JP4503418B2 - Method and apparatus for treating organic wastewater containing salts - Google Patents

Description

  The present invention relates to methane fermentation treatment of organic wastewater, and in particular, targets organic wastewater containing high-concentration salts discharged from various factories such as chemical factories and food factories. The present invention relates to a method and apparatus for treating organic wastewater.

  Compared with aerobic treatment such as activated sludge method, the methane fermentation treatment method that decomposes organic wastewater or organic waste by methane fermentation and treats it requires less energy for aeration and less excess sludge. Since energy can be recovered from the generated biogas, it is excellent in terms of energy saving. However, since methane-producing bacteria or methane-fermenting bacteria have a small amount of growth and poor sedimentation, the microorganisms easily flow out together with the treated water. Therefore, it was difficult to increase the microorganism concentration in the fermenter used for the methane fermentation treatment. Furthermore, there were problems in terms of cost and site.

  There is an upflow anaerobic sludge bed method (hereinafter referred to as “UASB”) as a high-efficiency fermenter having a high microorganism concentration. This is a method that has become popular in recent years, and is characterized by the ability to maintain a high concentration of methane bacteria in the reactor by granulating anaerobic bacteria such as methane bacteria into granules. Even when the organic matter concentration in the wastewater is considerably high, it can be efficiently treated.

  However, organic wastewater such as chemical factory wastewater, food factory wastewater, wastewater treated with livestock waste, and biological wastewater treatment wastewater such as shellfish includes sodium chloride, potassium chloride, ammonium chloride, magnesium chloride, calcium chloride, etc. Salts may be included in high concentrations. In general, moderate concentrations of salt promote the methane fermentation process and allow good treatment, while high concentrations of salt inhibit the biological reaction of methane bacteria. For example, in the case of sodium ions, the biological reaction of methane bacteria is promoted when the concentration is in the range of 100 to 200 mg / liter, but a strong inhibitory effect is imparted when the concentration is 8000 mg / liter or more.

As a method for treating organic wastewater containing such salts, Patent Document 1 discloses a method in which a desalting treatment using a reverse osmosis membrane and a desalting treatment using electrodialysis are combined. The reverse osmosis method is a method in which desalted water is obtained by applying a mechanical pressure equal to or higher than the osmotic pressure to salt water in a room partitioned by a semipermeable membrane and discharging the water to the outside through the semipermeable membrane.
Patent Document 2 discloses a method of subjecting an organic waste containing salts to a desalination treatment followed by a methane fermentation treatment.

Japanese Patent Laid-Open No. 10-272495 JP 2002-273488 A

However, the desalting method described above is a method aimed at removing salts, and organic substances are not decomposed, making it difficult to treat concentrated salts. Furthermore, the reverse osmosis method and the electrodialysis method have a problem that calcium scale is easily generated.
Therefore, the provision of the desalination treatment step in front of the methane fermentation treatment step only for performing a good methane fermentation treatment not only makes the treatment step complicated, but also generates a new problem of treatment of concentrated salts. It will be.

  Moreover, simply diluting organic wastewater containing high-concentration salts with industrial water or city water (tap water, well water), etc. not only increases the amount of treated water, but also increases the size of the methane fermentation treatment equipment. Devices subsequent to the fermentation treatment, such as activated sludge treatment, coagulation sedimentation treatment, and filtration, become large, and cannot be said to be an efficient method.

  The present invention has been made in view of the above-described conventional problems, and the problem of the present invention is to solve the above-described problems, that is, stable treatment is possible without a decrease in methane production activity. Another object of the present invention is to provide a method and apparatus for treating organic wastewater containing high-concentration salts.

The present inventors have conducted intensive research to solve the above-mentioned problems, and are treated water to be treated in a methane fermentation treatment apparatus for performing methane fermentation treatment of organic wastewater containing high-concentration salts, that is, the above-mentioned If the conductivity of mixed raw water of organic waste water and dilution water is 20 mS / cm or less, stable methane fermentation treatment can be continued without lowering methane production activity based on the salt concentration in the methane fermentation treatment apparatus. The present invention has been completed based on the finding and the findings.

