Drying Technology
Keywords:sludge drying treatment、urban wastewater treatment plants
Municipal sludge is usually the product of biochemical treatment of industrial wastewater and municipal wastewater. It has complex components and contains a variety of organic matter. It is a reusable resource. For sludge treatment, the traditional treatment methods are landfill and composting. In addition, there are incineration methods. Although incineration methods have many advantages, there are also many problems, which will not only cause environmental pollution, but also waste resources. Therefore, at present, the treatment of urban sludge is actively promoting drying technology, realizing the development of sludge recycling and achieving the goal of energy conservation and consumption reduction.
Sludge is a by-product of sewage treatment, accounting for 0.3% - 0.5% of the total sewage, but the treatment cost of sludge is as high as 30% - 40%. Comprehensive analysis shows that the management cost and investment cost of sludge treatment can reach more than 50% of the total investment. There are many difficulties in sludge treatment, such as high water content, many microorganisms, parasitic eggs, etc. if it is not treated carefully, secondary pollution may be induced. Nowadays, the state pays more and more attention to the ecological environment, urban domestic sludge treatment has received more attention, and more and more relevant workers have invested in its research.
Basic characteristics of sludge
Physical characteristics. Sludge refers to all kinds of solid precipitates produced in the process of water and muddy water treatment. During the process of water and muddy water precipitation, urban domestic sludge will form different polymerization products in the water. It is distributed in various pipelines in the city and does not have a specific shape and is difficult to be treated. Chemical characteristics. Domestic sludge is rich in microorganisms, including not only organic matter, heavy metals, sediment, animals and plants, but also salt, parasitic eggs, pathogenic microorganisms and other substances. Sludge is rich in a variety of trace elements, which can maintain the normal growth and development of plants and improve soil structure. Biological characteristics. The solid costs in sludge are mainly organic residues, bacteria, inorganic particles, colloids, reagents, etc. the components are complex, and the trace elements with utilization value include nitrogen, phosphorus, potassium and so on. Calorific value characteristics. Although sludge has many harmful substances, it also has biological elements that can be used as nutritional elements, so it has the characteristics of combustion. If the water content of sludge is low, the calorific value of sludge will become higher and can be burned, which provides a basis for dry incineration.
Sludge disposal status
Land use. Land use treatment will be carried out during sludge disposal, which is divided into direct and indirect. Direct land use has the characteristics of simplicity and convenience and low cost, but it may leave environmental problems. Direct utilization has certain disadvantages. It will be directly used as agricultural land, and the harmful substances are not conducive to the growth of crops. Indirect utilization of sludge is the application of sludge to farmland after certain treatment, which can provide necessary nutrition for crop growth and improve soil structure. security landfill. Sanitary landfill is a scientific innovation based on the most traditional sludge treatment method. This treatment method has less investment and rapid effect, and does not need too many technical requirements in the early stage. However, in the process of actual landfill, the municipal sludge contains harmful substances, which will cause groundwater pollution; The rapid growth of sludge resources leads to the lack of land resources; Finally, methane may appear during landfill, which may lead to explosion if not treated reasonably. Put it into the sea for treatment. Marine landfill is a simple and low-cost treatment method, but it may have an adverse impact on the marine environment. It only transfers the land problem to the sea. The impact of sludge into the sea on the marine ecological environment is huge
Therefore, all countries strictly prohibit the release of urban sludge into the sea to avoid marine pollution. Digestion treatment. Anaerobic and aerobic digestion are the two main means of digestion technology. After high-temperature treatment of sludge, it can reduce the water content, stabilize the properties and kill insect eggs and bacteria. However, in practical application, aerobic digestion technology requires a lot of cost and energy consumption. Anaerobic digestion produces methane, which is recognized by people. With the continuous development of science and technology, anaerobic and aerobic digestion technologies are also being innovated and integrated, which greatly improves the applicability and effectively increases the use of processed products. Dry incineration. There are two ways of sludge incineration: ① dehydration incineration is the direct treatment of sludge incineration, which requires high energy consumption and other auxiliary materials; ② The sludge is dried and then incinerated. At present, the second method is more widely used and more used abroad, mainly because it covers a smaller area, has faster application speed and does not need long-term storage. The time of applying this technology in China is short, there is a lack of perfect treatment measures, and further research and development is needed.
