Biofilm on anode can influence anode's performance in microbial fuel cells(MFCs). Biofilm growth is influenced by anode surface area. The effect of anode structure on the maximum power output of MFC was investigated by changing lengths or numbers of carbon fibers as anode. For the length effect of carbon fiber anode

the highest maximum power density 10.50 W·m-2 is appeared at 1 cm-length. The maximum power density decreases sharply as the carbon fiber length further increase. When the anodes are constructed with different numbers of 2 cm-length of carbon fibers

the maximum power is proportional to amount of carbon fiber(s) (1-4 carbon fiber(s)). The maximum power for the anode with 4 pieces of 2 cm-length carbon fiber is 2.92 W·m-2

which is 2.78 times that generated with a single carbon fiber with the length of 8 cm. The biofilm on the carbon fibers surface could be observed by optical microscopy. The biofilm is much thicker at the place near current leading-out terminal than that at other parts of carbon fiber due to the resistance of the carbon fiber. These results indicate that increase of carbon fiber length can enlarge anode surface area

but can not significantly improve performance of anode.