Light Influence on the Performances of Air-Cathode Floating MFC for Wastewater Monitoring
Authors: Tucci Matteo , Barontini Enrico , Schievano Andrea , Papacchini Maddalena , Espinoza-Tofalos Anna , Franzetti Andrea , Cristiani Pierangela 
Published: February 2020

In many recent studies, the current generated by Microbial Fuel Cells (MFCs) has been evaluated as signal for wastewater monitoring, since various physical-chemical factors (e.g. BOD, dissolved oxygen, temperature etc.) can affect the microbial metabolism and thus the cell performance. Moreover, these systems require minimum maintenance and do not need external power source, so they are especially suitable for remote sites and diffuse environmental monitoring. However, few attempts have been made to study this technology in real field applications. An interesting approach to this subject is represented by floating MFCs located directly in the tank of a wastewater treatment plant: oxidation of the organic matter present in the wastewater occurs at the submerged anode, while oxygen is reduced at the air-cathode. In this kind of systems, a clear understanding of the parameters that can influence the current output is necessary to analyse the signal. For instance, light variation is an environmental condition that can have a strong influence on the system in direct and indirect ways (e.g. temperature change, enhancement of photosynthetic organisms, etc.). The oscillation of power produced in flat MFC during the circadian cycle was recently underlined, especially for flat MFC of small geometry which strongly increase the current generated in the light [1,2].
Herein, the impact of light and other physical-chemical factor on the microbial communities sustaining the performance of floating MFCs has been investigated. Five types of cells were placed in the denitrification tank of the wastewater treatment plant of Bresso-Niguarda (MI). An array of sensors was set in the same tank in order to continuously monitor light irradiation, temperature, pH, redox potential and dissolved oxygen. Wastewater samples were analysed in terms of soluble COD, and ammonium content. Taxonomic characterization of the bacterial communities present in the biofilm of anodes and cathodes was performed by Illumina sequencing of the 16S rRNA gene.
From the microbiological analysis, Nocardiaceae, Rhodocyclaceae and Aeromonadaceae respectively were the most abundant families detected on the anodes. Rhodocyclaceae and Nocardiaceae were enriched mostly also on the cathode, with Rhodobacteraceae and of Planococcaceae. This last constituted almost the full pool in one underperforming case. Most importantly, the results underline that photosynthetic bacteria were present on both anodes and cathodes performing cells, pointing to an important role of this bacteria in the electrocatalyses of the global MFC process.

1. 32. E. Martinucci, F. Pizza, E. Guerrini, A. Colombo, S.P.M. Trasatti, A. Lazzarini Barnabei, A. Liberale, P. Cristiani Energy balance and microbial fuel cells experimentation at wastewater treatment plant Milano-Nosedo. International Journal of Hydrogen Energy IJHE 40 (42) 9 (2015), 14683–14689
2. P. Cristiani, F. Pizza, I. Gajda, J. Greenman, P. Bonelli, I. Ieropoulos. Long term field testing of floating microbial fuel cells for energy harvesting from wastewaters and monitoring, in progress.