JP2018167177A - Wastewater treatment method and wastewater treatment apparatus - Google Patents

Abstract

To provide a wastewater treatment method and a wastewater treatment apparatus capable of appropriately performing both an acid fermentation tank and methane fermentation.SOLUTION: There is provided a wastewater treatment method for causing acid fermentation of organic wastewater in an acid fermentation tank 1 to obtain acid fermentation wastewater; and causing methane fermentation of the acid fermentation wastewater in a methane fermentation tank 2 to obtain methane fermentation wastewater, the method including: a first returning step of returning the methane fermentation wastewater to the acid fermentation tank 1; and a second returning step of returning the methane fermentation wastewater to the methane fermentation tank 2.SELECTED DRAWING: Figure 1

Description

  The present invention provides a wastewater treatment method for performing an acid fermentation process in which organic wastewater is acid fermented in an acid fermenter to obtain acid fermentation wastewater, and a methane fermentation process in which the acid fermentation wastewater is subjected to methane fermentation to obtain methane fermentation wastewater. The present invention relates to a wastewater treatment apparatus including an acid fermenter for acid fermentation of organic wastewater, and a methane fermentation tank for methane fermentation of acid fermentation wastewater from the acid fermentation tank.

  Methane fermentation has long been known as an important unit process for wastewater treatment, but there is a problem that the equipment is bulky, and introduction as a relatively large-scale water treatment equipment is often considered. As such a water treatment facility, a sewage treatment system combining acid fermentation and methane fermentation is known.

  In the wastewater treatment equipment used in such a sewage treatment system, the microbial growth conditions in the acid fermentation tank and the microbial growth conditions in the methane fermentation tank are different, so both the acid fermentation tank and methane fermentation tank environments are maintained well. It was difficult. For example, acid fermentation wastewater components generated in an acid fermenter contain various components that inhibit methane fermentation, and the processing efficiency in the acid fermenter decreases to maintain the load of the methane fermenter. In such a case, the pH of the acid fermentation effluent and the organic matter concentration are mentioned as factors that inhibit methane fermentation (for example, Patent Documents 1 and 2). And in order to eliminate these factors, it is considered to perform the return process which returns the methane fermentation waste water from a methane fermentation tank to an acid fermentation tank.

Japanese Patent Publication No. 3-011835 JP 2004-098003 A

  However, even if the environment of the acid fermenter is adjusted so that acid fermentation wastewater suitable for methane fermentation can be obtained, when the quality and quantity of organic wastewater fluctuate, Even if the water quality of the wastewater is suitable as a component, there is a problem that the organic matter concentration becomes incompatible and the methane fermentation in the methane fermentation tank may not proceed properly. Specifically, when the methane fermentation does not proceed well in the methane fermentation tank, there is a problem that the organic acid contained in the methane fermentation wastewater after the methane fermentation becomes high in concentration and does not meet the wastewater standard.

  Therefore, an object of this invention is to provide the waste water treatment method and waste water treatment apparatus which can perform both an acid fermenter and methane fermentation appropriately in view of the said actual condition.

The characteristic configuration of the wastewater treatment method of the present invention for the above purpose is as follows:
An acid fermentation process in which organic wastewater is acid fermented in an acid fermenter to obtain acid fermentation wastewater;
A methane fermentation process in which the acid fermentation wastewater is subjected to methane fermentation in a methane fermentation tank to obtain methane fermentation wastewater;
A wastewater treatment method,
A first returning step of returning methane fermentation wastewater to the acid fermentation tank;
A second returning step of returning the methane fermentation wastewater to the methane fermentation tank;
The point is to do.

