Comparative evaluation of methanogenesis suppression methods in microbial fuel cell during rice mill wastewater treatment

A major constraint to attaining higher power output from microbial fuel cell (MFC) is the loss of substrate due to methanogenesis. Controlling methanogenesis is imperative to enhance the coulombic efficiency (CE). This study compares the influence of three inoculum treatment methods i.e., heat-treatment (MFC1), ultrasonication (MFC2) and air exposure (MFC3), on suppressing methanogenesis while treating rice mill wastewater. MFC2 and MFC3 exhibited a maximum volumetric power density of 525.62 mW/m(3) and 656.10 mW/m(3), respectively, which were 1.7 and 2.1 times higher than that of MFC1. Similarly, CE of 9.27%, 14.14% and 17.21% was observed in MFC1, MFC2 and MFC3, respectively. MFC1 shown higher COD removal efficiency (85.22 +/- 2.12%) than MFC2 (76.18 +/- 1.36%), and MFC3 (71.88 +/- 1.71%). Linear sweep voltammetry demonstrated enhanced electrochemical activity in MFC3 (peak current: 15.92 mA) compared to MFC2 (8.40 mA) and MFC1 (3.61 mA). An internal resistance of 294 Omega was observed in MFC3, which was lower than MFC2 (320 Omega) and MFC1 (415 Omega). Intermittent air exposure of the inoculum was found to be more effective for power generation in the MFC. The contribution of planktonic archaeal community towards power generation was studied by removing the suspended inoculum from the anode chamber of all the MFCs. The maximum power density obtained in sludge deprived condition in MFC1, MFC2 and MFC3 was 1.2, 1.4 and 1.2 times less than that obtained when MFCs were operated with suspended inoculum. The study concludes that suspended anaerobic sludge should be used after proper pre-treatment for improved electricity harvesting and efficient wastewater treatment.