Methane emissions along biomethane and biogas supply chains are underestimated

•The biomethane and biogas supply chain may emit up to 18.5 Tg CH4 per year•Biomethane much less than oil natural gas•CH4 loss rates in exceed those gas•The top 5% of emitters account for 62% emissions An immediate shift away from coal energy is necessary limit rising temperatures but challenging due needs, particularly areas like heating cooling that require substantial all year round. Natural gas presently being used as a bridging fuel. It delivers the same performance has lower CO2 emissions. However, releases methane (CH4), which more powerful warming agent CO2. Biomethane have emerged strong candidates replace these replacement fuels are not emission free. Indeed, released at various points during production distribution, thorough understanding where, when, how remains absent. A synthesis analysis existing data reveal throughout chains been underestimated. The majority comes just few super-emitters mainly digestate stage. Mitigating urgently needed if we global 1.5°C. Although generates emissions, extraction, processing, distribution release methane, greater potential use organic wastes feedstock alternatives gas, with carbon extent still emitted stages along unclear. Here, adopt Monte Carlo approach systematically synthesize each key stage using collected literature. We show responsible Methane could be two times previously estimated, handling released. To ensure climate benefits production, effective methane-mitigation strategies must designed deployed IntroductionAs move further into 21st century, systems fossil grow renewable capacity Paris Agreement temperature targets met. challenges adopting low-carbon technologies, certain difficult decarbonize. These include heavy industry, transport, systems, together significant portion dioxide (CO2) emissions.1The Royal SocietyLow-carbon Heating Cooling: Overcoming One World’s Most Important Net Zero Challenges.https://royalsociety.org/-/media/policy/projects/climate-change-science-solutions/climate-science-solutions-heating-cooling.pdfDate: 2021Google Scholar therefore an important alternative fuel, can offer large-scale supply, especially domestic space hot water electricity generation, industrial applications, compared coal. replacing reduces fugitive gas—gas distribution—can CH4. Around 39.6 million tonnes were 2021,2IEAGlobal Tracker 2022. IEA, Paris2022https://www.iea.org/reports/global-methane-tracker-2022Google representing 61% 30% total-energy-sector Since stronger currently least one-quarter warming, there calls reduced by 35% 2050 70% 2100 relative 2019;3Speirs J. Dubey L. Balcombe P. Tariq N. Brandon Hawkes A. Best Uses Gas within Climate Targets. Sustainable Institute, Imperial College London, therefore, clean-energy methods vital 1.5°C.An method decarbonizing via it or biogas, mixture gases (mostly CO2) produced biodegradable materials. put forward part mitigation efforts,4Nisbet E.G. Fisher R.E. Lowry D. France J.L. Allen G. Bakkaloglu S. Broderick T.J. Cain M. Coleman Fernandez et al.Methane mitigation: reduce on path Agreement.Rev. Geophys. 2020; 58 (e2019RG000675)https://doi.org/10.1029/2019rg000675Crossref Google 37 exajoule (EJ)/year biomass-based Intergovernmental Panel Change Special Report Global Warming 1.5°C (IPCC SR1.5C) scenarios,5Huppmann IAMC 1.5° C Scenario Explorer Data Hosted IIASA. Integrated Assessment Modeling Consortium & International Institute Applied Systems Analysis, 2018https://doi.org/10.22022/SR15/08-2018.15429Crossref limits rises below 2°C. Energy Agency (IEA)6IEAOutlook Biogas Biomethane: Prospects Organic Growth. Paris2020Google reported satisfy nearly 20% demand its sustainable was fully utilized.6IEAOutlook Because similar easily stored injected infrastructure, potentially providing reliable affordable energy.7Marc-Antoine E.M. Mathieu C. Europe: Lessons Denmark, Germany Italy. Études de l’Ifri, 2019https://www.ifri.org/en/publications/etudes-de-lifri/biogas-and-biomethane-europe-lessons-denmark-germany-and-italyGoogle At time writing, Europe world leader upgrading followed United States, China, Canada.8The World Association Potential Biogas. Association, 2019https://www.worldbiogasassociation.org/wp-content/uploads/2019/07/WBA-globalreport-56ppa4_digital.pdfGoogle According (2019), 700 biogas-upgrading plants operating worldwide, 195 (the largest producer), dominating