Direct N2O Emissions Constrain the Net Climate Benefits of Anammox Based Nitrogen Removal

Direct N2O Emissions Constrain the Net Climate Benefits of Anammox Based Nitrogen Removal | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Direct N 2 O Emissions Constrain the Net Climate Benefits of Anammox Based Nitrogen Removal Zhiyong Ren, Yuqing Yan, Lin Du, Junjie Zhu, Mark Zondlo, Ruqiao Shen, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9502209/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Anammox-based nitrogen removal is widely viewed as a lower-carbon alternative to conventional nitrification-denitrification because it reduces aeration demand and external carbon addition. Yet its net climate performance depends on whether these resource savings are sufficient to compensate for system-level nitrous oxide (N2O) emissions. Here, we compiled a global database of over 500 observations encompassing mainstream and side-stream configurations of novel nitrogen pathways, including partial nitrification-anammox (PNA), partial denitrification-anammox (PdNA), partial nitrification (PN), anammox (AMX), and partial denitrification (PD), paired with functionally equivalent conventional baselines matched by volumetric loading rate. Using harmonized emission factors and study-specific electricity carbon intensities, we quantified the net carbon intensity change relative to baseline emission distributions, with the 25th and 75th percentiles serving as conservative and optimistic comparison benchmarks, respectively. Across pathways, direct (Scope 1) emissions overwhelmingly dominated climate outcomes: even under generous baselines, 56.9-78.6% of observations did not yield a net climate benefit. Under coal-fired grids, up to 29.9% of side-stream PNA achieved climate benefit, but this fraction declined to 17.4% under natural gas and 0% under solar, indicating that the climate value of electricity savings diminishes as power systems decarbonize. Mixed-effects analyses identified hydraulic retention time, nitrogen conversion efficiency, dissolved oxygen control and nitrogen loading as key predictors of climate outcome. These results show that N2O mitigation, rather than energy efficiency alone, will determine whether anammox-based nitrogen removal delivers robust decarbonization. Earth and environmental sciences/Environmental sciences Physical sciences/Engineering/Civil engineering Anammox Carbon Footprint Nitrous Oxide (N2O) Energy Full Text Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryTables.xlsx SUPPLEMENTARY DATA SET 1 AnammoxSupplementaryInformation3.30.docx SUPPLEMENTARY INFORMATION Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9502209","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":628510707,"identity":"280fa5eb-cbf0-469d-80df-40ebb6f25851","order_by":0,"name":"Zhiyong Ren","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2klEQVRIiWNgGAWjYFCCA0BcwcDAhhBJIEbLGaiWA8RpAQLGNiTtBLXIN559+Lhw3p18Punmh48/VNxh4GfPMcBvQcNxY+OZ255ZtskcMzY4cOYZg2TPG/xamBmOsUnzbjtswCaRwyZxsO0wg8ENArawMRxj/807B6yF/QdIiz0hLTxAW5h5GyC2MIBtkSCgRYLhGLM0z7FnQC1pxhJnzhzmkTjzrACvFvkZxxg/89TcMZCfkfzwQ0XFYTn+9uQNeLUwSBwAkQeQXEoQ8DegahkFo2AUjIJRgAEAwl1GM5cL7rMAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0001-7606-0331","institution":"Princeton University","correspondingAuthor":true,"prefix":"","firstName":"Zhiyong","middleName":"","lastName":"Ren","suffix":""},{"id":628510708,"identity":"a1e83dcd-4e25-4865-9a26-6e3c1fd7eaad","order_by":1,"name":"Yuqing Yan","email":"","orcid":"https://orcid.org/0000-0001-6403-8620","institution":"Princeton University","correspondingAuthor":false,"prefix":"","firstName":"Yuqing","middleName":"","lastName":"Yan","suffix":""},{"id":628510709,"identity":"6bef6ba6-0025-4522-b301-2bed5dfd0a30","order_by":2,"name":"Lin Du","email":"","orcid":"","institution":"Princeton University","correspondingAuthor":false,"prefix":"","firstName":"Lin","middleName":"","lastName":"Du","suffix":""},{"id":628510710,"identity":"8b531d41-99a9-46f2-be9e-5ef7f812d85a","order_by":3,"name":"Junjie Zhu","email":"","orcid":"https://orcid.org/0000-0002-7546-2870","institution":"Princeton University","correspondingAuthor":false,"prefix":"","firstName":"Junjie","middleName":"","lastName":"Zhu","suffix":""},{"id":628510711,"identity":"8d9e90da-3ffd-469c-bb78-07413caa0c2f","order_by":4,"name":"Mark Zondlo","email":"","orcid":"https://orcid.org/0000-0003-2302-9554","institution":"Princeton University","correspondingAuthor":false,"prefix":"","firstName":"Mark","middleName":"","lastName":"Zondlo","suffix":""},{"id":628510712,"identity":"379477ff-b28a-498c-9468-d794dc145594","order_by":5,"name":"Ruqiao Shen","email":"","orcid":"https://orcid.org/0000-0003-3463-6042","institution":"Jacobs Consultancy Canada","correspondingAuthor":false,"prefix":"","firstName":"Ruqiao","middleName":"","lastName":"Shen","suffix":""},{"id":628510713,"identity":"97850269-c907-4241-9c0d-fe953708cf95","order_by":6,"name":"Krishna Pagilla","email":"","orcid":"","institution":"University of Nevada Reno","correspondingAuthor":false,"prefix":"","firstName":"Krishna","middleName":"","lastName":"Pagilla","suffix":""}],"badges":[],"createdAt":"2026-04-23 04:40:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9502209/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9502209/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108182723,"identity":"597859f8-fa36-4d6c-b6a5-247a694d3d82","added_by":"auto","created_at":"2026-04-30 08:59:31","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1392809,"visible":true,"origin":"","legend":"","description":"","filename":"AnammoxManuscript3.30.