Inoculum sources related to electrochemically active biofilm (EAB) development or electricity production from different wastewater tanks of a wastewater treatment plant (WWTP) were studied. EABs established on working electrodes and the related microbial communities in three different inoculum sources from the various stages of wastewater treatment in the same WWTP including primary clarifier wastewater (PCW), aeration tank wastewater (ATW), and anaerobic activated sludge (AAS), were explored for the first time. Enriched EABs, including PCW, AAS, and ATW-EABs, were further selected using Fe(III) oxide/acetate medium and their electricity generation capability were systematically compared. The results showed that the mean current densities of PCW-EAB after selection using Fe(III) oxide achieved a higher plateau of 1500 mu A.cm(-2) than the 1250 mu A.cm(-2) of AAS-EAB. Meanwhile, the corresponding microbial diversities of three EAB varieties were characterized with polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE). More bacterial diversity was found in PCW-EAB with the highest current density. This indicated that the microbial community structures of enriched EABs were highly dependent on initial inoculum sources. On the other hand, sequencing and relative abundance analysis of bacterial diversities showed that all three kinds of enriched EABs mainly contained gamma-proteobacteria and Bacteroidia at the class level with main functions of fermentation and electricity generation. This study revealed that the inoculum sources from various stages of wastewater treatment in the same WWTP are all suitable to grow EABs, which is the first time to study the community composition of the enriched EAB at different treatment stages of a WWTP. This work will help investigators in understanding the characteristics of wastewater from different treatment tanks for a single WWTP in terms of microbial communities and their related influence on the electricity generation capability of enriched EABs.