Characteristics of electricity generation and biodegradation in tidal river sludge-used microbial fuel cells

• The sludge deposited on a riverbank was used as fuel in microbial fuel cells.
• The maximum current density was at least 5-fold higher than that of freshwater sediment.
• The biodegradation was 10-fold enhanced comparing with the natural biodegradation.
• The biodegradation was in association with sulfate reduction reactions.
• The oxygen consumption speed increased along with the electricity generation.

The electricity generation behavior of microbial fuel cell (MFC) using the sludge collected from the riverbank of a tidal river, and the biodegradation of the sludge by the electricity generation are evaluated. Although the maximum current density (150–300 mA/m2) was higher than that of MFC using freshwater sediment (30 mA/m2), the output current was greatly restricted by the mass transfer limitation. However, our results also indicate that placing the anode in different locations in the sludge could reduce the mass transfer limitation. After approximately 3 months, the removal efficiency of organic carbon was approximately 10%, demonstrated that MFC could also enhance the biodegradation of the sludge by nearly 10-fold comparing with the natural biodegradation. We also found that the biodegradation could be identified by the behavior of oxygen consumption of the sludge. Importantly, the oxygen consumption of the sludge became higher along with the electricity generation.