Collect! Aeration Tank Operation and Maintenance Manual (Part 3)
Written by: Jasmine
Contact email: Jasmine@juntaiplastic.com
1. Five major items of routine monitoring of aeration tank water intake
1.1 Temperature
1.2 PH value
1.3 COD and BOD5
1.4 Ammonia nitrogen and phosphate
1.5 Toxic substances
2. Routine monitoring project of mixed liquid in aeration tank
2.1 How to control the MLSS or MLVSS value of the aeration tank?
2.2 What is the sludge settling ratio (SV) of the aeration tank mixture? What is the function?
2.3 What abnormal phenomena are prone to occur when measuring the SV value? Why?
2.4 What is Sludge Volume Index (SVI)?
2.5 What is the reason for the increase in the SVI value of the aeration tank mixture?
3. Operation management of aeration tank - foam problem
3.1 Brown-yellow foam
3.2 gray-black foam
3.3 White foam
3.4 Colored foam
4. Operation management of aeration tank - sludge expansion
4.1 The environmental conditions that cause the expansion of filamentous bacteria in activated sludge are:
4.2 Conditions and causes that lead to the expansion of non-filamentous bacteria
4.3 Measures to control sludge bulking in aeration tank
Written by: Jasmine
Contact email: Jasmine@juntaiplastic.com
3. Operation management of aeration tank - foam problem
The best classification method of biochemical system foam is to classify by color and viscosity, because confirming the different colors and viscosity of foam can guide us to judge the current state of activated sludge.
3.1 Brown-yellow foam
Symptom:
When the foam is generated, the amount is small, and a small amount is generated near the liquid level around the aeration mass, which gradually dissipates along the radiation direction, and starts to accumulate in the surrounding corners. During the whole process of foam formation to accumulation, the foam is in a brittle state, so this type of foam will not cause serious accumulation in a short period of time, resulting in a large amount of scum.
Cause Analysis:
The activated sludge is in an aging state, and part of the activated sludge disintegrates due to aging, is suspended in the activated sludge mixture, and evenly adheres to the foam under aeration state, resulting in prolonged foam bursting, which creates conditions for foam accumulation .
Process judgment:
This kind of foam is a manifestation of the sludge in or about to enter the aging state of activated sludge.
3.1.1 The settling ratio of activated sludge.
The observation of the sedimentation ratio of activated sludge is one of the important methods to determine whether the activated sludge is aging. By confirming whether the sedimentation ratio is too small, whether the settled activated sludge is dark yellow in color, and whether the sedimentation speed is too fast, etc. The brown-yellow foam produced on the surface can more accurately judge whether the activated sludge is aging.
3.1.2 In terms of SVI value.
SVI value is indeed a good indicator for judging the looseness of activated sludge, but it also has the function of judging whether activated sludge is aging. When the SVI value is lower than 40, the activated sludge is usually aged, and it can be more accurately judged whether the activated sludge is aged by combining with the brown-yellow foam produced by the liquid surface.
3.1.3 Microscope observation results.
For the aged activated sludge, microscopic observation can also be well found. The key point is the density of bacteria micelles and the proportion of metazoans. If the observed bacteria micelles are relatively dense and there are a large number of metazoans, combined with the brownish yellow foam on the liquid surface, it can be judged whether the activated sludge is in the aging stage.
Written by: Jasmine
Contact email: Jasmine@juntaiplastic.com
3.2 gray-black foam
Symptom:
The amount of foam, production process, accumulation, and friability are the same as those of brown-yellow foam, but its color has black components, and the accumulated product is also gray-black. The color of activated sludge in the entire biochemical system is also slightly gray. black feeling.
Cause Analysis:
The activated sludge is in an anoxic state, and the anoxic state can cause a local anaerobic reaction in the activated sludge. In this way, the activated sludge that was originally in the aerobic state will die in the process of this transformation, and it will also Attached to the air bubbles during aeration.
Therefore, if we see that the generated foam is gray-black, in addition to confirming whether the influent water contains black dye wastewater, the main thing is to confirm whether there is an anaerobic situation caused by insufficient aeration in the biochemical tank.
Process judgment:
Most of the gray-black foam is anoxic or anaerobic state in the activated sludge system, and the confirmation of the corresponding process control indicators needs to be carried out around this aspect. When the gray-black foam is generated, it is necessary to comprehensively judge the DO value.
