Due to the increase in energy demand and decrease in its supply, besides destructive environmental effects of fossil fuels overusing, such as greenhouse effect, alternative energy sources have received interest. Microbial fuel cells are interesting sources of renewable energy able to produce electricity from organic compounds using microorganisms as biocatalysts and simultaneously treat the waste water. Due to their mild operating conditions and using variety of biodegradable substrates as fuel, they have become one of the major research areas in many countries. Sediment microbial fuel cells (SMFCs) are a certain type of microbial fuel cells that produce electricity current using sediment’s organic matter content by anaerobic bacterial metabolism. They are single-compartment cells composed of a cathode suspended in the aerobic sediment-water interface and an anode embedded in anaerobic marine or river sediment. The main purpose of this study is investigating the effect of different catholyte conditions, presence/absence of separator at catholyte-anolyte interface and also using algae as an alternative oxygen producer instead of oxygen spargers and air pumps to reduce start up and operating expenses. To achieve this purpose, algae was used in cathode compartment of sediment microbial fuel cells to produce oxygen for reduction reactions and the effect of substrate sterilization (by autoclaving) for use in catholyte as well as use of gravels as separators between anode and cathode compartment were investigated using three SMFCs that contained raw sewage catholyte, autoclaved sewage catholyte and sewage catholyte with gravels between cathode and anode compartments. All the cells were exposed to illumination using a light-dark cycle of 16:8. The electricity generation of all cells enhanced during light cycle while it showed a significant decrease during dark cycle as the voltage of the cells approached nearly zero during dark cycle. Investigating the results and polarization curves after 14 days of operation indicated that growth of algae in raw (non-autoclaved) wastewater in the cathode of SMFC led to the maximum power density of 1.6 mW/m2 which was higher than SMFC with autoclaved wastewater cathode (power density of 0.008 mW/m2). In addition, using gravels as separators between anolyte and catholyte resulted in the significant improvement in SMFC performance so that the SMFC with gravels between anode and cathode compartment produced maximum power density of 7.5 mW/m2 while maximum power density of SMFC without gravels was 1.6 mW/m2. Results of this study can help further identifications of operating conditions influencing the performance of SMFCs with algal cathode.

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