Nanofiltration
Encyclopedia
Nanofiltration is a relatively recent membrane filtration
process used most often with low total dissolved solids
water such as surface water
and fresh groundwater
, with the purpose of softening (polyvalent
cation removal) and removal of disinfection by-product precursors such as natural organic
matter and synthetic organic matter.
Nanofiltration is also becoming more widely used in food processing
applications such as dairy
, for simultaneous concentration and partial (monovalent
ion
) demineralisation.
technology which ranges somewhere between ultrafiltration
(UF) and reverse osmosis
(RO). The nominal pore size of the membrane is typically about 1 nanometre
. Nanofilter membranes are typically rated by molecular weight cut-off (MWCO) rather than nominal pore size. The MWCO is typically less than 1000 atomic mass units (daltons).
The transmembrane pressure (pressure drop across the membrane) required is lower (up to 3 MPa) than the one used for RO, reducing the operating cost significantly. However, NF membranes are still subject to scaling and fouling and often modifiers such as anti-scalants are required for use.
world, clean drinking water
is hard to come by, and nanotechnology provides one solution. While nanofiltration is used for the removal of contaminants from a water source, it is also commonly used for desalination
. In a study in South Africa
, tests were run using polymer
ic nanofiltration in conjunction with a reverse osmosis
process to treat brackish groundwater. These tests produced potable water, but as the researchers expected, the reverse osmosis removed a large majority of solutes. This left the water void of any essential nutrients (calcium
, magnesium
ions, etc.), placing the nutrient levels below that of the required World Health Organization
standards. This process was probably a little too much for the production of potable water, as researchers had to go back and add nutrients to bring solute levels to the standard levels for drinking water consumption.
Providing nanofiltration methods to developing countries, to increase their supply of clean water, is a very inexpensive method compared to conventional treatment systems. However, there remain issues as to how these developing countries will be able to incorporate this new technology into their economy without creating a dependency on foreign assistance.
Membrane technology
The membrane technology covers all process engineering measures for the transport of substances between two fractions with the help of permeable membranes...
process used most often with low total dissolved solids
Total dissolved solids
Total Dissolved Solids is a measure of the combined content of all inorganic and organic substances contained in a liquid in: molecular, ionized or micro-granular suspended form. Generally the operational definition is that the solids must be small enough to survive filtration through a sieve...
water such as surface water
Surface water
Surface water is water collecting on the ground or in a stream, river, lake, wetland, or ocean; it is related to water collecting as groundwater or atmospheric water....
and fresh groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
, with the purpose of softening (polyvalent
Polyvalent
In chemistry, polyvalence or multivalence refers to species that are not restricted to a distinct number of valence bonds....
cation removal) and removal of disinfection by-product precursors such as natural organic
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
matter and synthetic organic matter.
Nanofiltration is also becoming more widely used in food processing
Food processing
Food processing is the set of methods and techniques used to transform raw ingredients into food or to transform food into other forms for consumption by humans or animals either in the home or by the food processing industry...
applications such as dairy
Dairy
A dairy is a business enterprise established for the harvesting of animal milk—mostly from cows or goats, but also from buffalo, sheep, horses or camels —for human consumption. A dairy is typically located on a dedicated dairy farm or section of a multi-purpose farm that is concerned...
, for simultaneous concentration and partial (monovalent
Monovalent
Monovalent may refer to:*In chemistry, valence is a measure of the number of chemical bonds formed by the atoms of a given element. Monovalent is a synonym of univalent.*Monovalent ions contain one valence electron....
ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
) demineralisation.
Principle
Nanofiltration (NF) is a cross-flow filtrationCross-flow filtration
In chemical engineering, biochemical engineering and protein purification, crossflow filtration is a type of filtration...
technology which ranges somewhere between ultrafiltration
Ultrafiltration
Ultrafiltration is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane...
(UF) and reverse osmosis
Reverse osmosis
Reverse osmosis is a membrane technical filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and...
(RO). The nominal pore size of the membrane is typically about 1 nanometre
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
. Nanofilter membranes are typically rated by molecular weight cut-off (MWCO) rather than nominal pore size. The MWCO is typically less than 1000 atomic mass units (daltons).
The transmembrane pressure (pressure drop across the membrane) required is lower (up to 3 MPa) than the one used for RO, reducing the operating cost significantly. However, NF membranes are still subject to scaling and fouling and often modifiers such as anti-scalants are required for use.
Water purification applications
In much of the developingDeveloping country
A developing country, also known as a less-developed country, is a nation with a low level of material well-being. Since no single definition of the term developing country is recognized internationally, the levels of development may vary widely within so-called developing countries...
world, clean drinking water
Drinking water
Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...
is hard to come by, and nanotechnology provides one solution. While nanofiltration is used for the removal of contaminants from a water source, it is also commonly used for desalination
Desalination
Desalination, desalinization, or desalinisation refers to any of several processes that remove some amount of salt and other minerals from saline water...
. In a study in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, tests were run using polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
ic nanofiltration in conjunction with a reverse osmosis
Reverse osmosis
Reverse osmosis is a membrane technical filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and...
process to treat brackish groundwater. These tests produced potable water, but as the researchers expected, the reverse osmosis removed a large majority of solutes. This left the water void of any essential nutrients (calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
, magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
ions, etc.), placing the nutrient levels below that of the required World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
standards. This process was probably a little too much for the production of potable water, as researchers had to go back and add nutrients to bring solute levels to the standard levels for drinking water consumption.
Providing nanofiltration methods to developing countries, to increase their supply of clean water, is a very inexpensive method compared to conventional treatment systems. However, there remain issues as to how these developing countries will be able to incorporate this new technology into their economy without creating a dependency on foreign assistance.
See also
- List of nanotechnology applications
- NanomaterialsNanomaterialsNanomaterials is a field that takes a materials science-based approach to nanotechnology. It studies materials with morphological features on the nanoscale, and especially those that have special properties stemming from their nanoscale dimensions...
- NanotechnologyNanotechnologyNanotechnology is the study of manipulating matter on an atomic and molecular scale. Generally, nanotechnology deals with developing materials, devices, or other structures possessing at least one dimension sized from 1 to 100 nanometres...
- UltrafiltrationUltrafiltrationUltrafiltration is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane...
External links
- Project ETAP-ERN, that uses renewable energies for desalinization.
- Nano based methods to improve water quality - Hawk's Perch Technical Writing, LLC