Article pubs.acs.org/est
In Situ Sequestration of Hydrophobic Organic Contaminants in Sediments under Stagnant Contact with Activated Carbon. 1. Column Studies Yongju Choi, Yeo-Myoung Cho, and Richard G. Luthy* Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305-4020, United States S Supporting Information *
ABSTRACT: The effectiveness of activated carbon (AC) treatment to sequester hydrophobic organic contaminants in sediments under stagnant contact was comprehensively studied for the first time. Two years of column experiments were conducted to simulate field conditions with two study sediments contaminated with petroleum and polychlorinated biphenyls, respectively, and variations in AC-sediment contact times, initial AC mixing regimes and distribution, AC particle sizes, and porewater flow. The benefit of AC treatment was gradually enhanced with time toward the end point of the treatment, where sorption equilibrium is established between sediment and AC. After two years of stagnant contact, the contaminant uptake in polyethylene passive samplers embedded in the columns was reduced by 95−99% for polycyclic aromatic hydrocarbons and 93−97% for polychlorinated biphenyls with 5 and 4 wt % AC dose, respectively, when AC was initially applied by mechanical mixing. These results verify that AC treatment can effectively control the availability of hydrophobic organic contaminants under stagnant conditions within a reasonable time frame following an initial distribution of AC into the sediment. The effectiveness of AC treatment was strongly dependent on AC particle size and AC distribution, while the effect of AC initial mixing regimes and porewater flow was not pronounced.
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INTRODUCTION
1, 2, 8, and 12 months showed up to 99.5% reduction in PAH uptake in polyethylene (PE) samplers.10 Pilot-scale trials for in situ AC amendment have been performed in several sites in the U.S. and Norway to study the effectiveness of AC amendment under field conditions.11 These studies have successfully demonstrated the proof-of-concept of the technology for field application.11 The results of the pilotscale studies indicate that the potential performance of AC observed in continuously mixed laboratory tests may not be realized as readily under field conditions.12−14 The pilot-scale trial at HPS found that the short-term benefit of AC amendment observed by ex situ PCB bioaccumulation tests and in situ passive sampler uptakes was less in the field than in the continuously mixed laboratory tests.12,13
Over the past decade, various studies have clearly demonstrated the potential of activated carbon (AC) amendment for the in situ treatment of hydrophobic organic contaminants (HOCs) in sediments. Laboratory studies in continuously mixed batch reactors with AC amendment show the potential for significant reductions in equilibrium pore-water concentration, bioaccumulation in benthic organisms, and contaminant flux into water for polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and organochlorine pesticides.1−9 For example, Zimmerman et al.1 conducted a 6-month continuously mixed, laboratory study wherein the aqueous PCB concentration was reduced by 92% after contacting 3.4 wt % AC with sediment collected from Hunters Point Shipyard (HPS), San Francisco Bay. A laboratory study by Choi et al.10 with petroleum-impacted sediment demonstrated the effectiveness of AC amendment to sequester a suite of parent- and alkylatedPAHs. Slurry phase experiments with an AC dose of 5 wt % for © 2013 American Chemical Society
Received: Revised: Accepted: Published: 1835
July 27, 2013 September 20, 2013 October 1, 2013 October 1, 2013 dx.doi.org/10.1021/es403335g | Environ. Sci. Technol. 2014, 48, 1835−1842
Environmental Science & Technology
Article
mixing, passed through a 2-mm sieve, and stored at 4 °C until use. Type TOG AC obtained from Calgon Corporation (Pittsburgh, PA, 50 × 200) was ground and sieved by a stack of sieves (No. 100, 200, and 325) to obtain particle sizes of 75− 150 μm and
