Effect of submerged and floating cathodes on sustainable bioelectricity generation and benthic nutrient removal in sediment microbial fuel cells

Sediment microbial fuel cells (SMFC) are a potential alternative for benthic sediment remediation in bioelectricity generation. The cathodic oxygen reduction rate is an important limiting factor in SMFC. This study aims to evaluate the effects of submerged and floating cathodes on bioelectricity generation and benthic nutrient removal in SMFC. Based on the generated current density, SMFC with a wick-air cathode, 10 cm from the top sediment surface and partially submerged in water and exposed to air (SMFC-CW) was found to be superior to those with bottom cathode, 1 cm from the top sediment surface (SMFC-C1), a middle cathode, 5 cm from the top sediment surface (SMFC-C5), and a floating cathode, 10 cm from the top sediment surface and placed under the overlying surface water (SMFC-C10). In the polarization test, SMFC-CW contributed to the lowest concentration loss with a maximum current density of 236.4 mA/m2. The overshoot phenomenon in SMFC-C1 is not a good indicator of the SMFC system, despite the generation of a high maximum power density. This study has shown that a large pH difference between the anodic and cathodic regions in SMFC-CW is important for bioelectricity generation as it was observed that the internal resistance of SMFCs changes. SMFC-CW showed the largest reduction in phosphate concentration, from 0.61 mg/L to 0.14 mg/L. These results provide a simple strategy for sustainable bioelectricity generation in SMFC systems while remediating benthic sediments.