JP5801769B2 - Method and apparatus for anaerobic digestion treatment of organic wastewater - Google Patents

Description

  The present invention relates to an organic anaerobic digestion treatment method and apparatus for treating organic wastewater containing a large amount of solids by anaerobic digestion, such as fermentation wastewater and food-based industrial wastewater.

Examples of organic wastewater treatment methods include aerobic biological treatment and anaerobic biological treatment.
Anaerobic biological treatment has less sludge generation than aerobic biological treatment and does not require an electricity bill such as a blower (aeration), so it can reduce running costs and can effectively use the generated methane gas. In recent years, it is a treatment that has become widespread in fields such as sewage treatment, human waste treatment, and industrial wastewater treatment.

  As such anaerobic treatment, floating type anaerobic digestion method that floats anaerobic bacteria, such as digestion tank method, UASB (upstream anaerobic sludge bed) method and anaerobic bacteria adhere There is known a fixed type anaerobic digestion method in which anaerobic bacteria are fixed in a reaction tank and fixed, such as a method in which a growing medium is filled.

Of these, the floating type anaerobic digestion method typically supplies organic wastewater to an anaerobic digestion tank (referred to as a “digestion tank”) and blows gas phase gas into the digestion tank or stirs with a machine. It is the processing method which performs biodegradation of organic substance in anaerobic state by stirring.
In general, high-molecular organic substances such as carbohydrates, proteins, and fats are hydrolyzed into volatile organic acids such as acetic acid, propionic acid, and butyric acid and lower alcohols in the digester by the action of acid-producing bacteria. In the process, the pH is lowered to 5 to 6 (acid fermentation period), then rises to about 6.8 (acid decline period), and then an intermediate product such as the organic acid by the action of the methanogen Is decomposed into final products such as methane, carbon dioxide, and ammonia, and the pH becomes about 7.0 to 7.4 (alkaline fermentation period).

  Such a floating anaerobic digestion method can treat organic wastewater containing a high concentration of SS, while the HRT (hydraulic water residence time) and SRT (sludge residence time) are the same. For this reason, in order to maintain the growth of the methanogen having a slow growth rate, a long residence time is required, the digester is enlarged, and the processing efficiency per volume is poor.

  On the other hand, fixed anaerobic digestion methods such as UASB can cause scum, granule sludge rising and flowing out, and the quality of the treated water when the water to be treated contains a lot of solids. Since problems such as deterioration occur, it is unsuitable for the treatment of organic wastewater containing high concentrations of SS, but because it can maintain the concentration of methanogens regardless of HRT, it is short with a relatively small device. There is a merit that it is possible to process efficiently with the residence time.

  Thus, since the floating type anaerobic digestion method and the fixed type anaerobic digestion method have advantages and disadvantages, a method for treating organic wastewater by combining them has been proposed.

  For example, in Patent Document 1, wastewater containing organic solids is separated into solid and liquid in a first solid-liquid separation device, and separated into high SS wastewater having a high solid content concentration and low SS wastewater containing soluble organic matter. The high SS wastewater is anaerobically digested in an anaerobic digester, a part of the digested liquid is solid-liquid separated by a second solid-liquid separator, and the resulting separated sludge is returned to the anaerobic digester. A method of treating the low SS wastewater with a high load anaerobic treatment device (UASB) has been proposed.

  Patent Document 2 proposes a method in which organic sludge is subjected to an acid fermentation treatment, followed by solid-liquid separation, and the separated sludge and separated water obtained by the solid-liquid separation are treated with a digester and UASB, respectively. Yes.

JP 7-39897 A JP 2002-361293 A

The present inventor conducted the following experiment on a method for treating organic wastewater by combining a floating anaerobic digestion method and a fixed anaerobic digestion method.
In accordance with the flow of FIG. 1, a high concentration organic wastewater (raw water) 1 is used as a test wastewater, and the solid-liquid separator 2 has a low solids concentration 3 containing a soluble organic substance and a low solids concentration 3 Separated into SS wastewater 10, low SS wastewater 3 is treated with UASB (anaerobic digester) 4, high SS wastewater 10 is treated with digestion tank (anaerobic digester) 13, and UASB (anaerobic digester) 4 effluent water 6 was sequentially treated by an ultrafiltration membrane device (SS removing device) 7 and a reverse osmosis membrane device (membrane separation device) 9.

