Endogenous inorganic carbon buffers accumulation and self-buffering capacity enhancement of air-cathode microbial fuel cells through anolyte recycling.

Anolyte acidification is inevitable in the operation of buffer-free microbial fuel cells (MFCs), which restricts the proliferation and metabolism of electroactive bacteria, and results in electric-power deterioration. The anodic metabolic end-products, inorganic carbons (IC), which are composed of HCO (dissolved CO), HCO, and CO, are ideal endogenous buffers, whereas the naturally accumulated IC are far from enough to prevent anolyte acidification. In this work, different volume ratios of the anolytes (10%, 30%, and 50%) were recycled to increase the IC concentrations of the single-chamber air-cathode buffer-free MFCs. Under anolyte recycling running mode, IC accumulation agreed with the SGompertz model and the fitting IC-asymptotic concentrations (IC) grew exponentially to 18.5 mM, 24.4 mM, and 32.8 mM as the anolyte recycling ratio increased from 10% to 30% and 50%. Self-buffering running can be realized when the anolyte recycling ratio exceeds 50% for the MFC feeding on 1 g·L of acetate. The electric power for the 50% recycling scenario increased from the baseline control of 272.4 mW·m to 628.5 mW·m. The coulombic efficiency (CE) was also apparently improved. This paper for the first time clarifies the accumulation law of endogenous IC buffers under anolyte partially recycling mode and their self-buffering effects.