Experimental investigation on influence of foam mobility on polychlorinated biphenyl removal in foam flushing

Foam flushing is an in situ soil remediation technology based on the traditional surfactant flushing method. The mobility control by introduction of foam is helpful in improving this technology. In this study, foam flushing ofpolychlorinatedbiphenyl (PCB)-contaminated media was performed to evaluate the effect of foam mobility on PCB removal. The conductivity and sweep efficiency (SE) of foam with different Triton X-100 concentrations and gas contents through two sands (with permeability of 15 darcy and 120 darcy) were tested. The results indicate that the presence of foam can not only reduce the mobility and increase the SE values of washing agent in single media, but can also reduce the discrepancy of fluid mobility and SE values between different sands, primarily due to the additional capillary resistance arising from the Jamin effect. The increases of PCB removal by foam agreed with the increases of SE values: foam (5.00 g/L) flushing increased the PCB removal from 79.4% by solution flushing to 85.1% for coarse sand, and increased the value from 64.2% to 79.1% for fine sand. When surfactant concentration and gas-liquid ratio vary, the variation of PCB removal showed the same trend with the change of SE, and an opposite trend with the change of foam mobility. High concentration of surfactant (5.00 g/L) and a foam quality of 97.0% are most favourable for the reduction of foam mobility. On the other hand, the negative effect of foam caused by the reduction of effective cross-section will reduce the foam remediation efficiency, especially under a low Triton X-100 concentration condition.