<h1>Activated sludge method is the most widely used method in water treatment, today a brief elaboration of 10 basic knowledge about activated sludge. </h1>
1. What is activated sludge?
Activated sludge is a flocculent with strong adsorption and decomposition capacity. At the heart of activated sludge is a "living" word. As we all know, natural rivers have self-purification functions, because there is a group of microorganisms living in the water, and microorganisms eat pollutants, so the water will be restored clean. So "living" is embodied in the microbial community.
Microorganisms are part of the activated sludge, in addition, the activated sludge also includes residues produced by microbial metabolism, organic and inorganic substances adsorbed in microorganisms. The mixture in the aeration tank that you usually see is the form of activated sludge in the water.
2. What is the relationship between fungal gel groups and filamentous bacteria? What does it do?
Hysteroids and filamentous bacteria are important components of activated sludge.
The bacterial gel group is formed by the flocculant bacteria with mucus or pod membrane, which can adsorb impurities and free microorganisms in the wastewater, and the bacteria glue group makes the activated sludge have good sedimentation performance, and protects the micro-animals in the wastewater from being swallowed or poisoned.
Filamentous bacteria are the skeleton of activated sludge, which continue to grow and elongate under the adhesion of the fungal gel group, which can make the floc form larger particles while maintaining the looseness of the activated sludge.
Filamentous bacteria and fungal gel groups belong to the relationship between you and me. Filamentous bacteria can grow well under the attachment of mycoplasmic mass, and their growth is not conducive to exposure to the mixture. When in a low-oxygen environment, filamentous bacteria multiply in large numbers cause the sludge to swell.
3. Growth curve of activated sludge
4. Performance indicators of activated sludge
There are 3 performance indicators of activated sludge: sludge sedimentation ratio SV, sludge concentration MLSS and sludge volume index SVI.
SV is easy to determine, but the results do not fully reflect the nature and quantity of sludge. The normal SV value of urban sewage treatment plants is generally between 20% and 30%, while the normal SV value of some industrial wastewater treatment plants is above 90%. Therefore, each wastewater plant should determine the optimal SV value of its own plant based on its own operating experience. SV is explained in diagrams as follows:
MLSS can react to the amount of sludge. The aeration tank mixture must maintain a relatively fixed sludge concentration in order to maintain the treatment effect and the stable operation of the treatment system. Each activated sludge process has its optimum sludge concentration. MLSS is explained in diagrams as follows:
SVI provides a comprehensive reflection of sludge agglomeration and settlement properties. In general, SVI is too low to indicate that the sludge particles are small and lack of activity; SVI is too high to indicate poor sludge settlement performance, and sludge expansion is about to occur or has occurred.
The reasons for the elevation of SVI in aeration tank mixtures are as follows:
5. The indicative role of microorganisms
The protozoa that appear are mainly solid ciliates, such as bellworms, prunes, coverworms, polycontosperms, etc., indicating that the sludge condensation and sedimentation performance is better. Moreover, when microscopic examination, it will find offspring such as rotifers;
When a large number of swimming ciliate protozoa appear, such as bean-shaped worms, kidney-shaped worms, and grasshoppers, it means that the fungal glue mass of activated sludge has not yet formed a good state and is in the stage of aeration initiation;
When a large number of twisted worms appear in the aeration mixture, an anaerobic reaction has occurred in the aeration tank;
When a large number of various amoeba and rotifers in the mixture appear, it indicates excessive aeration and poor sedimentation performance of activated sludge;
When a large number of protozoa such as the genus Zyperus, The genus Saddle Beetle, and the genus Xenocythus appear, it indicates that the concentration of water inlet is extremely low;
When the number of shield fibrigods decreases sharply, it indicates that the mixture has an impact load and toxic substances entering;
When flagella appears (generally only Bodoupes and House trichomoniasis), it indicates poor performance of activated sludge;
When both protozoa and protozoa disappear, it indicates an extreme deterioration in the state of activated sludge;
When protozoa such as roaming insects, intracerated tubeworms, and pinnacles are present ( similar to the aeration initiation phase ) , the activated sludge condition is gradually improving.
6. The cause of the swelling of filamentous bacteria
Because of the large surface area of filamentous bacteria, they have a greater advantage over bacterial gel groups when competing for food in the mixture, resulting in large multiplication leading to swelling. For example: the competition for carbon sources, the competition for other nutrients;
Also because of the large surface area of filamentous bacteria, under suitable water temperature conditions, filamentous bacteria are more conducive to growth than hysteroidal mass, resulting in swelling;
Filamentous bacteria are suitable for production under low oxygen conditions, so when dissolved oxygen is reduced, it can lead to swelling of filamentous bacteria;
In the case of low pH, it is conducive to the survival of fungal filamentous bacteria, but not conducive to the survival of hysteroids, so it causes excessive multiplication of filamentous bacteria.
7. The cause of non-filamentous bacteria swelling
Non-filamentous bacteria are inflated, which is the deterioration of the sedimentation performance of activated sludge caused by abnormal physiological activity of bacteria in the bacterial gum mass.
This kind of sludge expansion can be divided into two types: one is due to too much dissolved organic matter in the inlet water, so that the sludge load F/M is too high, and nitrogen, phosphorus and other nutrients are too little, or the dissolved oxygen in the mixture is insufficient.
Another non-filamentous bacteria is that the inlet water contains more toxic substances, resulting in activated sludge poisoning, bacteria can not secrete a sufficient amount of viscous substance base, forming a floc, so that it is impossible to separate the sludge in the second sedimentation tank and eventually lead to sludge disintegration.
In fact, more than 90% of sludge expansion is caused by filamentous bacteria, and less than 10% is caused by non-filamentous bacteria.
8, the cause of sludge aging
When the sludge aging phenomenon is observed from the surface, it is mainly reflected as: the activated sludge is dark in color and the biological flocculation ability is poor; the biological foam accumulation occurs on the surface of the aerobic pool; the sludge floc is well compressed, but the fine activated sludge floc that is difficult to settle in the supernatant will remain, so that the effluent is turbid; sometimes the second sedimentation tank will have a thin layer of floating mud affecting the quality of the effluent water.
There are two reasons for this. The first is the high-load operation of the aerobic system, at this time the organic matter of the mixture is sufficient, the synthesis and catabolism of microorganisms are exuberant, resulting in excessive sludge production; the sedimentation performance of the newborn sludge floc is poor, and the supernatant is rich in free bacteria to cause turbidity in the effluent.
Secondly, under low-load operation, the anabolic metabolism of microorganisms dominates, and oxygen is mainly used for endogenous respiration. In this way, the aging phenomenon of sludge will occur.
9. The reason for the floating of activated sludge
Excessive amount of surfactants and oils and fats; pH value is too low or too high; salt content is too high or too variable; water temperature is too high and too low; high toxic substrate; overaeration; mixture hypoxia; denitrification produces nitrogen; return flow is too large; sedimentation pond sludge is too much; filamentous bacteria grow excessively.
10. Focus on the daily operation of the activated sludge method
Observe the color and odor of activated sludge; observe the aeration effect; pay attention to the aeration time; pay attention to the aeration volume; pay attention to the remaining sludge discharge; pay attention to the amount of refluded sludge; observe the sludge status of the second sedimentation tank. (Specific operation next analysis)