JP6834733B2 - Wastewater treatment equipment - Google Patents

Description

The present invention relates to a wastewater treatment device.

Conventionally, the activated sludge method has been widely used as a treatment technique for organic wastewater. The activated sludge method is applied to sewage treatment plants and the like. Wastewater to be treated flows into the reaction tank of the activated sludge method, and aggregates of microorganisms called activated sludge flocs held in the tank are mixed with the inflowed wastewater. While the mixed solution stays in the tank, the object to be treated (for example, an organic substance, a nitrogen compound, a phosphorus compound, etc.) is decomposed by a microorganism or taken into the microorganism. The mixed solution flowing out of the reaction tank flows into the settling basin. Activated sludge flocs settle while taking in floating microorganisms to some extent and are separated as settled sludge. The supernatant water is either discharged or sent to the next step. Sedimented sludge settled in the settling basin is returned to the reaction tank or its upstream side in order to maintain the microbial concentration in the reaction tank or MLSS (Mixed Liquor Suspended Solids) as an index thereof. .. The sedimented sludge is appropriately extracted as excess sludge from the sedimentation basin and sent to the sludge treatment step.

When the concentration of the object to be treated is high or the amount of wastewater is large, there is a method of maintaining the MLSS concentration high in order to obtain a desired treatment speed. The membrane separation activated sludge method is known as a technique for maintaining a high MLSS concentration. As described in Patent Documents 1 and 2, in the membrane separation activated sludge method, a membrane separation device is provided in the aeration tank. The membrane separation device has a separation membrane, and a suction pump is usually connected to the membrane separation device. Moisture is extracted and filtered through the separation membrane by this suction pump. The discharge port of the suction pump is connected to the discharge channel. According to the membrane separation activated sludge method, microorganisms are separated, the microorganisms are concentrated in the reaction vessel without a settling basin, and clear treated water can be obtained.

Special Fair 7-20592 Japanese Patent No. 3918304

As mentioned above, in the so-called membrane separation active sludge method, the MLSS concentration can be maintained high, but in order to obtain treated water, the piping may be set up once, penetrated into the wall, or sucked by a pump. It is necessary to wash the membrane as appropriate. On the other hand, in the activated sludge method using a normal gravity sedimentation type sedimentation basin that does not use a membrane separation device, the runoff water from the reaction vessel is usually obtained by overflow. That is, the treated water from the reaction tank flows out through, for example, an overflow trough. As described above, the membrane separation activated sludge method requires a special design as compared with the ordinary activated sludge method in order to allow the treated water to flow out from the reaction tank at the cost of omitting the settling basin.

An object of the present invention is to provide a wastewater treatment apparatus capable of maintaining a high MLSS concentration and allowing effluent to flow out of a reaction vessel with a simple design.

In one aspect of the present invention, a mixed solution containing microorganisms and wastewater contained in a reaction tank is aerated through an air diffuser provided in at least a part of the reaction tank to treat an object to be treated in the wastewater. It is a wastewater treatment device using the activated sludge method, and the reaction tank consists of an upstream section provided on the upstream side based on the flow of wastewater, a downstream section provided on the downstream side of the upstream section, and a downstream section. A filter made of woven fabric is provided between the upstream section and the downstream section, including a partition portion for partitioning the upstream section and the downstream section, and at least an aeration section provided in the upstream section. The partition and the filter are configured so that the mixed liquid flowing down from the upstream compartment to the downstream compartment passes through the filter.

According to this wastewater treatment device, the air diffuser is provided at least in the upstream section, and aerobic treatment with activated sludge is performed in this upstream section. A filter is provided between the upstream compartment and the downstream compartment. The mixture flowing down from the upstream compartment to the downstream compartment passes through the filter. A filter made of woven fabric can exert advantageous effects in a plurality of viewpoints. First, since the MLSS concentration flowing out from the upstream compartment is reduced as compared with the conventional standard activated sludge method, the MLSS concentration in the upstream compartment can be increased. That is, most of the activated sludge flocs that are about to flow out of the upstream compartment are captured by the filter and stay in the upstream compartment, which occupies most of the reaction vessel volume, so the reaction vessel does not have to be returned from the settling basin. The MLSS concentration in is maintained. Further, by adjusting the opening of the filter to be small, the MLSS concentration in the upstream section can be further increased. As a result, a higher treatment speed than the conventional standard activated sludge method can be obtained. Since the MLSS concentration of the mixed solution flowing out from the downstream section is significantly reduced, the load on the settling basin is reduced. Secondly, the opening of the filter can be made larger than that of the filtration membrane used in the conventional membrane separation activated sludge method. This reduces clogging due to activated sludge flocs. As a result, the permeation flux is improved and the labor for cleaning the membrane is reduced, so that the cost can be reduced. As described above, since the downstream section contains a mixed solution having a very low MLSS concentration, the mixed solution may be allowed to flow down into the settling basin (for example, by natural flow). This means that a simple device design equivalent to overflow from the reaction tank in the conventional standard activated sludge method is sufficient. Therefore, the special design of piping and flow path required in the membrane separation activated sludge method is not required. And thirdly, the opening of the woven fabric is constant unlike the non-woven fabric. Thereby, the opening can be easily set in advance according to the particle size of the suspension in the wastewater or the target value of the MLSS concentration in the upstream section. Since the woven fabric has a single layer of fibers, there are no intricate gaps and it is easy to wash, and the filtration efficiency is unlikely to decrease due to clogging of suspension. Cleaning is easy even if suspensions adhere to the surface of the filter. As a result, the MLSS concentration in the reaction vessel can be increased and the treatment speed can be increased by a means that is much easier to maintain than the activated sludge method incorporating the non-woven fabric. As described above, the MLSS concentration is equal to or higher than that of other methods for increasing the MLSS concentration and the reaction rate, and the effluent can be discharged from the reaction tank by simple design and maintenance. it can.

