Pressure retarded osmosis (PRO) is a technique to separate a solvent (for example,
fresh water
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
) from a solution that is more concentrated (e.g.
sea water
Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approx ...
) and also pressurized. A
semipermeable membrane
Semipermeable membrane is a type of biological or synthetic, polymeric membrane that will allow certain molecules or ions to pass through it by osmosis. The rate of passage depends on the pressure, concentration, and temperature of the molecul ...
allows the solvent to pass to the concentrated solution side by
osmosis
Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region of ...
. The technique can be used to generate power from the
salinity gradient energy resulting from the difference in the salt concentration between sea and river water.
In PRO, the
water potential
Water potential is the potential energy of water per unit volume relative to pure water in reference conditions. Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure and mat ...
between
fresh water
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
and sea water corresponds to a pressure of 26
bar
Bar or BAR may refer to:
Food and drink
* Bar (establishment), selling alcoholic beverages
* Candy bar
* Chocolate bar
Science and technology
* Bar (river morphology), a deposit of sediment
* Bar (tropical cyclone), a layer of cloud
* Bar (u ...
s. This pressure is equivalent to a column of water (
hydraulic head
Hydraulic head or piezometric head is a specific measurement of liquid pressure above a vertical datum., 410 pages. See pp. 43–44., 650 pages. See p. 22.
It is usually measured as a liquid surface elevation, expressed in units of length, ...
) 270 meters high.
However, the optimal working pressure is only half of this, 11 to 15 bar.
History
This method of generating power was invented by
Prof. Sidney Loeb in 1973 at the
Ben-Gurion University of the Negev
Ben-Gurion University of the Negev (BGU) ( he, אוניברסיטת בן-גוריון בנגב, ''Universitat Ben-Guriyon baNegev'') is a public research university in Beersheba, Israel. Ben-Gurion University of the Negev has five campuses: the ...
,
Beersheba
Beersheba or Beer Sheva, officially Be'er-Sheva ( he, בְּאֵר שֶׁבַע, ''Bəʾēr Ševaʿ'', ; ar, بئر السبع, Biʾr as-Sabʿ, Well of the Oath or Well of the Seven), is the largest city in the Negev desert of southern Israel. ...
, Israel.
In 2014 researchers verified that 95% of a PRO system's theoretical power output can be produced with a membrane that is half (or less) the size needed for achieving 100%. Output is proportional to the salinity. Desalination yields very salty brine, while treated municipal wastewater has relatively little salt. Combining those streams could produce energy to power both facilities. However, powering an existing wastewater treatment plant by mixing treated wastewater with seawater could require a membrane area of 2.5 million square meters.
To deal with these membrane requirements, scientists are working on rolled membranes that will take up much less space.
Testing
The world's first osmotic plant with capacity of 10 kW was opened by
Statkraft, a state-owned
hydropower
Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water to Electricity generation, produce electricity or to power machines. This is achieved by energy transformation, converting the Pot ...
company, on 24 November 2009 in
Tofte, Norway.
[
] In January 2014 Statkraft terminated their osmosis pilot project due to economic feasibility concerns.
It is estimated that each year 1600 TWh could be generated worldwide, and 12 TWh in
Norway
Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
, sufficient to meet 10% of Norway's total demand for electricity.
In Denmark, SaltPower is building the worlds first commercial osmitic power plant using high salinity brine.
See also
*
Electrodialysis reversal
Electrodialysis reversal (EDR) is an electrodialysis reversal water desalination membrane process that has been commercially used since the early 1960s. An electric current migrates dissolved salt ions, including fluorides, nitrates and sulfate ...
(EDR)
*
Forward osmosis
Forward osmosis (FO) is an osmotic process that, like reverse osmosis (RO), uses a semi-permeable membrane to effect separation of water from dissolved solutes. The driving force for this separation is an osmotic pressure gradient, such that a "d ...
*
Green energy
Energy is sustainable if it "meets the needs of the present without compromising the ability of future generations to meet their own needs". Most definitions of sustainable energy include considerations of environmental aspects such as greenh ...
*
Osmotic power
Osmotic power, salinity gradient power or blue energy is the energy available from the difference in the salt concentration between seawater and river water. Two practical methods for this are reverse electrodialysis (RED) and
pressure retarde ...
*
Osmotic pressure
Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane.
It is also defined as the measure of the tendency of a solution to take in a pure ...
*
Renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
*
Reverse electrodialysis
Reverse or reversing may refer to:
Arts and media
* ''Reverse'' (Eldritch album), 2001
* ''Reverse'' (2009 film), a Polish comedy-drama film
* ''Reverse'' (2019 film), an Iranian crime-drama film
* ''Reverse'' (Morandi album), 2005
* ''Reverse'' ...
(RED)
*
Reverse osmosis
Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane to separate ions, unwanted molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pre ...
*
Semipermeable membrane
Semipermeable membrane is a type of biological or synthetic, polymeric membrane that will allow certain molecules or ions to pass through it by osmosis. The rate of passage depends on the pressure, concentration, and temperature of the molecul ...
*
Van 't Hoff factor
The van 't Hoff factor (named after Dutch chemist Jacobus Henricus van 't Hoff) is a measure of the effect of a solute on colligative properties such as osmotic pressure, relative lowering in vapor pressure, boiling-point elevation and freez ...
References
Further reading
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{{Fuel cells
Fuel cells
Sustainable technologies
Sustainable energy
Energy conversion
Israeli inventions
Membrane technology