Accelerating anodic biofilms formation and electron transfer in microbial fuel cells: Role of anionic biosurfactants and mechanism

Anodic electron transfer is the predominant electricity generation process of MFCs. To accelerate anodic biofilms formation and electron transfer, 40 mg/L, 80 mg/L, and 120 mg/L of rhamnolipid biosurfactants were added to the anolyte, resulting in an increased abiotic capacitance from 15.12 F/m² (control) to 16.54 F/m², 18.00 F/m², and 19.39 F/m², respectively. Anodic biofilm formation was facilitated after dosing 40 mg/L of rhamnolipids on the 7th day after inoculation, resulting in an increased anodic biofilm coverage from 0.43% to 42.51%, and an increased maximum power density from 6.92 ± 1.18 W/m³ to 9.93 ± 0.88 W/m³. Furthermore, the adsorption of rhamnolipids on the anode caused the Frumkin effect, leading to a decrease of equilibrium potential from − 0.43 V to − 0.56 V, and an increase of exchange current density from 5.09 × 10^− 3 A/m² to 8.72 × 10^− 3 A/m². However, electron transfer was blocked when the rhamnolipid concentration was further increased to 80 mg/L, and 120 mg/L. Analysis of the anodic bacterial communities revealed that rhamnolipids facilitated the enrichment of exoelectrogen, increasing the total proportion from 65% to 81%. Additionally, biosurfactants were found to have significant impacts on the composition of exoelectrogens.