JP2745212B2 - Wastewater treatment method for sewer discharge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment technique for a facility that discharges wastewater directly to a sewer.

[0002]

2. Description of the Related Art At present, effluents from restaurants and food processing plants are discharged directly to sewage systems, and regulations on pH, BOD, SS, N-Hex, etc. are also set for these effluents. For example, in the case of Tokyo, if the discharge amount is 50 m ³ / day or more, pH: 5 to 9, BOD: 600 mg / l or less, S
Since standards are set for S: 600 mg / l or less and N-Hex: 30 mg / l or less, wastewater treatment that satisfies the standards is required at those facilities.

[0003] As such a wastewater treatment method, an activated sludge treatment method is widely adopted. FIG. 4 shows a typical apparatus configuration.
First, the raw water after the screen is poured into an oil / water separation tank (not shown) as a pretreatment, and a neutralizing agent and a flocculant are added thereto to flocculate the suspended substance, and the suspended substance is raised by blowing up bubbles. Then, the scum is continuously scraped and discarded, and the remaining raw water is poured into the adjusting tank 12. Adjustment tank 12
Raw water is injected into the aeration tank 13 from which the activated sludge is produced by long-time aeration. In the aeration tank 13, organic matter adheres around the activated sludge, and aerobic bacteria are decomposed by the aeration, whereby the activated sludge increases and the organic matter in the liquid decreases. Next, the liquid is poured into the sedimentation separation tank 14, where the activated sludge deposited at the lower part and the supernatant are separated, and the supernatant is discharged. Part of the activated sludge is returned to the aeration tank as return sludge, while the remaining part is treated as excess sludge and then discarded.

[0004]

By the way, when pollutants before treatment of wastewater (especially food processing factories, restaurants, canteens, etc.) discharged directly into the sewer are examined, BOD and SS
In most cases, the standard value was lower than the standard value, and it was found that only the N-Hex value greatly exceeded the standard value.

[0005] On the other hand, the activated sludge treatment method uses BOD or SS.
This is a process that focuses on the reduction of oil and fat,
This is performed in the coagulation / pressure separation process in the pretreatment process not shown in FIG. Although activated sludge treatment methods have recently been improved, there is a problem that it is difficult to control the treatment because it is a method of sedimentation and separation of activated sludge. As shown in 4, adjustment tank, aeration tank, sedimentation tank, sludge treatment
There are a lot of waste equipment and the process is complicated.Especially, it requires the treatment and removal of excess sludge, and the installation and operation costs are very high. Activated sludge treatment is not appropriate.

In order to solve such a problem, it is conceivable to perform the wastewater treatment only by the coagulation / pressure separation treatment in the pretreatment step. However, even with this method alone, the selection and adjustment work of the neutralizing agent and flocculant used for flocculation is complicated, and it is necessary to have a specialist in charge. In addition, operations and equipment for dewatering and further discarding it are required.

On the other hand, there is a treatment method called a grease trap as a treatment for removing high-concentration fats and oils. In this method, fats and oils are deposited in a treatment tank, scraped off and discarded. However, this treatment method is a simple treatment method used for facilities with a wastewater volume of less than 50 m ³ / day, and it is too simple to completely remove oils and fats. Similar to the sludge removal work, scraping and disposal of oils and fats and equipment are required.

The present invention has been made in view of the above-mentioned problems of the prior art, and does not require any process and equipment as in the conventional activated sludge treatment method. In addition, it is an object of the present invention to provide a wastewater treatment method capable of efficiently treating the wastewater with an extremely simple configuration.

[0009]

As described above, facilities and the like required for the activated sludge treatment method are relatively large-scale. However, such methods are widely used not only in large-scale facilities such as public sewerage treatment facilities, but also in facilities such as food processing factories, restaurants, and large dining halls that discharge wastewater directly to the sewerage system. .

For this reason, the present inventors first discharge the wastewater directly to the sewer in order to examine whether or not it is necessary to adopt the activated sludge treatment method even in various facilities that directly discharge the wastewater to the sewer. Investigation of pollutants before treatment of wastewater (especially food processing factories, restaurants, canteens, etc.)
In most cases, D and SS are less than the standard value.
It was found that only the x value greatly exceeded the standard (this is clear from Table 2 showing the sample components of the second test example described later).

This indicates that in such facilities, treatment of fats and oils in wastewater is important. On the other hand, the activated sludge treatment method is not a very efficient treatment method for removing fats and oils.

