阅读说明：本技术 有机废水处理方法以及有机废水处理装置 (Organic wastewater treatment method and organic wastewater treatment device ) 是由 矢次壮一郎 永江信也 柳瀬仁志 都筑佑子 于 2019-09-10 设计创作，主要内容包括：本发明提供一种有机废水处理方法,针对有机废水处理装置,能够在不增加成本的情况下对含氮和磷的有机废水有效地进行脱氮和脱磷。有机废水处理装置具有：生物处理池,将沿着有机废水的流向配设于上游侧的缺氧池、和配设于下游侧且在活性污泥中浸没配置有膜分离装置的好氧池作为一对生物处理单位,并且多个生物处理单位串联地连接；以及污泥返回路径,供活性污泥从配设于最下游的好氧池返回至配设于最上游的缺氧池；有机废水处理装置还设置有厌氧池,在该厌氧池中对有机废水进行厌氧处理之后,将有机废水分割开并供给至各生物处理单位的缺氧池,反复进行在所述缺氧池中的脱氮处理和在所述好氧池中的硝化处理,对有机废水进行生物处理,从各生物处理单位的膜分离装置送出膜渗透液作为处理水。(The invention provides an organic wastewater treatment method, which aims at an organic wastewater treatment device and can effectively carry out denitrification and dephosphorization on organic wastewater containing nitrogen and phosphorus without increasing the cost. The organic wastewater treatment device comprises: a biological treatment tank including an anoxic tank disposed on an upstream side in a flow direction of the organic wastewater and an aerobic tank disposed on a downstream side and having a membrane separation device immersed in the activated sludge as a pair of biological treatment units, the biological treatment units being connected in series; and a sludge return path for returning activated sludge from the aerobic tank disposed at the most downstream to the anoxic tank disposed at the most upstream; the organic wastewater treatment apparatus is further provided with an anaerobic tank, wherein after the organic wastewater is subjected to anaerobic treatment in the anaerobic tank, the organic wastewater is divided and supplied to an anoxic tank of each biological treatment unit, denitrification treatment in the anoxic tank and nitrification treatment in the aerobic tank are repeated to subject the organic wastewater to biological treatment, and membrane permeate is sent out from the membrane separation apparatus of each biological treatment unit as treated water.)

1. A method for treating organic wastewater, which aims at an organic wastewater treatment device and carries out biological treatment on organic wastewater containing nitrogen and phosphorus in activated sludge,

the organic wastewater treatment device comprises: a biological treatment tank including an anoxic tank disposed on an upstream side in a flow direction of the organic wastewater and an aerobic tank disposed on a downstream side and having a membrane separation device immersed in the activated sludge as a pair of biological treatment units, the biological treatment units being connected in series; and a sludge return path for returning activated sludge from the aerobic tank disposed at the most downstream side to the anoxic tank disposed at the most upstream side,

the organic wastewater treatment device is also provided with an anaerobic tank, after the anaerobic treatment is carried out on the organic wastewater in the anaerobic tank, the organic wastewater is divided and supplied to the anoxic tank of each biological treatment unit,

the denitrification treatment in the anoxic tank and the nitrification treatment in the aerobic tank are repeatedly carried out to carry out biological treatment on the organic wastewater,

membrane permeate was sent as treated water from the membrane separation apparatus of each biological treatment unit.

2. The method for treating organic wastewater according to claim 1,

returning activated sludge from the anoxic tank to the anaerobic tank.

3. An organic wastewater treatment device for biologically treating organic wastewater containing nitrogen and phosphorus in activated sludge,

the method comprises the following steps:

a biological treatment tank including a pair of biological treatment units, an anoxic tank disposed on an upstream side in a flow direction of the organic wastewater and an aerobic tank disposed on a downstream side in which a membrane separation device is immersed in the activated sludge, the biological treatment units being connected in series;

the anaerobic tank is used for carrying out anaerobic treatment on the organic wastewater;

a sludge return path for returning activated sludge from the aerobic tank disposed at the most downstream side to the anoxic tank disposed at the most upstream side;

a raw water supply path for dividing the organic wastewater from the anaerobic tank and supplying the organic wastewater to the anoxic tank of each biological treatment unit; and

a treated water transport path for sending a membrane permeate as treated water from the membrane separation device of each biological treatment unit.

4. The organic wastewater treatment apparatus according to claim 3,

an anaerobic tank return path is provided for return of activated sludge from the anoxic tank to the anaerobic tank.

5. The organic wastewater treatment apparatus according to claim 3 or 4,

the biological treatment tank is formed in a ring shape such that the anoxic tank and the aerobic tank are alternately arranged, and the anaerobic tank is arranged inside the ring shape.

