Comparative analysis of CH4 and N2O generation and emission characteristics in A2/O and A2/O-MBR wastewater treatment plants

SHANG Zhenxin; LIU Jia; GUO Yanli; HUANG Xiangfeng; CAI Chen

doi:10.13205/j.hjgc.202606013

Volume 44 Issue 6

Jun. 2026

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SHANG Zhenxin, LIU Jia, GUO Yanli, HUANG Xiangfeng, CAI Chen. Comparative analysis of CH4 and N2O generation and emission characteristics in A2/O and A2/O-MBR wastewater treatment plants[J]. ENVIRONMENTAL ENGINEERING , 2026, 44(6): 126-137. doi: 10.13205/j.hjgc.202606013

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SHANG Zhenxin, LIU Jia, GUO Yanli, HUANG Xiangfeng, CAI Chen. Comparative analysis of CH₄ and N₂O generation and emission characteristics in A²/O and A²/O-MBR wastewater treatment plants[J]. ENVIRONMENTAL ENGINEERING , 2026, 44(6): 126-137. doi: 10.13205/j.hjgc.202606013

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Comparative analysis of CH₄ and N₂O generation and emission characteristics in A²/O and A²/O-MBR wastewater treatment plants

doi: 10.13205/j.hjgc.202606013

SHANG Zhenxin^1,2,
LIU Jia^1,2,
GUO Yanli¹,
HUANG Xiangfeng^1,2,
CAI Chen^{1,2
,
,}

1. College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China;
2. Institute of Carbon Neutrality, Tongji University, Shanghai 200092, China

Received Date: 2025-08-06
Accepted Date: 2025-09-20
Rev Recd Date: 2025-09-10

Available Online: 2026-07-06

Abstract

Abstract

The A²/O-MBR process， owing to its superior effluent quality and smaller footprint， is increasingly adopted in newly built and upgraded wastewater treatment plants. However， systematic studies on its greenhouse gas （GHG） emissions remain scarce， and direct comparisons with the conventional A²/O process are lacking. In this study， two full-scale wastewater treatment plants employing the A²/O and A²/O-MBR processes under identical influent conditions， climate， and discharge standards were investigated. A high-frequency monitoring system covering the entire treatment train was established， and combined with measurements of dissolved CH₄ and N₂O， water quality parameters， and operational parameters， to elucidate the differences in GHG emission characteristics. Results showed that the daily average CH₄ emission intensities were not significantly different between the two plants ［（0.67 ± 0.22），（0.65 ± 0.18） g/m³， respectively］. CH₄ emissions mainly originated from sewer-derived anaerobic production and subsequent release in the pretreatment units （accounting for over 70% of the total emissions）， with partial in-plant oxidation by methanotrophs. Temperature and aeration-induced stripping were identified as key driving factors， as CH₄ emissions were positively correlated with ambient temperature and dissolved oxygen （DO）. In contrast， more than 90% of N₂O emissions occurred in the biological treatment units. The A²/O-MBR plant exhibited significantly higher daily N₂O emission intensity ［（0.132 ± 0.055） g/m³］ than the A²/O plant ［（0.060 ± 0.046） g/m³］， largely due to intensive aeration and oxygen-enriched internal/external recirculation in the membrane tank， which enhanced N₂O production and stripping. Correlation analysis further revealed that N₂O emissions in the A²/O plant were positively related to influent COD and BOD₅， indicating dominance of heterotrophic denitrification， whereas in the A²/O-MBR process they were mainly driven by NH₃-N loading and DO， reflecting a nitrification-based pathway. Importantly， both processes exhibited CH₄ and N₂O emission factors that were significantly lower than the reference values recommended by the IPCC and industry guidelines， underscoring the necessity of developing localized emission factors. This study fills a critical research gap concerning the greenhouse-gas generation and emission characteristics of the A²/O-MBR process， reveals the mechanistic differences between A²/O and A²/O-MBR process， and provides essential data to support greenhouse-gas emission inventories. The findings offer a scientific basis for targeted mitigation measures and can guide low-carbon process selection and planning for both upgrading existing urban wastewater treatment plants and designing new facilities.
- A²/O,
- A²/O-MBR,
- methane,
- wastewater treatment plant,
- nitrous oxide

