Charles E. Schaefer

Electrochemical treatment of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) in groundwater impacted by aqueous film forming foams (AFFFs)

Laboratory experiments were performed to evaluate the use of electrochemical treatment for the decomposition of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), as well as other perfluoroalkyl acids (PFAAs), in aqueous film forming foam (AFFF)-impacted groundwater collected from a former firefighter training area and PFAA-spiked synthetic groundwater. Using a commercially-produced Ti/RuO2 anode in a divided electrochemical cell, PFOA and PFOS decomposition was evaluated as a function of current density (0-20 mA/cm(2)). Decomposition of both PFOA and PFOS increased with increasing current density, although the decomposition of PFOS did not increase as the current density was increased above 2.5 mA/cm(2). At a current density of 10 mA/cm(2), the first-order rate constants, normalized for current density and treatment volume, for electrochemical treatment of both PFOA and PFOS were 46 × 10(-5) and 70 × 10(-5) [(min(-1)) (mA/cm(2))(-1) (L)], respectively. Defluorination was confirmed for both PFOA and PFOS, with 58% and 98% recovery as fluoride, respectively (based upon the mass of PFOA and PFOS degraded). Treatment of other PFAAs present in the groundwater also was observed, with shorter chain PFAAs generally being more recalcitrant. Results highlight the potential for electrochemical treatment of PFAAs, particularly PFOA and PFOS, in AFFF-impacted groundwater.

A Peat Moss-Based Technology for Mitigating Residues of the Explosives TNT, RDX, and HMX in Soil

There is increased interest in how to balance military preparedness and environmental protection at Department of Defense (DoD) facilities. This research evaluated a peat moss-based technology to enhance the adsorption and biodegradation of explosive residues at military testing and training ranges. The evaluation was performed using 30-cm-long soil columns operated under unsaturated flow conditions. The treatment materials were placed at the soil surface, and soil contaminated with 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) was spread over the surface. Simulated rainfall initiated dissolution and leaching of the explosive compounds, which was monitored at several depths within the columns. Peat moss plus soybean oil reduced the soluble concentrations of TNT, RDX and HMX detected at 10 cm depth by 100%, 60%, and 40%, respectively, compared to the no-treatment control column. Peat moss alone reduced TNT and HMX concentrations at 10 cm depth relative to the control, but exhibited higher soluble RDX concentrations by the end of the experiment. Concentrations of HMX and RDX were also reduced at 30 cm depth by the peat moss plus soybean oil treatments relative to those observed in the control column. These preliminary results demonstrate proof-of-concept of a low cost technology for reducing the contamination of groundwater with explosives at military test and training ranges.

Dissolution of explosive compounds TNT, RDX, and HMX under continuous flow conditions

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) are common contaminants around active military firing ranges. Dissolution of these compounds is usually the first step prior to their spreading in subsurface environments. Nevertheless, dissolution of individual TNT, RDX, and HMX under continuous flow conditions has not been well investigated. This study applied spectral confocal microscopy to observe and quantify the dissolution of TNT, RDX, and HMX (<100 μm crystals) in micromodel channels. Dissolution models were developed to describe the changes of their radii, surface areas, volumes, and specific surface areas as a function of time. Results indicated that a model incorporating a resistance term that accounts for the surface area in direct contact with the channel surfaces (and hence, was not exposed to the flowing water) described the dissolution processes well. The model without the resistance term, however, could not capture the observed data at the late stage of TNT dissolution. The model-fitted mass transfer coefficients were in agreement with the previous reports. The study highlights the importance of including the resistance term in the dissolution model and illustrates the utility of the newly developed spectral imaging method for quantification of mass transfer of TNT, RDX, and HMX.

Current and Future Bioremediation ApplicationsBioremediation Applications: Bioremediation from a Practical and Regulatory Perspective

Chlorinated solvents have been a primary focus of the remediation industry since the 1980s, and many remedial technologies have been developed, tested, and applied to remove these constituents from contaminated aquifers. The relative ease of stimulating organohalide-respiring bacteria in situ and the availability of low cost electron donor substrates and effective bioaugmentation cultures have allowed in situ bioremediation technologies to be applied successfully at thousands of sites around the world. Typically, the success of the remediation is dependent more on the site characteristics (e.g., geochemistry, geology, hydrology, contaminant concentration, etc.) than the fidelity of the microbes. As we begin to address the most challenging contaminated sites that remain to be remediated, including those with free product contamination, complicated geologies (e.g., low permeability soils or fractured rock), or complex contaminant mixtures, in situ bioremediation may not be the sole technology applied at these sites but it will likely be an important component of many remedies. Therefore, fundamental understandings of microbiology and the development of novel application approaches remain essential to ensure continued success in remediation of the most difficult chlorinated solvent-contaminated sites.

