consuming Organics of the Yellow River

The Yellow River has a high content of solids. The influence of solids on the measurement of oxygen-consuming organics (OCOs) such as chemical oxygen demand (COD(Mn)) has aroused attentions in recent years. However, no research about effects of humic substance in solids on the determination of COD(Mn) has been reported. Experiments have been carried out to study the influence of humic substance in solids (Loess soil) on COD(Mn) in this research. Several significant results have arisen from the study. (1) The total COD(Mn) of water sample including liquid and solid phases increased significantly with the increase of solid content; the COD(Mn) of liquid phase of water sample under pre-treatment with acid (LPUPA) also increased significantly with the increase of solid content while that without pre-treatment did not increased significantly. (2) With the increasing of solid content, the total BOD(5) of water sample increased much slower than the total COD(Mn) and the COD(Mn) of LPUPA. (3) The humic substances in solids contributed greatly to the total COD(Mn) of water sample. When the solid contents were 7.5 and 15.0 g/L, the humic substances in solids accounted for 15.9% and 17.1% of the total COD(Mn) of water sample, respectively; fulvic acid-one of the main compositions of humic substance-contributed to 23.6% and 46.3% of the COD(Mn) of LPUPA, respectively. (4) The humic substances can hardly be biologically oxidized under natural conditions, the COD(Mn) of LPUPA and the total COD(Mn) of water sample exaggerates the oxygen-consuming organic contamination of the Yellow River. Therefore, COD(Mn) was not suitable for being regarded as a parameter reflecting the pollution degree of OCOs in river water with a high solid content.