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Which of these 17 industrial wastewater treatment methods is right for you?
Published Time:
2025-02-06
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So what are the treatment processes?
What are the mainstream processes nationwide, and how effective are they?
In the treatment of industrial saline wastewater, the industrial saline wastewater enters a low-temperature multi-effect concentration crystallization device. After a concentration crystallization process of 3-6 effect evaporation and condensation, it is separated into desalinated water (desalinated water may contain trace amounts of low-boiling-point organic matter) and concentrated slurry waste liquid; inorganic salts and some organic matter can be crystallized and separated, and incinerated to form inorganic salt waste residue; organic matter concentrated waste liquid that cannot be crystallized can be treated using a rotary evaporator to form solid waste residue, which is then incinerated; desalinated water can be returned to the production system to replace softened water for use.
The low-temperature multi-effect evaporation concentration crystallization system can not only be used in the concentration and crystallization processes of chemical production but also in the evaporation concentration crystallization treatment process of industrial saline wastewater.
The multi-effect evaporation process only uses steam in the first effect, saving steam requirements, effectively utilizing the heat in the secondary steam, reducing production costs, and improving economic efficiency.
Biological treatment is one of the most commonly used methods for wastewater treatment. It has the characteristics of wide application range, strong adaptability, economic efficiency, and harmlessness.
Generally, the commonly used biological methods include traditional activated sludge method and biological contact oxidation method.
(1) Traditional activated sludge method
The activated sludge method is an aerobic biological treatment method for wastewater and is currently the most widely used method for treating urban wastewater. It can remove soluble and colloidal biodegradable organic matter and suspended solids and other substances that can be adsorbed by activated sludge from wastewater, and it can also remove some phosphorus and nitrogen.
The activated sludge method has a high removal rate and is suitable for treating wastewater with high water quality requirements and relatively stable water quality. However, it is not good at adapting to changes in water quality, and oxygen supply cannot be fully utilized; the air supply is evenly distributed along the pool, resulting in insufficient oxygen in the front section and excessive oxygen in the rear section; the aeration structure is large, and the land area is large.
(2) Biological contact oxidation method
The biological contact oxidation method mainly uses microorganisms (i.e., biofilm) attached to the surface of certain solid substances to treat organic wastewater.
The biological contact oxidation method is a submerged biofilm method, a combination of a biological filter and an aeration tank, combining the characteristics of the activated sludge method and the biofilm method, and has a good effect in water treatment.
The biological contact oxidation method has a high volumetric load and a strong adaptability to shock loads; the sludge production is small, the operation and management are simple, the operation is simple, the energy consumption is low, and it is cost-effective; it has the advantages of the activated sludge method, high biological activity, good purification effect, high treatment efficiency, short treatment time, good and stable effluent water quality; it can decompose substances that are difficult to decompose by other biological treatments, has the function of deoxygenation and phosphorus removal, and can be used as a tertiary treatment technology.
SBR is the abbreviation of Sequencing Batch Reactor. As an intermittently operated wastewater treatment process, it has been widely concerned and researched in recent years as a wastewater treatment technology at home and abroad.
The SBR operation procedure consists of five procedures: inflow, reaction, sedimentation, discharge, and idle. Wastewater enters each reaction process sequentially and intermittently in the reactor, and the operation of each SBR reactor is also sequentially arranged and intermittently operated in time.
The SBR method has the following characteristics: simple process, small land area, less equipment, and low investment. The ideal plug flow process makes the biochemical reaction have a large driving force, high treatment efficiency, flexible operation mode, phosphorus and nitrogen removal, high sludge activity, good sedimentation performance, shock load resistance, and strong treatment capacity.
Although the SBR method has the above advantages, it also has certain limitations, such as a large inflow, which requires adjustment of the reaction system, thus increasing investment; and special requirements for effluent water quality, such as denitrification and phosphorus removal, also require appropriate improvements to the process.
