JP3348904B2 - Recovery method of activated sludge tank capacity - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an activated sludge tank used for the purification treatment of organic waste water when its treatment capacity is reduced.
The present invention relates to a method for restoring normal processing ability in a short time.

[0002]

2. Description of the Related Art The activated sludge method utilizing the organic matter decomposing action of aerobic microorganisms is extremely effective for the purification treatment of organic wastewater such as food factory wastewater, chemical factory wastewater, domestic wastewater, and urban sewage. Have been. As is well known, in the activated sludge method, the wastewater to be treated is continuously flown into an activated sludge tank in which an appropriate amount of activated sludge is present, and while aeration is being performed to supply oxygen, microorganisms in the activated sludge are reduced by organic substances. Is disassembled.

[0003] Activated sludge includes inorganic substances such as silicon,
Most consist of many types of microorganisms and macromolecular compounds produced extracellularly by the microorganisms. Microorganisms are mainly bacteria, yeasts, molds and protozoa, of which bacteria are in fact involved in the breakdown of organic matter. Other microorganisms are thought to be organisms that either degrade excess organic matter or coexist in the food chain. The organic matter in the treated organic wastewater is partially CO ₂ , N ₂ ,
It is completely decomposed to inorganic substances such as H ₂ O, and part of it is used for bacterial growth. Since the amount of activated sludge in the activated sludge tank gradually increases due to the multiplied bacteria and the polymer compound produced by the bacteria, excess activated sludge is appropriately taken out of the tank.

[0004] The ability of activated sludge to decompose organic substances is not based on the action of a small number of microorganisms in the sludge, but is exerted by an extremely large number of microorganisms participating in the decomposition of organic substances in various aspects. is there. Therefore,
In an activated sludge tank in a stable and good operating condition,
Depending on the quality of the effluent that constantly flows in (ie, the type of nutrient source for the microorganism), a microflora unique to the activated sludge tank is formed. As described above, when the optimum activated sludge in terms of quality and quantity is not formed in the activated sludge tank, seed sludge is brought in from another activated sludge tank as needed, and sufficient activated sludge is sufficiently formed while inflowing wastewater. Wait for it to be done. This process, called acclimation, usually requires about 30-180 days for a newly activated activated sludge tank.

[0005] The complex and subtle balance of bacterial flora in activated sludge exhibiting good organic matter resolution is based on the stability of the quality of the treated wastewater. If the fluctuation range of water quality is large, the wastewater treatment using activated sludge is hardly feasible. For example, if the pH of the wastewater to be treated drops sharply, the number of bacteria that cannot withstand the pH change immediately drops. The processing performance of the device is significantly reduced. Therefore, in the activated sludge method, the pH, BOD, inflow amount, etc. of the wastewater supplied to the activated sludge tank are adjusted by providing an adjustment tank before the activated sludge tank.
Water quality fluctuations are kept within a certain allowable range. However, due to the characteristics of industrial wastewater and municipal sewage, it is inevitable that unpredictable large or sudden fluctuations in water quality will occur, and water quality control tanks may fail. An accident can occur in which drainage of water quality, which is fatal to bacteria inside, flows into the treatment tank.

[0006] When wastewater of undesired water quality flows in and the bacterial flora of the activated sludge suddenly changes and the wastewater treatment capacity is reduced, conventionally, the water quality of the inflowed wastewater is quickly returned to within a control range, and sometimes the activated water is activated. After replacing all the sludge with that of another activated sludge tank, it was necessary to wait for the activated sludge to recover its previous bacterial flora and quantity by habituation. However, in such a conventional method, it takes about one month or more long days before the activated sludge tank recovers its design capacity. In addition, it is necessary to prevent large economic losses due to such accidents and to prevent untreated wastewater from being discharged, and many safety measures and backup facilities are required for wastewater treatment by the conventional activated sludge method. Met.