6. The organic wastewater treatment apparatus according to any one of claims 3 to 5,

each of the anoxic tanks and each of the aerobic tanks are arranged in the vertical direction via a boundary wall, and the aerobic tank is arranged above and the anoxic tank is arranged below so as to sandwich the boundary wall.

Background

Conventionally, as an organic wastewater treatment method for biologically treating organic wastewater containing nitrogen and phosphorus with activated sludge, a circulating anaerobic-aerobic method (A2O method (also referred to as a "UCT method")) has been widely used, in which an anaerobic tank, an anoxic tank, and an aerobic tank are arranged in this order, and sludge in the aerobic tank is circulated and supplied to the anaerobic tank and the anoxic tank. In recent years, attention has been paid to an MBR method (UCT-MBR or the like) in which a membrane separation device is submerged in an aerobic tank instead of a settling tank for solid-liquid separation.

Patent document 1 discloses a compact nitrogen-containing waste liquid treatment facility having a nitrogen removal rate of 90% or more.

In the treatment apparatus, a plurality of anaerobic tanks and aerobic tanks are alternately combined in series in the order of anaerobic tank and aerobic tank, and there is a supply path for supplying a nitrogen-containing waste liquid to the most front stage anaerobic tank and at least one anaerobic tank after the second stage.

The system also includes an immersion type separation device for separating activated sludge in the last stage aerobic tank to obtain a treated liquid, and a path for returning the activated sludge liquid from the last stage aerobic tank to the first stage anaerobic tank. It should be noted that the anaerobic tank of the treatment plant functions exactly as an anoxic tank.

Patent document 2 discloses a membrane separation apparatus that performs a high-level treatment using only one treatment tank.

The membrane separation device comprises: a circular treatment tank for performing biological treatment on the water to be treated and forming a swirling flow of the water to be treated; a plurality of membrane units provided at intervals in a flow direction of the swirling flow, and performing membrane separation treatment on the water to be treated; and a raw water tank storing the water to be treated supplied to the treatment tank.

The raw water tank is provided inside the swirling flow, and the supply device for supplying the water to be treated from the raw water tank to the treatment tank is configured to perform multi-stage supply in the flow direction of the swirling flow.

In any of the above wastewater treatment facilities, since the organic wastewater is supplied to the anaerobic treatment zone formed adjacent to the aerobic treatment zone in which the separation membranes are immersed, high denitrification performance can be achieved at a high BOD concentration in the anaerobic treatment zone.

Therefore, in order to remove phosphorus contained in organic wastewater by using a membrane separation activated sludge method, a dephosphorization method of adding a flocculant to an aerobic tank or the like to precipitate the flocculant as insoluble phosphate and a biological dephosphorization method using an absorption effect of activated sludge on phosphorus have been conventionally used.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2000-140886

Patent document 2: japanese patent laid-open publication No. 2004-305916

Disclosure of Invention

Problems to be solved by the invention

However, when the dephosphorization method using a flocculant is applied to the membrane separation activated sludge method, there are problems that not only the cost of chemicals increases, but also the cost of sludge treatment increases with an increase in the amount of excess sludge generated, and the maintenance cost increases due to an increase in the frequency of cleaning a chemical solution caused by clogging of a membrane by an inorganic substance by the flocculant.

In addition, in the case of applying the biological dephosphorization method to the MBR, there are problems as follows: after the membrane is washed with the chemical solution, the concentration of phosphorus contained in the treated water temporarily increases, and when the number of treatment lines is small, care must be taken to deteriorate the quality of the treated water, which complicates management.

An object of the present invention is to provide a method and an apparatus for treating organic wastewater, which can efficiently denitrify and dephosphorize organic wastewater containing nitrogen and phosphorus without increasing the cost.

Means for solving the problems

In order to achieve the above object, a first feature of an organic wastewater treatment method according to the present invention is an organic wastewater treatment apparatus for biologically treating organic wastewater containing nitrogen and phosphorus in activated sludge, the apparatus comprising: a biological treatment tank including an anoxic tank disposed on an upstream side in a flow direction of the organic wastewater and an aerobic tank disposed on a downstream side and having a membrane separation device immersed in the activated sludge as a pair of biological treatment units, the biological treatment units being connected in series; and a sludge return path for returning activated sludge from the aerobic tank disposed at the most downstream side to the anoxic tank disposed at the most upstream side. The organic wastewater treatment apparatus is further provided with an anaerobic tank, wherein after the organic wastewater is subjected to anaerobic treatment in the anaerobic tank, the organic wastewater is divided and supplied to an anoxic tank of each biological treatment unit, denitrification treatment in the anoxic tank and nitrification treatment in the aerobic tank are repeated to subject the organic wastewater to biological treatment, and membrane permeate is sent out from the membrane separation apparatus of each biological treatment unit as treated water.

