"Microfiltration (MF) is a pressure-driven separation process, which is widely used in concentrating, purifying or separating macromolecules, colloids and suspended particles from solution. MF membranes typically have nominal pore sizes on the order of 0.1–1.0 μm. MF processing is widely used in the food industry for applications such as wine, juice and beer clarification, for wastewater treatment, and plasma separation from blood for therapeutic and commercial uses. In biotechnology industries, MF concerns applications such as cell recycle and harvesting, separation of recombinant proteins from cell debris, and purification of process streams.
MF is usually operated at relatively low TMPs (4 bar or 0.4 MPa) in a cross-flow configuration. The feed stream flows tangentially to the membrane surface to prevent cake formation and hence fouling of the membrane. The operation of cross-flow MF is often limited by membrane fouling caused by suspended solids in the feed stream. Permeate flux decreases with time as the retained particles accumulate on and within the membrane. Accumulation of cells, cell debris or other rejected particles on the membrane surface (external fouling or cake formation) is usually reversible, while deposition and adsorption of small particles or macromolecules within the internal pore structure of the membrane (internal fouling) is often irreversible.
Membranes with a pore size of 0.1 – 10 µm perform micro filtration. Microfiltration membranes remove all bacteria. Only part of the viral contamination is caught up in the process, even though viruses are smaller than the pores of a micro filtration membrane. This is because viruses can attach themselves to bacterial biofilm. Micro filtration can be implemented in many different water treatment processes when particles with a diameter greater than 0.1 mm need to be removed from a liquid.
Examples of micro filtration applications are:
Cold sterilisation of beverages and pharmaceuticals
Clearing of fruit juice, wines and beer
Separation of bacteria from water (biological wastewater treatment)
Separation of oil/ water emulsions
Pre-treatment of water for nano filtration or Reverse Osmosis
Solid-liquid separation for pharmacies or food industries
UF, a kind of membrane separation technique, is able to remove the particle materials in solutions. This separation process is usually used in industry and research areas for purifying and concentrating macromolecular (103–106 Da) solutions, especially protein solutions. Like microfiltration, ultrafiltration is based on size exclusion or particle capture. Ultrafiltration membranes are defined by the molecular weight cut-off (MWCO) of the membrane used, and cross-flow or dead-end mode is applied in different areas. The ultrafiltration membranes are only accessible for small molecules, such as leachate molecules, inorganic salts, and micromolecular organics, rather than some macromolecules like SS, colloid, protein, and bacteria. UF is always used as a way to pretreat leachate with lower organic concentration before nanofiltration (NF).
UF is used to treat wastewater to meet the municipal effluent discharge standards and to recover valuable component for recycle as in the case of oily wastewater. The sources of oily wastewater include metal works, textile industries, automotive, aeronautical and animal/vegetable fats industries and industrial laundromats. Hydrophilic UF membranes (e.g., polyacrylonitrile and PES) are used for recovering oil from oily waste waters instead of hydrophobic membranes (e.g., PVDF) that get fouled with oil resulting in loss of flux. The oil droplets are completely retained by the UF membrane, although the membrane is permeable to free (soluble) oil. UF permeate of highly stable emulsified feed stream can be discharged to a municipal wastewater system. The concentrated recovered oil is less than 5% of the original waste volume. Similarly, tubular UF membranes