In some embodiments, the opening of the filter is in the range of 10 μm or more and 200 μm or less. According to this aspect, the desired MLSS concentration can be suitably maintained. In addition, among the suspended organic matter in the wastewater, those with a large particle size are selectively filtered and held in the upstream section for a long time to promote decomposition, and the wastewater with a high concentration of suspended organic matter also suppresses clogging. Can be processed while.

In some embodiments, at least a portion of the filter is installed above the air diffuser. According to this aspect, the air aerated from the air diffuser hits the filter, and the cleaning effect of the filter can be obtained. For example, the filter can be shaken by the force of rising air, thereby peeling off the deposits on the surface of the filter.

In some embodiments, the divider is provided with one or more U-shaped notches that are open upwards from above the surface to below the surface of the mixture, and the filter is a U of the notches. It is installed along the edge of the character, extends in a U-shaped cross section at a height including the water surface in the upstream and downstream compartments, and the upper surface located on the water surface and the downstream end located in the downstream compartment. It is open only in the department. According to the U-shaped filter, since the shape of the lower part is rounded, damage (tear, etc.) of the filter can be prevented. Moreover, since the upper surface is open, maintenance of the filter is easy.

In some embodiments, a U-shaped holding plate having a large number of holes through which the mixed solution can pass is further provided, and the partition portion is U-shaped open upward from above the water surface to below the water surface of the mixed solution. A U-shaped notch is provided, the holding plate is fitted into the notch and extends at a height including the water surface, and the filter is attached to the outside of the holding plate and has a U-shape of the notch. It is installed along the edge and extends in a U-shaped cross section at a height including the water surface in the upstream section and the downstream section. According to this aspect, since the filter is attached to the outside of the holding plate, it is possible to prevent the thin filter from being dented inward by water pressure and being attached to each other. It is possible to prevent a decrease in permeation efficiency.

In some embodiments, the upstream compartment is further provided with a support for supporting the presser plate, the support having a U-shape that extends upward from above the surface of the mixture to below the surface. A notch is provided, and the holding plate is bridged between the support portion and the partition portion, the upstream end portion is fitted into the notch of the support portion, and the downstream end portion is the partition portion. It is fitted into the notch of. According to this aspect, since the holding plate is bridged between the support portion and the partition portion and supported by the support portion and the partition portion, it is possible to prevent the dent of the filter described above at least in the upstream section, and stable transmission is possible. You can get efficiency.

In some embodiments, the retainer includes a perforated portion located at least in the upstream compartment and a non-perforated portion located in at least the downstream compartment. According to this aspect, the filter can be firmly suppressed and sludge outflow from the gap can be prevented by installing the non-perforated portion so as to hit the notch while allowing the mixed solution to permeate in the perforated portion. Here, if the portion corresponding to the notch is perforated, it is conceivable that the filter floats at the perforated portion depending on the hole diameter and the mounting method, and sludge flows out from the gap.

In some embodiments, the volume of the downstream compartment is smaller than the volume of the upstream compartment and the downstream compartment is a non-stirring tank. According to this aspect, the volume of the upstream compartment for aerobic treatment can be secured as large as possible.

In some embodiments, the downstream compartment is provided with an air diffuser and a microbial attachment carrier. The downstream section is not agitated but an aeration tank, and the microbial attachment carrier is provided in the downstream section, so that a biofilm is formed on the microbial attachment carrier in the downstream section. Floating microorganisms and small activated sludge flocs that have flowed from the upstream compartment through the filter into the downstream compartment are taken up by the biofilm as they pass near the microbial attachment carrier. As a result, the load of suspension on the settling basin is further reduced. An aeration tank provided with a microbial attachment carrier is also effective in removing ammonia (promoting nitrification).

In some embodiments, the reaction vessel is provided upstream of the upstream compartment and further comprises a stirring chamber without forced oxygen supply, the downstream compartment being provided with a return pump and connected to the return pump. A return line is provided that includes one end and the other end that opens toward the inside of the stirring tank. According to this aspect, ammonia nitrogen is oxidized (nitrified) in the upstream compartment and converted to nitrate nitrogen. When the mixture containing nitrate nitrogen is returned to the stirring tank by a return pump and return line, nitrate nitrogen can be converted to nitrogen gas. That is, denitrification treatment can be performed in the stirring tank.

In some embodiments, another partition and another filter made of woven fabric are provided between the stirring tank and the upstream section, and the other partition and another filter are provided in the stirring tank. The mixture flowing from the upstream compartment to the upstream compartment is configured to pass through the filter, and the opening of another filter is larger than the opening of the filter between the upstream compartment and the downstream compartment. According to this aspect, among the suspended organic substances in the wastewater, those having a large particle size can be selectively held in the stirring tank. That is, fine suspensions can flow down to the upstream compartment, while suspended organic matter useful for denitrification and accumulation of phosphorus-accumulating bacteria and microorganisms attached thereto can be selectively retained in the stirring tank.

In some embodiments, the wastewater treatment apparatus further comprises a second reaction vessel provided on the upstream side of the reaction vessel, and the second reaction vessel is provided on the second upstream side with reference to the flow of wastewater. The second upstream side compartment includes the compartment, the second downstream side compartment provided on the downstream side of the second upstream side compartment, and the second partition portion that separates the second upstream side compartment and the second downstream side compartment. A second filter made of woven fabric is provided between the second downstream section and the second downstream section, and the second partition and the second filter flow down from the second upstream section to the second downstream section. The mixture is configured to pass through a second filter, a slow stirrer is provided in the second upstream compartment, a return pump is provided in the downstream compartment of the reaction vessel, and is connected to the return pump. A return line is provided that includes one end and the other end that opens into the second upstream compartment. In this way, a second reaction tank and a reaction tank are provided, and a total of four compartments are provided. Denitrification treatment is performed in the first compartment (second upstream compartment of the second reaction tank), and oxidation of organic nitrogen and ammonia nitrogen is performed in the third compartment (upstream compartment of the reaction tank). As a result, it is not necessary to match the shape of the first section with the shape of the third section (for example, a rectangle), and the first section can be a circular slow sand stirring tank. Slow sand stirring contributes to the improvement of the denitrification rate.

