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# What do you consider about dissolved air flotation design calculations？

Author: Site Editor     Publish Time: 2023-10-12      Origin: Site

A dissolved air flotation is a device used in water treatment and wastewater treatment. Dissolved air flotation working principle is by dissolving gas (usually air) in water and then releasing bubbles to float or remove suspended matter or contaminants. When designing a dissolved air flotation equipment, multiple factors need to be considered, including the flow rate of the treated water, the required flotation efficiency, the dissolution efficiency of the gas, etc. The following are the general steps and calculation parameters for designing a dissolved air flotation machine:

## 1. Determine the flow rate of the water to be treated:

First, determine the flow rate of the water you need to treat. This is usually measured in cubic meters per hour (m³/h) or cubic meters per day (m³/day). The flow rate will determine the size and capabilities of the air flotation machine.

## 2. Flotation efficiency requirements:

Determine the flotation efficiency you need to achieve. This can be the removal rate of suspended matter or contaminants, usually expressed as a percentage. This will help determine the amount of bubbles and number of flotation units required.

### 2.1 Removal Efficiency:

Flotation efficiency is usually measured by removal rate, which is the percentage of pollutants or suspended solids removed from wastewater. Removal rates can be adjusted based on different pollutants and water quality standards, and are usually required to meet regulatory water quality discharge standards. For example, common requirements in wastewater water treatment include removal of suspended solids, chemical oxygen demand (COD), biochemical oxygen demand (BOD), nitrogen, phosphorus, etc.

### 2.2 Suspended solid concentration:

DAF system is usually used to treat water with high suspended solid concentration, such as sludge slurry, industrial wastewater treatment, etc. Flotation efficiency requirements depend on the type and concentration of suspended solids in the wastewater. The system needs to be efficient enough to remove suspended solids from the water.

### 2.3 Bubble lifting efficiency:

The bubble generation and bubble lifting efficiency of the DAF system are key factors. The bubbles need to be small enough and in full contact with the contaminant particles in the mixing chamber to achieve efficient flotation. The bubble flotation efficiency should be high enough to ensure that the pollutant particles are effectively lifted to the surface of the flotation tank.

## 3. Gas dissolution efficiency:

The key part of the suspended air flotation is the gas dissolution system. You need to calculate the required gas dissolution rate to ensure that enough gas is dissolved into the water. This typically involves gas pressure, dissolution chamber design, and gas dissolver selection. The gas is usually air or carbon dioxide. This depends on the nature of the suspended matter in the water and the required flotation efficiency. Usually, gas dissolution efficiency is expressed in terms of mass fraction or volume fraction.

## 4. Bubble generation system:

Choose an appropriate bubble generation system, usually by spraying air into the water or through a gas diffuser. Calculate the required size and number of bubble generators based on the required bubble volume and gas dissolution efficiency.

## 5. Air flotation tank size:

The size of the air flotation tank is determined based on the flow rate of the treated water, flotation efficiency and characteristics of the bubble generation system. Typically, a flotation tank includes a flotation unit, mixer and clarification area.

## 6. Bubble distribution and stirring:

Ensure that bubbles are evenly distributed and suspended substances in the water can effectively contact the bubbles. This may require the addition of stirring equipment or flow control devices.

## 7. Clarify areas:

Design clarification areas so that floating suspended solids can be easily separated from the water. Consider a settling tank or other separation device to collect and discharge raised suspended solids.

## 8. Control system:

Design and install a control system to monitor and adjust the rate of bubble generation, agitation, and discharge of suspended matter to meet processing requirements.

## 9. Safety and maintenance considerations:

Ensure the safety of the system and consider maintenance requirements to maintain dispersed air flotation performance.

Please note that dissolved air flotation design requires engineering expertise and detailed engineering calculations, so it is recommended to work with a water treatment engineer or professional consultant to ensure that the dissolved air flotation system is designed and operated in compliance with required technical specifications and environmental regulations. Additionally, specific water quality characteristics and treatment objectives need to be taken into account during the design process, so design calculations may vary.

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