The process of zero-discharge desalination of industrial wastewater inevitably produces a large amount of concentrated brine.
The main components of concentrated brine are inorganic salts, heavy metals, and a small amount of chemicals used in pretreatment, chlorination, dechlorination and desalination processes, such as scale inhibitors, acids and other reaction products. This incompletely treated and toxin-containing water can cause serious environmental pollution problems if it is discharged into the external environment without strict control, so the treatment of concentrated brine has been a key technology in restricting the discharge of industrial wastewater.
Concentrated brine treatment technologies adopted in industry are:
Reduction treatment method
In the concentrated brine in the main scaling ions are: Ca2 +, Mg2 +, Ba2 +, Sr2 +, in order to ensure that the scaling components are thoroughly removed, the more commonly used methods are two: chemical softening, resin softening.
Membrane treatment of concentrated brine: Membrane separation technology is a separation membrane as the core, separation, concentration and purification of substances of emerging technologies. Semi-permeable membrane, also known as separation membrane or filter membrane, the membrane wall is covered with small holes, according to the size of the pore can be divided into: microfiltration membrane, ultrafiltration membrane, nanofiltration membrane, reverse osmosis membrane, etc., the membrane separation using the staggered flow filtration or dead-end filtration mode. Membrane separation technology is applied to the industrial water treatment process, with the help of the pressure of the external environment to separate the different substances contained in the solution.
Curing method
Evaporation pond: the evaporation of concentrated brine is basically the earliest use of evaporation ponds for natural evaporation and crystallization, evaporation ponds are dug out of a depression in the ground as a concentration of concentrated water storage ponds, in the right climatic conditions, you can make effective use of the ample solar energy, concentrated brine stored in the evaporation ponds to allow its gradual evaporation, and regularly remove the residual solid salts.
Evaporation crystallizer: evaporation crystallizer mainly refers to the use of a variety of processes to make the solution in the production of working conditions to achieve supersaturation, and then crystallization precipitation crystallizer.
The use of evaporation technology to deal with high salt content of wastewater, in the evaporator evaporation process, very easy to be concentrated in excess of its solubility limit, the salt in the water is very easy to crystallize attached to the surface of the heat exchanger tube to form scaling, affecting the efficiency of the heat exchanger, and in serious cases, block the heat exchanger tube. The technology of "crystal seeding method" solves the scaling problem of heat exchanger tube of evaporator, and is successfully applied in the treatment of various industrial wastewater containing salt.