High-salinity wastewater refers to the concentrated brine produced by evaporation or other desalination technology after the qualified discharge water recovers most of the “fresh water” through reverse osmosis technology, and the mass fraction of total dissolved solids (TDS) is greater than 8%, which is difficult to be treated biochemically; or it is directly produced in the chemical production process. The wastewater has a high COD content, a mass fraction of total dissolved solids (TDS) greater than 15%, and cannot be treated biochemically. In order to completely cure the pollution of this high-salinity wastewater, it is necessary not only to reduce its COD content, but more importantly, to achieve the complete separation of soluble salt substances from the wastewater.
Treatment technology of high-salinity wastewater
1 Disc-tube reverse osmosis (DTRO) technology + evaporation crystallization technology Disc-tube reverse osmosis (DTRO) technology is a high-efficiency reverse osmosis technology. Compared with spiral reverse osmosis, it has more obvious characteristics of high pressure resistance and anti-pollution. Even under the conditions of high turbidity, high SDI value, high salinity, and high COD, it can operate stably and economically, and is more suitable for the treatment of high-salinity wastewater. The DTRO salt retention rate is 98%~99.8%, and the crystallized dry solids are recycled and reused, ultimately reaching the zero liquid discharge requirement.
2 Combustion process technology
For high COD and high salt wastewater, direct combustion can be used for treatment. The combustion method for treating high salt wastewater is to spray high salt wastewater into a high temperature combustion furnace in a mist form, so that the water mist is completely vaporized, and the organic matter in the wastewater is oxidized and decomposed into carbon dioxide, water and a small amount of inorganic ash in the furnace.
Before the high salt organic wastewater is burned, the suspended matter in the wastewater should be filtered, or the viscosity of the wastewater should be reduced by heating and other methods to prevent nozzle blockage and improve the atomization efficiency of the waste liquid. For different types of industrial high salt wastewater, acid-base neutralization treatment is sometimes required to prevent acid corrosion of equipment and excessive alkali from causing dirt.
3 Evaporation concentration-cooling crystallization process technology
Evaporation concentration-cooling crystallization process technology is a process technology that concentrates high salt wastewater by evaporation and finally cools the concentrated liquid, so that the soluble salt substances in the high salt wastewater are crystallized and separated. This process can separate local salt substances to obtain crystalline salt compounds, and the crystallization mother liquor needs to be returned to the previous evaporation stage for recycling evaporation and concentration treatment.
This process technology is suitable for high-salt wastewater with relatively low COD and relatively sensitive solubility of salts in high-salt wastewater. By controlling the crystallization temperature, relatively pure crystallized salt can be obtained.
4 Evaporation-thermal crystallization process technology
In the evaporation-thermal crystallization process, the high-salt wastewater is first evaporated and concentrated, and then the high-salt wastewater concentrate is continuously heated by a rotary film evaporator to further evaporate and concentrate it to form a supersaturated salt solution. Finally, by cooling, the temperature of the supersaturated salt solution is reduced to below 40°C to obtain salt mud, thereby achieving a complete separation of soluble salt substances in the high-salt wastewater.
How to choose the appropriate treatment process?
The evaporation-thermal crystallization process has no special requirements for the salt substances contained in high-salinity wastewater. It can achieve efficient and continuous treatment of all high-viscosity and high-salinity wastewater, and can achieve 100% separation of salt substances. It is suitable for the recovery and treatment of acidic high-salinity wastewater.
For some high salinity and high COD wastewater, when direct combustion is used for treatment, it is necessary to strengthen the control of waste gas pollution. For high-salinity wastewater with low COD and soluble salts that are sensitive to temperature, the evaporation concentration-cooling crystallization process technology can be used to separate local soluble salt substances.
Disc tube reverse osmosis technology + evaporation crystallization process technology is suitable for treating high COD and high-salinity wastewater. This process technology has no special requirements for the types of soluble salts in high-salinity wastewater, and the higher the salt content, the higher the separation efficiency.
