Revealed mechanism of micron-pore size of 3D bio-anode on the behavior of biofilm and system performance in microbial electrochemical system

Abstract

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.