A microbial fuel cell (MFC) with multiwall carbon nanotube (CNT) coated stainless steel mesh (SSM) coated anode (S-MFC) was operated with a filtrate generated by the fermentation of municipal primary sludge. The S-MFC's maximum power density (MPD: 69.8-164.9 W/m3) and energy recovery (ER: 0.15-0.60 kWh/kgCOD) were 7-21 times higher than those (3.8-27.3 W/m3 and 0.01-0.11 kWh/kgCOD) of MFC with a graphite felt as an anode (G-MFC). The microbial communities of S- and G-MFCs varied slightly depending on the electrode material. Chloroflexi (23.5%) was dominant in S-MFC, and Proteobacteria (25.3%) in G-MFC. Fermenting bacteria such as Rhodanobacter lindaniclasticus and Anaerolineaceae bacterium were dominated by continuous non-electrochemically active bacteria invasion because the actual fermentation filtrate was directly utilized as the substrate. Nevertheless, the CNT-coated SSM anode and the fermentation filtrate of primary sludge improved the power generation in MFC, which demonstrates the significant potential of this sidestream process for sludge treatment.