Under the new normalcy of the environmental protection industry, China has promulgated a series of national policies and industry standards. Among them, "Water 10" clearly defined that the existing sludge treatment and disposal facilities should be basically completed before the end of 2017 and that urban sewage sludge of prefecture level and above Harmless disposal rate should be applied before the end of 2020 to achieve more than 90%. Driven by favorable policies and high growth factors, the sludge treatment and disposal industry is expected to break the bottleneck and enter the fast lane.
Pathfinder sludge treatment technology four principles help green treatment
Nowadays, a large amount of domestic sewage is generated daily in the city. When the domestic sewage is treated, a large amount of excess sludge will be generated. This part of residual sludge exudes odor and contains a large amount of parasites, pathogens, Salts and other substances, and a variety of heavy metals such as chromium, mercury, copper and so on.
In addition, the remaining sludge also contains two VA British, radionuclides and PCBs and other toxic and refractory substances. If untreated directly discharged, it will endanger the soil, water quality, plants and animals as well as human health. The following sections discuss the status of remaining sludge treatment and disposal in urban WWTPs and the general principles for disposal of excess sludge for reference.
Sludge land use is relatively early, in recent years, sewage treatment plants on the sludge treatment technology continues to mature, sludge production in recent years is also significantly increased, the proportion of sludge in agriculture is also gradually increased. According to the latest data show that in the city's sewage treatment plant sludge on the proportion of agricultural sludge is still relatively large, has become the main treatment of sludge treatment, but the sludge of agricultural use is a certain risk, because our country The current level of research and research system is not yet complete, the impact of sludge on agricultural crops may have not been fully studied, nor accurate data, the main source of these data is more complex, the need for long Time field trials, resulting in a lack of data.
Although there are many harmful substances in the remaining sludge in domestic sewage, at the same time, it also contains abundant elements such as potassium, phosphorus and nitrogen. These elements play a very good role in the growth of plants and can improve the soil structure, Realize the material and energy recycling. Therefore, the sludge treatment and disposal technology is particularly important, how to minimize the hazards of sludge under the premise of as much as possible on the sludge useful substances for recycling and recycling, there is a very good environmental protection Significance.
Status of sludge treatment and disposal
Throughout our country for the study of sewage treatment, sewage treatment industry in China pay more attention to sewage treatment, but more neglect of sludge treatment. And because of the existence of less sewage treatment plants in our country, and the resulting smaller amount of sludge, the treatment of excess sludge has not been given high priority.
Nowadays, with the rapid increase of urban population in our country and the development of society and economy, the amount of urban sewage produced has sharply increased. As the amount of domestic sewage treated increases, the pressure to deal with the sludge increases . With the development of the city, the problem of sludge disposal has become a major problem that restricts the development and construction of the city. Some cities even have the phenomenon of "Sludge Besieged City".
As some of the early WWTPs had flaws in the wastewater treatment facilities and processes, it was common to divide the wastewater and sludge treatment into two separate units. Pay attention to the sewage treatment unit to obtain a higher rate of sewage treatment, but no strict regulation of sludge emissions. Some more treatment plants, in order to save costs and time, directly ignore the sludge treatment, directly through the simple stacking, landfill and free disposal of sludge out of the way. Due to the natural degradation of sludge for a long time, no degradation of the previous sludge, the new sludge piled up and the sludge on the land and the surrounding environment will have pollution, over the long run, will have a serious impact on the city's ecological environment , Thus limiting the city's development.
Sludge treatment and disposal of the general principles
The remaining sludge treatment and disposal of urban sewage treatment plants generally follow the four principles, namely reduction principle, harmless principle, stabilization principle and resource principle. The ultimate goal of sludge treatment is to achieve the sludge "resource", and "detoxification" is the focus of the sludge treatment process. Sludge treatment by technology to make the sludge from waste into usable material, can fundamentally solve the problem of sludge pollution to the environment. The following four principles of sludge disposal will be further elaborated.
1 reduction principle. The specific requirement of the principle of reduction is to reduce the volume of the sludge by sludge reduction technology, so as to reduce the time and cost of disposing of the sludge. Sludge reduction is generally accomplished by burning and stabilizing it to reduce its mass and to reduce the sludge volume by dewatering and concentrating. Techniques to achieve reduction generally include the ozone method, ultrasonic technology, chlorination and so on.
2 harmless principle. The specific requirements of the principle of harmlessness is to use reasonable engineering techniques to remove the harmful substances in the sludge, and to take compulsive decomposition and disinfection methods so that the treated sludge will not have an impact on the environment. After the sludge is prevented from being in contact with other substances, part of the pollutants are transferred through other substances to ensure the safety of discharged sludge while also protecting the environmental sustainability and stability.
3 stabilization principle. The principle of stabilization is that, according to the characteristics of biological anaerobic or aerobic, the digestion process or the direct addition of chemical agents decomposes the organic substances in the sludge to finally form a harmless and stable product. Stable product means that the various components of the sludge are in a relatively stable state, including the bacteria and pathogens in the sludge and odor removal. Finally, it will ensure that the sludge will not cause secondary pollution to the surrounding environment after disposal.
4 resource principle. Specific requirements of the principle of recycling refers to the sludge in the treatment, the sludge contained in the phosphorus and nitrogen and other elements recovered and processed to form a useful energy can be used, while protecting the environment but also Change for Lee. Therefore, recycling is the ultimate goal of sludge disposal.
Sludge final disposal and utilization
Sludge after a series of methods to deal with the disposal, for the resulting sludge after drying, the final disposal of the following general types:
(1) sanitary landfill. The sanitary landfill method is the traditional mature sludge disposal method with low investment requirements and good effect, and at the same time it can increase some urban construction land. Generally, the dried sludge is selected to be landfilled through the solid waste landfill together with the daily garbage of the city, and a special sludge landfill may also be set up to landfill it. However, sludge treatment technology is not perfect at present, some of the sludge may not be able to be cleaned of harmful substances, after the landfill may have some potential threat to the surrounding environment.
(2) Incineration. Incineration is the most thorough way to dispose. Because the sludge contains a lot of organic matter and fiber
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