Wastewater aeration is the process of adding air into wastewater to allow aerobic biodegradation of pollutant components. It is an integral part of most biological wastewater treatment systems. Unlike chemical treatment which uses chemicals to react and stabilize contaminants in the wastewater stream, the biological treatment uses microorganisms that occur naturally in wastewater to degrade wastewater contaminants.
Aeration provides oxygen to bacteria for treating and stabilizing the wastewater. Oxygen is needed by the bacteria to allow biodegradation to occur. The supplied oxygen is utilized by bacteria in the wastewater to break down the organic matter containing carbon to form carbon dioxide and water. Without the presence of sufficient oxygen, bacteria are not able to biodegrade the incoming organic matter in a reasonable time. In the absence of dissolved oxygen, degradation must occur under septic conditions which are slow, odorous, and yield incomplete conversions of pollutants. Under septic conditions, some of the biological processes convert hydrogen and sulfur to form hydrogen 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 odor formation. Bio-degradation of organic matter in the absence of oxygen is a very slow biological process.
In municipal and industrial wastewater treatment, aeration is part of the stage known as the secondary treatment process. The activated sludge process is the most common option in secondary treatment. Aeration in an activated sludge process is based on pumping air into a tank, which promotes microbial growth in the wastewater. The microbes feed on the organic material, forming flocks that can easily settle out. After settling in a separate settling tank, bacteria forming the “activated sludge” flocs are continually recirculated back to the aeration basin to increase the rate of decomposition.
Aeration is the most critical component of a treatment system using the activated sludge process. A well-designed aeration system has a direct impact on the level of wastewater treatment it achieves. An ample and evenly distributed oxygen supply in the aeration system is the key to rapid, economically-viable, and effective wastewater treatment. The membrane aerated biofilm reactor is a game-changer for wastewater treatment.
Surface aerators push water from under the water’s surface up into the air, then the droplets fall back into the water, mixing in oxygen. The jets of water break the surface with varying degrees of force. In diffused aeration, submerged devices release air or oxygen into the wastewater, as bubbles rise through the wastewater, oxygen is transferred from a gaseous state to a liquid state, thus adding dissolved oxygen to the water and they keep the microorganisms suspended, so they do not settle out.