JP2021194616A - Anaerobic wastewater treatment method - Google Patents

Abstract

To provide an anaerobic wastewater treatment method that can significantly reduce the time required for start-up operation and is capable of performing efficient treatment after the start-up of the reaction tank.SOLUTION: An anaerobic wastewater treatment method in which organic substances-containing wastewater is passed through a carrier-holding reaction tank and treated biologically by anaerobic microorganisms grown on the carrier, wherein the wastewater treatment method comprises a start-up operation that comprises at least: a first step of passing the wastewater through the reaction tank in the presence of the carrier and suspended substances that contain methane bacteria-containing aggregates at a rate of 1-900 g per L of the carrier; and a second step in which the CODcr load of the wastewater flowing into the reaction tank is increased at the time when it reaches a state where the amount, evaluated in terms of VSS, of bacteria (including methane bacteria) attached to the carrier is 0.5 g or more per 1 L of carrier and the suspended substances that contain methane bacteria-containing aggregates is less than 5 g per 1 L of carrier.SELECTED DRAWING: Figure 1

Description

The present invention relates to an anaerobic wastewater treatment method. More specifically, the present invention relates to an anaerobic wastewater treatment method in which wastewater containing an organic substance is passed through a reaction vessel holding a carrier and biologically treated with anaerobic microorganisms grown on the carrier.

As a treatment method for wastewater containing organic matter (hereinafter sometimes referred to as "organic wastewater"), an anaerobic treatment method capable of recovering and reusing methane gas is widely used as a treatment method for industrial wastewater. .. Among them, the UASB (Upflow Anaerobic Sludge Blanket) method, which forms a granule with good sedimentation property, allows organic wastewater to flow in an upward flow, and performs high-load high-speed treatment, is particularly effective. It has been developed as a method for treating medium to high concentration wastewater. In addition, as an extension of this UASB method, the EGSB (Expanded Granule Blanket) method, in which water is passed at a higher flow rate using a high reaction tank and anaerobic treatment is performed with a high load, has also been put into practical use. ..

Further, as a method for treating organic wastewater, a method using a fixed bed carrier or a fluidized bed carrier is also used. The fixed-bed carrier fixes a support bed that holds a biofilm inside the reaction vessel, and treats wastewater using microorganisms that grow on the surface (hereinafter sometimes referred to as "bacteria"). In the fluidized bed carrier, a carrier whose specific gravity and size have been adjusted is allowed to flow inside the reaction vessel, and organisms are propagated on the carrier to treat wastewater.

However, when a carrier is used regardless of whether it is a fixed bed carrier or a fluidized bed carrier, there is a big drawback that it takes time for microorganisms to grow on the carrier, and as a result, it takes a lot of time to set up the reaction vessel. ..

To address such issues, for example, Patent Document 1 describes the treatment of organic wastewater in the presence of an abiotic carrier and granules (average particle size 0.5 to 3.0 mm). A method of starting up the reaction tank has been proposed.

Further, Patent Document 2 is a method for treating organic wastewater, which starts the passage of organic wastewater in a state where a carrier and agglomerates of methane bacteria are present in the reaction tank when the reaction tank is started up. Therefore, a method has been proposed in which the average particle size of the methanogen aggregate is 10 μm or more and 450 μm or less to improve the contact efficiency with the carrier.

Japanese Unexamined Patent Publication No. 2012-110821 Japanese Unexamined Patent Publication No. 2014-100680

However, in either of the methods described in Patent Document 1 and Patent Document 2, even if the bacteria adhere to and proliferate on the carrier sufficiently and the wastewater can be treated while sufficient granules and methanogen aggregates are present, the wastewater can be treated. Granules and methanogen aggregates may be disassembled and flowed out before the bacteria sufficiently adhere to and multiply on the carrier, causing a problem that the wastewater treatment capacity is reduced, and it is difficult to say that this is a sufficient method.

INDUSTRIAL APPLICABILITY In the present invention, in a method in which organic wastewater is passed through a reaction vessel holding a carrier and biologically treated with anaerobic microorganisms grown on the carrier, the time required for the start-up operation of the reaction vessel is significantly increased. It is an object of the present invention to provide an anaerobic wastewater treatment method capable of shortening the time and performing efficient treatment even after the reaction tank is started up. In the following, the process of starting up the reaction tank, which is a treatment device, by passing organic wastewater through the reaction tank holding the carrier is referred to as a start-up operation.

