Biodegradation of phenol in batch and continuous flow microbial fuel cells with rod and granular graphite electrodes

Phenol biodegradation was evaluated in batch and continuous flow microbial fuel cells (MFCs). In batch-operated MFCs, biodegradation of 100-1000 mg L^-1 phenol was four to six times faster when graphite granules were used instead of rods (3.5-4.8 mg L^-1 h^-1 vs 0.5-0.9 mg L^-1 h^-1). Similarly maximum phenol biodegradation rates in continuous MFCs with granular and single-rod electrodes were 11.5 and 0.8 mg L^-1 h^-1, respectively. This superior performance was also evident in terms of electrochemical outputs, whereby continuous flow MFCs with granular graphite electrodes achieved maximum current and power densities (3444.4 mA m^-3 and 777.8 mW m^-3) that were markedly higher than those with single-rod electrodes (37.3 mA m^-3 and 0.8 mW m^-3). Addition of neutral red enhanced the electrochemical outputs to 5714.3 mA m^-3 and 1428.6 mW m^-3. Using the data generated in the continuous flow MFC, biokinetic parameters including μ_m, K_S, Y and K_e were determined as 0.03 h^-1, 24.2 mg L^-1, 0.25 mg cell (mg phenol)^-1 and 3.7 × 10^-4 h^-1, respectively. Access to detailed kinetic information generated in MFC environmental conditions is critical in the design, operation and control of large-scale treatment systems utilizing MFC technology.