Wastewater treatment technology in the chemical industry

Modern industry, as a pillar industry of the national economy, has increasingly prominent value in the process of economic construction. However, in the process of industrial development, it often causes serious harm to the social environment. At present, the number of domestic industrial enterprises is gradually increasing, and the degree of environmental pollution is becoming more and more serious, especially wastewater pollution. Once it is not properly supervised and managed during the development process, it will seriously threaten the physical health of the general public and have an extremely negative impact on the development of the social environment. Therefore, the department responsible for wastewater treatment must do a good job in wastewater treatment to promote sustainable and healthy development of the environment. In order to improve the efficiency and quality of industrial wastewater treatment, chemical enterprises and relevant environmental protection departments must optimize sewage treatment technology, scientifically apply sewage treatment technology, and effectively improve the level of wastewater control and treatment.

1. The basic sources and characteristics of chemical wastewater

1.1 Basic sources of chemical wastewater

The production and operation process of chemical enterprises involves a lot of chemical raw material production activities, and the chemical raw materials themselves contain a certain amount of water. After the water is discharged, it naturally becomes industrial wastewater. In addition, chemical enterprises use a large amount of water in the production process, and the production of chemical raw materials is also accompanied by the discharge of wastewater. Special chemical products are subject to reactions between chemicals and agents during the production process, and industrial wastewater will definitely be generated. Cooling water will also produce a large amount of wastewater. Furthermore, in the process of raw material production, transportation, and storage in chemical production, industrial wastewater can also be generated due to material loss during transportation, erosion caused by rainfall and precipitation during transportation.

1.2 Main Performance Characteristics

There are many types of chemical wastewater, such as petrochemical wastewater, synthetic industrial wastewater, textile printing and dyeing wastewater, medical and chemical wastewater, etc. The petrochemical wastewater mainly comes from the gas generated in the refining process, as well as the chemical raw material production wastewater generated in the thermal cracking of clean oil and heavy oil. This type of wastewater has a high organic content, and some industrial wastewater also has a clear pungent odor. The basic source of synthetic chemical wastewater is production wastewater generated from synthetic dyes, rubber, detergents, etc. This type of industrial wastewater has a heavy color, is difficult to degrade, and is also toxic. The wastewater generated by the textile printing and dyeing industry mainly comes from the dyeing, printing, and upper garment processes of cotton and linen processing and blending. The organic content in this type of wastewater is quite high, the color of the wastewater is deep, the pH value of the wastewater is generally high, and the overall water quality of the wastewater changes significantly. A large amount of wastewater will also be generated in the medical chemical production process. The main components of medical wastewater are antibiotics, synthetic drugs, traditional Chinese patent medicines and simple preparations, etc. Wastewater is generated not only during the production process, but also during the drug cleaning process. Medical wastewater has a high organic content, significant changes in water acidity and alkalinity, and some drug components remain, which poses certain difficulties for wastewater treatment work. In summary, the pollutant components in comprehensive chemical wastewater are quite complex, with high TDS in water quality. Both acidity and alkalinity cannot be efficiently controlled, and there are also many toxic, harmful, and even non degradable substances. Once the discharge of chemical wastewater reaches a certain level, its biodegradability will become very poor.

2. The Importance of Effectively Treating Wastewater from Chemical Enterprises

2.1 Promoting the improvement of water resource utilization efficiency

With the continuous development of the chemical industry, the amount and complexity of wastewater generated in production are increasing. The effectiveness of wastewater treatment will have an impact on the health and safety of the general public. Effectively protecting the environment can not only improve the efficiency of water resource utilization, but also improve the problem of water shortage. In addition, it can effectively reduce the breeding of harmful bacteria, prevent water sources from being polluted, and efficiently promote the purification of industrial wastewater, achieving the goal of secondary utilization of water resources, such as using treated wastewater for irrigation, flower cultivation, etc. In short, doing a good job in chemical wastewater treatment can greatly improve the efficiency of water resource utilization, highlight the value of water resources, and maximize their application advantages.

