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FAQ.(April 2024)
Brine (or briny water) is
water with a high-concentration
solution of
salt (typically
sodium chloride or
calcium chloride). In diverse contexts, brine may refer to the salt solutions ranging from about 3.5% (a typical concentration of
seawater, on the lower end of that of solutions used for
brining foods) up to about 26% (a typical
saturated solution, depending on temperature). Brine forms naturally due to
evaporation of ground saline water but it is also generated in the mining of sodium chloride.[1] Brine is used for food processing and cooking (
pickling and
brining), for
de-icing of roads and other structures, and in a number of technological processes. It is also a by-product of many industrial processes, such as
desalination, so it requires
wastewater treatment for proper disposal or further utilization (
fresh water recovery).[2]
Brines are produced in multiple ways in nature. Modification of seawater via evaporation results in the concentration of salts in the residual fluid, a characteristic geologic deposit called an
evaporite is formed as different dissolved ions reach the saturation states of minerals, typically
gypsum and
halite. Dissolution of such salt deposits into water can produce brines as well. As seawater freezes, dissolved ions tend to remain in solution resulting in a fluid termed a cryogenic brine. At the time of formation, these cryogenic brines are by definition cooler than the freezing temperature of seawater and can produce a feature called a
brinicle where cool brines descend, freezing the surrounding seawater.
The brine cropping out at the surface as saltwater springs are known as "licks" or "salines".[3] The contents of dissolved solids in
groundwater vary highly from one location to another on Earth, both in terms of specific constituents (e.g.
halite,
anhydrite,
carbonates,
gypsum,
fluoride-salts,
organic halides, and
sulfate-salts) and regarding the concentration level. Using one of several classification of groundwater based on
total dissolved solids (TDS), brine is water containing more than 100,000 mg/L TDS.[4] Brine is commonly produced during well completion operations, particularly after the
hydraulic fracturing of a well.
Elemental chlorine can be produced by
electrolysis of brine (
NaCl solution). This process also produces
sodium hydroxide (NaOH) and
Hydrogen gas (H2). The reaction equations are as follows:
Brine is used as a secondary
fluid in large refrigeration installations for the transport of
thermal energy. Most commonly used brines are based on inexpensive
calcium chloride and
sodium chloride.[5] It is used because the addition of salt to water lowers the freezing temperature of the solution and the heat transport efficiency can be greatly enhanced for the comparatively low cost of the material. The lowest freezing point obtainable for NaCl brine is −21.1 °C (−6.0 °F) at the concentration of 23.3% NaCl by weight.[5] This is called the
eutectic point.
Because of their corrosive properties salt-based brines have been replaced by organic liquids such as
ethylene glycol.[6]
Sodium chloride brine spray is used on some fishing vessels to freeze fish.[7] The brine temperature is generally −5 °F (−21 °C). Air blast freezing temperatures are −31 °F (−35 °C) or lower. Given the higher temperature of brine, the system efficiency over air blast freezing can be higher. High-value fish usually are frozen at much lower temperatures, below the practical temperature limit for brine.
Water softening and purification
Brine is an auxiliary agent in
water softening and
water purification systems involving
ion exchange technology. The most common example are household
dishwashers, utilizing sodium chloride in form of
dishwasher salt. Brine is not involved in the purification process itself, but used for regeneration of
ion-exchange resin on cyclical basis. The water being treated flows through the resin container until the resin is considered exhausted and water is purified to a desired level. Resin is then regenerated by sequentially backwashing the resin bed to remove accumulated solids, flushing removed ions from the resin with a concentrated solution of replacement ions, and rinsing the flushing solution from the resin.[8] After treatment, ion-exchange resin beads saturated with
calcium and
magnesium ions from the treated water, are regenerated by soaking in brine containing 6–12% NaCl. The
sodium ions from brine replace the calcium and magnesium ions on the beads.[9][10]
De-icing
In lower temperatures, a brine solution can be used to
de-ice or reduce freezing temperatures on roads.[11]
Quenching
Quenching is a heat-treatment process when forging metals such as steel. A brine solution, along with oil and other substances, is commonly used to harden steel. When brine is used, there is an enhanced uniformity of the cooling process and heat transfer.[12]
The characteristics of the
discharge depend on different factors, such as the desalination
technology used,
salinity and
quality of the water used,
environmental and
oceanographic characteristics, desalination process carried out, among others.[14] The discharge of desalination plants by
seawater reverse osmosis (SWRO), are mainly characterized by presenting a salinity concentration that can, in the worst case, double the salinity of the seawater used, and unlike of
thermal desalination plants, have practically the same
temperature and
dissolved oxygen as the seawater used (Abessi, 2018; Mezher et al., 2011).[15][16]
Dissolved chemicals
The discharge could contain
trace chemical products used during the industrial treatments applies,such as
antiscalants,
coagulants,
flocculants, which are discarded together with the discharge, and which could affect the physical-chemical quality of the
effluent. However, these are practically consumed during the process and the
concentrations in the discharge are very low, which are practically
diluted during the discharge, without affecting
marine ecosystems (Blanco-Murillo et al., 2023; Fernández-Torquemada et al., 2019).[17][18]
The discharge is generally dumped back into the sea, through an underwater outfall or coastal release, due to its lower
energy and
economiccost compared to other discharge methods.[18][22] Due to its increase in
salinity, the discharge has a greater
density compared to the surrounding seawater. Therefore, when the discharge reaches the sea, it can form a saline plume that can tends to follow the
bathymetric line of the bottom until it is completely