MBR is a new type of high-efficiency wastewater treatment process that combines high-efficiency membrane separation technology with the traditional activated sludge method. It uses MBR flat-sheet membrane components with a unique structure placed in the aeration tank. The water after aerobic aeration and biological treatment is pumped out through the filter membrane.
The MBR process has compact equipment and small land occupation; the effluent water quality is high and stable, and the organic matter removal efficiency is high; the amount of excess sludge is small, reducing production costs; ammonia nitrogen and refractory organic matter can be removed; it is easy to be retrofitted from traditional processes. However, the membrane is expensive, making the infrastructure investment of membrane bioreactors higher than that of traditional wastewater treatment processes; membrane fouling is prone to occur, which brings inconvenience to operation and management; energy consumption is high, and process requirements are high.
Under high salinity conditions, wastewater has high conductivity, which provides good development space for electrochemical methods in the treatment of high-salinity organic wastewater.
High-salt wastewater undergoes a series of oxidation-reduction reactions in the electrolytic cell, generating insoluble substances, which are removed by precipitation (or flotation) or directly oxidized and reduced to harmless gases, thereby reducing COD.
When sodium chloride in the solution is electrolyzed, part of the chlorine gas generated at the anode dissolves in the solution and undergoes secondary reactions to generate hypochlorite and chlorate, which has a bleaching effect on the solution. It is the above comprehensive synergistic effect that degrades organic pollutants in the solution.
Because Limitations of electrochemical theory, high energy consumption, and lack of electricity These problems mean that the current technology for treating high-salt wastewater through electrolysis is still in the research stage.
Ion exchange is a unit operation process that typically involves an exchange reaction between ions in solution and counterions on insoluble polymers (containing fixed anions or cations).
When using the ion exchange method, the wastewater first passes through a cation exchange column, where positively charged ions (such as Na+) are replaced by H+ and retained in the exchange column; then, negatively charged ions (such as Cl-) are replaced by OH- in the anion exchange column to achieve desalination.
However, a major problem with this method is that solid suspended matter in the wastewater can clog the resin and render it ineffective. Another issue is the high cost of regenerating the ion exchange resin and the difficulty in handling the resulting waste.
Membrane separation technology is a new separation technology that uses the difference in the selective permeability of a membrane to the various components in a mixture to separate, purify, and concentrate the target substance.
Currently commonly used membrane technologies include: Ultrafiltration, microfiltration, electrodialysis, and reverse osmosis. 。其中的 When ultrafiltration and microfiltration are used in the treatment of industrial wastewater, they cannot effectively remove salts from the wastewater, but they can effectively retain suspended solids (SS) and colloidal COD; electrodialysis and reverse osmosis (RO) technologies are the most effective and commonly used desalination technologies. 。
The main difficulties restricting the widespread engineering application of membrane technology are the high cost, short lifespan, susceptibility to pollution, and fouling of the membranes. With the development of membrane production technology, membrane technology will be increasingly applied in the field of wastewater treatment.
Iron-carbon microelectrolysis method is a good process for treating wastewater using the principle of Fe/C battery reaction, also known as internal electrolysis method, iron filings filtration method, etc. The iron-carbon microelectrolysis method is a comprehensive effect of electrochemical oxidation-reduction, electrochemical electric pair electro-enrichment of flocs, coagulation of electrochemical reaction products, adsorption of newly generated flocs, and bed filtration, mainly oxidation-reduction, electro-enrichment, and coagulation.
When iron filings are immersed in wastewater containing a large amount of electrolyte, countless tiny batteries are formed. After adding coke to the iron filings, the iron filings and coke particles contact each other to further form a large battery, causing the iron filings to be corroded by the micro-battery and the large battery, thereby accelerating the electrochemical reaction.
This method has many advantages, such as wide applicability, good treatment effect, long service life, low cost, and convenient operation and maintenance. It also uses waste iron filings as raw materials and does not consume electricity, which has the meaning of "using waste to treat waste". Currently, iron-carbon microelectrolysis technology has been widely used in the treatment of wastewater from dyeing, pesticides/pharmaceuticals, heavy metals, petrochemicals, and oil, as well as leachate from garbage, achieving good results.
