Impact of temperature on the performance and fouling behavior of a forward osmosis membrane system for concentrating low-strength sewage

The forward osmosis (FO) process relies on the natural osmosis phenomenon, which is influenced by temperature through its effects on osmotic pressure and hydrodynamic properties. However, the impact of temperature on the FO membrane system for concentrating real sewage has not been clearly studied, with conflicting results reported. This study investigated the effects of temperature on the performance and fouling behavior of a laboratory-scale FO membrane system used to concentrate low-strength sewage with 1.2 M NaCl as the draw solution (DS). Permeate flux was found to increase notably with increasing temperature; however, it decreased by 30-40 % over 24 h due to membrane fouling. Additionally, while solute concentration efficiency improved with increasing temperature, particularly for nutrients, it remained lower than anticipated compared to the volume reduction ratio of the feed solution, which is attributable to solute accumulating within the fouling layers, diffusion into the DS, and degradation. Other notable observations include the heightened penetration of ammonia nitrogen into the DS with increasing temperature and the pronounced biodegradability of organic matter. Despite the observed drawbacks, the improved filtration performance, increased solute concentration, and mitigated fouling are significant findings, suggesting a path for optimizing future FO membrane filtration through temperature control.