{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,11]],"date-time":"2026-03-11T04:42:19Z","timestamp":1773204139905,"version":"3.50.1"},"reference-count":77,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2020,2,20]],"date-time":"2020-02-20T00:00:00Z","timestamp":1582156800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Preludium 6 Program, the National Research Center, Poland","award":["#UMO-2013\/11\/N\/NZ9\/04587"],"award-info":[{"award-number":["#UMO-2013\/11\/N\/NZ9\/04587"]}]},{"name":"Fulbright Poland Foundation","award":["Research on pollutants emission from Carbonized Refuse Derived Fuel into the environment"],"award-info":[{"award-number":["Research on pollutants emission from Carbonized Refuse Derived Fuel into the environment"]}]},{"name":"Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa","award":["Project no. IOW05556 (Future Challenges in Animal Production Systems: Seeking Solutions through Focused Facilitation) sponsored by Hatch Act and State of Iowa funds"],"award-info":[{"award-number":["Project no. IOW05556 (Future Challenges in Animal Production Systems: Seeking Solutions through Focused Facilitation) sponsored by Hatch Act and State of Iowa funds"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>Sewage sludge (SS) recycling is an important part of the proposed \u2018circular economy\u2019 concept. SS can be valorized via torrefaction (also known as \u2018low-temperature pyrolysis\u2019 or \u2018roasting\u2019). SS can, therefore, be considered a low-quality fuel or a source of nutrients essential for plant growth. Biochar produced by torrefaction of SS is a form of carbonized fuel or fertilizer. In this research, for the first time, we tested the feasibility of torrefaction of SS with high ash content for either fuel or organic fertilizer production. The research was conducted in 18 variants (six torrefaction temperatures between 200~300 \u00b0C, and three process residence times of 20, 40, 60 min) in 5 repetitions. Fuel and fertilizer properties and multiple regression analysis of produced biochar were conducted. The higher heating value (HHV) of raw SS was 21.2 MJ\u00b7kg\u22121. Produced biochar was characterized by HHV up to 12.85 MJ\u00b7kg\u22121 and lower H\/C and O\/C molar ratio. Therefore, torrefaction of SS with high ash content should not be considered as a method for improving the fuel properties. Instead, the production of fertilizer appears to be favorable. The torrefaction increased C, N, Mg, Ca, K, Na concentration in relation to raw SS. No significant (p &lt; 0.05) influence of the increase of temperature and residence time on the increase of biogenic elements in biochar was found, however the highest biogenic element content, were found in biochar produced for 60 min, under the temperature ranging from 200 to 240 \u00b0C. Obtained biochars met the Polish regulatory criteria for mineral-organic fertilizer. Therefore SS torrefaction may be considered a feasible waste recycling technology. The calculation of torrefaction energy and the mass balance shows energy demand &lt;2.5 GJ\u2219Mg\u22121 w.m., and the expected mass yield of the product, organic fertilizer, is ~178 kg\u2219Mg\u22121 w.m of SS. Further investigation should consider the scaling-up of the SS torrefaction process, with the application of other types of SSs.<\/jats:p>","DOI":"10.3390\/ma13040954","type":"journal-article","created":{"date-parts":[[2020,2,21]],"date-time":"2020-02-21T08:59:47Z","timestamp":1582275587000},"page":"954","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":31,"title":["Waste-to-Carbon: Is the Torrefied Sewage Sludge with High Ash Content a Better Fuel or Fertilizer?"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-6438-3608","authenticated-orcid":false,"given":"Jakub","family":"Pulka","sequence":"first","affiliation":[{"name":"Faculty of Agronomy and Bioengineering, Poznan University of Life Sciences, 28 Wojska Polskiego Str., 60-637 Pozna\u0144, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4067-8556","authenticated-orcid":false,"given":"Piotr","family":"Manczarski","sequence":"additional","affiliation":[{"name":"Department of Environmental Engineering, Faculty of Building Services, Hydro and Environmental Engineering, Warsaw University of Technology, 20 Nowowiejska Str., 00-653 Warszawa, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5144-9495","authenticated-orcid":false,"given":"Pawe\u0142","family":"St\u0119pie\u0144","sequence":"additional","affiliation":[{"name":"Institute of Agricultural Engineering, Faculty of Life Sciences and Technology, Wroclaw University of Environmental and Life Sciences, 37a Che\u0142mo\u0144skiego Str., 51-630 Wroclaw, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8015-797X","authenticated-orcid":false,"given":"Marzena","family":"Styczy\u0144ska","sequence":"additional","affiliation":[{"name":"Faculty of Biotechnology and Food Sciences, Wroclaw University of Environmental and Life Sciences, 37\/41 Che\u0142mo\u0144skiego Str., 51-630 Wroclaw, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2387-0354","authenticated-orcid":false,"given":"Jacek A.","family":"Koziel","sequence":"additional","affiliation":[{"name":"Department of Agricultural and Biosystems Engineering, Iowa State University, 4350 Elings Hall, Ames, IA 50011, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5871-2129","authenticated-orcid":false,"given":"Andrzej","family":"Bia\u0142owiec","sequence":"additional","affiliation":[{"name":"Institute of Agricultural Engineering, Faculty of Life Sciences and Technology, Wroclaw University of Environmental and Life Sciences, 37a Che\u0142mo\u0144skiego Str., 51-630 Wroclaw, Poland"},{"name":"Department of Agricultural and Biosystems Engineering, Iowa State University, 4350 Elings Hall, Ames, IA 50011, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2020,2,20]]},"reference":[{"key":"ref_1","first-page":"191","article-title":"Ilo\u015b\u0107 osad\u00f3w pochodz\u0105cych z wiejskich oczyszczalni \u015bciek\u00f3w i kierunki ich unieszkodliwiania","volume":"5","author":"Heidrich","year":"2008","journal-title":"Infrastruktura i Ekologia Teren\u00f3w Wiejskich"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"116","DOI":"10.1016\/j.rser.2006.05.014","article-title":"Utilization of sewage sludge in EU application of old and new methods\u2014A review","volume":"12","author":"Fytili","year":"2008","journal-title":"Renew. 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