  By such treatment, it was possible to obtain reusable water quality in the initial stage. However, in the digester tank 13 for treating high SS wastewater, the pH tends to decrease, the decomposition rate of organic matter decreases, and the BOD concentration of the effluent 6 cannot be sufficiently reduced. This is because the SS concentration of the water to be treated in the digestion tank 13 is high, and as a result, the volume load of the organic matter is increased. As a result, the organic acid production rate becomes higher than the methane conversion rate, and the pH is lowered during the reaction. This is probably because

  In order to solve such problems, it is conceivable to add a pH adjuster to the digester, but adjusting the pH by adding a pH adjuster to the digester that treats high SS wastewater is a cost and efficiency aspect. This is not a realistic method.

  Accordingly, an object of the present invention is to efficiently treat with a high organic load and stably for a long period of time by stabilizing the pH in a floating anaerobic digestion process for treating high SS wastewater with a high solid content concentration. It is intended to provide a new anaerobic treatment method and apparatus capable of performing the above.

The present invention relates to a solid-liquid separation process for separating organic wastewater containing solids into low SS wastewater having a low solid content concentration and high SS wastewater having a high solid content concentration, and anaerobic method of immobilizing anaerobic bacteria. An anaerobic digestion process A for anaerobically digesting the low SS wastewater by sexual digestion, and an anaerobic digestion process B for anaerobically digesting the high SS wastewater by an anaerobic digestion method of floating anaerobic bacteria. , A membrane separation step of separating the effluent from the anaerobic digestion step A into permeated water and salt concentrated water by a reverse osmosis membrane , and all or part of the salt concentrated water obtained in the membrane separation step The present invention proposes an anaerobic digestion treatment method for organic wastewater, comprising: a salt concentrate supply process for supplying anaerobic digestion process B.

The present invention also connects a solid-liquid separation device that separates organic wastewater containing solids into low SS wastewater having a low solid content concentration and high SS wastewater having a high solid content concentration, and a supply pipe for the low SS wastewater. An anaerobic digester A of a method for immobilizing anaerobic bacteria, an anaerobic digester B of a system for connecting the high SS drainage supply pipe and floating the anaerobic bacteria, and the anaerobic digester A Separation Concentration for Supplying All or Part of Salt Concentrated Water Obtained by Membrane Separator with Reverse Osmosis Membrane and the Membrane Separator to the Anaerobic Digestor B An organic anaerobic digester with a water supply pipe is proposed.

According to the method and apparatus for anaerobic digestion of organic wastewater proposed by the present invention, organic wastewater containing solids is separated into low SS wastewater and high SS wastewater in a solid-liquid separation process, and low SS wastewater is obtained. As for, while anaerobic digestion process A with a method of immobilizing anaerobic bacteria, a large amount of water can be efficiently processed at a high load, while for high SS wastewater, anaerobic with a method of floating anaerobic bacteria. It can process reliably by the sex digestion process B.
Moreover, the salt concentration water contains the component which raises an alkalinity by supplying the salt concentration water obtained by carrying out the membrane separation of the effluent of the anaerobic digestion step A to the anaerobic processing step B. Therefore, pH in the anaerobic digestion process B which processes high SS wastewater can be stabilized, and methane fermentation of the anaerobic process B can be promoted.
Thus, according to the anaerobic digestion treatment method and treatment apparatus for organic wastewater proposed by the present invention, organic wastewater with a high solid content concentration is efficiently treated with a high load of organic matter and stably for a long period of time. be able to.

It is the figure which showed the flow as a comparative example of the anaerobic digestion processing method of the organic waste_water | drain of this invention, and a processing apparatus. It is the figure which showed the flow as an example of the anaerobic digestion processing method and processing apparatus of the organic waste_water | drain of this invention.

  Next, an example of an embodiment for carrying out the present invention will be described.

<This processing method>
As shown in FIG. 2, the organic wastewater anaerobic digestion treatment method (referred to as “the present treatment method”) according to the present embodiment converts an organic wastewater (raw water) 1 containing solids into a solid-liquid separation device 2. Is separated into a low SS wastewater 3 having a low solid content concentration and a high SS wastewater 10 having a high solid content concentration (“solid-liquid separation process”), while supplying the high SS wastewater 10 to the anaerobic digester 13, as required Accordingly, after adding the chemical 16 for increasing the alkalinity to the low SS wastewater 3, the low SS wastewater 3 is supplied to the anaerobic digester 4, and the anaerobic bacteria are immobilized in the anaerobic digester 4. The anaerobic digestion method is used to recover the biogas 5 and obtain the effluent 6 as a digestion liquid (“anaerobic digestion step A”), and remove the SS as necessary from the effluent 6 Is supplied to the apparatus 7, and the SS removal apparatus 7 fixes the effluent water 6 Minute (SS) is removed to obtain SS-removed water 8 and SS-concentrated water 11, SS-removed water 8 is supplied to the membrane separation device 9. 12 (“membrane separation step”), the SS concentrated water 11 and the salt concentrated water 12 obtained in the membrane separation step are supplied to the anaerobic digester 13 through the salt concentrated water supply pipe (“the salt concentrated water”). In the anaerobic digester 13, the high SS wastewater 10 together with the SS concentrated water 11 and the salt concentrated water 12 is subjected to anaerobic digestion by an anaerobic digestion method in which anaerobic bacteria are suspended. And effluent 14 as digestive fluid is obtained (“anaerobic digestion step B”).

