Phosphatase and dehydrogenase activities in anodic chamber of single chamber microbial fuel cell (MFC) at variable substrate loading conditions

Performance of microbial fuel cell (MFC) was evaluated with the function of phosphatase and dehydrogenase activities at increasing organic loading rate (OLR) (0.195 kg chemical oxygen demand (COD)/m3-day; 0.458 kg COD/m3-day; 0.911 kg COD/m3-day; 1.589 kg COD/m3-day). Variation in enzyme activities along with power generation and substrate degradation was observed during MFC operation with the function of organic loading rate (OLR). Phosphatase activity showed a decreasing trend with time from 24 to 36th hour depending on OLR which is a good sign of substrate utilization. Dehydrogenase activity was observed to be high at the 12th hour irrespective of the OLR. However, the activity was increased with increasing OLR. Higher dehydrogenase activity was observed at 1.589 kg COD/m3-day representing the possibility of higher redox reactions. Higher power output was recorded at the 12th hour with 53.58 mW/m2 (0.195 kg COD/m3-day) and 24th hour with 60.29 mW/m2 (0.458 kg COD/m3-day) and 76.17 mW/m2 (0.911 kg COD/m3-day). At higher OLR studied (1.589 kg COD/m3-day), maximum power generation (49.86 mW/m2) was observed at 12th hour indicating decreased performance. Electron discharge and recovery properties observed during MFC operation were supporting higher performance at 0.911 kg COD/m3-day. Increase in OLR showed improvement in substrate degradation [OLR1, 56.32% (0.11 kg COD/m3-day); OLR2, 56.42% (0.26 kg COD/m3-day); OLR3, 59.53% (0.54 kg COD/m3-day); OLR4, 64.40% (1.78 kg COD/m3-day)].