Benedetti, Lorenzo

Ekström, Sara Elisabet Margareta

Jensen, Marlene Mark

Lemaire, Romain

Plósz, Benedek G.

Smets, Barth F.

Thornberg, Dines

Valverde Pérez, Borja

Vangsgaard, Anna Katrine

Nitrous oxide (N2O) is a strong greenhouse gas (GHG) and ozone depleter, with a warming potential 300 times higher than carbon dioxide (CO2). 1.2% of the total antrophopogenic N2O emissions are believed to originate from the wastewater treatment (WWT) sector. Conventional biological nutrient removal processes relying on nitrification and denitrification are known to produce N2O. A one year long-term study of N2O production and emissions was performed at Lynetten, Denmark’s largest WWTP. Nitrification and denitrification takes place by alternating process conditions as well as influent and effluent flows in 20 pairs of interconnected and surface aerated reactors. The long-term data revealed that the N2O emissions contribute to as much as 30% of the total CO2 footprint from the WWTP. High ammonium concentrations and long aeration phases lead to high N2O production and emissions rates. Nitrification phases were identified to produce and emit most of the N2O. High production and emissions were also associated with the afternoon loading peaks at the WWTP. During denitrification phases N2O was produced initially but consumed consequently. An effective control strategy was implemented, whereby N2O emissions were reduced from 0.8% to 0.3% of the nitrogen load during the mitigation period

