Insights into temporal and spatial evolutions of air saturation and its effects on nitrobenzene removal during air sparging remediation

Air saturation (Sa) can significantly influence the removal effect during air sparging (AS). However, there have been few studies focused on the temporal and spatial distribution of the Sa, which is adverse to precise remediation of AS technology. In this study, temporal and spatial evolutions of the Sa and its effects on nitrobenzene removal were investigated by the one-dimensional column experiments during AS. Experimental results demonstrated that the variation of Sa at different positions of the aquifer was significantly different with the increase of sparging time under the same air injection rate (Qinj), and the variation of middle and lower position was 0.3%-11.0%, however, the variation of Sa at the upper position was 21.0%-40.0%. When the Qinj was small, the number of airflow channels was little, and the nitrobenzene removal rates at the middle and upper position were low. With the increase of Qinj, the number of airflow channels was many, and the main region of airflow (Trapezium distribution) began to appear at the lower position, and the nitrobenzene removal rate at the upper position was low, which showed that the nitrobenzene removal rate was mainly affected by the spatial and temporal distribution of Sa in AS process. Based on the above, the mathematical model of relationship between nitrobenzene removal rate, sparging time and Sa was established, which was conducive to the accurate design of AS technology in the site application.