Nanoparticles of zero-valent iron are very effective for the cleaning of water originating from small-scale biologically-based wastewater treatment plants. During the cleaning process a number of complex reactions take place (of which the most the most important is oxidation, from Fe° to Fe2+ and Fe3+). As a result the bacteria still present in the water are destroyed, and the majority of other pollutants are decomposed, which happens due to their adsorption onto the so-created iron oxides and hydroxides. Those pollutants which are not decomposed by the zero-valent iron will be removed by means of ionic interchange using, for example, a specially synthesized zeolite. Thus the cleaning process will take place in two stages.
Nanoparticles and safety
Nanoparticles have a strong tendency to agglomerate. This means that smaller nanoparticles rapidly join together and form larger clusters whose sizes are of the order of a few micrometres. Apart from this, due to their reactivity they rapidly oxidize, and are transformed into non-reactive iron oxides and hydroxides. The nanoparticles of zero-valent iron will, during the cleaning process, be added in a water-based solution, and after their action is completed will be removed, which means that they will be fully removed from the cleaned water, and will thus not enter the environment.