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References(51)

References

[1]	NAYEB H，MIRABI M，MOTIEE H，et al. Estimating greenhouse gas emissions from Iran's domestic wastewater sector and modeling the emission scenarios by 2030[J]. Journal of Cleaner Production，2019，236：117793.
[2]	BARTRAM D，SHORT M，EBIE Y，et al. VOL 5 refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories Chapter 6 Wastewater Treatment and Discharge[J]. Wastewater Treat Disch，2019，5：7-65.
[3]	VASILAKI V，MASSARA T M，STANCHEV P，et al. A decade of nitrous oxide（N₂O）monitoring in full-scale wastewater treatment processes：a critical review[J]. Water Res，2019，161：392-412.
[4]	MOORE D P，LI N P，WENDT L P，et al. Underestimation of sector-wide methane emissions from United States wastewater treatment[J]. Environ Sci Technol，2023，57（10）：4082-4090.
[5]	TONG Y，LIAO X，HE Y，et al. Mitigating greenhouse gas emissions from municipal wastewater treatment in China[J]. Environ Sci Ecotechnol，2024，20：100341.
[6]	RENA Y G，WANG J H，LI H F，et al. Nitrous oxide and methane emissions from different treatment processes in full-scale municipal wastewater treatment plants[J]. Environ Technol，2013，34（21/24）：2917-2927.
[7]	RODRIGUEZ-CABALLERO A，AYMERICH I，MARQUES R，et al. Minimizing N₂O emissions and carbon footprint on a full-scale activated sludge sequencing batch reactor[J]. Water Res，2015，71：1-10.
[8]	LI H J，PENG D C，LIU W B，et al. Emissions of non-CO₂ greenhouse gases from different wastewater treatment processes[J]. Environmental Science，2017，38（4）：1640-1646. 李惠娟，彭党聪，刘文博，等. 不同污水处理工艺非二氧化碳温室气体的释放[J]. 环境科学，2017，38（4）：1640-1646.
[9]	YU L，PENG K，HUANG Y，et al. Application of a water-energy-carbon coupling index to evaluate the long-term operational stability of the anaerobic-anoxic-oxic-membrane bioreactor（A²/O-MBR）process under the influence of rainstorms[J]. Water Res，2024，255：121489.
[10]	HU Y F，LIANG M，ZHANG Y X，et al. Operation performance and carbon emission characteristics of A²/O+MBR process[J]. China Environmental Science，2021，41（9）：4439-4446. 呼永锋，梁梅，张永祥，等. A²/O+MBR工艺运行效果与碳排放特征研究[J]. 中国环境科学，2021，41（9）：4439-4446.
[11]	State Environmental Protection Administration. Discharge standard of pollutants for municipal wastewater treatment plant[Z]. Beijing：General Administration of Quality Supervision，Inspection and Quarantine of the People's Republic of China，2002：1-13. 国家环境保护总局. 城镇污水处理厂污染物排放标准[Z]. 北京：国家质检总局，2002：1-13.
[12]	SHANG Z，CAI C，GUO Y，et al. Direct and indirect monitoring methods for nitrous oxide emissions in full-scale wastewater treatment plants：a critical review[J]. J Environ Manage，2024，358：120842.
[13]	XIONG P Y，QIAN X Y，WANG L H，et al. In-situ measurement of N₂O emissions and calculation of localized emission factors in fully covered wastewater treatment plants[J]. China Water& Wastewater，2024，40（15）：28-35. 熊鹏宇，钱晓雍，王丽花，等. 全覆盖污水处理厂N₂O排放实测及本地化因子测算[J]. 中国给水排水，2024，40（15）：28-35.
[14]	KOSONEN H，HEINONEN M，MIKOLA A，et al. Nitrous oxide production at a fully covered wastewater treatment plant：results of a long-term online monitoring campaign[J]. Environ Sci Technol，2016，50（11）：5547-5554.
[15]	ZHANG L M，CHEN M，HUANG Z C，et al. Monitoring method and device for dissolved greenhouse gases in sewage[P/OL].（2025-07-11）[2026-02-24]. CN 118465123B. 张莉敏，陈鸣，黄昭昶，等. 一种污水中溶解态温室气体的监测方法及装置[P/OL].（2025-07-11）[2026-02-24]. CN 118465123B.
