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How to deal with high-salt wastewater of pharmaceutical and chemical industry

Time:

2022-03-21 10:40


In recent years, with the rapid development of my country's industry, industrial water consumption has also increased, so industrial wastewater is also increasing year by year. Among them, the increase in the amount of wastewater in the pharmaceutical and chemical industry is particularly obvious. During this process, pharmaceutical and chemical wastewater also gradually showed the characteristics of difficult degradation, high salinity and complex composition, coupled with the continuous development of production technology. The difficulty of wastewater treatment is greatly increased, which poses a great threat to our country's environment.

1 Definition of high-salt wastewater

The so-called high-salt wastewater refers to the use of reverse osmosis technology to recycle most of the fresh water from the wastewater that meets the discharge standard, and the resulting concentrated salt wastewater is treated with evaporation technology or other various desalination technologies. Concentrated waste liquid whose mass fraction of TDS (that is, total dissolved solids) exceeds 8%, which is difficult to carry out biochemical treatment, or high COD content and TDS (that is, total dissolved solids) directly generated in the entire production process of pharmaceutical and chemical industry. Wastewater with a fraction of more than 15% that is difficult to biochemically treat. In order to completely solve the pollution problem of this type of high-salt wastewater, it is not only necessary to effectively reduce the COD content in the high-salt wastewater, but also to separate the soluble salts in the wastewater. In order to truly achieve the expected treatment target of high-salt wastewater.

2 Conventional treatment technology for high-salt wastewater from pharmaceutical and chemical industries

At this stage, in the production process of pharmaceutical and chemical substances, a large amount of acidic or alkaline substances will be used, so a large amount of inorganic salts will be produced after the neutralization of the two. The inorganic salt solution is subjected to washing treatment, and finally a large amount of high-salt wastewater from pharmaceutical and chemical industries is formed. According to relevant data, the total salinity of pharmaceutical and chemical high-salt wastewater exceeds 100,000 mg/L, and the CODer content exceeds 50,000 mg/L. After mixing with other dilute wastewater, the total salinity of pharmaceutical and chemical wastewater is extremely high. In most cases, it will exceed 30,000 mg/L, and the CODer content will also exceed 15,000 mg/L. It can be seen that ordinary biochemical treatment methods have been difficult to meet the current demand for high-salt wastewater treatment in pharmaceutical and chemical industries. This is because on the one hand, the total salinity in pharmaceutical and chemical wastewater is too high, and on the other hand, the CODer content in wastewater is also too high. Therefore, the osmotic pressure outside the microorganisms is greatly increased, so that it is difficult for biological strains to grow and survive in a high salinity environment. According to relevant data at home and abroad, the current conventional treatment methods of pharmaceutical and chemical wastewater are mainly: first, applying multi-effect distillation device or MVR distillation technology to remove salt in the front-end link; second, applying biochemical treatment method in the back-end link It is treated by means of combining with method, biochemical treatment method and physicochemical treatment method, electrochemical treatment method and biochemical treatment method. Below, this article will focus on the distillation technology and dilution technology.

2.1 Distillation technology

The biggest application advantage of using distillation technology for desalination of pharmaceutical and chemical wastewater is that the water quality of the fresh water obtained by the final treatment is better. At present, most of the distillation technology of pharmaceutical and chemical wastewater is developed based on seawater desalination technology. In essence, distillation technology uses thermal energy to evaporate the solution, and then cool the water vapor. Realize the recovery of fresh water. Due to the continuous development and progress of science and technology, distillation technology is also constantly innovating. Currently, the more mature applications include multi-effect distillation device and membrane distillation technology.

2.1.1 Multi-effect distillation unit

This distillation device was first used in the desalination of seawater, and at this stage, the research on it in the field of water treatment is also increasing. Since the multi-effect distillation device is located in a low temperature environment, it has a very significant energy saving advantage. In recent years, the development has been very rapid, the specifications of the device have gradually expanded, and the application cost has gradually decreased. The current main development trend of the multi-effect distillation unit is to further improve the water-making performance of the unit, use cheap materials to reduce the cost of the project, increase the temperature of the operating environment, and improve the heat transfer efficiency of the unit.

