Common technologies for chemical wastewater treatment

A large amount of wastewater will be produced in the production process of organic chemicals, such as petrochemical, pesticide, pharmaceutical, leather, metal surface treatment, and other production will produce a lot of wastewater, and the wastewater has complex components, high pollutant concentration and difficult to degrade, causing serious environmental pollution. If it is not degraded effectively, it will cause serious pollution to the surrounding environment. Based on this, the following is a discussion of the commonly used technologies for organic chemical wastewater treatment.

Overview of chemical wastewater

Chemical wastewater refers to the wastewater produced in the production process of chemical plants, such as wastewater from the production of ethylene, polyethylene, rubber, polyester, methanol, ethylene glycol, oil tank farms, air separation and air compressor stations and other devices. Chemical wastewater has complex components, and the reaction raw materials are often solvent substances or compounds with a ring structure, which increases the difficulty of wastewater treatment; chemical wastewater contains a large number of pollutants, mainly due to incomplete reaction of raw materials and the use of large amounts of solvents in raw materials or production. Caused. There are many toxic and harmful substances in chemical wastewater, among which many organic pollutants are toxic and harmful to microorganisms, such as halogen compounds, nitro compounds, dispersants or surfactants with bactericidal effect, etc.; and there are many biodegradable substances, BOD/ Low COD and poor biodegradability.

Main characteristics and hazards of organic chemical wastewater

(1) The characteristics of organic chemical wastewater are mainly as follows:

First, the COD value of organic pollutants in organic chemical wastewater usually exceeds 2000 mg/L, and some even reach tens of thousands or hundreds of thousands of mg/L;

Second, the composition of organic chemical wastewater is very complex and difficult to degrade, including not only toxic substances such as heterocyclic compounds and aromatic compounds, but also heavy metals, nitrides and sulfides;

Third, organic chemical wastewater has high pH, so it is very corrosive.

(2) The harm caused by organic chemical wastewater to the environment. It mainly includes the following aspects:

①Aerobic hazard, because organic pollutants need to consume a lot of oxygen during biodegradation, which will lead to a significant reduction in the oxygen content in the water body, resulting in the occurrence of oxygen deficiency in the water body, which will lead to the death of aquatic animals and plants in the water body.

② Organic chemical wastewater contains a lot of toxic substances, which will cause serious pollution to soil and water bodies for many years, and even threaten human life and health.

③Organic chemical wastewater has sensory pollution. Since organic chemical wastewater has strong irritating odors such as stench, it will have a negative impact on the daily life of nearby residents.

Analysis of common technologies for chemical wastewater treatment

4.1 Analysis of Physical Treatment Technology of Organic Chemical Wastewater

4.1.1 Adsorption method.

The principle of adsorption method of organic chemical wastewater treatment is to use loose porous structure adsorbent to absorb pollutants in wastewater, so as to achieve the purpose of purifying wastewater. Activated carbon, resin and other substances are commonly used adsorbents. For example, after printing and dyeing wastewater passes through activated carbon, most of the organic components can be removed and a good treatment effect can be achieved; when resin is used in the treatment of cephalosporin G acid pharmaceutical wastewater, a good treatment effect can be achieved.

4.1.2 Membrane separation method.

The membrane separation method of organic chemical wastewater treatment is to make the substances in the wastewater selectively pass through the membrane with the help of external force, and then achieve the purpose of removing organic substances. For example, in the treatment of urban sewage, the use of ultrafiltration can remove more than 95% of the turbidity in the water; when the nanomembrane is used to treat dye wastewater, more than 96% of the dye components in the wastewater can be retained without being affected by the pH of the solution. Membrane separation technology has low operating cost and simple operation, but is prone to structural phenomena that affect the treatment effect and limit the use of membrane separation technology.