According to the organic wastewater treatment method, all organic acids contained in the organic wastewater can be used for phosphorus release in the anaerobic tank, so that high dephosphorization performance can be obtained without using a flocculant.

Further, the stop or operation of the membrane separation apparatus can be switched and adjusted in each biological treatment unit depending on the degree of load of the nitrification/denitrification treatment of the organic wastewater, so that the power required for the aeration apparatus provided in the membrane separation apparatus can be optimized and the running cost can be reduced while securing high denitrification performance.

Moreover, chemical cleaning of the membrane can be performed independently for each aerobic tank, and an increase in the phosphorus concentration in the treated water after cleaning can be suppressed.

A second characteristic configuration of the organic wastewater treatment method is that, in addition to the first characteristic configuration, activated sludge is returned from the anoxic tank to the anaerobic tank.

The release of phosphorus from the returned activated sludge becomes remarkable by the organic acid contained in the organic wastewater fed into the anaerobic tank, and the excessive absorption of phosphorus by the activated sludge subsequently flowing into the aerobic tank is promoted, thereby efficiently removing phosphorus.

A first characteristic configuration of the organic wastewater treatment apparatus of the present invention is an apparatus for biologically treating organic wastewater containing nitrogen and phosphorus in activated sludge, comprising: a biological treatment tank including a pair of biological treatment units, an anoxic tank disposed on an upstream side in a flow direction of the organic wastewater and an aerobic tank disposed on a downstream side in which a membrane separation device is immersed in the activated sludge, the biological treatment units being connected in series; the anaerobic tank is used for carrying out anaerobic treatment on the organic wastewater; a sludge return path for returning activated sludge from the aerobic tank disposed at the most downstream side to the anoxic tank disposed at the most upstream side; a raw water supply path for dividing the organic wastewater from the anaerobic tank and supplying the organic wastewater to the anoxic tank of each biological treatment unit; and a treated water transport path for sending the membrane permeate from the membrane separation device of each biological treatment unit as treated water.

Organic wastewater containing nitrogen and phosphorus is introduced into an anaerobic tank, subjected to anaerobic treatment in which phosphorus is released from activated sludge, and then divided by a raw water supply path and supplied to an anoxic tank constituting each biological treatment unit.

The organic wastewater, which is divided and supplied to the anoxic tank, flows down from the anoxic tank to the aerobic tank and from the upstream side to the downstream side together with the activated sludge in each biological treatment unit, and is subjected to repeated denitrification and nitrification, and is returned from the aerobic tank disposed at the most downstream side to the anoxic tank disposed at the most upstream side via the sludge return path, whereby the denitrification is efficiently repeated, and the treated water is extracted by performing solid-liquid separation by the membrane separation device disposed in each aerobic tank while being immersed.

A second characteristic configuration of the wastewater treatment apparatus is that, in addition to the first characteristic configuration, the apparatus includes an anaerobic tank return path through which activated sludge is returned from the anoxic tank to the anaerobic tank.

The organic acid contained in the organic wastewater fed into the anaerobic tank can significantly release phosphorus from the returned activated sludge, and promote the excessive absorption of phosphorus by the activated sludge subsequently flowing into the aerobic tank, thereby effectively removing phosphorus.

A third characteristic configuration of the wastewater treatment apparatus is that, in addition to the first or second characteristic configuration, the biological treatment tank is formed in a ring shape so that the anoxic tank and the aerobic tank are alternately arranged, and the anaerobic tank is arranged inside the ring shape.

Since the plurality of biological treatment tanks are arranged in the form of a ring, the sludge return path can be formed in the shortest possible length, and the anaerobic tank is arranged inside the ring, the flow paths connecting the anaerobic tank and the anoxic tank can be formed in the shortest possible length, and the wastewater treatment apparatus can be constructed compactly.

A fourth characteristic configuration of the wastewater treatment apparatus is such that, in addition to the characteristic configuration described in any one of the first to third characteristic configurations, each anoxic tank and each aerobic tank are disposed in the vertical direction via a boundary wall, and the aerobic tank is disposed above and the anoxic tank is disposed below with the boundary wall interposed therebetween.

Since the aerobic tank is disposed above the anoxic tank, the installation area can be significantly reduced, and a compact organic wastewater treatment apparatus can be realized. Further, the anoxic tank is disposed below the aerobic tank with the boundary wall interposed therebetween, and as a result, it is not necessary to provide the anoxic tank with a special cover or the like for blocking the outside air, and the facility cost is also reduced.

Effects of the invention

As described above, according to the present invention, it is possible to provide an organic wastewater treatment method and an organic wastewater treatment apparatus capable of efficiently removing nitrogen and phosphorus from organic wastewater containing nitrogen and phosphorus without increasing the cost.

Drawings

FIG. 1 is a schematic explanatory view of a wastewater treatment apparatus of the present invention corresponding to organic wastewater containing nitrogen and phosphorus.

