High-salt wastewater treatment technology and three-effect evaporator application
There are physicochemical treatment technology, biological treatment technology and steam treatment technology for high-salt wastewater treatment methods. According to the different nature of wastewater and different effluent uses and water quality requirements, the treatment methods are different. Generally, the treatment of high-salt wastewater is to reduce the COD and salt content of wastewater, so as to achieve the purpose of discharge standards.
Overview of High-Salinity Wastewater
High-salt wastewater refers to saline-containing wastewater with a total salt content of more than 1%, including high-salt domestic wastewater and high-salt industrial wastewater. It mainly comes from industrial production, domestic sewage, food processing plants, pharmaceutical plants, chemical plants, etc. that directly utilize seawater. In addition to organic pollutants, these wastewaters also contain a large number of inorganic salts, such as Cl-, SO32-, SO42- and other ions. If these high-salt and high-organic waste waters are directly discharged without treatment, they will inevitably cause great harm to aquatic organisms, drinking water, and industrial and agricultural production water.
Analysis of High-Salinity Wastewater Treatment Technology
Physical and chemical processing technology.
(1) Electrolysis method.
High salinity wastewater has high conductivity due to the existence of high salinity, which provides the possibility for electrochemical degradation of high salinity wastewater. During the electrolysis process, the organic electrolyte solution can undergo a series of redox reactions to reduce COD. The treatment of this method is also related to the type of organic matter and inorganic salt. In the presence of Cl-, it can be discharged at the anode to generate ClO- to degrade COD. There are also experiments showing that the treatment of phenol wastewater by electrolysis only changes the existence of COD and does not reduce TOC. There is a total amount.
(2) Membrane separation process.
At present, the commonly used membrane separation processes are microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. For most soluble substances, nanofiltration can intercept most divalent ions, and reverse osmosis can intercept monovalent ions, so different membrane separation processes can be selected for treatment according to different requirements. higher, and the membrane fouling problem is more prominent, so it is subject to certain restrictions. There are also some new membrane separation processes, such as the membrane distillation process and the “NANO” membrane developed by Tsinghua University. The membrane distillation process utilizes the hydrophobicity of the hydrophobic membrane to allow water vapor to pass through the membrane to isolate other substances, thereby ensuring the cleanness of the effluent. Combining the process characteristics of reverse osmosis and membrane distillation, it has a strong anti-pollution ability and strong interception ability and has a good development prospect.
(3) Adsorption process.
Activated carbon has a unique lattice structure, and there are many oxygen-containing functional groups on the surface, which can adsorb a large amount of inorganic and organic substances on the surface. The Fenton oxidation process produces strong oxidative free radicals, which can cleave organic matter to increase biochemical activity or remove organic matter. The activated carbon adsorption-Fenton oxidation process introduces activated carbon into the Fenton reagent system. Due to the efficient adsorption of activated carbon, the concentration of organic matter near the oxidation group is increased, thereby improving the oxidation efficiency and avoiding secondary pollution.
Biological treatment technology.
Since the high salinity in the high salinity wastewater inhibits the metabolic function of microorganisms, the biochemical treatment effect of the high salinity wastewater cannot meet the standard, so the biological process focuses on the use of halophilic bacteria to enhance the biochemical treatment effect of the high salinity wastewater. Halophilic bacteria refer to bacteria that can grow in a high-salt environment and mostly live in a high-salt environment. Generally, bacteria that can survive well in a water environment with a salinity of 2% to 5% are called halophilic bacteria, and bacteria that can survive in an environment of 3% to 15% salinity are moderately halophilic bacteria, generally fungi. 15%-30% of the survivors become extremely halophilic bacteria, generally archaea. They can maintain low water activity in the body under high salinity conditions, maintain enzyme activity, and grow into dominant bacteria in a high salinity wastewater environment to degrade wastewater COD so that the discharged water meets the standard. At present, the research on halophilic bacteria is still in the test. With the maturity of the technology, because the biological method has no secondary pollution and low cost, this technology can be widely used in engineering practice. The purpose of the biological method is to degrade the organic pollutants in the water body. For the inorganic ions in high-salinity wastewater, it is necessary to cooperate with the physicochemical method for advanced treatment.
