Nitrate promotes biological oxidation of sulfide in wastewaters: Experiment at plant‐scale

Biogenic production of sulfide in wastewater treatment plants involves odors, toxicity and corrosion problems. The production of sulfide is a consequence of bacterial activity, mainly sulfate-reducing bacteria (SRB). To prevent this production, the efficiency of nitrate additiontowastewaterwastestedatplant-scalebydosing concentrated calcium nitrate (Nutriox TM ) in the works inlet. Nutriox TM dosing resulted in a sharp decrease of sulfide, both in the air and in the bulk water, reaching maximum decreases of 98.7% and 94.7%, respectively. Quantitative molecular microbiology techniques indi- cated that the involved mechanism is the development of the nitrate-reducing, sulfide-oxidizing bacterium Thio- microspira denitrificans instead of the direct inhibition of the SRB community. Denitrification rate in primary sedi- mentation tanks was enhanced by nitrate, being this almost completely consumed. No significant increase of inorganic nitrogen was found in the discharged effluent, thus reducing potential environmental hazards to receiv- ing waters. This study demonstrates the effectiveness of nitrate addition in controlling sulfide generation at plant- scale, provides the mechanism and supports the environ- mental adequacy of this strategy. 2005 Wiley Periodicals, Inc.