Five common types of membrane modules in industry and their applications

Five commonly used membrane modules in industry:

Plate and frame, spiral wound, tubular, hollow fiber, and capillary. The first two use flat sheet membranes, while the latter three use tubular membranes. Tubular membranes have a diameter >10mm; capillary membranes 0.5-10.0mm; hollow fiber membranes <0.5mm.

Commonly used membrane module types in MBR processes include: plate and frame, tubular, and hollow fiber.

（ 1) Plate and frame

One of the earliest membrane module types used in MBR processes, similar in appearance to a conventional plate and frame filter press.

Advantages: Simple manufacturing and assembly, easy operation, easy maintenance, cleaning, and replacement.

Disadvantages: Complex sealing, high pressure loss, low packing density.

（ 2) Tubular

Consists of a membrane and its support, with two operating modes: internal pressure and external pressure. Internal pressure is more commonly used in practice, where feed water flows from inside the tube and permeate flows from outside. The membrane diameter is between 6-24mm.

Advantages: Turbulent flow of material can be controlled, less prone to clogging, easy to clean, low pressure loss.

Disadvantages: Low packing density.

（ 3) Hollow fiber

Assembly form is shown in the figure below: The outer diameter is generally 40-250μm, and the inner diameter is 25-42μm. In MBR, the module is often placed directly into the reactor without a pressure-resistant container, forming a submerged membrane-bioreactor. It is generally an external pressure membrane module.

（ 4) Cylindrical hollow fiber membrane

Advantages: High pressure resistance, not easily deformed, no support material needed; high packing density; relatively low cost; long lifespan; stable physical and chemical properties, low water permeability nylon hollow fiber membranes can be used.

Disadvantages: Sensitive to clogging, fouling and concentration polarization significantly affect membrane separation performance.

（ 5) Spiral wound

Spiral wound, also known as rolled type, the main components are porous support material, membranes on both sides, three sides sealed, the open side is sealed with a porous central product water collection tube. A mesh-type spacer material is placed on the raw water side outside the membrane bag, and the membrane bag -The mesh is stacked in turn, tightly rolled around the central water collection tube to form a membrane roll, which is placed in a cylindrical pressure vessel to form a spiral wound membrane module.

Advantages: High membrane packing density; simple membrane support structure; low concentration polarization; easy adjustment of membrane surface flow.

Disadvantages: Easy leakage at the center tube; membrane is prone to rupture and leakage at the bonding point between the membrane and the support material; difficult membrane installation and replacement.

Application areas

1. Industrial wastewater treatment

Since the 1990s, the treatment objects of MBR have been continuously expanded. In addition to water reuse and fecal sewage treatment, the application of MBR in industrial wastewater treatment has also received widespread attention. For example, the treatment of food industrial wastewater, aquatic product processing wastewater, aquaculture wastewater, cosmetic production wastewater, dye wastewater, and petrochemical wastewater has achieved good treatment effects.

2. Micro-polluted drinking water purification

With the widespread use of nitrogen fertilizers and pesticides in agriculture, drinking water has been polluted to varying degrees. In the mid-1990s, LyonnaisedesEaux developed an MBR process with simultaneous biological denitrification, pesticide adsorption, and turbidity removal functions. The nitrogen concentration in the effluent is below 0.1mgNO2/L, and the pesticide concentration is below 0.02μg/L.

3. Fecal sewage treatment

Fecal sewage has a very high organic matter content. Traditional denitrification methods require a very high sludge concentration, and the solid-liquid separation is unstable, affecting the tertiary treatment effect. The emergence of MBR has solved this problem well and makes it possible to treat fecal sewage directly without dilution.

4. Landfill/compost leachate treatment

Landfill/compost leachate contains high concentrations of pollutants, and its water quality and quantity vary with climatic conditions and operating conditions. MBR technology was used by many wastewater treatment plants for the treatment of this type of wastewater before 1994. By combining MBR and RO technology, not only SS, organic matter, and nitrogen can be removed, but also salts and heavy metals can be effectively removed. This type of MBR uses a naturally occurring mixed bacteria to decompose hydrocarbons and chlorinated compounds in the leachate, with a pollutant concentration 50-100 times that of conventional wastewater treatment plants. The reason for this treatment effect is that MBR can retain highly efficient bacteria and increase the bacterial concentration to 50000g/. In field pilot tests, the influent COD was several hundred to 40000mg/L, and the pollutant removal rate was over 90%.