JP5759839B2 - Anaerobic treatment equipment for organic wastewater - Google Patents

Description

  The present invention is intended for organic wastewater discharged from various factories such as food factories, chemical factories, and pulp and paper factories, whose main component is alcohol such as distilled wastewater and whose SS is extremely small for all organic substances. The present invention relates to a methane fermentation treatment apparatus for treating this waste water.

The methane fermentation treatment method, which decomposes organic wastewater by methane fermentation and treats it, requires less energy for aeration than the aerobic treatment such as the activated sludge method, reduces the amount of excess sludge, and generates energy from the generated biogas. Is excellent in terms of energy saving. However, since the methanogen has a small amount of growth and poor sedimentation, the microorganism tends to flow out 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.
As a high-efficiency methane fermenter with high microorganism concentration, an up-flow anaerobic sludge bed process (hereinafter referred to as “UASB”) and an expanded sludge bed process (hereinafter referred to as “Expanded Granular Sludge Bed”). Abbreviated as “EGSB”). This is a method that has become widespread in recent years, characterized by the ability to maintain a high concentration of methane bacteria in the methane fermentation tank by granulating anaerobic bacteria such as methane bacteria into granules. Even when the concentration of organic matter in the wastewater is considerably high, it can be treated efficiently.

In wastewater composed of sugar and protein, a two-phase method (acid fermentation-methane fermentation) in which acid fermentation is performed before methane fermentation is generally used as a method for performing high-efficiency treatment. In the case of this two-phase system, waste water is converted into a volatile organic acid such as acetic acid and carbon dioxide gas is generated while the organic matter is reduced in molecular weight in an acid fermenter. In this acid fermenter, since the pH decreases due to the production of organic acid, the pH is set in the range of approximately 6 to 7 with alkali, and in order to save the alkali, a part of the methane fermentation treated water from the methane fermenter is adjusted to pH. It also circulates to replenish alkali for adjustment. The acid fermenter effluent becomes the raw water for the methane fermenter. In general, when performing UASB treatment, the acid fermentation broth is 5000 mg / L of COD _Cr , and the range of M-alkalinity is 2000 mg / L or more in terms of CaCO ₃ . That is, the alkalinity of the acid fermentation liquor is usually in the range of 40% to 150% of COD _Cr .

The acid fermentation broth is processed in a methane fermentation tank, and the organic acid is decomposed into methane gas and carbon dioxide gas and discharged as biogas. When the acid fermentation water is subjected to methane fermentation, the alkalinity increases and the pH also increases. This is because hydrogen ions are converted to methane due to decomposition of the organic acid, the hydrogen ion concentration decreases, and the organic acid decreases. The alkalinity is a necessary amount of acid when the pH in the liquid is lowered to 4.8.
Organic waste such as sludge and livestock waste is processed in a temporary anaerobic digester for the purpose of reducing sludge volume and generating biogas. The sludge concentration is at least 1%, the M-alkalinity becomes several thousand mg / L during decomposition in the digestion tank, the pH rises to about 8.5 to about 9, and the buffering property is very high. Raised as a process.

However, in the case of methane fermentation of distilled waste liquid containing alcohol as the main component, the operating conditions for treating this wastewater have many specific aspects because it is completely different from the sugars, organic acids, sludge and the like. In this waste water discharging step, carbon dioxide gas is released into the atmosphere during the distillation process, so that the waste water has a low pH buffering property. There are very few examples of methane fermentation treatment of this wastewater treatment, and there is no example of treating this wastewater in the literature so far. When the present inventors performed UASB treatment of pulp and paper mill wastewater containing methanol as a main component, the UASB reactor observed a phenomenon different from conventional wastewater treatment mainly containing carbohydrates and organic acids. did.
First, it is decomposed directly into methane and carbon dioxide gas by methane bacteria belonging to the genus Methanosarcina. In this process, as shown in the formula (3), weak acid carbonic acid is generated from neutral methanol, and the pH in the methane fermentation tank is lowered.
4CH ₃ OH → 3CH ₄ + H ₂ CO ₃ + H ₂ O (3)
Second, when methane fermentation is performed with a methanol substrate, acetic acid is generated from methanol when stress such as lack of nutrients is applied to the methane-fermenting bacteria. The process was extremely unstable.

