| The results of the report on the national general survey of soil contamination in2014 showed that the total exceeding rate of soil was 16.1 %.At present,the overall situation of soil environment in China was not optimistic,and soil pollution has attracted wide attention.Among them,organic polycyclic aromatic hydrocarbons（PAHs）and their derivatives in soil had mutagenesis,carcinogenesis and teratogenesis effects.The heavy metals adversely affect the natural environment and human health through continuous long-term interactions and sequential enrichment in the food chain.Therefore,there is the current research hotspots for the integrated removal of soil organic matter and heavy metal contamination.The decontamination technology of soil organic-heavy metal composite contamination,which mainly includes improved soil imported from other places,thermal desorption-solidification method,washing/oxidation-electrical joint remediation,microorganism-plant joint remediation,etc.These removal methods have certain removal efficiency for soil organic-heavy metal compound pollutants,but there are problems that need further improvement.For example,thermal desorption was only suitable for the treatment of organic and metal pollutants with high volatility;the improved soil imported from other places method was prone to secondary contamination due to the difficulty of completely eradicating soil contaminants;washing/oxidation-electric remediation fails to completely remove contaminants while requiring more energy and money.;microbial-plant combined remediation not only required a long remediation time,but was only suited for soils with low concentrations of complex contamination.In recent years,leaching remediation technology has been regarded as one of the soil pollution remediation technologies with integrated removal of multiple pollutants,simple process equipment,thorough removal of pollutants,and low operating costs.However,the washing efficiency of this technology was not ideal for cohesive soil,required multiple washings,difficult solid-liquid separation,large amount of detergent,high price,difficult to recycle and difficult to degrade.Therefore,the application of this technology was limited.Therefore,in this paper,microbubbles with small particle size,large specific surface area,and small bubble density were bubbled into the washing liquid during the washing process,and various detergents were coupled to achieve strengthening and simultaneous removal of complex soil pollutants.At the same time,it was desirable to enrich pollutants by means of air bubbles and reduced the concentration of pollutants in the washing liquid.The main research conclusions were as follows:（1）The microbubble-coupled detergent greatly improved the removal rates of fluorene and pyrene by 28.87% and 13.40%,respectively.The solubilization and washing effects of the three surfactants on PAHs（fluorene and pyrene）were TW-80>SDS>SDBS.When the microbubbles were introduced,the removal rate of fluorene and pyrene by TW-80 with the increase of time,TW-80 concentration,liquid-solid ratio and gas-liquid volume ratio;acidic was better than alkaline,decreased with the increase of salinity,first decreased and then increased with the increase of hydrothermal carbon.The addition of hydrothermal carbon willed adsorb a large amount of organic pollutants,reduced the concentration of pollutants in the washing liquid,and reduced secondary pollution.When the washing time was 120 min,the TW-80 was 4 g/L,the solid-liquid ratio was 1:25,the gas-liquid ratio was 1:1,and the p H was 5,the removal rates of fluorene and pyrene were 84.15% and 72.36%,respectively.（2）The microbubble-coupling mixed detergent could also greatly improve the removal rates of copper（Cu）and cadmium（Cd）by 27.28% and 34.96%,respectively.Removal rate of heavy metals by microbubble coupled mixed detergent increased with time,EDTA-2Na and TW-80 concentrations,solid-liquid ratio and gas-liquid ratio first,then reached the maximum,and decreased with the increase of p H,and the modified hydrothermal.The addition of carbon willed inhibit the strengthening effect of microbubbles,and a higher amount of hydrothermal carbon can be added to achieve a higher removal rate.When the washing time was 120 min,the EDTA-2Na was 1 g/L,the TW-80 was 2 g/L,the solid-liquid ratio was 1:30,the gas-liquid ratio was 1:3,and the p H was 3,the desorption of Cu and Cd removal rates were 86.67% and 85.52%,respectively.Microbubble enhanced washing mainly removes the acid-soluble（F1）and reducible（F2）forms of heavy metals in the soil,thereby reducing their damage to the soil ecological environment.（3）When the washing time was 120 min,the EDTA-2Na was 1 g/L,the TW-80 was 6 g/L,the solid-liquid ratio was 1:25,the gas-liquid ratio was 1:3,and the p H was5,The removal rates of fluorene,pyrene,Cu and Cd were 82.59%,72.45%,75.51%and 90.93%,respectively.Comparing the simultaneous washing and step washing of complex pollutants,it was found that the removal rate of pollutants was not much different.Compared with synchronous washing,step washing had higher soil acidity,more cations（CEC）in soil,and increased possibility of sandification;however,hydrothermal carbon could remove fluorene and pyrene contamination in washing liquid and microfoam liquid through chemical adsorption.From the perspective of washing liquid regeneration and water treatment,step-by-step washing was more scientific.（4）The main reasons for the removal of PAHs and heavy metals in soil by microbubbles coupled with detergents were the "solubilization" of TW-80 to remove PAHs and the "complexation" of EDTA-2Na to remove heavy metals;microbubbles were small in size,strong in stability,destroy soil viscosity,so promote soil desorption of more pollutants;microbubbles had large specific surface area and strong hydrophobicity,which could "adsorb" and "carry" organic pollutants and heavy metal complex substances,breaking the soil-pollutant-detergent gap balance,increasing soil desorption of pollutants. |
