1. Department of Civil & Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong 999077, China 2. Department of Civil and Environmental Engineering, Faculty of Science and Technology, University of Macao, Macao 999078, China 3. Institute of Applied Physics and Materials Engineering, University of Macao, Macao 999078, China 4. Water Technology Center, The Hong Kong University of Science and Technology, Hong Kong 999077, China 5. Hong Kong Branch of Chinese National Engineering Research Center for Control & Treatment of Heavy Metal Pollution, The Hong Kong University of Science and Technology, Hong Kong 999077, China 6. Wastewater Treatment Laboratory, FYT Graduate School, The Hong Kong University of Science and Technology, Guangzhou 511458, China
• 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.
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.
Seawater-impregnated sludge pyrolyzed at 600°C, 750°C, 900°C followed by washing with acids and deionized water.
SC-600, SC-750, SC-900
Freshwater sludge directly pyrolyzed at 600°C, 750°C, 900°C followed by washing with acids and deionized water.
SWC-600 (ww), SWC-750 (ww), SWC-900 (ww)
Seawater-impregnated sludge pyrolyzed at 600°C, 750°C, 900°C followed by washing with deionized water only.
SC-600 (ww), SC-750 (ww), SC-900 (ww)
Freshwater sludge directly pyrolyzed at 600°C, 750°C, 900°C followed by washing with deionized water only.
Tab.1
Fig.2
Fig.3
Sample
SBET (m2/g)
Vtotal pore (cm3/g)
Vmicro (cm3/g)
Vmeso (cm3/g)
Vmicro/Vtotal pore
SC-600
16.3
0.05
N.A.
0.05
N.A.
SC-750
24
0.045
0.0028
0.0422
6.2%
SC-900
99.8
0.153
N.A.
0.153
N.A.
SWC-600
153.1
0.305
0.0229
0.2821
7.5%
SWC-750
480.3
0.527
0.1175
0.4095
22.3%
SWC-900
457
0.462
0.1565
0.3055
33.9%
SWC-600 (ww)
24.1
0.049
N.A.
0.049
N.A.
SWC-750 (ww)
103.3
0.115
0.031
0.084
27.0%
SWC-900 (ww)
159.3
0.283
0.0243
0.2587
8.6%
Tab.2
Fig.4
Fig.5
Fig.6
Fig.7
Fig.8
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