Water Filtration via Membrane Technology

Purification or Filtration by Membrane technology is primarily used in commercial and industrial applications

membrane vacuum pump

There are 4 membrane processes that operate by applying water pressure to a membrane; ie. Reverse Osmosis :

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Microfiltration

(MF) is a process where water is forced under pressure through a porous membrane. Membranes with a pore size of 0.45 Microns are normally used.This size is relatively large compared with the other membrane filtration processes. This process has not been generally applicable to drinking water treatment because it either does not remove substances that require removal from potable water, or the problem substances can be removed more economically using other processes.

The primary use of MF is by industries to remove very fine particles from process water, as in electronic manufacturing. Additionly MF is often used as a pretreatment for other membrane processes. In particular, RO membranes are susceptible to clogging or filter binding unless the water being processed is already quite clean.

Ultrafiltration

(UF) is a process that uses a membrane with a pore size generally below .1 microns. The smaller pore size is designed to remove colloids and substances that have larger molecules, which are called high-molecular-weight materials. UF membranes can be designed to pass material that weigh less than or equal to a certain molecular weight. This weight is called the molecular weight cutoff (MWC) of the membrane. Although UF does not generally work well for removal of salt or dissolved solids, it can be used effectively for removal or most organic chemicals.Again often used in combination with Reverse Osmosis as a very effective pretreatment.

Nanofiltration

(NF) is a process using membranes that will reject even smaller molecules than UF. The process has been used primarily for water softening and reduction of total dissolved solids (TDS). NF operates with less pressure that reverse osmosis and is still able to remove a significant proportion of inorganic and organic molecules.

Reverse Osmosis

(RO) is a membrane process that has the highest rejection capability of all the membrane processes. These RO membranes have very low MWC pore size that can reject ions at very high rates, including chloride and sodium. Water from this process is very pure due to the high reject rates. R.O is used mainly in the water industry for desalinization of seawater because the costs are equitable with other processes for this service

The RO also works effectively on most organic chemicals, and radionuclides and microorganisms. Industrial water uses such as semiconductor manufacturing is also an important RO process. Unlike domestic R.O units industrial strength membranes are able to dump less than 30% of the flush water to waste. This reject water is very concentrated, difficult to eradicate and in the case of desalination it is often pumped deep offshore into drill holes.

Domestic R.O units are particularly inexpensive and do a fantastic job of purifying drinking water for the home. They do, however, require relatively clean pretreated water in order to protect the membranes.

Water Filtration via Membrane Technology

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