Modelling the full-scale N2O emissions from wastewater treatment plants for identifying mitigation strategies
(2023) VVAM01 20231Chemical Engineering (M.Sc.Eng.)
- Abstract
- Nitrous oxide (N2O) emissions, which primarily originate from the biological nitrogen removal process, dominate the release of greenhouse gases (GHGs) in wastewater treatment plants (WWTPs). N2O production occurs through dynamic microbial pathways that have a significant impact on the environment compared with other GHG emissions. Reducing these substantial emissions aligns with the objectives of minimizing the carbon footprint of WWTPs and achieving sustainability. This study aims to investigate the pathways responsible for N2O production through a comprehensive model-based approach on a full-scale basis to identify effective mitigation strategies.
To model N2O emissions, this study employs the activated sludge model (ASM), specifically... (More) - Nitrous oxide (N2O) emissions, which primarily originate from the biological nitrogen removal process, dominate the release of greenhouse gases (GHGs) in wastewater treatment plants (WWTPs). N2O production occurs through dynamic microbial pathways that have a significant impact on the environment compared with other GHG emissions. Reducing these substantial emissions aligns with the objectives of minimizing the carbon footprint of WWTPs and achieving sustainability. This study aims to investigate the pathways responsible for N2O production through a comprehensive model-based approach on a full-scale basis to identify effective mitigation strategies.
To model N2O emissions, this study employs the activated sludge model (ASM), specifically ASM2dISS, which incorporates two N2O production pathways: nitrifier denitrification and heterotrophic denitrification pathways. The collected measurements are pre-processed in MATLAB by filling in the missing values and removing the outlier values using flow balances and the data is analyzed for obtaining clean data for modelling the treatment plant and for choosing the periods for model simulations. With the available data, the model is constructed in the WEST and firstly, steady-state simulations are calibrated, and then dynamic calibrations are performed using dynamic data of 24-hour daily measurements. Calibrations are executed for solids, nitrogen species and N2O emissions of the treatment process and the calibrated model is validated for different periods. Kinetic parameters are adjusted in the model and calibration and validation results are compared with the plant measurements. Model simulations generally predicted well with the measured values in most of the simulated days except nitrate content in the activated sludge units which is slightly underestimated than the measurements. It is identified that nitrate concentration is strongly correlated with N2O emissions and as calibration is focused on N2O emissions, nitrate calibration is limited considering its effect on N2O emissions. Model results revealed that N2O emissions are contributed by both nitrifier denitrification and heterotrophic denitrification pathways with heterotrophic denitrification as a dominant pathway.
The calibrated model is used for implementing the mitigation strategies in the activated sludge process. Two approaches have been proposed as mitigation strategies, one is to vary the SRT of the system and another approach is to introduce internal recirculation in the secondary treatment process. The second approach is evaluated with four cases, by varying recirculation flow rates and the number of anoxic zones in the process. Results are compared with calibrated values as a reference, in which results from both approaches showed a good reduction of N2O emissions. When results from all the strategies are compared, 3 times the internal recirculation with 1 anoxic zone showed good possibilities for lowering N2O emissions from the treatment process. Each strategy comes with certain positives and negatives in terms of process modifications and energy demands, therefore every aspect needs to be considered for implementing the proposed mitigation strategies. (Less) - Popular Abstract
- Traditional operation of wastewater treatment plants is solely focused on efficient pollutant and nutrient removal to protect the health and environment of society. Recently, a new aspect came into consideration with respect to mitigating greenhouse gas specifically N2O emissions and energy demands for the sustainability of WWTPs. Klagshamn WWTP, located in southern Malmö is discharging high N2O emissions from the treatment process and for this reason, VA SYD wants to explore different operating strategies to mitigate nitrous oxide emissions from the biologically activated sludge treatment process, using the N2O measured data from floating hoods arranged at the treatment plant. Modelling a mechanistic model is a cost-efficient way to... (More)
- Traditional operation of wastewater treatment plants is solely focused on efficient pollutant and nutrient removal to protect the health and environment of society. Recently, a new aspect came into consideration with respect to mitigating greenhouse gas specifically N2O emissions and energy demands for the sustainability of WWTPs. Klagshamn WWTP, located in southern Malmö is discharging high N2O emissions from the treatment process and for this reason, VA SYD wants to explore different operating strategies to mitigate nitrous oxide emissions from the biologically activated sludge treatment process, using the N2O measured data from floating hoods arranged at the treatment plant. Modelling a mechanistic model is a cost-efficient way to investigate different strategies for mitigating N2O emissions.
