JPH05317878A - High-temp. anaerobic treatment for organic waste water - Google Patents

Abstract

PURPOSE:To stably and efficiently proceed the reaction in a high-temp. acid producing tank, to minimize the volume of the tank and to enable a stable and high-load operation by specifying a free organic acid concentration in the high-temp. acid producing tank. CONSTITUTION:Raw water is introduced to the high-temp. acid producing tank 1 together with circulating water from a high-temp. methane producing tank 2 which is returned via a piping 13 to produce the acid. The circulating rate is adjusted so that the COD concentration of inflow water to the high-temp. acid producing tank 1 is made at 1000mg/l. In the high-temp. acid producing tank 1, the circulating rate is properly adjusted by considering the relation among the raw water concentration, circulating water quantity, inflow water concentration, residence time and pH so that the free organic acid concentration is <=400mg/l. The pH in the high-temp. acid producing tank 1 is controlled to 6-7 for controlling methane fermentation. Thus, both acid producing efficiency in the high-temp. acid producing tank and methane producing efficiency in the high-temp. methane producing tank can be maintained high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high temperature anaerobic treatment method for organic wastewater, in particular, introducing the organic wastewater into a high temperature acid generation tank to generate an organic acid, and then treating the outflow water of the high temperature acid generation tank. The present invention relates to improvement of a high-temperature anaerobic treatment method for organic wastewater which is introduced into a high-temperature methane production tank and produces methane.

[0002]

2. Description of the Related Art Conventionally, in the high-temperature anaerobic treatment of organic wastewater, particularly sugar-based wastewater, even in a high temperature range of 45 ° C. or higher and 60 ° C. or lower, acid generation is carried out in the preceding stage of the methane fermentation process to produce methane. It is known that the stability of the fermentor can be increased and the tank load can be increased.

In such a two-tank type anaerobic treatment, however, a method has been proposed in which the pH adjusting agent (alkali) required for the acid production tank is reduced by mixing the methane fermentation treated water with the raw water. (Japanese Patent Publication No. 3-7439).

[0004]

[Problems to be Solved by the Invention] However, in the past,
In the two-tank type anaerobic treatment of acid production and methane production in a high temperature region, there are few cases where detailed examination results have been reported for both the acid production process and the methane production process,
At present, the suitable operating conditions are not clarified.

In particular, no study has been made on the optimum conditions of pH and the concentration of raw water, which has been an obstacle to the design of actual equipment and the establishment of operating methods.

The present invention has been made in view of the above-mentioned conventional circumstances, in which organic waste water is introduced into a high temperature acid generation tank to generate an organic acid, and then the outflow water of the high temperature acid generation tank is changed to a high temperature methane generation tank. In the high-temperature anaerobic treatment method for organic wastewater that produces methane, clarify the operating conditions for the stable and efficient progress of the reaction in the high-temperature acid production tank, and minimize the volume of the high-temperature acid production tank. By doing so, the initial cost can be reduced and stable high load operation can be performed. Alternatively, a method for efficiently performing acid generation and methane fermentation without diluting the raw water concentration more than necessary is provided, and the methane fermentation process is efficiently performed while minimizing the energy required for heating. The running cost is reduced by the effect of reducing the required amount of alkali. It is an object to provide a high temperature anaerobic treatment method for organic wastewater.

[0007]

A method for high temperature anaerobic treatment of organic wastewater according to claim 1, wherein the organic wastewater is introduced into a high temperature acid generation tank to generate an organic acid, and then the outflow water of the high temperature acid generation tank. In a high-temperature anaerobic treatment method of organic waste water for introducing methane to a high-temperature methane production tank to generate methane, the concentration of free organic acid in the high-temperature acid production tank is 400 mg / l (that is, 400 pp
m) It is characterized by adjusting to the following.

According to a second aspect of the present invention, there is provided a high temperature anaerobic treatment method for organic wastewater, which is characterized in that, in the method of the first aspect, a part of outflow water of the high temperature methane production tank is circulated to the high temperature acid production tank. ..

