Without a microscope, how can you tell if the filamentous bacteria are swollen?

Pay more attention to the public account: environmental protection water treatment

There are many ways to determine whether the filamentous bacteria are swollen, and microscopic examination is one of the most direct judgment methods, but many sewage treatment is not equipped with microscopes because of funds or lack of attention, and only through non-microscopic methods can the existence of filamentous bacteria swelling be detected as soon as possible, and the problem can be detected early, the cause can be analyzed and effective measures can be taken.

1. The structure of filamentous bacteria and the hazards of swelling

The normal activated sludge structure is relatively dense, the mycelium grows well, and the outer edge of the mycoccal pellet is neat and clear under the microscope, and ciliated protozoa can be found. The sludge is in the shape of alum flowers, and has good flocculation, sedimentation and thickening properties. The sludge volume index (SVI) is about 100, the sludge sedimentation volume (SV) is about 30%, and the moisture content is about 90%. From the perspective of the structure of the sludge, the activated sludge floc is composed of a combination of colloidal and filamentous bacteria. The filamentous fungus resembles the skeleton of a flocculent, and the colloidal mass is bonded to the skeleton and intertwined with each other like the relationship between bone and flesh. For normal activated sludge, there is an appropriate ratio between the two. If the growth and reproduction of filamentous bacteria is excessive, the growth and reproduction of mycelium will be inhibited, and many filamentous bacteria will stretch out of the sludge surface, which will loosen the flocculents, deteriorate the sedimentation performance, and the sludge volume (%) and sludge volume index (SVI) will be very high, which is the filamentous bacterial sludge expansion. When the swelling is severe, almost the entire field of view under the microscope is filamentous bacteria. The sludge volume index (SVI) of this filamentous bacterial expansion can generally reach 200~2000, depending on the degree of expansion. The appearance of filamentous bacterial expansive sludge is different from that of normal sludge, with little supernatant but also very clear.

After sludge expansion, the SS of the effluent from the secondary sedimentation tank will increase significantly until it exceeds the national discharge standard, and the CODcr and BOD5 of the effluent will also exceed the standard. If no immediate control measures are taken, the continuous loss of sludge will cause the number of microorganisms in the aeration tank to drop sharply, and the normal need to decompose organic pollutants cannot be met, resulting in the performance of the entire system degrading or even collapsing. If it is recovered, it needs to start over from cultivating and domesticating activated sludge.

2. Judge the expansion state of filamentous bacteria by observing the sedimentation ratio of activated sludge

The direct consequence of the swelling of filamentous bacteria is the deterioration of the sedimentation compressibility of the activated sludge and the increase of the moisture content of the activated sludge. In the whole process of activated sludge sedimentation, it can be found that the activated sludge sedimentation time is prolonged and the sedimentation rate is slowed down. The sedimentation characteristics of activated sludge with different swelling degrees are as follows.

(1) Activated sludge sedimentation performance during slight expansion of filamentous bacteria

In general, the settling property of lightly expanded activated sludge is slightly worse than that of normal conditions, which is mainly reflected in the increase in the volume of the whole mixture after sedimentation. Generally, the normal sedimentation ratio of activated sludge is between 10%~30%, and the sedimentation ratio of activated sludge swelled by mild filamentous bacteria is usually about 25%~40%. In terms of the flocculation of activated sludge in the early stage of sedimentation, its flocculation rate will be lower than the flocculation rate of activated sludge with normal performance, and the flocculation time will be extended by about 2~4 times. (Normal activated sludge has excellent initial flocculation performance, and the flocculation process can be completed within 1min).

(2) Activated sludge sedimentation performance when filamentous bacteria are moderately expanded

When the filamentous bacteria swell moderately, the relative volume expansion of the activated sludge is more obvious, and the color of the activated sludge will become lighter. In terms of sedimentation rate, due to the expansion of filamentous bacteria, the flocculation performance of activated sludge is reduced, so the time taken in each stage from the beginning of flocculation to free precipitation, group precipitation, and compression precipitation will be prolonged. In particular, the compression and precipitation stage is more obvious, which will be twice the normal compression and precipitation time. In terms of sedimentation ratio, the final sedimentation ratio of activated sludge is about 40%~60%.

(3) Activated sludge sedimentation performance when filamentous bacteria are highly expanded

When the filamentous bacteria are highly expanded, the sludge and water separation effect of activated sludge is very poor, we can not see the obvious sedimentation effect in the first 15min, the activated sludge shows a high degree of fineness, the color is bright and light, and the free sedimentation, group sedimentation and compression precipitation of activated sludge are not distinguished, especially in the compression and sedimentation stage. From the results of the sedimentation ratio observation, it can be seen that the sedimentation ratio of highly expanded activated sludge is about 90%. At this time, the settling of activated sludge in the secondary sedimentation tank is very difficult. Therefore, in the stage of high expansion of activated sludge, a small amount of activated sludge can be observed flowing out of the secondary sedimentation tank, and at the same time, the activated sludge floc will be very large and obvious on the entire secondary sedimentation tank level.

(4) Sedimentation of activated sludge when filamentous bacteria are extremely expanded

The extreme expansion of filamentous bacteria is catastrophic for the entire biochemical system, because in the case of extreme expansion of filamentous bacteria, the sedimentation ratio of activated sludge is usually 100%, that is, there is no sedimentation within 30min, and the activated sludge mixture at this time is fine, light in color, and white as a whole, and the sedimentation ratio of 99% can only be seen within 1h after sedimentation. A large amount of activated sludge flows into the secondary sedimentation tank, and the concentration of activated sludge decreases rapidly. Therefore, when the filamentous bacteria of activated sludge swells extremely, not only the effluent exceeds the standard, but the concentration of activated sludge is also greatly affected, which is very likely to lead to system collapse.

3. Judge the swelling state of filamentous bacteria by sludge volume index

The sludge volume index has a good role in judging the swelling state of activated sludge, especially for mild and moderate filamentous swelling. In particular, when we find that the sedimentation ratio of activated sludge is greater than 40% when we observe it, it is easy to misjudge if the concentration of activated sludge is too high if it is not ruled out. However, the sludge volume index value can well avoid this situation, because in the calculation formula of activated sludge volume index, the denominator is the activated sludge concentration value, and the concentration value of activated sludge itself is also taken into account in the calculation of sludge volume index.

For filamentous bacteria in different swelling stages, the sludge volume index value is different. We usually think that it is normal for the sludge volume index value to be between 50~150. For industrial wastewater, the value can be relaxed to between 50~200. When the activated sludge swells with mild filamentous bacteria, the sludge volume index can rise to about 250, in the moderate filamentous bacteria swelling stage, the sludge volume index is between 300~350, in the state of high filamentous bacteria swelling, the sludge volume index is about 500~700, and the extreme filamentous bacteria swelling, because the sedimentation ratio of activated sludge is 100%, so it also loses the significance of calculating the sludge volume index.