Fig. 2 is an explanatory view of a membrane element having a membrane separation device.

FIG. 3A is a top explanatory view showing an embodiment of the wastewater treatment apparatus of the present invention.

FIG. 3B is a front explanatory view showing an embodiment of the wastewater treatment apparatus of the present invention.

FIG. 4A is a bottom view showing another embodiment of the method for treating wastewater according to the present invention.

FIG. 4B is an explanatory view showing a cross section A-A of FIG. 4A, showing another embodiment of the method for treating wastewater of the present invention.

FIG. 5A is a top explanatory view showing another embodiment of the method for treating wastewater of the present invention.

FIG. 5B is a sectional view taken along line B-B of FIG. 5A, showing another embodiment of the method for treating wastewater according to the present invention.

Detailed Description

Hereinafter, embodiments of the wastewater treatment method and wastewater treatment apparatus according to the present invention will be described with reference to the drawings. The wastewater treatment apparatus of the present invention is an organic wastewater treatment apparatus for biologically treating organic wastewater containing nitrogen and phosphorus in activated sludge.

The concept of the organic wastewater treatment apparatus is shown in FIG. 1. The wastewater treatment apparatus 1 includes a biological treatment tank 2 having a pair of anoxic tanks 10(10a, 10b, 10c, 10d) disposed upstream and aerobic tanks 20(20a, 20b, 20c, 20d) disposed downstream in a flow direction of organic wastewater containing nitrogen and phosphorus (hereinafter also referred to as "raw water"), and a plurality of biological treatment units are connected in series.

In the aerobic tanks 20(20a, 20b, 20c, 20d), the membrane separation device 30 is disposed submerged in the activated sludge, and a sludge return path 3 is provided through which the activated sludge is returned from the aerobic tank 20d disposed most downstream to the anoxic tank 10a disposed most upstream.

The wastewater treatment apparatus 1 further comprises: an anaerobic tank 50 for performing anaerobic treatment on the organic wastewater introduced through the raw water guide path 4; raw water supply paths 5(5a, 5b, 5c, 5d) for dividing the organic wastewater from the anaerobic tank 50 and supplying the organic wastewater to the anoxic tanks 20 of the respective biological treatment units; an anaerobic tank return path 6(6a, 6b, 6c, 6d) for returning activated sludge from the anoxic tank 10 to the anaerobic tank 50; and a treated water transport path 7 for sending the membrane permeate as treated water from the membrane separation device 30 of each biological treatment unit.

According to the wastewater treatment apparatus 1 as described above, the organic acid contained in the organic wastewater as the raw water is used for the release of phosphorus in the anaerobic tank 50, so that high dephosphorization performance can be obtained without using a flocculant. That is, the activated sludge returned through the anaerobic tank return path 6 can be remarkably discharged with the organic acid contained in the organic wastewater fed into the anaerobic tank 50, and the excessive uptake of phosphorus by the activated sludge subsequently flowing down into the aerobic tank 20 is promoted, whereby phosphorus can be efficiently removed without using a flocculant for precipitating as insoluble phosphate.

Further, nitrate nitrogen obtained by nitrification of ammonia nitrogen in the aerobic tank 20 is reduced to nitrogen in the anoxic tank 10, and thus effective denitrification can be achieved.

In the example of fig. 1, the circulation amount 3Q of the activated sludge in the biological treatment tank 2, the total extraction amount 1Q (═ 0.25Q × 4) of the treated water by the membrane separation device 30, the supply amount 2Q (═ 0.5Q × 4) of the activated sludge including the raw water supplied from the anaerobic tank 50 to the anoxic tank 10, and the return amount 1Q (═ 0.25Q × 4) from each anoxic tank 10 to the anaerobic tank 50 are set with respect to the inflow amount 1Q of the raw water. As a result, in the biological treatment unit of the pair of anoxic tank and aerobic tank, a circulation ratio of 12Q (circulation amount 3Q × 4 biological treatment unit) can be virtually realized for an inflow amount of 1Q.

In the example of fig. 1, the return of the activated sludge from all the anoxic tanks 10 constituting the biological treatment unit to the anaerobic tank 50 is described, but the return of the activated sludge from at least one anoxic tank 10 to the anaerobic tank 50 may be performed.

Fig. 3A and 3B show an example of a wastewater treatment apparatus 1 in which a pair of biological treatment units, i.e., an anoxic tank 1 and an aerobic tank 20, are alternately arranged and a biological treatment tank 2 is formed in an annular shape as a whole. In the wastewater treatment apparatus 1, one anaerobic tank 50 is provided for the biological treatment tank 2, and the anaerobic tank 50 and each anoxic tank 10 are connected by the raw water supply path 5 and the anaerobic tank return path 6, respectively.