According to a third aspect of the high temperature anaerobic treatment method of organic waste water, the organic waste water is introduced into a high temperature acid generation tank to generate an organic acid, and then the outflow water of the high temperature acid generation tank is changed into a high temperature methane generation tank. In the high-temperature anaerobic treatment method of organic wastewater, in which the pH is set to 6 in the high-temperature methane production tank.
It is characterized by adjusting to ~ 7.

In the method for high temperature anaerobic treatment of organic waste water according to claim 4, the organic waste water is introduced into a high temperature acid generation tank to generate an organic acid, and then the outflow water of the high temperature acid generation tank is changed into a high temperature methane generation tank. In the high temperature anaerobic treatment method of organic waste water for producing methane, the free organic acid concentration in the high temperature acid generation tank is adjusted to 400 mg / l or less, and the pH in the high temperature methane generation tank is adjusted to 6 to 7 It is characterized by adjusting to.

That is, the inventors of the present invention conducted extensive studies on the acid production characteristics and methane fermentation characteristics in the high temperature region in order to establish the operating method and the processing conditions of the two-tank type high temperature anaerobic treatment method, and as a result, In the acid production tank, the rate of organic acid production reaction is significantly impaired under the condition that the total amount of free organic acid concentration exceeds 400 mg / l, while in the high temperature methane production tank, acetic acid assimilating methane production occurs in the environment where pH exceeds 7. It was found that the activity was significantly impaired, and the present invention was completed based on this finding.

The treatment temperature range of the high temperature anaerobic treatment in the present invention is usually a high temperature region of 45 to 60 ° C.
A treatment temperature higher than that of a general anaerobic treatment in the medium temperature range of 0 ° C. or more and less than 45 ° C. is adopted.

In the method of the present invention, the high temperature acid generator may be a suspension type or a fluidized bed type, and the UASB may be used.
(Upflow sludge blanket) type may be used.

On the other hand, the high temperature methane production tank is, for example, a UA which is prepared by acclimatizing pelletized sludge produced at the fluidized bed type anaerobic treatment apparatus disclosed in Japanese Patent Publication No. 1-59037 at high temperature.
SB devices are preferred.

[0015]

The present inventor conducted a study using synthetic sugar-based wastewater in order to clarify the acid generation characteristics in the high temperature region in the high temperature anaerobic treatment method of organic wastewater, especially the influence of the organic acid produced as a result of the reaction. As a result, under the condition that the total amount of organic acid concentration in free form exceeds 400 mg / l, the organic acid production in the high temperature acid production tank (chemostat tank) does not proceed sufficiently even if it exceeds 24 hours, and the system becomes It was found to be unstable and difficult to drive practically. This condition is stricter than the organic acid concentration reported in the medium temperature range of 20 ° C. or higher and lower than 45 ° C., and it has become clear that an operating method different from the medium temperature range is required.

Therefore, in the method of claims 1 and 4 of the present invention, the upper limit of the total free state concentration of the produced organic acid is 400 m as a condition for favorably promoting the acid production in the high temperature acid production tank.
g / l, and based on this condition, the raw water concentration and the pH range of the high temperature acid generation tank are defined so that this condition can be satisfied, and stable and efficient operation is performed.

The free organic acid concentration in the high temperature acid production tank is determined by the concentration of raw water, the control pH value of the high temperature acid production tank, and the residence time. These control factors are set to a total free organic acid concentration of 400 mg / l or less. By controlling by using as an index, even a relatively simple apparatus such as a chemostat tank can stably maintain the acid generation reaction and operate at a speed that can be practically used.

The actual control mode of the apparatus is 400 mg of free organic acid concentration based on the concentration of raw water organic substance, examination of kinds of organic acid components produced, and evaluation of related biodegradation rate.
/ L may be set in advance, or the operating conditions may be changed by online evaluation of the free organic acid concentration while operating the device. A specific method for adjusting the organic acid concentration to 400 mg / l or less does not matter.

Further, the present inventors have examined the methane production characteristics of the high temperature methane production tank in the high temperature anaerobic treatment method of organic waste water, and as a result, p
It has been found that in a high pH region where H exceeds 7, the acetic acid assimilating methane-forming activity decreases and the treatment efficiency decreases.