Typical Fenton's reagent is the decomposition of H2O2 catalyzed by Fe2+ to produce ·OH, thus initiating the oxidation degradation reaction of organic matter. Because the Fenton method requires a long processing time for wastewater treatment, uses a large amount of reagents, and excessive Fe2+ will increase the COD in the treated wastewater and cause secondary pollution.
In recent years, people have introduced ultraviolet light, visible light, etc., into the Fenton system and studied the use of other transition metals to replace Fe2+. These methods can significantly enhance the oxidation degradation ability of Fenton's reagent to organic matter, reduce the amount of Fenton's reagent, and reduce the treatment cost. They are collectively referred to as Fenton-like reactions.
Fenton method has mild reaction conditions, relatively simple equipment, and a wide range of applications; it can be used as a stand-alone treatment technology or in combination with other methods, such as coagulation-sedimentation, activated carbon, and biological treatment, as a pretreatment or post-treatment method for refractory organic wastewater. 。
Ozone is a strong oxidant. It reacts quickly with reduced pollutants, is easy to use, does not produce secondary pollution, and can be used for wastewater disinfection, decolorization, deodorization, removal of organic matter, and reduction of COD, etc. Using ozone oxidation alone is expensive and has high treatment costs. Also, its oxidation reaction is selective and has a poor effect on some halogenated hydrocarbons and pesticides.
Therefore, in recent years, combined technologies aimed at improving ozone oxidation efficiency have been developed. Combinations such as UV/O3, H2O2/O3, and UV/H2O2/O3 not only improve the oxidation rate and efficiency but can also oxidize organic matter that is difficult to oxidize and degrade by ozone alone. Because the solubility of ozone in water is low, and the ozone generation efficiency is low and energy-consuming, increasing the solubility of ozone in water, improving the utilization rate of ozone, and developing high-efficiency and low-energy-consuming ozone generators have become the main research directions.
Magnetic separation technology is a recently developed new type of water treatment technology that uses the magnetism of impurity particles in wastewater for separation . For non-magnetic or weakly magnetic particles in water, magnetic inoculation technology can make them magnetic.
There are three methods for applying magnetic separation technology to wastewater treatment: Direct magnetic separation, indirect magnetic separation, and microbial-magnetic separation. 。
Currently researched magnetization technologies mainly include magnetic flocculation technology, iron salt co-precipitation technology, iron powder method, ferrite method, etc. Representative magnetic separation equipment includes disc magnetic separators and high-gradient magnetic filters. Currently, magnetic separation technology is still in the laboratory research stage and cannot be applied to actual engineering practice.
Low-temperature plasma water treatment technology, including High-voltage pulsed discharge plasma water treatment technology and glow discharge plasma water treatment technology utilize discharge to directly generate plasma in aqueous solutions, or introduce active particles from gas discharge plasma into water, allowing for the complete oxidation and decomposition of pollutants in the water.
Direct pulsed discharge in aqueous solutions can be operated at room temperature and pressure. The entire discharge process does not require the addition of catalysts to generate in-situ chemically oxidizing species in the aqueous solution to oxidize and degrade organic matter. This technology is economical and effective for treating low-concentration organic matter.
In addition, the reactor form of pulsed discharge plasma water treatment technology can be flexibly adjusted, the operation process is simple, and the corresponding maintenance costs are also lower. Due to limitations of the discharge equipment, the energy utilization efficiency of this process for degrading organic matter is relatively low, and the application of plasma technology in water treatment is still in the research and development stage.
Electrochemical (catalytic) oxidation technology directly degrades organic matter through anodic reactions, or degrades organic matter by producing oxidizing agents such as hydroxyl radicals (˙OH) and ozone through anodic reactions.
