The plant microbial fuel cell (PMFC) is a novel technology that integrates plants, microbes and electrochemical elements together to create renewable energy. However, research is still limited regarding the application of PMFCs. Here we will provide examples of their application conducted in our research group in the past several years.
In the first example, PMFCs were installed as green roofs in a subtropical metropolis (Taipei city). 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. The PMFCs based green roofs could mostly achieve electricity production; however, little output voltage of Dwarf rotala PMFCs indicated different plant species in PMFC systems would result in varied efficiencies of electricity generation. The PMFCs based green roofs could also largely lower the temperature of underneath floor slabs compared with bare slabs at noon. Our roof-top research demonstrated that using PMFCs based green roofs for urban greening is promising and warrants the potential for future application.
In the second example, we intended to evaluate the use of PMFCs for bioremediation of Cr(VI)-contaminated soils and also produce energy at the same time, and explore the chemical and microbial characteristics under long-term operation. PMFCs with Chinese pennisetum and common reeds were employed to treat different levels of Cr(VI)- contaminated soil for evaluating the treatment performance. We have also demonstrated that PMFCs could be applied in treating real field contaminated soil containing Cr(VI). Our results suggest that using PMFCs to remediate metal contaminated soils is promising, and the effects of decontamination are mostly contributed by bioelectrochemical processes and plant uptake.
In the end, since in the second example of PMFCs, Chinese pennisetum could absorb heavy metals during soil remediation similar to phytoremediation. After plants are harvested, the system will generate biomass waste. After drying and crushing of plant waste, the biomass waste can be collected and valorized for biorefinery. This example presents the catalytic valorization of PMFC waste into levulinic acid (LA). Under microwave heating, increasing temperature to 180oC increased the yield of LA in water with sulfuric acid. Furthermore, gamma-Valerolactone (GVL)/H2O ratios could affect LA yields. These findings help to better understand the acid catalytic conversion of biomass under microwave heating for future application of valorization of plant waste.