In the present embodiment, the biological treatment tank 2 has the following structure: four pairs of biological treatment units are arranged in series and circularly along the flow direction of the organic wastewater. The number of biological treatment units is not limited to four pairs as in this example, and may be a plurality of units.

A plurality of biological treatment units can be constituted by dividing a single biological treatment tank 2 into a plurality of zones, and in addition, the biological treatment tank 2 can be constituted by arranging a plurality of pairs of the individual anoxic tank 10 and the aerobic tank 20 along the flow direction of the organic wastewater.

Organic wastewater as raw water is introduced into the anaerobic tanks 50 through the raw water guide paths 4, anaerobic treatment, that is, treatment for discharging phosphorus from activated sludge is performed in the anaerobic tanks 50, and the raw water and the activated sludge are divided substantially equally from the anaerobic tanks 50 through the raw water supply paths 5 and supplied to the respective anoxic tanks 10.

After the anaerobic treatment, i.e., the denitrification treatment, is performed in each anoxic tank 10, raw water flows into the aerobic tank 20 on the downstream side together with activated sludge, and the aerobic treatment, i.e., the nitrification treatment, is performed.

The membrane separation device 30 is arranged in each aerobic tank 20 in a submerged manner, and an auxiliary air dispersing device 40 for aerobic treatment is arranged in the vicinity thereof. A part of the activated sludge is returned from each anoxic tank 10 to the anaerobic tank 50 via the anaerobic tank return path 6, and phosphorus discharge is performed in the anaerobic tank 50.

An air lift pump AP is provided in the most upstream anoxic tank 10(10a), and activated sludge is discharged to the downstream aerobic tank 20(20a) together with organic wastewater by an updraft generated in the air lift pipe by bubbles supplied from the blower B via the valve V10, and then naturally flows down in the order of the anoxic tank 10(10B), the aerobic tank 20(20B), the anoxic tank 10(10c), the aerobic tank 20(20c), the anoxic tank 10(10d), and the aerobic tank 20(20 d).

Since the air-lift pump AP is provided in the anoxic tank 10, an increase in the dissolved oxygen amount DO in the anoxic tank 10 is not caused as compared with the case where the air-lift pump AP is provided in the aerobic tank 20 and liquid is delivered to the anoxic tank 10.

In the present embodiment, four pairs of biological treatment units are arranged in a circulating manner along the flow direction of the organic wastewater, the aerobic tank 20(20d) disposed at the most downstream side and the anoxic tank 10(10a) disposed at the most upstream side are arranged adjacently with a partition wall interposed therebetween, and the sludge return path 3 for returning the activated sludge of the aerobic tank 20(20d) disposed at the most downstream side to the anoxic tank 10(10a) disposed at the most upstream side is formed as a part of the partition wall.

A partition wall W1 is formed between the anoxic tank 10 and the aerobic tank 20, and a notch 11 is provided in a part of the partition wall W1 on the upper end side thereof in order to allow the organic wastewater containing the activated sludge in the anoxic tank 10 to overflow to the aerobic tank 20 (see fig. 3B).

A partition wall W2 is formed between the aerobic tank 20 and the anoxic tank 10, and an outflow portion 21 through which the organic wastewater containing activated sludge flows is provided at a position corresponding to the vicinity of the bottom of the membrane separation device 30 in the vertical direction of the partition wall W2.

The upper end of the opening of the outflow part 21 is submerged and is provided at a position 30cm or less from the water surface of the aerobic tank 20. The flow velocity of the activated sludge flowing out of the outflow portion 21 is set to 0.5m/sec or less. The outflow portion 21 formed in the most downstream aerobic tank 20(20d) serves as the sludge return path. In fig. 3A, the arrows indicated by the two-dot chain lines indicate that the activated sludge flows through the biological treatment unit and forms a circulation flow.

The membrane separation device 30 includes a plurality of membrane members 31 and an aeration device 32 (see fig. 3B) provided below the membrane members 31. The plurality of film members 31 are arranged in a vertical direction at predetermined intervals and are accommodated in the housing in two stages.

As shown in fig. 2, the membrane member 31 is configured such that separation membranes 31b are disposed on both front and rear surfaces of a resin film support body 31a having a water collecting pipe 31c at an upper portion thereof. In the present embodiment, the separation membrane 31b is composed of a microfiltration membrane having a nominal pore diameter of about 0.4 μm, and the filtration membrane is provided with an organic polymer membrane having porosity on the surface of a nonwoven fabric.

The kind of the separation membrane 31b and the membrane member 31 are not limited to the above embodiments, and any kind of separation membrane and any type of membrane member (hollow membrane member, tubular membrane member, monolithic membrane member, etc.) can be used.

