Results

Results

      Research activities carried out within the project were related to the investigation of nanocomposites based on PANI with different metal nano-oxides (TiO2, WO3, ZnO, NiO, Fe3O4, CuO, Fe-Ni-O) and PPY with nano-oxides (WO3 and TiO2) for the anode modification in MFC anode, as well as their impact on bioenergy production and wastewater treatment. The correlation of polymer/nano-oxide composition together with the composition of the anodic biofilm developed on the surface of the modified anode can bring new useful knowledge for the development of practical applications of MFC and can suggest certain types of modification of MFC anodes to improve MFC performance.

     In the case of the anode modification with PANI based nanocomposites, the MFC experiments were carried out both in the light and in the dark. Thus, the experiments in the light led to the best performance of the MFC operating in the light was obtained for anode modification with PANI/ZnO, and for those operating in the dark, the best performance was obtained for the anode modification with PANI/WO3. Based on the analysis of the microbial communities of wastewater and anodic biofilm, the difference between the results light vs dark) was attributed to the different microbial diversity present in the initial municipal water used for ligh experiments reveal the presence of the class Chlorobia, also known as green sulfur bacteria, affiliate with the genus Chlorobium, which was also identified on anodic biofilm.  The modification with PANI/ZnO favors the development of the biofilm with an increased abundance of the genus Chlorobium at the level of the bacterial community, the results being in agreement with the concentrations of total DNA extracted from the biofilm deposited on the surface of the anode, which were much lower for the modification of PANI/WO3 (13.4 ng/µL) compared to PANI/ZnO (34.7 ng/µL). The presence of the genus Geobacter was identified only in the case of modification with PANI/WO3, but its electrogenic activity, in light experiments, was probably inhibited by the presence of Chlorobium in the bacterial community of the biofilm. For the tests performed in the dark, the presence of green algae was not detected either at the water level or at the level of the bacterial community of the biofilms.

       In terms of the maximum power density obtained (dark), the results showed that the modification of the anode (CC) with both nanocomposites, PANI/nano-oxides and PPY/nano-oxides, leads to a significant improvement of the MFC performance as compared with unmodified anode (CC). In addition, all the results suggest that the presence of WO3 in the nanocomposite materials has a decisive role in improvement of MFC performance. The presence of WO3 in both PANI- and PPY- based  nanocomposites, being correlated with the synergistic effect of the two components: WO3 nano-oxides, which give nanocomposite materials a better biocompatibility and conducting polymers that contribute to their conductivity. The maximum power density obtained for the modification with PANI/WO3 (39.5 mW/m2) being approximately 2.26 times higher than of MFC using unmodified anode-CC (19.7 mW/m2).

     The correlation of the MFC performance with the composition of the microbial community of the anodic biofilm, showed that the modification with PANI/WO3 favors an increased abundance of the genus Geobacter (22.2%), the model microorganism for exoelectrogenic activity, and the lower performance of the anode modified with PANI-ZnO (dark), it can be associated with an increased abundance of the genus Methanosaeta (32.5%), a microorganism capable of methanogenesis and which leads to a loss of electrons to methane, decreasing the output power of the MFC.

    In addition, it was observed that all analyzed anodic biofilms have as major representatives the same bacterial classes, with variations in terms of the ratio between them and which depends on the material used to modify the anode, and depending on their activity can be directly correlated with the MFC performances, as shown in the discussions above. In terms of alpha-diversity, the wastewater samples presented a number of species observed, as well as values ​​of Faith's phylogenetic distances, on average lower as compared with anodic biofilms. The lowest number of observed species on unmodified anode compared to all other samples show that the anode modification have a significant impact on the microbial communities developed on the surface and consequently on MFC performance. The results showed that the composition of the microbial communities at the level of the anodes, beside the type of nanocomposite material used for anode modification, is dependent on the microbial diversity of the initial wastewater and operating conditions (light/dark).

    In term of wastewater treatment, the results showed a significant reduction of the main characteristics analyzed (BOD, COD and TOC) with the performance increases in the order: carbon cloth <PANI-ZnO<PANI< PANI-WO3 < PANI-TiO2, and the highest efficiencies for anode modification with PANI-WO3 and PANI-TiO2 of over 90%.

    As a conclusion, the research activities carried out in this project showed that the correlation of the properties/composition of the nanocomposite material used for anode modification together with the microbial community's analysis of wastewater and anode biofilm, can bring new knowledge for the design of MFC experiments, so that they can become a viable alternative for the efficient wastewater treatment and bioenergy production.