Abstract 8 Two spiral wound forward osmosis (SWFO) membrane modules with different spacer design (CS; 9 corrugated spacer and MS; medium spacer) were investigated for the fertilizer drawn forward osmosis 10 desalination of brackish groundwater (BGW) at a pilot-scale level. This study mainly focused on 11 examining the influence of various operating conditions such as feed flow rate, total dissolved solids 12 (TDS) concentration of the BGW feed, and draw solution (DS) concentrations using ammonium 13 sulphate ((NH 4 ) 2 SO 4 , SOA) on the performance of two membrane modules. The feed flow rate played 14 a positive role in the average water flux of the pilot-scale FO membrane module due to enhanced 15 mass transfer coefficient across the membrane surface. Feed TDS and DS concentrations also played a 16 significant role in both FO membrane modules because they are directly related to the osmotic driving 17 force and membrane fouling tendency. CS module performed slightly better than MS module during 18 all experiments due to probably enhanced mass transfer and lower fouling propensity associated with 19 the corrugated spacer. Besides, CS spacer provides larger channel space that can accommodate larger 20 volume of DS and hence could maintain higher DS concentration. However, the extent of dilution for 21 the CS module is slightly lower. 22 2