That is, the present invention can solve the above problems by the following configuration.
(1) A method for treating organic wastewater in which high-concentration organic wastewater containing high-concentration salts is treated in a methane fermentation treatment step and low-concentration organic wastewater is aerobically treated. CODcr is 1000 mg / l or more, the low-concentration organic waste water is CODcr of less than 1000 mg / l, depending on the value of the installed conductivity meter in the methane fermentation step, the high-concentration organic waste water low A method for treating organic wastewater containing salts, comprising diluting with a part of organic wastewater having a concentration to obtain mixed wastewater having a conductivity of 20 mS / cm or less, and then subjecting the mixed wastewater to methane fermentation .
(2) The method for treating organic wastewater according to (1) above, wherein conductivity is measured after adding a nutrient necessary for biological treatment to the mixed wastewater.

(3) A methane fermentation treatment apparatus for methane fermentation treatment of high-concentration organic wastewater containing a high-concentration salt having a CODcr of 1000 mg / liter or more, and a low-concentration organic wastewater having a CODcr of less than 1000 mg / liter aerobic A part of the low-concentration organic waste water is introduced into the methane fermentation treatment apparatus, and the high-concentration organic waste water is part of the low-concentration organic waste water. The organic wastewater containing salts, characterized in that it comprises a pipe for diluting the mixture into a mixed wastewater having a conductivity of 20 mS / cm or less and a conductivity meter for measuring the conductivity of the mixed wastewater. Processing equipment.
(4) The organic wastewater according to (3), characterized in that a nutrient supply means for adding a nutrient necessary for biological treatment to the mixed wastewater is provided before the installation position of the conductivity meter. Processing equipment.

  According to the present invention, the method for treating organic wastewater has a methane fermentation treatment process for treating organic wastewater containing a high concentration of salts, and the value of the conductivity meter installed in the methane fermentation treatment process. In accordance with the above, by introducing dilution water into the methane fermentation process, the conductivity of the mixed raw water of the organic waste water and dilution water is set to 20 mS / cm or less, so that the methane production activity does not decrease and stable treatment is achieved. Became possible.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments and examples.
As the methane fermentation treatment step in the present invention, anaerobic digestion in which organic substances are introduced and digested, an upflow sludge bed method in which soluble organic substances are anaerobically treated (for example, UASB method, EGSB method), fluidized bed method, fixed Although high load anaerobic processing, such as a floor method, is mentioned, any method may be sufficient. Moreover, methane fermentation step, even one-tank performing acid fermentation and methane fermentation in a single vessel, even double-chamber type performing both reactions in separate reaction vessel may be either. For this reason, this invention is applied to all the methods and apparatuses which perform an anaerobic treatment process including a methane fermentation process.

FIG. 1 is a schematic view showing a first embodiment of a treatment apparatus for performing a method for treating organic wastewater containing salts according to the present invention.
In general, food factories, chemical factories, etc. may consist of wastewater systems containing high-concentration organic matter and wastewater systems containing low-concentration organic matter. For organic wastewater treatment, aerobic treatment is often performed.

  In the example of FIG. 1, there are a high-concentration organic waste water 1 containing a high-concentration salt and a low-concentration organic waste water (raw water in an aerobic treatment process) 2 containing a low-concentration salt. Here, the high-concentration salt concentration is about 10 mS / cm or more in terms of conductivity, the high-concentration organic substance concentration is about 1000 mg / liter or more in terms of CODcr, and the low concentration means a concentration of less than about 1000 mg / liter in terms of CODcr.

High-concentration organic wastewater 1 containing high-concentration salts is methane-fermented in a methane fermentation treatment process. The methane fermentation treatment apparatus 3 used in the methane fermentation treatment process includes a methane fermentation tank, a gas holder, and the like, and in some cases, a raw water adjustment tank and an acid fermentation tank are installed (not shown). The methane fermenter is used by introducing anaerobic bacteria. In the upward flow type methane fermentation treatment apparatus 3, granular sludge made of anaerobic bacteria is introduced. The anaerobic treatment that is the subject of the present invention is an anaerobic treatment in the temperature range of a medium temperature methane fermentation treatment with an optimum temperature of 30 to 35 ° C. and a high temperature methane fermentation treatment with an optimum temperature of 50 to 55 ° C. Yes. The optimum pH in the methane fermentation tank is 6.5 to 7.5 in the case of a single tank type in which acid fermentation and methane fermentation tank are performed in one tank , and in the case of a two tank type in which both are performed in separate reaction tanks, It is 4 to 6 in an acid fermenter and 7.0 to 8.8 in a methane fermenter. In order to maintain anaerobic bacteria, the above temperature control and pH control are extremely important. Conventionally, the temperature and pH of the methane fermentation tank, raw water of methane fermentation, treated water, etc. are detected and their values are detected. Each control is performed by feedback or feedforward.