According to the above characteristic configuration, by performing the first return step of returning the methane fermentation wastewater to the acid fermenter, the acid fermentation step of acid fermentation of the organic wastewater to obtain the acid fermentation wastewater is more suitable for the acid fermenter. You can do it. For example, since the pH of the acid fermenter is low and the pH of the methane fermentation wastewater is high, the pH in the acid fermenter can be adjusted so that the pH of the acid fermenter does not decrease too much. Moreover, by maintaining the residence time of the organic wastewater in the acid fermentation tank constant regardless of the flow rate of the organic wastewater, the acid fermentation is sufficiently performed and the discharge amount of the acid fermentation wastewater can be constantly stabilized.
Moreover, by performing the 2nd return process which returns methane fermentation wastewater to a methane fermentation tank, the acid fermentation wastewater is methane-fermented and the methane fermentation process which obtains methane fermentation wastewater is performed in a suitable environment in a methane fermentation tank Can do. For example, since the organic matter concentration can be lowered by methane fermentation wastewater, stable methane fermentation can be performed by returning the methane fermentation wastewater to the methane fermentation tank, regardless of the organic matter concentration from the acid fermentation tank.

  Therefore, the acid fermentation in the acid fermenter and the progress of methane fermentation in the methane fermenter can be individually optimized, and wastewater treatment under conditions where both acid fermentation and methane fermentation are performed stably is suitably performed. Is called.

  In the first return step, the amount of returned water can be controlled so that the acid fermenter has a predetermined residence time based on the amount of the organic waste water supplied to the acid fermenter and the amount of returned water returned to the acid fermenter. .

  That is, according to the said structure, the residence time in an acid fermenter is controlled uniformly by the quantity of the waste_water | drain (organic waste water and return water) in an acid fermenter. Thereby, stable acid fermentation can be performed regardless of the amount (concentration) of organic wastewater.

  Moreover, the said 2nd return process can control the amount of returned water so that the organic substance density | concentration in the tank in the said methane fermentation tank may be maintained below a predetermined value.

  That is, according to the said structure, since the organic substance density | concentration of the waste_water | drain (acid fermentation waste_water | drain and return water) in a methane fermenter is controlled uniformly, the load in the methane fermenter of the waste_water | drain will be controlled uniformly. Accordingly, stable methane fermentation can be performed regardless of the organic matter concentration of the acid wastewater, and more specifically, regardless of the organic matter concentration of the organic wastewater.

  Moreover, since the above-mentioned first return process and second return process are controlled by completely different parameters such as the amount of treated water and the concentration of organic matter, they can be controlled independently, and the properties of organic wastewater, acid fermentation The methane fermentation environment in the methane fermenter can be suitably maintained without being affected by environmental changes.

Moreover, the characteristic configuration of the wastewater treatment apparatus of the present invention is a wastewater treatment apparatus comprising an acid fermentation tank for acid fermentation of organic wastewater, and a methane fermentation tank for methane fermentation of acid fermentation wastewater from the acid fermentation tank,
A storage tank for storing methane fermentation wastewater from the methane fermentation tank is provided, a first return path for returning the methane fermentation wastewater from the storage tank to the acid fermentation tank, and the methane fermentation wastewater from the storage tank to the methane fermentation tank A second return path for returning to the first return path, and a return water distribution section capable of independently controlling the amount of returned water returned to the first return path and the amount of returned water returned to the second return path. It is in.

  That is, since the storage tank which stores methane fermentation wastewater is provided, when returning methane fermentation wastewater to an upstream side, the methane fermentation wastewater for return water can be provided stably. When this methane fermentation wastewater is used as return water, the methane fermentation wastewater can be returned to the acid fermentation tank by the first return path, and the methane fermentation wastewater can be returned to the methane fermentation tank by the second return path. . These return water amounts can be controlled independently by the return water distribution section, so the environment of the acid fermenter and methane fermenter can be adjusted respectively, and the final organic wastewater treatment efficiency can be optimized. it can. Therefore, the waste water treatment apparatus which can exhibit high treatment efficiency stably was able to be provided.

  Moreover, the said return water distribution part may be equipped with the residence time adjustment mechanism which adjusts the organic waste water residence time in an acid fermentation tank, and the organic substance density | concentration maintenance mechanism which adjusts the organic substance density | concentration of a methane fermentation tank.

