Sulfide-driven autotrophic denitrification significantly reduces N2O emissions

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Technologies
• Greenhouse Gas Mitigation

Background:

• The Sulfate reduction-Autotrophic denitrification-Nitrification Integrated (SANI) process combines biological sulfate reduction and autotrophic denitrification.
• Sulfide, a byproduct of sulfate reduction, is utilized in autotrophic denitrification.
• Controlling nitrous oxide (N2O) emissions is crucial in biological nutrient removal.

Purpose of the Study:

• To investigate N2O reduction, accumulation, and emission during sulfide-driven autotrophic denitrification.
• To determine the impact of varying sulfide/nitrate (S/N) mass ratios on N2O dynamics.
• To assess the role of sulfide concentration and granule size on N2O reductase activity.

Main Methods:

• Long-term laboratory-scale granular sludge autotrophic denitrification reactor experiments.
• Controlled variation of sulfide/nitrate (S/N) mass ratios at pH 7.
• Measurement of N2O reduction rates, accumulation of N2O and nitrite, and free nitrous acid (FNA) levels.

Main Results:

• N2O reduction rate was linearly proportional to sulfide concentration, indicating no sulfide inhibition of N2O reductase.
• Sulfide stimulates N2O reduction across different granule sizes.
• Optimal S/N ratio of 5.0 g-S/g-N yielded the highest N2O reduction rate (27.7 mg-N/g-VSS/h).
• Accumulation of FNA inhibited N2O reduction and increased N2O accumulation.
• Decreased S/N ratio led to significant N2O gas emission increases.

Conclusions:

• Sulfide-driven autotrophic denitrification effectively reduces N2O emissions.
• Sulfide concentration is a key factor in optimizing N2O reduction.
• Managing FNA accumulation is important for maximizing N2O reduction efficiency.
• The SANI process offers a promising strategy for reducing greenhouse gas emissions in wastewater treatment.