Effective water depth of aeration tank and its influence on sewage treatment effect
Reasons for selecting effective water depth range:
1. Aeration efficiency: Within the water depth range of 4.0m to 6.0m, the bubbles stay in the water for a long enough time to fully contact with sewage and improve the oxygen transfer efficiency.
2. Floor space: Properly increasing the water depth can reduce the floor space of the aeration tank and save land resources.
3. Equipment performance: Aeration equipment (such as microporous aerators, submersible aerators, etc.) can operate efficiently within this water depth range.
4. Operating cost: Reasonable water depth helps to reduce energy consumption while ensuring the stable operation of the system.
5. Special cases:
(1) Oxidation ditch: When the oxidation ditch process is adopted, the effective water depth can be appropriately increased to 3.5m to 4.5m.
(2) Aerated biological filter: For aerated biological filter, the effective water depth is usually 5m to 7m.
When designing an aeration tank, it is also necessary to combine specific process requirements, geological conditions and equipment selection for comprehensive consideration.
How much influence does the water depth of 4.0m to 6.0m have on the sewage treatment effect?
In sewage treatment, the effective water depth of the aeration tank is generally between 4.0m and 6.0m. The water depth in this range has many effects on the sewage treatment effect:
1. Aeration efficiency
- Oxygen mass transfer efficiency: Increasing the water depth can extend the residence time of bubbles in the water, thereby improving the oxygen mass transfer efficiency. For example, when the water depth increases from 0.5m to 4.6m, the oxygenation capacity is significantly improved.
- Energy consumption: Although increasing the water depth can improve the oxygen mass transfer efficiency, it will also increase energy consumption. Therefore, it is necessary to find a balance between oxygen mass transfer efficiency and energy consumption.
2. Land occupation
- Saving land: Properly increasing the water depth can reduce the land occupation of the aeration tank, which is particularly important for areas with tight land resources.
3. Treatment effect
- Pollutant removal rate: Within the water depth range of 4.0m to 6.0m, sufficient reaction time and space can be ensured, thereby improving the pollutant removal rate.
- Sludge sedimentation: The appropriate water depth helps the sedimentation and separation of sludge and reduces the loss of sludge.
4. Operation stability
- Shock resistance: Within the water depth range of 4.0m to 6.0m, the system has better shock resistance and can better cope with fluctuations in influent water quality and water volume.
5. Design flexibility
- Adaptability to different processes: This water depth range is suitable for a variety of sewage treatment processes, such as traditional activated sludge method, oxidation ditch method, etc.
Special cases
- Oxidation ditch: When the oxidation ditch process is adopted, the effective water depth can be appropriately increased to 3.5m to 4.5m.
- Aerated biological filter: For aerated biological filter, the effective water depth is usually 5m to 7m.
Sewage Mechanical Screen Design
1. Screen Gap
(1) The screen bar gap in front of the water pump should be determined according to the requirements of the water pump.
(2) The screen bar gap in front of the wastewater treatment system should meet the following requirements: the maximum gap is 40mm, of which 25~40mm is for manual cleaning and 16~25mm is for mechanical cleaning. Wastewater treatment plants can also set up coarse and fine screens, with a coarse screen bar gap of 50~100mm.
(3) Large wastewater treatment plants can set up coarse, medium and fine screens.
(4) If the screen gap in front of the pump is not greater than 25mm, no screen is required in front of the wastewater treatment system.
2. Screen Residue
(1) The amount of screen residue is related to many factors
Screen gap 16~25mm; 0.10~0.05m3/103m3 (screen residue/wastewater).
The screen gap is 30~50mm; 0.03~0.01m3/103m3 (screen residue/wastewater).
(2) The moisture content of screen residue is generally 80%, and the bulk density is about 960kg/m3.
(3) For large screens in front of large wastewater treatment plants or pumping stations (daily screen residue volume greater than 0.2m3), mechanical slag removal should generally be adopted.
3. Other parameters
(1) The flow rate through the screen is generally 0.6~1.0m/s.
(2) The water flow rate in the channel in front of the screen is generally 0.4~0.9m/s.
(3) The screen inclination angle is generally 45°~75°. A small angle is more labor-saving, but it occupies a large area.
(4) The power device of the mechanical screen should generally be installed indoors, or other measures to protect the equipment should be taken.
(5) The structure where the screen device is installed must be considered to have good ventilation facilities.
(6) Lifting equipment should be installed in large and medium-sized screen rooms to facilitate equipment maintenance and daily removal of screen residue.