Thin film nanocomposite membrane incorporated with palygorskite/chitin hybrid for forward osmosis desalination

Abstract

Desalination technology has become more relevant as a result of increasing demands for clean water and shortcomings of surface water. In forward osmosis (FO) system, the difference in osmotic pressure resulting from the difference in concentration of feed solution (FS) and draw solution (DS) acts as the driving force of water molecules transportation across the membrane. FO membranes are faced with the issue of dilution of the DS which gives rise to internal concentration polarization (ICP) that results in the reduction of the osmotic pressure difference across the active layer of the membrane, hence leading to low water flux. Improving the hydrophilicity of the substrate of the FO thin film composite membranes has been proven as a feasible strategy to address this issue and enhance the desalination performance of the FO membranes. The objectives of the study are to synthesize PAL-CH based on different compositions of palygorskite and chitin and to characterize the material of the physic-chemico-chemical properties. Fabricate and characterize thin film nanocomposite (TFN) membrane with its substrate incorporated with synthesized PAL-CH hybrid, and evaluation of the TFN membrane performance in terms of rejection, flux and anti-fouling properties. To achieve these objectives, a thin film nanocomposite membrane incorporated with palygorskite/chitin (PAL-CH) hybrid nanomaterial had been successfully fabricated. The incorporation of PAL-CH material enhanced the hydrophilicity of the FO membrane, resulting in the formation of hydration layer at the membrane interface, thereby facilitating the transportation of water across the membrane. The PAL-CH hybrid nanomaterial was synthesized via ball milling method. The substrates were developed with 15 wt % of polysulfone (PSF) and various loads of PAL-CH hybrid nanomaterial (range 0 – 0.015 wt %). The first stage of this study was the synthesis of hybrid nanomaterial. At the second stage of this study, the synthesized hybrid nanomaterial was incorporated in the substrate of the TFN membrane and its performance was studied employing the reverse osmosis system. Water permeability of 2.4 Lm-2 h-1 was achieved when 0.01 wt % of PAL-CH hybrid nanomaterial was incorporated into the substrate of the TFN membrane. The water permeability was approximately 192.7 % higher than that of pristine membrane. The sodium chloride rejection was 98.5 % and 98 % for PAL-CH hybrid incorporated membrane and pristine membrane respectively. At the final stage of the study, the fabricated PAL-CH based TFN membrane was subjected to FO performance test. The PAL-CH incorporated TFN membrane showed good FO performance with water fluxes of 11.68 Lm-2 h-1 (in active layer facing FS mode) and 34.39 Lm-2 h-1 (in active layer facing DS mode) while maintaining small structure parameter (S) and reverse solute flux (Js) value. The PAL-CH nanomaterial incorporation led to the formation of higher pronounced ridges in membrane which is a confirmation of improved surface roughness which facilitates higher degree of cross-linking. Besides, the modified membrane exhibited less severe membrane fouling and high pure water flux recovery which is an indication of a good quality FO membrane. The introduction of PAL-CH into the substrate enhanced the separation features of the membrane in terms of S parameter, rejection and water flux. The introduction of PAL-CH reduced the S parameter hence restricting the ICP phenomenon impact in the thin firm composite FO process. It is concluded from the research findings that the addition of the PAL-CH hybrid nanomaterial within substrate has substantial effects on the performance of the TFN-FO membrane. The facile substrate modification promotes the applicability of this nanocomposite membrane for desalination application.