According to some aspects of the present invention, the MLSS concentration can be maintained high, and the effluent can be discharged from the reaction vessel with a simple design.

It is a figure which shows the wastewater treatment system to which the wastewater treatment apparatus which concerns on 1st Embodiment of this invention is applied. It is a perspective view which shows the schematic structure of the reaction tank in FIG. 1 and its periphery. It is a figure which shows the wastewater treatment system to which the wastewater treatment apparatus which concerns on 2nd Embodiment of this invention is applied. It is a figure which shows the wastewater treatment system to which the wastewater treatment apparatus which concerns on 3rd Embodiment of this invention is applied. It is a figure which shows the wastewater treatment system to which the wastewater treatment apparatus which concerns on 4th Embodiment of this invention is applied. It is a figure which shows the wastewater treatment system to which the modified form of 1st Embodiment is applied. (A) to (c) are graphs showing the test results by the wastewater treatment apparatus according to the first embodiment, respectively. It is a perspective view which shows the schematic structure of the reaction tank and its periphery in FIG. 1, and is the figure which shows another example of the attachment structure of a filter. (A) is an exploded perspective view showing the filter mounting structure of FIG. 8, and (b) is a cross-sectional view of the filter mounting structure. (A) to (c) are side views which show various forms of a holding plate, respectively.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted.

As shown in FIG. 1, the wastewater treatment system S is a system for treating wastewater such as sewage. The wastewater treatment system S decomposes the treatment target (for example, organic matter, nitrogen compound, etc.) contained in the wastewater. The wastewater treatment system S retains activated sludge flocs, which are aggregates of microorganisms, in the reaction tank 2. In the wastewater treatment system S, a mixed solution obtained by mixing activated sludge flocs and wastewater is retained in the reaction tank 2 to biologically treat the above-mentioned object to be treated. That is, in the wastewater treatment system S, a kind of activated sludge method is used. The object to be treated may be only an organic substance, or may be a nitrogen compound in addition to the organic substance. The wastewater treatment system S is not limited to sewage, and any organic wastewater can be applied.

The wastewater treatment system S realizes a treatment method that makes it possible to increase the MLSS concentration, instead of the so-called standard activated sludge method. The MLSS concentration in the reaction vessel in the standard activated sludge method is generally about 2000 to 4000 mg / L. On the other hand, the MLSS concentration in the reaction tank 2 (particularly, the upstream compartment 3) in the wastewater treatment system S is at a level equal to, for example, the MLSS concentration in the membrane separation activated sludge method, and is, for example, 6000 mg / L or more. The MLSS concentration in the wastewater treatment system S can be, for example, 10000 mg / L or more.

The wastewater treatment system S includes a wastewater treatment device 1 having a reaction tank 2 for accommodating the mixed liquid, and a settling basin 10 for solid-liquid separation of the mixed liquid flowing out from the reaction tank 2 of the wastewater treatment device 1. The inflow line L1 is connected to the reaction tank 2. The waste water flows into the reaction tank 2 through the inflow line L1. The reaction tank 2 and the settling basin 10 are connected by a reaction tank outflow line L2. The mixed solution flows out from the reaction tank 2 through the reaction tank outflow line L2 and is sent to the settling basin 10. A settling basin outflow line L3 is connected to the upper part of the settling basin 10. The treated water of the wastewater treatment system S is discharged or sent to a subsequent process through the settling basin outflow line L3. A sludge discharge line L4 is connected to the lower part of the settling basin 10. The sedimented sludge is extracted as excess sludge through the sludge discharge line L4 and sent to, for example, a sludge treatment step.

In addition, in this specification, "line" means a pipe or a flow path through which a fluid (liquid or gas) flows inside. When the "line" is a flow path, it may be an open flow path (gutter-shaped flow path) like a trough. In addition, the expressions "the line is connected to the tank" and "the tank and the tank are connected by the line" are based on the flow and movement of the fluid. That is, these expressions include the case where the end of the line is physically connected to each tank, but the end of the line is not physically connected (not in contact) to each tank. This also includes the case where the end portion is open toward each tank and the fluid flowing through the line flows into each tank. Each tank may be a water tank made of concrete or a water tank made of steel plate.

In the wastewater treatment system S, wastewater basically flows (moves) due to natural flow due to gravity. That is, a head difference is provided between each tank of the wastewater treatment system S (the head difference is not represented in FIG. 1). In the present specification, the expression "upstream" or "downstream" is used with reference to the flow of wastewater. For example, a settling basin 10 is arranged on the downstream side of the reaction tank 2.

The reaction tank 2 of the wastewater treatment apparatus 1 includes an upstream compartment 3 provided on the upstream side and a downstream compartment 4 provided on the downstream side of the upstream compartment 3. The upstream section 3 and the downstream section 4 are partitioned by a partition wall (partition) 5. The partition wall 5 extends substantially vertically. The partition wall 5 is provided perpendicular to the flow direction (longitudinal direction of the reaction tank 2). The partition wall 5 blocks the flow of water. In this way, the reaction vessel 2 is composed of two compartments. The upstream section 3 and the downstream section 4 are, for example, rectangular (square) water tanks. The volume of the downstream section 4 is smaller than the volume of the upstream section 3. The volume of the downstream compartment 4 may be, for example, 10% or less, 5% or less, or 3% of the total volume of the reaction tank 2 including the upstream compartment 3 and the downstream compartment 4. It may be less than%. As described above, the volume of the upstream compartment 3 occupies most of the volume of the reaction vessel 2.