[0007] The addition of nutrients generally preferred by bacteria, such as glucose, to the activated sludge tank for the purpose of shortening the number of days required for acclimation, requires that the nutrients are preferentially used by the bacteria group having the highest growth ability. Therefore, even if it is effective in recovering the amount of activated sludge, it brings about an undesirable change in bacterial composition.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the bacterial sludge composition of activated sludge due to a sudden accident, as described above, so that the treatment capacity of the activated sludge tank is significantly reduced. It is to provide a way to recover in time.

[0009]

SUMMARY OF THE INVENTION The present invention, which has succeeded in achieving the above object, has an advantage that when the wastewater treatment capacity of the activated sludge decreases due to the fluctuation of the water quality of the wastewater flowing into the activated sludge tank, the number of bacteria is reduced by the fluctuation of the water quality. The bacteria in the sludge that has been drastically reduced are rapidly grown outside the activated sludge tank by individual cultivation using a complete nutrient medium, and are fed into the activated sludge tank to shorten the days required for acclimation. In advance, the activated sludge was collected from an activated sludge tank showing good wastewater treatment capacity, and a large number of bacteria involved in organic matter decomposition were separated from the collected activated sludge, and the characteristics of those bacteria were confirmed. It is something to keep.

Hereinafter, the method of the present invention will be described in detail. Activated sludge in an activated sludge tank exhibiting a good wastewater treatment capacity contains a large number of bacteria as described above, which share a plurality of processes of organic matter decomposition. For example, proteins are converted into N ₂ gas from amino acids via acetyl-CoA, organic acids, and NH ₄ ^{+, and} are converted again into amino acids to become bacterial cell components. Bacteria are involved.

In order to carry out the present invention, as many useful bacteria as possible are collected in each step of the above-mentioned organic matter decomposition.
In addition, it is necessary to confirm the characteristics of each of the collected bacteria and group them. Specifically, a number of pure strains which are regarded as pure strains are isolated from normal activated sludge in accordance with an ordinary method for separating bacteria, and their characteristics are examined. No identification of bacterial species is required. The characteristics of bacteria are examined, for example, for the following items.

A. Whether or not the strain is capable of decomposing major organic matter in wastewater (this indicates whether the strain is a primary decomposer for organic matter in wastewater). B. The ability to decompose organic matter into inorganic matter (CO ₂ , N _2, etc.) (whether or not the strain is the final decomposer for organic matter in wastewater). C. Whether or not the activated sludge has the ability to maintain the preferable physical properties (floc-forming ability) (this indicates whether or not the activated sludge has the ability to form a floc for facilitating separation and discharge of the treatment liquid as well as simple organic substance resolution). D. The speed of growth in the wastewater to be treated (this allows
It has a high ability to decompose, absorb, and use organic matter, indicating that it is likely to become a priority bacterium in activated sludge.) E. FIG. The abundance ratio in activated sludge-constituting bacteria (the higher the abundance ratio, the higher the resolution is not necessarily higher, but it greatly affects the physical properties of the activated sludge in some way).

The items to be emphasized are determined according to the type of the activated sludge treatment method, the purpose of the treatment, and the like. For example, in the case of an aerobic activated sludge tank not intended to remove nitrogen compounds, it is not important to confirm the ability to decompose nitrogen compounds to N ₂ gas, but to emphasize the ability to decompose and remove carbohydrates. From the above, it is possible to confirm in which scene of the activated sludge the bacteria are involved.

Next, a resistance test is performed on each bacterium against fluctuations in water quality of the wastewater to be treated. The test items are determined in consideration of the type of wastewater to be treated, the type of activated sludge treatment method, the surrounding environment of the facility, and the like. For example, confirm the following characteristics. a. Resistance to pH changes b. Resistance of the wastewater to be treated to changes in BOD c. Resistance to accumulation of organic matter decomposition reaction intermediate products (organic acid, NO ₂ ⁻ , NH ₄ ⁺ , P, etc.) in the activated sludge tank d. Toxic substances for bacteria (organic solvents, surfactants,
Resistance to heavy metal ions, fats and oils, etc. e. Resistance to temperature changes

Based on the characteristics confirmed as described above, all bacteria are first classified from the viewpoint of organic matter decomposition characteristics (primary classification), and the classified bacteria are further classified from the viewpoint of resistance to fluctuations in water quality. (Secondary classification). The classified bacteria are stored in a state where they can be cultured at any time after confirming a medium and culture conditions suitable for growing the bacteria.

