Sodium metasilicate sol-gel draw solution for seawater desalination and supplementing nutrients to soil

A novel sol-gel using sodium metasilicate (SMS) was used as a draw solution (DS) in the forward osmosis (FO) to provide nutrients to soil and plants without a regeneration step. SMS sol-gel has an osmotic pressure of 55 bar and 73.4 bar for 0.75 M and 1 M of SMS, respectively, which is higher than 1 M NaCl (48.9 bar). To test the novelty of the SMS sol-gel as DS, two concentrations of 0.75 M and 1 M were tested against DI water and 0.5 M NaCl feed solution (FS), and 1 M of SMS for real seawater at 35 g/L. A commercial cellulose triacetate (CTA) membrane was used, where experimental results showed SMS at 1 M using DI water as FS at active layer draw solution (ALDS) membrane orientation had a 42 % recovery rate, compared to active layer feed solution (ALFS) at 36 % recovery. The highest average flux achieved was 23.24 LMH with DI water as FS, using 1 M SMS sol-gel as DS at ALDS. Whereas using seawater at ALDS had a 23.5 % recovery and ALFS had a 15.2 % recovery. Testing seawater at ALDS with three 24-h cycles had 55.8 %, 45.4 %, and 32.9 % recovery for the first, second, and third cycles, respectively. There was a 99 % rejection of silicon and sodium ions for both SMS concentrations. The specific energy consumption was lowest at 0.00717 kWh/m3 in the first 24-h cycle of seawater as FS. [Display omitted] •Sodium metasilicate was used as a draw solution for seawater desalination by forward osmosis.•Reaction products of Na2SiO3 with HNO3 are sol-gel of silicic acid and Na2NO3 plant nutrients.•A water flux of 23.24 LMH was achieved with 1 M sol-gel DS and DI water feed solution.•CTA membrane rejected 99 % of silica resulting in 8.85 g/Lm2 RSF only for 1 M sol-gel.•The specific energy consumption was as low as 0.00717 kWh/m3 for 1 M sol-gel DS.