New comprehensive utilization of sludge: sludge brick making
Natural drying
Natural drying can be divided into sand drying field and drying field. The former is used for dewatering the sediment in the grit chamber; The latter is used for dewatering of primary precipitated sludge, humic sludge, digestion sludge, chemical sludge and mixed sludge. The moisture content of dried mud cake is generally 75% - 80%.
Sludge thickening
Sludge thickening is the most economical and effective way to reduce the volume of sludge. No matter how the sludge is treated and disposed, sludge thickening is essential. At present, the most commonly used methods of sludge concentration are gravity concentration, air flotation concentration, centrifugal concentration and hydrocyclone concentration.
Gravity concentration is to concentrate sludge by forming a high concentration sludge layer in sedimentation. Separate gravity concentration is completed in an independent gravity concentration tank. The process is simple and effective, but odor may be generated when the residence time is long; Gravity concentration method is applicable to primary sludge, chemical sludge and biofilm sludge.
Contrary to gravity concentration, air flotation concentration relies on a large number of small bubbles attached around sludge particles to reduce the specific gravity of particles and force them to float upward. Therefore, the air flotation method is especially suitable for sludge with a specific gravity close to 1. Air flotation concentration method is easy to operate, has a certain odor in operation, has high power cost and is sensitive to sludge sedimentation performance (SVI); It is suitable for activated sludge treatment system with small excess sludge output.
(3) Centrifugation
Centrifugal concentration is to concentrate by using different centrifugal force due to different specific gravity of solid and liquid in sludge. Centrifugal concentration is characterized by its own system, good effect and simple operation; However, the investment is high, the power cost is high, and a high level of maintenance is required; It is suitable for biological and chemical sludge of large and medium-sized sewage plants.
(4) Hydrocyclone concentration
Hydrocyclone concentration is to use the centrifugal sedimentation separation phenomenon produced by hydrocyclone to replace the centrifugal sedimentation separation in the mechanical rotating body to achieve the purpose of concentration. However, the hydrocyclone concentration operation is complex, and it is easy to be blocked by concentration, so the large-scale sludge concentration device is rarely used.
Mechanical dehydration
Mechanical dehydration is a method widely used all over the world. Commonly used dewatering machines include vacuum filter, plate and frame filter press, belt filter press and centrifuge. In recent years, rotary centrifuge and belt filter press have developed rapidly. As the main machinery of sludge dewatering, they are widely used all over the world.
The main feature of the belt filter press is to use the tension and pressure of the filter cloth to exert pressure on the filter cloth to dehydrate the sludge. It does not need vacuum or pressurization equipment, has less power consumption and can be operated continuously. Its operation only depends on the speed and capacity of the filter cloth. It can dehydrate stably even if the load changes during operation, and the structure is simple; No noise and vibration, easy to realize closed operation. Belt filter press is suitable for dewatering activated sludge and organic hydrophilic sludge. At present, it is widely used in sludge dewatering.
Centrifugal dehydrator
Centrifugal dewatering mainly uses centrifugal force instead of gravity or pressure as driving force for sludge dewatering. Generally, it forms its own system, which does not need too much monitoring during operation, and the dryness is good; However, special maintenance is required, which is generally not suitable for intermittent operation; It is applicable to the treatment of a large amount of solid in large and medium-sized sewage plants that can operate continuously.
Sludge drying
Sludge drying belongs to heat treatment process, which is a process of completely drying the sludge by heating the sludge and evaporating the water in the sludge. The system directly or indirectly heats the dewatered sludge (the moisture content of mechanically dewatered sludge before drying is 75% - 80%) with hot gas to reduce the moisture content of sludge to about 10%. At this time, the sludge volume is greatly reduced and the pathogenic bacteria in sludge are effectively eliminated. The sludge products produced by granulation equipment are granular, which is more convenient for transportation and storage. Because the water in the sludge is only evaporated in the treatment process, the organic matter content in the sludge products is high and the nutrient content is sufficient, so it can be used in landscaping or agriculture. This process covers a small area and has obvious sludge volume reduction effect. Moreover, because the treatment process is carried out in closed equipment, it has little impact on the environment, but the investment of this process is relatively high.