That is, the conventional UASB method using organic wastewater having a low pH buffering property such as pulp and paper mill wastewater has the following problems.
(1) The pH of methane fermentation tank influent water is said to be suitable for methane fermentation 6.5.
When the pH is adjusted to 8.0, the wastewater has a low pH buffering property. Therefore, the pH in the fermenter is 6.5 or less, which inhibits methane fermentation, due to the decomposition product, carbon dioxide and the generated organic acid. In extreme cases, it drops to 6 or less.
(2) Addition of an excessive alkali agent increases the operating cost.
(3) When the water depth of the methane fermentation tank is deep, dissolved carbon dioxide increases at the bottom of the tank, and the bottom pH of the methane fermentation tank having a depth of 10 m is 0. 0 compared with the treated water pH measured at atmospheric pressure. 3 is also lower. As a result, the activity of the methane bacterium is greatly reduced due to the pH drop in the tank, and the removal rate is kept low.

Japanese Patent Publication No. 5-67358 Japanese Patent Laid-Open No. 7-136694

  In view of the above-mentioned known facts, the present invention is mainly composed of alcohol such as specific distilled waste water among organic waste water discharged from various factories such as food factories, chemical factories, and pulp and paper factories, and SS for all organic matters. An object of the present invention is to provide a stable and high-performance methane fermentation treatment apparatus with extremely little organic wastewater.

In order to solve the above problems, the present invention, the total COD _Cr in wastewater, the alcohol component in COD _Cr in terms of 60% or more, in the anaerobic treatment apparatus SS processes the organic wastewater of less than 1%, A wastewater conditioning tank, and a single tank type methane fermentation tank to which treated water flowing out of the wastewater conditioning tank is supplied. The methane fermentation tank includes an inflow portion of treated water and an outflow portion of treated water. The wastewater adjustment tank is equipped with a water quality meter that can measure pH, and the outflow part is equipped with a water quality meter that can measure pH, M-alkalinity, and organic acid concentration, respectively, and the methane The biogas outflow part from the fermenter is equipped with a meter for measuring the partial pressure of carbon dioxide in the gas, and is calculated by subtracting the M-alkalinity conversion value of the organic acid concentration measurement value from the M-alkalinity measurement value. The effective M-alkalinity is 100 mg / L or more. M-Alkalinity adjusting agent added amount is controlled, or the effective K value related to the alkalinity calculated from the pH measurement value and the carbon dioxide partial pressure measurement value of the outflow part is 1 or more. -Organic having a control device for controlling the amount of alkalinity adjusting agent added, and having an adding device for adding an M-alkalinity adjusting agent to the wastewater adjusting tank based on a signal from the control device It is a wastewater anaerobic treatment equipment.
The methane fermentation tank 1 tank type keep anaerobic treatment method may be a fermenter using the upflow anaerobic sludge blanket or inflatable sludge bed.

  By adding an M-alkaline adjuster controlled to the methane fermenter influent by the anaerobic treatment apparatus of the organic wastewater of the present invention, the pH in the methane fermenter is kept within an appropriate range, and a high load and The removal rate can be maintained.

The flow block diagram which shows an example of the anaerobic processing apparatus of this invention. The graph which shows the relationship between the operation days used in the Example, and COD _Cr volumetric load. (A), (b) is a graph which shows process progress of Example 1. FIG. (A), (b), (c) is a graph which shows process progress of Example 2. FIG. (A), (b), (c) is a graph which shows process progress of Example 3. FIG. (A), (b), (c) is a graph which shows process progress of Example 4. FIG.

