Thin film composite hollow fibre forward osmosis membrane module for the desalination of brackish groundwater for fertigation

• Performance of PA hollow fibre FO membrane module was studied for FDFO process.
• Ion and membrane charge played a significant role in HFFO module performance.
• Membrane charge determined selective ion transfer sometimes resulting in scaling.
• Scaling occurred both on the active and support layer sides of the HFFO membrane.
• HFFO module with high packing density has high volumetric output per module.

The performance of recently developed polyamide thin film composite hollow fibre forward osmosis (HFFO) membrane module was assessed for the desalination of brackish groundwater for fertigation. Four different fertilisers were used as draw solution (DS) with real BGW from the Murray–Darling Basin in Australia. Membrane charge and its electrostatic interactions with ions played a significant role in the performance of the HFFO module using fertiliser as DS. Negatively charged polyamide layer promotes sorption of multivalent cations such as Ca2 + enhancing ion flux and membrane scaling. Inorganic scaling occurred both on active layer and inside the support layer depending on the types of fertiliser DS used resulting in severe flux decline and this study therefore underscores the importance of selecting suitable fertilisers for the fertiliser drawn forward osmosis (FDFO) process. Water flux under active layer DS membrane orientation was about twice as high as the other orientation indicating the need to further optimise the membrane support structure formation. Water flux slightly improved at higher crossflow rates due to enhanced mass transfer on the fibre lumen side. At 45% packing density, HFFO could have three times more membrane area and four times more volumetric flux output for an equivalent 8040 cellulose triacetate flat-sheet FO membrane module.