A “Seawater-in-Sludge” approach for capacitive biochar production via the alkaline and alkaline earth metals activation

Highlights

• Capacitive biochar was produced from sewage sludge.

• Seawater was proved to be an alternative activation agent.

• Minerals vaporization increased the surface area of biochar.

• Molten salts acted as natural templates for the development of porous structure.

Abstract

Sewage sludge is a potential precursor for biochar production, but its effective utilization involves costly activation steps. To modify biochar properties while ensuring cost-effectiveness, we examined the feasibility of using seawater as an agent to activate biochar produced from sewage sludge. In our proof-of-concept study, seawater was proven to be an effective activation agent for biochar production, achieving a surface area of 480.3 m²/g with hierarchical porosity distribution. Benefited from our design, the catalytic effect of seawater increased not only the surface area but also the graphitization degree of biochar when comparing the pyrolysis of sewage sludge without seawater. This leads to seawater activated biochar electrodes with lower resistance, higher capacitance of 113.9 F/g comparing with control groups without seawater. Leveraging the global increase in the salinity of groundwater, especially in coastal areas, these findings provide an opportunity for recovering a valuable carbon resource from sludge.

Graphical abstract

Keywords

Sewage sludge / Biochar / Seawater / Recourse recovery / Capacitor

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Acknowledgements

This research was supported by the National Natural Science Foundation of China (Grant No. 51778165), Key Program of National Natural Science of China (Grant No. 51638005), Science and Technology Development Fund, Macao Special Administrative Region, China (File No. FDCT-0104/2018/A3, FDCT-0057/2019/A1), Start-up Research Grant of University of Macao (Grant No. SRG2018-00110-FST), the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. [T21-604/19-R]).

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11783-020-1295-0 and is accessible for authorized users.

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