If there is a large fluctuation in the water quality of the treated wastewater flowing into the activated sludge tank and the activated sludge is damaged and there is an accident that significantly reduces the wastewater treatment capacity, the contents of the water quality fluctuation are immediately confirmed. (If the water quality remains out of the management range, eliminate the identified cause and stabilize the water quality.)

On the other hand, from the contents of the confirmed water quality fluctuations, it is known that the bacteria are presumed to have died or the number of bacteria has been drastically reduced. Therefore, those bacteria are selected from the above-mentioned preserved strains (the resistance which became the standard for the secondary classification). Select with reference to the results of the sex test). Selection is performed for each group strain of the primary classification. Then, the plurality of selected strains are individually cultured under suitable culture conditions using a medium suitable for them. Cultivation of individual strains using a suitable medium and culture conditions is carried out in a short period of about 5 to 7 days for organic matter-degrading bacteria growing in a complete nutrient medium containing glucose, to about 1000 times the number of inoculum. Can be done.

If a sufficient number of bacteria is obtained to restore the abundance ratio in normal activated sludge, the culture as it is or the cells separated from the culture can be transferred to an activated sludge tank having the above-mentioned reduced capacity. To The input amount is the amount required to restore the activated sludge of the bacterial composition before the accident, the percentage of each bacterium in the isolated bacteria, the total number of heterotrophic bacteria in the activated sludge, the death rate of the heterotrophic bacteria due to the accident (Measured separately)
Although it is desirable to determine in consideration of such factors, the purpose of shortening the acclimatization period can be achieved without calculating so strictly.
As a result, the bacterial composition of the activated sludge in the tank is almost returned to the state before the accident, and thereafter, by performing acclimation for a very short time, the wastewater treatment capacity of the treatment tank can be completely recovered.

[0019]

【Example】

Example 1 Activated sludge 3000 mg MLSS / l, BOD-SS load 0.05 kg / kg / day, wastewater organic matter concentration, using two bench-scale batch activated sludge tanks (volume 10 liters) for treating protein-based food factory wastewater 1200 mg / l, pH
Aerobic treatment was performed under the conditions of 6.8, and the state reached a BOD removal rate of 95%.

A part of the activated sludge in the activated sludge tank was collected, and the bacteria were separated by the following procedure. First, the activated sludge was homogenized with a homogenizer, and the obtained activated sludge suspension was diluted with sterile physiological saline to prepare diluents having five concentrations in the range of 10 ⁴ to 10 ^8. The mixture is mixed with 10 ml of agar plate medium and cultured at 25 ° C. for 3 to 10 days. The procedure of separating the expressed colonies on a daily basis and inoculating them on a standard agar medium is repeated several times. On day 10 of the culture, 109 colonies / plate of bacterial colonies were obtained on the 10 ^6- fold diluted wastewater agar medium.
A total of 67 colonies were randomly picked using a random number table in four stages on day 5, day 7, day 7, and day 10.
Each colony was replanted twice on a standard agar medium to obtain 67 strains of activated sludge-derived bacteria.

