Engineering topics

Bagwell, Christopher E.

Publications and source records attributed to Bagwell, Christopher E..

22 records · Page 2

DOE OSTI2020

Non-contact electrochemical evaluation of biofilms

Abstract Here, we demonstrate a non-contact technique for electrochemical evaluation of biofilms on surfaces in relation to corrosion. Electrochemical impedance spectrometry was employed, incorporating flat patterned electrodes positioned over the surfaces of aluminum and glass with and without biofilms. Signal communication from the working electrode to the counter electrode followed electric field lines passing tangentially through the biofilms. Electrochemical impedance parameters that were evaluated included complex impedance, phase angle, imaginary (out of phase) conductivity and Cole–Cole plots with a corresponding equivalent circuit. Changes in the impedance properties due to the presence of biofilms were monitored and correlated through microbiological, chemical and electrochemical assays. Impedance parameters associated with microbial activity correlated with biofilms on aluminum and glass surfaces. This technical approach provides impedance information about the biofilm without the signal traveling through the underlying conductive media or disrupting the biofilm. In this way, biological contributions to surface fouling can be evaluated with minimal contribution from the inorganic surface under the biofilm. In addition, this technique can be used to monitor biofilms on electrochemically inert surfaces as well as electrically conductive surfaces. Graphic abstract

Turick, Charles E. (ORCID:0000000307815846)↗

DOE OSTI2019

Microbial Methylation of Iodide in Unconfined Aquifer Sediments at the Hanford Site, USA

Incomplete knowledge of environmental transformation reactions limits our ability to accurately inventory and predictably model the fate of radioiodine. The most prevalent chemical species of iodine include iodate (IO 3 - ), iodide (I - ), and organo-iodine. The emission of gaseous species could be significant loss or flux term but these processes have not been investigated at radioiodine impacted sites. We examined iodide methylation and volatilization for Hanford Site sediments from 3 different locations under native and organic substrate amended conditions at 3 iodide concentrations. Aqueous and gaseous sampling revealed methyl-iodide to be the only iodinated compound produced under biotic conditions. No abiotic transformations of iodide were measured. Methyl-iodide was produced by 52 out of 54 microcosms, regardless of prior exposure to iodine contamination or the experimental concentration. Interestingly, iodide volatilization activity was consistently higher under native (oligotrophic) Hanford sediment conditions. Carbon and nutrients were not only unnecessary for microbial activation, but supplementation resulted in > 3 fold reduction in methyl-iodide formation. This investigation not only demonstrates the potential for iodine volatilization in deep, oligotrophic subsurface sediments at a nuclear waste site, but also emphasizes an important role for biotic methylation pathways to the long-term management and monitoring of radioiodine in the environment.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2019

Review of Amendment Delivery and Distribution Methods, and Relevance to Potential In Situ Source Area Treatment at the Hanford Site

The U.S. Department of Energy’s Hanford Site in southeastern Washington State is a complex of multiple facilities where historical release events in the Central Plateau area have resulted in subsurface contamination of the vadose zone, a perched-water zone, and underlying aquifer. Although some contaminants have already migrated through the vadose zone into the groundwater, contaminants remaining in the unsaturated zone are a potential long-term risk as a source for further groundwater contamination. Moreover, a perched-water zone located in the 200-DV-1 Operable Unit at Hanford creates further remediation difficulties. Remediation options are limited for contaminants located in the vadose and perched-water zones within the Central Plateau due to considerable depth, co-located contaminants, and complexities associated with physical and biogeochemical heterogeneities. Existing comprehensive reviews discuss potential remedial technologies relevant to Hanford Site conditions (e.g., deep vadose zone and perched water) and provide treatment technology recommendations. Many of the recommended in situ remediation technologies rely on introduction of amendments into the subsurface to achieve remedial goals. However, there are currently few review or guidance documents that provide a comprehensive look at mechanisms and considerations related to amendment delivery and distribution. This document summarizes amendment types, delivery techniques, subsurface access methods, and the applicability of delivery methods and amendments for specific subsurface target zones, including in the context of Hanford Central Plateau applications. Guidance on the appropriateness of a remedial technology for a specific site and contaminant is not included within this document. Rather, this document is intended to be used when considering remediation technologies and the associated amendments. An overview of amendment types (i.e., liquid, gas, and solids) and access/distribution methods used in subsurface remediation is provided, along with discussion of the maturity level (low, medium, or high), advantages, and limitations that relate to the potential effectiveness of each approach in the context of site-specific factors (subsurface geology, geochemistry, contaminant properties, etc.). There are many Hanford Site-specific factors that influence the suitability and appropriateness of amendment delivery strategies. Excluding amendment delivery approaches that are unsuitable for the Hanford context, each approach was assessed for applicability to the following target zones: unsaturated high permeability, unsaturated low permeability, perched water, saturated high permeability, and saturated low permeability zones. This compilation and discussion related to amendment delivery mechanisms provides a useful resource for evaluating remedial alternatives for source area contamination in the Hanford Central Plateau.

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DOE OSTI2019

Chemical and Biological Characterization of the 200 West Pump-and-Treat for Performance Assessment and Operational Improvement

Contaminated groundwater in the 200W Area of the Hanford Site is being treated ex situ by the 200W Pump-and-Treat (P&T) Facility and the subsurface plume is under hydraulic containment. The 200W P&T Facility removes several contaminants of concern from groundwater, as well as nitrate. Groundwater treatment capacity at the facility is currently constrained by the biological treatment of nitrate. In FY19, preparation of a 200W P&T Optimization Plan proposes to bypass all nitrate treatment to (1) allow the facility to operate at its original design capacity of 2500 gal/min, (2) provide the option for increasing capacity to 3750 gal/min, and (3) enable reliable injection of treated effluent water back into the subsurface. Nitrate will continue to be treated through blending of water within the aquifer.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