Analysis of Sludge Dewatering Technologies for Wastewater Treatment in Chemical Enterprises

Thread Content

Chemical production generates large amounts of sludge, which is composed of substances that cannot be degraded in wastewater treatment processes as well as dust generated during production. As China places increasing emphasis on environmental issues, the requirements for wastewater treatment in the chemical industry are also rising, forcing chemical companies to handle sludge properly. In the past, chemical companies used traditional natural air-drying methods for sludge dewatering; as production efficiency improved, this method proved to be far too limited and outdated. Currently, the sludge dewatering technology adopted by most chemical enterprises is mechanical dewatering. However, the efficiency, effectiveness, and treatment costs of mechanical dewatering still need improvement, which is precisely the focus of this article. 1. Analysis of wastewater treatment systems in chemical enterprises. Generally, in chemical enterprises, wastewater is highly prone to forming gaseous pollutants. When chemical industry wastewater is discharged, it inevitably comes into contact with and reacts with other liquids or gases, such as ammonia and hydrogen sulfide. The situations involved include the following: (1) The sealing of production equipment is compromised, or the operator performs improper operations, which can easily lead to material leakage, with raw materials entering the sewage treatment pipelines directly. (2) The sewage system, due to continuous operation in high-temperature environments, causes flammable gases to evaporate, resulting in mixed ** or toxic gases. (3) During the absorption and desorption processes, gases enter the waste discharge channels; for example, in chlor-alkali plants, when hydrogen chloride is being absorbed, leaks may occur at the liquid outlet of the absorption tower, allowing the acid to enter the sewer system where it mixes with air to form **. Secondly, the range designed in case of danger is quite large. Wastewater treatment systems generally consist of a network of pipes and channels. It takes some time for wastewater to enter these systems, and the extensive network of pipes allows hazardous substances to spread over a wide area; in the event of an explosion or gas leak, this can lead to a chain reaction. Characteristics of wastewater from the coal chemical industry: The coal chemical industry makes extensive use of water resources, and its wastewater originates primarily from the coal coking process and gas purification processes, as well as from other related chemical product recovery processes. Based on the current research and analysis, the wastewater from the coal chemical industry is problematic; its main pollutants are phenols and ammonia. On one hand, the amount of wastewater generated is large and its utilization rate is low. On the other hand, this wastewater is highly toxic with high pollutant concentrations, making it difficult to decompose using existing technologies. When discharged into the environment, it poses a serious threat to humans, animals, and crops. 2. Sludge dewatering technologies in chemical enterprises: Traditional sludge dewatering technologies require very high environmental standards, which is why they are generally suitable for areas with dry climates. However, even when the drying time is extended, these traditional technologies still fail to achieve complete sludge dewatering, resulting in the accumulation of large amounts of toxic substances. The specific procedure involves using natural drying methods to concentrate the sludge, transporting it to a drying facility where it dries naturally, and finally disposing of the dried sludge through burial or incineration. Generally speaking, drying plants using traditional sludge dewatering technologies need to be located in areas with ample lighting and flat terrain; on one hand, a spacious flat area is required for the natural drying of sludge before concentration processing takes place. On the other hand, it is necessary to lay gravel in the drying plants to prevent harmful substances in the sludge from seeping into the soil and causing contamination. Typically, the gravel in drying plants must be over 35 millimeters in size, and the water supply pipes are installed beneath the gravel. The natural drying of sludge usually takes three to five weeks; of course, the exact time depends on the climate and lighting conditions in the drying facility. Mechanical dewatering technology: When treating sludge using mechanical dewatering methods, it is necessary to carry out preliminary treatment on the sludge first, that is, to concentrate it in order to reduce its volume and improve its dewatering properties. The dewatering capabilities of the sludge can generally be enhanced through the use of chemical reagents or heat treatment; common chemical reagents include inorganic salts and coagulants. After that, the sludge can be treated through mechanical dewatering methods. Filtration and centrifugation are two common techniques for mechanical dewatering of sludge. In filtration, filter paper or filter cloth is used to create a filtering layer, through which the sludge is filtered; this process separates the sludge into two components: solid sludge and liquid wastewater. The liquid portion then needs to be treated using wastewater purification techniques, while the solid sludge requires further drying ； Since