Microbial Fuel Cells (MFCs) are a promising technology to harvest energy from aquatic environments and act as sensing devices at the same time. Several prototypes of sediment MFCs have been tested in the past and more recently floating systems have been investigated as well, with encouraging results both in terms of energy harvesting and sensing. The challenge is now to scale up laboratory MFC designs for self-powering water quality sensors and implement these in real environments, where electricity sources may not be available. In this work, the performances of floating MFCs, suitably designed for aerobic and anaerobic water environments, were studied in long-term experiments. Several designs of flat and tubular cells were tested, using low-cost materials, such as plastic lunch boxes, and polystyrene or wood to keep the system afloat. Untreated carbon cloth, free of any chemical catalyst, was used for the electrodes. Flat MFCs were able to generate up to 15 mW/m², depending on nutrient availability in the water. The electric performance of cathodes and anodes were differently correlated to chemical and physical water parameters (day/night cycle, chemical oxygen demand, total carbon content, nitrates and temperature among others). The Total Organic Carbon and Total Inorganic Carbon in the tank were continuously monitored with Sievers 820 Portable Total Organic Carbon Analyzer and compared to the current production of the cells.

Different types of power management systems had to be suitably designed, depending of the range of power produced by the MFC prototypes. A new generation of low-energy remote system (LORA) was integrated in an electronic circuit to harvest the power generated from MFCs and to transmit signals over long distance.

The experimentation was carried out in the wastewater plant site at Carimate (Figure 1), Como (Italy) and in the pool of the city garden “Orto Botanico Città Studi” at Milan (Italy).