Treatment of drinking water with nanocomposite membranes

In recent years, effects such as economic developments, industrialization, rapid population growth, migrations and climate changes have reduced the amount of water resources and adversely affected water quality. The fact that more than 70% of the world is covered by water does not change the fact that drinking water is scarce in many regions. Membrane filtration systems are good alternatives to conventional systems used in the treatment of drinking water because of their high separation efficiency, simple operation, low space requirements, and lack of need for chemicals during filtration. The limitations of water resources and the development of alternative technologies in response to the increase in pollutant parameters have increased the number of studies on nanocomposite membrane applications in the removal of pollution from drinking water. Recently, studies on nanocomposite blended polymeric membranes have increased on a global scale in order to use water efficiently and to meet the need for high quality, reliable drinking water. Polymeric membranes are widely used in water treatment because of their ease of fabrication and low cost. The flux and purification performance of membranes can be significantly improved by incorporating appropriate amounts of nanomaterials into the polymeric membrane matrix. Nanocomposite membranes are modified form of traditional polymeric membranes for water treatment with characteristics of enhanced permeation, improved rejection and reduced fouling. Polymeric nanocomposite membranes are widely used to improve the properties of standard membranes. The addition of nanocomposite materials such as copper oxide, zinc and zinc oxide to the membrane matrix structure improves selective permeability, thermal and mechanical strength, permeability, pollution resistance and treatment performance. In this study, ZnO and CuO based polymeric Microfiltration (MF) membranes were synthesized and their potential for use in drinking water treatment was investigated. The hydrophobic structure of Polyether Sulfone (PES) polymer, which is an undesirable feature, brings with it the need to improve it with the addition of nanomaterials. PES polymeric material is preferred due to its advantages such as being suitable for different membrane experiments, thermal and chemical resistance, high performance and low cost. Due to the hydrophobic nature of the PES polymer, it is a disadvantage that large molecules accumulate on the membrane surface and become contaminated. Polyethersulfone is preferred in RO, UF and MF processes as the pore size can be adjusted to the desired size and can be used in tubular and sheet form. In this study, bare polyethersulfone (PES), PES/nano copper oxide (CuO), and PES/nano zinc oxide (ZnO) membranes were fabricated via submerged phase inversion method dissolving in Dimethyl Sulfoxide (DMSO) solvent. The type of material used as a solvent also affects membrane porosity, contact angle, fouling resistance, permeability and thus treatment performance. For nanocomposite membranes, there is a strong connection between the membrane fabrication method, the properties of fabricated membranes such as porosity, and membrane performance. In this study, porosity, surface contamination and surface roughness of %0.5- %1 ZnO and %0.5 - %1 CuO based MF membranes synthesized by phase inversion method using %16 by weight PES, Electron Scanning Microscope (SEM) and Atomic Force Microscope (AFM) were examined using imaging devices. SEM surface images of the contaminated membranes after filtration were compared and evaluated. The filtration and permeability tests of the synthesized membranes were carried out with a dead-end device, which is a vertical flow and pressure driven membrane filtration system, under 3 bar pressure. The pure water flux of the bare PES membrane, which was 355.14 L/m2.h, increased significantly with the addition of nano-CuO and nano-ZnO, and the pure water fluxes of the nanocomposite membranes varied in the range of 392.65-429.74 L/m2.h. The 1% ZnO-PES membrane with the highest permeability is the pure PES membrane with the lowest. Iron, Conductivity, pH, TOC, Barium, by using Atomic Emission Spectrometer (ICP) for heavy metal analysis in determination of filtration performance of membranes, Ion Chromatography (IC) for ion analysis, TOC analyzer for total organic carbon analysis, pH-Conductivity analyzers for pH-Conductivity determination, Boron, Total Chromium and Selenium removal efficiencies were compared. As a result, nano CuO and nano ZnO doped PES nanocomposite membranes exhibited higher conductivity, color, total organic carbon, boron, iron, selenium, barium and total chromium removal efficiencies than bare PES membrane. It was determined that the conductivity, color, total organic carbon, boron, iron, selenium, barium and total