Understand the sludge treatment process and how to select the type

Welcome to call and order! A typical sludge treatment process consists of four stages. The first stage is sludge thickening, the main purpose of which is to reduce the initial sludge volume and reduce the volume of subsequent treatment structures or equipment capacity; the second stage is sludge digestion to decompose the organic matter in the sludge; the third stage is sludge dewatering to further reduce sludge volume; the fourth stage is sludge disposal, in which the final sludge is absorbed by some way. The clear liquid or filtrate produced in the above stages still contains a lot of pollutants, so it should be sent back to the sewage treatment system for treatment. The above typical sludge treatment process can realize "four modernizations" after sludge treatment

(1) Reduction: due to the high water content, large volume and fluidity of sludge. After the above process, the sludge volume is reduced to one tenth of the original, and the sludge is transformed from liquid to solid, which is convenient for transportation and absorption.

(2) Stabilization: the content of organic matter in sludge is very high, which is easy to rot and produce odor. After the treatment in the digestion stage of the above process, part of the organic matter that is easy to corrupt is decomposed and transformed, which is not easy to corrupt, and the odor is greatly reduced, which is convenient for transportation and disposal.

(3) Harmless: sludge, especially the primary sludge, contains a large number of pathogenic bacteria, parasitic eggs and viruses, which is easy to cause large-scale spread of infectious diseases. After the digestion stage of the above process, most of the in-situ eggs, pathogens and viruses can be killed, and the sanitary index of the sludge can be greatly improved.

(4) Resource utilization: sludge is a kind of resource, which contains a lot of heat. Its calorific value is between 10000 and 15000kj / kg (dry sludge), which is higher than that of coal and coke. In addition, the sludge also contains rich nitrogen, phosphorus and potassium, which is an organic fertilizer with high fertilizer efficiency. Through the digestion stage of the above process, the organic matter can be converted into biogas, so that the heat can be used, and the fertilizer efficiency can be further improved. Gravity concentration, centrifugal concentration and air flotation concentration are commonly used in sludge thickening. Sludge digestion can be divided into anaerobic digestion and aerobic digestion. Sludge dewatering can be divided into natural drying and mechanical dewatering. The commonly used mechanical dewatering processes are plate and frame pressure filtration dehydration, belt type pressure filtration dehydration, centrifugal dehydration, etc. There are many ways of sludge disposal, including agricultural and forestry use, sanitary landfill, incineration and production of building materials.

The above is a typical sludge treatment process, which has been widely used in various places. However, due to the different conditions and specific conditions in different regions, there are still some simplified processes, depending on the specific situation.

[equipment selection]

1. Centrifugal dehydrator

The horizontal screw centrifugal dehydrator is mainly composed of a drum and a screw pusher with a hollow shaft. After the sludge is fed into the drum by the hollow shaft, it is immediately thrown into the drum cavity under the action of centrifugal force thousands of times greater than gravity generated by high-speed rotation. Due to the large proportion of sludge particles, the centrifugal force generated is also large, which is thrown onto the inner wall of the hub to form a solid layer; the water density is small, and the centrifugal force is small, and only a liquid layer is generated inside the solid layer. The sludge in the solid layer is slowly pushed by the screw pusher, and is transported to the cone end of the drum, which is continuously discharged through the sludge outlet of the drum, and the liquid is overflowed from the water outlet to the outside of the drum and discharged into the dehydrator after collection.

The characteristics of horizontal screw centrifugal dehydrator are: small floor area, simple operation, continuous operation, high degree of automation, less pollution to the working environment and less labor intensity of operators; the horizontal screw centrifugal dehydrator is less affected by the fluctuation of sludge load. Due to the large centrifugal force, the requirements for sludge pretreatment (flocculation) are not high. Therefore, flocculants with small molecular weight can be selected and used Small volume and low operation cost.

The dewatering technology of centrifugal dehydrator has made great progress in recent years, especially some advanced technologies abroad, such as Alfa layal company in Sweden, flowttwey company in Germany, Sharples company in the United States, Ishikawa grinding company in Japan, etc. the solid content of sludge cake can reach more than 30%, and the slurry can be continuously operated, stable and reliable, and the slurry can not be concentrated, High degree of automation; and the operation is carried out in a fully enclosed environment, there is no sludge and sewage around the dehydrator, and there is no odor, which can greatly improve the working environment of operators, so it is favored by the industry and has great market potential.

2. Belt filter press dehydrator

The belt filter press dehydrator is composed of two tensioned filter belts carrying the sludge layer, passing through a series of regularly arranged roller pressing cylinders in S shape. Depending on the tension of the filter belt, it forms the pressing and shearing force on the sludge layer, and operates continuously to squeeze out the water in the sludge layer, so as to realize sludge dewatering.

The belt filter press dehydrator is greatly affected by the fluctuation of sludge load. When the sludge load is large, the sludge will overflow from both sides of the filter belt and pollute the site; after the filter belt in operation is transferred to the lower part, a large amount of water is needed to backwash the sludge adhered to the filter belt, so that the belt filter press dehydrator does not block the filter belt pores. Because the belt filter press dehydrator is open, it will pollute the working environment and consume more water; The operation of the belt filter press dehydrator is complicated, the filter belt often deviates and the filter belt is worn greatly during the operation process, so it is necessary to adjust and replace the new filter belt in time. Therefore, the management and control is relatively complex, and the quality of the operation personnel is required. The pressure filter dehydrator has higher requirements for sludge pretreatment (flocculation), and needs high molecular weight flocculant and large dosage. Therefore, the price is expensive and the cost is high.

3. Plate and frame filter press dehydrator

The plate and frame filter press makes the water in the sludge discharged through the filter cloth through the extrusion of the plate and frame, so as to achieve the purpose of dehydration. It is mainly composed of concave type filter plate, frame, automatic pneumatic closing system, side plate suspension system, filter plate vibration system, air compression device, filter cloth high-pressure washing device and photoelectric protection device on one side of the fuselage. The following aspects should be considered in equipment selection:

(1) The requirement of solid content of mud cake. Compared with other types of dehydrators, the solid content of sludge cake of general plate and frame filter press is higher, up to 65%.

(2) Material of filter plate and filter cloth. It is required to be corrosion-resistant, with certain tensile and compressive strength.

(3) How to move the filter plate. It is required that the hydraulic pneumatic device can be fully automatic or semi-automatic to reduce the labor intensity of operators.

(4) The operator has the characteristics of high labor intensity, large floor area, large site pollution, large loss of filter cloth and filter plate, and low production efficiency.