[0012] From such a viewpoint, the present inventors have intensively studied and studied a treatment technique capable of efficiently treating oils and fats in wastewater by a simpler method without using sludge. By making the treatment tank structure use almost no sludge and making effective use of fat-decomposing bacteria and ultra-fine bubbles in the structure, the present inventors have come to invent the present invention that can remove fat and oil very easily and effectively. Things.

[0013] For this reason, in the wastewater treatment method for sewage discharge according to the present invention, a water supply channel is formed in a treatment tank into which raw water is injected at an intermediate portion located at a predetermined distance from both the tank bottom and the water surface. The partition body, divided into a primary processing unit and a secondary processing unit, in the primary processing unit, the fat and oil components and fat-decomposing bacteria in raw water are raised and retained by blowing up ultra-fine bubbles from below, and the retained fat and oil components are removed. While being decomposed by the fat-and-oil decomposing bacteria, the treated water in the intermediate part of the primary treatment part is guided to the secondary treatment part through the water conduit of the partition body, and the primary treated water is stirred in the secondary treatment part. While returning, a part is returned to the said processing tank, and another part is discharged | emitted from a tank bottom.

Here, as a mode of blowing up the ultrafine bubbles, a mode in which air is blown out from a diffuser having an ultrafine hole arranged at the bottom of the tank with a blower or the like can be considered, but air is mixed with raw water. If the high-pressure pressurized air water is blown out from the bottom of the tank, the pressurized air water is blown out at once at the bottom of the tank where the pressure is reduced. The efficiency is maximized, which is a more preferable embodiment. In addition, in order to create ultra-fine bubbles by blowing air with a blower, it is necessary to form ultra-fine holes in the diffuser, but if the ultra-fine holes become clogged, repair work must be performed in the treatment tank. I have to do it in On the other hand, in the mode using pressurized air water, since ultra-fine bubbles are generated only by blowing it out from the bottom of the processing tank, it is not necessary to form ultra-fine holes in the diffuser pipe, and in repair work thereof. It has the advantage that the labor required can be saved.

Next, the operation of the present invention will be described. First, raw water that has been filtered through a screen is injected into a primary processing section of a processing tank. In the primary processing section, ultrafine bubbles are blown up from below. The fat content in the raw water increases due to the ultrafine bubbles. Fat and oil-decomposing bacteria are continuously injected into the primary processing unit,
You may arrange | position a contact material in the intermediate | middle part, and may make fat-and-oils-decomposition bacteria adhere thereto. In the configuration where this contact material is arranged,
The fat-decomposing bacteria grow in the contact material, and a part of the fat-degrading bacteria rises together with the fat due to the blowing of the ultrafine bubbles, so that the treatment can be performed efficiently.

Near the water surface of the primary treatment section, the raised fats and oils are decomposed by the fat-decomposing bacteria. In particular, since the bubbles to be blown up are ultra-fine, the fat and oil-decomposing bacteria stay on the surface of the water while promoting the decomposition of the ultra-fine bubbles,
The decomposition efficiency of fats and oils can be maximized.

On the other hand, a water conduit is formed in an intermediate portion of the partition body, and the treated water in the primary treatment section is guided to the secondary treatment section through the water conduit. Since the water conduit is formed at an intermediate portion located at a predetermined distance from both the tank bottom and the water surface, the following effects are particularly recognized. First, by having a predetermined distance from the bottom of the tank, the sludge deposited on the bottom of the primary processing unit does not flow into the secondary processing unit as it is. The wastewater that is directly discharged to the sewer targeted by the present invention has a small sludge content, so that there is no problem in discharging the sludge as it is, but all the sludge in the primary treatment section flows into the secondary treatment section. Then, in the secondary treatment section, the amount of sludge deposited increases remarkably and becomes high concentration, and it cannot be discharged as it is.As a result, the same complicated treatment as the removal of excess sludge in the activated sludge treatment method is necessary. Becomes That is, since the headrace has a predetermined distance from the bottom of the tank, treated water having an appropriate amount of sludge always flows to the secondary treatment unit, and is discharged without treating the sludge in the secondary treatment unit. Can be done. Although sludge accumulates at the bottom of the primary treatment section, it flows into the secondary treatment section when the accumulated amount reaches the headrace, and the accumulated amount is always below a certain value. Absent.

Next, since the headrace has a predetermined distance from the water surface, the oil / fat decomposing action performed near the water surface in the primary treatment section is ensured. That is, in the vicinity of the water surface of the primary treatment section, the fats and oils and their decomposing bacteria are raised by the ultrafine bubbles, and an efficient decomposition reaction is performed by the stagnation action of the ultrafine bubbles. In the vicinity of the water surface, the treated water during the decomposition reaction is prevented from flowing into the secondary treatment section by the closing by the partition body, and the stagnation action is reliably performed to secure the oil and fat decomposition action. Is what it is.

