Optimization and Performance of ZVI Amendments for In-Situ Chemical and Biological Reduction

In Situ Chemical Reduction (ISCR) is an innovative environmental remediation technique used for soil and/or groundwater remediation that involves the placement of a reductant or reductant generating material in the subsurface to reduce the concentrations of targeted environmental contaminants to acceptable levels. Zero valent iron (ZVI) is most commonly used for remediating halogenated ethenes and ethanes, pesticides, energetic compounds and some metals/metalloids into harmless end products. [ITRC 2011]. The process combines both biological processes and ZVI particle-driven abiotic pathways to chemically reduce the contaminants. The incorporation of ZVI enhances remediation by enabling various chemical reduction pathways and for halogenated ethenes limits the formation of undesirable breakdown products such as Cis-DCE and vinyl chloride.

Recent studies were undertaken to evaluate the reactivity, surface passivation, and pH fluctuation of various commercially available ZVI powders and an engineered ZVI media with a greater surface area. The ZVI samples were under identical conditions for 103 days with a solid to liquid ratio was 1:20 by weight. Particle size of all ZVI was <100 mm. The lab-scale kinetic experiment demonstrated accelerated abiotic reactivity of the engineered ZVI media towards a mixture of c-VOC composing of tetrachloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (c-DCE), and 1,1,1-trichloroethane (111TCA) in synthetic groundwater (each compound at 5 mg/L).

The study concluded that the major difference between engineered ZVI media and off-the-shelf ZVI powders is the increased reactivity of the engineered ZVI media. The engineered ZVI media was also able to maintain circumneutral pH, generate higher rates of hydrogen and sustain the production of hydrogen for a longer duration.