Redox distribution profiles of flooded paddy soils with microbial fuel cell applications

Abstract

Microbial fuel cell is one of our considerations to control denitrification redox reactions in flooded rice soils. An independent study was conducted after a nitrogen behavior study in flooded rice soils accounted for microbial fuel cell systems and microbial fuel cell systems with an externally applied voltage. External voltage was applied in the aim of increasing microbial fuel cell efficiencies, for the better control of soil redox potential. But, their redox controlling potentials and denitrification controlling were lower than that of microbial fuel cell systems. It is hypothesized, that the lower controlling potentials were due to the redox distributions effected with the distance to the anode of the circuit where the external voltage was connected through. Therefore, soil redox distributions at three depth profiles were compared in both systems and controls over the period of flooding. In external voltage applied systems, the redox potential of the soil away from anode was not much effectively controlled as of microbial fuel cell systems, although the middle soil portions near anode area were of higher redox potentials. At depths of 10 and 20 cm away from the soil surface, the redox potential increased more with MFCs and moderately with MFC-extV, but reduced with non-MFCs over the period. Accordingly, most electrons from whole soils were not freely transferred to the anode, except that from near anode areas where the external voltage was connected through. Microbial fuel cell systems with externally applied voltage had a lower impact on controlling denitrification than that of microbial fuel cell systems alone.