Microbial biofilm-based hydrovoltaic system for degradating organic pollutants

Electron donors are the central drivers of microbial biodegradation, yet conventional sources-derived from light (photoelectrons), electrodes (bias-injected electrons), or chemical substrates (valence electrons)-are scarce in oligotrophic or lightless environments, limiting their environmental applicability. Here, we report the first microbial biofilm-based hydrovoltaic system (mBio-HS) that harnesses the hydrovoltaic effect of water evaporation to provide a sustainable electron source for pollutant degradation. The mBio-HS, constructed simply with electroactive microorganisms, continuously generates a stable electron flow (∼20 μA, ∼0.3 V) solely through the hydrovoltaic effect, without any external energy input. These water-evaporation-induced hydrovoltaic electrons (WEH-e) perform dual functions: sustaining microbial metabolism to form a self-sufficient community and directly reducing organic pollutants. Using methyl orange (MO) as a model azo dye, the system achieved efficient azo-bond cleavage and 90% decolorization within 72 h. This work not only presents the first prototype of a simple biofilm-based hydrovoltaic pollutant-degradation system, but also establishes a mechanistic foundation for harnessing the ubiquitous hydrovoltaic effect in microbial biofilms to power redox reactions-offering a practical route toward zero-energy, environmentally adaptive bioremediation.