Superfund Research Program
Funnel and Gate Innovations - Stabilization and Treatment of Contaminated Sediments
Project Leader: Danny D. Reible
Grant Number: R01ES016154
Funding Period: 2007-2011
Sediment caps can be designed to actively control or degrade contaminants through the addition of amendments. These amendments may be placed over the entire area of contaminated sediments or placed more efficiently over a small section (gate) to where contaminants may be directed by upwelling ground water (funnel). In this project, a variety of technologies are under development that can be used as an active treatment layer in either scenario. The effectiveness of conventional sorbents have been evaluated but the primary focus is on technologies that can enhance microbial degradation in the cap or gate. This entails modifying the sediment environment to encourage more reduced conditions (e.g. to promote reductive dechlorination) or more oxidized conditions (e.g. to promote aromatic oxidation). Hollow fiber membranes have been used to introduce oxygen into the reducing sediment environment and graphite cloth electrodes have been used to encourage oxidizing or reducing conditions at the anode and cathode, respectively.
The hollow fiber technology takes advantage of the development of biofilms on the membrane and can be used to supply oxygen at higher rates and transfer efficiencies, resulting in an improved biofilm activity. The degradation performance of naphthalene was studied in a simulated sand cap aerated through a hollow fiber membrane and inoculated with microbes isolated from PAH contaminated sediments. The effects of air pressure, the presence of other sources of COD, and the formation of nitrogen bubbles as a result of nitrogen saturation were investigated to evaluate the proposed technology.
The graphite cloth electrode technology was used to encourage reductive dechlorination of tetrachlorobenzene in a slurry reactor though the application of a small voltage of 2-4 V. No degradation was observed in killed controls or without the application of voltage. These voltages were also applied a simulated capping scenario to evaluate the ability to modify redox conditions. Oxidation and Reduction Potential (ORP) profiles showed redox changes of 2-300 mV that could be sustained within the cap. Studies of the microbial community structure and the resulting degradation are underway. Complementary studies providing fundamental process knowledge are also underway at both the University of Texas and Carnegie Mellon University to assist in optimization and design of a reactive cap based on this approach.