| This paper investigated and analysed the heavy metal pollution of an industrial wastewater-receiving pond in Tianjin,and carried out the human health risk assessment and potential ecological risk assessment.According to the pollution characteristics of the wastewater-receiving pond sediment,the dosage of solidifying agent and the optimization of solidifying mixing method were studied,and the leaching of metal in the limestone solidified sediment under different environmental conditions.A new modified nano-zero-valent iron immobilizing agent was developed,and its effect on the solidification of heavy metals in sediment and the activities of urease and catalase in sediment were investigated.The main heavy metals in the industrial wastewater-receiving pond sediment are Zn and Cr,which were 27.12 times and 2.47 times higher than the GB15618-2018standard values respectively.According to health risk assessment,the total carcinogenic risk and non-carcinogenic risk of industrial wastewater-receiving ponds exceeded the acceptable level.Specific risks include the carcinogenic risk of As and Cr through soil intake pathway,and the non-carcinogenic risk of As,Zn and Pb through soil intake pathway.The total potential ecological risk level of industrial wastewater-receiving ponds was very strong,and the main heavy metal elements leading to potential ecological risk were Cd and Zn.The immobilization efficiency of four common immobilizing agents,limestone,calcium oxide,phosphate and diatomite?1:2?for heavy metals?Cd,Cr,Ni,Cu,Zn?in sediment was compared.The maximum immobilization efficiency was 95%,80%,57%,82%and 85%,respectively.The optimum dosage of these immobilizing agents was 6 g/kg,6 g/kg,18 g/kg and 12 g/kg,respectively.Wet stirring was more conducive to the immobilization of heavy metals by immobilizing agents.The leaching concentration of Cd,Zn and Cr after immobilization under wet stirring was lower than that of dry stirring,and the leaching concentration of Cu and Cd could reach equilibrium in a shorter time.The immobilization efficiency of the four immobilizing agents for heavy metals could reach a stable level at 42 days.The concentration of heavy metal exudation increases with the decrease of pH.The dissolution concentration of amphoteric metals?such as Zn and Pb?increased when the pH was above 8.Reducing the redox potential?Eh from 274 mv to-251 mv?of the sediment makes the leaching concentration of Cd,Cu and Ni in immobiliazed and unfixed sediment increase.The leaching concentration of limestone-solidified sediment at different pH and Eh was lower than that of non-solidified sediment.Compared with other environmental conditions,solid-liquid ratio has less influence on leaching concentration of limestone solidified sediment.Humic acid could promote the leaching of Cr and Cu from sediment,but has no obvious effect on the leaching concentration of Cd and Ni.Low concentration of humic acid(<10 mg·L-1)reduced the leaching of Zn,but high concentration of humic acid(10-50 mg·L-1)promoted the leaching of Zn.Low concentration of humic acid(<10 mg·L-1)increased the leaching of Pb,while high concentration of humic acid(10-50 mg·L-1)inhibited the leaching of Zn.Modified nano-zero-valent iron immobilizing agent was successfully prepared.The immobilization efficiency of 0.1%nano-zero-valent iron for Cr,Ni,Cu and Zn elements was better than that of several commonly used immobilizing agents,reaching 83.4%,76.9%,66.4%,90.5%respectively,and 94.8%for Cd,which was only lower than phosphate.According to the morphological distribution of BCR,the modified nano-zero-valent iron has better immobilization effect on Cd,Cr and Zn.Modified nano-zero-valent iron does not cause sediment hardening,and can improve the activity of urease and catalase in sediment,and maintain the ecological activity in soil. |
PDF Full Text Request