JP2002086196A - Waste water treating method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process step and device which improve a digesting efficiency, reduce the volume of organic solids and improve the recovery rate of gaseous methane and does not substantially discharge excess sludge in a treating system which has the process steps of treating medium-SS concentration organic waste water in night soil, etc., and high-SS concentration organic waste water in garbage, etc., in combination. SOLUTION: In the treating system which has the process steps of treating the medium-SS concentration organic waste water in the night soil, etc., and the high-SS concentration organic waste water in the garbage, etc., in combination, the medium-SS concentration organic waste water in the night soil, etc., is subjected to biological treatment and thereafter the excess sludge in the sludge subjected to the separation of the solid from the treating liquid is subjected to methane fermentation treatment in a methane fermentation process step. On the other hand, the high-SS concentration organic waste water in the garbage, etc., is subjected to solubilizing treatment and is then subjected to the methane fermentation treatment together with the excess sludge in the methane fermentation process step described above and the dewatered methane fermentation sludge obtained by further concentrating the sludge formed by subjecting the methane fermentation treated liquid to the separation of the solid from the liquid is again subjected to the solubilizing treatment in the solubilizing process step and is then returned to the methane fermentation process step.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for complexly treating various kinds of organic waste.

[0002]

2. Description of the Related Art Conventionally, wastes containing a large amount of organic solids such as human waste, livestock wastewater, kitchen waste, food processing wastewater, and the like, are solubilized by methane fermentation, and at the same time, organic matter is converted to methane and recovered. The method is generally performed. However, the conventional single method generally does not necessarily correspond to the type of waste containing various organic solids, but improves digestibility, reduces sludge volume, and improves methane gas recovery rate. Many innovations are needed for improvement.

[0003] For example, in the anaerobic treatment step, the sludge returned in the anaerobic treatment step is solubilized or further subjected to ozone treatment and then returned to the anaerobic treatment step for the improvement. There are problems in that the processing capacity of the solubilization treatment and the ozone treatment is large and the cost is problematic, and the efficiency of the solubilization treatment and the ozone treatment is low.

[0004] Further, the reaction time of methane fermentation in the methane fermentation treatment step is long, and a large-capacity treatment tank is required to give a required residence time.

[0005] Also, due to the variety of wastewater, the organic SS concentration, the hardly decomposable organic solids, the ratio of easily decomposable organic solids, and the like are various, and a system that can flexibly cope with them has been required. .

[0006]

DISCLOSURE OF THE INVENTION The present invention relates to SS in human waste and the like.
This is a treatment system that combines the process of treating high-concentration organic wastewater and high SS-concentration organic wastewater such as kitchen waste, such as organic SS concentration, hardly decomposable organic solids, and easily decomposable organic solids ratio. The waste is sludge-treated based on wastewater, and a new and improved method of returning excess sludge is used to improve the digestibility, reduce the volume of organic solids, and improve the methane gas recovery rate, etc., resulting in substantial surplus. The purpose is to provide a process and a device that do not discharge sludge.

Another object of the present invention is to improve the processing speed of the methane fermentation treatment, which is the methane fermentation treatment step of the treatment system.

SUMMARY OF THE INVENTION The present invention relates to a treatment system having a process for treating an organic wastewater having an SS concentration in human waste and the like and an organic wastewater having a high SS concentration in kitchen waste and the like.
S-concentration organic wastewater is subjected to biological treatment and then excess sludge from solid-liquid separated sludge is subjected to methane fermentation in the methane fermentation process, while high SS concentration organic wastewater such as kitchen waste is solubilized. Then, methane fermentation treatment is performed together with the surplus sludge in the methane fermentation step, and the sludge obtained by solid-liquid separation of the methane fermentation treatment liquid is further concentrated to obtain a dehydrated methane fermentation sludge that can be reused in the solubilization step. After solubilization, it is returned to the methane fermentation step.

Here, the inflow wastewater is, for example, S
For the S concentration organic wastewater and the high SS concentration organic wastewater such as kitchen garbage, the former performs biological treatment once and separates the treatment liquid into solid and liquid, and the solid-liquid separated biologically treated sludge is about 1 to 2%. Since the concentration is relatively low, a part of the sludge is directly transferred to the anaerobic treatment. The latter is subjected to solubilization before the anaerobic treatment to reduce the volume of organic solids, so that the anaerobic treatment proceeds efficiently.

