Sulfide-oxidizing autotrophic denitrification: an evaluation for nitrogen removal from anaerobically pretreated domestic sewage.

Nitrogen removal from effluents of anaerobic reactors using conventional nitrification/denitrification processes depends on the availability of electron donors for denitrification. As sulfide is normally present in such effluents, autotrophic denitrification using sulfide can be an alternative to avoid or reduce the requirements of exogenous organic carbon sources. This study evaluated the application of sulfide-oxidizing autotrophic denitrification to anaerobically pretreated domestic sewage. A denitrifying reactor was fed with a mixture, at different proportions, of anaerobically pretreated (containing sulfides and residual organic matter) and nitrified (containing nitrates) effluents produced by reactors treating synthetic domestic sewage. Autotrophic denitrification was responsible for most of the nitrogen removal and coexisted with heterotrophic activity, resulting in high denitrification efficiencies. Efficient denitrification could be attained at a molar NO3 (-)/S(2-) ratio of 2.1, higher than values reported before, and this represents an important parameter for the strategic application of the process. Under the experimental conditions studied, autotrophic denitrification showed to be an efficient and feasible alternative to conventional denitrification using exogenous electron donors.