The present invention is to perform a stable methane fermentation treatment by minimizing pH drop due to carbon dioxide and organic acid generated in the methane fermenter, and adding an M-alkalinity adjusting agent to the methane fermenter A device that minimizes the volume.
That is, it is possible to stop the vicious cycle in which the decrease in pH due to the generation of carbon dioxide and organic acid and the inhibition of methane fermentation due to the decrease in pH occur, and the operation can be continued without stopping the methane fermentation apparatus.
The present invention calculates the effective M-alkalinity obtained by correcting the M-alkalinity of the methane fermenter effluent water with the organic acid concentration, and at least has a value equal to or greater than the set effective M-alkalinity. This is an anaerobic treatment method for organic wastewater in which an M-alkalinity adjusting agent is added to inflow water in a controlled manner. As described above, an index of effective M-alkalinity is used in consideration of pH reduction due to carbon dioxide and organic acid.
Effective M-alkalinity (mg / L) = M-alkalinity (mg / L)-[organic acid concentration (mg / L) × 0.83] Formula (1)

Although the formula (1) is theoretical, the coefficient 0.83 is set to 1 for convenience, and depending on the wastewater, the following formula (2) can be substituted, and there is no practical problem. Actually, it is preferable to measure the M-alkalinity and the organic acid concentration in the methane fermentation tank where the reaction takes place, but there is no practical problem with the water quality data of the methane fermentation tank effluent.
Effective M-alkalinity (mg / L) = M-alkalinity (mg / L)-[organic acid concentration (mg / L)] Formula (2)
Further, the present invention is from carbon dioxide partial pressure Pco ₂ in pH and generation gas methane fermenter effluent, the effective K values related to the alkalinity (3) halt than formula.
Effective K value = 7.36 × 10 ^pH-6 × partial pressure Pco ₂ Formula (3)

In order to stabilize methane fermentation, it has become experimentally clear that at least 1 is required as the effective K value. This method has a feature that an effective K value as an operation parameter can be continuously measured with high accuracy from automatic measurement of pH and carbon dioxide. Experimentally, it has been found that the K value needs to be 1 or more in order to stabilize the treatment.
Furthermore, the present invention is a method of using liquid alkali and setting the pH of the methane fermenter influent water at least to 8.5 or more, and using this operation method and the above-described method of the present invention in combination. .
By determining the supply amount of the alkaline agent by combining a plurality of methods, it is possible to obtain an appropriate supply amount of the alkaline agent, and not only can suppress an increase in running cost due to an excessive supply of the alkaline agent. The problem of the scale which arises when using the contained alkaline agent can be avoided.

The wastewater targeted by the present invention is organic wastewater discharged from various factories such as food factories, chemical factories, and pulp and paper factories. Among them, it is distilled wastewater and the like, and alcohol is the main component instead of organic acid. Yes, organic wastewater with extremely low SS for all organic substances is targeted. Specifically, the alcohol component to the total _{COD Cr} in wastewater _{COD Cr} in terms of 60% or more, preferably 70% or more, SS is less than 1% _{COD Cr} terms, M- alkalinity of terms of CaCO ₃ 10% The alcohol is a compound in which a hydrocarbon hydrogen atom such as methanol, ethanol or isopropanol is substituted with a hydroxyl group, and is represented by the general formula R—OH. Monohydric alcohols, dihydric alcohols, there is a trihydric alcohol, which dissolves the C ₅ or less of water of interest in the present invention. In particular, in such wastewater, the organic acid is less than 10% with respect to the total COD _Cr .
In addition, organic waste such as sludge and livestock waste is less than 70% of alcohol component in terms of COD _Cr and SS is 1% or more in terms of COD _Cr. Such organic waste is other than alcohol The pH buffering property is increased by the methane fermentation treatment with the substance, and when the M-alkalinity in terms of CaCO ₃ is more than 10%, the pH can be maintained with the alkalinity in the wastewater. Since it is not necessary to control the addition of the degree adjusting agent, the present invention defines the organic wastewater to which the present invention is applied as described above.

