Hydrophilic Mineral Coating of Membrane Substrate for Reducing Internal Concentration Polarization (ICP) in Forward Osmosis

Abstract

Internal concentration polarization (ICP) is a major issue in forward osmosis (FO) as it can significantly reduce the water flux in FO operations. It is known that a hydrophilic substrate and a smaller membrane structure parameter (S) are effective against ICP. This paper reports the development of a thin film composite (TFC) FO membrane with a hydrophilic mineral (CaCO3)-coated polyethersulfone (PES)-based substrate. The CaCO3 coating was applied continuously and uniformly on the membrane pore surfaces throughout the TFC substrate. Due to the intrinsic hydrophilicity of the CaCO3 coating, the substrate hydrophilicity was significantly increased and the membrane S parameter was reduced to as low as the current best of cellulose-based membranes but without the mechanical fragility of the latter. As a result, the ICP of the TFC-FO membrane could be significantly reduced to yield a remarkable increase in water flux without the loss of membrane selectivity.

Improved performance of thin-film composite membrane with PVDF/PFSA substrate for forward osmosis process

“…9. It can be seen that, the water flux increases The ICP impact in FO process can be evaluated appropriately by the structure parameter S, and a lower S value generally indicates the subdued ICP effect, favoring a higher FO water flux in actual applications [6,7,13]. As listed in Table 5, the S parameter of the resultant TFC samples exhibits an overall decreasing tendency with the increasing PFSA content in the membrane substrate (except for MT-5), which should be resulted from the enhanced hydrophilicity, higher porosity and less tortuosity of the substrate as aforementioned.…”

“…In the FO process, the water flows from the feed solution (lower osmosis pressure) to the draw solution (higher osmosis pressure) across the designed semi-permeable membrane without any external energy consumption. Therefore, FO process possesses unique advantages of high water recovery, low fouling tendency, simplicity and reliability, compared to other pressure-driven membrane separation processes, such as nanofiltration (NF) and reverse osmosis (RO) [7].…”

Advances in forward osmosis membranes: Altering the sub-layer structure via recent fabrication and chemical modification approaches

“…An alternative hydrophilization procedure is the bio-mineral coating of CaCO3 on the PES substrate to improve wettability, which decreases the S value and ICP effects in TFC-FO membrane [200]. This coating was used for other polymeric membranes in previous studies [14,201,202].…”

Enhanced performance of forward osmosis membranes by incorporating PVDF substrates with hydrophilic nanofillers

“…Lately, forward osmosis (FO) process works with lower external pressure while the reverse osmosis (RO) process is widely used to produce pure water as an advanced and energy-saving technology [4][5][6][7]. FO process shows excellent superiority of high water recovery being possible, lower fouling tendency and with lower energy consumption while other osmosis-driven separation processes are opposite to FO process, for instance, nanofiltration (NF) and reverse osmosis (RO) [8,9].…”