Floating microbial fuel cells as energy harvesters for signal transmission from natural water bodies

A new type of floating microbial fuel cell (fMFC) was developed for power supply of remote environmental sensors and data transmission. Ten operating fMFCs generated a cell potential in the range 100–800 mV depending on the external resistance applied. Power production peaked around 3–3.5 mW (power density of 22–28 mW m−2 cathode) after about 20–30 days of start-up period. The average of daily electrical energy harvested ranged between 10 and 35 mWh/d. Long-term performances were ensured in the presence of dense rice plants (Oryza Sativa). A power management system, based on a step-up DC/DC converter and a low-power data transmission system via SIGFOX™ technology, have been set up for the fMFCs. The tested fMFCs systems allowed to: i) harvest produced energy, ii) supply electronic devices (intermittent LED-light and a buzzer); iii) transmit remote data at low speed (three message of 12 bites each, in 6 s). Several ‘floating garden’ MFCs were set in the context of demonstrative events at EXPO2015 world exposition held in Milan between May–October 2015. Some of the ‘floating garden’ MFCs were operating for more than one year.