Performance and fouling analysis of osmotic microbial fuel cells for simultaneous treatment of real wastewater and desalination of natural seawater

The practical application of osmotic microbial fuel cells (OsMFCs) is often limited by a knowledge gap concerning their long-term performance and fouling mechanisms when using real-world influents. This study addresses this gap by assessing an OsMFC operated with real domestic wastewater as its feed and seawater as its draw solution over nine consecutive batch cycles, totaling approximately 600 hours. The system demonstrated robust performance, achieving a peak chemical oxygen demand (COD) removal of 86.9% (average 75.7±11.2%) and generating sustainable bioelectricity with a maximum power density of 0.65 W/m³ and a stable voltage output (550–650 mV). Simultaneously, the OsMFC enabled effective seawater desalination, resulting in an average water recovery of 15% (with a peak of 19.7%) and an average draw solution salinity dilution of 23% (with a peak of 33%). However, a key operational challenge was a progressive decline in water flux from an initial 0.66 L/m²/h to 0.3 L/m²/h by the final cycle, indicating significant membrane fouling. A post-operational analysis of the forward osmosis membrane using SEM, EDS, and FTIR revealed a complex fouling layer. This layer consisted of organic biofouling, characterized by extracellular polymeric substances like proteins and polysaccharides, and significant inorganic scaling. The inorganic scaling was dominated by seawater-derived elements, primarily Cl (28.0 wt%), Ca (13.7 wt%), and P (5.9 wt%). These findings provide critical insights into the complex fouling that occurs under realistic conditions, underscoring the need for targeted anti-fouling strategies to advance this technology for sustainable water-energy nexus applications.