  That is, the residence time of waste water is mentioned as a particularly important parameter that affects the efficiency of waste water treatment in an acid fermentation tank. When the amount of the organic waste water supplied to the acid fermentation tank varies, the time during which the acid fermentation is performed on the organic matter in the acid fermentation tank varies. Then, among the organic substances in the organic waste water, the organic substances that are to be consumed by the acid fermentation are not necessarily completely converted into acids. Furthermore, there is a risk that the organic matter concentration may fluctuate or components that may become a fermentation inhibition factor remain in the wastewater treatment in the subsequent methane fermentation tank. In contrast, if a residence time adjusting mechanism is provided, the acid fermentation is sufficiently performed (acid is generated) by ensuring the residence time of the wastewater in the acid fermentation tank regardless of the amount of organic wastewater, and the acid It is possible to easily maintain an environment where the pH in the fermenter does not decrease too much. As such a residence time adjusting mechanism, for example, the return water amount can be controlled so that the sum of the organic waste water amount and the return water amount returned to the acid fermentation tank becomes a predetermined amount, but is not limited thereto.

  Moreover, organic substance concentration (load) is mentioned as an especially important parameter affecting the wastewater treatment efficiency in a methane fermentation tank. If the organic matter concentration contained in the acid fermentation effluent supplied to the methane fermenter fluctuates, it will not be possible to secure a sufficient amount of microorganisms for methane fermentation with respect to the organic matter in the methane fermenter, making it difficult for effective methane fermentation to proceed. . On the other hand, if an organic matter concentration maintaining mechanism is provided, the organic matter concentration in the wastewater can be kept constant regardless of the organic matter concentration in the acid fermentation wastewater, and thus stable methane fermentation can be performed. As such an organic substance concentration maintaining mechanism, for example, a mechanism that controls the amount of returned water so as to maintain the organic substance concentration below a predetermined value can be adopted, but it is not limited thereto.

  Therefore, both the acid fermenter and methane fermentation can now be performed properly, and advanced wastewater treatment can be performed by linking them together.

Flow chart of wastewater treatment equipment

  Below, the waste water treatment equipment concerning the embodiment of the present invention is explained. Preferred embodiments are described below, but these embodiments are described in order to more specifically illustrate the present invention, and various modifications can be made without departing from the spirit of the present invention. The present invention is not limited to the following description.

[Wastewater treatment equipment]
As shown in FIG. 1, the waste water treatment apparatus according to the embodiment of the present invention includes an acid fermentation tank 1 for acid fermentation of organic waste water, a methane fermentation tank 2 for methane fermentation of acid fermentation waste water from the acid fermentation tank 1, and And a storage tank 3 for storing the methane fermentation waste water from the methane fermentation tank 2. Moreover, the 1st return path R1 which returns the methane fermentation wastewater of the storage tank 3 to the acid fermentation tank 1 and the 2nd return path R2 which returns the methane fermentation wastewater of the storage tank 3 to the methane fermentation tank 2 are provided. Thereby, the return water distribution part W which can control independently the return water amount returned to 1st return path R1 and the return water amount returned to 2nd return path R2 is provided.

[Acid fermenter]
The acid fermenter 1 accepts organic wastewater from above, acid ferments the organic wastewater in the acid fermenter 1, and introduces organic wastewater into the acid treatment vessel 10 that performs an acid fermentation process to obtain acid fermentation wastewater. Part 11, acid fermentation waste water discharge part 12 discharged in a form in which acid fermentation waste water staying in acid treatment vessel 10 for a predetermined time overflows, and first return water introduction part 13 for introducing return water from storage tank 3 With.
Moreover, the organic waste water introduction part 11 is provided with the organic waste water flowmeter 14, detects the flow rate of the organic waste water introduced into the acid treatment container 10, and the amount of organic waste water introduced into the organic waste water introduction part 11 and the first return. A first return process is performed for controlling the amount of returned water so that the sum of the amount of returned water returned to the water introduction unit 13 becomes a predetermined amount.
The return water amount is controlled by the return water distribution unit W, and the return water distribution unit W is connected to the first return water introduction unit 13 according to the output from the organic waste water flow meter 14. Has a dwell time adjustment mechanism W1 for controlling the first flow rate adjustment valve V1 provided in the vehicle. Thereby, the amount of wastewater introduced into the acid fermentation tank 1 is kept constant, and the organic wastewater introduced into the acid fermentation tank 1 is adjusted based on the return water flow meter 15, thereby organic It controls so that the residence time of drainage is kept constant. Specifically, the amount of wastewater introduced into the acid fermentation tank 1 is kept constant by decreasing the amount of returned water as the amount of organic wastewater increases.

