Pilot Trial on Endogenous Pollution Control in Hejia Ditch, Harbin: Efficacy and Mechanisms of Sediment Elutriation
To support the construction of an ecologically clean small watershed in Harbin, a pilot-scale trial of sediment elutriation was conducted in the Hejia Ditch to evaluate its effectiveness in controlling endogenous pollution and to elucidate the underlying mechanisms. After treatment, sediment organic matter, total nitrogen (TN), and total phosphorus (TP) decreased by 5.11%, 10.19%, and 8.71%, respectively. Water transparency, dissolved oxygen (DO), and oxidation-reduction potential (ORP) increased by 102.46%, 11.07%, and 15.66%, while chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) removal rates reached 35.67% and 22.65%. The technology effectively removed surface suspended sediment, leaving a stable layer of coarse inorganic particles that formed a clear mud-water interface. Post-treatment, clay content decreased by 8.87%, sand content increased by 12.37%, and median (D50) and 90th percentile (D90) particle sizes increased by 32.39% and 159.97%, respectively. Mechanical disturbance and particle size redistribution enhanced oxygen transfer at the interface, increasing the abundance of facultative anaerobic phyla such as Chloroflexi and Spirochaetes, thereby suppressing the generation of odorous gases (H2S, NH3) and preventing sediment resuspension. Increased microbial diversity and richness improved ecosystem stability and self-purification capacity. These results demonstrate that sediment elutriation is an effective method for controlling endogenous pollution in Hejia Ditch, providing a scientific basis for ecological restoration and long-term management.