Sulfide-driven nitrous oxide recovery during the mixotrophic denitrification process

Area of Science:

• Environmental Science
• Biotechnology
• Chemical Engineering

Background:

• Denitrification is crucial for nitrogen removal but can produce nitrous oxide (N₂O), a potent greenhouse gas.
• Traditional denitrification processes lack efficient N₂O recovery methods.
• Sulfide's role in denitrification is complex and warrants further investigation for N₂O management.

Purpose of the Study:

• To develop and investigate a novel sulfide-driven process for N₂O recovery during denitrification.
• To determine the optimal conditions for sulfide concentration in N₂O recovery.
• To elucidate the mechanism by which sulfide influences N₂O accumulation.

Main Methods:

• Experimental investigation of a sulfide-driven denitrification process.
• Optimization of initial sulfide concentration for N₂O recovery.
• Analysis of gaseous products using gas chromatography.
• Enzyme activity assays for nitrous oxide reductase (N₂OR).
• Spectroscopic techniques (cyclic voltammetry, circular dichroism, fluorescence) to study protein structure and function.

Main Results:

• The optimal initial sulfide concentration for N₂O recovery was 120 mg/L.
• N₂O constituted up to 82.9% of the gaseous products (N₂O+N₂) at 120 mg/L sulfide.
• Sulfide effectively substituted for organic carbon as an electron donor (1 g sulfide ≈ 0.5-2 g COD).
• Sulfide inhibited N₂OR activity to 36.8% of its original level at 120 mg/L.
• Sulfide altered the conformation and function of cytochrome c, impairing electron transport to N₂OR.

Conclusions:

• A novel sulfide-driven process enables efficient N₂O recovery during denitrification.
• Sulfide inhibits N₂OR by disrupting electron transfer via cytochrome c.
• This process offers a new strategy for N₂O mitigation and recovery in denitrification systems.