diluted.[23][24][25] The distribution of the salt plume may depend on different factors, such as the
production capacity of the plant, the discharge method, the
oceanographic and environmental conditions of the discharge point, among others.[15][23][22][26]
Marine environment
Brine discharge might lead to an increase in salinity above certain threshold levels that has the potential to affect
benthic communities, especially those more sensitive to osmotic pressure, finally having an effect on their abundance and diversity.[27][28][29]
However, if appropriate
mitigation measures are applied, the potential environmental impacts of discharges from SWRO plants can be correctly minimized.[18][26] Some examples can be found in countries such as
Spain,
Israel,
Chile or
Australia, in which the mitigation measures adopted reduce the
area affected by the discharge, guaranteeing a
sustainable development of the desalination process without significant impacts on
marine ecosystems.[30][31][32][33][34][26][35] It should be notices that when noticeable effects have been detected on the
environment surrounding discharge areas, it generally corresponds to old desalination plants in which the correct
mitigation measures were not implemented.[36][30][37] Some examples can be found in Spain, Australia or Chile, where it has been shown that saline plumes do not exceed values of 5% with respect to the natural salinity of the sea in a
radius less than 100 m from the point of discharge when proper measures are adopted.[32][26]
Mitigation measures
The mitigation measures that are typically employed to prevent negatively impact sensitive marine enviorment are listed below[38][39][40]:
A well-designed discharge mechanisms, employing the use of efficient
diffusers or
pre-dilution of discharges with seawater
The implementation of an adequate environmental
surveillance program, which guarantees the correct operation of the desalination plants during their operational phase, allowing an accurate and early
diagnostics of potential environmental threats
Regulation
Currently, in many countries, such as
Spain,
Israel,
Chile and
Australia, the development of a rigorous
environmental impact assessment process is required, both for the
construction and operational phases [41][42][43]. During its developent, the most important
legal management tools are established within the local environmental
regulation, to
prevent and adopt
mitigation measures that guarantee the sustainable development of desalination projects. This includes a series of administrative tools and periodic environmental
monitoring, to adopt preventive, corrective and further monitoring measures of the state of the surrounding
marine environment. [44][45].
Under the context of this environmental assessment process, numerous countries require compliance with an
Environmental Monitoring Program (PVA), in order to evaluate the effectiveness of the preventive and corrective measures established during the environmental assessment process, and thus guarantee the operation of desalination plants without producing significant environmental impacts[46][47]. The PVAs establishes a series of mandatory requirements that are mainly related to the monitoring of discharge, using a series of
measurements and
characterizations based on physical-chemical and biological information. [46][47]. In addition, the PVAs could also include different requirements related to monitoring the effects of seawater intake and those that may potentially be related to effects on the
terrestrial environment.
Brine is a byproduct of many industrial processes, such as
desalination, power plant
cooling towers,
produced water from oil and
natural gas extraction,
acid mine or acid rock drainage,
reverse osmosis reject,
chlor-alkali wastewater treatment, pulp and paper mill effluent, and waste streams from food and beverage processing. Along with diluted salts, it can contain residues of pretreatment and cleaning chemicals, their reaction byproducts and heavy metals due to corrosion.
Wastewater brine can pose a significant environmental hazard, both due to corrosive and sediment-forming effects of salts and toxicity of other chemicals diluted in it.[48]
Unpolluted brine from desalination plants and cooling towers can be returned to the ocean. From the desalination process, reject brine is produced, which proposes potential damages to the marine life and habitats.[49] To limit the environmental impact, it can be diluted with another stream of water, such as the outfall of a
wastewater treatment or power plant. Since brine is heavier than seawater and would accumulate on the ocean bottom, it requires methods to ensure proper diffusion, such as installing underwater
diffusers in the
sewerage.[50] Other methods include drying in
evaporation ponds, injecting to deep wells, and storing and reusing the brine for irrigation, de-icing or dust control purposes.[48]
Technologies for treatment of polluted brine include: membrane filtration processes, such as
reverse osmosis and
forward osmosis; ion exchange processes such as
electrodialysis or
weak acid cation exchange; or evaporation processes, such as thermal brine concentrators and
crystallizers employing
mechanical vapour recompression and steam. New methods for membrane brine concentration, employing osmotically assisted reverse osmosis and related processes, are beginning to gain ground as part of zero liquid discharge systems (ZLD).[51]
Composition and purification
Brine consists of concentrated solution of Na+ and Cl− ions. Sodium chloride per se does not exist in water: it is fully ionized. Other cations found in various brines include K+, Mg2+, Ca2+, and Sr2+. The latter three are problematic because they form scale and they react with soaps. Aside from chloride, brines sometimes contain Br− and I− and, most problematically, SO2− 4. Purification steps often include the addition of calcium oxide to precipitate solid
magnesium hydroxide together with gypsum (CaSO4), which can be removed by filtration. Further purification is achieved by
fractional crystallization. The resulting purified salt is called evaporated salt or vacuum salt.[1]
See also
Brine mining – Extracting materials from saltwater
^3. Luís H. Pizetta Zordão, Vinícius A. Oliveira, George E. Totten, Lauralice C.F. Canale, "Quenching power of aqueous salt solution", International Journal of Heat and Mass Transfer, Volume 140, 2019, pp. 807–818.
^5. A. Giwa, V. Dufour, F. Al Marzooqi, M. Al Kaabi, S.W. Hasan, "Brine management methods: Recent innovations and current status", Desalination, Volume 407, 2017, pp. 1–23