Flotation Tank and Flotation in Air for Water Treatment

Flotation in air is a method that uses small air bubbles to remove particles in water.

These particles include oil, grease, and solid waste. A flotation tank is the equipment used for this process.

The flotation tank works by dissolving air into water under pressure. This water is then released into the tank. When the pressure drops, small air bubbles appear. These bubbles attach to the suspended matter. As a result, the matter becomes lighter and floats to the surface.

In most systems, coagulants and flocculants are added before the water enters the tank. Coagulants help bring small particles together. Flocculants make them larger and easier to float. This step improves the flotation results. A scraper on top of the tank removes the floating layer. This layer is sent to a sludge tank.

The tank often uses recycled water from its own output. This water is mixed with air in a pressure vessel or by an air pump. Then it is brought back into the system. Some tanks use lamella plates inside to help particles float more easily. These plates give more surface area for separation.

This type of flotation is called dissolved air flotation (DAF).

It is used in many industries. These include food processing, oil refining, and chemical plants. It also helps treat wastewater with animal fat or vegetable oil. In tank and barrel washing, DAF removes solid waste. It is also useful in rainwater treatment.

DAF is popular because it removes more solids than other methods. It can remove 50–90% of suspended matter. It removes 80–99% of oils and grease. It can lower chemical oxygen demand (COD) by up to 90%. The exact numbers depend on the pollution level and chemical dosing.

The flotation tank needs clean operation.

It should work at normal pressure and temperature. The capacity can range from 100 liters per hour to over 1,000 cubic meters per hour. Most systems are built to match the needs of each site.

In the flotation tank, the buoyancy of the water helps particles rise. This is because the water is full of small bubbles. These bubbles are like what you see in carbonated water. They make the solid waste float to the surface.

DAF also works well with salt water. The salt increases the buoyancy and helps particles rise. This process is like what happens in a float tank filled with Epsom salts. In both cases, the high concentration of salt improves the ability to float.

Sometimes DAF units are used instead of sedimentation tanks. This is common when the sludge is light or oily. DAF tanks are smaller. They take up less space and are easy to move. Many are delivered pre-made and installed quickly.

Flotation in air is not just for industry. Some systems also remove gases like hydrogen sulfide (H₂S) and ammonia (NH₃). These gases float with the help of air bubbles. Removing them improves water quality.

When using a flotation tank, operators must check the water regularly.

They must also adjust the amount of chemical added. The goal is to reach a good balance. Too little chemical leads to poor removal. Too much increases costs and sludge volume.

Some flotation tanks include extra equipment. These may include chemical mixers, dosing pumps, and sensors. These tools help control the system. They also help track water quality and sludge thickness.

DAF technology is always changing. Some systems now use fine-tuned air injection. Others have better flow designs. Some can even treat water with high oil content. These updates help make the system more efficient.

A flotation tank does not remove all waste. It cannot treat dissolved chemicals or very small particles. For full treatment, it is often used before or after other steps. For example, biological treatment may follow DAF.

Flotation in air is an effective way to treat wastewater.

It removes oils, solids, and some chemicals. The process uses basic science. Air bubbles lift waste to the surface. A scraper removes it. The system is simple. But it must be set up and run well.