<Raw water>
The organic waste water (raw water) 1 containing solids, which is the water to be treated in this treatment method, is an organic waste water containing organic solids or inorganic solids. Examples of such organic wastewater include slurry-like organic wastewater containing a high concentration of organic solids such as fermentation wastewater, food-based industrial wastewater, and livestock manure.

  The solid matter concentration of the organic waste water (raw water) 1, that is, the SS concentration is preferably higher than 5000 mg / L, more preferably 7500 mg / L or more, and particularly preferably 10,000 mg / L or more. When the organic wastewater (raw water) 1 has an SS concentration higher than 5000 mg / L, it cannot be treated by an anaerobic digestion method of immobilizing anaerobic bacteria such as UASB. Can be enjoyed even more.

<Solid-liquid separation process>
In this step, the organic waste water (raw water) 1 containing the solid content is solid-liquid separated by the solid-liquid separation device 2, and the low SS waste water 3 having a low solid content concentration and the high SS waste water 10 having a high solid content concentration, To separate.

  Here, the low SS wastewater 3 having a low solid content concentration preferably has an SS concentration of less than 5000 mg / L, more preferably 2000 mg / L or less, and particularly preferably 1000 mg / L or less.

  Examples of solid-liquid separation methods that can be employed in this step include known solid-liquid separation methods such as sedimentation separation, clarification filtration, flotation separation, filtration separation, membrane separation, and centrifugal separation. A plurality of solid-liquid separation methods can also be implemented in combination.

<Anaerobic digestion process A>
In the anaerobic digestion step A, the low SS wastewater 3 separated in the solid-liquid separation step is anaerobic digestion apparatus 4 in which anaerobic bacteria are immobilized (an “immobilized anaerobic digestion”). The anaerobic digestion is also carried out by the “method” to collect the biogas 5 and to obtain the effluent 6 as a digested liquid.

  The anaerobic digestion method of immobilizing anaerobic bacteria is an anaerobic digestion method of retaining anaerobic bacteria in a reaction tank by some method. For example, a method using a self-immobilization (self-granulation) phenomenon of a methanogen such as the UASB method (also called “self-granulating anaerobic methane fermentation method”), honeycomb type plastic, granular Examples include an anaerobic fluidized bed method and an anaerobic fixed bed method using a microorganism-adhering carrier such as ceramic, granular activated carbon, and granular zeolite (these are collectively referred to as “adherent type anaerobic methane fermentation method”).

Among them, the typical UASB method (upward-flow anaerobic sludge bed method) uses highly agglutinating action of anaerobic microorganisms to granulate highly active cells (granular sludge with a diameter of 2 to 3 mm, filamentous acetic acid). It is a method of maintaining a large amount in the reaction tank as a dense floc centered on assimilable methanogens), and injecting waste water (treated water) from the bottom of the reaction tank to remove organic matter in the anaerobic state. It is a method of decomposing.
The upflow anaerobic sludge filter bed method (UASB) uses the self-granulating function of anaerobic microorganisms to maintain highly settled granular sludge in the tank at a high concentration, thus increasing the CODcr load. Can do. Moreover, compared to ordinary anaerobic treatment, it can be applied to wastewater with a relatively low concentration, and high-speed treatment is possible and aeration is not required. Can be generated.

  The anaerobic digester A includes, for example, a gas-solid-liquid separator (GSS) inside the methane fermentation tank, and discharges the hydrated water supply pipe, the methane fermentation treated sludge discharge pipe for transferring sludge, and the methane fermentation treated water. The methane fermentation treated water discharge pipe and the generated gas discharge pipe are preferably connected.