Therefore, in the method of claims 3 and 4,
The high temperature methane production tank has a pH of 6 to 7, preferably 6.0 or more and less than 6.8.

In the present invention, the method for measuring the concentration of free organic acid in the high temperature acid production tank is as follows. That is, the concentrations of acetic acid, propionic acid, butyric acid, etc. are measured by liquid chromatography, and the free organic acid concentration is determined from the pKa values of these acids and the pH value of the acid generator.

Further, the following simple method utilizing acid or alkali titration can also be used. That is, in a system in which the types of organic acids existing in the dissociated state are limited, such as the acid generation step in anaerobic treatment, it is possible to estimate the approximate amount of organic acid using acid titration and alkali titration values. It has been known. Usually, butyric acid, acetic acid, propionic acid, and the like are the main organic acids present in a well-operated acid generator, and the pKa values of these acids are all 4.
Use that is around 8.

The operation generally follows the following procedure. First, an acid is added to a fixed amount of the solution in the high temperature acid generator to temporarily lower the pH to a predetermined value (for example, 1.5). At this point, the dissolved carbon dioxide gas that affects the alkalinity measurement is removed. After that, alkali titration was performed to obtain pH 4.8.
The alkali demand before and after is measured from the titration curve. Since the pKas of the acids present are all around 4.8, the total amount of organic acids present can be estimated from the alkali demand. These measurements can be performed immediately if there is an automatic titrator linked with a pH meter, and if a personal computer for analysis is attached, the organic acid concentration can be estimated in real time.

According to the method of claim 2, in the method of claim 1, a part of the outflow water of the high temperature methane production tank is circulated to the high temperature acid production tank. The action mechanism of this effluent circulation is as follows.

That is, as described above, in order to maintain a good rate in the acid production reaction, the concentration of free organic acid is 40%.
It is necessary to control either the concentration of the raw water in the high temperature acid generation tank to be thinner or the control pH value to be higher so as not to exceed 0 mg / l.

Assuming now that substances such as glucose and sucrose that do not pose a problem of biodegradation as sugar components in the raw water, the free organic acid concentration gives an approximate allowable raw water sugar concentration according to the pH of the acid production tank. Can be asked. For example, based on the results of an experimental study using glucose as a model substrate, the organic acid was changed to butyric acid (pKa = 4.90).
As represented by 1), the conversion rate of sugar to total organic acid (40.25
%), The glucose concentration capable of acid production in the high temperature acid production tank is 1400 mg / l at pH 4.5,
2200 mg / l at 5.0, 4900 at pH 5.5
It becomes about 13000 mg / l at mg / l and pH 6.0.

On the other hand, in the case of the high temperature anaerobic treatment of normal temperature wastewater, the COD concentration of the raw water is 1 if the temperature is raised by methane generated from the organic substances contained in the raw water in the treatment.
It is necessary to be 0000 mg / l or more, but in this case,
It is necessary to control the pH of the high temperature acid production tank to around 5.8. It is well known that the pH is preferably 6.0 or less in order to suppress methane fermentation inside the high temperature acid production tank.

Furthermore, it is necessary to consider that the pH of the high temperature acid production tank is regulated by the pH of the high temperature methane production tank in the subsequent step. Generally, in the high temperature methane production tank, the organic acid component in the high temperature acid production tank is consumed, so that the alkaline component which is a counter ion remains and the pH tends to rise. Further, if the content of N or S in the raw water is large, the pH tends to increase. Therefore, raising the pH in the high temperature acid generation tank more than necessary will cause the pH increase in the high temperature methane generation tank, which may affect the methane generation activity. Influence. That is, the research conducted by the present inventors has revealed that the methane production tank has a reduced acetic acid assimilating methane production activity in a high pH range exceeding pH 7. This problem becomes particularly important in high temperature anaerobic conditions. In this sense, it is advantageous that the concentration of raw water is low because the amount of alkali added to increase the pH in the high temperature acid production tank is reduced, and as a result, the pH increase in the high temperature methane production tank is suppressed. ..