As a result of diligent studies, the present inventors have found that the above problems can be solved by the following inventions.

The anaerobic wastewater treatment method according to one aspect of the present invention is anaerobic in which wastewater containing organic substances is passed through a reaction vessel holding a carrier and biologically treated with anaerobic microorganisms grown on the carrier. In the wastewater treatment method, the wastewater is passed through in a state where the carrier and a suspended solid containing methane bacteria aggregates so as to be 1 to 900 g per 1 L of the carrier are present in the reaction tank. When the step and the amount of adhered cells containing methane bacteria to the carrier were evaluated by VSS (Volatile Suspended Solids), the amount of VSS was 0.5 g or more per 1 L of the carrier, and the methane bacteria aggregated. From the state where the suspended solids containing substances are less than 5 g per 1 L of the carrier, a start-up operation having at least a second step of increasing the CODcr load of the wastewater passing through the reaction tank is performed.

According to the present invention, it is possible to provide an anaerobic wastewater treatment method capable of significantly shortening the time required for the start-up operation of the reaction tank and performing efficient treatment even after the start-up of the reaction tank. ..

It is a figure which represented the flow of an example for carrying out this invention schematically.

As a result of diligent studies, the present inventors pass water containing organic substances (organic wastewater) through a reaction vessel holding a carrier and biologically treat it with anaerobic microorganisms grown on the carrier. In the anaerobic wastewater treatment method, organic wastewater is started to flow in a state where the carrier and methanogen aggregates are present in the reaction tank, and after a certain amount of bacterial cells are attached to the carrier, the reaction tank is subjected to. The amount of methanogen aggregates was reduced to less than a certain amount, and COD (Chemical Oxygen Demand: chemical oxygen demand, especially COD measured using potassium dichromate is called CODcr) adhered mainly to the carrier from the stage when the load was low. It has been found that by removing organic substances with methane bacteria and performing a start-up operation, methane bacteria can be efficiently attached and propagated on the carrier. The present invention has been made based on such findings, and an embodiment of the present invention will be described below.

The anaerobic wastewater treatment method according to the present embodiment is an anaerobic wastewater treatment method in which organic wastewater is passed through a reaction vessel holding a carrier and biologically treated by anaerobic microorganisms grown on the carrier. The first step of passing the waste water through the carrier and a suspended substance containing methanogen aggregates so as to be 1 to 900 g per 1 L of the carrier in the reaction vessel. When the amount of bacterial cells containing methane bacteria attached to the carrier was evaluated by VSS, the amount of VSS was 0.5 g or more per 1 L of the carrier, and the suspended substance containing the agglomerates of the methane bacteria was less than 5 g per 1 L of the carrier. It is a method of performing a start-up operation having at least a second step of increasing the CODcr load of the wastewater flowing through the reaction tank from the state.

According to this method, bacterial cells containing methane bacteria adhere to the carrier from the aggregates of methane bacteria, and organic substances are distributed to the bacterial cells attached to the carrier, and the growth of the bacterial cells on the carrier can be promoted.

It will be explained in more detail. In the reaction tank for anaerobic wastewater treatment, bacterial cells decompose organic matter in organic wastewater and proliferate. However, if a large amount of methanogen aggregates are present in the reaction tank at the time of starting up the reaction tank, the organic matter does not spread to the cells adhering to the carrier, and the growth of the cells is not promoted on the carrier. In addition, when methane bacteria aggregates are disassembled and flowed out under a high CODcr load, the decomposition of organic matter in the wastewater cannot catch up with the cells attached to the carrier alone, and the abundance ratio of the cell growth inhibitor increases in the carrier. Cell growth is not promoted.

In response to these problems, in the anaerobic wastewater treatment method according to the present embodiment, a certain amount of methanogen aggregates are attached to the carrier using methane bacteria aggregates at the start of the start-up operation, and then the methane bacteria aggregates are formed. It was decided to take a method of gradually increasing the CODcr load after the amount becomes less than a certain amount. As a result, the organic matter is sufficiently distributed to the cells adhering to the carrier, and the adhesion and proliferation of the cells to the carrier are promoted, the time required for the start-up operation is greatly shortened, and the start-up operation of the reaction tank is carried out. Efficient processing can be performed even after the completion of.