2.2 Enhancing the Stability of Social Environment Development

Highly valuing the wastewater treatment work of chemical enterprises plays an important role in promoting the stable development of the social environment. The amount of industrial wastewater generated by industrial production is large and miscellaneous. Proper treatment of such wastewater can greatly reduce the harm it brings to the social environment. Therefore, it is necessary for relevant enterprises to timely and efficiently carry out wastewater treatment work, effectively ensure the health of the ecological environment, and help society develop towards a more harmonious and stable direction. At the same time, in the process of treating wastewater, many useful substances can be obtained for secondary utilization, which improves the overall utilization rate of water resources and effectively alleviates the problem of water scarcity, thereby improving the overall economic benefits of our country.

2.3 Beneficial for protecting organisms and crops

The wastewater generated in industrial production, especially chemical production, mainly includes strong acids, strong alkalis and other substances, which can directly harm crops and aquatic organisms. Therefore, in the chemical production process, effectively solving the problem of water resource treatment is crucial, and only by doing a good job in water resource treatment can favorable growth space be provided for crops, aquatic organisms, etc.

3. The problems in the treatment of chemical production wastewater

The rapid development of modern society has led to an increasing demand for chemical products, and the amount of wastewater generated during the production process of chemical products is also increasing. With the continuous development of China's chemical industry, the treatment of chemical wastewater has gradually become an important problem that needs to be solved in the current social development, and relevant enterprises and environmental protection departments should pay attention to it. For example, refinery wastewater mostly presents in the form of emulsions, with complex water quality and a large amount of wastewater. The organic chemical components in the wastewater are also very complex, such as sulfides, ammonia nitrogen, COD, TP, nitrate nitrogen, fluoride, phenols, etc. These types of wastewater are not easy to degrade and have extremely poor biodegradability, making their treatment difficult to carry out. Once these chemical production wastewater is discharged directly into the water without standard treatment, it will cause large-scale ecological damage, thereby threatening various aspects of the public's clothing, food, housing, and transportation. At present, the prominent problems exposed in the wastewater treatment work of chemical enterprises are as follows: there is obvious resource waste in the wastewater treatment process, and the quality and efficiency of wastewater treatment are not high, with the most common problem being severe resource waste. In the process of chemical production, many by-products are produced, which have different acidity and alkalinity. It is almost impossible to achieve resource mutual assistance. Therefore, chemical enterprises often choose to treat them in a classified manner before discharging, which increases the burden of wastewater treatment work. Some reusable resources are seriously wasted, while some enterprises blindly focus on immediate interests and do not strictly follow regulations and standards to complete wastewater treatment work, resulting in serious waste of some chemical raw materials. Some enterprises have not done a good job in planning and implementing wastewater treatment, resulting in poor wastewater treatment results.

4. Chemical wastewater treatment technology

4.1 Chemical treatment method

Chemical treatment method is commonly used in the treatment of wastewater in chemical enterprises, mainly consisting of coagulation method, oxidation-reduction method, etc. Chemical treatment method can effectively separate dissolved toxic substances, and change the structure of toxic substances by adding corresponding agents to the wastewater, thereby weakening their toxicity. In order to improve the treatment efficiency of pollutants with different properties in industrial production and chemical wastewater, relevant enterprises should choose diversified treatment strategies based on their own specific situations. For example, for low concentration phenolic wastewater, coagulation and redox methods are generally used for treatment, which can efficiently remove high molecular weight organic compounds and harmful heavy metals in the wastewater.

4.1.1 Coagulation method

The coagulation method has unique advantages in reducing sewage turbidity and can effectively remove heavy metal ions from water bodies. Directly adding coagulants to wastewater can greatly reduce the mutual repulsion between colloidal particles, causing them to collide and settle, resulting in the formation of coagulants. The coagulants can be easily separated from water, thus achieving the goal of water quality purification. The coagulation method also has significant advantages in pre-treatment, especially in the removal of small suspended particles and colloidal particles, with a removal rate of up to 90%.