  By the way, in the case of organic wastewater such as organic waste containing high-concentration salts, the above temperature control and pH control are not sufficient, and sometimes anaerobic bacteria become inactive. In order to eliminate this defect, in the present invention, the conductivity meter 4 is installed in the methane fermentation treatment process, and the operation control of the methane fermentation treatment process is performed using the obtained conductivity value. The place where the conductivity meter 4 is installed may be the raw water adjustment tank, the acid fermentation tank, the raw water inflow pipe 5, or the treated water 6 discharge pipe of the methane fermentation tank, in addition to the inside of the methane fermentation tank. Since the electrical conductivity of the liquid is not particularly changed by methane fermentation, the place where the conductivity meter 4 is installed is not limited to the methane fermentation tank. In the present invention, a device including all of these is called a methane fermentation treatment apparatus. The conductivity varies depending on the type of salt, and is 1.5 mS / cm at an acetic acid concentration of 10 wt%, 136 mS / cm at 10 wt% potassium chloride, and 121 mS / cm at 10 wt% sodium chloride.

In the operation control method, the dilution water is introduced into the methane fermentation treatment step so that the value detected by the conductivity becomes a desired conductivity and becomes a desired conductivity or less. The introduction position of the dilution water may be in the raw water supply pipe 5 of the methane fermentation treatment process, the raw water adjustment tank, the acid fermentation tank, or the methane fermentation tank. When returning a part of treated water 6 as circulating water, you may supply to circulating water.
The whole or part of the treated water 6 in the methane fermentation treatment process is introduced into the aerobic treatment process 7 to further remove organic matter.

  In this invention, the electrical conductivity of the mixing raw | natural water which mixed the raw | natural water and dilution water of a methane fermentation treatment process is 20 mS / cm or less. In the methane fermentation treatment of a chemical factory or the like, the methane activity may be reduced in the same wastewater process even though there is no CODcr concentration fluctuation or water volume fluctuation. As a result of intensive studies by the present inventors, it has been found that even if the CODcr concentration does not vary, the salt concentration varies greatly. FIG. 2 is a graph showing the relationship between the conductivity and the decomposition rate of CODcr. The higher the conductivity, the lower the CODcr decomposition rate, and it was 50% or less at 20 mS / cm. In the present invention, the raw water introduced into the methane fermentation treatment step is 20 mS / cm, preferably 10 mS / cm or less by dilution with dilution water.

  The 2nd aspect (refer FIG. 3) of this invention uses the raw | natural water 2 of the aerobic treatment process 7 and / or the treated water 8 of an aerobic treatment process as dilution water. Conventionally, when salt concentration is high, city water and / or industrial water may be used. However, these waters have a problem of increasing the total amount of water in the water treatment process while having an excellent dilution effect with a conductivity of several μS / cm or less. In the water treatment process using both the methane fermentation treatment step and the aerobic treatment step of the present invention, the salt concentration can be reduced by diluting the raw water 1 of the methane fermentation treatment step with the raw water 2 of the aerobic treatment step. In addition, there is an advantage that the amount of water during the whole water treatment process does not change.

By the way, in the growth of anaerobic bacteria in methane fermentation, in addition to macronutrients such as N, P and S, micronutrients such as Fe, Co, Ni, Zn, Cu, Mn, Mo, Se, W and Br is required. The required amount is very small and may be several tens to several μg per 1 g COD. High-concentration wastewater from chemical factories and the like has many single-component wastewaters, and when these wastewaters are methane-fermented, the above-mentioned micro nutrients are often insufficient. On the other hand, when a variety of components, particularly macro nutrients and micro nutrients, are contained in the raw water for aerobic treatment, the treatment is improved by introducing these waste waters into the methane fermentation treatment step.
The electrical conductivity of the raw water 2 and the treated water 8 in the aerobic treatment step is 20 mS / cm or less, preferably 10 mS / cm or less, more preferably 1 mS / cm or less.

