Twelve single chambered, air-cathode Tubular Microbial Fuel Cells (TMFCs) have been filled up with fruit and vegetable residues. The anodes were realized by means of a carbon fiber brush, while the cathodes were realized through a graphite-based porous ceramic disk with Nafion membranes (117 Dupont). The performances in terms of polarization curves and power production were assessed according to different operating conditions: percentage of solid substrate water dilution, adoption of freshwater and a 35mg/L NaCl water solution and, finally, the effect of an initial potentiostatic growth.All TMFCs operated at low pH (pH= 3.0 ± 0.5), as no pH amendment was carried out. Despite the harsh environmental conditions, our TMFCs showed a Power Density (PD) ranging from 20 to 55 mW/m 2 ·kg waste and a maximum CD of 20 mA/m 2 ·kg waste , referred to the cathodic surface. COD removal after a 28−day period was about 45%.The remarkably low pH values as well as the fouling of Nafion membrane very likely limited TMFC performances. However, a scale-up estimation of our reactors provides interesting values in terms of power production, compared to actual anaerobic digestion plants. These results encourage further studies to characterize the graphite-based porous ceramic cathodes and to optimize the global TMFC performances, as they may provide a valid and sustainable alternative to anaerobic digestion technologies.

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Summary Performance of sediment microbial fuel cells (SMFCs) with aerated (A‐SMFC) and nonaerated (NA‐SMFC) cathodes was evaluated at different operating conditions in toxic metal removal and power generation. The A‐ and NA‐SMFC open‐circuit voltages were respectively about 665 and 275 mV, with quite steady performances for 120 days. The cell design points of both SMFCs were calculated by implementing polarization curves, and they were at 1 kΩ (power density 8.1 mW/m2 and current density 0.0504 mA/m2 with voltage 150 mV) for NA‐SMFC and 100 Ω (power density 252.81 mW/m2 and current density 0.954 mA/m2 with voltage of 275 mV) for A‐SMFC, respectively. Cathode potentials were at 30 kΩ 290 mV (NA‐SMFC) and 500 mV (A‐SMFC). As to the anode, at 30 KΩ, it was −180 mV (NA‐SMFC) and 190 mV (A‐SMFC). The voltammetry profiles of A‐SMFC showed maximum current (forward scan, 22.7 μA; reverse scan, −19.4 μA) followed by NA‐SMFC (forward scan, 11.3 μA; reverse scan, −9.5 μA). The cell design points of A‐SMFC and NA‐SMFC were altered after pH and temperature amendments at 200 and 700 Ω, respectively. As to metal removal rate, the maximum arsenic cadmium and lead removal was observed in A‐SMFC at pH 7.0 (77.70%, 90.86%, and 83.91%) and 45°C (66.22%, 79.03%, and 71.17%). Scanning electron microscopy confirmed, at pH 7.0 and 45°C, an optimal biofilm growth at cathode and anode graphite of both SMFCs. After 120 days of operation, genomic DNA was extracted from biofilms and analyzed for rDNA 16S sequences. Similarity search was performed by using Basic Local Alignment Search Tool algorithm against the National Center for Biotechnology Information Gen Bank showing Pseudomonas spp. dominance at both anode and cathode. The results revealed that the A‐SMFC system could be employed as an effective and long‐term tool for power generation as well as stimulated bioremediation of the polluted sediments.

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