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Sludge has high moisture content, contains a large number of pathogens and microorganisms and other pests, high levels of heavy metals and organic matter, if not treated before discharge, it will cause secondary pollution to the environment. Therefore, how to introduce a quick and effective sludge dewatering technology in sewage treatment plants needs to be solved urgently.
Sludge dehydration is not optimistic about the status of the urgent need to introduce rapid dehydration technology
With the increasing emphasis on sewage treatment in various countries and the continuous construction of new urban sewage treatment plants, the output of sludge has been continuously increasing. Therefore, the rapid and effective treatment of sludge has become urgent. Sludge has high moisture content, contains a large number of pathogens and microorganisms and other pests, high levels of heavy metals and organic matter, if not treated before discharge, it will cause secondary pollution to the environment. Under normal circumstances, the cost of sludge treatment up to the entire sewage treatment plant construction and operation costs of 50% to 60%, therefore, the sludge treatment is facing a huge challenge.
Sludge treatment principle is to achieve sludge reduction, stabilization, decontamination and recycling, of which sludge reduction is undoubtedly the key to sludge treatment and sludge disposal. Sludge reduction can be two ways, one is to reduce the content of organic matter in the sludge, the second is to reduce the sludge moisture content. The second route is simpler and easier to implement than the first route, both technically and financially. The purpose of sludge dewatering is to remove large amounts of water in the sludge, thereby reducing its volume and weight, in order to facilitate the sludge transport and further processing. Studies have shown that if the sludge moisture content from about 99.3% to 60% to 80%, the volume can be reduced to 1/10 ~ 1/15 of the original volume, greatly reducing the cost of sludge outbound and further The amount of leachate produced during the treatment. Although sludge dewatering theory and technology have achieved great development, sludge dewatering is still a major technical challenge for wastewater treatment projects.
This article summarizes the development characteristics and existing problems of sludge dewatering from two aspects of theory and technology. The microscopic process of sludge dewatering is analyzed emphatically from the perspective of drainage channel. It is concluded that the microscopic study of sludge dewatering can not combine the sludge solid particles with Water separated, but should be the drainage channel as a "link" to treat it as a whole, the microscopic study of sludge dewatering should focus on the drainage channel from the perspective of its clogging mechanism. Then, the status of sludge dewatering in WWTPs at home and abroad is emphatically introduced, and the essence, theoretical core and technical core of sludge dewatering are elucidated based on the multi-field joint effects. Finally, on the basis of summarizing the status of sludge dewatering, Direction of development.
Sludge Dehydration Theory and Technology
Sludge dewatering is a solid-liquid separation process, the basic theory is based on the theory of filtration, infiltration, sediment and other developed. The theoretical study of sludge dewatering began in the 1930s. From the 30s to the 60s of the 20th century, the theoretical research of sludge dewatering mainly lies in the founding of the basic theory. The concrete manifestation is the establishment of the basic concept and the establishment and amendment of the dehydration model. Cogger and Merker realized the concept of filter aid, relying solely on the difficulty of mechanically dewatered sludge and its unsatisfactory results. Later appeared flocculation dehydration, ultrasonic dehydration, electrodialysis dehydration and other technologies, in essence, belong to the category of filter aid.
In the 1970s and 1990s, scholars gradually turned their research focus from the dehydration model to the physicochemical properties of sludge. Based on the analysis of physical properties, the influencing factors of sludge dewatering performance were discussed. At the same time, sludge conditioning and modification technology began to develop. The physicochemical properties of sludge, such as the size, shape, composition and the like of solid particles, have drawn much attention. Based on the study of sludge physical properties, the technology of sludge conditioning and modification based on physics, chemistry and biology has started to develop. However, the study of sludge conditioning and modification in this period remains in the pursuit of macroscopic improvement of sludge dewatering performance and efficiency, and lack of mechanism analysis of the modification and modification at the microscopic scale.
Since 1990s, on the basis of continuous development of sludge conditioning and modification technology, electroosmosis technology, flocculation technology and ultrasonic technology have drawn attention. Mechanical dewatering instead of natural drying has become the main water treatment plant dehydration technology, but due to the traditional mechanical dewatering effect is not satisfactory, there are many new technologies and many shortcomings can not be overcome in time, many scholars try to solve the problem from a micro scale, sludge The research of water is getting more and more attention.
In fact, as early as 1956, Heukele Kian and Weinberg proposed to separate the water in the sludge into two types of free water and bound water, but such a simple classification obviously can not satisfy the study of sludge dewatering. Tsang et al. Classified the water in the sludge into free water, interstitial water, adsorbed water and bound water according to the contact relationship between the sludge solid particles and water.
In the next 20 years, many scholars have carried out a series of theoretical and experimental research on the water in sludge, and have made a great deal of achievements, which are summarized in several aspects: the distribution of water in sludge, combined with the water content test Technology, combined with water on the sludge dewatering performance. Based on the previous studies on the bound water in sludge, some scholars have made good use of the combined water as a "bridge" to improve the sludge dewatering performance.
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