Functions of the Air Flotation Tank
The air flotation tank primarily serves as a pretreatment stage for wastewater, removing suspended solids, colloids, and the majority of organic matter. In the reaction zone, the formation of flocs is highly effective (resulting in large, dense aggregates); in the flotation zone, the agglomeration of scum is excellent, allowing for its timely removal via scraping. The effluent discharged from the air flotation tank must be relatively clear, thereby reducing the treatment load on subsequent biochemical treatment tanks.
Typically employed prior to biochemical treatment, this process removes suspended solids from wastewater by utilizing a large volume of microscopic air bubbles that attach to the solids, causing them to float to the water's surface where they are subsequently collected and processed. This method is faster than conventional sedimentation, offers a higher removal efficiency, and can, to a certain extent, reduce the volume of sludge generated during subsequent biochemical treatment stages.
Air Flotation Tank Operation Guidelines
1. Equipment Lifting:
Four lifting lugs are welded to the inner wall of the air flotation tank to facilitate hoisting; these lugs should be utilized whenever the equipment requires lifting.
2. Installation:
A. Equipment Elevation: Depending on project requirements, the equipment may be installed on an elevated platform or placed directly on level ground. The load-bearing surface area of the equipment corresponds to the length multiplied by the width of its base frame.
B. Leveling: Once the equipment is positioned, it is essential to ensure that it is perfectly level.
C. Drain Outlet: For the equipment's drain outlet, either an open trench may be excavated or a direct pipeline connection may be established leading to a balance tank or collection sump; this facilitates the draining of the air flotation tank and the discharge of flushing wastewater.
D. Inlet Piping: The connecting pipe between the wastewater inlet and the reaction tank should be kept as short as possible to prevent the flocs from being sheared and broken apart while flowing through the pipe.
E. Effluent Outlet: The clarified water outlet may be connected to a sewer system for discharge. Alternatively, if the water requires further processing by downstream equipment, it may be connected directly to the next stage of the treatment system.
F. Sludge Outlet: The sludge outlet may be connected to a dedicated sludge storage tank or a sludge dewatering/processing unit.
G. Electrical Control Cabinet: The placement of the electrical control cabinet should be guided primarily by the principle of convenience, typically situated adjacent to the access ladder or in a nearby, easily accessible location.
3. Equipment Commissioning:
Prior to commissioning the equipment, all debris and foreign objects must be removed from within the air flotation tank to prevent clogging. Lubricants must be applied to all designated lubrication points on components such as the gearbox reducer and air compressor. Ensure that all air is purged from the working pump casing to guarantee that the pump is filled with water; the pump must never be allowed to run dry (run without fluid). Once the pump is connected to the power supply, start the pump briefly to verify that its direction of rotation aligns with the directional arrow indicated on the unit. After connecting the power supply to the scum scraper, start the machine to verify that the scraping direction is correct; the scraper blade should move toward the scum trough. Switch to manual mode to start the air compressor and check for normal operation. Verify that the air valve control button located on the compressor head is in the "closed" position; if not, switch it to the closed position. If any abnormalities are detected, immediately investigate and identify the cause.
4. Trial Run:
A. Water Filling: Fill the air flotation tank with clean water.
B. Dissolved Air System Trial Run: Open the water inlet control valve and close control valve as well as the dissolved air outlet valve . Turn the aeration rotary switch to the "Auto" position and start the water pump. Then, gradually open control valve; the readings on Pressure Gauge 1 and Pressure Gauge 2 should rise steadily until they reach the maximum pressure attainable by the pump-typically 4.5 to 5 kg/cm². At this point, open the dissolved air outlet control valve to allow the dissolved air water to flow through the dissolved air release unit and discharge into the air flotation tank. The appearance of a large volume of micro-bubbles in the tank water, causing the clear water to turn a milky-white color, indicates that the dissolved air system is functioning correctly. The pressure of the dissolved air water can be monitored via the reading on Pressure Gauge 2 located on the dissolved air tank; this pressure can be adjusted within a certain range by varying the opening degree of the dissolved air water control valve . The typical operating range is 3.5 to 5 kg/cm².
C. KDAF Integrated Air Flotation Operation: Once the dissolved air system is confirmed to be operating normally, introduce the wastewater-which has already undergone chemical dosing and reaction-into the air flotation system. Begin with a low flow rate, and once stable operation is established, gradually increase the flow rate to the rated capacity. The influent flow rate can be estimated visually or measured using an installed flow meter.
D. Adjustment of Air Flotation Tank Water Level: The water level within the air flotation tank directly impacts the efficiency of scum scraping. If the water level is too low, the floating scum will be difficult to scrape into the sludge trough; conversely, if the water level is too high, an excessive amount of water will spill over into the sludge trough. The water level in the air flotation tank can be adjusted by raising or lowering the liquid level adjustment sleeve located on the water collection pipe. Ideally, the water level should be maintained approximately 1 to 2 cm below the upper edge of the scum guide plate (5).
Precautions for Operating the Air Flotation Unit
1. Before operating this equipment, thoroughly read the user manuals for the unit itself and all associated electromechanical components. Operation of this equipment by personnel who have not undergone professional operational training is strictly prohibited.
2. When starting the air flotation unit, the effluent control valve must be in the closed position. Subsequently, start the water pump , and then gradually open the effluent control valve .
3. When shutting down the air flotation unit, the dissolved-air water outlet control valve must be closed *before* stopping the water pump ; only then should the influent control valve be closed. Failure to follow this procedure may result in compressed air surging directly into the flotation tank, thereby disrupting or destroying the scum layer.
4. During air flotation operations, regularly monitor all equipment components to ensure they are functioning correctly. If any issues are detected, immediately halt operations and conduct an inspection; the unit may only be restarted once the fault has been completely resolved.
5. Lubricating grease must be applied periodically to the speed reducer, water pump, and air compressor, in accordance with the specific instructions provided in the respective equipment manuals.
6. When the scum scraper and its associated chain drive system are in operation, strictly observe all safety precautions and protective measures.
7. The air flotation tank should be cleaned after a period of operation. It is recommended to flush the tank once every 20–30 days during the summer season, and once every 50–60 days during the winter season.
8. If the dissolved-air water pump is to remain out of service for an extended period, the water inside the pump casing must be completely drained; particular attention should be paid to frost protection measures during the winter season.
