Why Are Aeration Tanks in Sewage Treatment Plants Full of Foam?
We have all seen children playing the bubble blowing game. The bubbles are very magical and fun; but the operation and maintenance engineers in the water treatment industry avoid bubbles. Even removing bubbles is one of their jobs.
Foaming in aeration tanks is a common problem in water treatment operation and maintenance. Once it occurs, it may cause some adverse effects:
- 1. Affecting the normal operation of instruments and meters, which will mislead the operation of the system and cause process disorder for processes using automatic control.
- 2. Foam enters the secondary sedimentation tank and affects the effluent water quality.
- 3. For processes using surface aeration equipment, it will prevent normal aeration and oxygenation, resulting in insufficient dissolved oxygen in the aerobic tank.
Therefore, it is very important to pay attention to, understand and solve the foam problem in the aeration tank.
Where Does the Foam Come From?
To understand the foam problem in aeration tanks, we must first understand its principle. The article begins with an analogy of "blowing bubbles", and the principle of aeration tank bubbling is the same as "blowing bubbles", with two similarities: one is blowing air; the other is that the water being blown contains surfactants, sugars and other substances.
The ingredients used to prepare bubble water usually include detergent (soap), sugar, tea, etc., which are different, but basically there are two types of substances, one is surfactants, such as detergents, soaps, etc., which have a foaming effect, and the other is foam stabilizers, such as sugar, tea, etc., which can enhance the viscosity of bubbles, make them easier to form, and make them more stable.
The above-mentioned bubble water ingredients or similar substances are very easy to appear in sewage, such as surfactants, filamentous microorganisms, organic matter, etc., and when these substances appear, they will blow up bubbles in the aeration tank.
How to Judge?
Unlike the bubbles blown by the bubble machine, the bubbles blown by the aeration tank have different characteristics because of their complex ingredients. Therefore, the cause of the foam can be analyzed and judged according to its color, shape, size, and viscosity of the mixed liquid. Several common types are listed:
/ White, Large Amount of Foam
Characteristic description: The color is snow-white. In severe cases, it looks like a snowy field from a distance.
Cause judgment: The activated sludge load is too high, aeration is excessive, and surfactants flow in. This situation is closest to bubble water. The load and aeration need to be controlled to a reasonable stage, and excessive surfactants should be prevented from entering the aeration tank.
/ White, Small Amount Of Foam
Characteristic description: The color is white, thin, scattered around the aeration area, unstable, easy to break, and short-lived.
Cause judgment: It is easy to occur in the initial start-up of the aeration tank and when denitrification occurs in a local area. This type of foam problem will not affect the operation of the process and does not require treatment measures.
/ Khaki Foam
Characteristic description: The surface of the foam is turbid, the color is khaki, which is close to the color of activated sludge, easy to break, and not easy to accumulate.
Cause judgment: The sludge is aged or about to age. Some of the sludge disintegrates and dissipates in the water. Under aeration, it evenly adheres to the foam, which enhances the stability of the bubbles and causes foam accumulation.
/ Gray-black Foam
Characteristic description: The foam accumulates around the aeration group, and the water body is gray-black as a whole, and it is not easy to accumulate.
Cause judgment: Anaerobic areas appear in parts of the aeration tank, and some activated sludge dies and disintegrates, attaching to the bubbles generated by aeration, which prolongs the time for the foam to burst and produces gray-black bubbles.
In addition, there are other situations such as biological foam, which are too numerous to count.
Countermeasures
Facing the foam problem in the aeration tank, we must first know that it is inevitable to produce bubbles when a tank of water containing activated sludge and pollutants is continuously aerated. Most of the foam phenomena in aeration tanks are normal and do not need to be treated. The individual situations that need to be focused on are nothing more than starting from the three aspects of influent water quality, activated sludge and aeration.
The influent water quality is to control the acidity, temperature, surfactant, etc. The sludge activity is to control the food-micro ratio, and then control aeration, mainly in the aeration method and aeration volume. This is the fundamental control measure. The emergency measures include spraying water and adding defoaming agents.