JP2000271589A - Method for treating oil-containing drainage by activated sludge and culture medium for propagating bacteria for treating oil-containing drainage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To treat oil-containing drainage, whose treatment has been difficult, easily and effectively by activated sludge by cultivating a group of mixed microorganisms in cutting oil drainage integrally and adding the group when drainage is introduced. SOLUTION: In order to prepare an activated liquid (sludge) to be added before sub-anaerobic treatment, a group of mixed microorganisms, after being cultivated integrally from oil-containing drainage and propagated, is added into sludge to prepare activated sludge for drainage treatment. Next, drainage to be treated is introduced into a treatment tank, and the activated liquid is added further into the tank as required. Subsequently, it is maintained in a sub-anaerobic state and only agitated to prevent separation into the drainage and the sludge. In the sub-anaerobic treatment, DO(dissolved oxygen) is not 0 mg/liter in general but kept extremely low. After the sub-anaerobic treatment, aerobic treatment is done so that aerobic conditions in which DO is about to be about 1.5 mg/liter on average are brought. After the aerobic treatment being done, anaerobic treatment is done for about 0.5-2 hr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating oil-containing wastewater containing a large amount of water-soluble cutting oil by a batch activated sludge method. Furthermore, the present invention relates to a culture medium for growing bacteria in pretreatment by a treatment method in which bacteria are introduced to treat oil-containing wastewater by the activated sludge method.

[0002]

2. Description of the Related Art Conventionally, the treatment of oil-containing wastewater is greatly affected by oil (hexane extract, for example, cutting oil), and it is difficult for microorganisms to survive in general activated sludge. Therefore, it is difficult to perform microbial treatment by an activated sludge method on oil-containing wastewater, and physical and chemical treatments such as the addition of a flocculant in a pressurized flotation tank are performed. Among them, it is known that treatment of oil-containing wastewater containing cutting oil with microorganisms is difficult.

[0003] Recently, a method of treating oil-containing wastewater with yeast has been announced, but it concerns animal and vegetable oils discharged from food factories and the like. Further, as the primary treatment, an aeration tank and a sedimentation tank dedicated to yeast were installed, and as a secondary treatment, an aeration tank and a sedimentation tank of a usual activated sludge method were installed.

Japanese Patent Application Laid-Open No. 9-75075 discloses a method in which a bacterium, Stenotrophomonas maltophilia, is brought into contact with oil-containing wastewater under aerobic conditions, and particularly used for treating kitchen wastewater containing animal and vegetable oils. Have been.

[0005]

As described above, since the wastewater containing cutting oil is special, even if bacteria for the activated sludge method commercially available are introduced, the seed sludge will die. The usual habituation method cannot keep the microorganisms in the seed sludge alive. In addition, in the enrichment culture using a bacterial culture medium for ordinary experiments (such as a general bacterial culture medium) from the oil-containing wastewater, it was not possible to acclimate special oil-degrading bacteria in the seed sludge. A conventional facility for physical and chemical treatment by adding a coagulant or the like becomes considerably large, and the cost for chemicals is large.

In particular, wastewater containing a large amount of cutting oil discharged from a factory is emulsified and contains a large amount of a surfactant, so that the aqueous phase becomes anaerobic,
It is more difficult for microorganisms to survive and proliferate for use in the activated sludge method. It is also possible to dilute the cutting wastewater to reduce the oil concentration and treat it with microorganisms.However, dilution increases the amount of treated wastewater, further requires dilution equipment, and increases costs. It is desired to process with. Accordingly, an object of the present invention is to develop a microorganism growth medium for treating activated oil-containing wastewater, which has been conventionally difficult to treat, with an activated sludge, and an activated sludge treatment method for the wastewater.

[0007]

SUMMARY OF THE INVENTION The present invention treats oil-containing wastewater containing a large amount of cutting oil by an activated sludge method. Microorganisms that decompose cutting oil are special in that their growth medium and culture method have not been established, and seed sludge is killed by shock due to oil content, so that normal acclimation is difficult. In a normal acclimatization method, the seed sludge is killed within 7 days from the start of acclimation and floats on the water surface at rest. Therefore, a mixed microbial population capable of treating cutting oil from the oil-containing wastewater is to be cultured, grown, and added. In addition, in the enrichment culture, microorganisms capable of treating cutting oil can be grown using the medium of the present invention.