[Methane fermentation tank]
The methane fermentation tank 2 accepts acid fermentation wastewater from the bottom, introduces acid fermentation wastewater into the methane fermentation vessel 20 that performs the methane fermentation process to obtain methane fermentation wastewater by methane fermentation of the acid fermentation wastewater. Unit 21 and a methane fermentation drainage discharge unit 22 that is discharged in a form in which the methane fermentation wastewater methane fermented in methane fermentation vessel 20 overflows. Further, the methane fermentation vessel 20 is provided with a stirring device 23 for stirring the inside of the methane fermentation vessel 20 and uniformly maintaining the wastewater stored therein. Further, a methane gas passage 24 for taking out methane produced in the methane fermentation tank 2 is connected.
Moreover, the organic substance concentration meter 25 which monitors the organic substance density | concentration of the waste_water | drain stored in the methane fermentation container 20 is provided, and the 2nd return process which controls the amount of returned water is performed so that organic substance density | concentration may be maintained below a predetermined value.
A second return path R2 for returning the methane fermentation wastewater in the storage tank 3 to the methane fermentation tank 2 as return water is connected to the transfer path L1 that connects the acid fermentation wastewater discharge section 12 and the acid fermentation drainage introduction section 21. A second return water introduction section 26 is provided. The return water amount returned to the second return water introduction unit 26 is controlled by the return water distribution unit W. The return water distribution unit W is connected to the second return path R2 according to the output from the organic substance concentration meter 25. An organic matter concentration maintaining mechanism W2 for controlling the second flow rate adjusting valve V2 provided is provided. Thereby, the organic matter density | concentration of the acid fermentation waste water introduce | transduced into the methane fermentation tank 2 is hold | maintained uniformly, and it controls so that the load in the methane fermentation tank 2 is maintained constant. Specifically, the organic matter concentration in the methane fermentation tank 2 is controlled to be constant by increasing the amount of returned water as the concentration of organic matter in the acid fermentation wastewater increases. This corresponds to increasing the amount of returned water as the amount of organic waste water increases, and is therefore the opposite of the control in the first returning step.

[Reservoir]
The storage tank 3 has a methane fermentation wastewater introduction part 31 that receives the methane fermentation wastewater from above into a storage container 30 that stores the methane fermentation wastewater, and a treated wastewater discharge that discharges excess methane fermentation wastewater to the outside as treated wastewater by overflow. Part 32. Moreover, the return water extraction part 33 which takes out the stored methane fermentation waste water as return water is provided, and the return pump P provided in the return water extraction part 33 seems to pump up the methane fermentation waste water in the storage tank 3 as return water. It is configured.

[Return path]
The return water extraction unit 33 erected in the storage tank 3 is connected to a return path R that returns the return water to the upstream side via a return pump P. The return path R has a first return path R1 that returns methane fermentation wastewater as return water to the acid fermentation tank 1, and a second return path R2 that returns methane fermentation wastewater as return water to the methane fermentation tank 2, The return path R is provided with a return water adjustment valve V for adjusting the return water amount. Moreover, as mentioned above, the 1st return path R1 which returns return water to the acid fermenter 1 is provided, and the 2nd return path R2 which returns return water to the methane fermentation tank 2 is provided, Return water adjustment A return water distribution section W for adjusting the valve V and the first and second flow rate adjusting valves V1, V2 provided in the first and second return paths R1, R2 is provided. The return water distribution unit W independently controls the return water flow rate based on the organic waste water flow rate and the organic matter concentration in the methane fermentation tank 2.

