The Study On Low-temperature Thermal Desorption Technology For Contaminated Soil Using Co-boiling And Co-dissolving

Thermal desorption is one of the main remediation technologies for contaminated soil and groundwater with organic pollutants.Due to the use of high temperature up to 350?600?,the energy consumption and thus the cost of remediation are very high for this technology,thus hindering its practical engineering application.It is important to achieve effective removal of pollutants by thermal desorption at low temperature.This thesis aims to use the co-boiling and co-dissolving at lower temperatures to promote the dissolution and removal of organic pollutants in the soil,so as to reduce the heating temperature and to improve the efficiency of thermal desorption.In this thesis,the removal of 1,2-dichloroethane(1,2-DCA)was firstly studied,under the condition of low heating temperature(95?),through single co-boiling treatment,co-boiling and co-dissolving combined.The solubilization effect of pyrene and anthracene in the soil and the influencing factors were then explored by the treatment of co-boiling and co-dissolving.Finally,a co-boiling and co-dissolving experimental study was carried out on the actual contaminated soil from a petrochemical site in Tianjin.The findings supported the in situ low temperature thermal desorption of organic contaminated soil with lots of experimental data.The main results are shown as follows:(1)The co-boiling treatment of 1,2-DCA in artificially contaminated soil showed that a single co-boiling treatment can effectively remove 1,2-DCA in the soil.The combination treatment of co-boiling and co-dissolving can further improve its removal effect,and the type and addition method of surfactants have a significant impact on its treatment effect.At a lower temperature(95?),the concentration of 1,2-DCA in the soil was reduced from 8700 mg/kg to 1.36 mg/kg within 2 h of co-boiling treatment,and the removal rate was as high as 99.98%;Triton X-100 was added first and then rose the temperature for co-boiling and co-dissolving treatment,the concentration of 1,2-dichloroethane in the soil can be reduced to 1.07 mg/kg within 1 h,and the cost of processing 1 kg of soil is 7.36 yuan,which is only 64%of a single co-boiling,the treatment effect is significantly better than the single co-boiling treatment,but the concentration was continuously increased to 49.38 mg/kg after continuous addition of 50 mmol/L SDS after heating;the temperature risen to the co-boiling limit before adding Triton X-100 for the co-boiling and co-dissolving treatment would also increase the concentration of 1,2-DCA,which rose to 4.05 mg/kg after 2 h.(2)The co-boiling and co-dissolving treatment of pyrene and anthracene in artificially contaminated soil showed that:a single co-boiling treatment cannot effectively solubilize pyrene and anthracene in soil.The type and combination of surfactants have a significant effect on the treatment effect,and when the surfactant concentration is the same,anthracene is more easily solubilized by the surfactant than pyrene.Solubilization effect of surfactant with 10 times the critical micelle concentration(10×CMC)on pyrene and anthracene:SDS>KANEKA·Surfactin>Triton X-100>CTAB,and add this concentration of SDS and heat to 95?,4 h of co-boiling and co-dissolving could make the concentration of pyrene in the water phase reach 0.87 mg/L,1 h could make the concentration of anthracene reach 2.79 mg/L,and the heating temperature of 15 ? and 55? had no effective effect;the added mass ratio was 1:1,10×CMC SDS/Triton X-100,heated to 95?,co-boiling and co-dissolving for 4 h,the pyrene concentration in the water phase could reach 1.46 mg/L,and the anthracene concentration could reach 4.85 mg/L within 2 h,the treatment effect is obviously better than single surfactant..(3)The co-boiling and co-dissolving treatment of anthracene and benzo[a]pyrene in the actual contaminated soil of a petrochemical site in Tianjin showed that the combined co-boiling and co-dissolving treatment can effectively solubilize anthracene and benzo[a]pyrene in the soil.The heating temperature,the mass ratio and concentration of the anionic-nonionic mixed surfactant have a significant effect on its treatment effect,and when the surfactant concentration is the same,benzo[a]pyrene is more easily solubilized by surfactant than anthracene.Adding 10×CMC,solubilizing effect of SDS/Triton X-100 with different mass ratios on anthracene and benzo[a]pyrene:1:1>2:1>3:1,and when the ratio was 1:1,the concentration of anthracene in the water phase reached a maximum of 1.89 mg/L in 1 h,and benzo[a]pyrene could reach 53.12 mg/L during the heating process;added the same ratio of 30×CMC SDS/Triton X-100 and heated to 18 min,when the temperature was 80?,the benzo[a]pyrene in the water phase reached the maximum value of 65.43 mg/L.After reaching 95?,the concentration dropped instead.It can be seen that the temperature increase process is the main period of increasing the concentration of pollutants in the water phase.Under the conditions of the same surfactant system,the benzo[a]pyrene in the water phase could reach a maximum of 98.15 mg/L after reaching the target temperature of 80? and maintaining a constant temperature for 1 h.Conclusively,low-temperature thermal desorption technology through co-boiling and co-dissolving can effectively accelerate the removal of 1,2-DCA in the soil by adding Triton X-100 at 95?,and can promote significantly the solubilizing effect of polycyclic aromatic hydrocarbon in the contaminated soil by adding SDS/Triton X-100 at 80?.