JPH05253594A - Anaerobic treatment of waste water - Google Patents

Abstract

PURPOSE:To simply and inexpensively remove SS from waste water without applying high-degree expensive pretreatment, to efficiently and stably treat waste water by an ascending stream anaerobic sludge blanket(UASB) method and to also increase the yield of methane gas. CONSTITUTION:Waste water wherein SS is 6g/l or more and CODcr is 9g/l or more is adjusted in the concn. of SS so that an SS/CODcr wt. ratio becomes 0.35 or less and subsequently subjected to anaerobic treatment by a UASB method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anaerobic treatment method by an upward flow anaerobic sludge blanket (hereinafter sometimes referred to as UASB) method for organic waste water.

[0002]

2. Description of the Related Art An anaerobic treatment method called an upflow anaerobic sludge blanket method (UASB method) is a method for inexpensively and efficiently treating organic wastewater such as food industry wastewater.

The UASB method is a method in which anaerobic bacteria (mainly methanogens) are retained in the reaction tank as pellet-like lumps called granules for anaerobic treatment, and the sludge retention concentration is 40,000. Since it is as high as ~ 60,000 mg / l and the pellet has a high methanogenic activity, it is considered to be the most efficient anaerobic treatment method. Also, in terms of equipment, since a filler or the like is not incorporated in the reaction tank, there is no fear of blockage, and it is an excellent method in terms of stability and maintainability as compared with the fixed bed method.

However, in the UASB method, when a large amount of SS is contained in the waste water, the formation and growth of granulation are inhibited, so that the SS concentration is less than 20%, preferably less than 10% with respect to CODcr. It is required to do the processing.

Therefore, when the wastewater containing a high concentration of SS is treated by the UASB method, it is necessary to separate and remove the SS in advance by a method such as precipitation, floatation under pressure, and coagulation precipitation. Therefore, there is a problem that an expensive processing device required for these pretreatments increases the initial cost. In addition, the sedimentation basin requires a large site area, and there is a problem in that the chemical cost becomes enormous in pressurized flotation and coagulation sedimentation.

However, in the case of wastewater having a CODcr of 9 g / l or more, if the SS concentration is 6 g / l or more, a large amount of scum is generated, so that treatment is impossible regardless of the SS / CODcr ratio. ing.

On the other hand, Japanese Examined Patent Publication No. 3-67760 discloses a method of subjecting organic sludge to acid fermentation, solid-liquid separation, and methane fermentation of the separated liquid by the UASB method. However, in this anaerobic treatment method, solid-liquid separation is performed so that the separated liquid contains almost no SS, so it is difficult to perform solid-liquid separation with a simple method or device, and the cost increases, and the methane gas collection There is a problem that the rate is low. Also, in this method, the concentration of SS should be adjusted to UASB.
There is no mention of whether to process by law.

[0008]

DISCLOSURE OF THE INVENTION An object of the present invention is to produce a wastewater containing CODcr and SS in a high concentration in UAS without separating and removing SS by advanced and high-cost pretreatment.
An object of the present invention is to propose a method for anaerobic treatment of wastewater, which enables efficient and stable treatment by the method B and can increase the yield of methane gas.

[0009]

The present invention is the following anaerobic treatment method for wastewater. (1) Suspended solids (SS) concentration is 6
In a method of anaerobically treating organic wastewater having a CODcr of 9 g / l or more and a g / l or more by an upflow anaerobic sludge blanket method, the weight ratio SS / CODcr of the organic wastewater is 0.35 or less. An anaerobic treatment method for wastewater, characterized in that it is treated by an upflow anaerobic sludge blanket method after being adjusted to 1. (2) The method for anaerobic treatment of wastewater according to (1) above, wherein the weight ratio of SS / CODcr is adjusted to 0.2 to 0.35. (3) The anaerobic treatment method for wastewater according to (1) or (2) above, wherein SS is removed from the wastewater by a vibrating screen or a rotary screen to adjust SS / CODcr.

The waste water to be treated in the present invention is
SS concentration is 6g / l or more and CODcr is 9g / l
The above is organic wastewater. Specific examples include food factory wastewater such as beer manufacturing wastewater, and other industrial wastewater.