[0008] The present invention provides a method for treating oil-containing wastewater with activated sludge by a batch-type activated sludge method, wherein a mixed microorganism group in cutting oil wastewater is accumulated and cultured, and the cultured mixed microorganism group is added when the wastewater flows into the wastewater. Provide a way. here,
In the present processing method, it is preferable to repeat a processing cycle of sub-anaerobic state, aerobic state, and anaerobic state in order. In the sub-anaerobic state, the dissolved oxygen is about 0.5 mg / L or less, but not 0 mg / L, and it is preferable to stir during the sub-anaerobic state.

[0009] The growth medium for the oil-containing wastewater treatment bacteria in the present invention contains oil-containing wastewater to be treated, casein peptone and soybean peptone as a nitrogen source, and molasses as a carbon source.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The medium of the present invention is characterized in that casein peptone and soybean peptone are added together, and molasses is added in place of sucrose, as compared with general bacterial medium components.
It is characterized mainly by the addition of autoclaved wastewater. The culture medium for general bacteria is Peptone 5
g / L, yeast extract 2.5 g / L, glucose 1 g / L,
Those having a pH of 7.0 are conventionally known.

The medium of the present invention contains both casein peptone and soybean peptone as nitrogen sources. Soy peptone is suitable for culturing microorganisms, particularly for culturing difficult-to-grow bacteria. By the addition of soy peptone, a mixed microbial population capable of processing wastewater containing cutting oil and capable of growing in the oil-containing wastewater can be grown. For example, casein peptone and soy peptone in total are about 10-30
g / L, preferably about 14-25 g / L, of which casein peptone is about 8-25 g / L.
L, preferably about 13-20 g / L, and about 0.5-6 g / L, preferably about 1-5 g / L of soy peptone. A medium containing only casein-made peptone or only soybean peptone is not preferable because the growth rate is poor.

In the medium of the present invention, molasses is added as a carbon source in an amount of about 4 to 12 ml / L (about 0.03 to 0.1%), preferably about 8 to 10 ml / L. In a normal medium, sucrose is used, but in the wastewater treatment with activated sludge, molasses is often added when the state of sludge such as bulking deteriorates, and it is preferable because it is compatible with sludge. In addition, molasses suppresses the growth of various bacteria compared to sucrose, while flocculent bacteria (unidentified) useful in the present invention,
It is possible to grow special and characteristic bacteria effective for the method of the present invention. When molasses is added in an amount of 0.1% or more, the growth of bacteria is reduced.

[0013] As other medium components, inorganic salts such as potassium dihydrogen phosphate and sodium chloride are added. The amount of each addition is, for example, about 2 to 10 g / L, preferably about 3 to 8 g / L, and more preferably about 5 g / L.

The medium is supplemented with a wastewater component which has been sterilized in an autoclave in advance. The pretreatment of the wastewater component by autoclave is performed by using the usual autoclave treatment.
It is carried out at a temperature slightly lower than 1 ° C. and for a slightly longer time. The autoclaving is preferably performed at about 110 to about 118 ° C.
About 10 to 50 minutes, more preferably about 25 to 40 minutes. The temperature was set lower than 121 ° C., which is used for normal autoclave treatment, in order to prevent denaturation due to decomposition of proteins in wastewater due to high temperature.

The autoclaved oil-containing wastewater is added to the medium at about 50 to 170 ml / L, preferably about 80 to 120 ml / L.
It is preferable to add ml / L, but since the wastewater component varies from day to day, the addition amount is appropriately changed accordingly.
In general, if the amount is less than 50 ml / L, the bacterial flora changes. If the amount is more than 170 ml / L, the influence of the cutting oil is strong, and the proliferation power is undesirably reduced. However,
Depending on the drainage component, an amount not less than or more than these ranges can be added.