The treated water guided to the secondary treatment section is diffused and stirred there. Degradation reaction occurs in the treated water because oil-decomposing bacteria are mixed therein. A part thereof is returned to the primary processing section, where the decomposing process is performed again. By repeating this, the decomposition efficiency of the fats and oils is remarkably improved.

The treatment water is discharged from the secondary treatment section from the bottom of the tank. This is because the sludge concentration of the treated water is an appropriate amount due to the action of the above-mentioned headrace, so there is no problem with the sludge even if discharged at that concentration. Since the accumulated sludge is required to remove the accumulated sludge, the sludge is discharged from the tank bottom while containing the sludge. That is, in the present invention, not only the sludge is not utilized by utilizing only the fat / oil decomposing action of the fat / oil decomposing bacteria, but also the sludge treatment is not required at all due to the formation configuration of the headrace and the discharge configuration from the tank bottom. ing.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiments.

FIG. 1 is a schematic view showing an example of processing equipment to which the present invention can be applied. In the drawing, 1 is a processing tank, 2 is a primary processing unit, 3 is a secondary processing unit, and 4 is a partition. A partition plate, 5 is a water conduit, 6 is a superfine bubble diffusing tube, 7 is a contact material, 8 is a superfine bubble forming device, 9 and 10 are pumps, and 11 is a coarse bubble diffusing tube. It is assumed that the raw water to be injected into the treatment tank 1 has already been filtered through a net-like screen (mesh 2 to 5 mm).

The treatment tank 1 may have any shape and size as long as the diffuser tubes 6 and 11 can be arranged at the bottom thereof. For example, an aeration tank conventionally used in the activated sludge treatment method can be sufficiently diverted.

The processing tank 1 has a partition plate 4 at its center.
The processing tank 1 is divided into a primary processing section 2 and a secondary processing section 3 by the partition plate 4.

An introduction pipe into which raw water is injected is disposed above the primary treatment section 2, and an air diffuser 6 is provided at the bottom of the tank.
Further, contact members 7 are arranged on the upper portions of the air diffusers 6 respectively.

The partition plate 4 is provided with a gap that becomes the water conduit 5, and the gap is formed at an intermediate portion having a predetermined distance from both the tank bottom and the water surface.

The air diffuser 6 is a tube for spraying the pressurized air from the ultra-fine bubble forming device 8. The ultra-fine bubble generating device 8 includes a raw water pump 81, an air intake valve 82, a pressurized tank 83, and a back pressure valve 84. The raw water pumped from the processing tank 1 by the pump 81 is supplied from the valve 82. The air is mixed by taking in air, and the air mixed water is pressurized in the pressurized tank 83 by the pump 81 and the valve 84 to create pressurized air water. When the pressurized air is passed through the air diffuser 6, the pressure in the treatment tank 1 is reduced at a stretch, and the mixed air of the pressurized air rises as micron-sized bubbles. In addition, as another configuration of the ultrafine bubble forming device 8,
It is conceivable to blow out only the air from the air diffuser 6 with a blower. In this case, however, it is necessary to form the holes of the air diffuser 6 very finely. For example, a structure in which expanded rubber is covered around a tube having holes is considered.

The contact material 7 is a place where the fat-and-oil decomposing bacteria are adhered thereto and cultured and propagated. For this reason, a material suitable for culturing the bacteria, for example, a ceramic material, pumice or granite is preferable. The fat-decomposing bacteria used may be a known one.

The secondary processing unit 3 includes a return pump 10
And a discharge pump 9 and an air diffuser 11 are arranged at the bottom of the tank.

The air diffuser 11 of the secondary processing unit 3 is connected to the primary processing unit 2.
Unlike the air diffuser 6, the air diffuser 6 is formed of a tube having a large number of holes through which coarse air bubbles pass, and is connected to the blower 20 via a communication tube. The bubbles blown up from the air diffuser 11 become coarse, and the treated water in the secondary processing unit 3 is sufficiently stirred.

The processing in the simple equipment configuration as described above will be described below.