The treated water having permeated through the separation membrane 31B flows through the water collection pipe 31c along the groove portion formed in the membrane support body 31a, flows from the water collection pipe 31c into the air separation tank 35 via the header pipe 34, and is collected in the treated water tank 37 via the liquid sending pipe 36 connected to the air separation tank 35, as shown in fig. 3A and 3B.

Valves V5, V6, V7, and V8 for adjusting the flow rate are provided in the headers 34, and a suction pump P is disposed in the liquid sending pipe 36. The amount of membrane permeate from each membrane separation device 30 is adjusted by pressure regulation by the suction pump P and opening degree regulation of the valves V5, V6, V7, V8.

In order to detect the pressure difference between the membranes of the membrane separation device 30, a pressure sensor Pm is provided between the air separation tank 35 and the suction pump P. In fig. 3A and 3B, a motor for adjusting the opening degree of the valve is denoted by a symbol M. A path that flows from the water collection pipe 31c into the air separation tank 35 via the header pipe 34 and collects the treated water in the treated water tank 37 via the liquid sending pipe 36 connected to the air separation tank 35 is the treated water sending path 7.

The main air supply pipe Tm connected to the blower B is branched and connected to four sub air supply pipes Ts, and each aeration device 32 is connected to each sub air supply pipe Ts. The sub-air supply pipe Ts is provided with valves V1 and V2 … … for flow rate control, which are provided corresponding to the membrane separation tanks 30 provided in the respective aerobic tanks 20, and are configured to control the aeration amount and the stop and start of aeration.

The organic wastewater is aerated together with the activated sludge in the aerobic tank 20 by the auxiliary gas dispersing device 40, the organic matter is decomposed and the ammonia nitrogen is nitrified into nitrate nitrogen, and further, phosphorus is excessively taken in by the activated sludge, and a part of the organic wastewater is subjected to solid-liquid separation as treated water by the membrane separation device 30.

The organic wastewater nitrified in the aerobic tank 20 flows into the anoxic tank 10 adjacent on the downstream side together with the activated sludge which excessively takes in phosphorus, and is subjected to denitrification treatment for reducing nitrate nitrogen into nitrogen gas and removing the nitrogen gas, and further, the organic wastewater is returned from each anoxic tank 10 to the anaerobic tank 50 through the anaerobic tank return path 6, whereby phosphorus is discharged from the activated sludge and the denitrification treatment is promoted.

When the inflow amount of raw water per unit time is Q, the inflow amount of raw water flowing into each anoxic tank 10 is Q/4, the treated water of the permeate amount of Q is extracted from each membrane separation device 30, and the activated sludge of the most downstream aerobic tank 20(20d) returns 3Q of sludge to the most upstream anoxic tank 10(10a) via the sludge return path, the effective circulation ratio of sludge is 3Q × 4 biological treatment units, so that a high circulation ratio of 12Q can be achieved, and the MLSS concentration of the anoxic tank 10 can be increased, thereby enabling the capacity of the anoxic tank 10 to be reduced.

The organic wastewater treatment apparatus 1 is provided with a flow meter for measuring the inflow amount of organic wastewater, a liquid level meter for measuring the liquid level of the tank, pressure sensors for measuring the pressure difference between membranes of the membrane separation apparatuses, T-N of the treated water provided in the treated water tank 37, and NH of the treated water₃A plurality of measuring devices such as a measuring instrument S for the concentration of N.

A control unit 60 is provided as a control device, and the operation of the organic wastewater treatment apparatus 1 is controlled based on the values measured by these measuring devices. The control unit 60 is constituted by a control panel having a computer including an arithmetic circuit, an input circuit, an output circuit, and the like.

The controller 60 repeatedly operates the membrane separation devices 30 in two modes, i.e., a filtration operation mode and a relaxation operation mode, while monitoring the degree of inflow of raw water, the water level of the biological treatment tank 2, the values of the pressure sensors Pm, the value of the total nitrogen (T-N) concentration measurement device S provided in the treatment tank 37, and the like, which are measured by these measurement devices.

The filtration operation state is a state in which aeration is performed by the aeration device 32 and membrane permeate water is extracted from the water collection pipe 31c as treated water; the slack operation state is a state in which the surface of the separation membrane 31b is cleaned by the upward airflow generated by the air bubbles by the aeration device 32 in a state in which the valve provided in the header pipe 34 is closed or the suction pump P is stopped. The filtering operation for a first predetermined time (for example, 9 minutes) and the relaxing operation for a second predetermined time (for example, 1 minute) are repeated by the control unit 60.

Since the upper end of the opening of the outflow portion 21 of the aerobic tank 30 is submerged and is provided at a position of 30cm or less of the water surface of the aerobic tank 20 (see fig. 3B), the activated sludge is surely transported to the anoxic tank on the downstream side even in a state where the membrane separation device 30 of the aerobic tank 20 is stopped and the activated sludge is not stirred.

