JPS6344035B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for preventing the bulking phenomenon that occurs due to the dominance of filamentous bacteria of the genus Sphaerotilus in a wastewater treatment process using activated sludge. The biggest problem in the wastewater treatment process using activated sludge is the bulking phenomenon, and once this occurs, the flocculation of the sludge becomes poor and the settling property becomes poor, resulting in sludge being mixed into the wastewater and making operation impossible. It's coming. This bulking phenomenon can be roughly classified into the following two types. (1) High viscosity bulking: This is caused by the accumulation of highly viscous substances in activated sludge. (2) Filamentous bulking: This is caused by the proliferation of filamentous bacteria in activated sludge. The filamentous bacteria in this case of filamentous bulking include those of the genus Sphaerotilus and those of the genus Beggiatoa.
There are some depending on the genus, but most of them are
It is said to be caused by the genus Sphaerotilus. The cause of filamentous bulking is lack of dissolved enzymes,
nutritional imbalance, toxic contamination, temperature effects,
Fluctuations in the compositional concentration of the raw water can be considered, but these factors can also occur in complex combinations, and it is extremely difficult to eliminate them all at once. Even if daily operating operations are managed according to standards for each processing device, this bulking phenomenon usually occurs suddenly. When this occurs, it is urgent to first treat it symptomatically to eliminate the bulking, for example: (1) injection of chlorine or addition of sodium hypochlorite (2) injection of hydrogen peroxide etc. are possible. Both of these (1) and (2) are disinfectants that try to suppress the growth of filamentous bacteria, but they also have a negative effect on the good sludge that coexists, so they are expected to have a selective effect on filamentous bacteria. I can't. In addition, Venosa et al. (Applied Microbiol. 29
Volume, 702 pages 1957) by Bdellovibrio−
Sphaerotilus using a bacterium called bacteriovorus.
Research is being carried out to try to kill only this species.
This bacterium, B. bacteriovorus, has been confirmed to contribute to Sphaerotilus cells and to lyse the cells, but it has no effect on Sphaerotilus that has already grown into filaments. This became thread-like
This is thought to be because Sphaero-tilus is protected by a sheath, and is said to be effective only at the single cell stage. There is also a method of adding ferric chloride or a polymer flocculant to increase flocculation, but this does not damage the filamentous bacteria and returns to its original state as soon as the addition is stopped. Various other methods have been considered, such as changing the operating method, but no method has yet been discovered that directly acts on filamentous bacteria and quickly eliminates the problem. The present inventors focused on the fact that Sphaerotilus is an iron bacterium, and conducted research to find a drug and method that would kill and disintegrate only Sphaerotilus without affecting other microorganisms in sludge. In iron bacteria, Fe ⁺⁺ is the first hydrogen donor during respiration, and Fe ⁺⁺ plays an important role in basal metabolism for these bacteria. Therefore, by changing this Fe ⁺⁺ to a non-ionic form, we deduced that it would be possible to cause iron bacteria to lose their metabolic functions and gradually die. First, water-soluble sulfide was added and an inorganic or organic acid was added at the same time to inhibit the respiratory system by utilizing the Fe ⁺⁺ +S ^-- →FeS↓ reaction caused by hydrogen sulfide. PH in the aeration tank is 3.5~
4.5, hydrogen sulfide is generated,
The effect of this on microorganisms in sludge was investigated.
As a result, it was confirmed that only the filamentous bacteria rapidly declined and finally disappeared without affecting the growth of other useful microorganisms or the BOD removal effect. According to published books (for example, Makio Nakashio: Actual causes and countermeasures for bulking phenomenon 46, 1976), the presence of hydrogen sulfide in wastewater treatment is considered to be extremely inappropriate. As mentioned earlier, some of the filamentous bacteria that cause bulking include Beggiatoa thio−.
There is a sulfur bacterium called thrix, in which sulfur is the hydrogen donor in the respiratory system, and it obtains energy by decomposing and oxidizing hydrogen sulfide. Therefore, Beggiatoa is said to actively proliferate and cause bulking in the presence of hydrogen sulfide. Hydrogen sulfide is mainly generated in the adjustment tank before flowing into the aeration tank, so
