Interactions of nanoscale zero valent iron and iron reducing bacteria in remediation of trichloroethene

In this work we investigated the interactions between the nanoscale zero valent iron (nZVI) and iron reducing bacteria (IRB) during the remediation of trichloroethene (TCE). Dehalogenation of TCE was examined using nZVI NANOFER 25 (N25) and the Gram-negative bacterium Shewanella algae CCM 4595 in liquid and soil slurry microcosms. The rates of dehalogenation were determined by gas chromatography. The interactions between N25 and S. algae were investigated using X-Ray diffraction (XRD), ferrozine test, Tandem Scanning Confocal Microscope (TSCM) and viable cell counts. Results showed that S. algae impaired TCE removal by N25. TCE dehalogenatlon rates in liquid microcosms were 17 times faster in absence than in presence of S. algae, and 8 times faster in soil slurry microcosms. The concentrations of dissolved Fe2+ and Fe3+ ions in the N25 + S. algae microcosms were an order of magnitude higher than that in bacteria-free microcosms. Moreover, the XRD data showed that the presence of S. algae significantly increases the depletion of reactive Fe and causes the formation of poorly soluble and insoluble Fe3+ oxide-hydroxides that can inhibit electron transfer from iron to the contaminant. Viable cell counts showed that N25 considerably inhibited microbial growth. Furthermore, TSCM demonstrated that S. algae tends to adhere to the surface of N25 suggesting that direct nanoparticle attachment may impact both the microbial population and the electron transfer from the iron to the contaminant. Data suggested that S. algae contributes significantly to N25 anoxic corrosion through microbial iron respiration. Our findings provide better insights about the fate of nZVI in the subsurface and its interactions with surrounding microorganisms.