Experimental Investigation on the Relationship Between COD Degradation and Hydrodynamic Conditions in Urban Rivers.

Due to extensive pollution and the relatively weak flow replacement in urban rivers, determining how to fully utilize the self-purification abilities of water bodies for water quality protection has been a complex and popular topic of research and social concern. Organic pollution is an important type of urban river pollution, and COD (chemical oxygen demand) is one of the key pollution factors. Currently, there is a lack of research on the relationship between COD degradation and the flow characteristics of urban rivers. In this paper, COD degradation experiments were conducted in an annular flume with Jinjiang River water at controlled flow velocities and the COD degradation coefficients under different hydraulic conditions were analyzed. A good correlation was observed between the degradation coefficient and hydraulic conditions. According to dimensional analysis, the relationship between the COD degradation coefficient and hydraulic conditions such as the flow velocity, water depth, Reynolds number (), and Froude number () was established as K COD = 86400 u h F r 0.8415 R e - 1.2719 + 0.258 . The COD degradation coefficients of the Chishui River in Guizhou Province ranged from 0.175-0.373 1/d based on this formula, and the field-measured values varied from 0.234-0.463 1/d. The error in the formula ranged from 5.4-25.3%. This study provides a scientific basis for the prediction of the COD degradation coefficients of urban rivers.