The methane fermentation treatment in the present invention is a high load anaerobic treatment such as an upward flow sludge bed method (UASB), a fluidized bed method (EGSB), a fixed bed method or the like for anaerobic treatment of soluble substances, an anaerobic digester ( AD) method, but any method may be used.
The methane fermentation apparatus has GSS (separator that separates gas, granule, and processing liquid) in multiple stages, the angle between the external wall surface and GSS is 30 degrees or less, and the biogas in each stage passes through the water-sealed tank In the multistage UASB type or EGSB type reactor in which the water-sealed tank to be discharged is attached to the outside, the biogas can be discharged from each GSS, so that the reaction state below each GSS is judged from the biogas components. In particular, as in the present invention described above, since the treatment status can be monitored with biogas, the alkalinity can be easily adjusted.

FIG. 1 is a flow configuration diagram illustrating an outline of an embodiment of the upward flow anaerobic treatment apparatus (UASB) of the present invention that is preferable for carrying out a methane fermentation treatment method.
A cylindrical methane fermentation tank 2 in which the raw water feed pipe communicates and the upper and lower sides are closed is provided. The left and right side walls inside the methane fermentation tank 2 are provided with GSSs 4 each of which has one end fixed and extends while lowering the other end toward the opposite side wall. The GSS 4 is provided alternately in two places on the left and right in the vertical direction. In the gas phase part where the generated gas collects when the reaction starts, an outlet of the generated gas recovery pipe communicating with the outside is provided.
Note that the discharge port of the generated gas recovery pipe connected from the gas phase part opens in the water in the water-sealed tank 7 filled with water. The opening position is at an appropriate water depth with different water pressures, and the water sealing tank 7 is provided with a gas meter for measuring the flow rate of the gas discharged from the generated gas recovery pipe. A gas holder 8 is provided at the tip of the gas meter. Moreover, the upper end of the methane fermentation tank is connected to a treated water pipe for discharging the supernatant and a circulating water pipe for diluting the raw water as required.

The adjustment tank 1 is provided with a pH meter, a water quality meter (measuring pH, M-alkalinity, and organic acid) in the middle of the treated water piping, and a carbon dioxide concentration meter in the biogas line. These measuring instruments are appropriately installed according to the control method.
The methane fermentation tank 2 is used by introducing granular sludge made of anaerobic bacteria. 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 ° C. to 35 ° C. and a high temperature methane fermentation treatment with an optimum temperature of 50 ° C. to 55 ° C. Intended for processing. Granule sludge composed of anaerobic bacteria is introduced, and raw water 5 is introduced from the adjustment tank 1 to the methane fermentation tank 2. The raw water is diluted as necessary with the circulating fluid 6 that is part of the methane fermenter effluent, diluted water supplied from outside the system, etc., and the methane fermenter inflow water is the flow rate inside the methane fermenter. Is adjusted to 0.1 to 5 m / h.

By adding trace metals such as Co, Ni, and Fe to the raw water, the activity of methane bacteria can be increased and the granule forming ability can be improved. Here, the case where an alkaline agent is used when pH is lowered in a methane fermenter will be described.
The supply of the alkaline agent may be performed by providing the wastewater adjusting tank 1 in the preceding stage of the methane fermentation tank and supplying it to the methane fermentation tank 2. When supplying the alkaline agent directly into the methane fermentation tank, the supply location of the alkaline agent may be one or a plurality of locations, and in the case of a plurality of locations, the supply locations may be arranged at different positions in the height direction.
The supply method may be either continuous or intermittent. The supply method is selected according to the alkalinity of wastewater, the type and concentration of organic components.

One type of M-alkalinity adjusting agent to be used can be selected, but it can also be used in appropriate combination from a group with high solubility and a group with low solubility. (A) High solubility group (liquid alkali), NaOH, NaHCO ₃ , Na ₂ CO ₃ , (b) Low solubility group includes Ca (OH) ₂ , CaCO ₃ , CaO, phosphoric acid Examples include magnesium ammonium (MAP), Mg (OH) ₂ , and MgO. In addition, for example, chemicals such as black liquor, white liquor, weak liquor, and green liquor distributed in the factory in a paper pulp factory may be used, or waste liquid that generates M-alkalinity. May be used. When intermittently charged into the methane fermentation tank, it is retained as a solid, but by gradually dissolving according to the pH and carbon dioxide concentration in the fermentation tank, it is possible to supply alkalinity, and Low cost Ca (OH) ₂ and CaCO ₃ are suitable.

