Effects of phosphate limitation in feed water on biofouling in forward osmosis (FO) process

• Effects of phosphate limitation on biofouling in FO process were confirmed.
• Characteristics of biofouling in FO process were investigated.
• Role of accelerated BEOP and Gibbs–Donnan equilibrium in phosphate limitation was explored.
• Applicability of phosphate limitation as pretreatment in FO process was shown.

Forward osmosis (FO) has been applied to various water treatment processes because of its low energy consumption and lower fouling propensity. Fouling, however, especially biofouling, is still problematic in FO. To resolve the biofouling issue, phosphate limitation was investigated to reduce biofouling instead of commonly used chemical cleaning. To establish the effects of phosphate limitation on biofouling formation, various phosphate concentrations and nutritional conditions were tested to seek a basic correlation between phosphate limitation and biofilm formation, and effects of phosphate limitation on performance of FO were checked. As a result, it was discovered that the phosphate limitation in feed water greatly reduced microbial growth and biofilm formation, thereby FO performance was maintained. This phenomenon was explained in accelerated biofilm-enhanced osmotic pressure (Accelerated BEOP) and Gibbs–Donnan equilibrium mechanism, and it shows that phosphate limitation can effectively control biofouling by alleviating the accelerated BEOP and balancing the Gibbs–Donnan equilibrium. Therefore, it may be feasible to use the phosphate limitation in FO pretreatment to control biofouling.