Analysis of sludge treatment technology

First, the source of sludge

In a broad sense, sludge includes sewage sludge (ie, municipal sludge, products treated by municipal sewage treatment plants (sudden sludge, excess sludge, sludge from some grit chambers, etc.), industrial sludge) (Products after process wastewater treatment, different in nature due to different sources of industrial wastewater, such as oil may be contained, particularly high in certain substances), pipe network sludge (sludge obtained by pipe dredging), water supply pollution (from water plant The sludge produced) and the sediments of the rivers and lakes (such as the sediments dug out of the dredged rivers).

In a general sense, it refers to sewage sludge. This type of zui is common, its nature is close, and its output is huge. The so-called "sludge siege" is about it.

Second, the need to deal with disposal

The nature of the sludge has two sides:

1, containing a large amount of organic matter and nutrients such as NPK, making it a usable side;

2. Part of the pollutants contained in the sewage are transferred to the sludge, resulting in high water content and strong odor, and contains a large number of pathogenic bacteria, parasitic eggs, heavy metals such as chromium and dioxins, which are difficult to degrade. If it is not treated effectively, it will easily cause secondary pollution to groundwater and soil, directly threaten environmental safety and public health, greatly reduce the environmental benefits of sewage treatment facilities, and cause many public events.

Third, the treatment and disposal methods

The problem of sludge treatment is to solve the problem of continuous reduction of water content. At present, common treatment methods include deep dehydration, composting, digestion, etc., and the final disposal includes land use, incineration, and landfill.

After deep dewatering, the moisture content of the sludge is about 60%, which can be directly landfilled. In an emergency, it can be mixed in a small amount (along with household garbage). However, the current iron salt and lime used for chemical conditioning are mostly, and the inorganic matter is increased. The introduction of chloride ions has a certain impact on the incineration conditions and the furnace itself. However, this technology is low in cost, chemical conditioning agents are very common, all that is needed is a filter press device (many domestic products), as long as there are landfill facilities, downstream can be opened, and it is currently a process in many areas. The stench of composting is too serious, but the fatality of Zui is that the product chain has not been opened, and the end product of Zui has no way out. Anaerobic digestion is suitable for large-scale sewage plants. The equipment and self-control requirements are very high, and the operation is difficult. Especially the high sand content of domestic sludge, I do not know how many equipment manufacturers and operators are tossed.

From the perspective of the final disposal of zui, land use is prioritized at home and abroad, that is, the nutrients in the sludge are utilized as much as possible. However, land use must be pre-treated by composting, digestion, etc., to ensure that the standard can be applied. The big problem with zui is the heavy metal problem. China has standards for several aspects of land use (garden, greening, soil improvement, agricultural use, etc.), but it is still relatively strict. However, in the actual process, many areas have insufficient awareness, thinking that even if the sludge falls to the ground, it will be the land. The use of this, the consequences are very serious, the sludge can not be directly used by land!

to sum up:

With the development of China's social economy and the improvement of urbanization level, the sludge production of urban sewage plants in China has increased rapidly. It is estimated that China's sludge production (80% moisture content) exceeded 30 million tons in 2011. Sludge disposal technologies include sanitary landfill, incineration, aerobic fermentation, and resource utilization. Among them, sludge aerobic composting has moderate investment and operating costs, and at the same time, it can utilize organic matter and nutrients in sludge. It is the recommended technical route in the Technical Guidelines for Sludge Treatment and Treatment of Municipal Wastewater Treatment Plants (Trial).

At present, the domestic and foreign sludge aerobic fermentation technology mainly adopts the tank-type or silo structure constructed by concrete, and maintains the aerobic state in the pile by manual or mechanical turning, natural or forced ventilation to ensure the temperature of the pile. And the normal growth of microorganisms. The odor, water vapor, leachate and the like generated during the composting process are difficult to control, seriously affecting the surrounding environment and damaging public health. In addition, compost also has many problems such as long composting time and large floor space.

At present, the main methods of sludge disposal in use at home and abroad include landfill, incineration, composting, and resource utilization. Landfill technology has low processing cost, but it has a large area, and landfill gas and leachate are numerous and difficult to handle. The effect of reducing the capacity of the incineration technology is remarkable, and the calorific value of the sludge can be utilized, but the operation cost is high, and there is a problem of secondary pollution of the atmosphere. Anaerobic digestion technology can recover energy materials, but operation management is difficult and there are not many successful cases. The aerobic fermentation technology has low investment and operation cost, and the product can be used for fertilizer production, the resource utilization effect is remarkable, the management operation is simple, and the scale of the sewage treatment plant is wide. Through analysis and investigation of existing sludge treatment and disposal technologies, the R&D team selected the technical route of sludge aerobic fermentation to achieve the goal of low processing cost and product resource.

The mud out of the municipal sewage treatment plant is not very risky, but the sludge that is classified as dangerous solid waste such as electroplating sludge, printing and dyeing sludge, etc., has a large environmental risk if it is not properly disposed. At present, there are better sludge treatment technologies at home and abroad. The difficulty of treatment is actually small, but the key lies in the management level and the level of understanding. The management system is not detailed enough, and the sludge production unit is not paying enough attention. It is the main difficulty in treating sludge at present. The sludge is also in contact with municipal sewage. The sludge is classified into municipal sludge and industrial sludge in a large direction. Many industrial sludges have heavy metals and oils. , toxic and hazardous substances, etc., often do hazardous waste treatment, there are corresponding hazardous waste treatment processes, incineration, landfill and so on. Municipal sludge, most of the contact we are going to be transported to landfills, but the current 60% water content requirement is more awkward, the conventional sludge dewatering process, after treatment, the water content is 80%, to do 60%, no special mature and feasible, low cost process. For a long time, there has been heavy water and light mud in sewage treatment, but the pollutants have only been transferred to the mud. Therefore, in order to avoid secondary pollution, sludge must be resourced, stabilized, harmless and reduced. Common techniques There are landfills, incineration, composting and anaerobic digestion, but due to various reasons such as technology, cost and ideas, the treatment of sludge is still unsatisfactory.