A study of the effect of embedding ZnO-NPs on PVC membrane performance use in actual hospital wastewater treatment by membrane bioreactor
Graphical abstract
Introduction
Wastewater discharge containing abnormally high amounts contaminants, i.e., suspended or dissolved materials can lead to serious problems of water resources. Several separation techniques have been used and developed to remove these contaminants from wastewater, which is critical to environmental protection such as biological nutrient removal processes (BNR), activated sludge (CAS), and Membrane bioreactor (MBRs), etc. [[1], [2], [3], [4], [5]].
Among a challenges that affects the efficiency of MBRs process is membrane fouling, which decreases the permeate flux. This phenomenon imposes problems in the separation process efficiency and leads to frequent maintenance during membrane operations [6]. A variety of researches has been performed to overcome fouling issues. Several membrane modification methods have been widely practiced to improve membrane performance, i.e. development of composite membranes via interfacial polymerization, UV-initiated grafting, and incorporation of nanoparticles or antifouling agents [[7], [8], [9]].
During the phase inversion process and modify membranes structure and performance such as blending polymeric systems [10] and incorporation of nanoparticles in membranes [[11], [12], [13]] and membranes properties are a trade-off between thermodynamic enhancement and kinetic hindrance during the phase inversion process [14]. Different polymers have been used for membrane preparation via phase inversion for MBR application, such as polyethersulfone (PES) [[15], [16], [17]], polysulfone (PSF) [18], polyvinylidene fluoride (PVDF) [19,20], polyacrylonitrile (PAN) [21], polyvinyl chloride (PVC) [10,22,23], and cellulose acetate (CA) [24]. However, of these materials, PVC has attracted great attention because of its interesting mechanical and chemical resistance (to acids, halogens, or oxidants), lower cost, good stability at high temperatures and solubility in different solvents. The most important drawback of PVC is its hydrophobicity, which likely results in more fouling during ultrafiltration (UF). To resolve this problem, Peng and Sui [25] added poly (vinyl butyral) (PVB) to a PVC polymeric solution, and they observed improvement in surface hydrophilicity of the membranes, which indicates better fouling resistance compared to the neat PVC membranes. Mei et al. [22] found that increments of poly (vinyl pyrrolidone) PVP, poly(ethyleneglycol) (PEG), and sucrose to a PVC/dimethylacetamide DMAc system lead to a decrease in the thermodynamic stability of the dope solution in contact with water. In addition, they reported that the velocity of solvent-non-solvent exchange and membrane formation increases with these additives, and the increment of PVP needed is greater than that for PEG, thereby considerable changes in membrane morphology were observed due to changes in kinetic and thermodynamic properties.
To date, NPs made of numerous types of metal or metal oxides, such as silver (Ag), iron (Fe2O3, Fe3O4), silica (SiO2), aluminum (Al2O3), titanium (TiO2), magnesium oxide (MgO), and zirconium dioxide (ZrO2), have reportedly been used in membrane applications [9]. Some of these metal oxide NPs are quite expensive, and thus efforts have been focused on lower cost metal oxide options. One of the popular low-cost metal oxides is zinc oxide (ZnO), which has been used as a new alternative for titanium oxide [26]. ZnO-NPs are gaining increased attention in various industries such as biomedical, optics, and electronics and recently in the development of membrane technology, owing to their superb antimicrobial, anti-corrosive, and thermal and mechanical stability properties [27]. Studies have been reported on the incorporation of various concentrations of ZnO-NPs into different polymer matrices such as PSF, PES, and PVDF. These studies reported on the formation of membranes with improved membrane performances such as higher permeability, rejection capability, porosity, and hydrophilicity and enhanced antifouling properties [[28], [29], [30], [31]]. In light of the aforementioned issues, however, studies have reported the effects of nanoparticles on the several polymers are shown in Table 1.