The addition of the alkali agent is ineffective if it is small, and not only is it costly, but also there is a risk of scale formation. Therefore, it is important to select an appropriate alkalinity adjusting agent in consideration of this point.
By measuring the pH buffering property of methane fermentation treated water, that is, the M-alkalinity, it is possible to control the amount of the appropriate M-alkaliness adjusting agent added. However, when organic acid is contained in methane fermentation treated water, it is measured as M-alkalinity, but organic acid consumes M-alkalinity contained in methane fermentation tank inflow water. It is necessary to correct the M-alkalinity after using an organic acid as acetic acid.
In the correction, the M-alkaline conversion value of the organic acid is subtracted from the M-alkaline degree in the methane fermenter or methane fermenter effluent to be measured. If all organic acids are regarded as acetic acid, the correction coefficient is obtained as 0.83 from the equation (4).

50 (equivalent amount of calcium carbonate) / 60 (equivalent amount of acetic acid) = 0.83 Formula (4)
Effective M-alkalinity (mg / L) = M-alkalinity (mg / L)-[organic acid concentration (mg / L) × 0.83] Formula (1)
Although the equation (1) is theoretical, the coefficient 0.83 is set as the coefficient 1 for convenience, and depending on the wastewater, the following equation (2) can be substituted and there is no practical problem. Actually, it is preferable to measure the M-alkalinity and the organic acid concentration in the methane fermentation tank where the reaction takes place, but there is no practical problem with the water quality data of the methane fermentation tank effluent.
Effective M-alkalinity (mg / L) = M-alkalinity (mg / L)-[organic acid concentration (mg / L)] Formula (2)

  In the method of methane fermentation of organic wastewater with low pH buffering properties, the M-alkaliness and organic acid concentration in the methane fermenter or effluent from the methane fermenter are measured, and effective M-alkali is calculated from the above-mentioned formula (1). The effective M-alkalinity value is at least 100 mg / L or more, preferably 200 mg / L or more, and the upper limit is not particularly defined, but 400 mg / L is a standard. Methane can be stably operated by continuously or intermittently adding an M-alkali regulator to the methane fermenter influent or methane fermenter so as to satisfy an effective M-alkalinity of at least 100 mg / L or more. It was confirmed from the experimental results that fermentation treatment can be performed and the cost of the pH adjusting agent can be reduced. Here, the M-alkalinity and the organic acid may be measured by manual analysis or instrumental analysis, or may be measured by automatic measurement by a titration method.

Moreover, in this invention, the addition amount of an appropriate alkaline agent can be calculated | required also from the pH of carbon dioxide partial pressure in the methane fermentation tank inside or methane fermentation tank outflow water, and biogas.
A vapor-liquid equilibrium is established between carbon dioxide and water, and the relationship shown by the equation (5) is established.
^{_{[H +] = K 1 K}} H Pco 2 / [HCO 3 -] ··· Equation (5)
Here, at a water temperature of 35 ° C. and an ionic strength of 0.0, K ₁ = 0.48 × 10 ⁻⁶
K _H = 0.0257 mol / (L · atm)
pH: pH of treated water
Pco ₂ : partial pressure of carbon dioxide in the generated biogas (atm)
From Expression (5), Expression [6] is derived by converting [HCO ₃ ⁻ ] to alkalinity.
Alkalinity / 100 = 7.36 × 10 ^pH-6 × Pco ₂ = K value Equation (6)