To confirm whether the activated sludge system is in anoxic and anaerobic state, the best way is to conduct on-site testing directly through a dissolved oxygen meter. In this regard, the mistake our operators are prone to make is to detect only one point to judge the overall dissolution of the biochemical system. Oxygen conditions, this approach is one-sided.
In order to avoid this situation, it is necessary to conduct on-the-spot inspection on the uniform distribution of the entire biochemical system, and only in this way can the local lack of oxygen supply be found. If the monitoring value of dissolved oxygen is lower than 0.5ppm in some locations, we need to focus on confirming these locations.
Written by: Jasmine
Contact email: Jasmine@juntaiplastic.com
3.3 White foam
Symptom:
There are many reasons for the generation of white foam, but they are mainly caused by excessive load, excessive aeration, and inflow of detergent. When distinguishing what causes the white foam, the viscosity of the foam can give us a lot of reference.
Under normal circumstances, the viscous and unbreakable foam is often caused by the high load of activated sludge, and the color of the foam at this time is bright and white, and the stacking property is good, while the viscous and easily broken foam is often caused by the excessive aeration of activated sludge. , and the color of the foam at this time is old white, the accumulation is poor, only local accumulation occurs, and the inflow of detergent will also produce white foam, because the presence of detergent increases the surface tension of the water body, which eventually leads to the formation of foam.
Process judgment:
The generation of white foam is basically attributed to the excessive load of activated sludge, excessive aeration, and inflow of detergent.
Written by: Jasmine
Contact email: Jasmine@juntaiplastic.com
3.3.1 Relationship between F/M value and white foam.
We know that the index for judging the load of activated sludge is F/M (instant micro ratio). If the F/M value is too high (greater than 0.5) and a large amount of white viscous foam is produced, we can think that activated sludge is indeed is in high load operation.
3.3.2 The relationship between DO value and white foam.
Excessive aeration will also produce a large amount of white foam. Although the normal aeration volume will not lead to the production of foam in the biochemical system when the foam viscosity is not high, the activated sludge will partially activate under the action of excessive aeration volume. The sludge disintegrates and dissolves, resulting in an increase in the organic content of the activated sludge clear liquid, which is one cause of foaming at high aeration rates.
To this end, in the case of ensuring the oxygen supply of activated sludge, reducing the amount of aeration as much as possible can not only reduce the generation of foam, but also reduce energy consumption and operating costs. Usually, the DO value at the outlet of the aeration tank is controlled to be 1-3 mg/l. If the aeration volume is increased blindly so that the DO rises to 5.0 mg/l, the negative impact on the activated sludge system will be greater.
3.3.3 The problem of inflow of foaming substances.
In addition to the high treatment load and excessive aeration, the flow of foaming substances into the biochemical system can also cause foam in the activated sludge system. It is more common that detergents or surfactants flow into the biochemical system. Under the action of aeration, it is very A large amount of white foam will soon form. By monitoring the DO value and the sludge load of the biochemical system at that time, we can conversely infer whether the influence of the influent water quality caused the generation of foam in the activated sludge system.
Written by: Jasmine
Contact email: Jasmine@juntaiplastic.com
3.4 Colored foam
Symptom:
Colored foam often occurs when colored wastewater flows into the biochemical system. Usually, these colored wastewaters have a high concentration of organic matter. Under the action of aeration, it is easy to cause foams similar to those generated at high loads. Since water is inherently coloured, naturally occurring foam is also coloured.
Another situation is that sewage and wastewater are rich in surfactants or detergents. After flowing into the biochemical system, it will naturally lead to the generation of foam. Under the sunlight, the surface of these foams will produce colorful colors, which is very useful for judging such foam The cause of it helps a lot.
Process judgment:
The generation of colored foam is related to the inflow of colored wastewater and the inflow of detergents and surfactants. Therefore, it can be judged by observing whether the treated water in the physicochemical zone still has color. For example, whether some wastewater will also interfere with the color of the biochemical system. Regarding the issue of detergents and surfactants, the focus is also to confirm the accumulation of foam at the location of the physicochemical zone. From this, the influence of surfactants and detergents on the subsequent biochemical system on foam can be judged.
Activated sludge is a dynamic system, which means more observation, more thinking and more in daily operation. In addition to the observation of the foam on the pool surface, we must always pay attention to the scum on the liquid surface, and cooperate with a number of indicators, such as SV30, dissolved oxygen, microbiological ratio, biological phase observation, etc., in order to quickly and accurately make process judgments.
Written by: Jasmine
Contact email: Jasmine@juntaiplastic.com