Microfiltration is used for the separation of particles 0.02–10 μm in diameter, primarily during the primary recovery stages of DSP. Microfilters are available in materials such as ceramic and steel that can be aggressively cleaned and sterilized.
Ultrafiltration largely depends on effective fluid-management techniques. By using hydrodynamic considerations, polarized solutes can be sheared from the membrane surface, thereby increasing the back diffusion and reducing the decline in performance. UF is used for the separation of particles 0.02- 0.001 μm in diameter.
Nanofiltration is a membrane filtration-based method that uses nanometer sized through-pores that pass through the membrane. Nanofiltration membranes have pore sizes from 1-10 nanometers, smaller than that used in microfiltration and ultrafiltration, but just larger than that in reverse osmosis.
Reverse osmosis (RO) is completely the opposite of the process of osmosis. Osmosis occurs naturally without requiring external energy, whereas RO requires applying external energy/pressure using a high-pressure pump on the side of the highly concentrated solution. At osmotic pressure, the flow between two solutions will cease, whereas applying pressure or energy greater than osmotic pressure reverses the flow from a highly concentrated solution toward a less concentrated solution. The amount of pressure required depends on the salt concentration of the feed water. RO is used for the separation of particles 0.001- 0.0001 μm in diameter.
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