2.1.2 Membrane distillation technology

This kind of distillation is a brand-new separation technology, which refers to a new type of membrane separation process that organically integrates the traditional distillation process with the membrane separation technology. Compared with other membrane separation processes, the main advantage of membrane distillation technology is that the effect of solution concentration is very small. Researchers such as Schofield conducted related experiments on salt solutions, and finally proved that the saturated vapor pressure in 5mol/L sodium chloride solution was only 25% lower than that of pure water, and 30% by membrane distillation technology. It can be seen that compared with other various membrane separation processes, membrane distillation technology has a stronger treatment effect on high-concentration aqueous solutions. Researchers such as Zhao Jing have found that when using VMD (that is, vacuum membrane distillation technology) for the treatment of reverse osmosis concentrated water, although the flux of reverse osmosis concentrated water has declined in the entire concentration process, its salt removal rate is not high. At the same time, some high-salinity wastewater will also be generated, and its salinity exceeds 15%, which is more than 4 times that of reverse osmosis concentrated water. Due to the unique performance of membrane distillation technology, it has some obvious advantages compared with other separation technologies. Wait. It can be seen that the concentrated brine treated by distillation technology will obtain part of the high-salinity wastewater while obtaining part of the fresh water, so it needs to be further desalinated to fundamentally realize the soluble salts. separation of matter.

2.2 Dilution technology

The pharmaceutical and chemical wastewater treatment method is to directly drink clean water to dilute the pharmaceutical and chemical wastewater with high salt concentration until the wastewater is diluted to a salt content of about 8000mg/L and a CODer content of about 6000mg/L. biochemical treatment for further treatment. Due to the application of a large amount of clean water in the treatment process of the dilution technology, on the one hand, the industrial water consumption will increase significantly, thus causing a serious industrial water waste problem; on the other hand, it will also greatly increase the industrial investment and operating costs. It greatly affects the market competitiveness of pharmaceutical and chemical products. For details, please contact Shuibao or refer to http://www.dowater.com for more related technical documents.

3 New treatment technology for high-salt wastewater from pharmaceutical and chemical industries

At present, based on the new characteristics of pharmaceutical and chemical wastewater, new treatment technologies have been continuously developed, including new treatment technologies that combine iron-carbon devices and PSB biochemical treatment systems. This technology combines the application of iron-carbon device and Fenton reaction in the front-end link. Under normal circumstances, the CODer elimination rate can reach 40%-60%, and the B/C will be increased by 0.1-0.3, while in the back-end link, it is applied simultaneously. The A/O biochemical system and PSB biochemical system are used, and the salt-tolerant photosynthetic bacteria are used to make them work normally under the conditions of wastewater with salinity of 30,000-60,000mg/L and CODer content of 6,000-10,000mg/L, so that the final effluent It can reach the third-level treatment standard in the relevant national sewage discharge standard (GB8978-1996), and the optimal situation is to meet the national first-level treatment standard.

3.1 Iron carbon device

Iron-carbon device, also known as continuous high-activity iron bed, in which the new iron-carbon will be filled into iron-carbon tower under normal circumstances. It is a sewage treatment device belonging to the electrochemical treatment method. In most cases It will be applied to industrial sewage treatment, especially those high-concentration sewage that are difficult to be degraded by biochemical treatment methods, such as organic substances that carry benzene rings, chromaticity and have toxic effects on organisms. With the rapid development of the industry, the difficulty of handling naps is also increasing. As we all know, biochemical treatment is one of the most common, low-cost and effective sewage treatment methods, but it cannot be applied to various sewage conditions. Many industrial wastewaters are not only highly concentrated, but also difficult to be treated by biochemical treatment methods, and even hydrolysis treatment methods cannot be solved. At this time, various front-end and back-end treatment methods must be used, and iron beds just meet this treatment demand. However, although the conventional iron bed has a high treatment effect, the problems such as passivation of the filler and scarring have not been well solved, which greatly limits the popularization and application of this method.

According to the actual properties of the new iron-carbon, the redesigned and developed continuous high-activity iron bed has two major advantages: First, the continuous high-activity iron bed can always maintain the activity of the filler in the iron bed, and no longer need the iron window like the previous one. The filler also needs to be activated regularly and regularly, so this device has good reliability and stability. At the same time, after practical application, it is found that the continuous high-activity iron bed greatly avoids the long-term sewage treatment process. When the problems of passivation and scarring occur, the operation effect of the device is better; secondly, due to the integrated design, the structure of the device is very compact, and the sewage treatment effect is also very significant, and the elimination rate of CODer can reach 40%- 60%, the B/C will increase by 0.1-0.3, and the chromaticity can also be removed by about 80%-90%. The innovation of the micro-electrolysis pretreatment technology is mainly manifested in two aspects: first, the filler uses a flat shape Second, a special diversion system and inner and outer cylinders are designed, so that the sewage can be automatically recycled in the inner and outer cylinders. In general, the iron-carbon device has the advantages of long service life, strong seasoning activity, small footprint, high processing efficiency, good processing effect, high activity retention time, low operating cost, and no passivation and scarring problems, etc. many advantages.