4.1.2 Oxidation method

The oxidation method is applicable to the treatment of inorganic and organic pollutants in wastewater. The redox process of organic compounds involving covalent bonds is relatively complex when using the oxidation method, and some electron cloud densities may change. The oxidation method includes ozone oxidation, humidification oxidation, etc. Among them, ozone oxidation is more suitable for treating toxic pollutants and organic compounds with high degradation difficulty. It can also be used for disinfection, deodorization, turbidity reduction, etc. of wastewater. The operation process is relatively simple and does not produce secondary pollution. The use of ozone oxidation can improve the biodegradability of difficult to degrade organic compounds. However, ozone has poor stability, strong oxidizing properties, and a certain degree of corrosiveness, so it often requires on-site preparation and high power consumption, making the application cost of this method quite high. The application advantages of wet oxidation method are significant, with both oxidation rate and treatment rate being relatively high. It plays an important role in the treatment of highly toxic and difficult to degrade organic matter. At the same time, compared with ozone oxidation method, wet oxidation method has a shorter action time, lower cost, and is convenient and widely used.

4.2 Physical processing method

When treating suspended solids in wastewater, physical treatment methods are generally used, which can achieve the separation and recovery of pollutants without changing their properties. The physical treatment method is widely used in the degradation of difficult suspended solids and toxic substances, and when removing suspended particles and difficult to degrade organic matter, the operation is simple and the treatment cost is low. The commonly used physical processing methods include screening, precipitation, air flotation, adsorption, membrane separation, and evaporation.

4.2.1 Sieve filtration method

The screen filtration method is the use of corresponding media or equipment to intercept suspended solids and colloidal particles in wastewater after coagulation or biological treatment, to prevent these pollutants from forming blockages on pumps, valves, etc. Among them, grids are commonly used in wastewater treatment and are important auxiliary facilities, composed of a set of parallel grids. The sieve filtration method is divided into two stages: filtration and backwashing.

4.2.2 Precipitation method

The sedimentation method is based on the effect of gravity field, utilizing the density difference between suspended particles and water in wastewater to achieve organic separation of solid and liquid. If the density of suspended solids is lower than that of water, the suspended solids will float above the water, otherwise they will sink. The sedimentation method is mainly suitable for wastewater pretreatment and preliminary treatment stages.

4.2.3 Air flotation method

The air flotation method, as an intermediate treatment step, is generally used after coagulation to treat small diameter suspended solid particles. This method involves directly introducing air into the wastewater to directly precipitate tiny dispersed bubbles. Due to the presence of a large number of bubbles around, some hydrophobic small suspended pollutants will adhere to the bubbles, overcoming the influence of resistance and generating air flotation. When a large number of bubbles appear in the water, it represents the completion of separation. This method is suitable for the treatment of hydrophobic suspended particles. In order to improve the stability of foam, coagulants or surfactants can be added.

4.2.4 Adsorption method

The adsorption method has obvious advantages in color reduction and deodorization, but it requires a large amount of adsorbent and the adsorption cycle is not long. The influence of surface tension on an object can lead to uneven force on surface molecules, which cannot move and only allow solid molecules to adsorb gas molecules. The vast majority of suspended impurities choose porous oleophilic and high specific surface area solids as adsorbents, which can achieve ideal adsorption effects and enrich the adsorbed products. The adsorption method can also be combined with other wastewater treatment methods to achieve more significant wastewater treatment effects.

4.2.5 Membrane separation method

The membrane separation method can be divided into several categories based on the driving force of membrane separation, including natural dialysis, electrodialysis, reverse osmosis, ultrafiltration, liquid membrane technology, etc. According to the type of applied membrane, it can be divided into organic membrane treatment method and inorganic membrane treatment method. Membrane separation method selectively filters large molecular impurities through thin film materials with different pore sizes, and allows small molecular substances to pass through directly, achieving the goal of purifying water. The membrane separation method uses simple equipment, convenient regulation, small space occupation, and high treatment efficiency. However, the permeate membrane is easily contaminated, and due to the complexity of the operating system, regular disinfection treatment is required.

