Fe(II)-mediated autotrophic denitrification: A new bioprocess for iron bioprecipitation/biorecovery and simultaneous treatment of nitrate-containing wastewaters

The demand of iron is increasingly rising nowadays due to the growth of human population. The iron ore reserves are diminishing and this encourages the scientific community to look into the use of secondary sources of iron. When iron occurs with nitrate, Fe(II)-mediated autotrophic denitrification is an alternative biotechnology to simultaneously remove nitrate and recover iron through the formation of Fe(III) precipitates. In the last 20 years, a large number of microbial species have been isolated and observed to be capable of coupling Fe(II) oxidation to denitrification under both mixotrophic and strictly lithotrophic conditions. Within mixotrophic metabolism, acetate is the most effective organic electron donor enhancing denitrification rates. The use of mixed cultures results in a more robust process, especially when other contaminants are present. Organic chelating agents allow a higher Fe(II) solubilization at neutral pH but often induce inhibition of microbial activity. The mechanisms that promote the formation of the specific biogenic Fe(III) (hydr)oxides have to be yet elucidated. Further research is crucial in this direction for both environmental and commercial reasons.