After adjusting the medium, the medium is further sterilized under the above-mentioned autoclave conditions. The pH of the medium is adjusted so that when added to the sludge, the pH of the autoclaved medium after the medium adjustment is about 6.8 to 7.5 to prevent death due to shock due to the difference in pH from the sludge. I do.
At this pH value, general bacteria are easy to grow, so that it is considered that the pH is too high for bacteria for a commercial activated sludge method and the like.
Although the treatment for lowering H is performed, the medium of the present invention is in an environment where other general bacteria are unlikely to grow because the medium contains drainage components and molasses. Therefore, culture at a pH of about 6.8 to 7.5 becomes possible. In addition, p after autoclave
If H deviates from this value, it is prepared as appropriate with a suitable acid or alkali, such as HCl or NaOH.

The medium of the present invention may have a medium composition as shown in the following table, but is by way of example and not limited thereto.

[0018]

[Table 1]

The method of multiplying the cutting oil wastewater treatment bacteria will be described below.
The mixed microorganism population drained or accumulated is aseptically added to the adjusted medium (liquid) at a rate of about 0.1 to 3% (v / v), preferably about 1% (v / v). . Subculture is performed at the same ratio. The culture is 24 ~
After 48 hours, growth reaches equilibrium, after which the growth rate decreases. Therefore, it is desirable to add to activated sludge before 24-48 hours. After about 10 passages, no change occurs in the bacterial flora.

The culture temperature is 100 rpm at 30 to 37 ° C.
Shake culture below. Outside the above range, the growth rate is low and the bacterial flora sometimes changes. It also depends on the concentration of wastewater used,
In the case of stationary culture, the growth rate is low, and molasses as a medium component tends to precipitate.
Culturing with shaking at a speed higher than 00 rpm is not preferable because the medium becomes bubbles and becomes locally anaerobic. The degree of shaking should be changed according to the concentration of the surfactant in the waste water. The amount of the culture solution added to the activated sludge is about 0.01 to 1% (v / v), preferably about 0.1% (v / v) of the total amount in the treatment tank.

The oil-containing wastewater to be treated is cycled in the treatment step into three states: a sub-anaerobic state, an aerobic state, and an anaerobic state. This cycle can be about 15-30 hours, preferably about 24 hours. In the present invention, a sufficient residence time of the mixed microbial population in the sludge is ensured, and even in the case of including organisms having a relatively low growth rate, the fixation and growth are stabilized, and the subanaerobic state can be maintained. It is preferred to carry out batch culture with advantages. FIG. 1 shows an example of batch culture according to the present invention.

Before the sub-anaerobic treatment, in order to prepare an activating solution (sludge) to be added before the sub-anaerobic treatment, the mixed microbial population is accumulated and cultured from the oil-containing wastewater, grown, and then added to the sludge. To produce activated sludge for wastewater treatment. At this time, it is preferable to use the medium of the present invention as the medium for the enrichment culture and the culture in that the microorganisms grow well.

The wastewater to be treated is poured into a treatment tank, and an activating liquid is further added to the treatment tank as needed. The activation liquid is injected into the treatment tank every cycle or once every seven days, but is preferably performed every cycle. First, the mixture is placed in a sub-anaerobic state, and only stirring is performed so as not to separate drainage and sludge. If the stirring is not performed, the sludge is lifted by the oil, which is not preferable. This stirring is performed slowly so as not to cause foaming. Here, in the aerobic treatment (typically, DO (dissolved oxygen) is 1.5 to 3. mg / L) or in excess aeration, flocs are dispersed and precipitates increase. Therefore, it is not preferable because precipitation does not occur.

The sub-anaerobic treatment generally means DO (dissolved oxygen)
Does not become 0 mg / L, but refers to bringing DO to an extremely low state. For example, it means that DO is set to about 0.8 mg / L or less, preferably about 0.5 mg / L or less. In particular, the sub-anaerobic treatment here is about 0.8 mg of DO.
/ L or less, preferably DO is about 0.5 mg / L or less and not 0 mg / L. This is because the mixed microorganism population to be added grows under sub-anaerobic culture conditions, and cannot be grown and decomposed under anaerobic conditions (0 mg / L). On the other hand, oil-containing wastewater containing a large amount of water-soluble cutting oil
Since the surfactant is contained in a large amount, if the aeration treatment is performed without performing the sub-anaerobic treatment, bubbles are formed, and a portion that does not come into contact with air is generated by the bubbles, which is not preferable. By this sub-anaerobic treatment, the treatment of the SS (suspended matter) and hexane extract proceeds particularly suitably.