  The 3rd aspect (refer FIG. 4) of this invention adds the nutrient 9 required for biological treatment to the raw | natural water 1 and / or dilution water of a methane fermentation treatment process. It has already been mentioned that micronutrients are required together with macronutrients in methane fermentation. Also in the activated sludge treatment in the aerobic treatment step 7, etc., it is necessary to add the nutrients, particularly macro nutrients, in the raw water 2 of the aerobic treatment step. N and P necessary for biological treatment are BOD: N: P = 100: 2.5 to 5: 0.5 to 1.0 in aerobic treatment, and BOD: N: P = 100: 0.25 in methane fermentation. -0.5: 0.05-0.1 is optimal. These nutrients that are usually added are not always used in the biological reaction, and some of them are discharged as surplus nutrients together with the treated water 8. In the present invention, it is possible to prevent excessive injection of the nutrient 9 by measuring the electrical conductivity of the mixed raw water after adding the nutrient 9 (liquid obtained by mixing raw water and dilution water in the methane fermentation process). It is. Furthermore, the nutrient solution 9 can be effectively used by introducing the whole or part of the treated water for methane fermentation into the aerobic treatment step 7.

  In the drawings used for explaining the working mechanism of the organic wastewater treatment process containing high-concentration salts according to the present invention, FIG. 3 is a diagram using the treatment water of the aerobic treatment process as dilution water. FIG. 4 is a flowchart of the second embodiment of the invention, and FIG. 4 is a flowchart of the third embodiment of the present invention in which a nutrient is added to the raw water of the aerobic treatment step.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1
In this embodiment, processing is performed using the processing flow of FIG. The wastewater to be treated is chemical factory wastewater, and includes a high-concentration organic wastewater system (hereinafter referred to as A system) containing high-concentration salts and a low-concentration organic wastewater system (hereinafter referred to as system B). System A wastewater was treated with methane fermentation, and system B wastewater was treated with activated sludge (aerobic treatment). The methane fermentation treatment apparatus includes a raw water adjustment tank, a heating tank, an upward flow type EGSB type reactor (“EGSB” is an abbreviation for Expanded granular sludge bed), and a treatment water tank. A pH meter for controlling the pH in the reactor is installed in the upper part of the reactor, a temperature sensor for managing the temperature in the reactor is installed in the heating tank, and a conductivity meter 4 for measuring the conductivity of waste water is installed in the raw water adjustment tank. Has been. When the conductivity of the raw water adjustment tank becomes 8 mS / cm or more, the B system inflow valve 10 is automatically opened, and a part of the waste water of the B system is flowed into the raw water adjustment tank. The conductivity of the raw water adjustment tank is always 8 mS / It is controlled to be equal to or less than cm.

The waste water state of system A was CODcr 30000 mg / liter, conductivity 25 mS / cm, and the waste water state of system B was CODcr 1000 mg / liter, conductivity 4 mS / cm. The wastewater treatment amount of the A line is 35 m ³ / d, the waste water treatment amount of the B line is 400 m ³ / d, and the waste amount of the B line wastewater flowing into the raw water adjustment tank of the methane fermentation treatment process from the B line inlet valve 10 is It was 160 m ³ / d.
When the methane fermentation treatment was performed under the above conditions for about 6 months, the mixed raw water in the raw water adjustment tank was CODcr 6500 mg / liter, whereas the treated water CODcr was 1500 mg / liter, and the CODcr removal rate was 77 %Met.

Example 2
In Example 2, the processing flow of FIG. 3 was used. The same procedure as in Example 1 was performed except that the treated water 8 of the activated sludge treatment process was used as the dilution water.
The waste water state of system A was CODcr 30000 mg / liter, conductivity 25 mS / cm, and the activated sludge treated water properties were CODcr 50 mg / liter, conductivity 4 mS / cm. The treatment amount of waste water of the A line was 35 m ³ / d, and the treated water 8 of the activated sludge process that flowed into the raw water adjustment tank of the methane fermentation treatment process from the B line inflow valve 10 was 160 m ³ / d.
When the methane fermentation treatment was performed for about 6 months under the above conditions, the CODcr of the treated water in the raw water adjustment tank was 5500 mg / liter, the CODcr of the treated water was 1250 mg / liter, and the removal rate of CODcr was 77%. there were.

