Impact of filtration temperature on sewage concentration by forward osmosis for anaerobic digestion reuse

Sewage concentration by forward osmosis (FO) is strongly influenced by temperature, yet its effect remains unclear due to limited and inconsistent evidence. This study examined the effect of temperature through prolonged sewage filtration at 10–30 °C using 1.2 M NaCl as the draw solution, achieving a volume reduction factor of 20. Higher temperatures surprisingly lowered reverse solute flux, reducing concentrate salinity by 4.5 g NaCl/L, corresponding to a 40 % reduction compared with operation at 10 °C. Nitrogen and phosphorus concentration efficiencies declined with temperature, whereas organic enrichment showed little change and remained limited to 8–10-fold. Fouling was consistently rich in complex organics, but its dominant character shifted toward inorganic fouling, with increased phosphate mineral deposition at higher temperatures. Substantial nitrogen loss to the draw solution (31–50 %) and phosphorus buildup on the membrane (40–50 %), both intensified at higher temperatures, highlight the need for post-filtration nutrient recovery. Concentrates produced at 30 °C yielded more methane due to lower salinity, though production remained limited by salinity stress and low biodegradable organics. Temperature strongly governs FO performance, and proper control can enhance anaerobic digestion pretreatment and support circular wastewater strategies for reuse, nutrient recovery, and energy generation.