To summarize the above findings, in the high temperature anaerobic treatment, the heating energy of the raw water is reduced, and
From the viewpoint of taking a longer residence time in the high temperature acid production tank, it is desirable to treat the raw water as high concentration as possible without diluting it. On the other hand, the lower the concentration of raw water is, the better the concentration of raw water in consideration of the treatment rate per cell in the high temperature acid production tank and the suppression of the increase in pH in the high temperature methane production tank. As one solution to such contradictory conditions, in the method of claim 2, the outflow water of the high temperature methane production tank is circulated and used as dilution water of the inflow water of the high temperature acid production tank.
As a result, the pH of the high temperature acid production tank and the pH of the high temperature methane production tank are controlled to appropriate values, so there is no need to excessively dilute the raw water, and therefore the energy required to raise the temperature can also be minimized. Becomes Also, the alkali consumption is reduced.

In this case, it is important to determine the optimum dilution ratio of the raw water after considering the N and S concentrations of the raw water. In the present invention, the amount of free organic acid in the high temperature acid production tank and the pH of the high temperature methane production tank (as described above,
6 to 7. It is preferable to determine the optimum circulation ratio based on the above), and it is preferable to determine the circulation ratio based on the following conditions.

The raw water concentration in the high temperature acid generation tank is set to 10
The circulating water amount is determined so as to be 000 mg-COD / l or less. Under these conditions, the total concentration of free organic acid should be 40
Even if it is suppressed to 0 mg / l or less, the pH can be suppressed to 5.8 or less, and the acid production can be favorably maintained while suppressing the methane fermentation in the high temperature acid production tank.

When acid is produced under the conditions of
When the pH in the high temperature methane fermentation tank exceeds 7, the amount of circulating water is further increased, the amount of alkali added in the high temperature acid generation tank is reduced, and the pH of the high temperature methane fermentation tank is lowered.

Raw water concentration is 10000 mg-COD /
Even when it is lower than 1, it is desirable to perform circulation for the purpose of reducing the concentration of the inflow water of the high temperature acid generation tank in order to reduce the alkali consumption in the high temperature acid generation tank. In this case, the circulation amount is 3 times the flow rate of raw water from the viewpoint of increasing the power energy due to excessive circulation and preventing short-circuit flow due to the apparent retention time decrease based on the total flow velocity of circulating water and raw water. Is appropriate.

Further, from the above operating conditions (1) to (4), the following conditions are defined for the raw water concentration. The upper limit of the concentration of raw water is considered to be about 40,000 mg-COD / l, and the raw water having a concentration higher than that is 40000
Dilute so that the concentration becomes mg-COD / l or less.

[0035]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a system diagram showing an implementation method of the present invention.

In the figure, 1 is a high temperature acid production tank, 2 is a high temperature methane production tank, and raw water is introduced into the high temperature acid production tank 1 via a pipe 11 equipped with a pump P ₁ and flows out of the high temperature acid production tank 1. Water is introduced into the high temperature methane production tank 2 via a pipe 12 equipped with a pump P _2, and a part of the outflow water of this high temperature methane production tank 2 is introduced into the high temperature acid production tank 1 via pipes 13 and 11 equipped with a pump P _3. It is circulated and the rest is discharged as treated water from the pipe 14 to the outside of the system. The high temperature acid production tank 1 and the high temperature methane production tank 2 are respectively supplied with the NaOH aqueous solution in the NaOH storage tanks 3 and 4 through pipes 15 and 16 equipped with pumps P ₄ and P ₅ . The pumps P ₄ and P ₅ are configured to interlock with the pH controllers 5 and 6 provided in the high temperature acid production tank 1 and the high temperature methane production tank 2, respectively.

In this embodiment, the raw water together with the circulating water from the high temperature methane production tank 2 which is returned through the pipe 13,
It is introduced into the high-temperature acid generator tank 1 to generate an acid.

Here, the raw water is 40,000 mg-COD.
/ L or less, the raw water COD concentration is 40
If it exceeds 000 mg / l, dilute in advance.

COD of the inflow water into the high temperature acid production tank 1
The circulating water amount is adjusted so that the concentration becomes 10000 mg / l. The circulating water amount is preferably 3 times or less than the raw water amount.