Modeling the dissolution of various types of mixed energetic residues under different flow conditions

Energetic residues are scattered around active ranges due to the detonation events and dissolution is usually the first step for the entry of explosive compounds into the environment. The current models for describing the dissolution are subject to limitations in either model applicability or generality. This study attempted to develop a general model that is applicable to various types of energetic residues. Experimental data that were acquired from previous reports were used for testing the developed model. The results showed that the model captured well the dissolution processes of different types of energetic residues: 2,4,6-trinitrotoluene (TNT), Tritonal, Composition B, Octol, and Greener Insensitive Material (GIM). Moreover, it was observed that the mass transfer coefficients of TNT, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and/or octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) that were part of the energetic residues increased quantitatively with rising flow rates. In addition, the values of resistance coefficient, a model parameter, were negligible for the drop-impingement experiments, implying that under the conditions of rainfall and/or snowmelt flow, the surface attachment effect on the dissolution of energetic residues that rest on range soils is trivial. The study herein provides a general modeling approach for various types of energetic residues with additional insights in regards to their dissolution processes.

Electrochemical Transformations of Perfluoroalkyl Acid (PFAA) Precursors and PFAAs in Groundwater Impacted with Aqueous Film Forming Foams

While oxidative technologies have been proposed for treatment of waters impacted by aqueous film forming foams (AFFFs), information is lacking regarding the transformation pathways for the chemical precursors to the perfluoroalkyl acids (PFAAs) typically present in such waters. This study examined the oxidative electrochemical treatment of poly- and perfluoroalkyl substances (PFASs) for two AFFF-impacted groundwaters. The bulk pseudo first order rate constant for PFOA removal was 0.23 L h-1 A-1; for PFOS, this value ranged from 0.084 to 0.23 L h-1 A-1. Results from the first groundwater studied suggested a transformation pathway where sulfonamide-based PFASs transformed to primarily perfluorinated sulfonamides and perfluorinated carboxylic acids (PFCAs), with subsequent defluorination of the PFCAs. Transient increases in the perfluorinated sulfonamides and PFCAs were observed. For the second groundwater studied, no transient increases in PFAAs were measured, despite the presence of similarly structured suspected PFAA precursors and substantial defluorination. For both waters, suspected precursors were the primary sources of the generated fluoride. Assessment of precursor compound transformation noted the formation of keto-perfluoroalkanesulfonates only in the second groundwater. These results confirm that oxidation and defluorination of suspected PFAA precursors in the second groundwater underwent transformation via a pathway different than that of the first groundwater, which was not captured by total oxidizable precursor assay.

Detection of Dehalococcoides spp. by Peptide Nucleic Acid Fluorescent in situ Hybridization

Chlorinated solvents including tetrachloroethene (perchloroethene and trichloroethene), are widely used industrial solvents. Improper use and disposal of these chemicals has led to a widespread contamination. Anaerobic treatment technologies that utilize Dehalococcoides spp. can be an effective tool to remediate these contaminated sites. Therefore, the aim of this study was to develop, optimize and validate peptide nucleic acid (PNA) probes for the detection of Dehalococcoides spp. in both pure and mixed cultures. PNA probes were designed by adapting previously published DNA probes targeting the region of the point mutations described for discriminating between the Dehalococcoides spp. strain CBDB1 and strain 195 lineages. Different fixation, hybridization and washing procedures were tested. The results indicated that the PNA probes hybridized specifically and with a high sensitivity to their corresponding lineages, and that the PNA probes developed during this work can be used in a duplex assay to distinguish between strain CBDB1 and strain 195 lineages, even in complex mixed cultures. This work demonstrates the effectiveness of using PNA fluorescence in situ hybridization to distinguish between two metabolically and genetically distinct Dehalococcoides strains, and they can have strong implications in the monitoring and differentiation of Dehalococcoides populations in laboratory cultures and at contaminated sites.