The upstream section 3 is an aeration tank. An air diffuser 6 is installed near the bottom of the upstream section 3, and one end of the air line La is connected to the air diffuser 6. A blower 7 is provided at the other end of the air line La, and air is blown into the upstream section 3 by the blower 7 (aeration is performed in the upstream section 3). The air diffuser 6 agitates the inside of the upstream compartment 3 while supplying oxygen into the upstream compartment 3. The type of the air diffuser 6 is not particularly limited, but a cylindrical air diffuser is used. When an air diffuser is used, the air diffuser 6 creates a swirling flow in the upstream compartment 3. An air diffuser (disk-shaped diffuser or the like) may be used as the air diffuser 6. The diameter of the bubbles generated in the air diffuser 6 can be set by appropriately selecting the pore diameter of the air diffuser 6. The air line La may be provided with a valve or the like for adjusting the amount of air.

No stirring equipment is provided in the downstream section 4. That is, the downstream section 4 is a non-stirring tank. A reaction tank outflow line L2 is connected to the downstream section 4. The reaction tank outflow line L2 is provided near the water surface in the downstream section 4. The reaction tank outflow line L2 causes the mixed solution of the reaction tank 2 to flow down to the settling basin 10 by natural flow. The reaction tank outflow line L2 is a flow path that does not require a special design. For example, when there is an existing standard activated sludge method reaction tank and sedimentation basin, the flow path connecting the reaction tank and the sedimentation basin can be used as it is as the reaction tank outflow line L2.

In the wastewater treatment device 1, a filter 8 is installed between the upstream side section 3 and the downstream side section 4. The filter 8 separates the upstream section 3 and the downstream section 4 together with the partition wall 5. The partition wall 5 and the filter 8 are configured so that the total amount (or almost the total amount) of the mixed liquid flowing down from the upstream side compartment 3 to the downstream side compartment 4 passes through the filter 8. That is, the filter 8 is provided so as to be in close contact with the partition wall 5 and to face only one surface (upstream side surface) of the filter 8 with respect to the mixed liquid in the upstream side section 3. There is.

The filter 8 will be described in more detail with reference to FIG. As shown in FIG. 2, a U-shaped notch 5a is provided from the upper end of the partition wall 5 downward. The notch 5a is provided from above the water surface to below the water surface of the mixed solution. Further, a plate-shaped support 15 extending vertically is provided in the upstream section 3. The support 15 extends parallel to the partition wall 5 on the upstream side of the partition wall 5. The support 15 is provided with a U-shaped notch 15a having the same shape and size as the notch 5a. The notch 5a of the partition wall 5 and the notch 15a of the support 15 are both opened upward. The notch 5a and the notch 15a are provided at the same position when viewed from the longitudinal direction of the reaction vessel 2. The support 15 has a minimum structure (that is, size) that can hold the shape of the notch 15a. This is because the support 15 should not block the flow of the mixture in the upstream compartment 3, unlike the partition wall 5.

A single cloth-like (or sheet-like) filter 8 is attached so as to contact the notch 5a of the partition wall 5 and the edge of the notch 15a of the support 15. In other words, the filter 8 is installed along the notch 5a and the notch 15a. The filter 8 is a bag-shaped filter having a flexible structure. Although not shown, a U-shaped structure (for example, a holding plate) having the same shape as the edges of the notch 5a and the notch 15a and having a slightly smaller cross-sectional size is formed at the edges of the notch 5a and the notch 15a. It is installed so that it can be pressed down. The holding plate is fixed to the partition wall 5 and the support 15 by some fixing means. The reaction tank 2 is divided into an upstream compartment 3 having an inflow port and a downstream compartment 4 having an outflow port by a partition composed of a partition wall 5 and a filter 8.

The filter 8 is open upward. The filter 8 extends in the longitudinal direction of the reaction vessel 2 from the upstream compartment 3 to the downstream compartment 4. The filter 8 has a height including the water surface and extends substantially horizontally so that the cross section perpendicular to the longitudinal direction forms a U shape. The filter 8 is arranged on the upstream end portion 12 arranged on the upstream side of the support 15, the intermediate portion 11 arranged on the downstream side of the support 15 and upstream of the partition wall 5, and the downstream side of the partition wall 5. Includes the downstream end 13. The upstream end portion 12, the intermediate portion 11, and the downstream end portion 13 are continuous. The filter 8 is open only at the upper surface 11a located on the water surface and the open portion 13a of the downstream end portion 13 located in the downstream section 4. The upstream end portion 12 of the filter 8 is attached so that all the edges of the filter 8 are located on the water surface. As a result, all the water that passes through the partition composed of the filter 8 and the partition wall 5 from the upstream side passes through the filter surface and enters the downstream section 4. Since the pressure in the space surrounded by the filter 8 tends to be lower than that on the outside of the filter 8, a water-permeable spacer (not shown) such as a tubular net is provided so that the filter 8 is not crushed. May be good.

A woven cloth is used as the filter 8. The opening of the filter 8 is, for example, in the range of 10 μm or more and 200 μm or less. More preferably, the opening of the filter 8 may be in the range of, for example, 20 μm or more and 50 μm or less. The filter 8 may be made of resin. More specifically, the filter 8 may be made of, for example, polyester, polyethylene, or nylon. The opening of the filter 8 is larger than the pore size of the microfiltration membrane. The opening of the filter 8 is substantially constant regardless of the site. That is, the filter 8 has a uniform opening. The fibers of the filter are one layer, and there are no intricate gaps like non-woven fabric.

