Water Treatment Aeration

aeration

What is aeration?

Aeration is the process of bringing water and air into close contact to remove dissolved gases (e.g., carbon dioxide), oxidize dissolved metals (e.g., iron) and volatile organic chemicals (VOCs). Aeration is usually the first major process in a water treatment plant. During aeration, constituents are removed or modified before they interfere with the treatment process. An evenly distributed supply of oxygen in the aeration system is essential for effective wastewater treatment to promote microbial growth.

Aeration in water treatment

In industrial wastewater treatment, aeration is an activated sludge process in the secondary treatment process that promotes the growth of microorganisms in the wastewater. The microorganisms then feed on the organic material, creating a colony of bacteria that settles easily. Once settled in a separate settling tank, the bacteria that form the “activated sludge” population are continuously recirculated back to the aeration tank, thereby increasing the rate of decomposition.

Aeration is used in water treatment for the following operations.

  • Carbon dioxide reduction (decarbonization)
  • Oxidation of soluble iron and manganese to insoluble precipitates to reduce pollution
  • Aeration reduces ammonia and hydrogen sulfide and is an effective method of bacteria control

Types of aerators

Aerators are divided into two main categories. They either introduce air into the water or water into the air. The water-to-air method is designed to produce small droplets of water that fall from the air. The air-to-water method produces small bubbles injected into the water stream. All aerators are designed to create more contact between air and water to enhance the transfer of gas.

Packed Tower Aerator

In this system, water falls by gravity from the top of the tower, while air is blown from the bottom of the unit in the opposite direction of the water flow. Volatile contaminants are transferred to the air by rising to the top of the tower and discharging to the outside.

Diffusion bubble aerators

A diffusion bubble aerator has several chambers and a diffuser through which air is blown. The diffuser produces fine bubbles that rise in the water as it flows from one chamber to the other. These bubbles carry volatile chemicals through the ventilation system to the outside air. The more chambers in the system, the greater the air-to-water contact.

Spray aerators

Spray aeration removes low levels of volatile contaminants, especially radon. In a spray aeration system, water enters through the top of the unit and passes through the spray nozzles in the form of a fine mist. The treated water is collected in a vented tank below the spray nozzles. Radon and other volatile pollutants are released and vented to the outside.

Aeration blower

The use of a certain air volume and pressure blower air or other gases through the transport equipment and diffusion equipment forced to join the water or liquid process is called air blast aeration, with this purpose of the fan is called aeration fan. The aeration process of blower is the transfer of molecular mass between gas and liquid. In order to make the gas fully diffuse and contact in the liquid and prevent the suspended matter in the liquid from sinking, the aeration fan must be able to generate enough pressure.

Common operating problems

Aeration raises the dissolved oxygen content of the water. If too much oxygen is injected into the water, the water can become oversaturated, which can lead to corrosion or air binding in the filter. Other problems with aeration are slow removal of hydrogen sulfide from the tower, algae production, filter clogging and excessive energy use.

The operation of the aeration process involves the control of three basic parameters.

  • Dissolved oxygen
  • pH
  • Temperature

The concentration of dissolved oxygen can be used to estimate whether the process is over– or under-aerated. pH testing will give an indication of the amount of carbon dioxide removed. pH increases as carbon dioxide is removed. pH can also be used to monitor the effective range of hydrogen sulfide, iron and manganese removal. Temperature is important because the oxygen saturation point increases as the temperature decreases. As the water temperature decreases, the operator must adjust the aeration process to maintain the correct dissolved oxygen level.