the various components in sludge have different densities, the centrifugation method relies on this characteristic to separate the sludge. As the centrifuge rotates at increasingly high speeds, different substances within the sludge are thrown to different areas of the centrifuge. Thanks to the various discharge outlets available in the centrifuge, it is possible to separate the sludge from the wastewater separately. Both the filtration method and the centrifugation method require the use of numerous mechanical devices. In terms of filtration efficiency, the filtration method yields more significant results, as it enables effective sludge dewatering. Statistical analysis shows that this method can remove approximately 70% of the wastewater. However, it requires a large number of operators, and its operation is somewhat complex. The dewatering efficiency of the centrifugation method can reach 80%, and it is highly automated; no extensive equipment is required. However, the cost of using this method is high, and during the initial processing stage it is necessary to concentrate the sludge efficiently in order to reduce its volume as much as possible. Flocculation dewatering technology takes advantage of the fact that sludge contains negative ions; by continuously compressing the dual-layer charge of the sludge particles, it enables rapid separation of the liquid and solids in the slurry. Additionally, it utilizes the sedimentation properties of the sludge to reduce its water content. Keratin additives are an effective way to enhance the adsorption capacity of flocculants. Generally, positive and negative charges react with each other in slurry, and the main function of keratin additives is to form larger flocs, thereby causing the sludge particles in the slurry to become destabilized quickly – this is the best method for accelerating sedimentation rates. At the same time, by utilizing adsorption bridging, the colloids in the wastewater were reduced to about half of their original level. Changing the temperature of wastewater can adjust its pH to a certain extent, thereby affecting the effectiveness of sludge dewatering techniques from a chemical perspective. On the one hand, it can increase the settling rate; on the other hand, it can adjust the pH value in wastewater sludge to a range suitable for carrying out sludge dewatering techniques. Generally, this range is between 5 and 7, which creates an optimal environment for the implementation of such dewatering techniques. The amount of flocculant used is also a key factor affecting the efficiency of wastewater treatment; it is necessary for relevant personnel to carefully examine the sedimentation behavior and composition of the sludge in order to improve the effectiveness of flocculation and dewatering techniques. 3. Development trends in sludge dewatering technology. The 21st century is an era of rapid development and widespread application of biotechnology. There are many research achievements in the biological field, and those in the field of microorganisms can be applied to wastewater treatment and sludge dewatering in chemical enterprises. Integrating biotechnology into sludge dewatering technology can improve the efficiency and effectiveness of sludge dewatering. Different microorganisms have distinct characteristics, and the sludge from chemical plants contains a large amount of organic matter, an environment that is very suitable for microorganisms to thrive. Microorganisms can break down the large organic molecules in sludge into smaller ones, converting toxic polymers into small molecules that are non-toxic or of low toxicity. Furthermore, microorganisms can improve the dewaterability of sludge, making the filtration step in mechanical dewatering methods and the centrifugation step in centrifugal methods easier to carry out. In short, the future trend in sludge dewatering technology will surely be the organic integration of biotechnology, as using biotechnology enables more efficient and cost-effective operations. The by-products resulting from sludge dewatering will find wider applications, enabling resource reuse. The sludge generated by chemical enterprises contains a high amount of organic matter and various nutrients; after being treated through processes to render it non-toxic and to reduce its toxicity, the dried sludge has great value for utilization. Now, chemical companies are using it for fertilizing farmland, and practice has shown that its fertilizing effect is excellent ； Some chemical companies further process the dried sludge so that it can be burned as fuel, providing energy for these chemical enterprises ； Dried sludge is an excellent filling material that can be used to fill foundations and reinforce buildings. In summary, as industrial standards continue to improve, the capabilities of chemical enterprises will also enhance, and there will be an increasing range of ways to reuse sludge after dehydration. Chemical enterprises will thus be able to make better use of the value of waste recycling and achieve higher economic returns. Research in recent years has shown that the organic wastewater generated by the coal gasification industry holds great value for recycling. This not only requires companies to have a stronger awareness of environmental protection but also necessitates technological methods to turn waste into resources, thereby making maximum use of available resources, reducing pollution, and converting waste into valuable assets.