Improving power performance of sediment microbial fuel cell through Water lettuce (Pistia stratiotes) assisted boosting of cathodic activity

Sediment microbial fuel cells (SMFCs) are emerging as a promising green energy technology with enormous application potential for wastewater treatment and linked electrical energy production. However, the practical application of these devices is challenged by their low-performance factors pertaining to the imbalanced electrolyte and oxygen levels and weak cathodic functions in open environment conditions. This study explored to address the poor performance of the SMFC by coupling it with a free-floating aquatic plant, Water lettuce. Growth of the plant balanced the catholyte pH in the range of 7.2–7.6, increased the ionic conductivity by 60 %, stabilized the sub-surface water oxygen level, and boosted the cathodic potential by ∼102 mV and ∼49 mV in open and close circuit operations mode, respectively. The cumulative effect of these inputs led to producing a power density of 22.45 mW/m2 and a current density of 136.84 mA/m2 at 2 kΩ and 50 Ω loads, respectively. The enhanced cathodic performance was also attributed to the colonization of Water lettuce root bacteria as biofilm on the cathode that supported catalytic oxygen reduction on the graphite electrode. Metagenonic analysis indicated the biofilm is created mostly by aerobic microbes such as Ferrovibrio terrae, Comamonas aquatic, Achromobacter xylosoxidans, Hydrogenophaga taeniospiralis etc. bearing catalase enzyme, Pannonibacter phragmitetus, Streptococcus pyogenes, Streptococcus mutans etc. bearing heme enzyme and these microbes synergistically catalysed cathodic reduction reactions. This study demonstrated the positive role of Water lettuce in boosting the power performance of SMFC mainly by activating the cathodic functions of the setup.