Long-term nitrate removal through methane-dependent denitrification microorganisms in sequencing batch reactors fed...

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Engineering
• Biogeochemical Cycles

Background:

• Stringent nitrogen discharge standards necessitate advanced wastewater treatment methods.
• Denitrifying anaerobic methane oxidation (damo) bioprocesses offer a promising solution for nitrate removal using methane as an electron donor.
• Understanding the long-term stability and microbial dynamics of damo systems is critical for practical application.

Purpose of the Study:

• To achieve an engineering-acceptable nitrogen removal rate (NRR) in a damo system.
• To demonstrate the long-term stable performance of a damo system under nitrate and methane conditions.
• To investigate the microbial community structure and its role in the damo process.

Main Methods:

• Operation of two sequencing batch reactors (SBRs) with nitrate and methane for over 600 days at 30°C.
• Measurement of nitrogen removal rate (NRR).
• Analysis of the microbial community composition using real-time PCR.

Main Results:

• An exceptionally high NRR of 21.91 ± 0.73 mg NO₃⁻-N L⁻¹ day⁻¹ was achieved, the highest reported under similar conditions.
• The damo system demonstrated long-term stability, with damo archaea outnumbering damo bacteria (ratio 1.77).
• Temperature significantly impacted system performance, and damo archaea reducing nitrate to nitrite may be the rate-limiting step.

Conclusions:

• SBRs are suitable for enriching slow-growing damo microbes.
• The cooperative action between damo archaea and bacteria ensures long-term process stability.
• Damo processes show significant potential for nitrogen removal in low C/N ratio wastewater.