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. (c) 2010 Elsevier Ltd. All rights reserved.