To treat sludge, we must first understand the characteristics of sludge. The targets for characterizing sludge characteristics include water content and solid content, volatile solids, toxic and hazardous substances, dehydration function, and chemical kinetic properties.
The water content is the percentage of the water content in the sludge; the solid content is the percentage of the solid or dry sludge content in the sludge; the product of the wet sludge content and the solid content is the sludge content; the water content decreases (that is, the solid content Progress) will greatly reduce the amount of wet sludge (ie sludge volume); generally speaking, the water content is> 85%, and the sludge is fluid; the water content is 65%-85%, and the sludge is in a plastic state; the water content is< ; 65%, the sludge is solid. Volatile solids are generally used to characterize the amount of organic matter in sludge and are an important target for sludge to emit unpleasant odors. The higher the volatile solids, the worse the stability of the sludge. Toxic and harmful substances refer to germs, viruses, parasite eggs, etc. contained in the sludge, which must be treated before application. The dewatering function of sludge is usually evaluated by two goals, namely the specific resistance value of sludge filtration (r) and the time of sludge capillary water absorption (CST). The specific impedance value (r) is the resistance per unit dry weight of the filter cake. The larger the value, the more difficult it is to filter and the worse its dehydration function. The dewatering function of sludge is related to the properties of sludge, scheduling methods and conditions, etc., as well as the type of dewatering machinery. Before sludge dewatering, strong treatment is carried out to change the physical and chemical properties of sludge particles, damage its colloidal structure, reduce its affinity with water, and then improve the dewatering function. This process is called sludge scheduling or conditioning.
Sludge dewatering machineIntroduction of dehydration technology:
1. Drying dehydration technology
Drying is a treatment process that uses heat energy to quickly evaporate the water in the sludge. According to the source of heat and the heating method, it can be divided into fluidization drying, superheated steam drying, partition drying, infrared radiation drying, and collision flow drying. Wait. As long as very few sludge drying plants are built and operated in China, the common drying processes in foreign countries mainly include fluidized bed drying and other forms.
The advantages of drying and dewatering technology include stable properties of the sludge during the treatment process, not easy to stick, not easy to generate biogas, the generated gas is non-flammable and non-explosive, the moisture content of the sludge after drying is less than 10%, the volume is reduced a lot, and the area is small , Easy to control, safe and stable. Its disadvantages are large investment, high operating costs, and higher requirements for management and operation skills. It is suitable for the collection and treatment of sludge from large-scale sewage treatment plants with tight land or a number of small and medium-sized sewage treatment plants.
2. Ultrasonic dehydration technology
The water contained in the sludge can be divided into four types: free water (70%), globule containing water (27%), capillary water (2%) and bound water (1%). In the meantime, the removal of free water is easier, while capillary water and bound water are more difficult to remove. The center of the mycelium is a solid particle, surrounded by a lot of microbial and extremely metabolic products (sugars, lipids, organic acids, proteins, etc.). These adsorbents form a hydrophobic membrane on the outer layer of the mycelium, which is wrapped in the organic matter. The water in the membrane is called the bacteria gel group contains water, this part of the water is difficult to remove, and the amount is relatively large.
The frequency scale of ultrasound is generally 2.0×103~1.0×106 Hz. When a certain intensity of ultrasound is applied to a certain liquid system, the characteristics of the dissolved and particulate matter in the liquid are obviously changed. These reactions are caused by the occurrence and disillusionment of many cavitation bubbles under sound field conditions. Ultrasonic cavitation refers to the small bubble nucleus in the liquid under high sound intensity, a lot of cavitation bubbles will occur in the liquid. They will change the size of the sound wave and finally disappear in an instant. When the bubble disappears, the extreme time will occur. Short and strong pressure pulses form local hot spots in the bubbles and the small spaces around them. High temperature and high pressure (3000℃, 1000 atmospheres) and micro-jets with strong impact force can instantly damage the cell wall of the organism, and how can it damage the bacteria? The micelle structure improves the dehydration function of sludge, and the organic matter released into the water body can also be used as a nutrient source for anaerobic fermentation.
The effect of ultrasonic on sludge is affected by ultrasonic intensity, effect time and frequency. However, the effect mechanism and effect of sound waves are very complicated. Other effect conditions such as wave intensity, effect time, and frequency all affect the processing effect, and they also affect each other. At present, the optimization of operating conditions has not been systematically studied.
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