Methane mitigation via the nitrite-DAMO process induced by nitrate dosing in sewers.

Area of Science:

• Environmental Microbiology
• Biogeochemical Cycles
• Wastewater Treatment

Background:

• Nitrate or nitrite-dependent anaerobic methane oxidation (n-DAMO) is a key microbial process linking carbon and nitrogen cycles, acting as a methane sink.
• Sewer systems are significant sources of methane emissions, impacting climate and infrastructure.
• Controlling sulfide in sewers often involves nitrate dosing, with potential co-benefits for methane mitigation.

Purpose of the Study:

• To investigate the potential for stimulating nitrite-dependent anaerobic methane oxidation (nitrite-DAMO) in sewer systems.
• To quantify the impact of nitrate dosing on methane and sulfide removal in a laboratory sewer environment.
• To identify the microbial communities responsible for n-DAMO in sewer biofilms and sediments.

Main Methods:

• Laboratory-scale sewer system simulation with continuous nitrate dosing.
• Batch tests to confirm the coupling of methane oxidation with nitrate and nitrite reduction.
• Comprehensive microbial analysis using molecular techniques to identify n-DAMO bacteria and archaea.

Main Results:

• Continuous nitrate dosing achieved complete sulfide removal and approximately 50% reduction in dissolved methane concentration.
• Methane oxidation rates were comparable whether nitrate or nitrite was the electron acceptor (3.68 ± 0.5 and 3.57 ± 0.4 mg CH4 L−1 h−1, respectively).
• Candidatus Methylomirabilis (n-DAMO bacteria) were identified in sewer biofilms and sediments, indicating successful enrichment and contributing to significant nitrite reduction and methane removal.

Conclusions:

• Nitrite-DAMO can be effectively stimulated in sewer systems through nitrate dosing, offering a dual benefit of sulfide and methane control.
• The enrichment of n-DAMO bacteria, specifically Candidatus Methylomirabilis, plays a crucial role in methane mitigation within sewers.
• This study highlights a novel biological pathway for reducing methane emissions from wastewater infrastructure.