  The treatment temperature of the immobilized anaerobic digestion method is preferably set to a temperature suitable for the type of anaerobic bacteria. Therefore, in the case of a medium temperature methane fermentation treatment bacterium, it is preferable to adjust the temperature so that 35 to 38 ° C. becomes an optimum temperature, and in the case of a high temperature methane fermentation treatment bacterium, 50 to 55 ° C. is optimum. It is preferable to adjust the temperature so as to be the temperature.

In the case where the pH of the water to be treated in the anaerobic digestion step A is lower than 6.1, the agent 16 for increasing the alkalinity is added to the low SS wastewater that is the water to be treated in the anaerobic digestion step A, It is preferable to adjust the pH of the water to be treated to 6.5 to 7.8. By maintaining such a pH range, the reaction can be promoted without delay.
In this case, examples of the agent 16 to be added include alkaline agents such as sodium hydroxide and sodium hydrogen carbonate.

<Membrane separation process>
In the membrane separation step, the effluent 6 of the anaerobic digestion step A may be separated into the permeated water 17 and the salt concentrated water 12 by membrane separation using a membrane capable of concentrating salts in the membrane separation device 9. .
However, as shown in FIG. 2, it is still more preferable to remove the solid content (SS) from the effluent 6 in the SS remover 7 and treat the obtained SS removed water 8 in the membrane separator 9. preferable.

  The salt-enriched water 12 obtained in the membrane separation step contains organic and inorganic substances that have not been decomposed in the anaerobic digestion step A, and the alkalinity is increased, for example, sodium carbonate or ammonia salt. Ingredients that can be included. Moreover, as above-mentioned, when the chemical | medical agent 16 which increases alkalinity is added to the low SS waste_water | drain 3 which is the to-be-processed water of the anaerobic digestion process A, this chemical | medical component will also be contained. Therefore, the salt concentrated water 12 has the effect | action which raises alkalinity.

As a membrane separation using a membrane capable of concentrating salts, a reverse osmosis (RO) membrane can be given as a representative example, and other examples include NF (nanomembrane) and electrodialysis.
However, it is possible to use a membrane that cannot concentrate salts, such as a UF membrane, for SS separation before the membrane separation using a membrane that can concentrate salts.

  When the membrane is separated after removing the SS component, the SS component is removed by a method such as coagulation sedimentation, MF (microfiltration membrane) or UF (ultrafiltration membrane), and then the separated water from which SS has been removed. Is preferably separated using a membrane having a high ability to separate salts such as RO (reverse osmosis membrane) and NF (nanomembrane), and the alkalinity dissolved in the separated water is recovered and concentrated.

  On the other hand, the permeated water 17 desalted by solid-liquid separation can be used as process water in a treatment facility or a factory. When the concentration of the volatile alkalinity component is low, a known concentration method such as an evaporation method or a reduced pressure evaporation concentration method can be employed corresponding to the alkalinity component.

<Salt concentrate supply process>
In the salt concentrate supply process, the salt concentrate 12 to SS concentrate 11 obtained in the membrane separation process are supplied to the anaerobic digester 13 through the salt concentrate supply pipe.
At this time, all of the salt concentrate 12 to SS concentrate 11 may be supplied to the anaerobic digester 13, or a part of the salt concentrate 12 to SS concentrate 11 is supplied to the anaerobic digester 13. You may make it do.
Moreover, you may make it supply the salt concentration water 12 thru | or SS concentration water 11 directly to the anaerobic digester 13, or mix this after mixing the salt concentration water 12 thru | or SS concentration water 11 with the said high SS waste_water | drain 10. The liquid may be supplied to the anaerobic digester 13.

<Anaerobic digestion process B>
In the anaerobic digestion process B, the anaerobic digestion method of floating anaerobic bacteria in the anaerobic digester 13 together with the salt concentrated water 12 to the SS concentrated water 11 supplied from the membrane separation process. To obtain an effluent water 14 as a digestive liquid.

At this time, the sludge concentration in the reaction tank (referred to as “anaerobic digestion tank”) of the anaerobic digestion process B is adjusted by adjusting the amount of the salt concentrate 12 to the SS concentrate 11 supplied from the membrane separation process. Is preferably adjusted so that the SS concentration is 4% or less, particularly about 2-3%.
When the sludge concentration in the anaerobic digestion tank is high, it becomes difficult to sufficiently stir and the progress of the digestion reaction is hindered. Therefore, it is particularly preferable that the sludge concentration in the anaerobic digester is 2% to 3% as the SS concentration. For example, when the SS decomposition rate of the high SS separated water SS is 75%, the reaction tank SS becomes 2.5% when the separated water SS is adjusted to 10%.

