Water contamination by heavy metals, cyanides, and dyes is expanding globally and must be handled because it will lead to water scarcity and water quality issues. Various approaches for cleaning and renewing water for human consumption and agricultural reasons have been used, but each has limits. Among these solutions, membrane technology appears to be the most promising for resolving the challenges. Nanotechnology has the potential to significantly improve the treatment efficiency of wastewater treatment systems. Furthermore, nanotechnology augments the water supply by allowing the safe use of current water sources.
Clean water is essential for all living organisms to survive, yet due to fast population growth and industrialization, there is a greater demand for clean, safe, and drinking water . Only around 3% of the world's water is available for drinking and agricultural use, with the remaining 97% stored in oceans as saline water that is unfit for human consumption or agricultural use. Several approaches for wastewater treatment have been developed, including reverse osmosis, ion exchange gravity, and adsorption. Because of its low cost, availability of various adsorbents, and ease of operation, adsorption has been widely employed to remove water pollutants.
Material separation via the membrane is affected by pore and molecule size. As a result, numerous membrane processes with distinct separation methods have been created. Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), forward osmosis (FO), and reverse osmosis (RO) are examples.
Membrane technologies such as MF, NF, UF, and RO are currently employed for water reuse, brackish water treatment, and seawater treatment. Polymer-based membranes are the most often utilized membrane materials, but because hydrophobic polymers such as polysulfone and polyethersulfone are used, polymeric membranes are prone to fouling. This results in membrane pore obstruction and decreased membrane performance, as well as increased operating costs due to the additional cleaning process. Membrane fouling can be caused by a variety of causes, including inorganic component deposition on the surface membrane/solute absorption pore blockage, microorganisms, and feed chemistry. As a result, membrane fouling might be reversible or irreversible. Reversible fouling is caused by particle attachment to the membrane surface, but irreversible fouling occurs when particles tightly adhere to the membrane surface and cannot be removed.
Microfiltration is a pressure-driven technique in which separated components, such as nanoparticles, are 0.1-0.2 m in size. It is the initial pre-treatment step in the NF and RO membrane processes.
MF eliminates little to no organic matter; however, when pre-treatment is used, organic material removal can be boosted. To lessen fouling potential, MF can be applied as a pre-treatment to RO or NF. One of the main drawbacks of MF is that it cannot remove impurities (dissolved solids) smaller than 1 mm in size. Furthermore, MF is not an impenetrable barrier against viruses. MF, however, appears to suppress these microbes in water when applied in conjunction with disinfection.
The ultrafiltration membrane process can separate compounds between 0.005 ≈ 10 μm which is between MF and RO. UF membranes are highly prominent water filters with low energy consumption in removal of pathogenic microorganisms, macromolecules, and suspended maters among others. However, UF has some limitations including its inability to remove any dissolved inorganic substances from water and regular cleaning to maintain high pressure water flow.
A pressure infiltration membrane with an aperture between reverse osmosis and ultrafiltration membrane is known as a nanofiltration membrane. It offers a strong retention performance for organic compounds and a low retention performance for inorganic materials with molecular weights ranging from 200 to 1000. Water softening, organic bioactive compounds and dechlorination, purification, concentration, and wastewater decolorization are all common applications for nanofiltration. Nanofiltration technology research began towards the end of the 1980s, but it is still in the laboratory research and development stage, with no products on the market.
3.4. Reverse osmosis
RO is a pressure-driven technology for removing dissolved solids and tiny particles; RO is permeable only to water molecules.
The pressure delivered to the RO must be sufficient for water to overcome osmotic pressure. RO membranes have a significantly tighter pore structure than UF membranes, they convert hard water to soft water, they are essentially capable of eliminating all particles, germs, and organics, and they require less maintenance. Some downsides include the utilization of high pressure, the fact that RO membranes are more expensive than other membrane processes, and that they are prone to fouling. A significant level of pre-treatment is required in some circumstances. RO has incredibly narrow pores and can remove particles as small as 0.1 nm.
4.Application of membrane technology in wastewater
The primary application of membrane separation technology in water treatment is the manufacture of drinking water, the recycling of materials in industrial water, the reuse of water resources, and the treatment of industrial wastewater, among other things. The key research directions also include the large scale of the membrane and related processes, the monitoring and control of membrane fouling, and the optimization of operation conditions.
Below table represents some common membrane separation processes
The application of membrane technology in environmental protection will become a development priority both at home and overseas. As a result, we propose greater standards for membrane materials, particularly membrane materials with high strength, long life, anti-pollution, and high flux that are suitable for the protection industry environment.
fast, and the integration with other engineering sciences is becoming increasingly close, such as the integration with sensors for membrane sensors, etc. Membrane separation technology is increasingly being employed not just for traditional water treatment, but also for sterilization and a variety of other applications. It can be expected that as regulations and standards improve, more mature membrane technology continues to reduce costs, and water prices rise, there will be further improvement for membrane water treatment technology, and membrane materials adapting to the protection industry environment with high strength, long life, anti-pollution, and high flux will become more popular.
Membrane separation has been widely employed in a variety of fields. It is one of the future water treatment development directions. When utilized in wastewater treatment, it not only has a good treatment impact, but it can also be recycled and used to provide significant economic, social, and environmental advantages.
The biggest issue now facing membrane separation technology is membrane fouling, as well as the high cost of membrane materials and the relatively short operational life span, which has hindered its large-scale adoption to some extent. As membrane separation technology advances, a plethora of new membrane materials emerge, the issues will be resolved, and membrane separation technology will play an increasingly important role in the field of water treatment.