Nitrous oxide emissions from two full-scale membrane-aerated biofilm reactors

Area of Science:

• Environmental Engineering
• Wastewater Treatment Technologies
• Greenhouse Gas Emissions

Background:

• Upcoming legislation in Europe will tax wastewater treatment facilities based on direct greenhouse gas (GHG) emissions.
• This necessitates a closer examination of nitrous oxide (N₂O) production in treatment processes.
• Membrane aerated biofilm reactors (MABR) are an emerging technology for municipal wastewater treatment.

Purpose of the Study:

• To quantify and analyze nitrous oxide (N₂O) emissions from two full-scale membrane aerated biofilm reactors (MABR).
• To assess the impact of operational strategies, such as Oxidation Reduction Potential (ORP) control, on N₂O emissions.
• To compare different methods for calculating N₂O emission factors (EF_N2O) and their correlation with nitrogen loading rates.

Main Methods:

• Continuous monitoring of N₂O in MABR exhaust gas and liquid phase over 12 months.
• Application of multivariate analysis to assess process performance.
• Comparison of various N₂O emission factor calculation methodologies.

Main Results:

• N₂O emission factors (EF_N2O) for both MABRs were similar (0.88 ± 1.28% and 0.82 ± 0.86%) and below the IPCC 2019 standard (1.6%).
• N₂O emissions were primarily in the exhaust gas and correlated with ammonia load, but ORP control increased bulk N₂O contribution.
• Calculated EF_N2O varied from 0.6% to 5.5% based on calculation methods; an average EF_N2O of 0.86% was found for high nitrogen loading rates (>200 g N m⁻³ d⁻¹).

Conclusions:

• MABR technology demonstrates potential for intensified biological nutrient removal with low N₂O emissions.
• Operational control strategies, like ORP, can influence N₂O production pathways and mass transfer.
• Accurate calculation of N₂O emission factors is crucial and depends significantly on the methodology employed.