Air-water interfacial adsorption coefficients for PFAS when present as a multi-component mixture.

Surface tension isotherms and calculated air-water interfacial (AWI) adsorption data are presented for solution mixtures of per- and polyfluoroalkyl substances (PFAS), specifically a series of binary and one ternary mixtures of homologous linear perfluorocarboxylic acids (PFCAs) in a simulated groundwater, and two 8-component mixtures containing both PFCAs and linear perfluoroalkane sulfonates (PFSAs). In all cases, non-ideal competitive adsorption was observed that favored the most surface-active component(s) of the solution mixture. The multi-component extended Langmuir (EL) isotherm model was observed to accurately predict the competitive adsorption observed in the binary and ternary PFCA solution mixtures. However, the predictive utility of the EL model was observed to diminish when mixtures contained both PFCAs and PFSAs, which differ in their hydrophile structure, resulting in overpredictions and underpredictions of the AWI adsorption isotherms derived from measured data depending on the specific components present in the solution mixtures. Observations indicate that the individual component adsorptive affinities for the AWI can change in response to competitive preferential adsorption as their solution concentrations increase that is not being captured by the EL model. Our results demonstrate that alternative mathematical models are needed that support concentration dependent affinity coefficients for non-similar mixtures of PFAS, such that the transport of individual target PFAS components within a larger mixture of components can be accurately predicted across a wider range of solution concentration.

Amendment for increased methane production rate in municipal solid waste landfill gas collection systems.

Optimization of methane production rate can potentially decrease the operational lifetime of the landfill site and assist with better management of methane harvesting from the landfill cells. Increased moisture content in landfill cells is known to increase the rate of methane production. Several natural biopolymers can sustain moisture content in a solid matrix while providing a scaffolding for microbial communities to grow. This research examined the effect of the biopolymer, produced by Rhizobium tropici, on bench-scale methane generation from municipal solid waste. The addition of the R. tropici biopolymer increased the rate of methane production from 27% to 78% when compared to the control study for low and high concentrations of biopolymer amendment, respectively. R. tropici biopolymer shortened the lag phase by up to six days over the control, depending on the level of biopolymer amendment added to the solid waste. The mechanism appears to be facilitating biofilm formation through the combination of increased moisture retention and surface modification of the solid waste. Incorporation of biopolymer amendment in the alternative daily cover activities at commercial landfills could provide a viable approach for full scale application.

Environmental impact of metals resulting from military training activities: A review.

The deposition of metals into the environment as a result of military training activities remains a long-term concern for Defense organizations across the globe. Of particular concern for deposition and potential mobilization are antimony (Sb), arsenic (As), copper (Cu), lead (Pb), and tungsten (W), which are the focus of this review article. The fate, transport, and mobilization of these metals are complicated and depend on a variety of environmental factors that are often convoluted, heterogeneous, and site-dependent. While there have been many studies investigating contaminant mobilization on military training lands there exists a lack of cohesiveness surrounding the current state of knowledge for these five metals. The focus of this review article is to compile the current knowledge of the fate, transport, and ultimate risks presented by metals associated with different military training activities particularly as a result of small arms training activities, artillery/mortar ranges, battleruns, rocket ranges, and grenade courts. From there, we discuss emerging research results and finish with suggestions of where future research efforts and training range designs could be focused toward further reducing the deposition, limiting the migration, and decreasing risks presented by metals in the environment. Additionally, information presented here may offer insights into Sb, As, Cu, Pb, and W in other environmental settings.

Evaluating air-water and NAPL-water interfacial adsorption and retention of Perfluorocarboxylic acids within the Vadose zone.

The release and transport of linear perfluorocarboxylic acids (PFCA) within the vadose-zone beneath per- and polyfluoroalkyl substance (PFAS)- and non-aqueous phase liquid (NAPL)-contaminated source areas is influenced by multi-phase interfacial retention phenomena. Conceptually, interfacial adsorption results in retardation of PFCA velocities in subsurface multiphase systems. However, site hydrochemical factors influencing interfacial adsorption are not yet fully elucidated. Herein, air-water and NAPL-water interfacial tension isotherms were prepared for six homologous PFCAs of environmental significance for deionized water and five synthetic groundwaters of increasing ionic strength. The isotherms were successfully modeled by the Langmuir-Szyskowski equation and parameters used to fit the measured data are provided. Concentration-dependent interfacial adsorption coefficients and retardation factors are also provided for each PFCA and ionic strength condition and are evaluated to assess their significance. Simplifying relationships for predicting interfacial adsorption based on PFCA chain length were found to be less appropriate for natural groundwaters that contain a mixture of dissolved divalent and monovalent ions. Air-water interfacial (AWI) adsorption increased in a threshold manner with ionic strength from 0 to 6 mM, whereafter further adsorption was marginal. PFCA retention within water-unsaturated porous media is shown to depend on a number of inter-related factors and conditions that complicate the use of retardation factors within analytical models typically used for predicting transport rates under field conditions. Numerical simulation is thus necessary to model fundamental fate and transport processes. Mathematical relationships for incorporating interfacial adsorption in future and existing unsaturated flow and transport models are described.