Next, the following tests were performed for each strain,
Based on the number of days of colony expression and the results of the property test, 8 strains were
The strains were divided into groups, and the strains in each group were ranked in three stages based on pH resistance. Date of colony expression Gram stain Cytochrome oxidase test Catalase test Saccharolysis test (OF test and glucose, agar,
Starch, cellulose, glycerol) Proteolytic test (peptone, collagen, casein, liver extract, myocardial extract)

Specific substance degradation test (wastewater medium and raw material extract in food factory process) Cell morphology microscopy (confirmation of the presence or absence of a structure that causes floc formation) nitrate reduction ability test pH resistance test (7. A wastewater whose pH is adjusted stepwise within the range of 2 to 4.4 is prepared, and the same amount of bacterial cells is inoculated into the wastewater.
Incubate with shaking at 5 ° C for 3-7 days. During this time, the remaining amount of the organic matter to be decomposed is quantified daily. Thereafter, all strains were freeze-dried or stored as inoculum by repeated low-temperature storage and subculture.

On the other hand, the two activated sludge tanks in operation are:
Wastewater of pH 4.0 was supplied for 2 hours in anticipation of an accident in the preceding pH adjustment tank. As a result, the pH in the tank decreased from 6.8 to 4.4. The operation was restarted after the pH of the supplied wastewater was returned to 6.8, but the BOD removal rate had dropped to 66%. Thereafter, one of the two activated sludge tanks continued the conventional acclimatization operation for which natural recovery was expected for comparison.

For another activated sludge tank, an attempt was made to recover the processing capacity according to the present invention. That is, a bacterial group belonging to the group having the weakest pH resistance is selected from the above-mentioned stock strains, and furthermore, the resolution of organic matter in wastewater is high and cytochrome oxidase / catalase positive (energy is obtained using oxygen). This indicates that there is a cytochrome-based enzyme and catalase that decomposes toxic substances produced in the oxygen utilization system, which means that it has the ability to aerobically decompose organic substances to carbon dioxide.)
And from the group within 3 days of colony expression,
Two strains of morphologically different gram-negative bacilli, two strains of gram-negative bacilli having similar characteristics and morphologically different from the group having 3 to less than 5 days of colony expression, and morphologically colonized and isolated One strain was selected from a group of bacteria that accounted for about 36% of the strains, for a total of 5 strains, and they were combined with peptone 0.5.
%, Yeast extract 0.25%, glucose 0.1%, pH 7.
0 liquid medium for 7 days. Then, each culture was centrifuged to collect the cells, and the cells were weighed in an amount necessary for restoring the activated sludge to one having the same bacterial composition as the activated sludge before the pH was lowered. It was put in. In addition, the required input amount was confirmed by the percentage of each bacterium in 67 strains of bacteria initially separated from the activated sludge, the number of heterotrophic bacteria in the activated sludge (1.09 × 10 ⁸ cell / ml), and separately confirmed. It was calculated from the obtained heterotrophic bacteria kill rate (37%).

Two days after the introduction of the cultured strain and restarting the operation, the BOD removal rate recovered to 93%, and the number of days required for recovery was 9 days in total. On the other hand, another activated sludge tank which is expected to recover the processing capacity by simple acclimation has a BOD removal rate of 9%.
It took 35 days to recover to 3%.

[0026]

As described above, according to the present invention, the bacteria whose number of bacteria has been reduced due to water quality fluctuations are rapidly grown in a culture device different from the activated sludge tank and then injected into the activated sludge tank. The treatment capacity of the activated sludge tank, which has been lowered, can be recovered in a much shorter number of days than before.

Claims (1)

(57) [Claims] 1. Activated sludge is collected from an activated sludge tank exhibiting a good wastewater treatment capacity, a large number of bacteria involved in organic matter decomposition are separated from the collected activated sludge, and the characteristics of those bacteria are confirmed. And when the activated sludge is degraded due to water quality fluctuations of the wastewater flowing into the activated sludge tank and the wastewater treatment capacity is reduced, there is no resistance to the water quality fluctuations among the separated and preserved bacteria. Selecting a confirmed bacterium, culturing the bacterium in a complete nutrient medium, and introducing the grown cells into the activated sludge tank for acclimation; and recovering the processing capacity of the activated sludge tank.