Bioelectricity generation in plant microbial fuel cells: Influence of vegetation density and unsaturated soil properties

Plant microbial fuel cells (PMFCs) have promising potential in various geoenvironmental engineering applications such as green roofs, biosensors, water purification and soil remediation. However, the vulnerability of PMFCs to drought stress and the unknown interplay between bioelectricity, planting density, and unsaturated soil properties pose significant challenges for their applications. The research objective is to investigate the effects of planting density on bioelectricity generation under drought conditions. The research was conducted using vegetation Hydrocotyle vulgaris at four different planting densities in silty soil. Bioelectricity and unsaturated soil properties, including water content and suction, were monitored. The results indicated that moderate increase in planting density could enhance the power density of PMFCs up to 4.5 times. This is because of the increased availability of root exudates for microbial activity with increasing root biomass and decreased internal resistance by extending the soil pore space. It was also found that plant roots could affect bioelectricity generation by altering unsaturated soil properties, such as the air-entry value of soils and soil pore structure. However, high planting densities reduced bioelectricity due to increased internal resistance from roots occupancy and evapotranspiration-induced crack initiation. This research provides valuable insight into optimizing PMFC performance and sustainability.