At least a part of the filter 8 is installed above the air diffuser 6. The intermediate portion 11 and the upstream end portion 12 of the filter 8 are installed above the air diffuser portion 6. The filter 8 and the air diffuser 6 overlap each other in a plan view. With such a configuration, the filter surface is located above the air diffuser 6 of the upstream section 3, and the sludge adhering to the filter surface is washed by the air diffused and rising. Further, since the filter 8 has an open structure, low cost and low maintenance are realized.

The number of filters 8 may be one or a plurality.

An installation example of the inflow line L1 and the reaction tank outflow line L2 will be described with reference to FIG. An inflow line L1, which is an inflow flow path for drainage, is connected to one end in the longitudinal direction of the reaction tank 2 (upstream compartment 3). The tip of the inflow line L1 is bent in an L shape, for example, and its inflow port is directed into the upstream section 3. At the other end of the reaction tank 2 (downstream compartment 4) in the longitudinal direction, a reaction tank outflow line L2, which is an outflow flow path, is attached to the upper part of the wall surface. The outlet, which is the base end of the reaction tank outflow line L2, is provided at a position as far as possible from the notch 5a described above. That is, the filter 8 is provided at one end in the width direction of the downstream section 4, and the reaction tank outflow line L2 is provided at the other end in the width direction of the downstream section 4.

Subsequently, a method of treating wastewater by the wastewater treatment system S will be described. Activated sludge flocs and floating microorganisms are present in the reaction vessel 2. The treated object (organic matter, etc.) in the inflowing wastewater is decomposed and purified under aerobic conditions by activated sludge flocs and microorganisms using oxygen supplied from the air diffuser pipe. Activated sludge flocs and floating microorganisms flow downstream along with the flow of the mixture. Activated sludge flocs and floating microorganisms try to enter the downstream compartment 4 from the upstream compartment 3 through the filter 8, but at that time, the activated sludge flocs of a certain size or larger move in the filter 8. It is blocked and remains in the upstream compartment 3. As a result, the MLSS concentration in the upstream compartment 3 is maintained or increased. Only floating microorganisms and small flocs pass through the filter 8. These enter the settling basin 10 via the downstream section 4, and are settled and separated in the settling basin 10. In the settling basin 10, the supernatant is discharged or sent to the next step through the settling basin outflow line L3. The floating microorganisms and small flocs settled and separated in the settling basin 10 are extracted through the sludge discharge line L4 and sent to the sludge treatment step. By the above treatment, the wastewater is decomposed and purified, and clear treated water in which the concentration of the object to be treated (organic substance in the case of the wastewater treatment apparatus 1) and the SS concentration are reduced can be obtained.

According to the wastewater treatment device 1 described above, the air diffuser 6 is provided at least in the upstream section 3, and the aerobic treatment with activated sludge is performed in the upstream section 3. A filter 8 is provided between the upstream section 3 and the downstream section 4. The mixed solution flowing down from the upstream compartment 3 to the downstream compartment 4 passes through the filter 8. The filter 8 made of woven fabric exerts an advantageous effect from a plurality of viewpoints.

First, compared to the conventional standard activated sludge method that does not use a filter, most of the activated sludge flocs that are about to flow out from the upstream compartment 3 are captured by the filter 8 and occupy most of the reaction vessel volume upstream. Since the MLSS concentration in the upstream side compartment 3 is maintained by staying in the side compartment 3, the sludge return from the settling basin 10 can be omitted. Further, since the MLSS concentration of the mixed liquid flowing out from the downstream section 4 is significantly reduced, the load on the settling basin 10 is reduced, the settling basin 10 can be miniaturized, and bulking occurs. However, sludge does not easily overflow. Further, the MLSS concentration in the upstream compartment 3 can be further increased by reducing the opening of the filter to, for example, 50 μm or less. At this time, the downstream compartment 4 hardly contributes to the decomposition of organic substances and the like, but its volume is much smaller than the volume of the upstream compartment 3, so that the average MLSS in the reaction vessel 2 is higher than that of the conventional standard activated sludge method. The concentration becomes high, and as a result, the processing speed of the reaction tank 2 is improved, and it becomes possible to accept a higher load of wastewater and to reduce the size of the reaction tank 2. If the opening of the filter is further reduced, the concentration of suspension (SS) flowing into the downstream compartment 4 is further reduced, and there is a possibility that the sedimentation basin can be omitted depending on the discharge standard. That is, the processing speed can be increased while downsizing or omitting the equipment that was indispensable in the conventional standard activated sludge method.

Secondly, since the filter has a larger opening than the filtration membrane used in the conventional membrane separation active sludge method, clogging and filtration resistance of the filter due to activated sludge flocs and floating microorganisms are reduced. .. This improves the permeation flux. In addition, the labor cost for cleaning the membrane is significantly reduced. In terms of equipment, the same equipment as the standard activated sludge method, in which the mixed solution of the downstream section 4 is allowed to flow down into the settling basin 10 by natural flow, does not require special equipment such as penetrating the wall or sucking with a pump. is there. That is, the cost reduction merit over the conventional membrane separation activated sludge method outweighs the demerit that a sedimentation basin is required in principle.

Thirdly, the opening of the woven fabric is constant unlike the non-woven fabric. Thereby, the opening can be easily set in advance according to the particle size of the suspension in the wastewater or the target value of the MLSS concentration in the upstream section 3. Since the fibers of the woven fabric are one layer and the gaps are not intricate like the non-woven fabric, it is easy to wash the clogged suspension. That is, the MLSS concentration in the reaction vessel can be increased and the treatment speed can be increased by a means that is much easier to maintain and manage than the conventional activated sludge method incorporating a non-woven fabric.

According to the wastewater treatment apparatus 1 of the present embodiment that achieves the above effects, a simpler design or maintenance is achieved as compared with the activated sludge method or the method aiming at high MLSS concentration based on the activated sludge method. On the other hand, the MLSS concentration in the upstream compartment 3 which occupies most of the volume of the reaction tank 2 can be maintained high, and therefore the MLSS concentration in the reaction tank 2 can be maintained high. As a result, it is possible to provide an apparatus capable of simpler and higher-speed processing.