3.2PSB biochemical treatment system

PSB biochemical treatment system, also known as salt-tolerant photosynthetic bacteria, the PSB bacteria configured in this biochemical treatment system are bacteria with a certain color due to the presence of photosynthetic pigments. The so-called PSB (PhotoSynthetic Bacteria), that is, photosynthetic bacteria, is composed of a group of prokaryotes with a primitive photosynthetic system and capable of photosynthesis without releasing oxygen under anaerobic conditions. Under normal circumstances, the following seven types of PSB atmosphere can be classified as obligate aerobic bacteria containing bacteriochlorophyll, Helicobacteriaceae, multicellular filamentous green bacteria, green sulfur bacteria, purple non-sulfur bacteria, and outflow red bacteria. Spirobacterium and Chromobacteriaceae.

The main advantages of using the PSB biochemical treatment system are: first, high conformability and strong impact resistance, the device is filled with spherical fillers composed of special fibers, and the sludge storage capacity is large. At the same time, the clarification zone is also maximized. It ensures that the sludge is lost as little as possible. Therefore, the high load capacity of the device is guaranteed to a large extent, and the compliance ability and impact resistance of the oxidation bed are also effectively enhanced, so as to ensure the operation of the PSB biochemical treatment equipment. It creates a good operating environment; second, the treatment efficiency is high and the treatment effect is good. The microbial flora in the anaerobic, aerobic and facultative zones generated in the circulating biochemical zone are very rich and diverse, not only have good oxidation, but also At the same time, it also has excellent hydrolysis function, so that the substances that are difficult to be biochemically treated can be sublimated after the ring opening, and at the same time, the substances that can be biochemically treated can be better biochemically treated after chain scission. Then, with the effective interception treatment in the clarification zone, the biochemical treatment system has high treatment efficiency and good treatment effect; third, the energy saving effect is good. The vertical oxidation tank is a deepening structure corresponding to the horizontal flow direction. The vertical flow direction is formed by the air-lifting function of aeration and the special structure of the sealing cap and the guide tube. It does not need external power. The aeration head can be placed in a shallow layer, and a low-pressure fan is used. Therefore, the normal operation of the system can be guaranteed as long as a sufficient amount of wind is ensured. Therefore, the energy saving effect of the biochemical system is good. The elimination rate of CODer can reach 70%-80%, and the elimination rate of ammonia nitrogen can reach about 50%. It can also remove about 50%. In general, the concentration of the influent water is controlled at about 6000-10000mg/L, and the salt content is about 45000mg/L. Therefore, it can be said that the biochemical treatment equipment has high-strength salt tolerance and High concentration resistance; Fourth, the biochemical treatment equipment also has many advantages such as small footprint, small scale and low kinetic energy consumption. The footprint of the PSB biochemical treatment system is only 1/4-1 of that of the activated sludge treatment method. /5 or so, in addition, the maintenance and management of the equipment is very convenient, and it is less affected by seasonal changes.

3.3 Application effect

At present, in the treatment process of high-salinity wastewater in the pharmaceutical and chemical wastewater industry, the continuous high-activity iron-carbon bed and the PSB biochemical treatment system have passed the actual sewage treatment application and achieved good application results. Among them, Zhejiang Beide Pharmaceutical Effective Company has applied a new treatment technology that combines this carbon device and PSB biochemical treatment system. The equipment involved includes a new iron-carbon device, PSB biochemical treatment system, and Fenton reaction. And A/O biochemical treatment system for the treatment of pharmaceutical wastewater. The average daily wastewater treatment volume is 500T, the CODer content in the influent water quality is 20,000mg/L, and the total salt content is 30,000mg/L. After applying the new treatment technology combining iron carbon device and PSB biochemical treatment system, the CODer content dropped to below 500mg/L, thus meeting the tertiary treatment standard in the relevant national sewage discharge standard (GB8978-1996).

4 Conclusion

To sum up, doing a good job in the treatment of pharmaceutical and chemical wastewater is of great significance to protect the ecological environment and protect people's physical and mental health. Therefore, in view of the increasingly complex pharmaceutical and chemical wastewater, the relevant researchers in my country must actively absorb and learn from the advanced pharmaceutical and chemical wastewater treatment technology experience at home and abroad according to the actual wastewater situation, in order to develop more scientific and appropriate treatment technology for effective treatment. Pharmaceutical and chemical wastewater. (Source: Environment and Development Author: Hu Guoyun, etc.)