Zero Valent Iron (ZVI) for chlorinated organic compound remediation

​Last week, I was driving east of Houston and saw a survey crew examining the cap on the San Jacinto Waste Pits. These pits were used in the 1960s to dispose of paper mill bleaching waste which contained dioxin and other chlorinated organics. Over time, the pits were abandoned and the former barriers between the river and the landfill (pits) subsided and contaminants were being released from the site into the San Jacinto River and nearby Galveston Bay. In 2008, the site was give Superfund status by the EPA and an emergency cap was installed to contain the waste. As you can a see in the photo below, containing the waste in a pit located in a flood plain by the river is not a long run solution. So far the most proposed option is to excavate the waste and transport to incineration. Besides being expensive, excavation and transport could lead to more risks of exposure. So, this brings me back to thinking about the use of Zero Valent Iron (ZVI) or other metal and the ability of metals to dechlorinate many recalcitrant hydrocarbons.

San Jacinto Waste Pits - from Wired Jan 2014

In the 1970s researchers found that ZVI was effective in remediation of both heavy metals and chlorinated organics. The heavy metals were made insoluble by the donation of electrons from the ZVI.
In the case of chlorinated compounds, the electrons are transferred to the zero valent metal to the chlorine; releasing Cl- ions.

The resulting non-chlorinated or lower chlorinated compound is readily degraded by microorganisms in the groundwater or soil. Early work with ZVI included the development of Permeable Reactive Barriers (PRB) for groundwater. While effective, the need to build a barrier and pass contaminants through the barrier limited its application in soils and sludges.
​
With recent improvements in nano-particle technology, the ZVI can be incorporated into an injectable slurry where the surface of the ZVI is well exposed to surrounding chlorinated hydrocarbons. It would be interesting to see if the sites with PCB, DDT, and dioxin contamination can be field evaluated for cleanup using zero valent metals (in addition to iron you have zinc as a promising candidate). The new nano-particles combined with non-ionic surfactants and other carrier compounds could allow for a rapid conversion of the waste into forms that can be remediated in-situ by naturally occurring microorganisms. Thereby, reducing costs and risks associated with the traditional excavation and off-site disposal option.