FAQ

The purpose of aeration is to make in order to provide sufficient oxygen to the microbial reaction, common aeration methods are: 1. blast aeration 2. surface aeration 3. submerged jet aeration 4. submerged water aeration

  • Blast aeration: Using a blower with certain air volume and pressure to provide sufficient oxygen to the equipment through the pipeline aeration
  • Surface aeration: Using an impeller driven by an electric motor, the wastewater is sprayed in all directions by a conduit, forming water droplets in contact with air as well as splashing a large number of bubbles when they fall to increase the oxygen content in the water.
  • Submersible jet aeration: Aeration design special pump, air inlet conduit, nozzle seat, mixing chamber, diffusion tube, water flow through the nozzle seat connected to the pump outlet into the mixing chamber at high speed, the air is guided by the air inlet conduit to the mixing chamber and water flow combined, through the diffusion tube discharge. Also known as jet aeration machine.
  • Submerged aeration: Using the generator to directly drive the rotation of the impeller to cause centrifugal force, so that the nearby low-pressure suction into the water flow, at the same time, the impeller inlet to create a vacuum to suck in air, in the mixing chamber, these air and water mixed by centrifugal force after the rapid discharge.

Oxygen is injected into the water to be treated to ensure adequate oxygenation of the microorganisms in the pool. The general aeration system is mainly composed of a floating body, multiple aeration units and a controller. During operation, the group of aeration devices is placed on the float, draws water and then sprays, atomizes or aerosolizes the water drawn from the other direction. The controller is the terminal that controls this type of aeration unit, and it is able to generate the first thrust that drives the aeration unit towards the corresponding direction. For aeration equipment, its performance characteristics are mainly simple structure, stable performance, uniform mixing, low construction cost, low energy consumption, certain corrosion resistance, and does not generate noise or cause other public hazards.

There are two main aeration methods as follows.

1. Blower aeration
Blast aeration is the use of fans or air compressors to aeration pools filled with a certain pressure of air, on the one hand, supply the amount of oxygen needed for biochemical reactions, while keeping the mixture of suspended solids evenly mixed. Diffuser is the key component of blast aeration, its role is to disperse the air into air bubbles, increase the gas-liquid contact interface, and dissolve the oxygen in the air in the water. The aeration efficiency depends on the bubble size, the amount of oxygen deficit in the water, the gas-liquid contact time and the pressure of the bubble.

At present, the commonly used air diffusers are mainly
a. microporous diffuser; b. medium bubble diffuser; c. large bubble diffuser; d. jet diffuser; e. fixed spiral diffuser.
The blowers commonly used in blast aeration systems are Roots blowers and centrifugal fans. Roots blower is more commonly used in small and medium-sized sewage plants, single-unit air volume below 80m3/min, the disadvantage is that the noise is large, must take muffling, sound insulation measures. When the single machine air volume is greater than 80m3/min, the general use of centrifugal blower, noise is smaller, higher efficiency, suitable for medium and large sewage plants.

2. Mechanical aeration
Mechanical aeration is also known as surface aeration, mechanical aerator is mostly installed in the aeration pool water surface impeller rapid rotation, surface oxygenation. According to the different direction of rotation, can be divided into vertical and horizontal two categories. Commonly used vertical surface aerator has a flat impeller, inverted umbrella type impeller and pump impeller, etc., horizontal surface aerator has a rotary brush aerator and rotary disk aerator. Aeration impeller oxygenation capacity and lifting capacity with impeller submersion depth, impeller speed and other factors, in the appropriate submersion depth and speed, the impeller’s oxygenation capacity, and can ensure that the pool sludge concentration and dissolved oxygen concentration uniform.

Generally speaking, mechanical aeration is often used in aeration pool smaller occasions, can reduce power consumption, maintenance management is also more convenient. Blast aeration supply air scalability is larger, aeration effect is also better, generally used for larger aeration pools.

Aeration increases the oxygen content of the water. Aeration systems can help avoid the use of chemicals and create a healthy ecosystem. Aeration does not kill algae directly, so it is not always effective. It requires treatment of the entire water surface.

Three leaves roots blower aeration effect is the best, blast aeration is the use of a certain air volume and pressure of the aeration fan using the connection of the conveying pipeline, the air through the diffusion aerator forced to join the liquid, so that the pool of liquid and air in full contact. Can use a slightly higher pressure three-leaf Roots fan aeration is better, now sewage treatment, slurry mixing and many other places are using Roots fan to aeration mixing, aeration uniform mixing effect is very good, Roots fan than the mixer efficiency, but also power saving.

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