[0009] Thus, the biologically treated sludge and the solubilized solution are combined and subjected to methane fermentation in the methane fermentation process. The methane fermentation treated sludge after solid-liquid separation is further concentrated to a solid content of 8 to 10%. % (Dehydrated methane fermented sludge), and substantially the entire amount is returned to the solubilization treatment step, and solubilized together with high SS concentration organic wastewater such as kitchen garbage.
Thus, the liquid to be treated flowing into the methane fermentation step has a high concentration of solubilized organic substances, and the efficiency of the methane fermentation treatment is improved.

In the solubilization treatment, the liquid to be treated is kept under heating. Although the temperature conditions are relatively flexible, the preferred temperature range is 60 to 80 ° C. in consideration of the effectiveness of the heating energy, the solubilization reaction rate, and the effect on the next stage.

An apparatus for performing the above method of the present invention is a processing apparatus for biologically treating the organic wastewater having an SS concentration in human waste, a solid-liquid separator for solid-liquid separation of the processing liquid, and a solid-liquid separation of the processing liquid. At least one methane fermentation treatment tank for performing methane fermentation treatment on the excess sludge of the sludge, a solid-liquid separator for solid-liquid separation of the treatment liquid subjected to methane fermentation treatment in the treatment tank, and high S
A solubilization tank for solubilizing the S-concentration organic wastewater; merging the solubilized liquid with the excess sludge in the methane fermentation tank to perform methane fermentation; and solid-liquid separation of the combined methane fermentation liquid Solid-liquid separator, a concentrator for further concentrating the in-return of the solid-liquid separated sludge into dehydrated methane fermented sludge, and a solubilization tank for dissolving the dehydrated methane fermented sludge with the high SS concentration organic wastewater such as the kitchen waste. A transfer means including a transfer pipe for returning to the methane fermentation treatment tank after solubilization after merging, and a transfer pipe for transferring a processing liquid or a liquid to be processed so that each device and equipment function as described above. The wastewater treatment apparatus is characterized by comprising transfer means including:

The methane fermentation treatment tank referred to here is an existing methane fermentation tank and has an auxiliary device or the like for increasing the temperature by heating. In addition, a gas outlet for guiding methane gas generated from the inside of the tank to the outside of the tank and transferring it to a gas holder, an inlet for a liquid to be treated, an outlet for a processing liquid, and the like are provided. The solubilization tank is also provided with a heater for keeping the contents at a high temperature, and in some cases, a stirrer. The solid-liquid separator is a separator that can obtain low-sludge concentration sludge by natural sedimentation using gravity and particle specific gravity such as sedimentation separation, and the concentrator can perform forced separation such as a centrifugal separator and a filter. This is a device that can obtain high sludge concentration sludge.

A further feature of the present invention resides in that substantially all of the sludge obtained by solid-liquid separation of the treatment liquid in the methane fermentation step is concentrated and returned to the solubilization treatment step. In other words, if combined processing according to the present invention,
Practically no surplus sludge is discharged, but only water-soluble treated water and methane gas are discharged.

In the method of the present invention, the methane fermentation step may further comprise a completely mixed type tank, etc.
A methane fermentation step of treating water to be treated containing S, or a fixed-bed treatment tank or an upward-flow bed treatment tank (UASB)
It is a methane fermentation step for treating water to be treated containing a relatively low concentration of organic SS, and the like.

The apparatus according to the present invention also includes a methane fermentation tank for treating water to be treated containing a relatively high concentration of organic SS, such as a complete mixing type tank, or a fixed bed type treatment tank. It is a methane fermentation tank for treating water to be treated containing relatively low concentration of organic SS, such as a tank or an upward flow bed treatment tank.

That is, according to the present invention, the most efficient type of methane fermentation tank can be selected according to the SS concentration of the processing liquid flowing into the methane fermentation tank. When the SS of the liquid to be treated flowing into the methane fermentation tank has a high concentration, a completely mixed type treatment tank is suitable. Due to the high concentration of SS, fluidity is difficult in the tank where a large amount of stagnant, and it comes into uniform contact with methane bacteria by stirring, and by forced mass transfer by stirring,
It is possible to improve the reaction efficiency. However, in this case, the sludge carrying methane bacteria stays and flows out for the same time as the contents of the treatment tank, so the methane bacteria concentration in the tank can only be increased to a limited concentration, and The processing speed in the tank capacity is low (conventional average residence time 15-3
0 days), so to increase the speed, the capacity of the momentum tank must be large.

