Combination of polymer-stabilized nano zero-valent iron and biostimulated denitrifying bacteria for the removal of nitrate from groundwater

Abstract

Polymer-stabilization of nano zero-valent iron (nZVI) is becoming a matter of research, although its effect on the reactivity towards targeted contaminants is not clear yet. Concurrently, combination of Abiotic Chemical Nitrate Reduction (ACNR) via nZVI and Heterotrophic Denitrification (HDN) to enhance nitrate (NO) removal and/or improve the end product distribution has also gained attention of researchers. The objective of this study was, on one hand, to compare the potential of nZVI stabilized with four different polymers (PAA, PAP, CMC or Tween80) to remove NO from groundwater via nZVI-mediated ACNR and, on the other hand, to assess the effect of combined supplementation of polymer-stabilized nZVI and acetate on NO reduction. The results showed that Tween80-stabilized nZVI over-performed those stabilized with PAA, PAP or CMC in removing NO from water. Furthermore, coupling Tween80 coated-nZVI and acetate enhanced both the overall NO removal (63%–95%) and the conversion of reduced NO to N(g) (63%–80%) in comparison to when acetate or nZVI were applied alone (respectively 44%–62% and 30%–31%, with most of reduced NO converted to NO or NH). This study thus demonstrates that application of Tween80-stabilized nZVI has potential to make a significant contribution in remediating NO-contaminated groundwater.