Power output was related to the conductivity, pH and volume of the catholyte produced in each MFC. All the results were compared with two types of MFC, i.e. the controls, which (i) contained sludge and acetate described above ane were externally loaded with 100 omega, and (ii) the open circuit MFCs, which also conrained sludge and acetate at the same concentrations, but were not externally loaded (no alectron transfer).