Study On The Disturbing Effect Of Porous Media During Air Sparging In Sand Matrix

Water resources are the earth resources we depend on for survival.In recent years,with the rapid development of social economy,the pollution of soil and groundwater is becoming more and more serious,so pollution repair is imminent.Air Sparging?AS?is a technology of removal of volatile organic compounds?VOCs?pollutants from underground by injecting air in groundwater.It is widely used because of its low-cost and high-efficiency.It is one of the most popular in situ remediation technologies.However,the theoretical research of AS is far behind the engineering application in the world.Therefore,it is necessary to strengthen the theoretical study of AS.Some studies have found that the porosity and permeability coefficient of the media surrounding the well changed after AS,and the influence of the air sparging well decreased obviously.It may be that the preferential air flow around the air sparging well leads to a sharp decline of the radius of influence.Thus,it can be seen that the AS process can also effect the underground environment,which leads to the change of the parameters of the underground environment.Therefore,in order to solve this problem,the physical disturbing effect in the AS is studied in this paper.A series of sand column experiments were used to simulate the disturbance process of the AS.Comparing the permeability and dispersion of the medium during the process of the AS,the law of disturbance is explored.The porosity distribution in the medium is described by the ERT,and the disturbance law of AS to the medium is further obtained.At the same time,this paper introduces the micro-nano bubbles sparging method and it explores the physical properties and the physical disturbing effect on the medium.The experimental results are as follows:?1?Use the clean glass beads as the porous medium,the ERT method uses to establish the relation between the resistivity and porosity?=7.8144 n^-1.4098,R²>0.98.The result shows that the ERT method can represent the change of porosity of the porous medium before and after AS.The change of the resistivity obtained by the ERT method shows that the increase of porosity near the air injection port and the reduced far away from the air injection port.This shows that the fine particles move upward with the water-air flow.By studying on the different air flow rates,the results show that the change of porosity is related to the flow rate.The Darcy experiment and tracer test were conducted before and after AS.With the increase of air flow rate,the change of permeability coefficient and dispersion coefficient before and after AS is more obvious.The permeability coefficient of columns at 5 and 20 mL/min before AS were 3.88 and 3.40 m/d,they changed to 4.96 and 6.13 m/d after AS.The dispersion coefficient varied from 0.137 to 0.179 at 5 mL/min,whereas it varied from 0.110 to0.288 at 20 mL/min.The enhancement of permeability and dispersion proves that it can change the internal structure of the porous medium during AS.?2?The micro-nano bubbles should be used in the remediation of groundwater.The deionized water with dissolved oxygen of 4 mg/L was used in the experiments.Two methods are used to AS with 35 min,and the results show that the concentration of the dissolved oxygen in the water is saturated in a short time?160 s?during the micro-nano bubbles air sparging.The dissolved oxygen increased only 1.64 mg/L by the ordinary air sparging method with the same time.The data show that micro-nano bubbles sparging can improve the concentration of the dissolved oxygen in water in a short time.The change of dispersion before and after the micro-nano bubble sparing was obtained by the tracer tests.The results show that the dispersion of the medium will not change obviously before and after the micro-nano bubbles sparing.And the permeability coefficient in the porous medium was not changed obvious before and after micro-nano bubbles sparing.The tracer tests and Darcy tests show that the porous medium was not changed during the micro-nano bubbles sparing.