When the opening of the filter 8 is within the range of 10 μm or more and 200 μm or less, the desired MLSS concentration can be suitably maintained in the upstream compartment 3. Further, among the suspended organic substances in the wastewater, those having a large particle size are selectively filtered to facilitate the high concentration of MLSS.

Since at least a part of the filter 8 is installed above the air diffuser 6, the air aerated from the air diffuser 6 hits the filter 8, and the cleaning effect of the filter 8 can be obtained. For example, the filter 8 can be swung by the force of rising air, whereby the deposits on the surface of the filter 8 can be peeled off.

According to the U-shaped filter 8, since the shape of the lower portion is rounded, damage (tear, etc.) of the filter 8 can be prevented. Further, since the upper surface 11a is open, maintenance of the filter 8 is easy.

Since the volume of the downstream section 4 is smaller than the volume of the upstream section 3, the volume of the upstream section 3 for aerobic treatment can be secured as large as possible.

Next, with reference to FIG. 3, the wastewater treatment system SA to which the wastewater treatment apparatus 1A according to the second embodiment is applied will be described. The difference between the wastewater treatment device 1A and the wastewater treatment device 1 of the first embodiment is that the downstream section is an aeration tank on the downstream side of the upstream section 3 instead of the reaction tank 2 provided with the downstream section 4. The point is that the reaction tank 2A provided with 14 is provided. The volume of the downstream section 14 is larger than the volume of the downstream section 4. The volume of the downstream compartment 14 is, for example, equivalent to the volume of the upstream compartment 3. The downstream section 14 is provided with an air diffuser 16 and a microbial attachment carrier 17. The air diffuser 16 may be the same as the air diffuser 6, or may be of a different type from the air diffuser 6. The reaction tank outflow line L2 and the blower 7 are connected to the air diffuser 16. The blower 7 for the air diffuser 6 in the upstream compartment 3 and the blower 7 for the air diffuser 16 in the downstream compartment 14 may be shared. The microbial attachment carrier 17 is, for example, a fixed bed type carrier.

In the wastewater treatment apparatus 1A provided with such a reaction tank 2A, when a large amount of floating bacteria and small flocs are generated, the function of being taken up by activated sludge flocs and settling and separating in the settling basin 10 is not sufficiently exhibited. Is prevented. That is, the downstream section 14 is not agitated but an aeration tank, and the microbial attachment carrier 17 is provided in the downstream section 14, so that a biofilm is formed on the microbial attachment carrier 17 in the downstream section 14. Floating microorganisms and small activated sludge flocs that have flowed from the upstream compartment 3 through the filter 8 into the downstream compartment 14 are taken up by the biofilm as they pass near the microbial attachment carrier 17. As a result, the load of suspension on the settling basin 10 is reduced. This raises the possibility that the settling basin 10 can be made smaller or omitted. Further, the aeration tank provided with the microbial attachment carrier 17 is also effective for removing ammonia (promoting nitrification).

In the wastewater treatment system SA, if the performance of the microbial adhesion carrier 17 is good, the sedimentation basin 10 may be omitted. Although not shown, the same filter 8 as the wastewater treatment system S (see FIG. 1) and the same structure as the downstream section 4 may be installed further downstream of the downstream section 14. As the microorganism-adhering carrier 17, a floating carrier such as a sponge cube may be used.

Next, with reference to FIG. 4, the wastewater treatment system SB to which the wastewater treatment apparatus 1B according to the third embodiment is applied will be described. The difference between the wastewater treatment device 1B and the wastewater treatment device 1 of the first embodiment is that the first section is located upstream of the upstream section 3 instead of the reaction tank 2 composed of the upstream section 3 and the downstream section 4. The point is that the reaction tank 2B provided with the (stirring tank) 21 is provided. The reaction tank 2B includes a first compartment 21, a second compartment (upstream compartment) 22, and a third compartment (downstream compartment) 23 in this order from the upstream side, and is composed of three compartments. A stirrer 20 is installed in the first section 21, but an air diffuser is not installed. By providing only the stirrer 20, the first compartment 21 is a stirrer tank without forced oxygen supply. The first compartment 21 is, in other words, an oxygen-free tank. The configurations in the second compartment 22 and the third compartment 23 are the same as the configurations in the upstream compartment 3 and the downstream compartment 4 of the wastewater treatment apparatus 1. A partition wall 5 and a filter 8 are provided between the second section 22 and the third section 23. Further, a partition wall (another partition wall) 19 and a filter (another filter) 18 are also provided between the first section 21 and the second section 22. The filter 18 may be the same as the filter 8 but may be different. In particular, the opening of the filter 18 is set to an appropriate size for the purpose of selectively holding a large particle size of suspended organic matter in wastewater in the first compartment 21. The opening of the filter 18 may be, for example, 100 μm or more and 200 μm or less. Since aeration is not performed in the first section 21, it is effective to increase the opening of the filter 18 from the viewpoint of preventing clogging. The filter 18 is supported by the same structure as the filter 8. Most of the filter 18 is located above the air diffuser 6 of the second compartment 22. Only the upstream end of the filter 18 is located in the first compartment 21. The partition wall 19 and the filter 18 are provided substantially symmetrically with respect to the partition wall 5 and the filter 8 with respect to the second section 22.

Further, a return pump 26 is installed in the third section 23, and a return line L5 for returning the mixed solution in the third section 23 to the first section 21 by the return pump 26 is provided. One end of the return line L5 is connected to the return pump 26, and the other end of the return line L5 is open toward the first section 21. The return amount in the return pump 26 can be appropriately changed depending on the amount of wastewater, the concentration of the object to be treated in the wastewater, or the MLSS concentration.

