In Situ Sediment Remediation And Heavy Metal Stabilization In The Contaminated Creek:Technology Research And Application

Currently, most of the urban river has been seriously polluted in the process of urbanization. More and more ozone-depleting substances, nitrogen, phosphorus, nutrients, organic matter and heavy metal are silting up in the sediment. Fundamentally improving the quality of the river water not only need to cut off the external sources of pollution, but also address the problems of internal pollution from the sediment. In this paper, the Ronggui river was taken for example to solve the phenomenon of black-odor river and the bioavailability of heavy metals. The effect of calcium nitrate-regulatory agent on the pH-. oxidation-reduction potential (ORP)、black-odor sediment、sulfide、phosphorus、Cr(VI) in the sediments and its remediation mechanism was studied in the bath experiment. On the basis of the bath study, the calcium nitrate-regulatory agent was applied to restoring Ronggui river and its effect of repairing the black-odor river and the heavy metals were evaluated in a pilot-scale field experiment, in order to provide the basis theory and technical support for the implementation and improvement of the urban river remediation works. The mainly content and conclusions were summarized as follows:1. After dosing regulatory agent, for the non-sterile group, the pH of the overlying water and the sediment gradually increased over time, which is in the neutral range between7.1to7.5.However, the pH of the overlying water in the sterile group decreased at the addition of regulatory agent. Overall, the pH of the overlying water and sediment ranging from8.0to8.8in the sterile group which had not been treated by regulatory agent is higher than the other three groups.2. The regulatory agent can increase the ORP of the overlying water and the sediment, restore the black-odor sediment and remove the sulfide from the sediment in the non-sterile group. But the sterilization group did not produce the above results. It’s indicated that the key of increasing ORP, removing the black-odor and sulfide from the sediment by the treatment of the regulatory agent is the activity of the microorganisms which is directly inhibited or enhanced by the regulatory agent.3. With the addition of the regulatory agent, the concentration of the total phosphorus in the overlying water had shown an upward trend after the first drop in both sterilization group and non-sterile group, which indicated that the process of controlling phosphorus releasing from the sediment is the effect of the the activity of the microorganisms and the chemical reaction between the regulatory agent and the pollutants. The effect of regulatory agent on the Cr(Ⅵ) in the sediments was not obvious. The changes of the concentration of Cr(Ⅵ) may be related to the strength of sediment itself adsorption.4. In the pilot-scale study, after dosing the regulatory agent for4times, the regulatory agent did not cause secondary pollution of nitrate for the water body. The surface of the sediment gradually formed an oxide layer, which its color changed from deep black to brown within a week. Meanwhile, the concentration of sulfate in the interstitial water increased from0.56mg·L-1to4.86mg·L-1.In22days, the concentration of phosphate decreased to0.15mg·L-1and the organic matter in the sediment decreased from16.29%to9.88%,which indicated that the regulatory agent can effectively remove sulfide, inhibit phosphorus releasing to the overlying water and promote the degradation of organic matter.5. with the amendment of regulatory agent the relative abundances of the reducible fraction and oxidizable fraction of Cu、Zn、Pb and Cr were all decreased and the acid soluble fraction of the three heavy metals (Cu、Pb and Cr) were increased while Zn was decreased. After22days treatment, the percentages of the residual fraction of the four heavy metals in the sediment were increased by4%,20%,21%and23%. These results suggested that the treatment of calcium nitrate-regulatory agent could significantly change the chemical speciation and decrease the bioavailability of these four heavy metals in the sediment, which could efficiently reduce the ecological risk and enhance the bioremediation processes.