In the present embodiment, the organic wastewater to be treated may contain organic substances that can be treated by anaerobic microorganisms, and the CODcr concentration and the type of wastewater are not specified, but specifically, a food factory. Such as manufacturing wastewater, organic wastewater from chemical factories, general sewage, etc. However, it is not limited to these. The organic matter concentration of the organic wastewater is not particularly limited, and for example, the CODcr concentration can be 500 to 50,000 mg / L, and can be widely applied. The organic matter concentration of the organic wastewater is the CODcr concentration, and can be widely applied, for example, 500 to 50,000 mg / L. Next, each step will be described.

(First step)
Methanogen aggregates are required to attach methanogen-containing cells to the carrier. Therefore, at the time when the organic wastewater is started to flow through the reaction tank in the first step, the methanogen aggregate is present in the range of 1 to 900 g per 1 L of the carrier in the reaction tank holding the carrier. The amount of methanogen aggregates in the reaction vessel at the start of water flow is preferably 100 g or less, and more preferably 50 g or less per 1 L of the carrier. If the amount of methanogen aggregates is less than 1 g per 1 L of the carrier, the effect of the present invention cannot be sufficiently obtained, and if it is more than 900 g per 1 L of the carrier, the viscosity may increase and stirring may become difficult. In addition, a large amount of methanogen aggregates flow out from the reaction vessel, which is not preferable because there is a concern that the treated water may deteriorate. The amount of methanogen aggregates in the reaction vessel referred to here is the amount of VSS, that is, the amount of floating methanogen aggregates. VSS is used as a measure of the total amount of organic solids. The VSS amount is measured by the method described below.

<Measurement method of the amount of methanogen aggregates in the reaction tank>
First, the amount of suspended solids (SS: Suspended Solids) in the reaction vessel is measured according to JIS K 0102: 20134.1.1. However, if there is an SS that passes through the filter paper having a hole diameter of 1 μm, the filter paper having a hole diameter of 0.45 μm is used. After determining the SS amount (a) of the sample, the filter paper is sufficiently heated at 600 ± 25 ° C. for 30 to 60 minutes, and the weight (b) of the residue is measured. The amount of methanogen aggregate (VSS amount) in the reaction vessel is represented by the formula (I).
(Amount of methane bacteria aggregate in reaction tank (g)) = ((ab) / V) × V ′ ... (I)
a: SS amount (g)
b: Residue weight (g)
V: Sample (L)
V': Amount of water in the reaction tank (L)

Under the above conditions, the organic wastewater is started to flow through the reaction tank containing the carrier and the methane bacterium aggregate, and the methane bacterium aggregate adheres to the carrier of the reaction tank. At this time, the CODcr volumetric load of the organic wastewater is preferably 0.5 kg / m ³ / d or more and 5.0 kg / m ³ / d or less. Further, the CODcr volumetric load is ^{more preferably 2 kg / m 3} / d or more. If the CODcr volume load is too low, the period required for the cells to adhere to the carrier from the methane bacteria aggregates becomes long, and if it is too high, the methane bacteria aggregates are disassembled and discharged before the cells adhere to the carrier.

(Second step)
In the second step, the amount of VSS when the amount of adhered cells containing methanogens to the carrier was evaluated by VSS in the first step was 0.5 g or more per 1 L of the carrier, and the suspended solids containing methanogen aggregates were present. From the state where the amount is less than 5 g per 1 L of the carrier, the CODcr load of the organic wastewater passing through the reaction tank is increased. The CODcr load of the organic wastewater may be increased only once, continuously or gradually.

If the amount of bacterial cells on the carrier is too small when moving to the second step, when the amount of methanogen aggregates is low in the reaction tank, the bacterial cells attached to the carrier cannot sufficiently treat the organic wastewater and inhibit it. Since a large amount of the substance remains, it becomes difficult for the cells attached to the carrier to increase. Therefore, at the time of shifting to the second step, the amount of cells adhering to the carrier of the reaction tank needs to be a certain amount or more.

In the present embodiment, the amount of bacterial cells containing methane bacteria attached to the carrier contained in the reaction tank at the time of transition to the second step is 0.5 g or more per 1 L of the carrier. The amount of the cells attached to the carrier is preferably 0.6 g or more per 1 L of the carrier. In this embodiment, the amount of bacterial cells attached to the carrier is evaluated by VSS. In the present specification, the amount of adhered cells containing methane bacteria (VSS amount) to the carrier evaluated by VSS is also referred to as "VSS amount of carrier". The VSS amount of the carrier is measured by the method described below.