chromium removal efficiency of the membrane increased with the addition of 0.5 and 1% wt. nano CuO and nano ZnO to the bare PES membrane. The membrane surfaces examined by Scanning Electron Microscopy (SEM) after water filtration revealed that those containing 0.5% wt. nano CuO and nano ZnO were more resistant to fouling than the membrane surfaces containing 1% wt. nano CuO and nano ZnO. Based on the results of this study, 0.5% wt. nano ZnO doped PES membrane was found to be the most suitable membrane for use in water treatment due to its high pure water flux (427.14 L/m2.h), high pollutant removal efficiency and high fouling resistance. With the addition of 0.5% nano CuO and nano ZnO to the pure PES membrane, the pure water flux of the membrane increased by 16.9% and 20.2% respectively. Nanocomposite membranes containing 0.5% by weight nano CuO and nano ZnO exhibited better surface fouling resistance after filtration than the membrane containing 1% by weight nano CuO and nano ZnO. It has been concluded that the treatment efficiencies are generally close to each other, and the best performance in terms of porosity, permeability, hydrophilicity, and contamination resistance properties belongs to ZnO based membranes. Zinc oxide (ZnO), on the other hand, is a multifunctional inorganic nanoparticle that attracts attention due to its catalytic, antibacterial and bactericidal physical and chemical properties. ZnO nanoparticles can absorb more hydroxyl (OH-) groups compared to other inorganic materials, adding nanoparticles to the membrane as an additive improves the hydrophilicity, mechanical and chemical properties of the polymer. It is thought that the effect of copper ions (CuO) on nanocomposite membranes is limited and more effective in biopollution control by improving antibacterial properties. The addition of nanoparticles such as ZnO and CuO to polymeric membranes increases the resistance to contamination and prolongs the lifetime of the membranes. When the SEM images after filtration are examined, it is seen that the pure PES membrane is quite dirty, while the CuO-PES and ZnO PES membranes are less contaminated. It was observed that the amount of contamination in the 1% CuO-PES membrane was lower than the 1% CuO-PES membrane. In this study, Iron, which is an unwanted heavy metal in excess, is the most appropriate parameter to be evaluated in terms of purification performance. Iron removal efficiency was generally high in all synthesized membranes and was found to be very close to each other. The 0.5% ZnO-PES nanocomposite membrane has the highest iron removal efficiency with 84.1%, and the lowest is the 1% ZnO-PES membrane with 80.9% purification efficiency. The synthesized pure PES and ZnO, CuO nanoparticle doped nanocomposite polymeric membranes all showed very close performance in iron removal and were quite effective. If we order from the membrane with the highest purification efficiency in iron removal to the lowest, the purification efficiency of 0.5-ZnO-PES is 84.1%, 1-CuO-PES 82.4%, pure PES 81.5%, 1-ZnO-PES 80.9% and 0.5-CuO 80.4% type. The water treatment performance was the most successful with 0.5% ZnO-PES, which reduced the Iron concentration in raw water from 460 µg/L to 73 µg/L. When the percentage of ZnO doped membrane increased, the pore size increased and the particles accumulated in certain places and the aggregation increased, resulting in a decrease in the treatment performance. Since the increase in the amount of ZnO added to the PES polymer increases the pore size, a slight decrease has occurred in the membrane treatment performance. Since the increase in the amount of ZnO added to the PES polymer increases the pore size, a slight decrease has occurred in the membrane water treatment performance. Selenium and Total Chromium parameters were found in very low amounts in raw water and were completely removed with 100% efficiency. The 1%-ZnO-PES membrane has the highest TOC removal efficiency with 26.1% and the lowest is the 0.5%-CuO-PES membrane with 20.7%. The 1%-ZnO-PES membrane has the highest conductivity treatment efficiency with 20.9%, and the lowest is the pure PES polymeric membrane with 18%. Considering the results of the pH analysis, the pH values increased slightly compared to the pure PES polymer, since the nanomaterial additive increased the number of hydroxyl (OH-) groups. Within the scope of this study, the most suitable membrane for the water source to be treated is 0.5% by weight ZnO-PES nanocomposite membrane, due to the closeness of treatment performances and higher permeability when all membrane characterization is taken into account. The findings obtained may differ from other studies in the literature due to many different factors such as the homogeneity of the polymer solution to be used in membrane synthesis, the composition and temperature of the coagulation bath, and ambient conditions.