Geosyntec at the 253rd American Chemical Society National Meeting & Exposition
Mary deFlaun (New Jersey), Claire Wildman (California), and Neal Durant (Washington, D.C.) presented at the 253rd American Chemical Society National Meeting & Exposition entitled "Advanced Materials, Technologies, Systems & Processes" at the Moscone Center in San Francisco, California on April 3-4, 2017.
Mary was invited to present on bioreactors in South Africa, Claire's presentation was about chromium chemistry in bioreactors, she also co-moderated a session on metals treatment in remote areas, and Neal was invited to present on electrokinetics (EK). The abstracts are below.
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GEOC: Division of Geochemistry
79 - Bioreactors for the treatment of hexavalent chromium at remote locations in South Africa
Geosyntec Consultants, Ewing, New Jersey, United States; University of the Free State, Bloemfontein, South Africa
Bioreactors were developed for the treatment of industrial and mining leachates contaminating surface water with hexavalent chromium at various locations in South Africa; this talk will present the performance of the column studies and pilot-scale bioreactors designed and implemented for two of these sites. The reactors are designed to immobilize the soluble hexavalent chromium via microbial reduction to insoluble trivalent chromium. The treatment approach involves stimulating the indigenous biome to create anoxic conditions and enhancing bioreduction with the stoichiometrically-balanced addition of electron donor. At a dolomite stone mine in the Northern Province, the surface water contained up to 8 mg/L hexavalent chromium, while the site in Mpumalanga had ~5.5 mg/L. Due to the intermittent electrical service in these areas, a key component of the design was to use the water pressure produced by gravity feeding the influent water to run the fixed-film bioreactor filled with porous media, as well as sun panels for power. The contaminated water from each site was characterized geochemically and column studies were conducted to establish the efficacy of the indigenous bacteria, the choice of matrix to support microbial biofilm formation, as well as the choice of electron donor and its optimal stoichiometric balance for the reduction. Three reactor designs were tested: a fixed-film flatbed (PV 23,500 L), a deeper more compact bioreactor (PV 11,500 L) and four upflow-tank bioreactors (PV 9,600 L). Locally sourced citric acid was used as the electron donor and hydraulic retention time, reactor level, electron donor concentration, ORP, temperature and other chemical parameters were remotely controlled. In addition to the complete Cr6+ removal, the bioreactors could also reduce nitrate concentrations to below the SANS drinking water standard. The technology at the Mpumalanga site was extended to include a second stage barium carbonate reactor to remove high sulfate concentrations (>2,000 mg/L) from the fly ash leachate, where 90% of this contaminant could be removed with concomitant decreases in EC (15%), TDS (20%), calcium (88%), magnesium (25%) and total hardness (72%) observed. The successful up-scaling of the laboratory column studies to use fixed film reactors to treat industrial and mining leachates will be discussed.
GEOC: Division of Geochemistry
80 - Role of reduced chromium-organic complexes in performance of an ex situ bioreactor to remove hexavalent chromium
1 Geosyntec Consultants, Oakland, California, United States; 2 Geosyntec Consultants, Pasadena, California, United States
A two-stage pilot bioreactor was constructed to treat hexavalent chromium (Cr(VI)) in extracted groundwater at a site in southern California. In the first stage, extracted groundwater was dosed with acetic and phosphoric acids to stimulate microbial activity in the target redox window. In the design redox window, Cr(III) oxides would precipitate and settle out of solution. In the second stage, the reduced groundwater was passed through an aerated biofilter to remove residual organic carbon and dissolved iron and manganese, if any. Initially, Cr(VI) was rapidly reduced to low levels in the first stage, but reduced Cr passed into the second stage and was reoxidized, limiting the Cr(VI) removal efficiency of the overall system. Follow-up testing quantified complete Cr removal from effluent of the first stage upon the introduction of granular activated carbon, suggesting a role for organic compounds in Cr behavior. In batch and column experiments, anaerobic biofilms have been previously shown to produce organic ligands that bind with Cr(III), and these soluble organo-Cr complexes are susceptible to reoxidation. By lowering the target redox window into sulfate reduction and adding an anaerobic filter to the first stage, Cr removal to below 1 µg/L was consistently achieved. It is possible that reduced sulfur species may compete with organic ligands for Cr(III) or otherwise suppress microbial production of organic ligands. The results suggest that reducing conditions in excess of that predicted by thermodynamic equilibrium are required to remove Cr efficiently in bioreactors.
