Membrane

1. Membrane Processes Classifications:
– Microfiltration (MF): Removes particles higher than 0.08-2µm, operates within 7-100 kPa, used for residual suspended solids and bacteria removal.
– Ultrafiltration (UF): Removes particles higher than 0.005-2µm, operates within 70-700kPa, capable of removing dissolved compounds with high molecular weight.
– Nanofiltration (NF): Rejects particles smaller than 0.002µm, primarily used for removing selected dissolved constituents from wastewater.
– Reverse Osmosis (RO): Commonly used for desalination, requires high pressures, utilizes thin-film composite (TFC) membranes.
– Nanostructured Membranes: Rely on nanostructure channels for separations, include carbon nanotube, graphene, and MOF membranes, used for size and adsorption selective separations.

2. Membrane Configurations:
– Tubular Modules: Membranes inside support tubes, suitable for high solids and viscosity streams.
– Hollow Fiber Membrane: Consists of hollow fibers in a pressure vessel, effective for various applications.
– Spiral Wound Modules: Flexible permeate spacer between membranes, effective for different separation processes.
– Plate and Frame Modules: Consist of flat membrane sheets and support plates for effective filtration.
– Ceramic and Polymeric Flat Sheet Modules: Submerged vacuum-driven filtration systems with cleaning methods like aeration and backwash.

3. Membrane Process Operation:
– Membrane Permeability (k) influences permeate flux.
– Trans Membrane Pressure (TMP) is the operational driving force.
– Fouling and cleaning affect operation.
– Pressure of permeate stream (kPa) plays a role.
– Rejection rate (r) indicates particles removed from feedwater.

4. Fouling and Control:
– Fouling mechanisms include pore narrowing, blocking, scaling, and biofouling.
– Various cleaning agents are used to combat fouling.
– Control methods include physical and chemical cleaning, optimizing operation conditions, and membrane alteration.
– Irreversible fouling can reduce rejection efficiencies.
– Fouling can be caused by physicochemical and biological processes.

5. Recycling and Waste Prevention:
– Recycling methods include physical and chemical processes, energy recovery through incineration.
– Efforts are made to prevent waste through recycling and reapplication.
– Membranes follow the waste management hierarchy for responsible disposal.
– Upgrading membrane design is a sustainable approach to waste prevention.
– Recycling and energetic recovery are environmentally friendly alternatives to landfill disposal.

Membrane (Wikipedia)

This article is about selective barrier membranes. For other uses, see Membrane (disambiguation).

A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. Biological membranes include cell membranes (outer coverings of cells or organelles that allow passage of certain constituents); nuclear membranes, which cover a cell nucleus; and tissue membranes, such as mucosae and serosae. Synthetic membranes are made by humans for use in laboratories and industry (such as chemical plants).

This concept of a membrane has been known since the eighteenth century but was used little outside of the laboratory until the end of World War II. Drinking water supplies in Europe had been compromised by the war and membrane filters were used to test for water safety. However, due to the lack of reliability, slow operation, reduced selectivity and elevated costs, membranes were not widely exploited. The first use of membranes on a large scale was with microfiltration and ultrafiltration technologies. Since the 1980s, these separation processes, along with electrodialysis, are employed in large plants and, today, several experienced companies serve the market.

The degree of selectivity of a membrane depends on the membrane pore size. Depending on the pore size, they can be classified as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes. Membranes can also be of various thickness, with homogeneous or heterogeneous structure. Membranes can be neutral or charged, and particle transport can be active or passive. The latter can be facilitated by pressure, concentration, chemical or electrical gradients of the membrane process.