In a wastewater treatment system, the aeration tank plays a key role in decomposing organic matter through microbial activity. When the system begins operation, the appearance of white foam on the surface of the aeration tank is a common and often overlooked issue. Although it may seem harmless, if not properly addressed, this foam layer can significantly affect treatment efficiency and system operation. So, what causes this phenomenon, and how can it be resolved? The article below will help you understand the root causes and appropriate solutions.
1. What Is White Foam Formation in the Aeration Tank?
White foam in the aeration tank refers to the presence of a white foam layer on the surface of the biological tank, often occurring during the initial start-up phase or when the system experiences abnormal fluctuations. This foam can be thin or thick, easily dissolved or persistent, depending on the cause. Regardless, it signals that the biological treatment process is out of balance. In many cases, the foam forms due to unstable microorganisms, sudden increases in organic loading, or the presence of surfactants like soap or detergents in the influent.
If left uncontrolled, this condition can reduce treatment performance and cause foam overflow outside the system, affecting aesthetics and potentially leading to secondary pollution. Additionally, white foam can hinder oxygen transfer between the air and water, disrupting the activity of aerobic microorganisms. Therefore, identifying the cause and applying the right countermeasures is essential to maintaining stable operation of the wastewater treatment system.
White foam formation often signals system imbalance or abnormal fluctuations
2. Differentiating Types of Foam in the Aeration Tank
2.1 Thin, Easily Dissolved White Foam
This type of foam typically appears when the microbial population is active and thriving in the aeration tank. The foam is thin, breaks easily, and dissolves quickly when lightly stirred or when aeration stops. It’s commonly seen during system start-up or after introducing new microbial cultures and generally does not affect treatment efficiency unless it becomes widespread or persistent.
2.2 Thick, Persistent White Foam
This foam is durable, remains on the surface for a long time, and is often caused by surfactants such as soap, detergents, or grease in the wastewater. When strong aeration is applied, these substances create thick, stable foam that is difficult to biodegrade. If not treated, the foam can overflow from the tank, causing secondary pollution and interfering with normal system operation.
2.3 Brown/Gray Foam
Brown or gray foam usually indicates that the microorganisms in the tank are under stress or dying, often due to shock loading, low dissolved oxygen, or unfavorable pH conditions. This foam may also be accompanied by foul odors and changes in tank water color. When this type of foam appears, it is crucial to check parameters such as DO, pH, and MLSS to identify the root cause and restore microbial balance promptly.
3. Causes of White Foam in the Aeration Tank
3.1 Sudden Increase in Organic Load
When the organic load in the influent increases sharply—due to irregular discharges or production process changes—the microbial system may not adapt quickly, leading to intense decomposition and foam formation. The high rate of organic oxidation produces gases that encourage foam buildup on the surface, especially under continuous aeration.
3.2 Imbalanced Microbial Biomass
Microorganisms in the aeration tank are highly sensitive to fluctuations in pH, temperature, pollutant concentration, or DO levels. Adverse conditions can cause microbes to weaken, die, or become inefficient at degrading pollutants—resulting in white foam due to unprocessed compounds and gas release from dead cells. This imbalance also affects MLSS concentration and overall treatment effectiveness.
3.3 Presence of Surfactants (Soap, Grease, Detergents)
Wastewater containing surfactants such as dish soap, grease, or industrial detergents is highly prone to causing foam. When these substances enter the aeration tank, they react with aeration and biological processes to form thick, persistent foam. This is a common issue in systems treating effluent from restaurants, hotels, laundries, or food processing plants.
3.4 Lack of Mature Sludge and Stable Sludge Return
Mature sludge (fully developed microbial biomass) plays a critical role in maintaining treatment efficiency and biomass stability. If the tank lacks mature sludge or has insufficient sludge return, the microbial population becomes weak, leading to incomplete decomposition and foam formation. Young or newly seeded systems also tend to produce more foam due to lower surface stabilization capacity.
These are typical causes of white foam formation in aeration tanks of wastewater treatment systems
4. Solutions for White Foam in the Aeration Tank
4.1 Check and Stabilize Influent Load
The first step in addressing white foam is to inspect influent flow and pollutant concentrations. If significant fluctuations or sudden spikes in BOD/COD are detected, adjust the discharge process or add an equalization tank to level the load. Stabilizing the load allows microbes to function efficiently and reduces the risk of foam formation.
4.2 Add Microbial Cultures
If microbes are weak, imbalanced, or dying, adding beneficial microorganisms (specialized aerobic cultures) is an effective solution. These microbes help reestablish a balanced biological system, enhance organic degradation, and minimize foam. Choose microbial products with clear origins and compatibility with the wastewater characteristics.
4.3 Monitor DO and Adjust Aeration Accordingly
DO levels directly impact aerobic microbial activity. If DO is too low, microbes are inhibited; if too high, excessive gas release may lead to foam formation. Regularly monitor DO levels and adjust blower speed or airflow to maintain optimal DO (typically 2–4 mg/L).
4.4 Monitor pH, Temperature, and MLSS
Microbes perform best within a pH range of 6.5–8.5 and a temperature range of 25–35°C. Deviations from these ranges can stress or kill the biomass, causing foam. Maintain stable MLSS concentrations as well. Regular monitoring allows proactive adjustments before foam becomes excessive.
4.5 Work with a Reputable System Builder
If foam recurs frequently or cannot be controlled using basic methods, the root cause may lie in flawed design or system inefficiencies. In such cases, consult a reputable wastewater treatment contractor to assess the entire system and recommend upgrades—such as aeration adjustments, improved equalization, or process reconfiguration—to prevent recurring foam problems long term.
White foam in the aeration tank is not just an operational issue—it’s a warning sign of imbalance within the wastewater treatment system. Correctly identifying the foam type, analyzing root causes, and applying appropriate solutions are essential for ensuring the system runs efficiently, consistently, and meets discharge standards. If foam problems persist or cannot be resolved with standard measures, contact Dai Nam for expert consultation and comprehensive system improvements.
