Demonstration of a scalable process for remediation of petroleum-impacted soil using electron beam irradiation.

Petroleum-impacted soils pose several hazards and require fast, effective, and versatile remediation techniques. Electron beam irradiation provides a novel means of heating soil and inducing non-equilibrium chemical reactions and has previously been applied to environmental remediation. In this work a scalable process for remediation of petroleum-impacted soils using a 100 kW, 3 MeV industrial electron beam is investigated. The process involves conveying impacted soil through a beam at a controllable rate to achieve a desired dose of approximately 1000 kGy. Reductions to less than 1% Total Petroleum Hydrocarbon (TPH) content from an initial TPH of 3.3% were demonstrated for doses of 710-1370 kGy. These reductions were achieved in in conditions equivalent to 4 m3 per hour, demonstrating the applicability of this technique to remediation sites. TPH reduction appeared to be temperature-dependent but not heavily dependent on dose rate, with reductions of 96% achieved for a dose of 1370 kGy and peak temperature of 540 °C. The performance of the process at high dose rates suggests that it can be incorporated into remediation of sites for which a high rate of material processing is required with a relatively small device footprint.

Assessment and Management of Mercury Leaching from a Riverbank.

The South River located in the city of Waynesboro, Virginia, contains mercury (Hg) contamination due to historical releases from an industrial facility operating between 1929 and 1950. In 2015, two sampling events were conducted in two of the contaminated bank regions (Constitution Park and North Park) to evaluate non-particulate total mercury (THg) and methylmercury (MeHg) concentrations in bank interstitial waters during river base flows and during bank drainage after flooding events. Porewater THg and MeHg at the bank-water interface were measured using diffusive gradient in thin-film devices (DGTs). The results showed THg mercury concentrations during bank drainage were approximately a factor of 3 higher than during base flow conditions. To have a better understanding of the parameters that control Hg leaching, a series of laboratory experiments were designed using South River sediments. The field and laboratory assessment showed that drainage/inundation cycles can lead to high THg concentration leachate from contaminated sediment due to increased partitioning from solids under oxic bank conditions and mobilization by the drainage waters. The results also demonstrated that methyl mercury concentrations at the bank-water interface are highest under base flow when conditions are more reduced due to the absence of oxic water exchange with the surface water. A remedial approach was implemented involving partial removal of surficial sediments and placement of biochar (to reduce non-particulate THg) and an armoring layer (to reduce erosion). DGT Measurements after bank stabilization showed THg decreased by a factor of ~200 and MeHg concentration by a factor of more than 20.

Self-sustaining smouldering combustion for the treatment of industrial oily waste.

Significant onsite handling and offsite management costs are incurred by oilfield operators annually to properly manage hydrocarbon waste streams such as tank bottoms or other oily sludge or oil impacted soil generated during oil and gas production processes. The current study reports for the first-time technical results of a field trial on use of a smouldering combustion technology performed in an active oilfield. Two treatment batches with oily sludges, stabilized through blending with soil, resulted in permanent hydrocarbon removal (98-99.9% reduction) to create treated soil that met standards for reuse as clean backfill onsite. Emissions profile data collected pre- and post-thermal oxidizer indicated effective removal of volatile organic compounds, CO and SO2, but had increased NO and CO2 due to combustion of propane to affect the thermal oxidation. Regulatory, financial, environmental and safety considerations are discussed in context of future full-scale smouldering technology deployment. The technology has the potential to lower overall unit costs for management of hydrocarbon impacted waste and reduce waste sent to landfills, which can benefit more remote sites.

Impacts of Sediment Particle Grain Size and Mercury Speciation on Mercury Bioavailability Potential.

Particle-specific properties, including size and chemical speciation, affect the reactivity of mercury (Hg) in natural systems (e.g., dissolution or methylation). Here, terrestrial, river, and marine sediments were size-fractionated and characterized to correlate particle-specific properties of Hg-bearing solids with their bioavailability potential and measured biomethylation. Marine sediments contained ∼20-50% of the total Hg in the <0.5 µm size fraction, compared to only 0.5 and 3.0% in this size fraction for terrestrial and river sediments, respectively. X-ray absorption spectroscopy (XAS) analysis indicated that metacinnabar (ß-HgS) was the main mercury species in a marine sediment, whereas organic Hg-thiol (Hg(SR)2) was the main mercury species in a terrestrial sediment. Single-particle inductively coupled plasma time-of-flight mass spectrometry analysis of the marine sediment suggests that half of the Hg in the <0.5 µm size fraction existed as individual nanoparticles, which were ß-HgS based on XAS analyses. Glutathione-extractable mercury was higher for samples containing Hg(SR)2 species than ß-HgS species and correlated well with the amount of Hg biomethylation. This particle-scale understanding of how Hg speciation and particle size affect mercury bioavailability potential helps explain the heterogeneity in Hg methylation in natural sediments.