4.3 Biological treatment method

The biological treatment method fully utilizes the metabolic effects of microorganisms, decomposing and oxidizing organic matter that is dissolved or in a gel state in wastewater into relatively stable inorganic substances, thereby achieving the goal of purifying wastewater.

4.3.1 Activated sludge technology

As a widely used and mature aerobic biological treatment technology, the activated sludge method is treated under aeration conditions. Aerobic microorganisms proliferate in large quantities to form sludge like flocculent substances, which adsorb a large amount of organic matter in wastewater and decompose it, thereby achieving the goal of purifying water quality. However, the disadvantage of the activated sludge method is that it will produce a large amount of excess sludge, which is difficult to treat. Based on this, its research and development work should start from the source of pollution.

4.3.2 Biofilm Technology

Biofilm treatment technology is a means of treating organic wastewater by utilizing microorganisms attached to certain solid surfaces. Firstly, it adsorbs organic matter, which is decomposed by aerobic bacteria, and then undergoes anaerobic treatment. The aged biofilm is washed away using flowing water, and a new biofilm is grown, ultimately achieving the goal of purifying wastewater. This technology has great adaptability to changes in wastewater quality and quantity, and the remaining sludge amount is relatively small.

5. Development of Chemical Wastewater Treatment Technology

5.1 Physical methods

Firstly, analyze the physical treatment technology for chemical wastewater. Wastewater is treated by magnetic separation method, where magnetic seeds and coagulants are directly added to chemical wastewater. By utilizing the residual magnetism of magnetic seeds and coagulants, particles are attracted to each other, then agglomerate and become larger, and finally removed. This method improves the separation rate of suspended solids and effectively removes organic pollutants from wastewater using a magnetic separator; By utilizing sound wave technology, the frequency and saturation of ultrasound can be effectively controlled to effectively degrade and separate organic matter; Using non-equilibrium plasma technology, the plasma generated by high-voltage pulse discharge, glow discharge, etc. is used to oxidize and degrade organic pollutants in water.

5.2 Chemical method

In the process of sewage treatment, ozone oxidation can be used as a pre-treatment oxidation method in biodegradation treatment, which can turn pollutants into easily degradable organic compounds. This method has developed rapidly, but there are problems with low efficiency and high cost in ozone generation and treatment devices. The cost of treating wastewater with high concentration is too high, which is economically impractical. By using electrochemical oxidation technology, organic compounds that are difficult to degrade in water can be electrochemically oxidized into biodegradable substances using cyclic voltammetry in weak electrolysis tanks. High calorific value or high-risk waste liquids can often achieve ideal results through electrochemical oxidation. Supercritical method utilizes oxidants such as oxygen and ozone to completely oxidize organic compounds in a supercritical state, with relatively high reaction temperature and fast reaction rate. This is the application advantage of supercritical method. However, this type of process has very strict requirements for reactor materials, and materials with strong corrosion resistance and high temperature and pressure resistance have not yet been found, so its application is limited.

5.3 Biological treatment technology

When analyzing biological treatment technology, it is found through the analysis of the development of anaerobic technology that in addition to improving strains, the anaerobic process also needs to be improved, which has good economic advantages in removing organic matter with high degradation difficulty. As a highly toxic contact biological oxidation process, biofilm is not as effective in wastewater treatment as activated sludge method, and combining the two can improve the biochemical degradation efficiency. Biological adsorption and degradation technology utilizes the adsorption and biological effects of biological adsorbents to synergistically degrade biochemically difficult pollutants, effectively resisting strong shock loads and further improving pollutant removal rates.

6. Conclusion

In summary, there are many technologies applied to the treatment of wastewater in chemical enterprises. In order to improve treatment efficiency, further research is needed on biological treatment, chemical treatment, and physical treatment methods. Combined with the actual situation of enterprise wastewater treatment, different treatment methods can be combined to achieve more ideal treatment results, providing assistance for water resource protection work.

Post time: May-07-2024

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