Application of membrane technology in wastewater treatment and reuse2
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u003cbru003e Research shows that: membrane technology is the most suitable technology for wastewater recycling and reuse, and membrane technology will be the preferred technology for advanced wastewater treatment.
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u003cbru003e Its advantage is that it can almost completely remove SS, general bacteria, viruses, E. coli, etc., and can be decolorized, reducing the generation of trichloromethane (THM) precursors, and the effluent quality is excellent, due to the small space occupied by the membrane device , It is especially suitable for use under the conditions of renovation and upgrading of old factories or limited space for construction.
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u003cbru003e In the treatment and reuse of urban sewage, the membrane process is often used in the advanced treatment after the secondary treatment. Microfiltration (MF) and ultrafiltration (UF) are used to replace the precipitation, filtration and adsorption in the conventional advanced treatment. , Sterilization and other treatments, with nanofiltration membrane (NF) and reverse osmosis (RO) for water softening and desalination. In the reuse of reclaimed water, the membrane bioreactor composed of MF, UF and activated sludge is currently the most used.
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u003cbru003e The composition of industrial wastewater is different, the purpose of reuse is also different, and the application of membrane technology is also diverse. But no matter what kind of wastewater treatment, membrane technology must be reasonably matched with other technologies to play its role. Because the composition of sewage is extremely complex, different reuse purposes, required water quality standards and treatment processes are also different, any single water treatment technology is difficult to meet the water quality requirements for reuse.
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u003cbru003e It is generally believed that MF can remove microorganisms, bacteria, eggs, and viruses in sewage, and UF can remove macromolecules in sewage, such as proteins, humic acid, and some precursors and dyes that generate THM. The dissolved salts and most of the ions in wastewater treated by MF and UF are still difficult to remove, and these components must be removed by RO membrane. The secondary effluent can reach drinking water standard after RO treatment, its desalination rate can reach more than 90%, water recovery rate is more than 75%, and COD and BOD removal rate is more than 85%. However, RO needs to operate under higher pressure, and the cost is higher. In the past, MF and ultrafiltration membranes were used more in sewage treatment. The NF membrane developed in recent years can intercept low-molecular and divalent and high-valent ions with a relative molecular mass greater than 200, and has a very low interception rate for monovalent ions. Therefore, it can be operated under lower pressure, and has large water permeability and low operating cost. Sewage treatment can remove all viruses, bacteria, pesticides, surfactants and chloroform precursors, which will react with chlorine in the water (such as chlorination during sterilization) to form carcinogens such as THM. Because of these precursors Most of them are low-molecular organics, which are difficult to remove with conventional water treatment technology and MF and UF. NF can remove more than 90% of the dissolved carbon and THM precursors in the secondary effluent and 2/3 of the salinity, 4 The hardness is /5, and the effluent meets the pollutant regulations of the 1986 Safe Drinking Water Law of the United States.
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u003cbru003e Charged membrane electrodialysis is a membrane process under the action of an electric field. It is mostly used for the treatment and reuse of industrial wastewater, such as the separation and reuse of charged ions such as metal ions in electroplating wastewater.
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u003cbru003e Because the liquid membrane technology can utilize chemical reactions to promote the mass transfer process, it has fast mass transfer speed and high separation efficiency. It has been applied research on a pilot scale in the treatment of phenol-containing wastewater.
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u003cbru003e Membrane bioreactor (MBR), which combines membrane separation (mainly MF and UF, but also NF) and biological reaction, is the most used in sewage treatment is the membrane separation activated sludge method, that is, membrane separation It replaces the secondary settling tank that uses gravity to settle and separate the conventional activated sludge, and has the advantages of compact equipment and good effluent quality. u003cbr /u003e
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