In-situ Chemical Oxidation For TPH Contaminated Site In Dalian

Total petroleum hydrocarbon?TPH?is a widespread pollutants of urban industrial relocation sites and is strongly harmful to environment and people.For the effects of carcinogenic,teratogenic and mutagenic,how to quickly and effectively repair a TPH contaminated soil at the site is necessary,and also a difficult problem.Chemical oxidation technology is a fast and effective method to repair TPH contaminated soil,the key of which is the choice of oxidant and the application.The contaminated site of this research is in Dalian,Liaoning province.Through the investigation and risk assessment,we identified the type of pollutants,screening for the venue for the repair of oxidative agents in combination,and to study the best way of application.Repair effect,influencing factors and the mechanism of oxidation is investigated.Soil remediation equipment is used to simulate the process of oxidantion on the ground surface and deep soil.Probe chemicals is used to detective the process of migration and transformation rules.Last we design the in-situ chemical oxidation remediation technology plan of the site.The main results of this study as follows:?1?Through the investigation of natural geographical environment,hydrological and geological characteristics of the contaminated sites,we determined the production condition of the enterprise and organic matter and heavy metals in soil and groundwater.The soil TPH concentration ranged from 19.8 to 52500 mg/kg.Risk assessment calculated soil TPH repair target value is 1000 mg/kg and the repairing area were Sludge and enterprise solvent storeroom in surface layer?0²0 cm?,Iste warehouse?0⁴30 cm?and Sludge treatment in the surface layer?0⁶0 cm?,repair earthwork is 3168.4 m3.The key repair area is Iste warehouse and the surface product 615.7 m2 and repair earthwork is 2647.5 m3.?2?Through the calculation and the experimental analysis of commonly,the stability of soil natural oxidant demand,underground environment and mass transfer characteristics,repairing costs and natural field conditions factors,we chose sodium sulfate?Na₂S₂O₈?for the site remediation.Different methods of activation showed that adding Fe²⁺/citric acid?CA?is the most effective,Na₂S₂O₈ investment quantity in 2 mmol/g soil is suitable and TPH degradation is higher by adding for once than sequencing added.Soil p H had little effect on the removal of TPH by Na₂S₂O₈ oxidation.The study on the Fe²⁺ removal of TPH in soil by using the probe compound at different time nodes is indicated that: The activation of Fe²⁺/CA is fast,30 min reaction is basically completed,the main substance of the TPH degradation is SO4-· and ·OH,natural reducing substances produced in soil which promoted the TPH degradation.Na₂S₂O₈ /Fe²⁺/CA can be injected into the ground to remediate the deep TPH contaminated soil.?3?Using the combination of Na₂S₂O₈ /Calcium oxide?CaO₂?/Fe²⁺/CA to repair site surface TPH contaminated soil,to overcome the defects of soil acidification and the highly produced by-product SO42-.The results shows: using the combination of Na₂S₂O₈ / CaO₂ alone,the molar ratio of 2.5 is more appropriate,and the removal rate of TPH is 67.4%.Using Na₂S₂O₈ /CaO₂/Fe²⁺/CA method,when the molar ratio is 5/2/1/1,TPH degradation rate reached to 82.1%,after the reaction of the soil system p H is neutral,increase the content of TPH,CaO₂ in the soil removal rate can be further improved.TPH in the soil water is very little,SO42-is removed by the ways of CaSO4.Mechanism study showed that treatment with Na₂S₂O₈ /CaO₂/Fe²⁺/CA,the reaction is more moderate,168 h reaction is basically completed,TPH degradation process is not only the role of SO4-· and ·OH,CaO₂ also in the direct oxidation.?4?In order to obtain the parameters and conditions of in-situ chemical oxidation remediation,the soil of contaminated sites is collected by self-made soil remediation equipment.Using The methods of surface mixed soil,leaching,injection well injection,groundwater extraction preparation and oxidation agent solution recycling to simulated the process of in situ chemical oxidation.Results shows: Na₂S₂O₈ is capable to transport in the simulation of soil,after the in situ injection,Na₂S₂O₈ is migrated to the saturated layer in 3 days,it will continue to enter the saturated layer and vertical migration to the horizontal and vertical migration,the saturated layer after 7 days.In the condition of creep pump pressure 10 m L/min,flow rate 0.2 Mpa,the groundwater flow rate 0.08 m/d,continuous injection of 7 days,the impact radius is 0.4 m.The method of mixing CaO₂/Fe²⁺/CA with soil and spraying Na₂S₂O₈ can effectively repair the surface contaminated soil,and the longitudinal migration of Na₂S₂O₈ in the reaction process can further strengthen the repair of the upper layer soil.The bottom soil TPH degradation rate of injection after 7 days reached the highest,with an average of 95.6% and upper soil TPH degradation rate in the leaching after 20 days to reach a highest,with an average of 98.5%.Due to the buffering of soil,the effect of Na₂S₂O₈ on the p H and temperature of different soil layers is small,but it is affected by the environmental factors.?5?Based on the site investigation and the technical parameters of the pilot test,the technical scheme of in-situ chemical oxidative remediation of TPH contaminated soil is designed.The remediation method of surface soil?0⁶0 cm?is in-situ soil mixing and leaching,repair agent is Na₂S₂O₈/CaO₂/Fe²⁺/CA.The remediation method of deep soil?60⁴30 cm?is in situ injection,repair agent is Na₂S₂O₈ /Fe²⁺/CA.