  An anaerobic digestion method (apparatus) of a system in which anaerobic bacteria are suspended is typically an anaerobic digestion method (apparatus) using a digestion tank.

  Of these, the floating type anaerobic digestion method typically supplies organic wastewater to an anaerobic digestion tank (referred to as a “digestion tank”) and blows gas phase gas into the digestion tank or stirs with a machine. In this method, the organic substance is biodegraded in an anaerobic state.

  As an anaerobic digester 13, the apparatus of the structure which consists of a digester tank which is a methane fermentation tank and a sludge collection tank (for example, sedimentation pond) can be illustrated, for example, The excess sludge collect | recovered by the sludge collection tank is used as a digester tank. The structure which returns may be sufficient.

In the digestion tank, the organic substances are usually hydrolyzed into organic acids such as acetic acid and formic acid and lower alcohols by the action of acid-producing bacteria, and the pH is lowered to 5-6 (acid fermentation period), and then the pH. Rises to about 6.8 (acid decline period), and then intermediate products such as organic acids are decomposed into final products such as methane, carbon dioxide, and ammonia by the action of the methanogen, and the pH is 7.0. ˜7.4 (alkaline fermentation period).
At this time, if the SS concentration of the water to be treated is high, the volume load of the organic matter becomes high, and the organic acid production rate becomes higher than the methane conversion rate, so that the pH may be lowered. As described later, by supplying salt concentrated water obtained by membrane separation of the effluent from the anaerobic digestion step A to the anaerobic treatment step B, it is possible to suppress a decrease in pH in the anaerobic digestion step B. It is possible to maintain the organic matter decomposition rate and sufficiently reduce the BOD concentration of the effluent water.

  The treatment temperature of the floating anaerobic digestion method is preferably set to a temperature suitable for the type of anaerobic bacteria. Therefore, in the case of a medium temperature methane fermentation treatment bacterium, it is preferable to adjust the temperature so that 30 to 35 ° C. is the optimum temperature, and in the case of a high temperature methane fermentation treatment bacterium, 50 to 55 ° C. is optimum. It is preferable to adjust the temperature so as to be the temperature.

The effluent 14 of the anaerobic digestion process B, that is, the digested liquid, is supplied to, for example, the aerobic biological treatment apparatus 15, and remains BOD and COD remaining after biological aerobic treatment such as activated sludge treatment method and oxidation pond method. Etc. can be processed. However, it can also be used directly as liquid fertilizer.
Alternatively, the effluent 14 from the anaerobic digestion step B may be subjected to solid-liquid separation, and the separated water may be subjected to aerobic treatment as described above. In this way, undigested SS can be removed by solid-liquid separation, so that the pollution load in the aerobic treatment can be reduced.
In addition, the solid content separated at this time can be used for agriculture if fermented and composted.
Moreover, the biogas 5 generated in the anaerobic digestion step B can be recovered and used.

<Explanation of words>
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), unless otherwise specified, “X is preferably greater than X” or “preferably Y”. It also includes the meaning of “smaller”.
In addition, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably greater than X” or “preferably less than Y”. Includes intentions.

  Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the embodiments described here.

(Example 1)
This example was implemented according to the flow of FIG.

The raw water used was an organic distillation wastewater 1 containing solid content diluted with alcohol distillation waste liquid (CODCr 84000 mg / L, BOD 42000 mg / L) twice.
This raw water is separated into a low SS drainage 3 and a high SS drainage 10 by a centrifuge (solid-liquid separation device 2), and one of the low SS drainages 3 is supplied with sodium bicarbonate (drug 16) for replenishment of alkalinity. After adding and dissolving, it introduce | transduced into UASB (anaerobic digester 4) and performed the methane fermentation process by the fixed type anaerobic digestion method. The other high SS drainage 10 was introduced into a digester (anaerobic digester 13) equipped with a mechanical stirrer, and subjected to a methane fermentation treatment by a floating anaerobic digestion method.

The UASB effluent (effluent 6) is separated into UF membrane concentrated water (SS concentrated water 11) and separated water (SS removed water 8) by the UF membrane device (SS remover 7), and then the separated water (SS removed water). 8) was introduced into the RO membrane device (membrane separation device 9) and separated into RO permeated water 17 and RO concentrated water (salt concentrated water 12).
UF membrane concentrated water (SS concentrated water 11) and RO concentrated water (salt concentrated water 12) are mixed with the high SS drainage 10 and introduced into the digestion tank (anaerobic digester 13) together with the high SS drainage 10, Methane fermentation treatment by floating anaerobic digestion was performed.
The methane fermentation tank effluent 14 was subjected to an aerobic treatment by an MBR (membrane bioreactor) which is an aerobic biological treatment device 15.