ENVR: Division of Environmental Chemistry
464 - From infancy to full-scale demonstration: The twenty year development of electrokinetically-enhanced bioremediation for successful treatment of chlorinated solvents in clays and silts
Geosyntec Consultants, Columbia, Maryland, United States; ERDC EL, U.S. Army Corps of Engineers, Vicksburg, Mississippi, United States
Researchers have known since the early 1990s that application of a low-voltage electrical current can be used to manipulate and accelerate migration of ionically charged reagents to treat contaminants in low-permeability geologic matrices such as clays and silts. In this process, electrokinetics (EK) is used to induce the movement of water, ions, and charged particles by electroosmosis, electromigration, and electrophoresis, respectively, along with soil heating. EK-based remediation offers special promise for remediation of low-permeability silts and clays, as it has been demonstrated to increase groundwater flow rates (and ionic amendment delivery rates) that are 100 to 1000X greater than can be achieved by pumping. For EK, however, the road to technology scale-up and maturity has been a long one. Initial success with EK in bioremediation was reported in the 1990s in bench studies which showed that EK could achieve acetate propagation rates in clay of 2.5 - 3.0 cm/day, stimulating biological activity within the clay matrix. At the same time, significant EK research focused on use of electrical currents to facilitate extraction of metals from soil and groundwater. Several EK pilot tests for metals remediation were performed in the late 1990s and early 2000, but when the results of these tests showed that EK failed to achieve significant metals removal, general interest in EK diminished significantly for the next several years. Keen to find a solution to the problem of chlorinated solvent contamination in clay till, in 2009 the Danish government initiated research on use of EK to deliver organic substrates and bacteria to stimulate reductive dechlorination in chlorinated solvent source areas in clay till (K < 10-9 cm/s). Column tests demonstrated that EK applied in clay from a chlorinated solvent site could achieve lactate transport rates of 3 - 5 cm/day, and promote migration of dechlorinating Dehalococcoides bacteria, achieving complete dechlorination of tetrachloroethene (PCE) to ethene within the clay column. Based on the success of this bench test, field demonstrations of EK for bioremediation of chlorinated solvent source areas have been implemented at test sites in Denmark and Naval Air Station Jacksonville. Field results have demonstrated EK-stimulated high rates of PCE dechlorination to ethene, and growth and migration of Dehalococcoides in clay till. This presentation will describe key findings from the EK field demonstrations.
Moderated Session Description
Advances in treatment processes for metals and metalloids
This session will focus on technologies for in situ and ex situ remediation of metals and metalloids in surface water and ground water, including waters impacted by mining and metal processing. The recent accidental release at the Gold King Mine in Colorado has highlighted the need for advancement in remediation of metal and metalloid contamination in remote areas where novel technologies may be more effective and safe. This session will feature advances in the processes that enable in situ and/or passive treatment systems to successfully immobilize metals and metalloids. Fundamental scientific laboratory investigations, pilot studies, and full-scale treatment studies are welcome; preference will be given to recent studies that identify active treatment mechanisms (chemical, biological, physical, and some combination thereof) for metals immobilization and lessons learned for full-scale design and implementation.
The topics that would be covered in this session are, but are not limited to:
- Enhanced in situ bioremediation
- Passive ex situ bioreactors
- In situ stabilization
- Novel remediation techniques
U.S. Geological Survey
3215 Marine St, Bldg 6 Boulder, CO 80309
Geosyntec Consultants, Inc.
1111 Broadway, 6th Floor, Oakland CA 94607
For more information regarding the event, visit: National Meeting & Exposition
To learn more about Mary see her profile at: http://www.geosyntec.com/people/mary-deflaun
To learn more about Claire see her profile at: https://www.linkedin.com/in/cfwildman/
To learn more about Neal see his profile at: http://www.geosyntec.com/people/neal-durant