Fabrication of Fouling Resistant and Operationally Stable Nanocomposite Membranes for BTEX Wastewater Treatment

Abstract

This thesis details the fabrication of a fouling-resistant and operationally stable membrane developed for removing BTEX (benzene, toluene, ethylbenzene, and xylene) from wastewater. BTEX is among the top major organic contaminants that have been reported to pollute the aquatic system. BTEX contaminants in the water bodies are detrimental to both humans and aquatic organisms, as exposure to these contaminants could result in mild or severe health complications. With the major source of these contaminants originating from anthropogenic activities, especially the discharge of poorly treated industrial wastewater, it is essential to continuously explore better means of ensuring effective treatment of BTEX-contaminated wastewater before discharge to the environment. Membrane technology offers a low-cost, easy, and effective approach to removing such organic contaminants from wastewater. However, due to the hydrophobic nature of most membrane materials, there is a high fouling rate during the treatment process as a result of the interaction between the hydrophobic membrane and the hydrophobic organic contaminants. The fouling of the membrane leads to the deterioration of its properties, resulting in a severe decline in membrane performance. Addressing the issue of such membrane fouling is often done through hydrophilic modification, which entails using hydrophilic modifiers to enhance the hydrophilic property of the membrane. Once the membrane’s hydrophilicity is enhanced, the interaction between the membrane and the organic contaminants is reduced, thereby minimizing the fouling rate of the membrane during the treatment process and ensuring that the membrane maintains its performance for a longer duration. Therefore, the goal of this study was to fabricate a fouling-resistant membrane by incorporating biogenic-synthesized iron oxide nanoparticles and polyvinyl alcohol (PVA) as hydrophilic modifiers to improve and maintain the membrane performance in the treatment of BTEX-contaminated water. The first part of the study was to biogenically synthesize the iron oxide using the leaves, peels, and seeds extracts of the pomegranate and compare their properties and contributions in removing BTEX from contaminated wastewater. X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) were used to analyze the properties of the three different biogenic-synthesized iron oxide nanoparticles. The FTIR results showed that there is deposition of hydrophilic functional groups from the extracts to the synthesized nanoparticles, thus establishing that the biogenic-synthesized iron oxide nanoparticles have attached hydrophilic functional groups, which is beneficial in their use as hydrophilic modifiers. From the FTIR spectra, the iron oxide nanoparticles synthesized using the leaves extract have a more intense peak of the hydrophilic functional groups, such as the -OH group; thus, it was selected as the nanoparticle used for the hydrophilic membrane modification. It was also established that the biogenic-synthesized iron oxide nanoparticles have the capacity to remove BTEX from wastewater, as indicated in the batch adsorption study. The findings of this part of the study are presented in Paper 1, which is fully discussed in Chapter 4 of this thesis. In the second part of the study, the biogenic-synthesized iron oxide nanoparticles (NPs) (from the leaves extract of pomegranate) were blended into a polyvinylidene fluoride (PVDF) membrane, and the optimum blending amount of the NPs required for their optimum dispersion in the membrane was assessed. This was performed by varying the blending amounts of the NPs from 0.05 wt.% to 5.0 wt.%, and the ideal operating parameters were also identified. From the SEM and TEM images, the membrane modified with 1.0 wt.% of the NPs (denoted as PVDF 1.0) has the best dispersion of the NPs in the membrane matrix without agglomeration of the NPs. Among all the fabricated membranes, the PVDF 1.0 also has the lowest water contact angle (WCA) of 52o, the lowest irreversible fouling (Rir) of 18.3%, and the highest flux recovery ratio (FRR) of 81.3%. The PVDF 1.0 also performed better in the reusability test. Based on the properties and performance of PVDF 1.0, the optimum blending amount of the biogenic synthesized NPs in the PVDF membrane, using the fabrication conditions of this study, was established to be 1.0 wt%. The findings of this part of the study are presented in Paper 2, which is detailed in Chapter 5 of this thesis. The third part of the study focused on further enhancing the membrane's hydrophilicity and antifouling ability to ensure its good operational stability under long-term BTEX filtration. This was done by utilizing the synergistic impact of biogenic-synthesized iron oxide NPs and PVA as good hydrophilic modifiers to improve the membrane's hydrophilicity and performance. Biogenic-synthesized NPs and PVA were blended into the membrane, and the properties and performance of the modified membrane were assessed (optimum amount, 1.0 wt% of the biogenic-synthesized NPs, was used as established in the second part of the study, that is, in Chapter 5). The WCA of the modified PVA-Fe3O4-PVDF membrane reduced to 40.5o, and the Rir also reduced to 2%, while the FRR increased to 98%. The performance of the membrane under long-term filtration showed that the modified membrane had fairly good operational stability, as the membrane maintained its flux for 84 hour without any significant decline in flux. The findings of this section of the study are presented in Paper 3, which is discussed in Chapter 6 of this thesis. The fourth part of the study investigated the reproducibility of some of the properties and performance of the modified PVA-Fe3O4-PVDF membrane. Ten more of the modified membranes were re-fabricated at different times, and their SEM, BTEX flux and BTEX rejection were analyzed. In terms of the SEM result, seven out of the ten re-fabricated membranes showed good dispersion of the NPs in the membrane matrix. The BTEX flux and rejection of the re-fabricated membrane were also fairly close to the originally reported value in Chapter 6 of this thesis. The findings of this section of the study are detailed in Chapter 7 of this thesis.