Moisture-induced electrical power generation with waste activated sludge

Moisture-induced power generation from pure bacterial cultures has been demonstrated, but the feasibility of extending this renewable energy harvesting method to mixed bacterial cells from environmental samples is uncertain. Herein, waste active sludge (WAS) from wastewater treatment reactors was used to fabricate whole-cell film-based moisture-induced electricity generators (MEGs). Electrical power could be harvested from all four representative WAS samples, which were obtained from wastewater treatment reactors or plants treating liquid-ammonia mercerization, municipal, beer brewery, and printing-dyeing wastewaters. The highest performing MEGs were obtained from anammox activated sludge with an open circuit voltage of 0.45 ± 0.02 V and a maximum power density of 5.24 μW/cm2, which outperformed those MEGs with pure bacterial cultures. Physicochemical characterizations combined with partial least-squares path modeling suggested that the amount of microbial biomass and hydrophilicity of the as-prepared WAS films were the most important factors in determining the performance of the WAS-based MEGs. Extracellular polymer substances were essential in creating a water gradient inside the WAS, which was a crucial mechanism for generating electricity from MEGs based on WAS. This study not only provides a new approach for developing materials for moisture-induced energy harvesting but also presents a novel avenue for resource utilization of WAS.