Online Research Database In Technology

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Jul 07, 2018Simple control strategy for mitigating N2O emissions in phase isolated full-scaleWWTPsEkström, Sara Elisabet Margareta; Vangsgaard, Anna Katrine ; Lemaire, Romain; Valverde Pérez, Borja;Benedetti, Lorenzo ; Jensen, Marlene Mark; Plósz, Benedek G.; Thornberg, Dines; Smets, Barth F.Published in:Proceedings of 12th IWA Specialized Conference on Instrumentation, Control and AutomationPublication date:2017Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Ekström, S. E. M., Vangsgaard, A. K., Lemaire, R., Valverde Pérez, B., Benedetti, L., Jensen, M. M., ... Smets,B. F. (2017). Simple control strategy for mitigating N2O emissions in phase isolated full-scale WWTPs. InProceedings of 12th IWA Specialized Conference on Instrumentation, Control and Automation Quebec, Canada:IWA Publishing. Ekström et al. 1 Simple control strategy for mitigating N2O emissions in phase isolated full-scale WWTPs Sara Esktröm1*, Anna Katrine Vaansgard2, Romain Lemaire3, Borja Valverde-Pérez1*, Lorenzo Benedetti4, Marlene M. Jensen1, Benedek G. Plósz1, Dines Thornberg5 and Barth F. Smets1* 1Department of Environmental Engineering, Technical University of  Denmark, Denmark 2Krüger A/S, Denmark 3Technical & Performance Department, VEOLIA, France  4Waterways d.o.o., 44272, Lekenik, Croatia 5BIOFOS, Denmark  *Corresponding author: sarek@env.dtu.dk, bvape@env.dtu.dk; bfsm@env.dtu.dk Abstract Nitrous oxide (N2O) is a strong greenhouse gas (GHG) and ozone depleter, with a warming potential 300 times higher than carbon dioxide (CO2). 1.2% of the total antrophopogenic N2O emissions are believed to originate from the wastewater treatment (WWT) sector. Conventional biological nutrient removal processes relying on nitrification and denitrification are known to produce N2O. A one year long-term study of N2O production and emissions was performed at Lynetten, Denmark’s largest WWTP. Nitrification and denitrification takes place by alternating process conditions as well as influent and effluent flows in 20 pairs of interconnected and surface aerated reactors. The long-term data revealed that the N2O emissions contribute to as much as 30% of the total CO2 footprint from the WWTP. High ammonium concentrations and long aeration phases lead to high N2O production and emissions rates. Nitrification phases were identified to produce and emit most of the N2O. High production and emissions were also associated with the afternoon loading peaks at the WWTP. During denitrification phases N2O was produced initially but consumed consequently. An effective control strategy was implemented, whereby N2O emissions were reduced from 0.8%  to 0.3% of the nitrogen load during the mitigation period. Keywords: nitrous oxide emissions, mitigation strategies, biological nitrogen removal   INTRODUCTION Nitrous oxide (N2O) is a strong greenhouse gas with a warming potential 298 times higher than that of carbon dioxide (IPCC, 2013). Additionally N2O is a potent ozone depleter and the major current anthropogenic threat to the stratospheric ozone layer (Kanter et al., 2013). Globally, anthropogenic N2O emissions account for 6% of the total greenhouse gas emissions and 1.2% of the total N2O emissions are assumed to originate from the wastewater treatment (WWT) sector (U.S. EPA, 2016). The Intergovernmental Panel on Climate Change (IPCC) recommends to use a N2O emission factor of 0.0032 kg N2O-N person-1 year-1 equivalent to 0.035% of the nitrogen load to estimate N2O emissions from domestic wastewater treatment plants (WWTP) (IPCC, 2006). However full-scale N2O measurement campaigns have revealed that emissions can range from 0 -14.6% of the influent nitrogen load (Kampschreur et al., 2009). These findings suggests that IPCC emission factor may underestimate true emissions and there is a need to control and reduce N2O emissions originating from WWT operations. Process models are established tools for process optimisation, evaluation and prediction of operational strategies – even thought there is so far no consesus on how to model N2O dynamics. The objectives of this study is therefore to i) quantify the N2O emissions over long-term at a full-scale phase isolated WWTP (Lynetten WWTP); ii) develop a simulation model for the WWTP and calibrate it to predict N2O emissions; and  iii) develop, implement and evaluate Oral ICA2017 2 potential mitigation strategies based on model-based assesment and emperical knowledge gained from analysis of the long-term data set.   