Effect of H<sub>2</sub>S on N<sub>2</sub>O Reduction
and Accumulation during Denitrification by Methanol Utilizing Denitrifiers
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Abstract
Sulfide
is produced in sewer networks, and previous studies suggest
that sulfide in sewage could alter the activity of heterotrophic denitrification
and lead to N<sub>2</sub>O accumulation during biological wastewater
treatment. However, the details of this phenomenon are poorly understood.
In this study, the potential inhibitory effects of sulfide on nitrate,
nitrite, and N<sub>2</sub>O reduction were assessed with a methanol-utilizing
denitrifying culture both prior to and after its exposure and adaptation
to sulfide. Hydrogen sulfide was found to be strongly inhibitory to
N<sub>2</sub>O reduction, with 50% inhibition observed at H<sub>2</sub>S concentrations of 0.04 mg H<sub>2</sub>S–S/L and 0.1 mg
H<sub>2</sub>S–S/L for the unadapted and adapted cultures,
respectively. In comparison, both nitrate and nitrite reduction was
more tolerant to H<sub>2</sub>S. A 50% inhibition of nitrite reduction
was observed at approximately 2.0 mg H<sub>2</sub>S–S/L for
both unadapted and adapted cultures, while no inhibition of nitrate
reduction occurred at the highest H<sub>2</sub>S concentrations applied
(2.0 mg H<sub>2</sub>S–S/L) to either culture. N<sub>2</sub>O accumulation was observed during nitrate and nitrite reduction
by the adapted culture when H<sub>2</sub>S concentrations were above
0.5 and 0.2 mg H<sub>2</sub>S–S/L, respectively. Additionally,
we reveal that hydrogen sulfide (H<sub>2</sub>S), rather than sulfide,
was likely the true inhibitor of N<sub>2</sub>O reduction, and the
inhibitory effect was reversible. These findings suggest that sulfide
management in sewers could potentially have a significant impact on
N<sub>2</sub>O emission from wastewater treatment plants