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Extraction of Structural Extracellular Polymeric Substances from Aerobic Granular Sludge
Published on: September 26, 2016
Nitrous oxide production in autotrophic nitrogen removal granular sludge: A modeling study
Xueming Chen1, Bing-Jie Ni2, Gürkan Sin1
1Process and Systems Engineering Center (PROSYS), Department of Chemical and Biochemical Engineering, Technical University of Denmark, Lyngby, Denmark.
Nitrous oxide (N2O) emissions from autotrophic nitrogen removal systems are reduced by understanding microbial pathways. Mathematical modeling reveals operating conditions and heterotrophic bacteria influence N2O production, aiding mitigation strategies.
Area of Science:
- Environmental Microbiology
- Biogeochemical Cycles
- Wastewater Treatment Engineering
Background:
- Autotrophic nitrogen removal systems, crucial for wastewater treatment, face sustainability challenges due to nitrous oxide (N2O) byproduct.
- Nitrous oxide (N2O) is a potent greenhouse gas, and its mitigation is essential for sustainable nitrogen removal processes.
Purpose of the Study:
- To systematically analyze N2O production pathways in granular systems performing partial nitritation and anaerobic ammonium oxidation (anammox).
- To develop and validate a mathematical model for N2O production mechanisms involving ammonium-oxidizing bacteria (AOB), nitrite-oxidizing bacteria, heterotrophic bacteria (HB), and anammox bacteria.
- To investigate the impact of operating conditions on N2O generation within these granular systems.
Main Methods:
- Development of a comprehensive mathematical model integrating key microbial pathways (AOB denitrification, NH2OH pathway, heterotrophic denitrification).
- Model validation using experimental data from two independent autotrophic nitrogen removal granular systems.
- Application of the validated model to simulate N2O production dynamics under various operational scenarios.
Main Results:
- AOB contribute to N2O production via denitrification and the NH2OH pathway in aerobic zones; HB can indirectly enhance N2O via the NH2OH pathway.
- The anoxic zone, dominated by anammox bacteria, acts as a nitrite sink, reducing N2O from AOB denitrification.
- Operating parameters (DO, NH4+, granule size) primarily influence the AOB NH2OH pathway, accounting for 34-58% of N2O turnover.
- Heterotrophic bacteria play a dual role, consuming N2O but also potentially enhancing it via the NH2OH pathway, with organic matter influencing the net effect.
Conclusions:
- The NH2OH pathway in AOB is a critical N2O source in granular systems, significantly affected by operational parameters.
- Heterotrophic bacteria's role in N2O mitigation is complex, influenced by competition for intermediates and the availability of organics.
- Optimizing operating conditions and potentially co-feeding organics can enhance N2O reduction in autotrophic nitrogen removal granular systems.
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