production. expected further, predicted 9-fold 2040 2018 levels,6IEAOutlook Scholar,9ADBAAnaerobic Digestion Policy Report. Anaerobic Bioresources 2019Google driven increases volume waste generated modern societies, changes practices, phasing out aimed reducing greenhouse (GHG) meeting government targets. Given this host commitments, investments, developments, crucial helping establish clean, reliable, system.However, large quantities chains, including handling, anaerobic digesters, units, storages transmission, storage stages.4Nisbet relatively short-lived GHG (GWP) 27.2 ± 11 larger over 100-year horizon 80.8 25.8 20-year biogenic sources.10IPCCAR6 2021: Physical Science Basis. Cambridge University Press, importance meet Agreement11Paris AgreementUnited Nations Framework Convention Change. Agreement, 2015Google demonstrated Rogelj al.,12Rogelj Meinshausen Schaeffer Knutti R. Riahi K. Impact non-CO2 budgets stabilizing warming.Environ. Res. Lett. 2015; 10: 075001https://doi.org/10.1088/1748-9326/10/7/075001Crossref Scopus (55) terms overshooting targets, where exceeds “well 2°C” then returns target level 2100,10IPCCAR6 leading tipping physical socio-economic systems. IPCC (Intergovernmental Change) Sixth (AR6) (Working Group III)13IPCCClimate 2022: Mitigation Contribution Working III 2022https://report.ipcc.ch/ar6wg3/pdf/IPCC_AR6_WGIII_FinalDraft_FullReport.pdfGoogle highlighted playing role determining whether when achieved, will offset increase quickly CO2, short lifetime higher potency. AR6 report also noted reductions need occur rapidly (and other GHG) essential lowering warming.13IPCCClimate As scenarios predict 200-fold between 2020 2050,14Edward B. Volker Elmar Keywan Roberto Jarmo Robin Zebedee Marit Chris al.AR6 Scenarios Database 2022Google crucial.There some emissions-measurement studies date focusing specific facilities,4Nisbet Scholar,15Reinelt T. McCabe B.K. Hill Harris Baillie Liebetrau Field measurements three Australian management facilities.Waste Manag. 2022; 137: 294-303https://doi.org/10.1016/j.wasman.2021.11.012Crossref PubMed (2) Scholar, 16Reinelt Monitoring pressure relief valves plant.Chem. Eng. Technol. 43: 7-18https://doi.org/10.1002/ceat.201900180Crossref (9) 17Reinelt Delre Westerkamp Holmgren M.A. Scheutz Comparative different measurement approaches determine plant.Waste management. 2017; 68: 173-185https://doi.org/10.1016/j.wasman.2017.05.053Crossref (28) 18Liebetrau Reinelt Agostini Linke Emissions Plants. IEA bioenergy, 2017Google 19Liebetrau Clemens Hafermann Friehe Weiland Analysis 10 agricultural sector.Water Sci. 2013; 67: 1370-1379https://doi.org/10.2166/wst.2013.005Crossref (72) 20Bakkaloglu Brunner Chen H. Nisbet Quantification UK plants.Waste 2021; 124: 82-93https://doi.org/10.1016/j.wasman.2021.01.011Crossref (25) 21Scheutz Fredenslund A.M. Total losses 23 2019; 97: 38-46https://doi.org/10.1016/j.wasman.2019.07.029Crossref (41) 22Flesch T.K. Desjardins R.L. Worth Fugitive biodigester.Biomass Bioenergy. 2011; 35: 3927-3935https://doi.org/10.1016/j.biombioe.2011.06.009Crossref (101) measured site (measurement individual point source) off based observations made site). referred bottom-up (on-site) top-down (off-site) studies. found facilities 97 kg h−1 CH4.4Nisbet Scholar,16Reinelt 23Daniel-Gromke Denysenko V. W S J humelock hemiarthoplasty device both primary failed proximal humerus fractures: case series.Open Orthop. 9: 1-6https://doi.org/10.2174/1874325001509010001Crossref 24Balde VanderZaag A.C. Burtt S.D. Wagner-Riddle Crolla MacDonald D.J. plant.Bioresour. 2016; 216: 914-922https://doi.org/10.1016/j.biortech.2016.06.031Crossref (47) comprehensive evaluation characterizing unclear.Here, bring published CH4-measurement assess order characterize profile (see experimental procedures Figure S1 selected route). aggregation examines This allows characterized. find that, while emits chain, rate higher. Furthermore, cumulative emitters. digestate-handling contributed chain. Our results allow improve sustainability plant operators, investors policymakers information improvements well proposed regulations sufficient revised.ResultsMethod summaryTo overall divided five major stages: (1) feedstock; production; (3) upgrading; (4) storage; (5) storage. study compiled several on-site (taken off-site (reported entire kernel density estimation (KDE) function characteristics gathered sources Following simulation