Evaluation of plant microbial fuel cells for urban green roofs in a subtropical metropolis

Plantmicrobial fuel cells (PMFCs) is a sustainable technology that can convert sunlight to electricity through the integration of plants, microorganism and electrode systems. Urban greening, such as green roofs, is considered as one of the measures to resolve the urban heat island effect caused by the increasing urbanization. In this study, PMFCs were installed as green roofs in a subtropical metropolis. During the operation, the biomass of Chinese pennisetum, Dwarf rotala, and Narrowleaf cattail increased from spring to summer. Furthermore, the maximum daily average output voltage of Chinese pennisetum and Narrowleaf cattail PMFCs was 667.94 +/- 128.65 mV in March and 451.12 +/- 94.37 mV in June, respectively. For no plant conditions, the maximum daily average output voltage of soil MFCs was 243.70 +/- 128.93 mV in March and 100.16 +/- 23.43 mV in June. However, little output voltage of Dwarf rotala PMFCs indicated different plant species in PMFC systems would result in varied efficiencies of electricity generation. The trends of electricity generation in Chinese pennisetum and Narrowleaf cattail PMFCs were influenced by net solar radiation and air temperature, respectively according to the results of correlation analysis. The PMFCs based green roofs could lower the temperature of underneath floor slabs as many as 24.81 degrees C and 29.37 degrees C compared with bare slabs at noon in March and June. Vegetation of the PMFCs could relieve soil heat flux, and simulated results showed Chinese pennisetum PMFCs with higher vegetation had lower U-value for energy savings of air conditioning. Microbial community analysis showed Geobacter was among the dominant genera and had higher relative abundance in anode soils than cathode soils in Chinese pennisetum and Narrowleaf cattail PMFCs, which generated higher output voltage. Our roof-top research demonstrated that using PMFCs based green roofs for urban greening is promising and warrants the potential for future application. (C) 2020 Elsevier B.V. All rights reserved.