Application analysis of three-effect evaporator in high-salt wastewater treatment
In order to discharge high-salt wastewater up to the standard, the purpose can be achieved by rationally applying the three-effect evaporator. The specific application is as follows:
Three-effect evaporator desalination method in high-salt wastewater treatment.
Evaporation is one of the modern chemical unit operations, that is, using heating to vaporize and remove part of the solvent in the solution to increase the concentration of the solution or create conditions for solute precipitation. The three-effect evaporator desalination method is a method that uses a concentrated crystallization system to remove the inorganic salts in the waste liquid by evaporation. The three-effect evaporator is composed of three evaporators connected in series. The high-temperature (about 120°C) heating steam is introduced into the first effect to heat the waste liquid, and the generated steam is introduced into the second effect as heating steam so that the second effect is The waste liquid of the effect is evaporated at a lower temperature than the first effect, and this process is repeated until the last effect. The first effect is condensate returns to the heat source, and the other effect condensates are collected and output as desalinated water. At the same time, the high-salinity wastewater is concentrated from the first effect to the last effect in sequence, and at the last effect, it reaches supersaturation and crystallizes out, thereby realizing the solid-liquid separation of salt and wastewater. The salty wastewater enters the three-effect concentration and crystallization device, and is separated into desalinated water and concentrated crystal slurry waste liquid through the concentration and crystallization process of three-effect evaporation and condensation. Inorganic salts and some organic substances can be crystallized and separated for incineration treatment. Use instead of demineralized water.
Application analysis of triple-effect evaporator in high-salt wastewater treatment.
Mainly as follows:
(1) Composition of the three-effect evaporator.
The three-effect evaporator is mainly composed of three groups of evaporators, condensers, salt separators, and auxiliary equipment connected in series. Three sets of evaporators operate in series to form a three-effect evaporator.
(2) Application scope of the three-effect evaporator.
The three-effect evaporator can be used to treat high-salt wastewater produced by chemical production, pharmaceutical production, and other enterprises in the process of production. 10000ppm.
(3) Application principle of the three-effect evaporator.
The three-effect evaporator evaporation system adopts the production method of continuous feeding and continuous discharging. The high-salt wastewater first enters the first-effect forced circulation crystallization evaporator. The crystallization evaporator is equipped with a circulating pump, and the wastewater is pumped into the evaporation heat exchange chamber. In the evaporation heat exchange chamber, the external steam is liquefied to generate latent heat of vaporization to heat the wastewater. Due to the high pressure in the evaporative heat exchange chamber, the wastewater is heated to superheat at a pressure higher than the normal liquid boiling point in the evaporative heat exchange chamber.
After the heated liquid enters the crystallization evaporation chamber, the pressure of the wastewater drops rapidly, causing part of the wastewater to flash, or boil rapidly. The steam after the wastewater is evaporated enters the two-effect forced circulation evaporator as power steam to heat the two-effect evaporator.
The one-effect, two-effect, and three-effect forced circulation evaporators are connected through a balance pipe. Under the action of negative pressure, the high-salt wastewater flows from the first effect to the second effect and the third effect in turn. The concentration of salt is getting higher and higher. When the salt in the wastewater exceeds the saturated state, the salt in the water will be continuously precipitated and enter the salt collecting chamber at the lower part of the evaporation and crystallization chamber.
The salt suction pump continuously sends the salty wastewater to the vortex salt separator. In the vortex salt separator, the solid salt is separated into the salt storage tank, and the separated wastewater enters the two-effect forced circulation evaporator for heating. Final separation of water and salt.
And the condenser is connected with a vacuum system, and the vacuum system removes the uncondensed gas generated in the evaporation system so that the condenser and the evaporator maintain a negative pressure state, and the evaporation efficiency of the evaporation system is improved.
Under the action of negative pressure, the secondary steam generated by the wastewater in the three-effect forced circulation evaporator automatically enters the condenser, and under the cooling of the circulating cooling water, the secondary steam generated by the wastewater is rapidly converted into condensed water.
The condensed water can be recycled to the reuse pool by continuous effluent.
In summary, although the triple-effect evaporator has the disadvantages of high treatment cost, short equipment life, and a large amount of steam required, the application of the triple-effect evaporator desalination method in the high-salt wastewater treatment technology has mature technology and can be used. It has the advantages of a wide range of wastewater treatment, small footprint, fast treatment speed, and energy saving, so its analysis is of great significance.