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With the rapid development of industrialization and urbanization, oily wastewater increasingly threatens the environment and human health. It mainly comes from industries like food processing, oil exploitation, textiles, and metal processing. Its complex composition makes treatment difficult. Traditional methods, such as gravity sedimentation and chemical coagulation, can't effectively remove emulsified and dissolved oil, leaving treated water still harmful to the environment. Thus, developing efficient oily wastewater treatment technologies is urgent. In recent years, electrospinning technology has drawn much attention for its high separation performance, offering new solutions for this environmental problem.
Oily wastewater from industries like petroleum and food processing contains floating, dispersed, emulsified, and dissolved oil. Emulsified and dissolved oil, with small particle sizes and high stability, are hard to remove by traditional methods. They pose threats like reducing water's dissolved oxygen and endangering aquatic life. According to physical properties, oil - water contamination can be classified into four categories, as shown in Figure 1.
(Figure 1 Categorization and size distribution of oil droplets.)
Membrane technology, an emerging water treatment method, has advantages such as low energy consumption, less pollution, and simple operation. It separates oil and water through selectively permeable membranes. Common membrane types include MF, UF, NF, and RO. UF and NF membranes are widely used in oily wastewater treatment due to their suitable pore sizes and high separation efficiency. The separation ranges of different pressure - driven membranes are shown in Figure 2.
(Figure 2 Range of separation for pressure-driven membrane processes.)
Nanofiber polymer membranes have great potential in oily wastewater treatment because of their high porosity, good mechanical properties, and excellent separation effect. The main preparation methods are the phase inversion method and the electrospinning method, each with its own pros and cons for different scenarios.
Phase Inversion Method
The phase inversion method is a traditional membrane - making technology. It forms a porous structure through solution phase separation. The polymer is dissolved in a solvent to make a casting solution, and then phase separation is induced by solvent evaporation, non - solvent addition, or temperature change to form a porous membrane. It can be divided into solvent evaporation - induced, non - solvent - induced, and thermally induced phase separation. This method is simple and low - cost but hard to precisely control pore - related properties, and the membrane has weak mechanical properties. Its preparation process is shown in Figure 3.
(Figure 4 The phase inversion process.)
Electrospinning Method
The electrospinning method uses electric field force to stretch polymer solutions into nanofibers. It can precisely control fiber characteristics and prepare nanofiber membranes with high porosity (>90%) and good properties, suitable for oily wastewater treatment. This process is often carried out by an electrospinning machine or electrospinning device. It can be divided into:
Needle - type Electrospinning: Including single - needle, multi - needle, coaxial, and melt electrospinning. It's suitable for small - scale lab work but has issues like needle clogging and low production efficiency.
Needleless Electrospinning: Fibers are ejected through rotating or stationary spinnerets. It's suitable for large - scale industrial use but has high equipment costs.
(Figure 6 A simplified form of electrospinning technique.)
The electrospinning method has the following advantages:
High Porosity: Can prepare membranes with over 90% porosity, improving flux and separation efficiency.
Precise Fiber Structure Control: Can control fiber diameter and microstructure by adjusting parameters.
Good Mechanical Properties: Nanofiber membranes can withstand high pressures and have a long service life.
To optimize nanofiber membrane performance in oily wastewater treatment, we can focus on material selection, preparation method improvement, surface property regulation, and anti - fouling performance enhancement.
Selecting Appropriate Materials
Hydrophilic materials like PAN, with polar nitrile groups, are preferred as they can reduce membrane blockage and improve separation efficiency. PVDF is also commonly used for its chemical stability and mechanical properties. Blending polymers or adding nanomaterials, such as ZIF - 8 to PAN, can enhance membrane performance.
Improving Preparation Methods
Electrospinning technology can be optimized. Compared with needle - type electrospinning, needleless electrospinning has higher efficiency and less clogging. Adjusting electrospinning parameters can produce better - performing nanofiber membranes.
Regulating Surface Properties
Enhancing membrane surface hydrophilicity and oleophobicity can make the membrane allow only water to pass through. Surface modification, like chemically transforming PAN's nitrile groups, can achieve this. Special - structure membranes, such as Janus electrospun nanofiber membranes, can improve performance.
Enhancing Anti - Fouling Performance
Membrane fouling is a key problem. Cross - flow filtration can reduce fouling. Regular membrane cleaning, like backwashing, can restore performance. Developing self - cleaning membrane materials is also an important direction.
In the future, the development of eco - friendly nanofibers may bring new breakthroughs in water - oil separation. Mixing polymers with new additives during electrospinning and using nanomaterials can improve membrane properties, enhancing durability and long - term operation performance.
Electrospinning Nanofibers Article Source:
https://doi.org/10.1002/cjce.25449