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9502209/v1_covered_0046f11a-9176-45a2-b3f7-ba61eda76e7b.pdf"},{"id":108162021,"identity":"6d5ebb0e-6c1e-4659-bbff-b5ef4d32a1b4","added_by":"auto","created_at":"2026-04-30 04:30:28","extension":"xlsx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":271893,"visible":true,"origin":"","legend":"SUPPLEMENTARY DATA SET 1","description":"","filename":"SupplementaryTables.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-9502209/v1/853fcf8b6a2d45aab7b5e831.xlsx"},{"id":108162022,"identity":"5d0570f7-1904-449e-8857-ab3f6a5ae746","added_by":"auto","created_at":"2026-04-30 04:30:28","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":4177981,"visible":true,"origin":"","legend":"SUPPLEMENTARY INFORMATION","description":"","filename":"AnammoxSupplementaryInformation3.30.docx","url":"https://assets-eu.researchsquare.com/files/rs-9502209/v1/9f442de8360b74b9832c6f78.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"\u003cp\u003eDirect N\u003csub\u003e2\u003c/sub\u003eO Emissions Constrain the Net Climate Benefits of Anammox Based Nitrogen Removal\u003c/p\u003e","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Anammox, Carbon Footprint, Nitrous Oxide (N2O), Energy","lastPublishedDoi":"10.21203/rs.3.rs-9502209/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9502209/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Anammox-based nitrogen removal is widely viewed as a lower-carbon alternative to conventional nitrification-denitrification because it reduces aeration demand and external carbon addition. Yet its net climate performance depends on whether these resource savings are sufficient to compensate for system-level nitrous oxide (N2O) emissions. Here, we compiled a global database of over 500 observations encompassing mainstream and side-stream configurations of novel nitrogen pathways, including partial nitrification-anammox (PNA), partial denitrification-anammox (PdNA), partial nitrification (PN), anammox (AMX), and partial denitrification (PD), paired with functionally equivalent conventional baselines matched by volumetric loading rate. Using harmonized emission factors and study-specific electricity carbon intensities, we quantified the net carbon intensity change relative to baseline emission distributions, with the 25th and 75th percentiles serving as conservative and optimistic comparison benchmarks, respectively. Across pathways, direct (Scope 1) emissions overwhelmingly dominated climate outcomes: even under generous baselines, 56.9-78.6% of observations did not yield a net climate benefit. Under coal-fired grids, up to 29.9% of side-stream PNA achieved climate benefit, but this fraction declined to 17.4% under natural gas and 0% under solar, indicating that the climate value of electricity savings diminishes as power systems decarbonize. Mixed-effects analyses identified hydraulic retention time, nitrogen conversion efficiency, dissolved oxygen control and nitrogen loading as key predictors of climate outcome. These results show that N2O mitigation, rather than energy efficiency alone, will determine whether anammox-based nitrogen removal delivers robust decarbonization.","manuscriptTitle":"Direct N2O Emissions Constrain the Net Climate Benefits of Anammox Based Nitrogen Removal","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-30 04:30:24","doi":"10.21203/rs.3.rs-9502209/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-water","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"natwater","sideBox":"Learn more about [Nature Water](https://www.nature.com/natwater/)","snPcode":"44221","submissionUrl":"https://mts-natwater.nature.com/cgi-bin/main.plex","title":"Nature Water","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Research","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"208f1454-1505-4d9d-9dfe-ba4736704087","owner":[],"postedDate":"April 30th, 2026","published":true,"recentEditorialEvents":[{"type":"editorInvitedReview","content":"This content is not available.","date":"2026-05-13T07:32:19+00:00","index":3,"fulltext":"This content is not available."}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":67283804,"name":"Earth and environmental sciences/Environmental sciences"},{"id":67283805,"name":"Physical sciences/Engineering/Civil engineering"}],"tags":[],"updatedAt":"2026-04-30T04:30:24+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-30 04:30:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9502209","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9502209","identity":"rs-9502209","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}