An economic and simple sediment microbial fuel cell (SMFC) design is evaluated to improve the recovery of energy from a river sediment, in terms of power density output (maximum power pick) normalized to the cathode surface. The organic matter content in the sediment is boosted by adding abundant, natural, and waste biomass (chitin) near the anode surface. The sluggish kinetics in the two‐electron reduction reaction of O2 at the C‐cathode is replaced with an efficient four‐electron reduction reaction at the MnO2/C cathode. Five SMFCs composed of a common carbon fabric (CF) cathode and different unmodified anode materials, such as reticulate vitreous carbon (RVC: 10, 30, and 60 pore per inch, ppi), CF and commercial stainless‐steel (SS) mesh, are evaluated. The catholyte conductivity improved with Na2SO4. The results show that the power density output increased a 100‐fold when an MnO2/CF‐cathode is used with Na2SO4 catholyte and the anolyte contained chitin. A microbial analysis of the SMFC sediment is performed. The bacterial groups identified, mainly Aminicenantia and Deltaproteobacteria, offer metabolic capacities to participate in the degradation of organic matter in the presence of chitin. Therefore, bacterial groups enriched in the anode biofilm produce electrical energy.