Chemical Characterization of Coal Tar−Water Interfacial Films

Abstract

Semigelatinous interfacial films, which may influence the fluid mechanic and mass transfer properties of coal tar in porous media, have been observed to form in coal tar−water systems when coal tars are aged in water under quiescent conditions for a few days. Samples of the interfacial film were isolated after aging for a period of 1 year and compared to the bulk coal tar using GC/MS, 13C-NMR, 1H-NMR, and FTIR techniques. The results showed that these films were very similar in organic composition to the bulk coal tar with no significant enrichment, depletion, or polymerization of tar components. The notable difference in the composition of the film material was the presence of water bound to coal tar constituents by weak, reversible bonds. FTIR analysis of a sample of coal tar film kept in contact with deuterated water showed that the water molecules bound to the coal tar constituents would slowly interchange with water molecules that were not bound. Similar bonding of water molecules and coal tar constituents was observed in coal tar−water emulsions. These results suggest that the semigelatinous film formed at the coal tar−water interface is similar to a thin emulsion layer.

Subsurface ecosystem resilience: long-term attenuation of subsurface contaminants supports a dynamic microbial community

“…In 1991, B7000 m 3 of sediment containing the main mass of coal-tar waste was excavated from the site and the cavity was back filled with clean sand (Murarka et al, 1992), followed by natural attenuation (through solubilization, transport, sorption, dilution and microbial metabolism) of aromatic hydrocarbons that had been transported to downgradient sediments (USEPA, 1997;NRC, 2000). Detection of both the transient intermediary metabolite, 1,2-dihydroxy-1-2-dihydronaphthalene (Wilson and Madsen, 1996), and mRNA transcripts of the naphthalene dioxygenase gene (nahAc) (Wilson et al, 1999;Bakermans and Madsen, 2002a), and the stable-isotope probing analyses (Jeon et al, 2003) confirmed the on-going aerobic microbial metabolism of naphthalene, the major soluble component of the coal-tar waste (Nelson et al, 1996). However, oxygen depletion in the contaminated zone and the clear evidence for methanogenesis and sulfate reduction (strictly anaerobic processes incompatible with aerobic naphthalene degradation) (Bakermans et al, 2002;Bakermans and Madsen, 2002b;Yagi et al, 2009) signify that the on-site metabolism is limited by the influx of geochemical oxidants, especially naturally occurring nitrate, sulfate and dissolved oxygen delivered largely by flow from uncontaminated groundwater upgradient into the system (Bakermans et al, 2002b).…”

“…In the 1960s, coal-tar waste from a manufactured gas plant was buried in South Glens Falls, New York, resulting in a contaminant plume of polycyclic aromatic hydrocarbons and other monocyclic constituents dispersed by the groundwater flow ( Figure 1; Madsen et al, 1991;Murarka et al, 1992;EPRI, 1996;Nelson et al, 1996;Neuhauser et al, 2009). In situ biodegradation of contaminants was shown by the enhanced metabolism of naphthalene and phenanthrene in the sediment samples from inside the plume, but not from outside (Madsen et al, 1991).…”

Composition and Dissolution of a Migratory, Weathered Coal Tar Creosote DNAPL

“…There, depletion of hydrophobic compounds, bulk DNAPL diffusion effects and changed wetting properties were ruled out as driving factors. After 1 year of weathering, Nelson et al (1996) found no enrichment, depletion or polymerization at the interface, but the formation of a semigelatinous film formed by weakly bonded water in an emulsified interface. However, the formation of a skin could not be verified due to the in situ character of the study.…”

“…Moreover, coal tars undergo a variety of aging processes in the decades following their release into the subsurface that further complicate the prediction of their behavior (Liu and Haderlein, 2013). The effect of the genesis of phase-internal gradients within a multicomponent DNAPL due to leaching of well soluble compounds over time, and the development of high-viscosity skins (Alshafie and Ghoshal, 2004) or emulsions (Nelson et al, 1996) at the phase interface on coal tar dissolution have been noted and documented in laboratory studies (Nelson et al, 1996;Alshafie and Ghoshal, 2004) but to our knowledge, not under field conditions. In addition, contaminant transport may be increased by dissolved, possibly colloidal organic matter as carrier (Wehrer et al, 2013).…”

DOE-EMSP Final Report: Characterization of Changes in Colloid and DNAPL Affecting Surface Chemistry and Remediation

“…In the case of crude oil, these films are the result of the adsorption of high molecular weight polar molecules at the crude oil-water interface [Sun, 2003]. The investigations by Nelson et al [1996] concluded that the formation of an interfacial film on coal tar-water interface was due to weak, reversible bonding between water molecules and the coal tar constituents. No investigations have been carried out with the film formed on the interface of chlorinated hydrocarbon DNAPLs and water.…”