When the SS of the liquid to be treated flowing into the methane fermentation tank has a low concentration, a methane fermentation tank such as a fixed bed treatment tank or an upward flow bed treatment tank may be selected. The liquid to be treated having a low concentration of SS can uniformly contact sludge carrying methane bacteria without forcible stirring, and a high concentration of SS can be used in a fixed-bed treatment tank or an upward-flow bed treatment tank. In the case of the above, the clogging is likely to occur due to the SS due to the structural characteristics of the processing tank, but there is no such a problem with the liquid to be processed having the low concentration SS.

[0018] In addition, as is well known, in a fixed-bed treatment tank or an upward-flow bed treatment tank, sludge carrying methane bacteria is attached and held in a suitable single unit in the former case, and the sludge is held in a tank. In the latter case, only sludge flows and circulates in the tank, and methane bacteria do not flow out of the tank. The treatment rate is high because the methane bacterium concentration can be kept high (conventional average residence time is 4 to 8 hours).

In the method of the present invention, the methane fermentation treatment of the treated water after the solubilization treatment may further comprise the step of:
The first methane fermentation step of treating the water to be treated containing S and the second methane fermentation step of treating the water to be treated containing a relatively low concentration of organic SS are sequentially and continuously performed, After the biological treatment of the organic wastewater with the same SS concentration, the methane fermentation treatment of the excess sludge in the sludge obtained by solid-liquid separation of the treated liquid is carried out in the second step.
The methane fermentation step is performed in combination with the methane fermentation treatment of the treated water after the solubilization treatment.

The apparatus of the present invention also includes a treatment apparatus for performing methane fermentation treatment of the treated water after the solubilization treatment, and a first methane treatment for treating water to be treated containing a relatively high concentration of organic SS. A fermenter and a second methane fermenter for treating treated water containing a relatively low concentration of organic SS are sequentially connected and configured, and the SS concentration organic wastewater in the human waste, etc., after biological treatment, The methane fermentation treatment of the excess sludge of the sludge obtained by solid-liquid separation of the treatment liquid is performed in the second methane fermentation tank in combination with the methane fermentation treatment of the treated water after the solubilization treatment. And

As described above, a completely stirred methane fermentation tank is suitable for the methane fermentation treatment of the high-concentration SS organic wastewater, and the fixed-bed methane fermentation tank or the methane fermentation treatment of the low-concentration organic wastewater is suitable for the methane fermentation treatment. An upward-flow methane fermenter was considered suitable, but in the case of high-concentration SS organic wastewater, it was treated with a complete agitation type in the first stage to reduce the SS concentration, and then a fixed-bed methane fermenter in the second stage. Alternatively, if the treatment is performed in an upward-flow methane fermentation tank, the above-mentioned disadvantages of a single methane fermentation tank can be overcome, and the treatment can be performed smoothly and at a high speed.

Therefore, the present invention is characterized in that the first methane fermentation tank is a completely mixed type tank, and the second methane fermentation tank is a fixed bed treatment tank or an upward flow bed treatment tank. .

Further, the present invention is characterized in that the dehydrated methane fermented sludge is subjected to ozone treatment before the solubilization treatment. Similarly, in the apparatus of the present invention, an ozonation tank is arranged before the solubilization treatment of the dehydrated methane fermentation sludge so that ozone treatment can be performed. This chemically oxidizes and decomposes hard-to-decompose organic matter in the dehydrated methane fermentation sludge, enabling the subsequent solubilization treatment to a higher level, thereby contributing to the reduction of returned sludge in the methane fermentation treatment. This leads to an improvement in the overall system capacity.

The ozone treatment tank disposed here is not particularly limited, but a blowing pipe capable of dispersing ozone or an ozone air mixed gas generated by means such as high pressure discharge as uniform bubbles in a liquid layer in the tank. And a stirrer.

[0025]

Embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not merely intended to limit the scope of the present invention, but are merely illustrative examples unless otherwise specified. .