<Measuring method of VSS amount of carrier>
First, take the same amount of each of the carrier to which the bacterial cells are attached and the carrier to which the cells are not attached, and sufficiently dry the carrier at 95 ° C to 105 ° C to prepare a sample. The weight (c, d) of each sample is measured, and the amount of SS attached to the carrier represented by the following formula (II) is calculated (“carrier with bacterial cells and carrier without bacterial cells, respectively). "Take the same amount" means to take the same amount of carriers such as the number of carriers and the volume, but if the apparent value changes due to the growth of cells such as the volume, it is necessary to take it into consideration and correct it. The following will be explained based on the number of pieces). Next, each sample is sufficiently heated at 600 ± 25 ° C. for 30 to 60 minutes, and the weight of the residue (e, f) is measured. The VSS amount of the carrier is represented by the following formula (III).
(Amount of SS attached to the carrier per piece (g / piece)) = (cd) / M ... (II)
c: Dry weight (g) of the carrier to which the bacterial cells are attached.
d: Dry weight (g) of the carrier to which the cells are not attached.
M: Number of samples (pieces)
(VSS amount (g) of carrier) = ((s- (ef) / M) / N) × N'... (III)
s: Amount of SS attached to the carrier per piece (g / piece)
e: Residual weight (g) of the carrier to which the bacterial cells are attached
f: Residual weight (g) of the carrier to which the cells are not attached
N: Carrier volume (L / piece) to which bacterial cells are attached per piece
N': Carrier volume (L) in the reaction vessel

Here, even if the amount of VSS of the carrier is 0.5 g or more per 1 L of the carrier, if there are many methane bacteria aggregates in the reaction tank, the organic substances in the organic wastewater are mainly decomposed by the methane bacteria aggregates. Therefore, the organic matter does not spread to the cells attached to the carrier. Therefore, in the present embodiment, the amount of VSS of the carrier becomes 0.5 g or more per 1 L of the carrier, and the suspended solids containing methanogen aggregates become less than 5 g per 1 L of the carrier in the reaction vessel before shifting to the second step. do.

When the amount of VSS of the carrier is 0.5 g or more per 1 L of the carrier and the amount of methanogen aggregates in the reaction tank is 5 g or more per 1 L of the carrier, the suspended solids containing the methanogen aggregates in the reaction tank are per 1 L of the carrier. Suspended solids containing methanogen aggregates may be discharged from the reaction vessel until the amount is less than 5 g. The method for discharging the suspended solids containing methane bacteria aggregates from the reaction tank is not particularly limited, but the suspended solids containing methane bacteria aggregates and the carrier are extracted from the reaction tank and only the carrier is returned to the reaction tank. By installing a screen in the reaction vessel and increasing the circulating flow rate in the reaction vessel, the carrier and suspended solids containing methane bacteria aggregates are separated, and only the suspended solids containing methane bacteria aggregates are in the latter stage of the reaction vessel. A method of discharging to is conceivable. On the other hand, when the amount of VSS of the carrier becomes 0.5 g or more per 1 L of the carrier, if the suspended solids containing the methanogen aggregates in the reaction tank are less than 5 g per 1 L of the carrier, the methanogen aggregates in the reaction tank Move to the second step without discharging suspended solids containing.

The CODcr removal rate of the organic wastewater (water to be treated) treated in the reaction vessel can be used as an index for gradually increasing the CODcr volumetric load. As an example of a specific method of increasing the CODcr volumetric load, there is a method of increasing the CODcr volumetric load of the organic wastewater flowing through the reaction tank every time the CODcr removal rate becomes a predetermined value or more. As a predetermined value in this case, the CODcr removal rate is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. The CODcr removal rate is defined by the formula (IV) described below.

<CODcr removal rate>
CODcr removal rate (%) = ({treated water CODcr}-{treated water CODcr}) ÷ {treated water CODcr} × 100 ... (IV)
(Methanogen aggregate)
Next, the methanogen aggregate used in this embodiment will be described.

The smaller the particle size of the methanogen aggregate, the better the contact efficiency with the carrier. Therefore, the average particle size of the methanogen aggregate is preferably in the range of 10 to 450 μm, more preferably in the range of 100 to 400 μm.