The subanaerobic treatment time is about 15 to 60 minutes, preferably about 30 to 40 minutes. If the sub-anaerobic treatment time is shorter than 15 minutes, the treatment is insufficient, and even if the treatment is carried out for longer than 60 minutes, there is no difference in the treatment result, which is not economical.

After the sub-anaerobic treatment, the DO averaged 1.5 mg /
The aeration process is performed so that the aerobic condition is about L. The aerobic conditions are desirably maintained at a DO of 0.8 or more and a DO of about 3.0 mg / L or less at which floc dispersion does not occur.
It is also possible to achieve a similar DO by stirring without aeration. This aerobic treatment is performed for about 15 to 30 hours. If the aerobic treatment time is shorter than 15 hours, the treatment is insufficient, and if the aerobic treatment time is longer than 30 hours, there is no difference in the treatment result, so that it is not economical. In addition, it is preferably about 22 hours.

After the aerobic treatment, the anaerobic treatment is performed for about 0.5 to 2 hours. By this anaerobic treatment, the bacteria change from aerobic bacteria to a subanaerobic flora. Eventually, the DO of the processing solution approaches zero. In this process,
Anaerobic bacteria do not dominate because of slow growth. Therefore, there is an advantage that no rot occurs during the treatment and no odor is generated.

As described above, the drainage of cutting oil has a high oil content, which is not preferable for the growth of bacteria. However, it is desired to treat the raw wastewater as it is, and the present invention makes it possible. is there. However, according to the method of the present invention, it is also possible to treat wastewater diluted to an appropriate concentration.

[0029]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

The following table shows the culture medium used for the growth medium of the bacteria for treating oil-containing wastewater containing cutting oil. Regarding the peptone contained in the medium components, casein peptone is DEFCO
As BACTO PEPTONE (enzyme digest of protein) and soy peptone, Nippon Pharmaceutical's polypeptone S was used.

[0031]

[Table 2]

The oil-containing wastewater used was the oil-containing wastewater from the headquarters factory of Suzuki Motor Corporation (Hamamatsu City, Shizuoka Prefecture). The oil-containing wastewater at the Suzuki headquarters factory is wastewater from the machining process, not domestic water. 10:03 in the morning on the day of the experiment
At about 0 minutes, it was collected from the factory. It has the following pH, composition, etc. The values in the table are average values. Oil-impregnated wastewater at 115 ° C
For 30 minutes. In Table 3, B
OD indicates biochemical oxygen consumption, COD indicates chemical oxygen consumption, TN indicates total nitrogen amount, and TP indicates total phosphorus amount.

[0033]

[Table 3]

About 1% (v / v) of the mixed microbial population that had been enriched and cultured was added to the above-prepared medium, and batch culture was performed. As a result, the microorganisms proliferated, and by adding the increased microorganisms to the sludge, stable establishment and growth of the mixed microbial population in the sludge were obtained.

Influence of the composition of peptone in the growth medium on the growth of microorganisms The casein peptone 17 g / L of the medium of the present invention described above.
Medium containing only 20 g / L of casein peptone instead of 3 g / L of soy peptone and 2 g of soy peptone only
When a similar experiment was performed on a medium using 0 g / L, the number of bacteria was smaller than when the medium of the present invention was used.
The growth rate was low. Table 4 shows the results.

[0036]

[Table 4]

Effect of molasses on growth of microorganism in growth medium 1.5% agar was added to the above medium, and phosphate buffer (pH
1 mL of dilution-containing wastewater using 7.2) as dilution water was pour-cultured. The phosphate buffer is JIS K0102
72.2. The culture was carried out by shaking culture at 80 ° C. for 1 hour at 36 ° C., and after culturing, the cells were sown on a plate and observed. There was an increase. On the other hand, when a medium in which the same concentration of sucrose was added to the medium instead of molasses was used, propagation of general bacteria that did not decompose the oil was observed. It did not grow as much as it did. In addition, when a general bacterial medium (standard medium) was used, the number of bacteria, the number of colonies, and the type of bacteria were small, and the development of colonies was extremely poor.

