Searching for efficient and inexpensive catalysts to replace precious metal-based catalyst in air-cathode microbial fuels cells is crucial for the practical application and commercialization in wastewater treatment and energy generation. Here, through a simple pyrolysis process, sewage sludge could be converted into carbon material with hierarchically porous structure, which demonstrates oxygen reduction reaction (ORR) catalytic performances. Subsequently, co-doping Mn and N species on the carbonized sewage sludge matrix could further improve the ORR catalytic performance, which even demonstrates comparable performances to the commercial expensive Pt/C catalyst in air-cathode microbial fuels cells(MFC). The highest maximum power density of MFC with Mn-N/SC air-cathode is as high as 1,120 mW m−2, which is similar to the power density of the air-cathode MFC equipped commercialized Pt/C catalyst (1,240 mW m−2). Considering the simple operation, significant cost-saving and easy scale-up of the proposed ‘trash-to-treasure’ method, it is promising to convert harmful sewage sludge into efficient non-platinum cathode catalysts in microbial fuel cells.