SMF submerged membrane filtration technology is a new type of membrane filtration separation technology. It is a new type of membrane filtration process derived from the combination of low-pressure hollow fiber membrane technology and continuous membrane filtration technology. It uses the hollow fiber ultrafiltration membrane module to place the membrane directly in the membrane pool filled with water to be treated. Through the negative pressure suction of the self-priming pump, the water passes through the membrane surface and is extracted from the inner side of the hollow fiber membrane, while the pollutants are retained on the membrane surface. Through regular air washing, backwashing, sewage discharge, on-line dosing cleaning and off-line chemical enhanced cleaning, the combined process can eliminate membrane pollution and effectively restore the membrane flux to ensure the normal operation of the system. Submerged membrane filtration technology can replace the filtration process in the traditional water treatment process, and is widely used in wastewater treatment, water purification, reclaimed water reuse, seawater desalination and other fields. Its characteristics mainly include the following aspects:
① High solid-liquid separation efficiency. Due to the high efficiency of the membrane, the particles, colloids, macromolecular organics and bacteria in the sewage are intercepted at the inlet side of the membrane;
② The membrane pressure difference is evenly distributed along the length of the hollow fiber membrane, and there is no pressure drop loss on the water inlet side of the membrane;
③ Simple pretreatment requirements and strong anti pollution ability;
④ Compact equipment and small floor space;
⑤ It is suitable for large-scale water plant applications, and the output of a single system can reach more than 40000 m3/d;
⑥ Low energy consumption and operation cost.
In the 1980s, foreign countries have begun to study and apply submerged ultrafiltration in various fields of water treatment industry. In the early 1990s, a large water plant in Singapore chose the submerged ultrafiltration membrane system to upgrade the V-shaped filter in phase I. on the premise of maintaining the treatment scale, the quality of produced water was improved, and an engineering basis was provided for the phase II project to improve the treatment volume and quality. Subsequently, the submerged membrane filtration system has also been applied in the new construction and upgrading of the water supply plant.
The common polymer materials for submerged membrane components are polyvinylidene fluoride (PVDF), polyethylene (PE) and polypropylene (PP). PVDF has a wide range of applications at home and abroad because of its excellent physical and chemical properties (strength and corrosion resistance). There are also porous ceramic films prepared from inorganic materials such as Al2O3, ZrO2, TiO2 and SiO2. Comparatively speaking, the ceramic membrane has good chemical stability, acid, alkali and organic solvent resistance, and high mechanical strength, but it is expensive.
Submerged ultrafiltration has low energy consumption and is suitable for the transformation of sand filter station. The larger the project scale, the more obvious the advantages. For large projects, if one ton of water is treated, 0.1 kilowatt hour of electricity can be saved, which can save considerable operating costs. Moreover, the submerged process has small floor area, relatively loose requirements for inlet water quality, stable and excellent outlet water quality, and can make full use of the remaining site of the sewage plant. It is one of the options for the transformation of large-scale waterworks and municipal sewage plants in the future.
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