Operation of PMFCs
The medium used to feed the PMFCs was 1/2 Hoagland buffered with 0.008 mol l−1 potassium phosphate buffer solution as described by Timmers et al. (2010) (pH 6.8, conductivity between 1.5 and 1.7 mS m−1). The medium was fed through a sample point located 0.07 m above the graphite granules. The applied flow rate was 0.17 ml s −1 throughout the experimental period. The feeding frequency of the PMFC with buffered Hoagland medium was 5 min every 12 h.