Bioelectrochemical performance on constructed wetland-microbial fuel cells operated under diffuse and direct solar radiation using root exudates as endogenous substrate to feed an electroactive biofilm

Abstract

Exploiting fossil fuels through conventional technologies focused on energy production has led to severe environmental adversities, mainly affecting global warming and climate change. Constructed wetland-microbial fuel cells (CW-MFC) have emerged as an innovative technology that could mitigate these effects. One of the main limitations of the CW-MFC system is the low power density generated. This study evaluated the impact of diffuse (CW-MFC1) and direct (CW-MFC2) solar radiation intensity to enhance bioelectrochemical performance. To do this, the CW-MFC was inoculated with the Geobacter sulfurreducens bacteria as a bioelectrocatalyst, which was fed with the root exudates of the macrophyte Juncus effusus. The change from diffuse to direct solar radiation increased the electroactivity of the system by 43% in terms of power density, cathodic potential, anodic potential, and internal resistance, resulting in a maximum performance of 128.7 mW/m2, 172 mV, −290 mV, and 204 Ω respectively. This was obtained from a concentration of 35.3 mg/L of root exudates (total organic carbon). The analysis of results determined that solar radiation is a predominant factor that directly affects the photosynthetic efficiency and coulombic efficiency of CW-MFC by controlling the rhizodeposition process of the macrophytes, where the amount of bioelectricity produced depends on the amount of exudates discharged by the root system towards the rhizosphere.