〔Example〕
Table 1 shows the state of wastewater treatment in the case of treating sulfuric acid acidic 13000 mg / L organic wastewater in the wastewater treatment apparatus. In Table 1, the acid concentration and the organic matter concentration of the acid fermentation wastewater and the organic matter concentration of the methane fermenter when the flow rate of the organic wastewater fluctuates to 8.1 L / d to 14.5 L / d are obtained, respectively. The example which controlled to maintain the organic substance density | concentration of a methane fermenter in organic substance load capacity (5000 mg / L in this example) is shown by adjusting the 2nd return path return water amount.
First, the amount of organic wastewater introduced into the acid fermenter 1 and the return water of the first return path R1 determined by the return water flow meter 15 are introduced into the first return water introduction unit 13, so The amount of wastewater flowing into the fermenter 1 (the amount of organic wastewater + the amount of water returned to the first return path) is adjusted to 28 L / d (first return step). Then, it was found that the acid fermenter 1 can secure a residence time of 3 to 4 hours with respect to the organic wastewater, and generates organic acids (acetic acid and propionic acid) at a ratio corresponding to the amount of the organic wastewater. In addition, when this residence time is insufficient, acid fermentation does not advance sufficiently, and the amount of organic acid in the acid fermentation wastewater does not increase sufficiently.
Next, return water is supplied through the second return path R2 to adjust the organic matter concentration in the methane fermentation tank 2 to 5000 mg / L or less (second return step). Then, the organic matter concentration (adjusted organic matter concentration) supplied to the methane fermenter 2 is maintained at a load that can be treated in the methane fermenter 2, and the organic wastewater is sufficiently treated although there is an increase in the flow rate due to the return water. It became clear that we could do it. At this time, the amount of organic acid in the methane fermentation wastewater is 120 mg / L of acetic acid and 140 mg / L of propionic acid, which is 300 mg / L or less of propionic acid, which is the drainage standard, and 600 mg / L or less of the total organic acid amount. It was enough to meet the standards.

[Comparative example]
In addition, when the acid fermentation waste water obtained by the said Example was introduce | transduced into the methane fermenter 2 as it was, and methane fermentation was performed, that is, when only the 1st return process was performed and the 2nd return process was not performed, the methane fermenter Since the assumed organic matter concentration in 2 increases at a rate different from the organic acid concentration, the assumed organic matter concentration exceeds the organic load capacity of the methane fermentation tank 2. The amount of organic acid in the methane fermentation wastewater at this time was acetic acid 300 mg / L and propionic acid 460 mg / L, which did not satisfy the wastewater standards, and it was found that methane fermentation of organic acids was not sufficiently advanced. .

  According to the present invention, since both acid fermentation and methane fermentation can be performed appropriately, it can be used as a wastewater treatment apparatus capable of performing stable wastewater treatment.

1: Acid fermentation tank 2: Methane fermentation tank 3: Storage tank 14: Organic waste water flow meter 25: Organic substance concentration meter R1: First return path R2: Second return path W: Return water distribution section

Claims (5)

An acid fermentation process in which organic wastewater is acid fermented in an acid fermenter to obtain acid fermentation wastewater;
A methane fermentation process in which the acid fermentation wastewater is subjected to methane fermentation in a methane fermentation tank to obtain methane fermentation wastewater;
A wastewater treatment method,
A first returning step of returning methane fermentation wastewater to the acid fermentation tank;
A second returning step of returning the methane fermentation wastewater to the methane fermentation tank;
Wastewater treatment method.   The first return step controls the amount of returned water so that the acid fermenter has a predetermined residence time based on the amount of organic wastewater supplied to the acid fermenter and the amount of returned water returned to the acid fermenter. The wastewater treatment method according to claim 1.   The waste water treatment method according to claim 1 or 2, wherein the second returning step controls the amount of returned water so as to maintain the organic substance concentration in the tank in the methane fermentation tank below a predetermined value. A wastewater treatment apparatus comprising an acid fermentation tank for acid fermentation of organic wastewater, and a methane fermentation tank for methane fermentation of acid fermentation wastewater from the acid fermentation tank,
A storage tank for storing methane fermentation wastewater from the methane fermentation tank is provided, a first return path for returning the methane fermentation wastewater from the storage tank to the acid fermentation tank, and the methane fermentation wastewater from the storage tank to the methane fermentation tank Drainage provided with a return water distribution section capable of independently controlling the amount of return water returned to the first return path and the amount of return water returned to the second return path Processing equipment.   5. The wastewater treatment according to claim 4, wherein the return water distribution unit includes a residence time adjustment mechanism that adjusts an organic wastewater residence time in the acid fermentation tank and an organic matter concentration maintenance mechanism that adjusts an organic matter concentration in the methane fermentation tank. apparatus.

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