The methanogen aggregate in the reaction tank may contain acid-producing bacteria and methane-producing bacteria, but the methanogen granule (average particle size 0.5 to 0.5) used in the UASB method and the EGSB method. Since 3.0 mm) is anaerobically treated, it contains a large amount of acid-producing bacteria and methane-producing bacteria, and has high activity. Therefore, the methanogen aggregate is preferably a methanogen granule. When the methanogen granule is used, it may be used as it is, but it is preferable to use a crushed product of the methanogen granule having an average particle size of 10 μm or more and 450 μm or less. The lower limit of the average particle size of the crushed material is more preferably 100 μm or more, and the upper limit is more preferably 400 μm or less. The method for crushing and crushing the methanogen granule is not particularly limited, and examples thereof include a method of crushing with a ball mill or the like, a method of passing through a pump to crush, and a method of crushing by stirring.

(Carrier)
The carrier used in the reaction tank is a solid to which microorganisms (including bacterial cells such as methanogens) adhere, and various known microbial-immobilized carriers can be used, but gel-like carriers, plastic carriers and It is preferable to use at least one microbially immobilized carrier selected from the group consisting of fibrous carriers. The materials include vinyl alcohol resins such as polyvinyl alcohol; ether resins such as polyethylene glycol; acrylic resins such as polymethacrylic acid; acrylamide resins such as polyacrylamide; olefin resins such as polyethylene and polypropylene, and styrene resins such as polystyrene; polyethylene. Ester resins such as terephthalate and polybutylene terephthalate; Acrylonitrile resins such as polyacrylonitrile; Urethane resins such as polyurethane sponge; Polysaccharides such as calcium alginate, κ (kappa) carrageenan, agar and cellulose derivatives; polyester acrylate, epoxy acrylate, urethane acrylate Such as a photocurable resin; a porous inorganic compound such as activated carbon can be exemplified. Among them, a gel-like carrier is preferable from the viewpoint of excellent immobilization of microorganisms, and polyvinyl has a porous and reticulated structure up to the inside and can take a large amount of water into the gel. A polyvinyl alcohol-based hydrogel carrier made of an alcohol-based resin is preferable, and a polyvinyl alcohol cross-linked gel carrier such as a formalized polyvinyl alcohol-based hydrogel or an acetalized polyvinyl alcohol-based hydrogel is more preferable. The microorganism-immobilized carrier can be used alone or in combination. The filling rate is preferably 5% or more and 50% or less, and more preferably 10% or more and 40% or less of the tank volume from the viewpoint of wastewater treatment efficiency and carrier fluidity.

The equivalent sphere diameter of the carrier is preferably 1 to 10 mm. When the equivalent diameter of the sphere is small, when a screen for preventing the outflow of the carrier is installed in the aeration tank, it is necessary to reduce the mesh size of the screen, which may cause clogging. Therefore, it is more preferable that the equivalent diameter of the sphere is 2 mm or more. On the other hand, if the equivalent diameter of the sphere exceeds 10 mm, the fluidity of the carrier may decrease. Therefore, it is more preferable that the equivalent diameter of the sphere is 6 mm or less. Here, the sphere equivalent diameter is the diameter of a sphere having a volume equal to the volume of the particles.

The specific gravity of the carrier is slightly larger than that of water, and it is preferable that the carrier has a specific density that can be shaken in the aeration tank so as not to be washed away from the aeration tank. In the treatment method of the present invention, by using a carrier having a specific gravity slightly higher than that of water, wastewater can be treated more stably without causing the carrier to be washed away, so that the specific gravity of the carrier is 1.001 or more. It is preferably 1.005 or more, and more preferably 1.005 or more. On the other hand, the specific gravity is preferably 1.2 or less, more preferably 1.1 or less, and even more preferably 1.05 or less.

The carrier preferably has a communication hole, and the pore size of the communication hole is preferably a pore size in which only bacteria can live inside the carrier. The pore diameter near the surface of the carrier is preferably 0.1 to 100 μm. If the pore size is less than 0.1 μm, bacteria may not be able to invade the inside of the carrier. It is more preferable that the pore diameter near the surface is 0.5 μm or more. On the other hand, if the pore size near the surface exceeds 100 μm, large organisms other than bacteria may invade. The pore diameter is more preferably 50 μm or less. The pore diameter of the communication hole can be measured by a method such as observation using an electron microscope.