In the high temperature acid production tank 1, the free organic acid concentration is appropriately adjusted in view of the raw water concentration, circulating water amount, inflow water concentration, residence time and pH. The pH in the high temperature acid production tank 1 is
As described above, it is preferably 6.0 or less in order to suppress methane fermentation.

The outflow water from the high temperature acid production tank 1 is then piped 12.
It is introduced into the higher temperature methane production tank 2 and methane fermentation is performed. The pH in the high temperature methane production tank 2 is 6 to 7,
Preferably, the control is made to be 6.0 or more and less than 6.8.

Therefore, a part of the outflow water from the high temperature methane production tank 2 is returned as circulating water through the pipe 13, and the rest is discharged as treated water through the pipe 14.

According to the method of this embodiment, both the acid production efficiency in the high temperature acid production tank and the methane production efficiency in the high temperature methane production tank can be kept high, and efficient processing can be performed at low cost.

The present invention will be described in more detail with reference to specific experimental examples and examples. Experimental Example 1 To see the effect of the concentration of free organic acid on high temperature acid production, 1
The effect of pH on high temperature acid production was examined using synthetic sugar-based wastewater (addition of excessive amounts of N, P and trace metals) using glucose at a concentration of 0 g / l as a single carbon source as model wastewater.

A chemostat tank having a capacity of 1.05 liters was used as an acid generator, and the pH was 4.0 at a temperature of 55 ° C.
Lower limit of 5, 5.0, 5.5, 5.8 to 1N NaOH
Each adjustment was done by. Table 1 shows the shortest retention time based on a 90% sugar decomposition rate under each condition. However, even if the retention time is 24 hours, which is considered to be the upper limit in practice, the pH is 5.0.
Under the following conditions, the pH could not be lowered to 5.0 or lower and the system could not be maintained. Even when the pH was raised to 5.5, the system was very unstable, and washout of bacterial cells was often observed.

Raising the pH to 5.8 allowed the system to be maintained, in which case the minimum residence time was 10 hours. This large change in the acid generation state near pH 5.8 suggests the influence of the concentration of free organic acid, and the total concentration of free organic acid in this case was 400 mg / l.

[0047]

[Table 1]

Example 1 When the raw water is composed of an easily decomposable sugar substrate such as glucose or sucrose, the raw water concentration and the high temperature acid production tank control pH are determined from the upper limit of the free organic acid concentration of 400 mg / l.
Of the desired area can be defined. The area is shown in FIG. Note that FIG. 2 is a graph showing the relationship between raw water sugar concentration and pH, in which the region where the concentration of free organic acid is 400 mg / l or less, in which high-temperature acid production is favorably performed, is shown by a hatching, and shows the organic acid per sugar. The ratio of the amount produced is 0.3 g-organic acid / g-sugar based on the actual result, and is obtained by using the pKa value of 4.9 of butyric acid, which was the main produced organic acid component at the time of study. In this example, based on this condition, the operating conditions of the high temperature acid production tank were determined according to the present invention shown in FIG.
An example of high-load treatment of easily degradable sugar-based wastewater is shown.

COD concentration of raw water is 7960 mg / l on average
However, the raw water flowing into the high temperature acid production tank was diluted three times with the treated water from the high temperature methane production tank (that is, the circulating water amount was twice the raw water flow rate). Since the average COD flowing into the acid production tank was 2480 mg / l, the pH was controlled to 5.1 or higher from the region shown by the hatch in FIG. Temperature is 55 ℃
And

Acid was produced with a residence time of 5 to 10 hours in the high-temperature acid production tank to obtain raw water for the high-temperature methane production tank.
It is possible to stably maintain a sugar decomposition rate of 5% or more, and the sludge load in the methane production tank is 3.5 kg-COD /
It was possible to increase to kg-VSS / day.

In the one-tank system obtained from another study,
Maximum sludge load on sugar substrate is 0.9 kg-COD / k
It was g-VSS / day, and a clear effect was recognized. In addition, the alkali consumption of 0.2 g-NaOH / l expected when the treated water in the high temperature acid production tank was not circulated (raw water COD7960 mg / l, pH 5.7) was 0.1 g-NaOH / l due to the circulation of the treated water. It was also confirmed that it was reduced to 1. The average COD value of each part in the example is shown in Table 2.
In addition, the maximum sludge activity of the methane production tank is shown in Table 3 in comparison with the case of the single tank system, and the alkali consumption is shown in Table 4 in comparison with the case where the treated water is not circulated. ..

