Experimental investigation of the applications of natural freezing and curdlan biopolymer for permeability modification to remediate DNAPL contaminated aquifers in Alaska

摘要

Dense Non-aqueous Phase Liquids (DNAPL) contamination is one of the major environmental concerns today. DNAPL can remain in significant quantities as residual contaminants in the low permeability zones even after the bulk phase has been removed. As the drive fluid sweeps through the aquifer it follows the path of least resistance, which is the high permeability zone. Thus the contaminants trapped in the low permeability zones remain as residuals and serve as a source for prolonged contamination. Conventional remediation techniques are ill-equipped to deal with the heterogeneities of the aquifers. Various techniques to enhance the efficiency of the conventional methods have been tried without significant success. In this study we have tested a hypothesis, "A combination of natural freezing/thawing and microbial gel sealant in layered heterogeneous porous media along with a conventional remediation technique can be used effectively to reduce the volume of residual DNAPL in cold regions" to assess an alternative for remediation of residual DNAPL from soils and aquifers in cold regions such as Alaska. Reducing the temperature of soil formations can modify aquifer flow paths. The natural freezing of soils in winter may be used effectively to modify the flow paths. In summer, permeability modification can be accomplished by emplacement of microbial polymer gels. We have investigated a cost-effective and efficient technique to reduce the volume of residual DNAPL using a combination of natural freezing in winter and biopolymer application in summer through a series of one-dimensional laboratory scale column experiments. Specifically, we have investigated the amount of residual DNAPL volume reduction by utilizing the permeability modification approach and thus the modification of preferential flow path using freezing alone and by introducing curdlan biopolymer as a gelant to block the high conductive soil and sweep the DNAPL from residual zones. Our results suggest that a combination of natural freezing of soils in winter and a microbial biopolymer gelant in summer can be used effectively to reduce the volume of residual DNAPL by up to 90% of the total volume of residual DNAPL.