Influence of iron fertilizer form and concentration on bioelectricity and methane emission from hydroponic plant microbial fuel cells

Abstract

This study aimed to evaluate the effect of iron form (Fe2+ and Fe3+) and concentration (0 μM, 7.5 μM, and 15 μM) on the biomass production, bioelectricity generation, and methane (CH4) emissions of hydroponic plant microbial fuel cells (H-PMFCs). Rice plants (Oryza sativa L.) were grown in H-PMFCs. During the 90 days of operation, the highest power density (PDmax) was observed in Group 7.5–15 of 949.17 mW/m3. When adding single-form iron (Fe2+ or Fe3+), the PDmax of H-PMFCs was positively correlated with iron concentration. Further, the H-PMFC feed with Fe3+ showed higher power output than the feed with Fe2+. Adding 7.5 μM Fe2+ and 15 μM Fe3+ (Group 7.5–15) showed the highest overall biomass production, including plant lengthavg/plant (89.67 ± 1.17 cm) and plant weightavg/plant (14.91 ± 0.02 g dry mass) and lowest CH4 emission (43.15 ± 2.00 g/m2). The CH4 emission test indicated that the addition of iron in rice H-PMFCs can decrease the emission of CH4 in two ways: (i) iron electron acceptors directly inhibit methanogens; (ii) iron electron acceptor enhances the electricity production ability of MFC to inhibit CH4 production. Therefore, adding 7.5 μM Fe2+ and 15 μM Fe3+ showed great potential to enhance the performance of H-PMFCs on biomass production, bioelectricity generation, and CH4 emission inhibition.