In recent years, the coal chemical industry in China has developed rapidly, especially in this era of advocating water conservation. Coal chemical industry is beneficial to sustainable development and has attracted people's attention. Therefore, people pay great attention to environmental problems while considering the treatment methods of coal chemical wastewater.
Firstly, the problems existing in coal chemical wastewater treatment in China are analyzed.
At present, the highest proportion of wastewater from coal chemical enterprises in China is high-concentration gas washing wastewater. These gas washing wastewater contains a lot of harmful substances such as phenol and chloride, which has caused great harm to the environment. In addition, according to the test, the COD content in the wastewater is also kept at about 50,000 mg/L, and the chloride content is about 200 ~ 500 mg/L. In addition, most of the organic substances contained in the wastewater have a great impact on the environment because they are difficult to degrade. Generally speaking, the treatment of coal chemical wastewater in China is not perfect at present, which is mainly reflected in the following aspects:
1. Problems in pretreatment stage
In the process of coal chemical wastewater treatment, oil separation method is usually used for pretreatment, which is a traditional pretreatment method in China. Because the excess oil will directly affect the effect of the biochemical treatment stage, the excess oil is separated by oil separation to ensure the effectiveness of the biochemical treatment stage. However, this method has advantages and disadvantages, and there is no way to recover the collected oil.
2. Problems existing in biochemical treatment stage
In general, after pretreatment, coal chemical wastewater will be treated by anoxic-aerobic biological method. However, because the wastewater from coal chemical industry contains some polycyclic and heterocyclic compounds, it is difficult for ammonia nitrogen and COD in the discharged wastewater to meet the specified standards after anoxic-aerobic biological treatment, so there are also some defects in the biochemical treatment stage.
3. Problems existing in the advanced treatment stage
After pretreatment and biochemical treatment, advanced treatment is carried out. After the previous treatments, the indexes of ammonia nitrogen and COD in coal chemical wastewater have decreased, but they are still hindered by the degradation of organic matter to a great extent, resulting in a certain chromaticity of the treated wastewater, and the indexes of COD and ammonia nitrogen can not meet the discharge standards. However, after the above explanation, we can see that deep treatment is a necessary process, and traditional treatment methods are difficult to achieve considerable results. We should not be limited to the traditional advanced treatment methods, but should strive to innovate on the original basis.
Second, the countermeasures for various problems in China's coal chemical wastewater treatment
Through the above analysis of the problems existing in coal chemical wastewater treatment, we can know that although a large number of new scientific and technological means have appeared in coal chemical wastewater treatment in China in recent years, they all have certain advantages and disadvantages to a great extent, which need people to weigh. After the author's summary, the countermeasures are as follows:
1. Pretreatment stage-air flotation instead of oil separation.
In traditional pretreatment methods, people usually adopt the method of oil separation, which can greatly promote the effectiveness of biochemical stage, but people are often worried about the recovery and utilization of separated oil. Therefore, after years of development, the oil separation method is gradually replaced by air flotation. At present, in the treatment of coal chemical wastewater, air flotation is mainly used to remove oily substances contained in wastewater, and then it is effectively recycled. In addition, this method also has a certain blasting effect on the subsequent biochemical treatment.
2. Biochemical treatment stage-replacing aerobic biological method with biochar.
In the previous biochemical treatment stage, aerobic anoxic biological method is usually used to treat wastewater, and the ammonia nitrogen compounds and COD indexes in the wastewater discharged by this method are difficult to meet the standards, so biochar is considered to replace aerobic biological method. The main principle of biochar is that a certain amount of powdered activated carbon is added to the influent of biochemical process, and the carbon-containing sludge is mixed in the explosion tank, discharged into the sludge concentration tank, and finally dewatered in the sludge dewatering equipment. A layer of activated sludge is attached to the surface of powdered activated carbon in the explosion tank, which contains large specific surface area and strong adsorption capacity, so the adsorption capacity of sludge is greatly improved, especially at the critical point of activated sludge and powdered activated carbon, with high dissolved oxygen and degradation mechanism concentration, which provides a strong help for COD degradation.
3. Advanced treatment stage-advanced oxidation treatment process
Coal chemical wastewater usually contains high content of refractory organic matter, which will have a very serious impact on the later biochemical treatment. Therefore, advanced oxidation method is considered for advanced treatment, which can produce a large number of free radicals in wastewater, and then effectively degrade a large number of refractory organic compounds.
Although there are mature treatment methods for compound-free wastewater at all stages, it is difficult to achieve ideal results by any single treatment method. For the simplest example, in a single biological oxidation process stage, the discharged wastewater will contain some refractory organic substances, and the COD index is high, so it is difficult to meet the national discharge standards. At this time, adsorption method can be used to remove COD adsorbed on the surface, but at the same time, regenerated adsorbent will be produced, causing serious secondary pollution problems. At this time, the catalytic oxidation method can effectively degrade the bound organic matter, but in the actual operation process, this method will produce higher treatment costs. Therefore, at present, almost no wastewater treatment method can completely achieve the overall effect. In the actual treatment process, more consideration should be given to the combination of various ways, and their respective advantages should be used to optimize the treatment effect of coal chemical wastewater. This is not only the most ideal coal chemical wastewater treatment scheme at present, but also the development direction of coal chemical wastewater treatment industry in the next decade.
Third, the conclusion
According to the above analysis, we can find that the current energy structure of our country is mainly reflected in the lack of oil and gasoline and the abundance of coal, which is also the basic status quo of our country at this stage. These characteristics directly determine that coal resources have become the largest resource channel in China. For coal chemical industry, their existence can form a variety of new products from the perspective of coal, effectively improving the utilization mode and value of coal resources. In addition, the strengthening and improvement of coal chemical wastewater treatment methods have made great achievements in ecological environment and further promoted the economic development of coal chemical industry.
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