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[Display omitted] • Introducing pore on 3D anode enhanced system bio-electrochemical performance. • System start-up time negatively correlated with external surface area of 3D anode. • The abundance of Geobacter inside the pore decreased with the increased pore size. • Increased pore size reduced acidification and improved substrate supply inside the pore. • G-800 3D bio-anode achieved the highest power density of 4593.3 ± 78.2 mW/m3. Microbial electrochemical systems (MESs) are widely studied as a promising technology for recovering bioenergy from wastewater. The anode has a great impact on the performance of the MES and more and more three-dimensional (3D) porous anodes are constructed to improve the bioenergy recovery and the system performance. However, the establishment of suitable pore sizes for MES 3D anodes and the effect of different micron-pore sizes on system performance has not been thoroughly studied. Here, we found the change in pore size affected the start-up time and bio-electrochemical performance by affecting the physical characteristics (surface area and porosity) and mass transfer of the 3D anode. The introduction of pore size on 3D anodes led to the mass transfer limitation of substrate and buffer species, and this phenomenon was severe as pore size decreased. The mass transfer limitation of substrate supply inside the pore imposed a selective pressure to enrich Geobacter from 18.45% to 72.96% when the pore size decreased from 800 μm to 100 μm. However, the acidification brought by the mass transfer limitation of the buffer species affected the activity of microorganisms and played a more important role leading to the 3D anode with 800 μm pore size achieving higher power densities (4593.3 ± 78.2 mW/m3), 1.7 times that of the 3D anode with 100 μm pore size (2782.6 ± 79.2 mW/m3). The present research provides a reference for the construction of high-performance 3D structured anodes and an in-depth understanding of the effect of pore size on system performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sandwich structure anode was designed by help of COMSOL simulation. • 3D printing current collector was first used in microbial electrochemical system. • Corncob was used as sole carbon source for efficient denitrification. • Optimizing anode structure enhanced electrons generation and collection. • Sandwich structure anode improved autotrophic denitrification efficiency. Microbial electrochemical system autotrophic denitrification has attracted much attention due to its cost-efficiency and clean advantages. The autotrophic denitrification rate highly depends on the input electrons to the cathode. In this study, agricultural waste corncob was filled into sandwich structure anode as low-cost carbon source for electron production. The COMSOL software was used to guide the construction of sandwich structure anode to control carbon source release and enhance electron collection, including suitable pore size (4 mm) and current collector arrangement (five branches). Optimized sandwich structure anode system with the help of 3D printing obtained a higher denitrification efficiency (21.79 ± 0.22 gNO 3 --N/m3d) than anodic systems without pore and current collector. Statistical analysis showed that enhanced autotrophic denitrification efficiency was the responsible for enhanced denitrification performance of the optimized anode system. This study provides a strategy to improve the autotrophic denitrification performance of the microbial electrochemical system by optimizing the anode structure. [ABSTRACT FROM AUTHOR]

Regulating anode structure and component are necessary to the operation of the microbial electrochemical system (MES). In this work, graphene-based amino modification carbon nanotubes composite aerogel is prepared through simple hydrothermal reduction method. It is proved that the three-dimensional (3D) structure can provide a plenty of sites for microorganisms growth. The carbon nanotubes inserted in the graphene sheets can provide more paths for electron conduction in the anode and can enhance the electron transfer process. The introduction of amino groups promote the population of Geobacter in anode biofilm and further enhance the performance of the system. The maximum power density of the MES equipped with the composite anode can reach 944.3 W m−3, higher than previously reported high-output MESs with 3D graphene-based anodes. Meanwhile, the maximum current density of the system (2637.8 A m−3) increases 39.9% compared to the control anode system (1586.3 A m−3). The graphene-based amino modification carbon nanotubes composite anode in this study shows great potential for enhancing the performance of MES. Image 1 • 3D NH 2 -CNTs/Graphene composite was fabricated through sample method. • CNTs inserted in graphene sheets enhanced electron transfer process. • NH 2 -CNTs increased the accumulation of Geobacter in anodic biofilm. • The composite was first used as MES anode and achieved high system performance. [ABSTRACT FROM AUTHOR]