From the formula (6), in the method of methane fermentation of organic wastewater having a low pH buffering property, the pH of the methane fermenter or the effluent of the methane fermenter and the carbon dioxide partial pressure in the generated biogas are measured, The K value is calculated from the formula (6), and the K value is at least 1 or more, preferably 2 or more, and there is no particular upper limit, but 4 is sufficient as a guideline, and M-alkali adjustment to satisfy this It was confirmed from the experimental results that the methane fermentation treatment can be stably performed by adding the agent to the methane fermentation tank influent, and the cost of the pH adjuster can be reduced.
The pH of carbon dioxide in the methane fermentation tank or the methane fermentation tank effluent and the carbon dioxide in the biogas may be measured by manual analysis or instrumental analysis.
Since M-alkalinity, organic acid, treated water pH, and carbon dioxide in biogas can be continuously measured, the amount of pH regulator added can be automatically controlled based on these data.

Furthermore, the present invention is a method in which liquid alkali is used and the pH of the methane fermenter influent water is at least 8.5 or lower, and this operation method and the present invention are used in combination.
In order to perform stable methane fermentation treatment, it is necessary to maintain the pH of the treated water at 6.5 or higher. However, if the pH of the methane fermentation tank inflow water in which an alkaline agent is added to the raw water becomes too high, methane Inside the fermenter, it becomes locally highly alkaline and may inhibit methane bacteria. When organic wastewater with low pH buffering properties is subjected to methane fermentation, the pH immediately decreases due to the carbon dioxide that is decomposed and produced, so the pH in the methane fermentation tank can be maintained appropriately by increasing the pH of the methane fermentation influent water in advance. it can. The pH of the methane fermentation tank inflow water at this time is 11 or less, preferably 8.5 or more and 10 or less, so that the pH in the vicinity of the inflow water blowing portion in the methane fermentation tank is in a neutral region where methane fermentation is possible. Can keep. Although this operation can be performed alone, the combined use with the present invention described above is more effective in saving the M-alkali regulator and in the stability of the methane fermentation treatment than using the operation alone.
That is, by determining the supply amount of the alkaline agent by combining a plurality of methods, it is possible to obtain an appropriate supply amount of the alkaline agent, and not only can suppress an increase in running cost due to an excessive supply of the alkaline agent. The problem of the scale which arises when using Ca containing alkali agent can be avoided.

Hereinafter, the present invention will be specifically described by way of examples.
Examples 1-4
UASB treatment was performed on methanol-containing pulp and paper wastewater.
Processing was performed with the apparatus of the present invention shown in FIG. Capacity of the methane fermentation tank is 3m ^3. The amount of generated gas collected by each GSS was measured with a gas meter provided in a water-sealed tank. The temperature of the water inside the methane fermentation tank is controlled to be kept at 35 ° C. The flow rate was set to 3 m / h by allowing a part of the treated water to flow into the methane fermentation tank together with the raw water as a circulating liquid. The ratio of the raw water flow rate and the treated water circulating water amount was set according to the _CODCr load.
The raw water includes waste water mainly composed of methanol (COD _Cr : 2200 to 2500 mg / L, M-alkalinity 100 to 200 mg / L), inorganic nutrient salts such as nitrogen and phosphorus, Ni, Co, Fe as trace elements The one to which was added was used. The operation was performed with a COD _Cr volumetric load as shown in FIG. About 3rd invention, the driving | operation was switched to the Example from the comparative example on the 90th day.

(1) Example 1 and Comparative Example 1
Example 1 installs the water quality meter of treated water, measures M-alkalinity and organic acid concentration of treated water, and can maintain 200 mg / L as effective M-alkalinity (mg-CaCO ₃ / L). In addition, the amount of calcium carbonate (CaCO ₃ ) injected into the adjustment tank was controlled. Formula (1) was used for calculation of the effective M-alkalinity. At this time, the organic acid was approximately 0 mg / L, and the COD _Cr removal rate was 81%.
Effective M-alkalinity (mg / L) = M-alkalinity (mg / L)-[organic acid concentration (mg / L) × 0.83] Formula (1)
In Comparative Example 1, the same apparatus as in Example 1 was used, and the injection amount of calcium carbonate (CaCO ₃ ) was controlled in the adjustment tank so that the effective M-alkalinity was maintained at 50 mg / L. At this time, 460 mg / L of the organic acid remained, and the COD _Cr removal rate reached 55%.
FIG. 3 shows the process.

