A Mechanism Study Of Airflow Rate Distribution And The Effect Of Surfactant-enhancement In The Aquifer During Air Sparging

With the rapid development of a social economy,organic contamination of soil and groundwater is more and more serious throughout the world.Air sparging(AS)is known as one of the most effective ways for remediating volatile organic compounds(VOCs)in soil and groundwater.Now,the experimental study on AS has always been a hot discussion.However,the design and operation of AS technology can only be based on previous limited field experience.It is lack of airflow channel description of high precision and corresponding theory for airflow distribution and shape of the zone of influence(ZOI)in AS process.According to domestic and foreign researchers,an improved laboratory two-dimensional airflow visualization device was developed for the quantitative analysis of airflow distribution at different heights from the sparger(20,30,and 40 cm)within the ZOI.it is particularly important to find a reasonable theory,which can be applied to airflow distribution and predictive models of the ZOI.The airflow rate and variation in different media during surfactant-enhanced air sparging remediation was also studied.In this study,the main research results obtained are as follows:1.The measured airflow rate distribution appeared as a Trapezium when the vertical distance from the sparger to was 20cm;however,the airflow rate matched a Gaussian distribution when the height became 30cm and 40cm.It was illustrated that the airflow distribution within the ZOI conformed to the turbulent jet theory when the airflow distribution was uniform and forming region in AS process;which can be applied to airflow distribution and predictive models for the ZOI.Furthermore,the airflow distribution within the ZOI can be divided into two regions through the turbulent jet theory:the initial and main regions.2.Through the turbulent jet theory,the airflow rate distribution within the ZOI possesses some basic characteristics:(a)the similarity rule of airflow distribution within the ZOI;(b)The linear extension of boundary layer of ZOI:R/x = const;and(c) there is airflow conservation of momentum within the ZOI:? Qdm = ?A?Q2dA=const.3.The dimensionless airflow distribution curves are basically the same in the same region under different sparging pressures.The air distribution prediction equations can be established:Q/Qm = f1(D/D1/2)? C + A×exp(-2(D/D1/2-xc)2/w2?(for the main region),and Q/Qm = f2(?Dc//?Db)= G +J/(1+exp(?Dc/?Db-x1/v)),(for the initial region).4.The different heights of pressure distribution within the ZOI matched a Gaussian distribution.With the increase of the airflow rate,corresponding pressure increased linearly within the ZOI.The maximum airflow rate(Qm)with the increase of sparging pressure was also increased linearly under the different cross-sectional heights within ZOI,and equations of the slope were negatively related with the section heights.5.The air saturation of the aquifer was negatively related with the medium grain size under the same airflow rate condition.However,the air saturation was positively correlated with the medium grain size when surfactant(SDBS)was added in the aquifer.This showed that the coarser medium often required larger airflow rate,and it could be changed by adding the surfactant to the aquifer.6.The air saturation of the aquifer was inversely proportional to the surface tension of groundwater.However,the air saturation tended to be stable when the surface tension was greater than 49mN/m in coarse sand(0.5?1.0 mm).7.The addition of surfactant could effectively improve the removal efficiency of benzene and shorten the remedial time in medium sand(0.25?0.5 mm).