FIG. 1 is a schematic view showing an example of the apparatus and process of the present invention. 1 is a biological treatment tank, 2 is a solid-liquid separator, 4 is a solubilization tank, 5 is a methane fermentation tank, and 6 is solid-liquid separation. 7 is a concentrator, 8 is a transfer pipe, 9 is a return pipe, 11 is human waste, etc.
2 is kitchen waste, 13 is biologically treated sludge, 14 is returned biologically treated sludge, 15 is treated water, 16 is another treated water, and 17 is returned concentrated methane fermented sludge.

The medium SS-concentration organic wastewater 11 such as human waste flows into the biological treatment tank 1 through the transfer pipe 8 and is subjected to biological treatment.
Here, the biologically treated effluent treatment liquid is transferred to the solid-liquid separator 2 by the transfer pipe 8, where it is separated into the sedimented and separated biological treatment sludge 13 and a supernatant liquid, ie, treated water 15. The biological treatment sludge 13 is partially returned to the inflow side of the biological treatment tank 1 by the return pipe 9 as the biological treatment sludge 14. The amount of returned sludge is determined by the inflow load of the wastewater 11, the sludge generation capacity of the treatment tank 1, and the appropriate amount of sludge in the treatment tank 1. The remainder of the biological treatment sludge 13 is surplus sludge as a methane fermentation treatment tank, ie, methane fermentation treatment in this example. It is transferred to the tank 5.

The high SS-concentration organic wastewater 12 such as kitchen waste flows into the solubilization tank 4 through the transfer pipe 8 and is solubilized.
Here, the liquid to be treated is heated to 60 to 80 ° C., and after a certain residence time, the organic solid content of the treatment liquid is appropriately solubilized, and the organic components are transferred to the liquid layer, and the liquid is in a state suitable for methane fermentation. And flows into the methane fermentation tank 5 where it is treated together with the surplus of the biologically treated sludge 13.

In the methane fermentation tank 5, methane fermentation is carried out under stirring with a slightly elevated temperature, that is, maintained at 35 to 55 ° C., and an average residence time of about 15 hours is given. Collected in the holder. The outflowing treatment liquid is transferred to the solid-liquid separator 6 by the transfer pipe 8, where it is separated into sedimented and separated methane fermentation sludge 18 and a supernatant liquid, ie, treatment water 16.

The methane fermentation sludge 18 is transferred to the concentrator 7, in this example a centrifuge, where the sludge concentration is 8 to 10%.
After returning to the solubilization tank 4, substantially the entire amount of the returned concentrated methane fermented sludge 17 is returned to the solubilization tank 4 by the return pipe 9. The desorbed water is discharged as treated water 16 together with the supernatant of the solid-liquid separator 6 by the transfer pipe 8.

The return concentrated methane fermentation sludge 17 is returned to the return pipe 9
Is returned to the solubilization tank 4 where it is merged with the previous garbage and the like. Since the returned sludge has a high concentration, the solubilization tank fully demonstrates its ability without being diluted.

As described above, only the treated waters 15 and 16 and methane gas (not shown) are discharged from the present embodiment, which is a very convenient form for the subsequent use and handling of the discharged matter.

FIG. 2 is a schematic view showing another example of the apparatus and the process of the present invention, in which an ozone treatment tank is arranged in front of a solubilization tank. Attached. In FIG. 2, reference numeral 3 denotes an ozone treatment tank.

The arrangement of equipment, process flow and operation example are the same as the previous example except for the ozone treatment step. However, the returned concentrated methane fermented sludge 17 is introduced into the ozone treatment tank 3 before being returned to the solubilization tank. Here return concentrated methane fermentation sludge 1
In the biological treatment in 7, the hardly decomposable substance is chemically oxidatively decomposed, and a smoother solubilization reaction proceeds promptly in the subsequent solubilization treatment.

Although not shown, the ozone treatment tank 3 is provided with an ozone generator for generating ozone by high-pressure silent discharge, and the ozone generated from the generator is introduced into the ozone treatment tank 3, and The treatment is performed by bringing the liquid layer of the liquid to be treated that has flowed into the tank into dispersed contact with fine bubbles.