The carrier preferably has a settling speed of 100 to 500 m / hr. If the sedimentation speed of the carrier is low, it tends to float due to water flow and generated gas, and accumulates in a scum shape near the water surface. In the abiotic carrier, a biofilm is formed on the surface due to the adhesion of the bacterial cells, and the reaction of generating gas inside the biofilm proceeds, so that the apparent specific gravity of the carrier becomes lighter with the formation of the biofilm. It is necessary to determine the specific gravity and sedimentation rate of the carrier itself in consideration of the influence of this biofilm. On the other hand, if the sedimentation rate is too high, the contact efficiency with the organic wastewater will deteriorate, and sufficient treatment performance may not be obtained. In addition, solid matter will accumulate in the sedimentary layer of the carrier and the organic wastewater flow path will be created. There is a possibility that it will be blocked.

(Treatment conditions in the anaerobic wastewater treatment method)
FIG. 1 shows an example of a wastewater treatment flow including an anaerobic wastewater treatment method according to the present embodiment. The wastewater treatment method according to the present embodiment will be described with reference to FIG. 1, including treatment conditions other than the above treatment conditions. In the wastewater treatment flow shown in FIG. 1, an acid generation tank 2 that accommodates and treats the raw water of the organic wastewater 1, a reaction tank 3 that further treats the organic wastewater 1 treated by the acid generation tank 2, and a reaction tank. A treated water receiving tank 4 that accommodates the organic wastewater 1 treated in 3 and discharges the treated water 6, and a treated water return that returns a part of the treated water discharged from the treated water receiving tank 4 to the acid generation tank 2. A system comprising a tube 5 is used. The above-mentioned carrier and methane bacterium aggregates are contained in the reaction tank 3 at the time of startup, and the above-mentioned first step and second step are performed in the reaction tank 3.

In the present embodiment, the method for treating the organic wastewater 1 in the reaction tank 3 is not particularly limited, but an upward flow type in which the organic wastewater is passed through the reaction tank by an upward flow as in the UASB method and the EGSB method. Examples thereof include a method using a reaction tank, a method using a completely mixed reaction tank in which the inside of the tank is stirred and flowed with a stirrer or the like, and a method in which the inside of the tank is aerated and flowed with a gas containing no oxygen such as nitrogen and methane gas.

The treatment conditions for the organic waste water 1 in the reaction tank 3 differ depending on the conditions such as the biodegradability of the organic waste water 1, but the lower limit of the pH is preferably 6 or more, more preferably 6.5 or more. The upper limit of pH is preferably 8 or less, more preferably 7.5 or less. The lower limit of the temperature is preferably 20 ° C. or higher, more preferably 25 ° C. or higher. The upper limit of the temperature is preferably 40 ° C. or lower, more preferably 37 ° C. or lower. The lower limit of HRT (Hydraulic Retention Time) is preferably 1 hour or more. The upper limit of HRT is preferably 24 hours or less, more preferably 8 hours or less. The lower limit of LV (Linear Velocity) is preferably 1 m / hr or more. The upper limit of LV is preferably 20 m / hr or less. The HRT is an average time from when the organic waste water 1 flows into the acid generation tank 2 or the reaction tank 3 to when it flows out.

The acid generation tank 2 provided in front of the reaction tank 3 is for decomposing high molecular weight components such as proteins contained in the organic wastewater 1 into small molecule organic acids such as acetic acid. When the organic wastewater 1 contains almost no high molecular weight components such as proteins and the organic wastewater 1 contains only compounds that can be directly used by methane-producing bacteria such as methanol and acetic acid, the reaction tank 3 It is not necessary to provide the acid generation tank 2 in front of the above stage.

The treatment conditions of the acid generation tank 2 differ depending on the conditions of the organic wastewater, but the lower limit of the pH is preferably 5 or more, more preferably 5.5 or more. The upper limit of pH is preferably 8 or less, more preferably 7.8 or less. The lower limit of the temperature is preferably 20 ° C. or higher, more preferably 25 ° C. or higher. The upper limit of the temperature is preferably 40 ° C. or lower, more preferably 37 ° C. or lower. The lower limit of HRT is preferably 2 hours or more. The upper limit of HRT is preferably 24 hours or less, more preferably 8 hours or less.

In this system, after completing the start-up operation, it is preferable that CODcr volume loading is 1 to 50 kg ^{/ m} 3 / d in the reaction vessel 3 during steady operation, to be 5~30kg ^{/ m} 3 ^/ d More preferred. The higher the CODcr volumetric load, the smaller the size of the reaction vessel 3. The CODcr volume load is obtained by adding the daily flow rate to the CODcr concentration of the inflowing organic wastewater and dividing by the reaction tank volume.