In the present invention, the weight ratio of SS / CODcr in the waste water (hereinafter, simply referred to as SS / CODcr) is 0.3.
After adjusting to 5 or less, preferably 0.2 to 0.35, U
Anaerobic treatment is performed by the ASB method.

SS in the drainage is 0.3 in SS / CODcr
Even if it is contained at a high concentration of 5, the granule concentration and activity of the anaerobic bacteria in the UASB method are not adversely affected, and the granules are reliably maintained to have a high load, for example, 10 kg CODcr / m ³ · day or more. Wastewater can be treated with. In particular, in the wastewater having a CODcr concentration of 9 g / l or more, if SS is 6 g / l or more, a large amount of scum is generated in the UASB treatment, so that the treatment by the UASB method is impossible, but SS / CODcr is By setting the range, even when the SS concentration is 6 g / l or more, the treatment can be performed with a high load regardless of the SS concentration.

In order to adjust SS / CODcr within the above range, (a) SS which is easily separated is separated into SS.
Methods such as lowering the concentration and (b) adding a wastewater containing a large amount of soluble organic matter and having a low SS concentration to reduce the SS concentration can be adopted.

According to the method (a), a high degree and high cost are required.
It is not necessary to employ a separating device or method that increases the initial cost. In the method of the present invention, the separated water containing SS in a relatively high concentration can be treated by the UASB method, so that a simple and inexpensive screen device such as a vibrating screen or a rotary screen can be used as the separating device.

In the method (b), a COD meter, S
By linking with a measuring device such as an S meter and performing automatic control such that the SS / CODcr is in the above range, the organic wastewater having a low SS concentration is mixed, so that the treatment can be performed more stably. it can.

When treated under conditions where the value of SS / CODcr is relatively large, for example, 0.2 to 0.35, SS remaining in the waste water also serves as a substrate for digestion gas (methane gas), so that the yield of digestion gas is high. Will increase.

[0017]

The present invention will be described below with reference to the drawings. FIG. 1 is a system diagram showing an embodiment of a method for anaerobic treatment of waste water according to the present invention. In the figure, 1 is a screen device, 2 is a separated water storage tank, 3 is an acid fermentation tank, 4 is a mixing tank, and 5 is a UASB type methane fermentation tank.

The treatment method is as follows. First, the organic wastewater 6 is introduced into the screen device 1, and the SS in the wastewater 6 is SS / CODcr.
Solid-liquid separation is performed so that is within the above range. The solid content is discharged as a cake 7, and the separated water 8 is introduced into the separated water storage tank 2.
The separated water 8 is continuously supplied to the acid fermentation tank 3 by the pump P ₁ , and the SS which remains without being separated by the screen device 1
And other organic substances are decomposed into organic acids such as acetic acid, propionic acid, butyric acid and lactic acid by acid-producing bacteria. This acid fermentation step is preferably performed with stirring by the stirrer 9.

The acid fermentation liquor 10 in the acid fermentation tank 3 is circulated in a circulation path 11
Is continuously supplied to the mixing tank 4. U in the mixing tank 4
A part of the treated water 12 treated in the ASB type methane fermentation tank 5 circulates through the circulation path 11. The pH of the mixed water 13 in the mixing tank 4 is measured by a pH meter 14, and a pump P ₂ linked with this pH meter 14 adjusts the pH of the mixed water 13 to a pH suitable for methane fermentation in the UASB type methane fermentation tank 5 with sodium hydroxide. Alkali 15 such as.

The mixed water 13 mixed by the stirrer 16 is UAS
It is continuously supplied to the bottom of the B-type methane fermentation tank 5, and methane is fermented by the methanogens converted into granules 17.
A part of the treated water 12 treated in the methane fermentation step is returned to the mixing tank 4 by the circulation pump P ₃ , and the rest of the treated water 12 is further subjected to post-treatment such as biological oxidation treatment and discharged. Digestion gas generated in the methane fermentation process (methane gas)
18 is collected by the gas collector 19, and the drain trap 2
After removing the mist at 0, it is discharged out of the system through the gas meter 21.

