Brine
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).
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.
[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.
[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.
[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.
[20][14] Therefore, the concentration values of heavy metals in the discharge of SWRO plants are much lower than the acute toxicity levels to generate environmental impacts on marine ecosystems.
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.
[15][24][23][27] 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.
[19][27] 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.
[31][32][33][34][35][27][36] 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.
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.
[51] 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.
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).
Purification steps often include the addition of calcium oxide to precipitate solid magnesium hydroxide together with gypsum (CaSO4), which can be removed by filtration.