In the wastewater treatment apparatus 1B provided with such a reaction tank 2B, ammonia nitrogen is oxidized (nitrified) and converted into nitrate nitrogen in the second compartment 22 which is the upstream compartment. When the mixture containing nitrate nitrogen is returned to the first compartment 21 by the return pump 26 and the return line L5, the nitrate nitrogen can be converted to nitrogen gas in the first compartment 21. That is, the denitrification treatment is performed in the first section 21. In the wastewater treatment apparatus 1B, the microorganisms in the first compartment 21 for denitrification treatment and the second compartment 22 for oxidizing organic nitrogen and ammonia nitrogen are compared with the circulation modified method which is a general nitrification denitrification method. Microorganisms are difficult to mix with the filter 18. In this respect, microorganisms suitable for the function of each tank are accumulated, and the removal of nitrogen compounds is accelerated. The first compartment 21 can also be used for the accumulation of phosphorus-accumulating bacteria.

Further, when the opening of the filters 8 and 18 is within the range of 10 μm or more and 200 μm or less, the desired MLSS concentration can be suitably maintained in the first section 21 and the second section 22. In addition, when biological nitrogen removal or phosphorus removal is performed, since it is desired to supply as much organic matter as possible to the first compartment 21, suspension in wastewater including those having a large particle size that can be removed by pre-precipitation. It is conceivable that all the organic matter will flow in. In that case, the first compartment 21 may be filled with suspension and the filter 18 may be clogged. By setting the opening of the filter 18 to, for example, 100 μm or more and 200 μm or less, fine suspensions can flow down, and suspended organic substances useful for denitrification and accumulation of phosphorus-accumulating bacteria and microorganisms attached thereto are selectively selected first. It can be held in compartment 21.

Next, with reference to FIG. 5, the wastewater treatment system SC to which the wastewater treatment apparatus 1C according to the third embodiment is applied will be described. The difference between the wastewater treatment apparatus 1C and the wastewater treatment apparatus 1 of the first embodiment is that the wastewater treatment apparatus 1C is provided with a rear stage reaction tank 33 having the same configuration as the reaction tank 2, and is provided on the upstream side of the rear stage reaction tank 33. (Second reaction tank) 30 is further provided. The first stage reaction tank 30 includes a first compartment (second upstream compartment) 31 provided on the upstream side, a second compartment (second downstream compartment) 32 provided on the downstream side of the first compartment 31, and a second compartment. A partition wall (second partition) 37 that separates the first section 31 and the second section 32 is included. A filter portion (second filter) 38 made of woven fabric is provided between the first section 31 and the second section 32. The partition wall 37 and the filter section 38 are configured so that the mixed liquid flowing down from the first section 31 to the second section 32 passes through the filter section 38. The filter portion 38 is not U-shaped, but is provided so as to be continuous with the filter portion 38. Further, a slow sand filter 35 is provided in the first section 31.

A return pump 36 is installed in the downstream section 4 of the subsequent reaction tank 33, and a return line L6 for returning the mixed solution in the downstream section 4 to the first section 31 by the return pump 36 is provided. There is. One end of the return line L6 is connected to the return pump 36, and the other end of the return line L6 is open toward the first section 31. The return amount in the return pump 36 can be appropriately changed depending on the amount of wastewater, the concentration of the object to be treated in the wastewater, or the MLSS concentration.

In the wastewater treatment apparatus 1C provided with such a first-stage reaction tank 30 and a second-stage reaction tank 33, four sections are provided, and the stirring method is a stirring method in which the first section 31 is not forcibly supplied with oxygen in order from the upstream side. The second section 32 is unstirred, the upstream section 3 which is the third section is aerated, and the downstream section 4 which is the fourth section is not agitated. The second section 32 and the upstream section 3 may be connected by a pipe instead of a partition.

As described above, the wastewater treatment apparatus 1C includes the front stage reaction tank 30 and the rear stage reaction tank 33, and a total of four sections are provided. Denitrification treatment is performed in the first compartment 31 (second upstream compartment of the second reaction tank), and oxidation of organic nitrogen and ammonia nitrogen is performed in the upstream compartment 3 (upstream compartment of the reaction tank). This eliminates the need to match the shape of the first compartment 31 with the shape of the upstream compartment 3 (for example, a rectangle). For example, the first compartment 31 can be a circular slow sand stirring tank. Slow sand stirring contributes to the improvement of the denitrification rate. That is, in the first compartment 31, the denitrifying bacteria predominate and the denitrification priority treatment is performed, and in the upstream compartment 3, the nitrifying bacteria predominate and the nitrification priority treatment is performed. The first section 31 is not limited to the circular water tank, and may have a shape such that the corners of the square water tank are chamfered.

Although the embodiment of the present invention has been described, the present invention is not limited to the above embodiment. For example, the mode in which the filter is installed can take any modification. For example, as shown in FIG. 6, the partition wall 5 may be provided only in a part of the bottom portion, and may be a vertical filter portion 39 such that the partition wall 5 continuously protrudes above the water surface. In this case, in order to eliminate or prevent clogging of the filter unit 39, cleaning air or spray may be provided. A plurality of filters 8 may be provided between the upstream section and the downstream section. In that case, for example, the plurality of filters 8 may be installed so as to be arranged in parallel. A plurality of notches 5a and a plurality of notches 15a are provided according to the number of filters 8. Similarly, a plurality of filters 18 (another filter) may be provided between the stirring tank and the upstream section.

