Biomass-derived carbon catalysis (BCC) are a promising alternative as cathode materials for the next-generation fuel cells and metal air-batteries. In this regard, the development of numerous BCC toward the oxygen reduction reaction (ORR) have been reported in the last decade. The ORR catalytic activity has been observed to improve with heteroatom doping and is notably high when Fe-N-C type bonds are present. In this work, we have development a novel method to obtain Fe-N-C self-doped biocarbons from sewage sludge by intermittent microwave heating (IMH) technique using a home-made microwave oven. The effect of IMH treatment on the structural and textural properties of sewage sludge-derived biocarbons, and their correlation with the catalytic activity for ORR has been studied. The most active biocarbon has been labeled as SSF, which has been obtained by two-step process, first, it is subjected to chemical activation using KOH and then it is functionalized with methanol by IMH. Thus, SSF is a micro-mesoporous biocarbon with high surface area (1127 m² g^-1) and self-doped with heteroatoms such as N and S, forming quaternary-N and thiophene-S species, respectively. In addition, Fe-N-C bonds are also present on the surface of this catalyst. Among the most outstanding results, it has been observed that IMH treatment improves electrochemical parameters such as the on-set potential (E₀), current density (j), electron transfer number (n) and %HO₂^- production. In this regard, SSF (E₀= 0.89 V vs RHE, j= -3.01 mA cm^-2, n= 3.4 and %HO₂^- = 25.85) shows the better performance compared to the catalyst that has only been activated with KOH, labeled as SSA (E₀= 0.83 V vs RHE, j= -1.84 mA cm^-2, n= 3.1 and %HO₂^- = 36.47). These results indicate that sewage sludge could be used as raw material for the manufacture of cathodes, and that the treatment by IMH seems a promising eco-friendly alternative to improve the performance of BCC.