[Influence of humic substance in solids on CODMn of the Yellow River]

Experiments were carried out to study the influence of humic substance in solids (Loess soil) on CODMn in the Yellow River. Several significant results were abtained from the study: (1) The total CODMn of water sample including liquid and solid phases increased significantly with the increase of solid content; The CODMn of liquid phase of water sample under pre-treatment with acid (LPWSPC) 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 BOD5 of water sample increased much slower than the total CODMn and the CODMn of LPWSPC. (3) The humic substances with the content of 0.76% in solids (Loess soil) contributed greatly to the total CODMn of water sample. When the solid contents were 7.5 g/L and 15.0 g/L, the humic substances in solids accounted for 15.9% and 21.7% of the total CODMn of water sample, respectively. (4) When solid contents were 7.5 g/L and 15.0 g/L, fulvic acid,one of the main compositions of humic substance contributed to 23.6% and 50.6% of the CODMn of LPWSPC, respectively. Since the fulvic acid can hardly be biologically oxidized under natural conditions, the CODMn of LPWSPC in water quality monitoring exaggerates the oxygen-consuming organic contamination of the Yellow River.