Understanding the Different Methods of Water Aeration

For thousands of years, aerators have been used to keep water supplies healthy, with cascade aerators dating back to Roman times. Even before the Romans knew what oxygen was or how aerated water works, they understood the process’s importance.

The goal of aerating is to increase the oxygen levels in a body of water. Examples of how to aerate water include disturbing the water’s surface or creating bubbles below the surface. By mixing the water with air, gas exchanges are enhanced, allowing undesirable gases such as carbon dioxide and methane to be displaced by oxygen.

Without aerating a body of water such as a lake, pond or even wastewater, the water can decline in quality. From preventing stagnation to bad odors, aerating helps to keep water fresh and healthy.

There are many examples of aerated water methods, and understanding how they work is important. From stylish fountains to modern solar aerators, plenty of options are available, each better suited for different needs. However, most systems can be defined as either mechanical or diffused.

Mechanical Aeration of Water

Mechanical aeration is when a body of water is aerated by disturbing the water’s surface to mix it with air. The method of disturbance can vary, but often involves rotating shafts, turbines or propellors to agitate the surface of the water and create bubbles.

Common methods of mechanical aeration include:

• Paddlewheels: Paddles push air under the water, churning the surface. The churning action creates turbulence and mixes air into the water, promoting gas exchange.
• Floating surface aerators: Similar to fountains but usually not as aesthetically pleasing, floating surface aerators shoot water directly onto the water’s surface rather than into the air. This creates surface agitation and increases the contact between water and air for oxygen transfer.
• Low-speed surface aerators: These work similarly to paddlewheel aerators by churning the water with shafts. The slow rotation of the shafts creates a gentle mixing action, introducing air into the water and preventing stratification.
• Fountains: Fountain aerators shoot water into the air. As the water droplets fall back down, they capture oxygen from the atmosphere, increasing the oxygen levels in the water.
• Cascades: The oldest known method of aeration, cascade aeration involves water flowing down a series of steps. This increases the surface area of the water exposed to the air, facilitating oxygen absorption.

Diffused Aeration of Water

Diffused aeration, also known as bottom-up aeration, involves introducing air to the water by making bubbles near the bottom. This is done by using onshore diffusers, pipes and blowers. The most widely used methods are  fine bubble and coarse bubble aeration.

Fine bubble aeration involves injecting small bubbles underwater, making it one of the most efficient methods for transferring oxygen into water. It’s also energy-efficient, meaning lower costs for treatment plants that rely on aeration methods. Tube diffusers, disc diffusers and needle-perforated panels are the most common types of diffusers used in fine bubble aeration.

In practice, coarse bubble aeration is identical to fine bubble aeration, except larger bubbles are injected instead. While less efficient than fine bubble aeration, coarse bubble aeration can displace more liquid. This makes it an attractive option in wastewater treatment, as it’s more effective at preventing biosolids from settling.

Which Is Better: Mechanical Aeration or Diffused Aeration?

Each method of aeration has benefits and downsides, depending on the particular needs and preferences.

In general, mechanical aeration is preferable for shallow bodies of water. Since mechanical aeration typically affects the surface of the water directly, deeper water is less affected. If the main concern is visual appeal, mechanical aeration methods can fall on either side. While mechanically powered surface aeration has the potential to be a stunning water display, it can also be an eyesore if a strictly practical aerator is used.

Diffused aerators are ideal for deeper bodies of water because they usually aerate from the bottom up. Diffused aeration methods have their own aesthetic appeal, with the bubbles rising to the surface.

Other Aeration Methods

If the typical mechanical and diffused aeration methods aren’t preferable, there are other options available.

Natural aeration is when natural processes are utilized to keep water healthy. This is most often done by introducing aquatic plants to the body of water. Without needing a power source, these plants will take in carbon dioxide and other waste gases and expel oxygen through photosynthesis. They can also add a natural and visually appealing element to the body of water.

The types of plants needed will depend on the surface area and depth of the water body, with more care taken for smaller bodies of water. Otherwise, there could be a risk that the plants will spread and become difficult to manage.

Solar and windmill aerators can take many forms, though they’re usually diffused aerators. The main difference is how the aerators are powered. Solar aerators take their energy from the sun, storing the power in a battery, which is then used as the power source for the aerator. Windmill aerators harness wind power to directly operate the aerator.

While these are great eco-friendly options that can lower operating costs, they do have drawbacks. Solar aerators may not store enough power to operate around the clock, even during summer months. Windmill aerators face a similar problem in that they only operate in windy weather.

Aeration is a  crucial process in wastewater treatment because it provides the oxygen needed by microorganisms to break down organic pollutants. This biological treatment significantly reduces the levels of harmful substances in the water, making it safer for discharge or reuse.

Thanks to their simplicity, most mechanical aeration systems work well in harsh environments such as wastewater treatment plants. Made using corrosion-resistant metals, the paddles, blades and shafts can provide effective aeration.

While more complicated, diffused aeration systems are more effective in deep tanks. They also tend to have lower maintenance demands and are more efficient at aerating water. Diffused aerators are also generally more energy-efficient than mechanical aerators.

It’s possible to compare  mechanical aeration with diffused aeration, but each can be extremely useful in various stages of wastewater treatment.

When trying to decide on the right aerator, it’s important to understand that different methods of water aeration perform better in different environments and have their own pros and cons.

When looking for an aerator, it’s important to examine:

• Depth: How deep is the body of water? The depth will influence the type of aerator needed, as deeper bodies of water may require a diffused aeration system to effectively distribute oxygen throughout the water column.
• Surface area: How large is the body of water’s surface area? A larger surface area may necessitate multiple aerators or a more powerful aeration system to ensure adequate oxygenation.
• Power availability: How much power can be delivered to the aerator, and how easy is it to connect to that power source? This will determine the feasibility of using certain types of electric aerators and influence operating costs.
• Budget: How much can be spent on the aerator? Different types of aeration systems vary significantly in price, installation costs and long-term maintenance expenses.
• Water quality goals: What water quality levels need to be met? The desired parameters, such as dissolved oxygen levels and pollution reduction, will determine aeration capacity and the specific features needed in the aeration system.
• Type of aquatic life: Is there any wildlife living in the water body? The presence of aquatic life will influence the choice of aerator, as some aeration methods may be more suitable for sensitive ecosystems or specific species than others.

Aerators have several uses, from preventing a garden pond from becoming murky to ensuring a wastewater treatment site meets required quality standards. Diffused aeration systems offer more complete mixing, greater efficiency, low maintenance, and durability and longevity, among other benefits.

SSI Aeration, Inc. manufactures a range of aeration diffusers specifically designed for wastewater treatment plants. With decades of experience in the industry, SSI Aeration, Inc helps clients keep their wastewater sites operating smoothly. To find out which aerators can best serve a particular wastewater treatment site, request a quote today.