Addition of NZVI to anaerobic subsurface can result in the liberation of substantial amounts of hydrogen and the creation of reducing conditions conducive to anaerobic dechlorinating bacteria. Polymers and surfactant used to stabilize NZVI may also provide a source of reducing equivalents. The extent of the synergy between biological and chemical reduction has not been investigated, but this holds great promise as an effective coupling of nanotechnology and biotechnology.
H2 is formed during anaerobic corrosion of ZVI, which forms hydrogen gas from reduction of H2O:
Fe + 2H2O → Fe2+ + H2 + 2OH−
When a catalyst is present, i.e. microorganisms that can reduce contaminants using H2 as electron donor, dechlorination will happen. Dehalococcoides species can carry reaction (c) in the figure below.
(a) Surface reaction (b) Ferrous Iron (c) Catalyst + H2
Modified from Matheson and Tratnyek (1994) ES&T 28, 2045-2053.
Coupling nZVI Application and Bioremediation
Preliminary work in Prof Edwards’ lab has established that NZVI alone does not affect the anaerobic culture KB-1 and its dechlorination activity, but that certain emulsifying agents do. Emulsifying agents are often added to NZVI to help stabilize it chemically.
Our research team will perform batch experiments with the KB-1 culture, varying concentrations of NZVI and polymers/surfactants, and targeted chlorinated ethenes and ethanes. These tests will include soil samples from real field sites contaminated with chlorinated solvents. One-dimensional (1D) column tests will be used to assess processes under flowing conditions. In addition to NZVI and chlorinated ethene/ethane concentrations, pH, redox, chloride, vcrA genes, and fermentation products, stable isotopes of carbon and hydrogen will be measured to determine abiotic and biotic transformation processes (Elsner et al., 2010). Field tests will also be performed and will be essential to determine how these technologies intersect in a heterogeneous flowing system. Improved protocols for field implementation of NZVI and its synergy with the indigenous or bioaugmented microbial population will be obtained.
In parallel to the study of combined NZVI-Bio, combinations of NZVI with surfactants, other catalyst agents (formic acid), and polymers will be optimized. Besides, NZVI particle size optimization is required to enhance delivery to porous media. Lastly, the issue of gas generation, i.e. H2, during application of NZVI to natural systems will be investigated.