As described above, the present specification discloses various aspects of the technology, of which the main technologies are summarized below.

As described above, in the anaerobic wastewater treatment method according to one aspect of the present invention, wastewater containing organic substances is passed through a reaction vessel holding a carrier and biologically produced by anaerobic microorganisms grown on the carrier. In the anaerobic wastewater treatment method for treating water, the wastewater is discharged in a state where the carrier and a suspended solid containing methane bacteria aggregates so as to be 1 to 900 g per 1 L of the carrier are present in the reaction tank. In the first step of passing water, the amount of adhered cells containing methane bacteria to the carrier evaluated as the amount of VSS is 0.5 g or more per 1 L of the carrier, and the suspended solids containing the aggregates of the methane bacteria are per 1 L of the carrier. From a state of less than 5 g, a start-up operation having at least a second step of increasing the CODcr load of the wastewater passing through the reaction tank is performed.

According to this configuration, the time required for the start-up operation of the reaction tank can be significantly shortened.

In the first step of the above configuration, it is preferable that the CODcr volumetric load of the wastewater is 0.5 kg / m ³ / d or more and 5.0 kg / m ³ / d or less.

This makes it possible to efficiently attach the bacterial cells from the methane bacterial aggregates to the carrier.

In the above configuration, the average particle size of the methanogen aggregate is preferably 10 μm or more and 450 μm or less.

This makes it possible to efficiently attach the bacterial cells from the methane bacterial aggregates to the carrier.

In the above configuration, it is preferable that the methanogen aggregate is a methanogen granule or a crushed product of the methanogen granule.

Since methanogen granules have high activity, organic wastewater can be treated efficiently.

(Example 1)
According to the flow shown in FIG. 1, anaerobic wastewater treatment was carried out for actual wastewater (organic wastewater) of a chemical company. The specifications of the reaction tank and the initial treatment conditions are as follows.

・ Specifications of acid generation tank Acid generation tank capacity 4L, tank temperature: 35-37 ° C, pH: 7.5-7.7
-Reaction tank specifications Reaction tank capacity 5 L, tank temperature: 35-37 ° C, pH: 6.8-7.2
・ Specifications of treated water receiving tank Capacity of treated water receiving tank 1L, no agitation in the tank ・ Initial treatment conditions Raw water CODcr concentration: 3000mg / L
Initial flow rate 3.1 L / d
Amount of initial methanogen aggregate (average particle size 300 μm): 20 g
LV: 1.7m / hr

The reaction vessel was filled with an acetalized polyvinyl alcohol-based gel-like carrier (average particle size 4 mm, specific density 1.025, pore diameter near the surface 0.5 to 20 μm) in an amount of 40% by volume based on the tank volume. The flow of wastewater was started according to the above initial treatment conditions (start of the first process). During the start-up operation, suspended solids containing methanogen aggregates discharged from the reaction tank accumulated in the treated water receiving tank, and the suspended solids were removed from the tank. At the time when water flow was started, the amount of VSS of the carrier was 0 g per 1 L of the carrier, and the suspended solid containing the methanogen aggregate in the reaction tank was 10 g per 1 L of the carrier.

It was confirmed that the amount of VSS of the carrier was 0.6 g per 1 L of the carrier and the suspended solid containing the methanogen aggregate in the reaction tank was 3.2 g per 1 L of the carrier within 3 days after the start of drainage water flow. After confirming these values, the wastewater CODcr load was increased by gradually increasing the flow rate of the wastewater (start of the second step). The flow rate of wastewater was increased when the CODcr removal rate was 90% or more.

Within 40 days after the start of the second process, the CODcr volumetric load ^{could be increased to 13 kg / m 3} / d (second process completed, start-up operation completed). As described above, in Example 1, the start-up operation could be completed in 43 days. In addition, during the start-up operation, the CODcr removal rate always remained at 90% or more, which was very good. Subsequently, when steady operation was performed with the CODcr volumetric load of the wastewater kept ^{constant at 13 kg / m 3} / d, the wastewater could be treated without any problem even two months after the completion of the second step.

(Comparative Example 1)
In Comparative Example 1, the specifications of the reaction vessel and the initial treatment conditions were as follows. Comparative Example 1 is different from Example 1 in that the LV is reduced.

