Analysis of water quality and evaluation of water pollution during drainage and consolidation of dredged sediment

We carried out a series of tests to analyze the water pollution characteristics in drainage and consolidation process of dredged sludge. We first analyzed the grain proportion and its variation law of the soil sample, and studied the sedimentation and sorting features of particles in the dredge disposal site. The concentration and variation law of organic and inorganic pollutants in the drainage water were tested and studied. The studies show that the dredged soil, with larger specific-surface area and strong adsorption ability, is mainly composed of silt and clay. In the disposal site, an annular flow with differential head is formed by arranging overflow dam and longitudinal separation levee, which is conducive to the sorting and sedimentation of the particles as well as the adsorption of contaminants. Under the vacuum negative pressure suction, the drainage water, suspended solids and pollutants are sucked out to pipe network. Water pH change fluctuation is small, which meets the quality standards for surface water. The vacuum preloading technique can block, filter and adsorb suspended solids and pollutants and reduce SS value. Also the vacuum negative pressure suction is favorable for nitrogen dissolving and enrichment, but exerts little effect on total nitrogen (TN). Techniques like pipeline blocking adsorption, tail water precipitation and aquatic plant filter are effective to phosphorus dissolution and absorption, so the total phosphorus (TP) is decreasing and total dissolved phosphorus (TDP) is increasing, and total phosphorus (TP) in the discharge water is not worse than Ⅲ standard of lake and reservoir water. The water pollution index has been improved from nearly qualified to fully qualified.