Further, since the dissolved oxygen concentration DO in the vicinity of the bottom of the membrane separation device 30 is lower than that in the vicinity of the liquid surface, the increase in the dissolved oxygen concentration in the anoxic tank 10 on the downstream side can be suppressed.

Further, if the inflow velocity of the activated sludge is set to 0.5m/sec or less, the difference in water level between the aerobic tank and the anoxic tank due to the inflow of the activated sludge can be suppressed, and the aeration of the activated sludge in the aerobic tank can be made uniform. The cutout portion 11 is provided so that the inflow flow rate of the activated sludge is 0.5m/sec or less, and the amount of air supplied to the air lift pump AP is adjusted.

Fig. 4A and 4B show another example of the wastewater treatment apparatus 1.

In the wastewater treatment apparatus 1, a pair of anoxic tanks 10 and aerobic tanks 20, which are biological treatment units, are alternately arranged, the entire biological treatment tank 2 is formed in an annular shape, and an anaerobic tank 50 is arranged inside the annular shape.

Organic wastewater as raw water is introduced into the anaerobic tank 50 through the raw water guide passage 4 having a long tube length disposed near the bottom of the anaerobic tank 50, the raw water flows out of the anaerobic tank 50 to the anoxic tanks 20 through the raw water supply passage 5 together with activated sludge, and the activated sludge flows into the anaerobic tank 50 from the anoxic tanks 20 through the anaerobic tank return passage 6.

Each raw water supply path 5 is provided with an air lift pump, and is configured to convey activated sludge to the anoxic tank 10 by the air lift pump, and each anaerobic tank return path 6 is configured by an opening formed in the liquid by a partition wall between the anaerobic tank 50 and the anoxic tank 20.

As shown in fig. 4B, in the anaerobic tank 50, a trough-like ceiling 51 is formed at a position lower than the liquid level of the aerobic tank 10 and the anoxic tank 20, and a piping pit 52 in which a header pipe 34, an air separation tank 35, flow rate adjustment valves V5, V6, V7, V8, a liquid sending pipe 36, a suction pump P, and the like shown in fig. 3A are disposed is formed in the trough-like space.

Further, a cylindrical portion 53 is formed on the top plate 51, and a stirring blade 54 for stirring raw water and activated sludge in the anaerobic tank 50 is detachably attached via the cylindrical portion 53. In fig. 4B, reference symbol M denotes a motor for driving the stirring blade 54. The cylindrical portion 53 is covered with external air so that the external air does not flow into the anaerobic tank 50. The structure other than the anaerobic tank 50 is the same as that described with reference to fig. 3A and 3B.

By adopting such a configuration, the sludge return path 3 can be formed as shortest as possible by disposing the plurality of biological treatment tanks 2 in a ring shape, and the respective flow paths (the raw water supply path 5 and the anaerobic tank return path 6) connecting the anaerobic tank 50 and the anoxic tank 10 can be formed as shortest and equal in length by disposing the anaerobic tank 50 on the inner side of the ring shape, so that the wastewater treatment apparatus 1 can be configured compactly.

Fig. 5A and 5B show another example of the wastewater treatment apparatus 1. In this wastewater treatment apparatus 1, an anaerobic tank 50 is disposed inside a biological treatment tank 2 disposed in a ring shape, and each anoxic tank 20 and each aerobic tank 10 are disposed in parallel in the vertical direction via a boundary wall W, and the aerobic tank 10 is disposed above and the anoxic tank 20 is disposed below with the boundary wall W interposed therebetween.

Since the aerobic tank 10 is disposed above the anoxic tank 20, the installation area of the biological treatment tank can be significantly reduced, and the organic wastewater treatment apparatus 1 can be made compact.

Further, the anoxic tank 20 is disposed below the aerobic tank 10 with the boundary wall W interposed therebetween, and as a result, contact with air can be avoided even if no special cover or the like for blocking outside air is provided in the anoxic tank 20. Therefore, generation of scum is suppressed without providing a cover body, a defoaming mechanism, and the like for blocking outside air, and the equipment cost is low.

Although not shown in fig. 5B, the aerobic tanks 10d and 10c are disposed inside the aerobic tanks 10A and 10B on the paper surface, and the anoxic tanks 20d and 20c are disposed inside the anoxic tanks 20A and 20B on the paper surface.

Raw water, i.e., organic wastewater, is introduced into the anaerobic tanks 50 through the raw water guide path 4, and the raw water flows out to each anoxic tank 20 through the raw water supply path 5, which is an opening formed on a partition wall between the anaerobic tank 50 and the anoxic tank 20, together with activated sludge, and the activated sludge flows in from each anoxic tank 20 through the anaerobic tank return path 6, which is an opening formed on the same partition wall. As in fig. 4A, the raw water supply path 5 may be configured by an air lift pump.