Although the acid fermentation process and the methane fermentation process are carried out in separate tanks in FIG. 1, both fermentation processes can be carried out in one tank.

Example 1 By the treatment method shown in FIG. 1, an anaerobic treatment was carried out by using the beer lees dehydrated filtrate at the time of beer production as the waste water 6. That is, after fibrous SS was continuously solid-liquid separated and removed from the beer lees dehydrated filtrate using the screen device 1 equipped with a 0.1 mm mesh, the separated water 8 was directly removed by about 1 to about 1 by the UASB method. Anaerobic treatment was performed continuously over a period of months. The volume of each tank is 5 liters for the separated water storage tank 2 and 3 for the acid fermentation tank.
Is 2 liters and the mixing tank 4 is 0.5 liters.

The operating conditions of the UASB type methane fermentation tank 5 are as follows. Residence time (HRT): 1.9 days CODcr load: 9.9 kg / m ³ / day SS load: 3.3 kg-SS / m ³ / day Tank volume, inner diameter: 9 liter, inner diameter 10 cm Temperature: 35 ° C

Beer lees dehydrated filtrate (drainage 6), fibrous S
Table 1 shows the water quality of the separated water 8 and the treated water 12 from which S has been removed. Table 2 shows the retention concentration and methane production activity of sludge (granule 17) in the UASB type methane fermentation tank 5.
Shown in.

[0025]

[Table 1]

From Table 1, it can be seen that the removal rate of SS was less than 50%, but the removal of soluble CODcr was good. Further, it can be seen that almost no organic acid remained in the treated water, and the methanogenic reaction proceeded smoothly.

[0027]

[Table 2]

From Table 2, it can be seen that the retention concentration of granules at the start of the treatment and after 1 month (at the end) was almost the same, and the methanogenic activity did not change and was stable.

Comparative Example 1 In Example 1, acid fermentation and methane fermentation by the UASB method were carried out without removing SS from the beer lees dehydrated filtrate, but a large amount of scum was generated in the UASB-type methane fermentation tank 5, and the treatment was performed. Was difficult.

From the above, SS / CODcr of the wastewater can be reduced to 0.35 by a simple pretreatment with a 0.1 mm mesh.
By the following, it can be seen that wastewater which is difficult to treat by the UASB method can be treated.

[0031]

As described above, according to the present invention, since the weight ratio of SS / CODcr in the organic waste water is adjusted to a specific range, the anaerobic treatment is performed by the UASB method.
Even if wastewater containing high concentrations of CODcr and SS is used even if SS is not separated by advanced and high-cost pretreatment, U
The ASB method enables efficient and stable treatment. It is also possible to increase the yield of methane gas.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a method for anaerobic treatment of waste water according to the present invention.

[Explanation of symbols]

 1 Screen Device 2 Separation Water Storage Tank 3 Acid Fermentation Tank 4 Mixing Tank 5 UASB Type Methane Fermentation Tank 6 Drainage 7 Cake 8 Separation Water 9, 16 Stirrer 10 Acid Fermentation Liquid 11 Circulation Path 12 Treated Water 13 Mixed Water 14 pH Meter 15 Alkali 17 Granule 18 Digestion gas 19 Gas collector 20 Drain trap 21 Gas meter

Claims (3)

[Claims] 1. A method of anaerobically treating organic wastewater having a suspended solids (SS) concentration of 6 g / l or more and CODcr of 9 g / l or more by an upflow anaerobic sludge blanket method, wherein: The weight ratio of SS / CODcr of effluent is 0.35
An anaerobic treatment method for wastewater, which comprises treating by an upflow anaerobic sludge blanket method after adjusting to the following. 2. The weight ratio of SS / CODcr is 0.2 to.
The method for anaerobic treatment of wastewater according to claim 1, wherein the method is adjusted to 0.35. 3. The method for anaerobic treatment of wastewater according to claim 1, wherein SS / CODcr is adjusted by removing SS from the wastewater with a vibrating screen or a rotary screen.