A model of Klagshamn wastewater treatment plant process is developed in the WEST software with the ASM2dISS model. The model includes two pathways of N2O emissions (ie., Nitrifier denitrification pathway by AOBs and heterotrophic denitrification pathway by OHOs). Full-scale measurement data is carefully preprocessed and subjected to flow balances and linear regressions to eliminate outliners and select suitable simulation periods. The steady-state and dynamic model simulation results are calibrated and validated against measurements with showing a reasonable fit, considering parameters such as solids content, nitrogen species, and N2O by adjusting the kinetic parameters. Despite the limitations in the available production pathways within the model, the dominant pathway for N2O emissions is determined to be heterotrophic denitrification. Based on the simulation results, several strategies for mitigating N2O emissions are evaluated, and two particularly effective strategies are proposed in this study. The first strategy involves modifying the retention time of solids in the process, while the second strategy focuses on implementing internal recirculation within the treatment process. The second strategy is further explored through four different cases, considering variations in recirculate flow rates and the number of anoxic zones. Both proposed strategies yield positive outcomes, but the second strategy demonstrates a higher reduction in the N2O emission factor compared to the first. Among the four cases analysed for the second strategy, it is revealed that the third case, which involves internal recirculation at three times the influent flow rate with one anoxic zone, achieves a substantial 47% reduction in the N2O emission factor.
Furthermore, the proposed strategies are assessed for their impact on the treatment process, including nitrogen species concentrations, to evaluate their influence on process efficiency and identified to be within acceptable limits. It is recommended to thoroughly consider the advantages and disadvantages of each strategy before implementing the proposed mitigation measures. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9131005
- author
- Peddamudium, Naga Deepika LU
- supervisor
-
- Ramesh Saagi LU
- organization
- alternative title
- Mitigation strategies for N2O emissions from wastewater treatment plants with full-scale modelling studies
- course
- VVAM01 20231
- year
- 2023
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Modelling, simulation, ASM2dISS, N2O production pathways, N2O emission factor, mitigation strategies, water and environmental engineering
- report number
- 03
- language
- English
- id
- 9131005
- date added to LUP
- 2023-06-30 11:00:33
- date last changed
- 2023-06-30 11:00:33
@misc{9131005,
abstract = {{Nitrous oxide (N2O) emissions, which primarily originate from the biological nitrogen removal process, dominate the release of greenhouse gases (GHGs) in wastewater treatment plants (WWTPs). N2O production occurs through dynamic microbial pathways that have a significant impact on the environment compared with other GHG emissions. Reducing these substantial emissions aligns with the objectives of minimizing the carbon footprint of WWTPs and achieving sustainability. This study aims to investigate the pathways responsible for N2O production through a comprehensive model-based approach on a full-scale basis to identify effective mitigation strategies.
To model N2O emissions, this study employs the activated sludge model (ASM), specifically ASM2dISS, which incorporates two N2O production pathways: nitrifier denitrification and heterotrophic denitrification pathways. The collected measurements are pre-processed in MATLAB by filling in the missing values and removing the outlier values using flow balances and the data is analyzed for obtaining clean data for modelling the treatment plant and for choosing the periods for model simulations. With the available data, the model is constructed in the WEST and firstly, steady-state simulations are calibrated, and then dynamic calibrations are performed using dynamic data of 24-hour daily measurements. Calibrations are executed for solids, nitrogen species and N2O emissions of the treatment process and the calibrated model is validated for different periods. Kinetic parameters are adjusted in the model and calibration and validation results are compared with the plant measurements. Model simulations generally predicted well with the measured values in most of the simulated days except nitrate content in the activated sludge units which is slightly underestimated than the measurements. It is identified that nitrate concentration is strongly correlated with N2O emissions and as calibration is focused on N2O emissions, nitrate calibration is limited considering its effect on N2O emissions. Model results revealed that N2O emissions are contributed by both nitrifier denitrification and heterotrophic denitrification pathways with heterotrophic denitrification as a dominant pathway.
The calibrated model is used for implementing the mitigation strategies in the activated sludge process. Two approaches have been proposed as mitigation strategies, one is to vary the SRT of the system and another approach is to introduce internal recirculation in the secondary treatment process. The second approach is evaluated with four cases, by varying recirculation flow rates and the number of anoxic zones in the process. Results are compared with calibrated values as a reference, in which results from both approaches showed a good reduction of N2O emissions. When results from all the strategies are compared, 3 times the internal recirculation with 1 anoxic zone showed good possibilities for lowering N2O emissions from the treatment process. Each strategy comes with certain positives and negatives in terms of process modifications and energy demands, therefore every aspect needs to be considered for implementing the proposed mitigation strategies.}},
author = {{Peddamudium, Naga Deepika}},
language = {{eng}},
note = {{Student Paper}},
title = {{Modelling the full-scale N2O emissions from wastewater treatment plants for identifying mitigation strategies}},
year = {{2023}},
}