[0052]

[Table 2]

[0053]

[Table 3]

[0054]

[Table 4]

Example 2 In the method shown in FIG. 1, the pH of the high temperature methane production tank was controlled to the values shown in Table 5 and FIG. 3, respectively, and the acetic acid assimilating methane production activity was calculated for each pH value. 5, shown in FIG. From Table 5 and Figure 3, the pH of the high temperature methane production tank
It is apparent that the methanogenic activity is remarkably enhanced by adjusting the value of 6 to 7, particularly less than 6.8.

[0056]

[Table 5]

[0057]

As described in detail above, according to the method for high temperature anaerobic treatment of organic waste water according to claim 1, the organic waste water is introduced into the high temperature acid generating tank to generate the organic acid, and then the high temperature acid generating tank. In the high temperature anaerobic treatment method of organic wastewater that guides the effluent of the wastewater to the high temperature methane production tank and produces methane, it is possible to maintain the acid production reaction stably even in the high temperature region and obtain a practical reaction rate. it can. Since high-load acid production can be stably maintained, high-load methane production reaction can be realized even with sugar-based wastewater. As a result, the volume of the high temperature acid production tank can be reduced, and the initial cost can be reduced.

The effects such as the above are exhibited.

According to the method for high temperature anaerobic treatment of organic waste water according to the second aspect, it is possible to reduce the alkali consumption required for pH control of the high temperature acid production tank and the high temperature methane production tank. It is not necessary to dilute the raw water more than necessary, and the energy required for heating can be minimized. And the like.

According to the method for high temperature anaerobic treatment of organic waste water according to claim 3, the methane production activity of the high temperature methane production tank is significantly increased, and the treatment efficiency is improved. And the like.

According to the method for high temperature anaerobic treatment of organic wastewater according to claim 4, the effects of the methods according to claims 1 and 3 are exhibited together, and more efficient treatment and stable high load operation are possible. To be done.

[Brief description of drawings]

FIG. 1 is a system diagram showing an implementation method of a high temperature anaerobic treatment method for organic wastewater according to the present invention.

FIG. 2 is a graph showing a preferable range of raw water concentration and high temperature acid production tank control pH.

FIG. 3 is a graph showing the results of Example 2.

[Explanation of symbols]

 1 High temperature acid production tank 2 High temperature methane production tank 3,4 NaOH storage tank 5,6 pH controller

Claims (4)

[Claims] 1. A high-temperature anaerobic effluent of organic wastewater, which introduces organic wastewater into a high-temperature acid production tank to produce an organic acid, and then introduces effluent of the high-temperature acid production tank into a high-temperature methane production tank to produce methane. In the treatment method, the concentration of the free organic acid in the high temperature acid generator is 400 mg / l.
A method for high-temperature anaerobic treatment of organic wastewater, comprising the following adjustments. 2. The high-temperature anaerobic treatment method for organic wastewater according to claim 1, wherein a part of the outflow water of the high-temperature methane production tank is circulated to the high-temperature acid production tank. 3. A high temperature anaerobic effluent of an organic wastewater, which guides the organic wastewater to a high temperature acid generation tank to generate an organic acid, and then guides the effluent of the high temperature acid generation tank to a high temperature methane generation tank to generate methane. In the treatment method, the pH in the high temperature methane production tank is adjusted to 6 to 7, which is a high temperature anaerobic treatment method for organic wastewater. 4. A high temperature anaerobic effluent of organic wastewater, which guides organic wastewater to a high temperature acid generation tank to generate an organic acid, and then guides outflow water of the high temperature acid generation tank to a high temperature methane generation tank to generate methane. In the treatment method, the concentration of the free organic acid in the high temperature acid generator is 400 mg / l.
Adjust in the following and p in the high temperature methane production tank
A high-temperature anaerobic treatment method for organic wastewater, which comprises adjusting H to 6 to 7.