The whole process dissolved air floatation method is to pressurize all wastewater with water pump and inject air before or after the pump. In the air dissolving tank, air is dissolved in the waste water, and then the waste water is sent to the air floatation tank through the pressure reducing valve. Many small bubbles formed in the waste water adhere to the emulsified oil or suspended matter in the waste water and escape from the water surface, forming scum on the water surface. The scum is discharged into the scum tank by scraper and discharged out of the tank by scum pipe. The treated wastewater is discharged through overflow weir and outlet pipe. Advantages of the whole process dissolved air floatation method:
① large dissolved air volume increases the contact opportunity between oil particles or suspended particles and bubbles;
② under the condition of the same water treatment volume, it is smaller than the air flotation tank required by partial reflux dissolved air flotation, thus reducing the capital construction investment. However, as all the wastewater passes through the pressure pump, the emulsification degree of the oily wastewater is increased, and the required pressure pump and air dissolving tank are larger than the other two processes, so the investment and operation power consumption are larger.
Partial dissolved air floatation method is to take part of the waste water for pressurization and dissolved air, and the rest of the waste water directly enters the air floatation tank and mixes with the dissolved air waste water in the air floatation tank. Its characteristics are as follows:
① it is smaller than the pressure pump required for the whole process dissolved air floatation method, so the power consumption is low;
② the amount of emulsified oil caused by the pressure pump is lower than that by the whole process of dissolved gas floatation.
③ the size of the air flotation tank is the same as that of the whole process, but smaller than that of the partial reflux solution.
The partial reflux dissolved gas floatation method is to take a part of the waste water after oil removal for pressurization and dissolved gas. After decompression, it will directly enter the air floatation tank and mix with the oily wastewater from the flocculation tank and do the air floatation. The return flow is generally 25% - 100% of the oily wastewater.