The Role of Aeration in Wastewater Treatment
Industrial wastewater treatment is the process used to treat wastewater that is produced as a by-product of industrial or commercial activities. After treatment, the treated industrial wastewater may be reused or released to surface water in the environment.
What is Aeration?
Wastewater aeration is the process of adding air into wastewater to allow aerobic bio-degradation of the pollutant components. It is an integral part of most biological wastewater treatment systems. Chemical treatments make use of chemicals to react and stabilize the contaminants in the wastewater stream whereas biological treatments use microorganisms that naturally occur in wastewater to degrade contaminants.
When is Aeration Used?
The activated sludge process is the most common option under the secondary treatment used in municipal and industrial wastewater treatment. Aeration is part of the secondary treatment process. Aeration in an activated sludge process is based on pumping air into a tank, which promotes the microbial growth in the wastewater. The microbes feed on the organic material, forming flocs that can easily settle out. After settling in a separate settling tank, bacteria forming the “activated sludge” flocs are continually circulated back to the aeration basin to increase the rate of decomposition.
How does Aeration Work?
The bacteria in the water require oxygen for the biodegradation process to occur. Aeration provides oxygen to bacteria for treating and stabilizing the wastewater. The bacteria in the wastewater break down the organic matter containing carbon to form carbon dioxide and water utilizing the supplied oxygen. Without sufficient oxygen, bacteria are unable to biodegrade the incoming organic matter in a reasonable time.
In the absence of dissolved oxygen, degradation must occur under septic conditions that are slow, odorous, and yield incomplete conversions of pollutants. Under septic conditions, some of the biological process converts hydrogen and sulphur to form hydrogen sulphide and transform carbon into methane. Other carbon will be converted to organic acids that create low pH conditions in the basin and make the water more difficult to treat and promote odour formation. Biodegradation of organic matter in the absence of oxygen is a very slow biological process.
There are two common types of water aeration: subsurface and surface.
What is Subsurface Aeration?
Subsurface is the most common type of aeration. Large wastewater treatment plants in urban areas commonly use it. Subsurface aeration uses porous devices that are placed below the liquid’s surface. These diffusers or submersible aerators are lowered into the water or fluid and compressed air is released, creating bubbles. This method delivers the most oxygen available into the water and ensures the water and oxygen are thoroughly mixed.
What is Surface Aeration?
Surface aerators push water from under the water’s surface up into the air, and then the droplets fall back into the water, mixing in oxygen. The jets of water break the surface with varying degrees of force.
Why is Aeration Important for Wastewater Treatment?
Aeration is the most critical component of a treatment system using the activated sludge process. When properly implemented, aeration also eliminates seasonal problems such as algae growth or stratification. When exposed to heat and sun, still bodies of water such as reservoirs become stratified. This causes problems, such as foul odors, weed and algae growth, and fish kills. By improving the nutrient-oxygen balance, aeration helps improve water quality. A well-designed aeration system has a direct impact on the level of wastewater treatment it achieves. An evenly distributed oxygen supply in an aeration system is the key to rapid, economically viable, and effective wastewater treatment.