1. Overview of sludge treatment and disposal
In the treatment of feed water and wastewater, various types of sediments and floating materials produced by different sludge treatment processes are collectively referred to as sludge. The composition and properties of the sludge mainly depend on the composition, properties and treatment process of the treated water. The composition of the sludge is complex, and there are various classification methods and different names.
1.1 sludge classification
According to the source, the sludge is roughly divided into three categories: feed water sludge, domestic sludge and industrial wastewater sludge.
According to the separation process of sludge from water, it can be divided into sediment sludge (including physical sedimentation sludge, coagulation sludge, chemical sludge) and biological treatment sludge (sludge produced by sewage in the secondary treatment process, including biological filtration). Humic sludge obtained by methods such as pool and biological turntable, and activated sludge obtained by activated sludge method). Most of the sewage from modern sewage treatment plants is a mixed pollution of sediment sludge and biological treatment sludge.
According to the sludge composition and quality, it can be divided into organic sludge and inorganic sludge.
More commonly used are classified according to the different treatment stages of sludge: biological sludge, concentrated sludge, digested sludge, dehydrated and dried sludge, dry sludge and sludge incineration ash.
1.2 Characteristics of sludge
(1) Moisture content and solid content The water content is the percentage of the water content in the sludge, and the solid content is the percentage of the solid or dry mud content in the sludge. When the water content is high and the sludge is in a fluid state, the volume of the sludge is inversely proportional to the solid content: V1V2=Ps1/Ps2=(100-Pw2y(100Pw1)
In the formula: V1 and V2 are the volume of wet sludge when the water content is Pw1 (solid content Ps1) and Pw2 (solid content Ps2).
Example: The original moisture content of the sludge is 99.5%, and the percentage of sludge volume reduction when the water content is reduced to 98.5% and 95% is obtained.
Solution: Let V1 be the volume of sludge when the water content is 99.5%, and the volume when V2 and V3 respectively have water content of 98.5% and 95%, and substitute each value into the above formula to obtain V1/V2=Ps1/Ps2= (100-98.5/(100-99.5)=3 V1/N3=Ps1/Ps2=(100-95/(100-99.5)=10 As can be seen from the above example, when the moisture content of the sludge is reduced from 99.5% to At 98.5%, the volume of the sludge is reduced to about one-third of the original sludge, and then reduced to 95% (when the solid content is 5%, the volume of the sludge is reduced to about one-tenth of the original sludge). .
(2) Volatile solids Volatile solids refer to the part of solids in the sludge that can be burned in a furnace at 600 ° C and escaped by gas, reflecting the degree of stabilization of the sludge.
(3) Toxic and harmful substances in sludge The sludge in urban sewage treatment plants contains a considerable amount of nitrogen, phosphorus and potassium, which has certain fertilizer effects and can be used to improve the soil, but it also contains germs.
Viruses, parasite eggs, etc., should be treated as necessary before application. The heavy metals in the sludge are the main harmful substances, and the sludge with a heavy metal content exceeding the prescribed amount cannot be used as the clothing fertilizer.
(4) Dewatering performance of sludge When the water content of the sludge is separated by filtration, the commonly used index is used to evaluate the sludge dewatering performance than the resistance value or capillary water absorption time.
(5) Sludge specific gravity refers to the ratio of the weight of the sludge to the weight of the same volume of water. The specific gravity of the sludge depends mainly on the water content and the specific gravity of the round body. The proportion of domestic sludge and similar industrial sludge is generally greater than one.
Sludge treatment is the process of filling, training, water, stability, incineration or incineration. With the development of the economy, the discharge of urban wastewater is increasing, and the amount of sludge generated is also increasing. Sludge treatment and disposal has gradually become the focus of attention at home and abroad.
(6) Existing treatment and disposal methods at home and abroad mainly include sanitary landfill, water body consumption, incineration, composting, and land use. In view of the existing technology, the main sludge disposal method is landfill. The most suitable sludge treatment method is land use. With the advancement of science and technology, it is bound to introduce more effective and reasonable treatment and disposal methods, and ultimately realize the reduction, harmlessness, stabilization and resource utilization of urban sludge treatment and disposal.
The disposal method is simple, easy, and low in cost, and the sludge does not need to be highly dehydrated and has strong adaptability. However, there are also some problems with sludge landfill, especially the formation of landfill leachate and gas. Leachate is a heavily polluted liquid that can contaminate the underground water environment if the site is sited or not properly operated. The gas produced by landfills is mainly methane, which can cause explosions and combustion if appropriate measures are not taken.
Direct land use
Direct use of sludge land is considered to be the most promising disposal method due to the advantages of low investment, low energy consumption, low operating cost and organic component conversion into soil improver. Scientific and rational land use can be reduced. The negative effects of sludge. The use of forest land and municipal greening has become an effective way of sludge land use because it is not easy to cause pollution in the food chain. The use and use of sludge for the repair and reconstruction of heavily disturbed land (such as mine land, forest harvesting sites, landfills, and severely damaged areas) reduces the potential threat of sludge to human life. Both the sludge was disposed and the ecological environment was restored.
The application of wet sludge to direct incineration is more common. It is not only difficult to directly incinerate without drying the sludge, but it is also extremely uneconomical in terms of energy consumption. The incineration-based sludge treatment method is the most thorough sludge treatment method, which can completely carbonize organic matter and kill pathogens, thereby minimizing sludge volume. However, the disadvantage is that the treatment facility has large investment and high treatment cost. .
Powdered organic and inorganic fertilizers Powdered organic and inorganic fertilizers refer to mechanically mixed fertilizers containing two or more nutrients; the ratio of nutrients is determined according to crop varieties, target yield, soil and climate, etc. Different crops have their own unique growth needs; and they can be blended with auxiliary additives (such as limestone, dolomite powder, etc.) and herbicides, insecticides, etc., which have improved soil physiological characteristics according to the specific needs of the crop in specific regions and seasons. Become a nutrient-rich, multi-purpose special organic and inorganic fertilizer.
2. Sludge treatment process
1. The treated sludge (living sludge, industrial sludge, etc.), inorganic raw materials (urea, monoammonium phosphate, etc.), trace elements (borax, ferrous sulfate, etc.) filler (shadow earth, vermiculite, etc.) ) and other raw materials are sent to the automatic lifting silo in proportion;
2. Transported to the organic fertilizer mixer (continuous), while the organic fertilizer mixer rotates, the material advances 2/3 forward, and the remaining 1/3 of the material reciprocates back and forth, and continues to mix with the newly delivered materials. After two to three times of circulating mixing; after the material has reached the purpose of uniform mixing, it is slowly pushed to the discharge port along the inclined direction of the organic fertilizer mixer;
3. Transported to the organic fertilizer special screening machine, special design can completely solve the problem of screen adhesion;
4. The large particles are pulverized by the pulverizer and returned to the horizontal mixer;
5. The finished product is transported to the finished silo, and the automatic packaging scale is weighed, packed and stored.