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Effect of cathode structures on water diffusion, power generation and wastewater treatment in microbial fuel cell

pubblicazioni - Presentazione

Effect of cathode structures on water diffusion, power generation and wastewater treatment in microbial fuel cell

This study aims at developing novel 3-layer (3L) pt catalysed cathode structures to increase power generation and wastewater treatment in microbial fuel cells (MFCs). The configuration proposed should be particularly useful when a fast high power generation is request and the water (pollutant) leakage outside the cell have to be avoided. Three types of cathode structures were examined: two-layer (2-L) cathode structure consisting catalyst layer (CL) and gas diffusion layer (GDL) and, three-layer (3-L) cathode structure consisting of CL,  micro porous layer (MPL) and GDL, and multi-layer (M-L) cathode structure consisting of CL, GDL, carbon based layer (CBL) and hydrophobic layers (PTFE).  These three types of cathodes were tested in the single chamber MFCs inoculated with raw wastewater. Sodium acetate was added periodically as substrate in three different solution concentration (0.7, 1.5 and 3 g/L). Carbon cloth was used as anode. The cathode performance was evaluated in terms of biofilm formation, water loss, power generation and wastewater treatment. The results showed that biofilms grew on the water side of all the cathodes tested, while biofilm formation on the air side of the cathodes was detected only in the 2-L structure. The complete penetration of the biofilm in the structure caused severe water loss problems (Table 1). The MPL layer (pore sizes 0.1-1 µm) of the 3-L structure and the PTFE layers in the ML structure inhibited the biofilm complete penetration into the cathode structure avoiding leakage problem.The 3-L cathode structure with MPL had a power density of 501, 417 and 340 mW/m2 at COD concentrations of 3, 1.5 and 0.7 g/L, which were 18-21% greater than 2-L structure and were 42-44% than M-L structure. The MPL in the 3-L structure avoided the biofilm penetration and flooding conditions of the electrodes facilitating the oxygen reduction reaction at the cathode. The biofilm penetration in the 2-L structure partially consumed the oxygen necessary for the reaction causing a decrease in the performance. The PTFE external layers of the M-L structure instead avoided the biofilm penetration but increased significantly the oxygen transport resistance to the CL and facilitated electrode flooding conditions. In addition, the 3-L cathodes also had higher organic substrate removal efficiency (74-78%) than the 2-L cathodes (59-68%) and M-L cathodes (54-62%) (Table 1).The novel 3-L cathodes developed in this study demonstrate that the MPL between CL and GDL can substantially reduce water losses and prevent the biofilm growth into cathode structures, which is a promising approach to enhance cathode performance, improve power generation and organic substrate removal in MFCs.

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