Use of Peat Moss Amended with Soybean Oil for Mitigation of Dissolved Explosive Compounds Leaching into the Subsurface: Insight into Mass Transfer Mechanisms

Abstract

Peat moss and soybean oil are proposed as potential amendments for mitigating the dissolved transport of energetic compounds from military training facilities. Laboratory column experiments were performed to evaluate the migration of 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) through peat moss and peat moss amended with soybean oil. Results indicated that uptake into the sorbents significantly reduced the migration of these compounds, and that uptake into the peat was mass transfer limited. Addition of the soybean oil had a negligible effect on the transport of RDX and HMX, but had a significant impact on the transport of TNT through the columns. The relatively large impact of soybean oil on TNT transport was due, in part, to enhanced biotransformation of TNT. The TNT biotransformation rate constant in the presence of soybean oil was approximately 10 times greater than in the presence of peat alone, and at least 10 times greater than the biotransformation rate constant of RDX or HMX. The presence of the soybean oil also increased the rate of TNT mass transfer to kinetically controlled sorption sites, resulting in an overall decrease in TNT flux from the peat plus soybean oil columns. A diffusion model incorporating the effects of liquid viscosity and soybean oil–water contaminant partitioning was shown to accurately describe the impact of soybean oil addition on the transport of energetic compounds, indicating that mass transfer limitations in peat moss are the result of liquid phase diffusion, and that the presence of nonaqueous phase liquids affect sorption kinetics.