[16]	SUTKA R L，OSTROM N E，OSTROM P H，et al. Distinguishing nitrous oxide production from nitrification and denitrification on the basis of isotopomer abundances[J]. Applied and Environmental Microbiology，2006，72（1）：638-644.
[17]	WIESENBURG D A，GUINASSO Jr N L. Equilibrium solubilities of methane，carbon monoxide，and hydrogen in water and sea water[J]. Journal of Chemical and Engineering Data，1979，24（4）：356-360.
[18]	WEISS R，PRICE B. Nitrous oxide solubility in water and seawater[J]. Marine Chemistry，1980，8（4）：347-359.
[19]	WEISS R F. The solubility of nitrogen，oxygen and argon in water and seawater[C]// Deep sea research and oceanographic abstracts. Elsevier，1970，17（4）：721-735.
[20]	WANG J，ZHANG J，XIE H，et al. Methane emissions from a full-scale A/A/O wastewater treatment plant[J]. Bioresour Technol，2011，102（9）：5479-5485.
[21]	WANG S，LIU Q，LI J，et al. Methane in wastewater treatment plants：status，characteristics，and bioconversion feasibility by methane oxidizing bacteria for high value-added chemicals production and wastewater treatment[J]. Water Res，2021，198：117122.
[22]	SONG C，ZHU J J，WILLIS J L，et al. Methane emissions from municipal wastewater collection and treatment systems[J]. Environ Sci Technol，2023，57（6）：2248-2261.
[23]	BAETEN J E，WALGRAEVE C，GRANJA R C，et al. Unaerated feeding alters the fate of dissolved methane during aerobic wastewater treatment[J]. Water Res，2021，204：117619.
[24]	GUISASOLA A，DE HAAS D，KELLER J，et al. Methane formation in sewer systems[J]. Water Res，2008，42（6-7）：1421-1430.
[25]	China Urban Water Association. Guidelines for carbon accounting and emission reduction in the urban water sector[M]. Beijing：China Architecture& Building Press，2022：1-202.
[26]	YU W，LIU R，ZHU K，et al. Variable emission factors of CH₄ and N₂O from WWTPs：a model-based analysis on available data[J]. Environ Res，2025，264（Pt 1）：120380.
[27]	LIU Y，CHENG X，LUN X，et al. CH₄ emission and conversion from A²O and SBR processes in full-scale wastewater treatment plants[J]. J Environ Sci（China），2014，26（1）：224-230.
[28]	YAN X，LI L，LIU J. Characteristics of greenhouse gas emission in three full-scale wastewater treatment processes[J]. J Environ Sci（China），2014，26（2）：256-263.
[29]	CHEN H L，QI L，CHEN J B，et al. Differences and mechanisms of N₂O emission characteristics in typical wastewater treatment processes[J]. China Environmental Science，2025，45（2）：718-726. 陈慧玲，齐鲁，陈加波，等. 典型污水处理工艺中N₂O排放特征差异及机制[J]. 中国环境科学，2025，45（2）：718-726.
[30]	ZHANG Y L，LIU H，QIAN X Y. N₂O emissions from municipal wastewater treatment plants：emission characteristics and control measures[J]. Environmental Engineering，2024，42（4）：9-21. 张亦藜，刘辉，钱晓雍. 城镇污水处理厂N₂O排放：排放特征及控制措施[J]. 环境工程，2024，42（4）：9-21.
[31]	DAELMAN M R J，van VOORTHUIZEN E M，van DONGEN U，et al. Seasonal and diurnal variability of N₂O emissions from a full-scale municipal wastewater treatment plant[J]. Sci Total Environ，2015，536：1-11.
[32]	DOMINGO-FéLEZ C，JENSEN M M，BANG A，et al. Variability and uncertainty analysis of N₂O emissions from WWTP to improve the accuracy of emission factors and the design of monitoring strategies[J]. ACS ES&T Water，2024，4（6）：2542-2552.
[33]	FOLEY J，de HAAS D，YUAN Z，et al. Nitrous oxide generation in full-scale biological nutrient removal wastewater treatment plants[J]. Water Res，2010，44（3）：831-844.