For example, Alsalhy et al. [32] reported that the hydrophilicity, mean pore size and mean roughness of the Polyphenylsulfone PPSU/ZnO-NPs membranes were increased with the increase of ZnO-NPs concentration. The authors observed that with addition of 0.025 wt.% ZnO-NPs, no important change in solute rejection with significant enhancement in the PPSU-NPs flux (i.e., 76–107 (L/m2 h bar)). Hong and He [31], found that the hydrophilicity of the PVDF microfiltration with different concentrations of ZnO-NPs in casting solution (i.e., 0–1%) was considerable improved. Moreover, the results of Hong and He [36], showed that the hydrophilicity and the average pore diameter of PVDF membranes improved when the concentration of ZnO-NPs increased up to 1.5%. Also, they found that the COD removal efficiency reduced strongly when the concentration of ZnO-NPs surpassed 0.1% because of the increased pore diameter, whereas COD removal efficiency enhanced a little when the concentration of ZnO-NPS increased up to 1.5%, because of the hydrophilic character of the membrane.
In this work, PVC membranes were prepared to study the effects of various contents of ZnO-NPs as an inorganic additive on the performance of UCT-MBRs process for the first time for the treatment of actual hospital wastewater. The hypothesis of this effort was to use the ZnO as an anti-biofouling material to overcome the formation of a bio-cake layer on the PVC membrane surface, which in turn greatly extend the long-term of the membrane. Furthermore, in biological systems, microorganism contamination may take place in the membrane module, which affects the membrane performance and therefore the product quality. The efficiency of the flat-sheet membranes was measured in terms of permeation flux, and removal of chemical oxygen demand (COD) of the wastewater from an Iraqi hospital. The PVC/ZnO membrane structure was studied via scanning electron microscopy (SEM) and atomic force microscopy (AFM). In addition, modification of the hydrophilicity of the membrane surface was investigated using acontact angle measurement (Table 2).
Section snippets
Materials
The PVC resins (65 kg/mol) were obtained from the Georgia Gulf Company (Georgia, USA), and the DMAc solvent was supplied by Sigma-Aldrich, Germany. ZnO nanoparticles (99%, 10–30 nm, product no. 8411DL) were purchased from SkySpring Nanomaterials, Inc, company, USA.
Membrane preparation
The polymer material PVC was dried at 60 °C for 4 h in an oven device to remove its moisture content. The casting solution was prepared by adding dried 13 wt.% PVC to 87 wt.% DMAc solvent. After the PVC solution was homogeneous owing
Analysis of EDX
The EDX analysis was rather important for verifying the elements present in the membrane matrix, therefore all the membranes were examined for the presence of the zinc components. Fig. 2 shows the EDX photos of the PVC/ZnO NPs membranes prepared from various ZnO loadings of the casting solution. The corresponding Zn element mappings indicated scattering of nano-ZnO among the whole membrane. It can be seen that the best dispersion of the ZnO NPs in the membrane was obtained with addition of
Conclusions
In this effort, treatment of actual hospital wastewater was carried out by using UCT-MBR configuration process. A developed anti-biofouling PVC/ZnO flat-sheet membrane was prepared and used in an UCT-MBR. Based on this study, the following conclusions were made:
- •
The addition of ZnO NPs in PVC casting solution changed the morphological structure of the membranes.
- •
Addition of 0.1 g of ZnO NPs significantly increased the mean roughness by about 140%, with smaller mean pore size and narrow pore size
References (68)
- et al.
Simultaneous nitrogen and phosphorus removal by a novel sequencing batch moving bed membrane bioreactor for wastewater treatment
J. Hazard. Mater.
(2010) - et al.
Parameters affecting biological phosphate removal from wastewaters
Environ. Int.
(2004) - et al.
Drawbacks of applying nanofiltration and how to avoid them: a review
Sep. Purif. Technol.
(2008) - et al.
Nanofiltration membrane modification by UV grafting for salt rejection and fouling resistance improvement for brackish water desalination
Desalination
(2012) - et al.
Polymeric membranes incorporated with metal/metal oxide nanoparticles: a comprehensive review
Desalination
(2013) - et al.
Preparation, characterization and performance of Al2O3/PES membrane for wastewater filtration
J. Membr. Sci.
(2009) - et al.