4.1.3 Extraction method.

The principle of extraction method of organic chemical wastewater treatment is to use a solvent that has significantly different solubility to different substances to achieve the purpose of separating substance components. During the treatment, the extraction agent is put into the organic chemical wastewater. The extraction agent is insoluble in water and has a high solubility for organic substances, so the organic substances in the wastewater are dissolved in the extraction agent to achieve separation from the water phase

4.2 Analysis of chemical treatment technology of organic chemical wastewater.

4.2.1 Catalytic oxidation method.

The catalytic oxidation method is used in the treatment of organic chemical wastewater. The principle is similar to the operating conditions of the wet oxidation method, but the macromolecular organic compounds are converted into low-polluting or non-polluting small molecular substances through catalysis. Cu, Fe, Ni, Mn, etc. are commonly used. catalyst. For example, using this method to treat organic chemical wastewater, when the temperature is controlled at 240 ° C and the pressure is controlled at 6.5 MPa, the removal rate of CODCr can reach 96.9%; the catalytic oxidation method has good adaptability, but the reaction conditions are harsh, only limited A small amount of organic chemical wastewater can be treated within the scope.

4.2.2 Wet oxidation method.

Organic chemical wastewater is a process in which macromolecular organic matter in wastewater reacts with oxidant to produce inorganic or small molecular organic matter under high temperature and high pressure conditions, which is called wet oxidation. The wet oxidation method can be used in the treatment process of printing and dyeing waste liquid to improve the biodegradability of water. The wet oxidation method has a short reaction time, good treatment effect, and is not easy to produce secondary pollution, so it has a wide range of applications; however, this method requires high equipment, so the operating cost is relatively high, and it cannot be promoted in large-scale wastewater treatment. .

4.2.3 Supercritical water oxidation.

The organic chemical wastewater treatment uses supercritical oxidation. Under the action of a catalyst, organic matter reacts with oxygen in supercritical water, resulting in the reorganization of the structure of organic matter, thereby achieving the purpose of decomposing macromolecular organic matter. When using supercritical water oxidation to treat papermaking black liquor, the removal effect of CODCr and chroma in the waste liquor is very ideal. When the experimental conditions are controlled, the removal rate of CODCr in the waste water can reach 99.8%. The supercritical water oxidation method has a fast reaction speed and high treatment efficiency, but the reaction conditions are still high temperature and high pressure, which limits the wide application of this method.

4.2.4 Other oxidation methods.

In addition to the above chemical treatment methods, the treatment of organic chemical wastewater includes ozone oxidation and photocatalytic oxidation. Among them, the ozone oxidation method has strong oxidizing ability, no secondary pollution, good sterilization and decolorization effect, but has higher requirements on the pH and reaction time of the waste liquid; the photocatalytic oxidation method has strong oxidizing ability, fast processing speed and good effect, and can be used for ABS The treatment of organic chemical wastewater, but the application is also limited, and there are certain requirements for the color and cost of the waste liquid.

4.3 Biological treatment technology and micro-electrolysis technology of organic chemical wastewater.

4.3.1 Biological treatment technology.

The biological treatment method of organic chemical wastewater treatment is that aerobic or anaerobic microorganisms use the organic matter in the wastewater to metabolize, so as to achieve the purpose of removing organic pollutants. In the test of monosodium glutamate industrial wastewater, the removal rate of CODCr by SBR method reached more than 90%, reaching the national secondary discharge standard. Biological treatment technology has low energy consumption and meets the requirements of green environmental protection, but it covers a large area, the management process is relatively complicated, the removal rate of CODCr and chroma is relatively low, and it is greatly affected by temperature and pH, so it is generally not suitable to be used alone. .

4.3.2 Micro-electrolysis technology.

The micro-electrolysis method of organic chemical abolition treatment is to use the principle of metal corrosion to build a primary battery to achieve the purpose of treating organic chemical wastewater. During treatment, the micro-electrolytic material filled in the wastewater can self-electrolyze under the action of its own potential difference, consuming chromophoric groups, auxochromic groups, and even chain scission in the wastewater, reducing the content of CODCr. The micro-electrolysis method occupies a small area, the process is simple, the treatment effect is good, the service life is long, the maintenance is convenient, and the cost is low; However, the shortcomings of this technology are that the iron consumption and carbon consumption are not balanced, and it is easy to rust and scale, which affects the treatment effect.

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