Use of nitrate to control sulfide generation by sulfate-reducing bacteria associated with oily waste

Sulfide is a toxic and corrosive product of sulfate-reducing bacteria that can accumulate in oily waste streams to nuisance levels. Sludge associated with an oily waste stream was collected from a settling tank and used to as sess sulfide generation activities. Methanogenesis was a predominant proces s in sludge in the absence of sulfate, and was suppressed by nitrate. Sulfa te reduction and sulfide formation were evident when sulfate was available. Nitrate diminished sulfate reduction and prevented sulfide accumulation un der freshwater, brackish, and saltwater conditions. Sodium-, potassium-, an d calcium nitrate were equally effective in curtailing sulfide formation. T he effects of nitrate on sulfate depletion were concentration-dependent, wi th 50 mM nitrate diminishing sulfate reduction, yet as little as 16 mM nitr ate prevented sulfide accumulation. Sulfide was oxidized in nitrate-reducin g incubations, and accumulation of sulfur or sulfate was observed. Nitrate reduction was accompanied by production of nitrite and nitrous oxide, which probably helped prevent sulfate reduction in extended incubations. Our res ults suggest that nitrate amendments control the formation of sulfide in oi ly waste streams both by preventing sulfate reduction and by stimulating an aerobic sulfide oxidation.