Physical processes and influencing factors of contaminants release due to resuspended sediments in water environment

Abstract

Strong interaction exists in water flow, sediment movement and pollutants migration, resulting in an integrated environmental system of close contact with each other. Impact of sediment and suspended sediment on the water environment appears a combined dynamic coupling effect by complex hydrodynamic conditions. Three main ways of the pollutants entering water are studied by flume experiments. These three physical processes may be the static diffusion through sediment-water interface, the release due to sediment resuspension and the release of suspended sediment by turbulence. The results show that the sediment can be divided into two distinct muddy and sandy matters based on surface characteristics. Sediment grain size, porosity and initial contaminant amount are the main factors to determine static release of contaminants at the sediment-water interface. The pollutant quantity attenuation formula in sediment was established thereby, indicating that the contaminated attenuation time are proportional to the sediment thickness, density and distribution coefficient. The contaminant release process due to suspended sediment can be broadly divided into three stages: the initial stage, the alternating stage between suspension and settlement and the balance stage. The ratio of the solid/liquid distribution in the water body increases firstly and then decreases in the later two stages. Pollutants emission amount equations is derived based on the mass conservation law, and its contract with experimental results shows that the nature of the adsorption and desorption of contaminants to some extent alleviate the rate of its release. Water pollutant concentration distribution and velocity distribution as well as suspended sediment concentration distribution are closely related, showing the same variation. Vertical distribution difference of sediment contaminants becomes larger with the increase of flow velocity. The larger the initial sediment concentration is, the more uniform the distribution of sediment contaminants tends to be. The time to reach a uniform vertical concentration distribution takes more for sediment with smaller particle size.