In order to prevent this, this tank is also ventilated to avoid an anaerobic condition. There is also a statement that this hydrogen sulfide kills useful activated sludge bacteria and induces the disintegration of the sludge, making the sludge unusable. Therefore, in order to proactively introduce hydrogen sulfide into the aeration tank, sufficient countermeasures against the problems caused by hydrogen sulfide must be prepared. Furthermore, even if hydrogen sulfide succeeds in killing Sphaerotilus, if Beggiatoa proliferates in its place, it cannot be used as a countermeasure against bulking. It has been found that it can only live in a very limited pH range near neutrality. However, the method that the present inventors are trying to adopt is to acidify and generate hydrogen sulfide at the same time as adding sulfide, so when sulfide is present, the pH is on the acid side, There is no risk of developing Beggiatoa in the PH range. Also, when blowing hydrogen sulfide gas directly into the aeration tank, the same effect can be achieved by setting the pH to the acidic side in advance.
The risk of developing Beggiatoa can be avoided, and this was also confirmed through experiments. Next, considering the possibility that other useful bacteria may be killed by hydrogen sulfide and the activated sludge may be dismantled, the conditions under which hydrogen sulfide is naturally generated are anaerobic. It is easily understood that under these anaerobic conditions, high quality sludge is disintegrated under the influence of hydrogen sulfide. The inventors performed experiments on the assumption that even in the presence of hydrogen sulfide, general bacteria grow almost normally in an aerated state where there is sufficient dissolved oxygen. the result,
No disintegration of sludge was observed, and an increase in mixed liquid suspended solids (MLSS) was observed, validating the inventors' idea. That is, in order to prevent filamentous bulking, which accounts for most of the bulking phenomena that occur in the wastewater treatment process using the activated sludge method, by making the wastewater contain hydrogen sulfide and aerating it under acidic conditions, The purpose can be achieved by inhibiting the growth of the causative filamentous bacteria or destroying the grown bacterial cells. Next, the present invention will be explained in detail with reference to Examples. Example 1 Using a 5-volume water tank, a sludge culture experiment was conducted in the following categories. For each section, 4 sludge samples were collected from a factory-scale aeration tank, and the sludge was thoroughly aerated with the same type of aeration pipe as that in the aeration tank, resulting in a DO of 75 to 100%.
The MLSS of sludge is 3050PPm, which is already Sphaerotilus
was grown and had an SV ₃₀ of 95 to 96. A: Control B: PH maintained at approximately 4.5 with sulfuric acid C: 200 PPm of sodium sulfide added daily and PH
D: Add 200PPm of sodium sulfide daily and maintain pH between 6.0 and 5.0.
E: Blow in 250ml of hydrogen sulfide gas generated by Kippu's equipment once a day and maintain the pH between 4.5 and 3.5. Combined wastewater from a sake brewery (BOD approx. 900) is used as the inflow raw water. When the aeration was stopped for 2 hours a day, the supernatant liquid was added to replace the raw water at a ratio of 0.09 g-BOD/g-MLSS. This relationship is shown in FIG. In all the figures, the solid lines are
The dotted line shows the change in SV ₃₀ and the change in PH. According to this, there was not much change in SV ₃₀ between control A and B where only PH was lowered, and 96
However, in categories C, D, and E, where sodium sulfide was added and hydrogen sulfide was injected, a remarkable change was observed even under a microscope, and the filamentous bacteria rapidly disintegrated and broke off into short pieces. A large number of bacterial cells were observed floating, and the sludge was black in color.
As shown in Figure 1, the SV ₃₀ value decreased and the sedimentation properties were improved. Since the aqueous solution of sodium sulfide is highly alkaline,
When this is added, the pH will rise rapidly. This was adjusted to a predetermined pH value by adding sulfuric acid, and this value is also shown in FIG. It has already been confirmed that hydrogen sulfide is generated when sulfuric acid is added to an aqueous solution of sodium sulfide to bring the pH to near neutral. Therefore, in the case of Category C, the pH is adjusted after adding sodium sulfide, so the amount of hydrogen sulfide generated and dissolved is unknown, but when paper soaked in lead acetate solution is brought close to the sludge surface, it turns black. It was confirmed that hydrogen sulfide was generated. However, the change in the SV ₃₀ value of this C category is
The fact that the value on the 4th day was later than those in categories D and E and was slightly higher is presumed to be due to the fact that the PH did not decrease sufficiently and the amount of hydrogen sulfide generated was lower than in category D. Direct injection of hydrogen sulfide in category E is 200PPm.
The calculated amount of hydrogen sulfide generated by sodium sulfide was injected, but almost the same result as in Category D was obtained. Simply lowering the pH without adding sodium sulfide had no effect on Sphaerotilus. Since the amount of liquid was small, changes in MLSS could not be measured over time, but the initial MLSS was 3.052.
The classification for each category was as follows.

