Benchmarking of Industrial Synthetic Graphite Grades, Carbon Felt, and Carbon Cloth as Cost-Efficient Bioanode Materials for Domestic Wastewater Fed Microbial Electrolysis Cells

Abstract

Anode material selection is crucial when it comes to building up-scaled microbialelectrolysis cells (MEC), as it has a huge influence on the achievable current density and account for a large part of the MEC total investment cost. Graphite is a material that isperfectly suited to the creation of up-scaled bioanodes as it is conductive, chemically stable, biocompatible, and relatively cheap but there are a very large number of commercially available grades of industrial graphite. In this study, five grades of industrial synthetic graphite (named G1–G5) were bench tested to select the most suitable gradefor future development of 3D bioanode for domestic wastewater (dWW) fed MEC application. The five grades of graphite have been selected with similar physico-chemicaland surface properties (electrical resistivity, surface roughness, and hydrophobicity) theoretically appropriate for EA biofilm development. Nevertheless, significant current density disparities where observed with the five graphite grades, which can certainlybe explained by the fabrication procedures of the respective material grades. With thegraphite grade giving the most efficient anodes (G3), an average steady state currentdensity of 2.3 A/m²was produced, outperforming the other grades by at least 15%.Even though all graphites had very close physico-chemical characteristics, the gradehad a clear significant influence on the current densities produced. G3 graphite was finally compared to carbon felt (CF) and carbon cloth (CC) both in terms of bio-electrochemicalcurrent production and bacterial communities colonizing electrodes. G3 bioanodes outperformed CF and CC bioanodes by 50% in term of steady state current density.Biofilms microbial population analysis showed that theGeobacterspecies was presentat 82% on G3 bioanodes, 39% on CF bioanodes, and 61% on CC bioanodes when it was only present at 0.06% in the activated sludge used as inoculum. This significant difference in bacterial enrichment could come from the huge gap between materials resistivity, as graphite resistivity is 200-fold lower than CF and CC resistivities. The strongly hydrophilic surface of G3 graphite was also certainly beneficial for biofilm development compared tothe hydrophobic surfaces of CF and CC.