The difference between a high-density sedimentation tank and an ordinary sedimentation tank lies in the "sludge recirculation" and "sludge thickening" processes. It is precisely these two points that make the high-density sedimentation tank have higher surface load and higher removal efficiency.
There are significant differences between high-density sedimentation tanks and coagulation sedimentation tanks in terms of surface load and removal efficiency. The following is a detailed comparative analysis of the two:
I. Surface load
High-density sedimentation tank
High surface load: The high-density sedimentation tank significantly enhances the surface load through sludge circulation and inclined tube sedimentation technology. Its surface load can reach 10-15m³/(m²·h), which is 5 times that of traditional sedimentation tanks.
Low surface load: The surface load of a coagulation sedimentation tank is usually low, generally ranging from 1 to 3 m³/(m²·h), with specific values depending on factors such as raw water quality, type of coagulant, and dosage.
II. Removal efficiency
High-density sedimentation tank
High SS removal rate: The high-density sedimentation tank intercepts colloidal substances through large flocs, achieving a SS removal rate of over 95% and maintaining the effluent turbidity below 5 NTU.
Strong shock load resistance: The high-density sedimentation tank features a sludge circulation system, which can maintain a high sludge concentration required for uniform flocculation within the reaction cylinder, thereby enhancing shock load resistance. Even if the concentration and flow rate of raw water change, it can maintain stable effluent quality.
High sludge concentration: The sludge produced by the high-density sedimentation tank has a high solid content, which can reach 2%-3%. There is no need to set up a sludge thickening tank, reducing land occupation and energy consumption.
High SS removal rate: The coagulation sedimentation tank utilizes the action of coagulant to cause suspended particles to form alum and settle. The SS removal rate is usually high, but the specific value depends on factors such as raw water quality, type of coagulant, and dosage. Generally speaking, the removal rate of SS by traditional coagulation sedimentation process can exceed 80%.
Weak shock load resistance: The coagulation sedimentation tank has relatively weak shock load resistance, and changes in raw water concentration and flow rate may have a significant impact on effluent quality.
Low sludge concentration: The solid content of the sludge produced in the coagulation sedimentation tank is relatively low, typically ranging from 0.5% to 1%. A sludge thickening tank is required for further treatment.
III. Other differences
High-density sedimentation tank: Due to its high surface load and high treatment efficiency, the high-density sedimentation tank occupies a relatively small area, making it particularly suitable for projects with limited land.
Coagulation sedimentation tank: The coagulation sedimentation tank occupies a relatively large area, requiring sufficient space for the layout of facilities such as sedimentation tanks and sludge thickening tanks.
High-density sedimentation tank: The high-density sedimentation tank reduces the dosage of coagulant through a sludge circulation system, and the high-concentration sludge discharge reduces the cost of subsequent dewatering treatment, thus resulting in relatively low operating costs.
Coagulation sedimentation tank: The coagulation sedimentation tank requires the addition of a large amount of coagulant to ensure the quality of the effluent water. At the same time, the low sludge concentration leads to higher costs for subsequent dewatering treatment, thus resulting in relatively high operating costs.