The pretreatment effect of the paddle dosing agitator
The paddle dosing agitator is a common mixing device in water treatment processes, mainly used for the dosing and mixing of chemicals in the pretreatment stage. Its core function is to rapidly and evenly disperse chemical agents such as coagulants (such as polyaluminium chloride, aluminium sulfate, etc.), coagulant AIDS or pH regulators into the raw water to achieve effective physical and chemical reactions.
In the pretreatment stage, the raw water usually contains suspended solids, colloidal particles and some dissolved pollutants. These colloidal particles repel each other due to the negative charge on their surfaces and are difficult to settle naturally. By adding coagulants, its surface charge can be neutralized and its stability can be disrupted. The paddle agitator generates moderate turbulence through the low-speed rotating paddles, enabling the chemicals to be thoroughly mixed with the water body in a short time. This promotes the collision and aggregation of destabilized colloids, forming tiny flocs and laying the foundation for the subsequent flocculation and sedimentation processes.
The pretreatment effect of paddle agitators is influenced by multiple factors. First is the stirring intensity (usually measured by the velocity gradient G value). If the G value is too low, the mixing will be uneven and the reaction of the reagent will not be sufficient. If the G value is too high, it may destroy the already formed tiny flocs. The G value in the general mixing stage is controlled at 300 to 600 s⁻¹, and the reaction time is within 10 to 30 seconds. Secondly, the design and installation position of the blades should ensure there are no dead corners for mixing, so that the reagents can complete the initial reaction before entering the reaction tank.
Compared with other stirring forms (such as turbine type and frame type), the paddle agitator has a simple structure, lower energy consumption, is easy to maintain, and generates moderate shear force, which is conducive to the growth of flocs and avoids excessive fragmentation. Therefore, it is widely used in small and medium-sized water plants and in situations where there are high requirements for the control of flocs.
In addition, paddle-type dosing agitators are often used in conjunction with automated dosing systems. They can adjust the dosage of chemicals and stirring parameters in real time based on the quality of the raw water (such as turbidity and pH), achieving precise control and enhancing the stability and efficiency of pretreatment. Overall, this equipment has a remarkable effect in enhancing the utilization rate of chemicals, improving the quality of effluent, and ensuring the stable operation of subsequent treatment units. It is one of the indispensable pretreatment units in modern water treatment systems.
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