The ozone treatment tank 3 of this embodiment has a stirring tank type reactor equipped with a gas blowing tube. The stirring blades are provided in three stages in the rotation axis direction and the liquid tank up and down direction, and the blowing tube is provided immediately below the blades. It is a ring-shaped perforated tube arranged. In this example, the treatment was performed by heating to about 50 ° C.

FIG. 3 shows still another example of the apparatus and process of the present invention, in which methane fermentation as a methane fermentation treatment step is performed in two stages. That is, as a device,
The first methane tank and the second methane tank are arranged in series, and the ozone treatment tank is arranged before the solubilization tank.

In FIG. 3, components having the same contents as those in FIG. 2 are denoted by the same reference numerals. However, 21 is the first methane fermentation tank, 22
Indicates a second methane fermentation tank.

The equipment arrangement, process flow, and operation example are the same as those of the previous example except for the methane fermentation treatment step, except that the first methane fermentation tank is provided with a completely stirred methane fermentation tank, and the second methane fermentation tank is provided with an upper part. A counter-flow treatment tank (UASB) was provided. The treatment liquid discharged from the solubilization tank still contains a large amount of organic solids, and is introduced into a stirred tank type reactor.
It is methane fermented under gentle heating with stirring. Thus, the processing liquid flowing out of the first methane fermentation tank has a remarkably reduced organic solid content, and is transferred to the second methane fermentation tank of the next stage, in this example, an upward flow bed type processing tank, and further treated with methane. The fermentation was continued and completed. According to this example, the processing speed is remarkably improved, and the processing capacity of the system is increased.

[0040]

As described above, according to the present invention, the waste water composed of various forms of organic waste is converted into organic SS concentration, hardly decomposable organic solids, and easily decomposable organic solids ratio. Separation and treatment of the sludge, and adoption of a new and improved method of returning the generated sludge, could improve the digestibility, reduce the volume of organic solids, and improve the methane gas recovery rate. Furthermore, in the configuration of the present invention, the processing speed of the methane fermentation treatment, which is the methane fermentation treatment step, could be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of the apparatus and process of the present invention.

FIG. 2 is an example of the apparatus and process of the present invention,
It is the schematic which shows what arrange | positioned the ozone treatment tank in the former stage of the solubilization tank.

FIG. 3 is an example of the apparatus and process of the present invention,
It is the schematic which shows what arrange | positioned the 1st methane tank and the 2nd methane tank in series, and arrange | positioned the ozone treatment tank in the former stage of a solubilization tank.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 biological treatment tank 2 solid-liquid separator 3 ozone treatment tank 4 solubilization tank 5 methane fermentation tank 6 solid-liquid separator 7 concentrator 8 transfer piping 9 return piping 11 human waste 12 kitchen waste 13 biological treatment sludge 14 return biological treatment sludge 15 Treated water 16 Treated water 17 Return concentrated methane fermentation sludge 18 Methane fermentation sludge 21 First methane fermentation tank 22 Second methane fermentation tank

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Nokai Nobuyuki 1-8-1 Koura, Kanazawa-ku, Yokohama-shi Inside Mitsubishi Heavy Industries, Ltd. Yokohama Research Institute (72) Inventor Yuji Yasuda 12 Nishikicho, Naka-ku, Yokohama-shi Mitsubishi Heavy Industries, Ltd. Company F-term in Yokohama Works (reference) 4D028 BC01 BC28 BD11 BE01 BE04 BE08 4D050 AA13 AA14 AA15 AB23 BB02 CA17 4D059 AA07 BA12 CA22 DA43

Claims (11)