Comparative Example 1
In Comparative Example 1, the processing flow of FIG. 6 was used. It was the same as Example 2 except that no conductivity meter was installed in the methane fermentation treatment process.
Three processing conditions were used. The waste water state of the A line was CODcr 30000 mg / liter and conductivity 25 mS / cm. The city water used for dilution was CODcr 50 mg / liter and conductivity 0.27 mS / cm.
Condition 1: System A wastewater is diluted 4 times with city water.
Mixed raw water CODcr 7500 mg / liter, conductivity 6.3 mS / cm
Condition 2: A-system wastewater is diluted twice with city water.
Mixed raw water CODcr 15000mg / liter, conductivity 13mS / cm
Condition 3: System A wastewater is not diluted.
Mixed raw water CODcr 30000mg / liter, conductivity 25mS / cm

  When water was passed for 1 month under Condition 1, the CODcr removal rate was 75%. Subsequently, when water was passed for one month under condition 2, the CODcr removal rate was 65%. Subsequently, when water was passed under Condition 3, the CODcr removal rate was zero% and the amount of biogas generated was zero on the third day of water flow. Since the conductivity of the treated water was 25 mS / cm, it was determined that the anaerobic bacteria were killed due to the influence of salts.

  The organic wastewater treatment method and apparatus containing the salts of the present invention maintain the dielectric constant of water to be treated in the methane fermentation treatment step at 20 mS / cm by adjusting the mixing ratio of dilution water. Since stable methane fermentation treatment is possible without reducing the methane production activity in the fermenter, organic wastewater, livestock wastewater, seafood treatment wastewater discharged from various factories such as chemical factories and food factories, It is useful as a method and apparatus for treating organic wastewater with high salt concentration such as human waste and waste leachate, especially organic wastewater in chemical factories and food factories.

1 is a systematic schematic diagram of an apparatus for carrying out a processing method according to a first embodiment of the present invention. It is a graph which shows the relationship between electrical conductivity and CODcr decomposition rate. It is the systematic schematic of the apparatus which implements the processing method of the 2nd embodiment of this invention and Example 2. FIG. It is the systematic schematic of the apparatus which implements the processing method of the 3rd embodiment of this invention. It is the systematic schematic of the apparatus which enforces the processing method used in Example 1 of this invention. It is the systematic schematic of the apparatus which enforces the processing method used in the comparative example 1 of this invention.

Explanation of symbols

1 High-concentration organic wastewater containing high-concentration salts 2 Raw water for aerobic treatment process 3 Methane fermentation treatment device 4 Conductivity meter 5 Raw water inflow pipe 6 Methane fermentation treatment water 7 Aerobic treatment device 8 Aerobic treatment water 9 Nutrient 10 Inlet valve 11 City water

Claims (4)

An organic wastewater treatment method for treating high-concentration organic wastewater containing high-concentration salts in a methane fermentation treatment step and aerobically treating low-concentration organic wastewater, wherein the high-concentration organic wastewater has a CODcr of 1000 mg. / L or more, the low-concentration organic wastewater has a CODcr of less than 1000 mg / liter, and the high-concentration organic wastewater is converted into the low-concentration organic wastewater according to the value of a conductivity meter installed in the methane fermentation treatment process . A method for treating organic wastewater containing salts, comprising diluting with a part of wastewater to obtain mixed wastewater having an electrical conductivity of 20 mS / cm or less, and then subjecting the mixed wastewater to methane fermentation . The method for treating organic wastewater according to claim 1, wherein conductivity is measured after adding a nutrient necessary for biological treatment to the mixed wastewater. A methane fermentation treatment apparatus for methane fermentation treatment of high-concentration organic wastewater containing a high-concentration salt and having a CODcr of 1000 mg / liter or more, and a low-concentration organic wastewater having a CODcr of less than 1000 mg / liter A part of the low-concentration organic waste water is introduced into the methane fermentation treatment apparatus, and the high-concentration organic waste water is diluted with a part of the low-concentration organic waste water. An organic wastewater treatment apparatus containing salts, comprising: a pipe for making mixed wastewater having a conductivity of 20 mS / cm or less; and a conductivity meter for measuring the conductivity of the mixed wastewater. The organic wastewater treatment apparatus according to claim 3, further comprising a nutrient supply means for adding a nutrient necessary for biological treatment to the mixed wastewater before an installation position of the conductivity meter.

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