The aerobic tank 10 and the anaerobic tank 50 are covered with a lid, and stirring blades 24 and 54 for stirring raw water and activated sludge in the anoxic tank 20 and the anaerobic tank 50 are detachably attached to the lid via rectangular openings 15 and 55 formed in the lid. In fig. 5B, symbol M denotes a motor that drives the stirring blades 24, 54.

The cover covering the anaerobic tank 50 is provided to prevent contact with the outside air, and the cover covering the aerobic tank 10 is provided to be connected to the gas collecting pipe so that odor is not discharged to the atmosphere.

The activated sludge transferred from the anaerobic tank 50 to the anoxic tank 20A together with the raw water via the raw water supply path 5 is stirred by the stirring blade 24, transferred to the aerobic tank 10b via the aerobic tank transfer path 8, and directly transferred to the anoxic tank 20b via the anoxic tank transfer path 9.

Similarly, the anoxic tank 20b, the aerobic tank 10c, the anoxic tank 20d, and the aerobic tank 20A are circulated in this order, and activated sludge flows in and out between each anoxic tank 20 and the anaerobic tank 50. It is preferable to have an air lift pump structure as the aerobic tank transfer path 8.

The pair of aerobic tank 10 and anoxic tank 20 arranged above and below need not be entirely overlapped in a plan view, and may be only partially overlapped. That is, the plurality of aerobic tanks 10 and the anoxic tank 20 may be entirely overlapped in a plan view.

In fig. 5A and 5B, the configuration in which the biological treatment tank 2 is arranged in a ring shape and the anaerobic tank 50 is arranged inside the biological treatment tank 2 is described, but the anaerobic tank 50 may not be arranged inside the biological treatment tank 2 arranged in a ring shape. For example, the relationship between each anoxic tank 20 and each aerobic tank 10 shown in fig. 3A may be set such that each anoxic tank 20 and each aerobic tank 10 are arranged in parallel in the vertical direction via a boundary wall W, and the anoxic tank 20 may be arranged above and below the aerobic tank 10 with the boundary wall W interposed therebetween.

The organic wastewater treatment method of the present invention is an organic wastewater treatment method for biologically treating organic wastewater containing nitrogen and phosphorus in activated sludge, and is applied to the above-mentioned organic wastewater treatment apparatus.

Namely, an organic wastewater treatment apparatus comprises: a biological treatment tank including an anoxic tank disposed on an upstream side in a flow direction of the organic wastewater and an aerobic tank disposed on a downstream side and having a membrane separation device immersed in the activated sludge as a pair of biological treatment units, the biological treatment units being connected in series; and a sludge return path for returning activated sludge from the aerobic tank disposed at the most downstream side to the anoxic tank disposed at the most upstream side. The organic wastewater treatment apparatus is further provided with an anaerobic tank, wherein after the organic wastewater is subjected to anaerobic treatment in the anaerobic tank, the organic wastewater is divided and supplied to an anoxic tank of each biological treatment unit, the organic wastewater is subjected to biological treatment while repeating denitrification treatment in the anoxic tank and nitrification treatment in the aerobic tank, and a membrane permeate is sent out from a membrane separation apparatus of each biological treatment unit as treated water.

According to the organic wastewater treatment method, all organic acids contained in the organic wastewater can be used for releasing phosphorus in the anaerobic tank, so that high dephosphorization performance can be obtained without using a flocculant.

Further, since the stop or operation of the membrane separation apparatus can be switched and adjusted for each biological treatment unit based on the degree of load of nitrification and denitrification treatment of the organic wastewater, it is possible to optimize the power required for the aeration apparatus provided in the membrane separation apparatus while securing high denitrification performance, thereby reducing the running cost.

In addition, it is preferable to return the activated sludge from the anoxic tank to the anaerobic tank, and phosphorus from the returned activated sludge can be significantly released by the organic acid contained in the organic wastewater fed into the anaerobic tank, and excessive absorption of phosphorus by the activated sludge subsequently flowing into the aerobic tank is promoted, thereby efficiently removing phosphorus.

The above embodiments are merely examples of the present invention, and the present invention is not limited to the above embodiments, and the specific configuration of each part may be appropriately modified within a range in which the operational effect of the present invention is exhibited. In addition, any one or more of the above embodiments may be combined as appropriate.

Description of the symbols

1: waste water treatment device

2: biological treatment pool

3: sludge return path

4: raw water guide path

5: raw water supply path

6: anaerobic tank return path

7: treated water delivery path

8: aerobic tank transfer path

9: transfer path of anoxic tank

10: anoxic pond

11: notch part

20: aerobic tank

21: outflow part

30: membrane separation device

32: aeration device

40: auxiliary air diffusing device

50: anaerobic tank

60: control unit (control device)