[Claims] 1. A treatment system having a process for treating an SS-concentration organic wastewater in human waste and the like and a high SS-concentration organic wastewater such as kitchen waste, wherein the SS-concentration organic wastewater in the human waste and the like is subjected to biological treatment. The excess sludge from the sludge obtained by solid-liquid separation of the treatment liquid is
The methane fermentation process is performed in the methane fermentation process, while the high SS concentration organic wastewater such as kitchen garbage is subjected to the solubilization process, and then the methane fermentation process is performed together with the excess sludge in the methane fermentation process. A wastewater treatment method, wherein a dehydrated methane fermentation sludge obtained by further concentrating sludge obtained by solid-liquid separation of a treatment liquid is returned to the methane fermentation step after the solubilization treatment is performed again in the solubilization step. 2. The wastewater treatment method according to claim 1, wherein substantially all of the sludge obtained by solid-liquid separation of the treatment liquid in the methane fermentation step is concentrated and returned to the solubilization treatment step. 3. A methane fermentation step for treating water to be treated containing a relatively high concentration of organic SS, wherein the methane fermentation step comprises a completely mixed type tank or the like, or a fixed-bed treatment tank or upward Relatively low-concentration organic S equipped with a fluidized bed treatment tank
The wastewater treatment method according to claim 1 or 2, wherein the method is a methane fermentation step of treating water to be treated containing S. 4. The methane fermentation treatment of the treated water after the solubilization treatment is the same as the first methane fermentation step of treating the water to be treated containing a relatively high concentration of organic SS. The second methane fermentation step for treating the water to be treated containing organic SS is sequentially and continuously performed. The organic wastewater having the SS concentration in the human waste and the like is subjected to biological treatment, and then the sludge obtained by solid-liquid separation of the treated liquid 3. The wastewater treatment according to claim 1, wherein the methane fermentation treatment of the excess sludge is performed in the second methane fermentation step in combination with the methane fermentation treatment of the treated water after the solubilization treatment. 4. Method. 5. The first methane fermentation tank is a completely mixed tank, and the second methane fermentation tank is a fixed bed treatment tank or an upward flow bed treatment tank. 5. The wastewater treatment method according to any one of 1, 2, and 4. 6. The ozone treatment before the solubilization treatment of the dehydrated methane fermentation sludge.
A wastewater treatment method according to any one of claims 1 to 5. 7. A treatment system having a combined system and equipment for treating SS waste organic wastewater such as human waste and high SS waste organic wastewater such as kitchen waste, wherein the SS waste organic wastewater such as human waste is biologically treated. Processing apparatus, a solid-liquid separator for solid-liquid separation of the processing liquid, excess sludge of the sludge solid-liquid separated the processing liquid,
At least one methane fermentation treatment tank for methane fermentation treatment, a solid-liquid separator for solid-liquid separation of the treatment liquid subjected to methane fermentation treatment in the treatment tank, a solubilization tank for solubilizing high SS concentration organic wastewater such as kitchen waste A methane fermentation treatment of the solubilized liquid with the excess sludge in the methane fermentation tank, and a solid-liquid separator for solid-liquid separation of the combined methane fermentation liquid; A concentrator for further concentrating the dehydrated methane fermentation sludge into a dehydrated methane fermentation sludge, a transfer means including a transfer pipe for returning the dehydrated methane fermentation sludge to the methane fermentation treatment tank after being solubilized in the solubilization tank, and As described above, a wastewater treatment apparatus comprising a transfer means including a transfer pipe for transferring a processing liquid or a liquid to be processed so that each apparatus and apparatus functions. 8. A methane fermentation tank for treating water to be treated containing a relatively high concentration of organic SS, such as a completely mixed type tank, or a fixed-bed treatment tank or an upward flow. The wastewater treatment apparatus according to claim 7, wherein the wastewater treatment apparatus is a methane fermentation tank for treating water to be treated containing relatively low concentration of organic SS, such as a floor treatment tank. 9. A treatment apparatus for performing methane fermentation treatment of the treated water after the solubilization treatment, relative to a first methane fermentation tank for treating treated water containing a relatively high concentration of organic SS. A second methane fermentation tank for treating water to be treated containing low-concentration organic SS is connected in series, and the SS-concentration organic wastewater in human waste and the like is subjected to biological treatment, and the treated liquid is solidified. The methane fermentation treatment of the excess sludge of the liquid separated sludge is carried out in the second step.
The wastewater treatment apparatus according to claim 7, wherein the methane fermentation tank is configured to perform the methane fermentation treatment of the treated water after the solubilization treatment in combination therewith. 10. The first methane fermentation tank is a completely mixed type tank, and the second methane fermentation tank is a fixed bed treatment tank or an upward flow bed treatment tank. 10. The wastewater treatment apparatus according to 7 or 9. 11. The wastewater treatment method according to claim 7, wherein an ozone treatment tank is disposed so as to be capable of ozone treatment before the solubilization treatment of the dehydrated methane fermentation sludge.