[Table] The MLSS value decreases somewhat for each, but this tendency is noticeable for C, D, and E. This thing is
This seems to be the result of the amount of Sphaerotilus decaying and flowing out exceeding the increase in useful bacterial cells. Example 2 An experiment was conducted in a single aeration tank with a capacity of approximately 300 m ³ . Discharge was carried out by gate discharge, and aeration was carried out by a jet aerator using one 7.5Kw submersible pump.The inflow raw water was approximately 100m ³ /day, the total BOD amount was approximately 80Kg /day, and the discharge target was set to be less than 200 each for BOD and SS. The experiment was started in a state where filamentous bacteria were generated in this treatment tank, sludge did not settle at all, and SV ₃₀ =100. As the sulfide, we selected sodium sulfide, which is water-soluble, easily available, and harmless to waste water, and as the inorganic acid, we used 50% sulfuric acid. Sodium sulfide was added gradually after the gate discharge was completed, so that the amount of water was approximately 50 PPm for approximately 200 ^m3 of water, and at the same time, the pH in the tank was adjusted to approximately 4.0 to 4.5 using sulfuric acid.
After adjusting it so that it was, sufficient aeration was performed. The course of change in this case is shown in Figure 2. Addition of 10 kg of sodium sulfide per day becomes effective when the total amount reaches 40 kg, and the SV ₃₀ value becomes less than 100, and microscopic observation shows that filamentous bacteria are not present.
You can see that Sphaerotilus has started to tear. Furthermore, no sludge was seen flowing out, and an increase in MLSS was observed. Furthermore, as a result of continuing to add sodium sulfide, the SV ₃₀ value rapidly recovered from around 100 kg, and the cumulative amount reached 160 kg, 22 days after the start of adding sodium sulfide.
Sphaerotilus was usually only very slightly entangled in the sludge. At this point, we stopped adding sodium sulfide and observed the progress without adjusting the pH using sulfuric acid. As a result, the SV ₃₀ value improved as shown in Figure 2, and extremely normal operation was possible. Note that during the addition of sodium sulfide, raw water was inflowed and discharged in a predetermined amount. However, since the pH of the effluent water had decreased, it was discharged after neutralization with caustic soda, but during this period the BOD of the treated water was 30 to 70 PPm, and no change was observed compared to normal operation before the start of this experiment. I couldn't help it. From the above results, the addition of soda sulfide has no negative effect on high-quality sludge.
It selectively acts only on Sphaerotilus, a filamentous bacterium that causes the bulking phenomenon, without compromising BOD removal ability, and destroys it. Because it is cultured under low pH, no Beggiator is observed at all. I was able to restore it to a completely normal state.

[Brief explanation of the drawing]

Figure 1 shows the SV ₃₀ value and
Indicates changes in PH value. Figure 2 shows the results during the culture period.
The relationship between MLSS, SV ₃₀ , PH change, and addition of sodium sulfide is shown.

Claims (1)

[Claims] 1. In waste liquid treatment from brewing or fermentation processes, hydrogen sulfide is dissolved in activated sludge during aeration to a concentration of 1 ppm or more and 500 ppm or less to selectively kill filamentous bacteria that cause bulking phenomenon. A bulking prevention method that is characterized by 2. The method for preventing bulking according to claim 1, in which hydrogen sulfide generated by adding a water-soluble sulfide and an inorganic or organic acid is dissolved in activated sludge in order to dissolve hydrogen sulfide. 3. The bulking prevention method according to claim 1, wherein hydrogen sulfide is directly blown into the activated sludge under acidic conditions in order to dissolve the hydrogen sulfide.