MATERIALS AND METHODS A one year long N2O quantification campaign was performed at Lynetten WWTP, Denmark’s largest WWTP, with a design load corresponding to 1,000,000 population equivalents. The WWTP is configured as a phase isolated activated sludge system for biological removal of COD, phosphorous and nitrogen. Nitrification and denitrification takes place by alternating process conditions as well as influent and effluent flows in 20 pairwise interconnected and surface aerated reactors (total volume:147.000 m3; Figure 1). Quantification of N2O emission rates were performed through N2O measurements in one of the phase isolated reactors. Electrode and flux-chamber techniques in combination with an infrared off-gas analyser were used to determine both liquid and gaseous phase N2O concentrations, respectively. Off-gas measurements were performed during campaigns lasting for up to a month whilst liquid phase measurements were continuously taken during a whole year from May 2015 until May 2016. Nitrogen mass balances were based on results from the regular monitoring program at the WWTP and used to calculate N2O emission factors. A wastewater fractionation campaign was performed and used as input for model calibration of the ASM2d model extended with the ASM-N (Hiat and Graddy, 2008) and the NDHA models (Domingo-Felez and Smets, 2016) to describe N conversions and N2O dynamics in detail. After experimental data assessment and model-based analysis, two different control strategies were applied and compared to normal operation contiditions.    Figure 1A) BioDeniphoTM reactor configuration with i) influent distributor, ii) interconnection in reactor wall, iii) submerged mixers, iv) surface aerators, v) effluent weirs vi) discharge,●) DO sensors, ■) NH4-N and NO3-N sensors, ▲) N2O sensors. B) Illustration of alternating influent flows and reactor conditions through a phase cycle.    RESULTS AND DISCUSSION The long-term data set showed consistent daily dynamics, which strongly related to nitrogen loading rate (NLR), operational phase, and bulk phase NH4-N concentrations. As illustraded in Figure 2, the dissolved N2O concentration increased towards the second half of the day. This was also accompanied by increased duration of the operational phase lengths, ie. longer time intervals between the shifts regarding influent flow as well as between anoxic and aerobic conditions in the reactors. Liquid N2O concentrations were mainly increasing during the nitrification phase, whilst N2O was consumed after an initial increase during the denitrification phase.  A B3 421i iiiiiivvvi Ekström et al. 3   Figure 2. Daily dry weather dynamics during normal operation, Up: Liquid phase N2O (─) concentration (mg L-1); Middle: reactor concentrations of NH4-N (─) and NO3-N (mg L-1) (─); Bottom: bulk DO (─) (mg L-1), the current operation phase (─) is displayed in all graphs.     Based on these results a mitigation strategy was developed. Figure 3 and Figure 4 show a three day period of normal operation and operation with the mitigation strategy, respectively. As can be seen from these graphs the nitrogen loading rates during these days were similar corresponding to 5.1∙10-3 and 5.0∙10-3 (kgN m-3 d-1) respectively. Effluent ammonium concentrations was reduced from an average of 2.3 to 1.8 (mg L-1). N2O emissions corresponded to 0.3% of the nitrogen load during the mitigation period compared to 0.8% during normal operation conditions.   Oral ICA2017 4   Figure 3 Up: Dry weather influent flow (─) (m3 h-1) and NLR (─) (kgN m3 h-1); Middle: reactor concentrations of NH4-N (─) and NO3-N (─) (mg L-1); Bottom: bulk phase concentration of N2O (─) (mg L-1) and emitted N2O (─) (kg m-3d-1) during normal loading and operation conditions.    Figure 4 Up: Dry weather influent flow (m3 h-1) and NLR (─) (kgN m3 h-1); Middle: effluent reactor concentrations of NH4-N and NO3-N; Bottom: bulk phase concentrations of N2O (mg L-1) and N2O (kg m-3d-1) emission rates during N2O sensor controlled operation.    CONCLUSIONS In this work we revealed that, during dry weather conditions, mitigation strategies can reduce N2O production and emissions from a phase isolated full-scale WWTP. In addition, the liquied effluent quality from the biological reactor improved while the mitigation strategy was in operation.   Ekström et al. 5  Aknowledgement This work has been funded by the Innovation Fund Denmark (IFD; Project LaGas, File No. 0603-00523B).   REFERENCES  Domingo-Félez, C., Smets, B.F., 2016. A consilience model to describe N2O production during biological N removal. Environmental Science: Water Research & Technology  IPCC, 2006. 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Prepared by the National Greenhouse Gas Inventories Programme. Published: IGES, Japan. IPCC, 2013. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.  Hiatt WC, Grady CPL. 2008. An updated process model for carbon oxidation, nitriﬁcation, and denitriﬁcation. Water Environ Res 80:2145–2156. Kampschreur, M.J., Temmink, H., Kleerebezem, R., Jetten, M.S.M., van Loosdrecht, M.C.M., 2009. Nitrous oxide emission during wastewater treatment. Water Res. 43, 4093–4103. doi:10.1016/j.watres.2009.03.001 Kanter, D., Mauzerall, D.L., Ravishankara, A.R., Daniel, J.S., Portmann, R.W., Grabiel, P.M., Moomaw, W.R., Galloway, J.N., 2013. A post-Kyoto partner: considering the stratospheric ozone regime as a tool to manage nitrous oxide. Proc. Natl. Acad. Sci. U. S. A. 110, 4451–7. doi:10.1073/pnas.1222231110 U.S. Environmental Protection Agency, 2016. Inventory of U.S . Greenhouse Gas Emissions and Sinks : 1990 - 2014, EPA 430-R-16-002. Washington, DC.   

Simple control strategy for mitigating N<sub>2</sub>O emissions in phase isolated full-scale WWTPs

http://orbit.dtu.dk/ws/files/133729982/ICA2017_Ekstrom_final_revised4.pdf

Simple control strategy for mitigating N<sub>2</sub>O emissions in phase isolated full-scale WWTPs

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology