Author(s): Xiaocui Li

Linked Author(s): Xiaocui Li

Keywords: Contaminated sediment backfill technology (CSBT); Ceramsite; Bed stability; Dissolved oxygen; Sediment flux;

Abstract: The sediment is widely found in natural waters such as rivers, lakes and reservoirs, which is the habitat of many benthic organisms but also accumulates a large number of toxic and harmful pollutants. The contaminated sediment will be a potential internal pollution that releasing pollutants into the overlying water under certain hydrodynamic conditions. Dredging is the most commonly used method for seriously polluted areas, whereas a lot of lands are required for the stacking of dredged sediment, and the utilization of dredged sediment as a resource is also limited. In this paper, a contaminated sediment backfill technology (CSBT) was introduced, i.e. the dredged sediment is calcined into ceramsite after dewatering process and pollutant fixation, and then backfilled to the dredged area. The size and density of the produced ceramsite is pre-determined by the hydrodynamic condition to ensure the bed stability. The potential of CSBT for controlling internal pollution was evaluated by considering the bed stability, vertical distribution of dissolved oxygen and sediment flux. The high-temperature calcining during the ceramsite production would cause decomposition of organic matter, fixation or volatilization of heavy metals, thus greatly reducing the amount and mobility of pollutants in the dredged sediment. Compared to the fine sediment before dredging, the critical shear stress for incipient motion is greatly increased after the CSBT treatment, reducing the possibility of resuspension under the same hydrodynamic condition and thus ensure a clear sediment-water interface. Accordingly, the release flux of pollutants will be significantly inhibited, i.e. from a resuspension dominated process to a turbulent diffusion process. And the high porosity and rough surface of ceramsite is benefit for the adsorption of pollutants, which is also capable of reducing the sediment flux and improving the water quality. Moreover, the depth of dissolved oxygen permeating into the sediment is enhanced, which is especially important for the benthic organisms and will affect the related biogeochemical processes. The proposed CSBT is a combination of the ex-situ and in-situ treatments, providing a new idea for the environmental and ecological restoration of rivers, lakes and reservoirs.

DOI: https://doi.org/10.3850/38WC092019-0458

Year: 2019