(2) Example 2 and Comparative Example 2
In Example 2, a pH meter and a carbon dioxide concentration meter are installed in the treated water line, the effective K value is set to be at least 2 or more, and carbonation in the adjustment tank that is methane fermentation influent water. The injection amount of calcium (CaCO ₃ ) was controlled. At this time, the organic acid was almost 0 mg / L, and the COD _Cr removal rate was 80%.
In Comparative Example 2, the same apparatus as in Example 2 was used, and the injection amount of calcium carbonate (CaCO ₃ ) in the adjustment tank as methane fermentation influent was controlled so that the effective K value was maintained at 0.5. At this time, the organic acid remained at 400 mg / L, and the COD _Cr removal rate reached 62%.
FIG. 4 shows the process.

(3) Example 3 and Comparative Example 3
In Comparative Example 3, when the effective M-alkalinity was set to 100 mg / L or more, the addition rate of calcium carbonate was 170 to 300 mg / L. The pH of the influent of this time 7.5-8.0, the organic acid remains 190 mg / L, was a _{COD Cr} removal rate of 73%.
In Example 3, the amount of calcium carbonate added to the raw water was the same, and the pH of the influent water was raised to 9.0 using NaOH water-soluble alkali. As a result, the organic acid was almost 0 mg / L, and the COD _Cr removal rate was 83%. That is, the combined effect of increasing the inflow pH was confirmed.
FIG. 5 shows the process.

(4) Example 4 and Comparative Example 4
In Comparative Example 4, when the effective K value was set to at least 1, the addition rate of magnesium hydroxide was 100 to 180 mg / L. The pH of the influent of this time 7.5-8.0, the organic acid remains 220 mg / L, was a 72% _{COD Cr} removal rate.
In Example 4, the amount of magnesium hydroxide added to the raw water was the same, and the pH of the influent water was raised to 9.0 using NaOH water-soluble alkali. The effective K value at this time was 2.2. As a result, the organic acid was almost 0 mg / L, and the COD _cr removal rate was 85%. That is, the combined effect of increasing the inflow pH was confirmed.
FIG. 6 shows the process.
These results are shown in Table 1.

1: preparation tank, 2: methane fermentation tank, 3: treated water tank, 4: GSS, 5: raw water,
6: circulating water, 7: water seal tower, 8: gas holder,

Claims (2)

In an anaerobic treatment apparatus that treats organic waste water with an alcohol component of 60% or more and SS of less than 1% in terms of COD _Cr , the waste water adjustment tank and the waste water adjustment tank flowed out of the total waste water COD _Cr . and a 1-vessel methane fermentation tank of the water to be treated is supplied, the said methane fermentation tank, and a outflow portion of the treated water and the inlet portion of the water to be treated, the waste water regulation tank, A water quality meter capable of measuring pH is provided, and the outflow portion is provided with a water quality meter capable of measuring pH, M-alkalinity and organic acid concentration, and a biogas outflow portion from the methane fermenter is provided with a gas. comprising a meter of the carbon dioxide partial pressure in an effective M- alkalinity calculated by subtracting the M- alkalinity converted value of the organic acid concentration measurements from the M- alkalinity measurements 100 mg / L or more The amount of M-alkaline adjuster added is controlled so that Or, the outflow portion of the pH measurements and the carbon dioxide partial pressure measurement valid K values related to the calculated alkalinity than value is 1 or more and becomes as M- alkalinity adjusting agent amount for controlling the controlled device And an anaerobic treatment apparatus for organic wastewater, comprising an addition device for adding an M-alkaliness adjusting agent to the wastewater adjustment tank based on a signal from the control device.   2. The anaerobic treatment apparatus for organic wastewater according to claim 1, wherein the one tank type methane fermentation tank is a fermenter using an upflow anaerobic sludge bed or an expanded sludge bed.

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