Fabrication of polyethersulfone-mesoporous silica nanocomposite ultrafiltration membranes with anti-fouling properties
J. Membr. Sci.
(2012) - et al.
The performance of the PVDF-Fe3O4 ultrafiltration membrane and the effect of a parallel magnetic field used during the membrane formation
Desalination
(2012) - et al.
Trade-off between thermodynamic enhancement and kinetic hindrance during phase inversion in the preparation of polysulfone membranes
Desalination
(2003) - et al.
Synthesis, characterization and performance of asymmetric polyethersulfone (PES) ultrafiltration membranes with polyethylene glycol of different molecular weights as additives
Desalination
(2007)
Novel modified PVDF ultrafiltration flat-sheet membranes
J. Membr. Sci.
Preparation of asymmetric polyacrylonitrile membrane with small pore size by phase inversion and post-treatment process
J. Membr. Sci.
Cellulose acetate (CA)/polyvinylpyrrolidone (PVP) blend asymmetric membranes: preparation, morphology and performance
Desalination
Compatibility research on PVC/PVB blended membranes
Desalination
Preparation and characterization of ZnO/polyethersulfone (PES) hybrid membranes
Desalination
A novel ZnO nanoparticle blended polyvinylidene fluoride membrane for anti-irreversible fouling
J. Membr. Sci.
Improving permeability and antifouling performance of polyethersulfone ultrafiltration membrane by incorporation of ZnO-DMF dispersion containing nano-ZnO and polyvinylpyrrolidone
J. Membr. Sci.
Effects of nano sized zinc oxide on the performance of PVDF microfiltration membranes
Desalination
Development of polysulfone-nanohybrid membranes using ZnO-GO composite for enhanced antifouling and antibacterial control
Desalination
Hydrophilic fouling-resistant GO-ZnO/PES membranes for wastewater reclamation
J. Membr. Sci.
Effect of TiO2 nanoparticle size on the performance of PVDF membrane
Appl. Surf. Sci.
Poly(vinylidenefluoride) ultrafiltration membrane blended with nano-ZnO particle for photo-catalysis self-cleaning
Desalination
Graphene oxide nanoplatelets composite membrane with hydrophilic and antifouling properties for wastewater treatment
J. Membr. Sci.
Anti-bacterial properties of ultrafiltration membrane modified by graphene oxide with nano-silver particles
J. Colloid Interface Sci.
Preparation, performances of PVDF/ZnO hybrid membranes and their applications in the removal of copper ions
Appl. Surf. Sci.
Performance of a novel ZrO2/PES membrane for wastewater filtration
J. Membr. Sci.
Preparation and characterization of emulsion poly(vinyl chloride) (EPVC)/TiO2 nanocomposite ultrafiltration membrane
J. Membr. Sci.
Formation mechanism of asymmetric membranes
Desalination
Formation mechanism of phase inversion membranes
Desalination
Formation of membranes by means of immersion precipitation: part II. The mechanism of formation of membranes prepared from the system cellulose acetate-acetone-water
J. Membr. Sci.
Microstructures in phase inversion membranes. Part 2. The role of a polymeric additive
J. Membr. Sci.
The influence of nano-sized TiO2 fillers on the morphologies and properties of PSF UF membrane
J. Membr. Sci.
TiO2 entrapped nano-composite PVDF/SPES membranes: preparation, characterization, antifouling and antibacterial properties
Desalination
Morphological and separation performance study of polysulfone/titanium dioxide (PSF/TiO2) ultrafiltration membranes for humicacid removal
Desalination
Cited by (99)
Reduction of Recombination Processes in PVC Photocatalytic Membranes Modified with Green Prepared Nanoparticles
2024, Journal of Molecular StructureAdvances in ZnO nanoparticles in building material: Antimicrobial and photocatalytic applications – Systematic literature review
2024, Construction and Building MaterialsPreparation, characterization, and fouling analysis of PVC/ND-PEG ultrafiltration membranes for whey separation
2024, Diamond and Related MaterialsOptimum content of incorporated nanomaterials: Characterizations and performance of mixed matrix membranes a review
2024, Desalination and Water Treatment