Risk Assessment and Treatment of the Heavy Metals Contaminated Sediments via Stabilisation and Dewatering in Geotextile Tubes

Abstract

In this study, the heavy metals contaminated sediments were from the sewage reservoir with an area of 850,000 m2. To measure the concentrations of heavy metals in sediments, 484 grid sampling points was set with a grid size of 40 m × 40 m. The sampling depth was in the range of 0.75 - 1.5 m. The concentrations of As, Cd, Cr6+, Cu, Pb, Hg, and Ni were then measured in the laboratory. Subsequently, the single factor index and Nemerow index method were used to evaluate the potential risk of heavy metals in sediments. The results show that the maximum Nemerow index is 12.6, which is mainly from the contribution of Hg, Cr6+, Cd, and As. The total contaminated sediments were calculated as 445,634 m3, of which 336,081 m3, 85,721 m3, 23,832 m3 are slightly polluted (1 3) sediments. The combined technology, integrating the dredging, stabilisation of heavy metals and flocculation in the pipeline, dewatering in geotextile tubes, are proposed for the treatment of sediments. After dewatering, the slightly and moderately polluted sediments were artificially constructed as a landfill for further landscape planting, while the heavily polluted sediments were sent to a cement plant for further treatment. After the implementation of the project from May to December 2019, all the heavy metals polluted sediments were treated well with high stability and low environmental risk.