The specifications of the implementation apparatus are shown in Table 1, and the implementation conditions are shown in Table 2.
In addition, after 50 days have passed since the start of the implementation, each water quality is shown in Table 3 and each water amount is shown in Table 4 as a result (average value) of continuous measurement and analysis for 10 days.

(Example 2)
In this embodiment, in the flow of FIG. 2, the effluent 6 is directly introduced into the membrane separation device 9 without going through the SS removal device 7, and the salt concentrate 12 in which SS and salts are mixed in the membrane separation device 9. And permeated water 17 (not shown). The salt-enriched water 12 was introduced into the anaerobic digester 13 together with the high SS drainage 10 as in Example 1 (not shown).
As a result, although the membrane cleaning frequency of the membrane separation device 9 increased, the permeated water quality and MBR treated water quality similar to those in Example 1 could be obtained without adding an alkaline agent to the anaerobic digester 13.

(Results and discussion)
By concentrating the alkalinity component flowing out from UASB and introducing it into the methane fermentation tank as in the examples, the following effects that could not be achieved in the past could be obtained. That is, since the alkalinity used for the smooth reaction of UASB could be introduced into the digestion tank, the reaction was smoothed in the methane fermentation tank. Furthermore, by concentrating the amount of UASB reactor effluent, the amount of inflow into the methane fermentation tank could be reduced, so the HRT (hydraulic residence time) of the digester could be lengthened, making it more stable. Methane fermentation has become possible.

Furthermore, it has been found that efficient and stable wastewater treatment can be performed by the following effects. That is, by introducing the concentrated water of the membrane separation step into the digestion tank, it becomes easy to discharge the concentrated water, so that the membrane can be prevented from being clogged due to excessive concentration, and a stable permeation flux ( Flux) could be maintained.
Since the total outflow amount of the UASB and the digester was able to be reduced in the amount of permeated demineralized water, the water load in the final aerobic treatment process could be reduced.
By supplementing methane bacteria flowing out from UASB and introducing them into the methane fermentation tank together with concentrated water, it was possible to replenish methane bacteria in addition to the alkalinity in the digestion tank.
By using the RO membrane for alkalinity concentration and separation, demineralized water that can be used as process water could be obtained.

1 Organic wastewater (raw water)
2 Solid-liquid separator 3 Low SS drainage 4 Anaerobic digester (immobilization method)
5 Biogas 6 Outflow water 7 SS removal device 8 SS removal water 9 Membrane separation device 10 High SS drainage 11 SS concentrated water 12 Salt concentrated water 13 Anaerobic digester (floating method)
14 Outflow water 15 Aerobic biological treatment device 16 Drug 17 Permeated water

Claims (3)

Solid-liquid separation process that separates organic wastewater containing solids into low SS wastewater with low solids content and high SS wastewater with high solids content, and anaerobic digestion method that immobilizes anaerobic bacteria The anaerobic digestion process A for anaerobically digesting the low SS wastewater, the anaerobic digestion process B for anaerobically digesting the high SS wastewater by an anaerobic digestion method of floating anaerobic bacteria, and the anaerobic A membrane separation step for separating the effluent from the digestion step A into a permeated water and a salt-concentrated water using a reverse osmosis membrane , and an anaerobic digestion step for all or part of the salt-concentrated water obtained in the membrane separation step An anaerobic digestion method for organic wastewater, comprising: a salt-concentrated water supply step for supplying to B. The method for anaerobic digestion of organic wastewater according to claim 1, wherein a chemical that increases alkalinity is added to the low SS wastewater that is treated water in the anaerobic digestion step A. A solid-liquid separator that separates organic wastewater containing solids into low SS wastewater with low solids content and high SS wastewater with high solids content, and a supply pipe for the low SS wastewater are connected, and anaerobic bacteria The anaerobic digester A of the type that immobilizes the water, the supply pipe for the high SS drainage, and the anaerobic digester B of the type that floats anaerobic bacteria, and the effluent water from the anaerobic digester A A membrane separator having a reverse osmosis membrane to which a supply pipe is connected; a salt concentrate supply pipe for supplying all or part of the salt concentrate obtained by the membrane separator to the anaerobic digester B; An anaerobic digester for organic wastewater.

Images