Experiences of floating microbial fuel cells, supplying on-line sensors for water quality

Here we present original prototypes of floating MFCs (FMFC) meant to be used as auto-powered sensor of water quality, both in wastewater and natural water bodies. Two SMFCs (1 and 2), respectively from a wastewater treatment plant (Milano-Nosedo, Italy) and significant zones of water ecosystems (Bosco-in-città lake, Milano, Italy) were used as self-sustained source of energy for a new step-down DC/DC converter and data transmission system (Linear Tech LTC3108, Amel s.r.l., Italy). SMFC1, given a range of 2-25 mg COD/L at anode, gave a voltage output (range 30-40 mV), with night-day oscillation following COD loading. This input allowed complete capacitor (470 µF) charge in about 60 seconds, with output at 3.3 V. SMFC2, given a dissolved oxygen concentration in the range 0.5-10 mg/L, showed relatively constant voltage output (650-700 mV) and a relatively short charge time (< 1 second). These preliminary results will allow future development of this brand-new sensor platform.