In the primary treatment section 2 into which raw water is injected, fat and oil-decomposing bacteria are continuously introduced, and pressurized air water is sent from the ultra-fine bubble forming device 8 to the diffuser 6, and the micropores of the diffuser 6 are formed. More micron-sized ultra-fine bubbles are blown up. The fats and oils in the raw water will rise efficiently due to the ultrafine bubbles. The ultrafine bubbles also pass through the contact material 7, but an appropriate amount of fat-decomposing bacteria is attached to the contact material 7 in advance. To rise. The fat and oil and fat-decomposing bacteria rise to the surface of the water in the primary treatment section 2, but the rising bubbles are very fine in the order of microns, so that both stay near the surface of the water. The combination of the action of accumulating the ultrafine bubbles and the action of promoting the decomposition enables efficient decomposition of fats and oils near the water surface.

The treated water of the primary processing section 2 is guided to the secondary processing section 3 through the water channel 5 of the partition plate 4. Since the headrace channel 5 is formed at an intermediate portion located at a predetermined distance from both the bottom of the tank and the water surface, firstly, the sludge deposited on the bottom of the primary treatment portion 2 is directly treated in the secondary treatment portion 3. , And flows out only after being accumulated up to the height of the headrace 5. Therefore, the sludge concentration always becomes an appropriate amount and flows into the secondary processing unit 3. At the bottom of the tank of the primary treatment unit 2, sludge accumulates at the height of the headrace channel 5, but when it exceeds that, it flows out with the treated water as described above. No removal process is required. Next, since the water conduit 5 has a predetermined distance from the water surface, the water treated during the decomposition reaction is prevented from flowing into the secondary processing unit 3 by closing the partition plate 4 in the vicinity of the water surface. The stagnation action by the fine bubbles is surely performed to ensure the fat and oil decomposition action.

In the secondary processing section 3, coarse bubbles are blown up from the air diffuser 11, and the blown-up water agitates the treated water. The treated water from the primary treatment section 2 also contains fat-decomposing bacteria, and thus the decomposition of fats and oils is further promoted by stirring with coarse bubbles. Further, the stirring water is returned to the primary processing unit 2 by the pump 10 via a return pipe, and the oil and fat is decomposed again in the primary processing unit 2. After performing such treatment, the treated water is pumped up from the bottom of the tank of the secondary treatment unit 3 by the pump 9 and discharged to the sewer. Regarding the drainage of the treated water at the bottom of the tank, the sludge concentration of the treated water is an appropriate amount due to the action of the water conduit 5, so that not only there is no problem in discharging the sludge, but also the secondary treatment unit. 3 prevents sludge from accumulating on the bottom of the tank, and eliminates the need for complicated sludge removal work.

As described above, in the present embodiment, the sludge concentration is kept low and the sludge is not deposited more than necessary at the bottom of the tank. It can be well decomposed, and can be sufficiently applied to wastewater treatment regulations of facilities that discharge wastewater directly to sewerage, as shown in Examples described later.

[0036]

EXAMPLE In the equipment configuration of the above embodiment, a drainage test was conducted according to the following facility specifications. Treatment tank: 150 m ³ , pressurized tank: 3-7 kg / cm ² G, blower: 2.2 m ³ / min, pump: 150 l / min In addition, the standard of treated water was based on the following guaranteed water quality. pH: 5-9 BOD: 600 mg / l or less SS: 600 mg / l or less N-Hex extract: 30 mg / l or less

First test example: Kitchen drainage including oil extracted from a grease trap tank attached to a cafeteria facility (a water storage tank for separating oil and water. The oil floats on the upper surface and then sinks and deposits on the bottom). Was used. Water quality is pH 6.9, CO
D: 7800 mg / l, N-Hex extractables: 40,300 mg / l (100-200 mg / l for normal kitchen wastewater), which was diluted about 100-fold and adjusted (N-Hex extractables: 400 mg / l) l). The amount of fat-decomposing bacteria added to treatment tank 1 was 0.03
5 g / l and the fungal nutrient was 0.3 g / l. Such a processing tank 1
Then, 20 l of the test sample prepared above was injected and processed. The test results are shown in Table 1 (only the N-Hex value is shown in the graph of FIG. 2). In addition, all the units in Table 1 are mg / l except pH.

[0038]

[Table 1]

As is clear from Table 1, after 12 hours, the N-Hex value was almost the same as the allowable maximum standard value, and reached the allowable standard value (Tokyo) within 24 hours. 4
After 8 hours, the concentration decreased to 3 mg / l, which was extremely low.