・ Specifications of acid generation tank Acid generation tank capacity 4L, tank temperature: 35-37 ° C, pH: 7.5-7.7
-Reaction tank specifications Reaction tank capacity 5 L, tank temperature: 35-37 ° C, pH: 6.8-7.2
・ Specifications of treated water receiving tank 1L of treated water receiving tank, no agitation in the tank ・ Initial treatment conditions Raw water CODcr concentration: 3000mg / L
Initial flow rate 3.1 L / d
Amount of initial methanogen aggregate (average particle size 300 μm): 20 g
LV: 0.5m / hr

The reaction tank was filled with the same carrier as in Example 1 in an amount of 40% by volume based on the tank capacity, and drainage was started to flow according to the above initial treatment conditions. After that, the drainage CODcr load was increased by gradually increasing the flow rate and LV of the drainage. During the start-up operation, most of the suspended solids remained in the reaction tank, and the suspended solids discharged from the reaction tank were hardly found in the treated water receiving tank. At the time when water flow was started, the amount of VSS of the carrier was 0 g per 1 L of the carrier, and the suspended solid containing the methanogen aggregate in the reaction tank was 10 g per 1 L of the carrier. Further, the amount of VSS of the carrier at the time when the flow rate of waste water and the LV were first increased was 1.3 g per 1 L of the carrier, and the suspended solids containing methane bacteria aggregates in the reaction tank was 7.5 g per 1 L of the carrier. there were.

The flow rate and LV were increased 20 days after the start of water flow, and the CODcr volumetric load was increased to 7 kg / m ³ / d. After setting the CODcr volumetric load to 7 kg / m ³ / d, the CODcr removal rate gradually decreased and fell below 80% on the 26th day after the start of water flow. At this time, the carrier VSS was 1.8 g per 1 L of the carrier, and the suspended solid containing the methanogen aggregate in the reaction tank was 6.3 g per 1 L of the carrier.

On the 26th day after the start of water flow, the CODcr volumetric load ^{was reduced to 5 kg / m 3} / d and the LV was raised to 1.7 m / hr. Since the suspended solids containing methane bacteria aggregates in the reaction vessel became 4 g per 1 L of the carrier within 10 days after changing the CODcr volume load and LV, the wastewater CODcr load was increased by gradually increasing the flow rate of the wastewater. ..

^{After that, the CODcr volumetric load could be increased to 13 kg / m 3} / day within 30 days after the drainage CODcr load was started (start-up operation completed). As described above, in Comparative Example 1, the start-up operation could be completed in 66 days. In addition, during the start-up operation, the CODcr removal rate always remained at 90% or more, and wastewater could be treated without any problem even after 2 months with very good treatability.

From the above, it can be seen that both Example 1 and Comparative Example 1 were able to perform efficient treatment after the reaction tank was started up. Further, in Example 1, the time required for the start-up operation of the reaction tank could be significantly shortened as compared with Comparative Example 1.

1 Organic wastewater 2 Acid generation tank 3 Reaction tank 4 Treated water receiving tank 5 Treated water return pipe 6 Treated water discharge

Claims (5)

In an anaerobic wastewater treatment method in which wastewater containing an organic substance is passed through a reaction vessel holding a carrier and biologically treated with anaerobic microorganisms grown on the carrier.
The first step of passing the wastewater through the reaction tank in a state where the carrier and a suspended solid containing methane bacteria aggregates so as to be 1 to 900 g per 1 L of the carrier are present.
When the amount of adhered cells containing methane bacteria to the carrier was evaluated by VSS, the amount of VSS was 0.5 g or more per 1 L of the carrier, and the suspended solids containing the agglomerates of the methane bacteria were less than 5 g per 1 L of the carrier. The second step of increasing the CODcr load of the wastewater passing through the reaction tank from the state of being
An anaerobic wastewater treatment method that has at least a start-up operation. The anaerobic wastewater treatment method according to claim 1, wherein in the first step, the CODcr volumetric load of the wastewater is 0.5 kg / m ³ / d or more and 5.0 kg / m ^{3 / d or less.} The anaerobic wastewater treatment method according to claim 1 or 2, wherein the average particle size of the methanogen aggregate is 10 μm or more and 450 μm or less. The anaerobic wastewater treatment method according to any one of claims 1 to 3, wherein the methanogen aggregate is a methanogen granule or a crushed product of the methanogen granule. The anaerobic wastewater treatment method according to any one of claims 1 to 4, wherein the carrier is a polyvinyl alcohol-based carrier.

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