Unlocking the Fertilizer Potential of Waste-Derived Biochar

W. Buss, Anna Bogush, K. Ignatyev, O. Mašek

    Research output: Contribution to journalArticlepeer-review

    22 Citations (Scopus)
    27 Downloads (Pure)


    Mankind is facing a phosphorus (P) crisis. P recycling from anthropogenic waste is critical to close the P loop. Pyrolysis could be the ideal treatment for materials, such as sewage sludge (SS), producing a safe, nutrient-rich biochar product while sequestering the inherent carbon (C). However, pyrolyzed sewage sludge typically contains low levels of potassium (K) and plant available P, making the material rather unsuitable for use as fertilizer. Here, a novel treatment was investigated to produce an optimized P and K biochar fertilizer. We doped sewage sludge with a low-cost mineral (2 and 5% potassium acetate) and pyrolyzed it at 700 °C. The percentage water extractable of the total P content in biochar increased by 237 times with 5% K addition compared to the undoped biochar. After six water extractions, all of the K and 16% of P were obtained. Further optimization is feasible through adjustments of the biochar pH or doping the feedstock with other forms of K. Using X-ray absorption near-edge spectroscopy (XANES) and synchrotron X-ray fluorescence (XRF) mapping, we identified highly soluble potassium hydrogen phosphate up to 200–300 μm below the biochar surface. This simple and cost-effective modification enables the use of sewage sludge as safe biochar fertilizer with tailored P availability that also supplies K, improves soil properties, and sequesters C.
    Original languageEnglish
    Pages (from-to)12295-12303
    Number of pages9
    JournalACS Sustainable Chemistry & Engineering
    Issue number32
    Early online date23 Jul 2020
    Publication statusPublished - 17 Aug 2020

    Bibliographical note

    This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Sustainable Chemistry and Engineering, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acssuschemeng.0c04336

    Copyright © and Moral Rights are retained by the author(s) and/ or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This item cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder(s). The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders.


    • XANES
    • biochar
    • fertilizer
    • phosphorus
    • potassium
    • pyrolysis
    • sewage sludge

    ASJC Scopus subject areas

    • Chemistry(all)
    • Environmental Chemistry
    • Chemical Engineering(all)
    • Renewable Energy, Sustainability and the Environment


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