Second test example: A mixture of the respective wastewaters of a restaurant in a department store and an employee cafeteria in Oimachi, Tokyo at a ratio of 7: 3 was used as a sample. Table 2 shows the water quality.
It is as follows. In the water quality shown in Table 2, only the pH value was low, so it was adjusted to 7.1. The amount of fat-decomposing bacteria added to the treatment tank 1 was 0.035 g / l of the formulation and 0.3 g of the bacterial nutrient.
/ l. 20 l of the test sample thus prepared was injected into such a processing tank 1 for processing. Table 3 shows the test results.
(Only the N-Hex value is shown in the graph of FIG. 3). In addition,
All units in Tables 2 and 3 are mg / l except for pH.

[0041]

[Table 2]

[0042]

[Table 3]

As is clear from Table 3, after 12 hours, the N-Hex value was within the allowable standard value (Tokyo).
After 4 hours, the concentration was extremely reduced to 4 mg / l.
Although the BOD value was slightly higher than the initial value after 12 hours, the BOD value was still significantly lower than the standard value of 600 mg / l, and the SS value also slightly increased after 24 hours, but this also exceeded the standard value of 600 mg / l. It is much lower.

A test under the same conditions was conducted on May 30, 1995.
As a result of selecting an arbitrary 6 days within the period from September 29 to September 29 and examining N-Hex values of raw water and treated water at 12:00 pm on the selected day, N-Hex value removal rate Is up to 85
% (June 29) and a minimum of 45% (May 30), indicating an extremely effective removal rate of about 72% on average.

[0045]

As described above, according to the wastewater treatment method for sewerage discharge according to the present invention, the most suitable treatment for the property of the sewerage discharge wastewater in which only the oil and fat is above the standard value can be achieved with an extremely simple apparatus configuration. Can be done with

That is, the following effects can be obtained. The equipment required for the treatment is basically sufficient if it is enough to divide the inside of one treatment tank into two, and as in the conventional activated sludge treatment method,
There is no need to prepare a large number of components such as adjustment tanks, aeration tanks, sedimentation tanks, sludge treatment and disposal facilities,
Compared to the pressure separation treatment, there is no need to have a specialist to select and adjust the neutralizing agent and flocculant used for flocculation, and to scrape and accumulate floating scum and dewater it. No additional work or equipment is required. That is, in the method of the present invention, an extremely simple apparatus configuration is sufficient as compared with the conventional method, so that the installation and operation costs are significantly reduced. It is estimated that the cost will be reduced by about 1/7). As a process, it does not require much treatment unlike the activated sludge treatment method, and is particularly complicated sludge treatment (adjustment of sludge amount,
(Excess sludge treatment / removal, etc.) is not required at all, and the maintenance of the equipment is easy. By a process in which ultrafine bubbles are blown up, the fat and oil rises and stays near the water surface, thereby promoting a decomposition reaction with the fat and oil decomposing bacteria near the water surface.
The processing efficiency is significantly improved. Therefore, it is an optimal treatment method for treating wastewater for sewage discharge in which only the oil and fat content is higher than the reference value. Of course, even when compared with the conventional grease trap processing, which is a conventional simple processing method, the scraping / disposing work and equipment required for the grease trap processing are unnecessary, and the configuration is simple, and furthermore, the oil-water separation tank is simply used. Unlike removing fats and oils, the present invention decomposes and removes fats and oils, so that the efficiency of reducing fats and oils is significantly improved. In addition, in the treatment tank, it is basically necessary to provide a predetermined partitioning body and to provide a means for blowing up ultra-fine bubbles and a stirring means. Also, there is an advantage that the diversion of the sedimentation tank can be easily performed.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a processing facility according to an embodiment of the present invention.

FIG. 2 is a graph showing a change in an N-Hex extracted substance value in a first test example.

FIG. 3 is a graph showing changes in N-Hex extracted substance values in a second test example.

FIG. 4 is an explanatory view schematically showing processing equipment required for the activated sludge processing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Processing tank 2 Primary processing part 3 Secondary processing part 4 Partition plate 5 Water conduit 6 Diffusion tube for superfine bubbles 8 Ultrafine bubble creation device 11 Diffusion tube for large bubbles

Claims (1)

(57) [Claims] 1. A treatment tank for injecting raw water is divided into a primary treatment part and a secondary treatment part by a partition body having a water conduit formed in an intermediate part located at a predetermined distance from both the bottom of the tank and the water surface. In the primary processing section, the fats and oils and fat-degrading bacteria in the raw water are raised and retained by blowing up ultra-fine bubbles from below, and the accumulated fats and oils are decomposed by the fat-degrading bacteria, and the The treated water of the section is guided to the secondary treatment section via the water conduit of the partition body, and in the secondary treatment section, a part of the treated primary treated water is returned to the treatment tank while stirring the primary treated water. And a part of the wastewater is discharged from the bottom of the tank.