Author: Site Editor Publish Time: 2022-08-05 Origin: Site
Membranes can be prepared from a wide range of materials and can be liquid, solid or even gas phase. The majority of separation membranes used are solid phase membranes. Depending on the pore size, they can be divided into microfiltration, ultrafiltration, nanofiltration and reverse osmosis membranes; depending on the material, they can be divided into inorganic and organic membranes, with the inorganic membranes being mainly microfiltration grade membranes. The membranes can be homogeneous or non-homogeneous and can be charged or electrically neutral. Membranes widely used in wastewater treatment are mainly solid phase asymmetric membranes prepared from organic polymeric materials.
1. Polymeric organic membrane materials: polyolefins, polyethylene, polyacrylonitrile, polysulfone, aromatic polyamides, fluoropolymers, etc.
Organic membranes are relatively low cost, inexpensive, the membrane manufacturing process is more mature, membrane pore size and form is also more diverse, widely used, but the operation process is easy to pollution, low strength, short service life.
2. Inorganic membrane: is a solid membrane, is made of inorganic materials, such as metal, metal oxides, ceramics, porous glass, zeolite, inorganic polymer materials and other semi-permeable membrane.
The inorganic membranes used in MBR are mostly ceramic membranes. The advantages are: it can be used in pH=0~14, pressure P<10MPa, temperature<350 ℃, its high flux, relatively low energy consumption, and is very competitive in the treatment of high concentration industrial wastewater; the disadvantages are: expensive, not alkali resistant, small elasticity, and some difficulties in the processing and preparation of the membrane.
The membranes used in the MBR process are generally microfiltration membranes (MF) and ultrafiltration membranes (UF). 0.1 to 0.4 μm membrane pore size is used for microfiltration membranes, which is sufficient for solid-liquid separation type membrane reactors.
Commonly used polymer materials for MF membranes are: polycarbonate, cellulose ester, polyvinylidene fluoride, polysulfone, polytetrafluoroethylene, polyvinyl chloride, polyetherimide, polypropylene, polyetheretherketone, polyamide, etc.
Commonly used polymer materials for ultrafiltration include: polysulfone, polyethersulfone (PES), polyamide, polyacrylonitrile (PAN), polyvinylidene fluoride, cellulose ester, polyetheretherketone, polyimide, polyetheramide, etc.
In order to facilitate industrial production and installation, to improve the efficiency of the membrane and to achieve the maximum membrane area per unit volume, the membrane is usually assembled in some form in a basic unit of equipment, under a certain driving force, to complete the separation of the components in the mixture, this type of device is called membrane module.
There are five common forms of membrane modules used in industry.
Plate and Frame Module, Spiral Wound Module, Tubular Module, Hollow Fiber Module and Capillary Module. The first two use flat membranes and the last three use tubular membranes. The latter three use tubular membranes with diameters >10mm; capillary 0.5 to 10.0mm; and hollow fibre <0.5mm.
General requirements for MBR membrane module design.
(1) Adequate mechanical support for the membrane, with smooth flow paths and no flow dead ends or hydrostatic zones.
(2) Low energy consumption, minimising concentration polarisation, improving separation efficiency and reducing membrane contamination.
(3) The highest possible filling density, easy installation, cleaning and replacement.
(4) Adequate mechanical strength, chemical and thermal stability.
The selection of membrane modules should take into account their cost, filling density, application, system flow, membrane contamination and cleaning, service life, etc.