Electrochemical (catalytic) oxidation includes two-dimensional and three-dimensional electrode systems. Three-dimensional electrode systems, due to their micro-electric field electrolysis, are currently highly regarded. Three-dimensional electrodes are filled with granular or other fragmentary working electrode materials between the electrodes of a traditional two-dimensional electrolytic cell, and the surface of the filled material is charged to become a third electrode, and electrochemical reactions can occur on the surface of the working electrode material.
Compared with two-dimensional plate electrodes, three-dimensional electrodes have a large specific surface area, can increase the surface-to-volume ratio of the electrolytic cell, can provide a large current intensity at a lower current density, have a small particle spacing and high mass transfer rate, and high space-time conversion efficiency. Therefore, they have high current efficiency and good treatment effects. Three-dimensional electrodes can be used to treat domestic sewage, refractory organic wastewater such as pesticides, dyes, pharmaceuticals, and phenol-containing wastewater, metal ions, and leachate.
Since the 1970s, with the development of large cobalt sources and electron accelerator technology, the radiation source problem in the application of radiation technology has been gradually improved. Research on the treatment of pollutants in wastewater using radiation technology has attracted the attention and importance of various countries.
Compared with traditional chemical oxidation, the use of radiation technology to treat pollutants does not require or only requires a small amount of chemical reagents, does not produce secondary pollution, and has advantages such as high degradation efficiency, fast reaction speed, and thorough pollutant degradation. Moreover, when ionizing radiation is used in conjunction with catalytic oxidation methods such as oxygen and ozone, a "synergistic effect" is produced. Therefore, radiation technology for treating pollutants is a clean and sustainable technology and has been listed by the International Atomic Energy Agency as a major research direction for the peaceful use of atomic energy in the 21st century.
Photocatalytic oxidation technology is developed based on photochemical oxidation. Compared with photochemical methods, it has stronger oxidation ability and can more thoroughly degrade organic pollutants. Photocatalytic oxidation is photochemical degradation under the condition of a catalyst, and the oxidant produces free radicals with stronger oxidation ability under light irradiation.
Catalysts include TiO2, ZnO, WO3, CdS, ZnS, SnO2, and Fe3O4, etc. They are divided into homogeneous and heterogeneous types. Homogeneous photocatalytic degradation uses Fe2+ or Fe3+ and H2O2 as media, and degrades pollutants by producing hydroxyl radicals through photo-assisted Fenton reaction; heterogeneous catalytic degradation puts a certain amount of photosensitive semiconductor materials, such as TiO2 and ZnO, into the pollution system, and combines light radiation to make the photosensitive semiconductor generate electron-hole pairs under light irradiation. Dissolved oxygen and water molecules adsorbed on the semiconductor interact with electrons and holes to produce highly oxidizing free radicals such as ˙OH. TiO2 photocatalytic oxidation technology has obvious advantages in oxidizing and degrading organic pollutants in water, especially refractory organic pollutants.
SCWO uses supercritical water as a medium to homogeneously oxidize and decompose organic matter. It can decompose organic pollutants into inorganic small molecules such as CO2 and H2O in a short time, while sulfur, phosphorus, and nitrogen atoms are converted into sulfate, phosphate, nitrate, nitrite ions, or nitrogen gas. The United States has listed the SCWO method as the most promising waste treatment technology in the fields of energy and environment.
SCWO has a fast reaction rate and short residence time; high oxidation efficiency, with a treatment rate of most organic matter reaching over 99%; simple reactor structure and small equipment size; wide processing range, not only applicable to the treatment of various toxic substances, wastewater, and waste, but also to the decomposition of organic compounds; no external heating is required, and the processing cost is low; good selectivity, by adjusting the temperature and pressure, the density, viscosity, and diffusion coefficient of water can be changed, thereby changing its solubility of organic matter and achieving selective control of reaction products. 。
Supercritical oxidation technology has been applied in the United States, Germany, Sweden, Japan, and other European and American countries, but China's research started late and is still in the laboratory research stage.
Summary: Currently, the most widely used technologies for treating industrial wastewater are multiple-effect evaporation, biological methods, SBR technology, and MBR technology, because the theory is mature, the treatment effect is good, and it is cost-effective.
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