Ocean salinity varies from 33 to 37 g/L due to local geographic and climatic variations affecting ionic concentration, conductivity, microbial activity, and electron transfer rates. The impact of these natural salinity fluctuations on the performance of MFC remains underexplored. Hence, the present study investigates the influence of three salinity levels-lower (33 g/L, R33), optimum (35 g/L, R35), and higher (38 g/L, R38)-on power generation, bacterial viability, and biofilm formation in MFCs. Among the tested conditions, R35 exhibited the highest power and current density of 15.02 mW/m(2) and 103.59 mA/m(2), confirming that moderate salinity enhances microbial metabolism and electrochemical efficiency. At 160 mA/m(2), R33 displayed a second power peak with 16.5 mW/m(2), which indicates delayed concentration polarization and enhanced electron transport at higher current densities. Additionally, resulted in enhanced biofilm formation and the highest bacterial viability of 6.67 x 10(7) CFU/mL for R33. This indicates the gradual adaptation of Gram-negative bacteria and enhanced electron transfer rates. The power density varied from R33 and R35 by 17.3% and from R35 and R38 by 7.79%, which highlights the sensitivity of MFC performance to these narrow salinity changes. These results underscore the importance of salinity management during MFC operation in marine environments. Future work on microbial community analysis and adaptive salinity control strategies will help attain long-term stability and energy output in deep-sea environments.
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