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Anaerobic digestion of liquid products following hydrothermal carbonisation of faecal sludge at different reaction conditions

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journal contribution
posted on 16.11.2017, 14:07 by Eleni Nyktari, Eric Danso-Boateng, Andrew D. Wheatley, Richard Holdich
The hydrothermal carbonisation (HTC) conversion of wet wastes, such as sewage sludge, generates a carbon-rich material (called ‘hydrochar’), and an aqueous fraction with a small release of gas. The liquid fraction is high in soluble chemical oxygen demand, from 10 to 50 g/L, and could not be discharged to the natural environment without treatment. This study investigates the anaerobic digestibility of this HTC liquid stream from different HTC temperatures and retention times (140°C–200°C for 30–240 min). It is focused on biogas production in order to improve the energy input of the HTC process and to improve process sustainability. The results demonstrated that liquid products from the lower HTC temperatures gave better biogas production. The biogas yield from the 140°C HTC filtrate digestion was 0.45–0.86 L/L reactor/d, while 0.33 L/L reactor/d was obtained from 170°C and 0.31–0.45 L/L reactor/d from 180°C HTC filtrates. The lowest anaerobic digestion (AD) efficiency was recorded for the treatment from 200°C with biogas yield of 0.07 L/L reactor/d. The data also show that low AD hydraulic retention time (HRT), typical of high rate fixed biomass digesters can be used to treat the HTC filtrate. Halving the AD HRT to 0.9 d resulted in 1.8–6.8 times greater biogas yield.


The authors gratefully acknowledge the support of the Gates Foundation who funded this work through the Reinvent the toilet program.



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Desalination and Water Treatment


NYKTARI, E. ...et al., 2017. Anaerobic digestion of liquid products following hydrothermal carbonisation of faecal sludge at different reaction conditions. Desalination and Water Treatment, 91, pp. 245-251.


Desalination Publications


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 Desalination and Water Treatment and the definitive published version is available at https://doi.org/10.5004/dwt.2017.20782 The paper was presented at the 13th IWA Specialized Conference on Small Water and Wastewater Systems & 5th IWA Specialized Conference on Resources-Oriented Sanitation, 14–16 September, 2016, Athens, Greece.