Green PCB Remediation from Sediment Systems (GPRSS)

An ongoing problem facing the global environmental community including NASA centers is the removal and remediation of polychlorinated biphenyls (PCBs). PCBs were commonly used in a variety of materials including paints, caulking, and adhesives due to the advantageous physical and chemical properties that PCBs imparted to these various materials. Unfortunately, these properties have made the treatment of sites contaminated with these chemicals extremely difficult to deal with, due to their inherent chemical stability. The remediation of sediments contaminated with PCBs is especially difficult, primarily due to the risk of re-releasing the contaminant into the environment during the treatment process. Traditional treatment options involve the use of dredging and incineration of the contaminated soils/sediments, in which the chance of releasing of the contaminants is greatly increased. The purpose of this project is to develop a cleanup technology capable of remediating contaminated sediments in-situ, with minimal intrusion. This allows for the minimization of any potential contaminant release during the treatment process, providing a safer method for cleanup operations (as opposed to dredging/incineration) and still treating the basic problem of PCB contamination (as opposed to capping). The GPRSS technology is an in situ remediation technique for PCB-contaminated sediments. The technique provides an effective and safe method for sediment cleanup operations, eliminating some of the inherent risks associated with more traditional cleanup methods such as sediment dredging followed by incineration. The GPRSS technique offers both removal and degradation of the contaminant, in contrast to the capping in place method, which retains significant long-term environmental reliability. The envisioned re-useable, polymer-based PCB treating blanket has the potential to be a global, cost saving, game-changing technology. This technology utilizes a two-step process for the removal and degradation of the PCBs. In the first step, a "blanket" of inert material (such as a simple polymer, i.e. polyethylene) is gently lowered into the water system and pushed into the top layer of the sediments, penetrating into the zone where benthic population is at the greatest risk for bioaccumulation. This "blanket" acts as a PCB "sponge", absorbing the PCBs that are bound to the sediments. The second step consists of removing the "blanket", extracting the contaminants trapped within the blanket structure, and exposing the extracted PCBs to activated zero-valent magnesium in an acidified ethanol solvent to commence degradation. The "blanket" has a solid upper surface, providing a temporary cap to the contaminated sediments during the treatment period. Additionally, the "blanket" is manufactured with extruding points, or "fingers", that depress into the upper ten centimeters of the sediment layer, allowing for increased surface area contact with the deeper contaminated zone. Both the "fingers" and the backing of the "blanket" are hollow to allow for the incorporation of ethanol into the interior. This ethanol interior provides a major advantage to the GRPSSs. Since PCBs are lipophilic and hydrophobic, they prefer to dissolve into the ethanol (or similar non-aqueous solvent) if given the opportunity. This system affords that opportunity by generating a concentration gradient which enhances the rate of PCB transport from the sediment across the polymer blanket membrane and into the ethanol interior. Once the PCBs are in the "blanket," they entire system is removed from the sediment and the contaminants are extracted out of the blanket and degraded using stepwise reductive dechlorination in the presence of the magnesium reactant described above as step two. The polymer "blanket" is capable of being re-used multiple times. An entire riverbed for example would not be treated at a single event, but rather portions would be treated at a time. The reusability of the blankets allows them to be reapplied to different regions of the contaminated zone as remediation activities progress. Should additional applications prove necessary to remediate high starting PCB concentrations to acceptable levels at a single site, such as a holding or sludge pond, the reuseability of the blanket adds to its cost competitive nature, or to simply treat another contaminated sediment zone. More »