performed estimate total whole-site details).Total emissionsThe shown 1A. Median mean 40.0–42.3 g CO2-eq./MJHHV (41.1–41.3 95% confidence interval [CI]) 51.4–52.7 (52.2–52.4 CI), respectively, 5th percentile 11.0–16.3 (15.6–15.7 CI) 95th 118.2 144.0 (131–133 GWP100 values. Each curve defines single shows range 2.5 343 CO2-eq./MJHHV. highly upward skewed (Figure 1A), indicative disproportionately high emitting sites “super-emitters” identification section details). findings consistent observed natural-gas chains.25Balcombe Characterising chain.J. Clean. Prod. 2018; 172: 2019-2032https://doi.org/10.1016/j.jclepro.2017.11.223Crossref (53) 26Balcombe Anderson Speirs chain: emissions.ACS Sustain. Chem. 5: 3-20https://doi.org/10.1021/acssuschemeng.6b00144Crossref (70) 27Balcombe CO 2 Supply Chain. 28Brandt A.R. Heath G.A. Cooley leaks follow extreme distributions.Environmental science technology. 50: 12512-12520https://doi.org/10.1021/acs.est.6b04303Crossref (127) 29Omara Zimmerman Sullivan M.R. Li X. Ellis Cesa Subramanian Presto A.A. Robinson A.L. States: national estimate.Environmental 52: 12915-12925https://doi.org/10.1021/acs.est.8b03535Crossref (48) 30Zavala-Araiza Alvarez R.A. Lyon D.R. D.T. Marchese A.J. Zimmerle Hamburg S.P. Super-emitters infrastructure caused abnormal process conditions.Nat. Commun. 8: 14012https://doi.org/10.1038/ncomms14012Crossref (85) Using 35 megatonnes equivalent (Mtoe) (1.47 × 1012 MJ) 2018,6IEAOutlook our model-based teragram (Tg) (6.4–7.8 year−1 average 2.8–2.9 year−1), Agency’s (IEA’s) bioenergy (9.1 2021).2IEAGlobal significantly (82.5 2021);2IEAGlobal hand, comparable segment US (6.1–7.1 year−1)31Rutherford J.S. Sherwin E.D. Ravikumar A.P. Englander Omara Langfitt Q. Brandt Closing gap inventories.Nat. 12: 4715https://doi.org/10.1038/s41467-021-25017-4Crossref (22) measurements.The percentage 1B. 1.7%–2.0% (1.94%–2.0% 12.3%–13.4% (12.6%–12.8% ranges minimum, median, mean, maximum values fairly across estimates 1). While low median identical, disparity varies widely highest estimates. ranged 5.1% 5.3% (5.1%–5.2% 5.90%–6.04% (5.9%–6.0% (0.8%–2.2% production).25Balcombe Scholar,26Balcombe Rutherford al.31Rutherford natural-gas-production 1.3% (1.2%–1.4% findings. On despite declining one (Uinta Basin multi-year record in-site observations) reveals (6%–8%).32Lin J.C. Bares Fasoli Garcia Crosman E. Lyman Declining steady, leakage multiple years western oil/gas basin.Sci. Rep. 11: 22291https://doi.org/10.1038/s41598-021-01721-5Crossref year−1, production-normalized considerably variety factors, poorly managed facilities; lack attention industry resulting investments modernization, operation, monitoring; employment skilled operators16Reinelt Scholar,21Scheutz gas. In addition, poor design units33Paolini Petracchini F. Segreto Tomassetti Naja Cecinato Environmental impact biogas: review current knowledge.J. Environ. Health Tox Hazard Subst. 53: 899-906https://doi.org/10.1080/10934529.2018.1459076Crossref (169) limited interest result amount produced. primarily operated companies decades, they invested leak detection repair.34EDFMethane Oil Industry.https://business.edf.org/insights/methane-mitigation-in-the-oil-gas-industry/Date: Scholar,35IEADriving Down Leaks Industry. Paris2021Google given growth generation decarbonization strategies, urgent efforts address only biomethane.Identification super-emittersA small proportion equipment labeled super-emitters,36Zavala-Araiza Palacios Harriss Lan Talbot Toward functional definition super-emitters: application sites.Environ. 49: 8167-8174https://doi.org/10.1021/acs.est.5b00133Crossref (89) Scholar,37Brandt Kort E.A. O'Sullivan Pétron Jordaan S.M. Tans Wilcox Gopstein Arent North American systems.Science. 2014; 343: 733-735https://doi.org/10.1126/science.1247045Crossref (597) causing heavy-tailed S4). number cause under- overestimations rates38Duren R.M. Thorpe A.K. Foster K.T. Rafiq Hopkins F.M. Yadav Bue B.D. Thompson Conley Colombi N.K. al.California’s super-emitters.Nature. 575: 180-184https://doi.org/10.1038/s41586-019-1720-3Crossref (110) intermittent patterns, insufficient usage, inadequate operations maintenance strategies. study, investigated feeding systems; substrate runoff ponds; digesters holders; exhausts aeration lines units; ventilation such compressors closed tanks; open flaring. Within heavy-tail (Figures 1A 1B) boxplot stage’s 2), because Table informati