[34]	WANG Y，LIN X，ZHOU D，et al. Nitric oxide and nitrous oxide emissions from a full-scale activated sludge anaerobic/anoxic/oxic process[J]. Chemical Engineering Journal，2016，289：330-340.
[35]	SUN S，CHENG X，LI S，et al. N₂O emission from full-scale urban wastewater treatment plants：a comparison between A²O and SBR[J]. Water Sci Technol，2013，67（9）：1887-1893.
[36]	VIEIRA A，GALINHA C F，OEHMEN A，et al. The link between nitrous oxide emissions，microbial community profile and function from three full-scale WWTPs[J]. Sci Total Environ，2019，651（Pt 2）：2460-2472.
[37]	ROOTHANS N，PABST M，VAN DIEMEN M，et al. Long-term multi-meta-omics resolves the ecophysiological controls of seasonal N₂O emissions during wastewater treatment[J]. Nat Water，2025，3（5）：590-604.
[38]	CHONG Y，LI H，PAN T，et al. More applicable quantification of non-CO₂ greenhouse gas emissions from wastewater treatment plants by on-site plant-integrated measurements[J]. Sci Total Environ，2024，929：172598.
[39]	YAN Y，SONG C，ZHU J J，et al. Methodology discrepancy and data comparability of greenhouse gas monitoring from water resource recovery facilities[J]. Environ Sci Technol，2025，59（25）：12567-12583.
[40]	HOU F，LIU S，YIN W X，et al. Methane production mechanism and control strategies for sewers：a critical review[J]. Water，2024，16（24）：3456.
[41]	YANG Y N，LI Y C，LI J，et al. Research progress in denitrification technologies based on methanotrophs[J]. Microbiology China，2020，47（3）：967-975. 杨娅男，李彦澄，李江，等. 基于甲烷氧化菌的脱氮技术研究进展[J]. 微生物学通报，2020，47（3）：967-975.
[42]	DAELMAN M R，van VOORTHUIZEN E M，van DONGEN U G，et al. Methane emission during municipal wastewater treatment[J]. Water Res，2012，46（11）：3657-3670.
[43]	GRUBER W，MAGYAR P M，MITROVIC I，et al. Tracing N₂O formation in full-scale wastewater treatment with natural abundance isotopes indicates control by organic substrate and process settings[J]. Water Res X，2022，15：100130.
[44]	DUAN H，ZHAO Y，KOCH K，et al. Insights into nitrous oxide mitigation strategies in wastewater treatment and challenges for wider implementation[J]. Environ Sci Technol，2021，55（11）：7208-7224.
[45]	CHEN H，ZENG L，WANG D，et al. Recent advances in nitrous oxide production and mitigation in wastewater treatment[J]. Water Res，2020，184：116168.
[46]	NI B J，YUAN Z. Recent advances in mathematical modeling of nitrous oxides emissions from wastewater treatment processes[J]. Water Res，2015，87：336-346.
[47]	BLOMBERG K，KOSSE P，MIKOLA A，et al. Development of an extended ASM3 model for predicting the nitrous oxide emissions in a full-scale wastewater treatment plant[J]. Environ Sci Technol，2018，52（10）：5803-5811.
[48]	ARONIADA M，MAINA S，KOUTINAS A，et al. Estimation of volumetric mass transfer coefficient（K_La）—Review of classical approaches and contribution of a novel methodology[J]. Biochemical Engineering Journal，2020，155：107452.
[49]	MYERS S，MIKOLA A，BLOMBERG K，et al. Comparison of methods for nitrous oxide emission estimation in full-scale activated sludge[J]. Water Sci Technol，2021，83（3）：641-651.
[50]	KEMMOU L，AMANATIDOU E. Factors affecting nitrous oxide emissions from activated sludge wastewater treatment plants：a review[J]. Resources，2023，12（10）：114.
[51]	YAN X，HAN Y，LI Q，et al. Impact of internal recycle ratio on nitrous oxide generation from anaerobic/anoxic/oxic biological nitrogen removal process[J]. Biochemical Engineering Journal，2016，106：11-18.