Effect of the Addition of Culture Bacteria Using a container having a total volume of 20 L (including a treatment amount of 8 to 10 L), 20 ml (0.1% ratio) of the bacterial solution was added, and a normal acclimatization method was performed. As a result, the sludge floated on the surface of the water within 7 days after the start of acclimation, and the seed sludge was killed. Table 5 shows changes in ORP from immediately after injecting the wastewater as a substrate to 6 days after the addition. At the same time, the change in pH over time and the change in COD from immediately after the injection of the substrate to 24 hours are shown in Tables 6 and 7, respectively. The measurement was similarly performed for the sample to which no bacterial solution was added. In Tables 5, 6, and 7, the substrate is oil-containing wastewater, specifically, water in a pressurized flotation tank of a treatment facility or a dilution thereof, and the numerical value of the substrate is ORP, pH, and COD of the substrate itself. Yes, the value at time 0 is the pH and COD immediately after the addition of the active solution to the substrate.

[0039]

[Table 5]

[0040]

[Table 6]

[0041]

[Table 7]

From the table, it can be seen that when bacteria were added, the pH decreased,
Both of the COD reductions were accelerated as compared with the case where no additive was added.
That is, it was shown that the decomposition of oil was promoted by adding bacteria.

Effect of Sub-Anaerobic Condition According to the present invention, DO is treated in a sub-anaerobic state in the range of 0.5 to 0.3 mg / L, aerobically treated under aerobic conditions, and left standing. , The change in COD, the change in hexane extract (n-He extract), and the change in SS were measured. The results are shown in FIGS. 2 (a), (b) and (c), respectively. 1.5-0.3mg DO for first subanaerobic condition
FIG. 2 also shows the measurement results for aerobic conditions in the range of / L (average 1.5 mg / L). CO
The analysis of D, hexane extract and SS was conducted according to JIS K01.
02.

From FIG. 2, it can be seen that the treatment under the sub-anaerobic condition reduces COD, hexane extract and SS all faster than the treatment performed only under the aerobic condition, and is more suitable for the decomposition treatment of oil-containing wastewater. It has been shown.

[0045]

According to the present invention, the mixed microbial population in the cutting oil wastewater is accumulated and cultured and added to the treated wastewater at a rate of 0.01 to 1% to the mixed microbial population at the rate of 0.01 to 1% when the wastewater flows into the wastewater. In addition to preventing shock death of seed sludge, acclimatization is enabled, and treatment by activated sludge method using bacteria becomes possible. By treating in a batch type activated sludge method in which the sub-anaerobic state, aerobic state, and anaerobic state processing steps are sequentially repeated, it is possible to treat oil-containing wastewater of a water-soluble cutting oil, which is difficult to treat in the activated sludge method. . By performing the stirring process in a sub-anaerobic state, foaming due to the surfactant in the cutting oil can be prevented, and the processing of the SS and hexane extracts can be enhanced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a batch activated sludge treatment method according to the present invention.

FIG. 2 is a graph showing the difference in reduction of COD, hexane extract, and SS depending on the presence or absence of sub-anaerobic conditions.

Claims (4)

[Claims] 1. A method of treating oil-containing wastewater with activated sludge by a batch-type activated sludge method, wherein a mixed microorganism group in cutting oil wastewater is accumulated and cultured, and the cultured mixed microorganism group is added when the wastewater flows into the wastewater. 2. The processing cycle of setting a sub-anaerobic state, an aerobic state, and an anaerobic state in order is repeated.
The processing method described in 1. 3. The method according to claim 2, wherein the dissolved oxygen is about 0.5
The processing method according to claim 2, wherein the stirring is carried out during the sub-anaerobic state under a condition of not more than 0 mg / L but not more than 0 mg / L. 4. A growth medium for an oil-containing wastewater treatment fungus, which medium comprises oil-containing wastewater to be treated, casein peptone and soybean peptone as a nitrogen source, and molasses as a carbon source.