Effect of bimetallic and polymer-coated Fe nanoparticles on biological denitrification.

Bimetallic nanoparticles (nano Fe-Ni, nano Fe-Cu) and coated iron nanoparticles (chitosan-Fe(0), sodium oleate-Fe(0)) were utilized to support autotrophic denitrification. In comparison to nanoscale zero-valent iron (NZVI) particles, Ni-containing nanoparticles resulted in faster nitrate removal, but generated 17% more ammonium. The nano Fe-Cu integrated system, required two days less than the unmodified NZVI integrated system to remove all the nitrate and decrease ammonium by 13%, but a large amount of nitrite remained in the system. Compared to uncoated NZVI particles, chitosan-coated nanoparticles allowed the same nitrate removal time but 23% more ammonium production. The sodium oleate-Fe(0) nanoparticles did not only decrease the generation of ammonium by 17%, but also reduced the toxicity of the nanoparticles to bacteria. Therefore, sodium oleate-Fe(0) nanoparticles may be an appropriate substitute for NZVI particles to support autotrophic denitrification provided that additional time (two days) is allowed for complete nitrate removal.