Effects of air flowrate distribution and benzene removal in heterogeneous porous media during air sparging remediation

摘要

The decrease of remediation effect during air sparging (AS) remediation in heterogeneous porous media has attracted increasing attention. In this study, an improved light transmission visualization method was used to investigate the air accumulation, migration and flowrate distribution in benzene-contaminated heterogeneous porous media during AS. Experimental results indicated that the benzene removal rate in the porous media was mainly controlled by air flowrate distribution which could be used as a major factor to evaluate the remediation effect. Visualization of air migration showed that air accumulation occurred below the geologic heterogeneous interface when Delta Pe 0 kPa (Delta Pe: the air entry pressure difference of the media above and below the interface), and the accumulation thickness and length presented exponential decay increases with increasing Delta Pe and air injection rates. Air flowrate was monitored by gas flow sensors, and the flowrate distributions were found as Gaussian distribution when Delta Pc = 0 kPa, trapezoidal distribution when 0 Delta Pe 0.3 kPa and fingered distribution when Delta Pe = 0.3 kPa. Fingered distribution of air flowrate resulted in extremely nonuniform benzene removal above the interface and reduced the overall benzene removal rate. These findings reveal the reasons for the poor performance of AS remediation in heterogeneous porous media, leading to a better understanding of the remediation mechanisms in heterogeneous aquifer.