| 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. |
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