Evaluation of nitrous oxide reduction in solid carbon source-driven counter-diffusional biofilm denitrification...

Area of Science:

• Environmental Microbiology
• Environmental Chemistry
• Biotechnology

Background:

• Solid carbon sources in biofilm systems offer denitrification potential but can delay carbon-nitrogen contact, affecting electron transport and increasing nitrous oxide (N2O) emissions in wastewater treatment plants (WWTPs).
• The specific dynamics of N2O production and consumption during solid-phase denitrification (SPD) remain poorly understood, hindering optimization of nitrogen removal processes.

Purpose of the Study:

• To investigate the N2O dynamics and overall nitrogen removal efficiency in a polycaprolactone (PCL)-driven fixed-bed bioreactor for solid-phase denitrification.
• To elucidate the impact of electron competition on N2O emissions and nitrogen conversion under varying nitrogen oxide concentrations.

Main Methods:

• A fixed-bed bioreactor utilizing polycaprolactone (PCL) as a solid carbon source was operated for 180 days.
• Biochemical analyses were conducted to assess nitrogen removal efficiency, N2O dynamics, and microbial community composition under different nitrogen oxide (NOx) conditions.

Main Results:

• The PCL-driven system achieved high total nitrogen (TN) removal efficiencies of 97%-99%.
• Despite sufficient carbon supply, electron competition for N2O reductase (Nos) was observed, limiting N2O reduction (12.6% electron distribution, 1.42 mg/g VSS/h rate).
• Treating mixed nitrogen oxides (nitrate, nitrite, N2O) resulted in 1.75-2.3 times higher TN removal rates compared to sole nitrate treatment, alongside reduced N2O emissions.

Conclusions:

• PCL-driven biofilm denitrification effectively removes nitrogen but requires careful management to mitigate N2O emissions due to electron competition.
• The system demonstrates improved TN removal and reduced N2O byproduct formation when treating complex nitrogenous wastewater.
• The microbial community, particularly high abundances of Bacteroidota and Comamonadaceae, plays a crucial role in stable carbon release and nitrogen conversion.