Laboratory Studies On The Remediation Of High Concentration Organic Contaminated Soil By STAR Technique

Due to the improper use and leakage of oil storage tank explosion,oil storage equipment and oil pipelines,a large number of high-concentration petroleum pollutants enter the underground environment,forming a long-term and high concentration organic pollution source which has caused great harm to production and life of people.Among the soil remediation techniques,STAR remediation technique has advantages for removing high concentration organic pollutants.Because it has the advantages of low capital and operating costs,short remediation time and high removal efficiency,compared with physical and bioremediation techniques which have high capital and operating costs or harsh conditions and take a long time.STAR remediation technique has been put forward by foreign scholars.This technique is similar to the smoldering combustion of solid materials.Smoldering combustion is the exothermic oxidation of a condensed phase occurring on the fuel surface.Importantly,smoldering can be self-sustaining without energy input required after ignition when the fuel is embedded in a porous medium.The peak temperature and its appearance time have a great influence on the smoldering combustion products of coal tar.This paper presented the sensitivity of the process to a range of effect factors,including contaminant concentration,soil type,air flow rate and moisture content through one dimensional simulation column experiment.The changes of peak temperature occurrence time,peak temperature and propagation velocity of coal tar smoldering combustion in contaminant concentration,soil type,air flow rate and moisture content were analyzed,comparing the peak temperature and the occurrence time of coal tar smoldering combustion under different influencing factors.Further discussion the diffusion distance of coal tar under smoldering combustion conditions.When the concentration of coal tar is low,the chemical energy by the smoldering combustion of coal tar is not sufficient to support a self-sustaining smoldering reaction.At this time,consider utilizing vegetable oil as supplemental fuel for STAR technique,discuss the feasibility as supplemental fuel,determine the minimum coal tar concentration that can support a self-sustaining smoldering reaction,identify the effect factors of STAR technique to remove contaminants.The specific research results are as follows:(1)Smoldering combustion can not self-sustain when the concentration was lower than 80 000 mg/kg.Smoldering combustion is observed to be self-sustaining in the range 80 000 mg/kg to 110 000 mg/kg for coal tar despite increases temperatures and decreases peak temperature occurrence times and propagation velocity.Smoldering combustion is observed to be self-sustaining in the range of 1-6 mm for soil type despite increase first and then decrease increases temperatures and propagation velocity.But soil type has little effect on peak temperature occurrence time.Propagation velocity is observed to be highly dependent on air flow rates.Smoldering combustion can self-sustain in the range 2 cm/s to 10 cm/s for air flow rates despite decreases peak temperature occurrence times.The process remains self-sustaining and achieves effective remediation across a range of initial moisture content despite extends peak temperature occurrence times and decreases temperatures and propagation velocity.(2)When the coal tar concentration is within the range that can maintain the smoldering combustion and the air flow rate is sufficient.The coal tar remains self-sustaining and rapidly spread the heat outward,increasing the diffusion distance of combustion.When the coal tar concentration in the ignition zone is within the range that can maintain the smoldering combustion,even if the surrounding coal tar concentration is lowered,the purpose of removing the coal tar can be achieved.(3)When the coal tar concentration is lower than 80 000 mg/kg,the coal tar can be maintained smoldering combustion by adding vegetable oil(sunflower oil,soybean oil,corn oil)and the coal tar removal rate is above 99%.Among them,corn oil as the supplemental fuel produces the highest peak temperature and propagation velocity.When corn oil is used as supplemental fuel,coal tar can support a self-sustaining smoldering reaction when the total coal tar concentration and corn oil concentration reach 50 000 mg/kg.And 30 000 mg/kg of corn oil can treat 20 000 mg/kg of coal tar contaminated sites.