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Characterization of solid fuel chars recovered from microwave hydrothermal carbonization of human biowaste

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journal contribution
posted on 13.06.2017, 12:31 by Oluwasola Afolabi, M. Sohail (Khan), Paul Thomas
Microwave hydrothermal carbonization (M-HTC) is reported in this study as a viable sanitation technology that can reliably overcome the heterogeneous nature of human faecal biowaste (HBW) and realize its intrinsic energy value. Solid chars produced from the M-HTC process at 180°C and 200°C were characterized to further the understanding of the conversion pathways and their physicochemical, structural and energetic properties. The study revealed solid chars recovered were predominantly via a solid-solid conversion pathway. In terms of yield, more than 50% of solid chars (dry basis) can be recovered using 180°C as a benchmark. Additionally, the carbonized solid chars demonstrated enhanced carbon and energy properties following the M-HTC process: when compared to unprocessed HBW, the carbon content in the solid chars increased by up to 52%, while the carbon densification factor was greater than 1 in all recovered chars. The calorific values of the chars increased by up to 41.5%, yielding heating values that averaged 25MJ.kg-1. Thermogravimetric studies further revealed the solid fuel chars exhibited greater reactivity when compared with unprocessed HBW, due to improved porosity. This work strengthens the potential of the M-HTC sanitation technology for mitigating poor sanitation impacts while also recovering energy, which can complement domestic energy demands.


The authors wish to thank the Bill & Melinda Gates Foundation for its funding to Loughborough University, UK, on the ‘Reinvent the Toilet Challenge’ project.



  • Architecture, Building and Civil Engineering

Research Unit

  • Water, Engineering and Development Centre (WEDC)

Published in



AFOLABI, O.O.D., SOHAIL (KHAN), M. and THOMAS, C.L.P., 2017. Characterization of solid fuel chars recovered from microwave hydrothermal carbonization of human biowaste. Energy, 134, pp. 74–89.


© Elsevier


AM (Accepted Manuscript)

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This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

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This paper was accepted for publication in the journal Energy and the definitive published version is available at https://doi.org/10.1016/j.energy.2017.06.010






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