The change in biotic and abiotic soil components influenced by paddy soil microbial fuel cells loaded with various resistances

Purpose: Soil microbial fuel cells (sMFC) are novel technique that uses organic matters in soils as an alternative energy source. External resistance (ER) is a key factor that influences sMFC performance and also alters the soil biological and chemical reactions. However, little information is available on how the microbial community and soil component changes in sMFC with different ER. Thus, the purpose of this study is to collectively examine the effects of different ER on paddy soil biotic and abiotic components. Materials and methods: Eighteen paddy sMFC were constructed and operated at five different ER (2000, 1000, 200, 80, and 50 Ω) in triplicates for 90 days. The effects of the sMFC anodes at different ER were examined by measuring organic matter (OM) removal efficiency, trace elements in porewater, and bacterial community structure in contaminated paddy soil. Results and discussion: The results indicate that ER has significant effects on sMFC power production, OM removal efficiency, and bacterial beta diversity. Moreover, ER influences iron, arsenic, and nickel concentration as well in soil porewater. In particular, greater current densities were observed at lower ER (2.6 mA, 50 Ω) as compared to a higher ER (0.3 mA, 2000 Ω). The removal efficiency of OM increased with decreasing ER, whereas it decreased with soil distance away from the anode. Furthermore, principal coordinate analysis (PCoA) revealed that ER may shape the bacterial community that develop in the anode vicinity but have minimal effect on that of the bulk soil. Conclusions: The current study illustrates that lower ER can be used to selectively enhance the relative abundance of electrogenic bacteria and lead to high OM removal.