(Experimental example)

Of the above-described embodiments, a laboratory-scale experiment was carried out on the wastewater treatment apparatus 1 of the first embodiment, and the effect was confirmed. Specifically, a scaled-down reaction tank having a capacity of 3.2 liters was prepared, and the reaction tank was divided into 2.6 liters as the upstream compartment and 0.6 liters as the downstream compartment. A filter with an opening of 33 μm was installed in the partition. Aeration was performed in the upstream compartment. As raw water, soluble starch and polypeptone were dissolved at a ratio of 10: 1, and artificial wastewater containing 40 mgN / L nitrogen and 8 mgP / L phosphorus compound was passed through.

FIG. 7 (a) shows the BOD volume load and the TOC volume load, FIG. 7 (b) shows the MLSS concentration, and FIG. 7 (c) shows the raw water and the quality of the outflow water from the reaction tank. In each figure, the change with time with the number of operating days is shown. In this experiment, the settling of activated sludge flocs also occurred in the downstream section, so the quality of the runoff from the reaction tank corresponds to the quality of the runoff from the settling basin 10 in the actual machine. As a result of the experiment, a high concentration of MLSS was achieved without the sludge return step, and an organic matter removal performance of 95% or more was achieved with a ^{load of 1.2 kg / m 3 / day of BOD volume load.} The SS concentration of the effluent from the reaction vessel when the highest load was applied was 10 mg / L, but the SS concentration at the filter outlet (downstream compartment) estimated from the amount of sediment in the downstream compartment at that time was , It was found that the filter alone was 20 mg / L or less.
・ 24th day of operation 16mg / L
・ 28th day of operation 20mg / L

Subsequently, the mounting structure of the filter 8 will be described with reference to FIGS. 8 to 10. As shown in FIGS. 8 and 9 (a), the upstream section 3 is provided with a holding plate 40 for supporting the filter 8 and holding the shape of the filter 8. The pressing plate 40 extends in the longitudinal direction of the reaction tank 2 from the upstream side compartment 3 to the downstream side compartment 4. The holding plate 40 has a height including the water surface, and extends substantially horizontally so that its cross section perpendicular to the longitudinal direction forms a U shape. The downstream end of the holding plate 40 is fitted into the notch 5a of the partition wall 5. The upstream end of the holding plate 40 is fitted into the notch 15a of the support (supporting portion) 15. The holding plate 40 is bridged between the support 15 and the partition wall 5. The support 15 is a support portion for supporting the pressing plate 40. The upstream end of the holding plate 40 may be supported by another supporting member installed in the reaction tank 2.

The pressing plate 40 includes a perforated portion 41 having a large number of holes through which the mixed liquid can pass, and a non-perforated portion 42 in which such holes are not formed. For the perforated portion 41, for example, a punching metal made of SUS (stainless steel) is used. A plate made of SUS is used for the non-perforated portion 42. As shown in FIGS. 9A and 10A, the perforated portion 41 is provided on the upstream side portion of the pressing plate 40, and the non-perforated portion 42 is provided on the downstream side portion of the pressing plate 40. ing. The perforated portion 41 is located at least in the upstream section 3. The perforated portion 41 may be provided in the entire area of the upstream side section 3 (above the air diffuser portion 6). The non-perforated portion 42 is located at least in the downstream section 4. The pressing plate 40 may be installed so that the non-perforated portion 42 is pressed against the edge portion of the notch 5a.

A filter 8 is attached to the outside of the holding plate 40. As shown in FIG. 9B, the filter 8 is attached to the outside of the perforated portion 41 of the holding plate 40, and is installed along the U-shaped edge portion of the notch 5a. The filter 8 may be installed along the U-shaped edge of the notch 15a. In other words, the filter 8 is sandwiched between the pressing plate 40 and the partition wall 5 and the support 15, and is in close contact with them. When the holding plate 40 floats, a holding wood, a rubber stopper, or the like may be inserted.

By using one continuous pressing plate 40 and attaching the filter 8 to the outside of the pressing plate 40 in this way, it is possible to prevent the thin filter 8 from being dented inward by water pressure and being attached to each other. Therefore, it is possible to prevent the permeation efficiency from being lowered. For example, in the mounting structure in which the holding plate is provided only in the notch 5a of the partition wall 5, since the filter 8 is thin, it is considered that the filters 8 stick to each other due to water pressure and the permeation efficiency is lowered. However, according to the above embodiment, since the filter 8 is supported by the pressing plate 40 and maintains its shape, the transmitted light coefficient can be maintained.

Since the holding plate 40 is bridged between the support 15 and the partition wall 5 and supported by the support 15 and the partition wall 5, the dent of the filter 8 can be reliably prevented and stable at least in the upstream section 3. Permeation efficiency can be obtained.

By installing the non-perforated portion 42 so as to hit the notch 5a while allowing the mixed liquid to permeate through the perforated portion 41 of the pressing plate 40, the filter 8 can be firmly suppressed and sludge can be prevented from flowing out from the gap. Here, if the portion corresponding to the notch 5a is perforated, it is conceivable that the filter floats at the portion of the hole depending on the hole diameter and the mounting method, and sludge flows out from the gap. Since there is no hole in the portion corresponding to the notch 5a, the outflow of such sludge is prevented.

The configuration of the holding plate can be changed as appropriate. The presser plate preferably includes at least a perforated portion arranged in the upstream side compartment 3 and at least a non-perforated portion arranged in the downstream side compartment 4. The holding plate may be made of a material other than SUS. As the material of the pressing plate, it is preferable to have appropriate flexibility. For example, as shown in FIG. 10B, the holding plate 50 made of a wire including the perforated portion 51 and the non-perforated portion 52 may be used. As shown in FIG. 10 (c), the holding plate 60 made of a wire mesh including the perforated portion 61 and the non-perforated portion 62 may be used.

The filter mounting structure using such a holding plate may be applied to the mounting of the filter 8 and the filter 18 of each of the above-described embodiments.

1 Wastewater treatment equipment 1A, 1B, 1C Wastewater treatment equipment 2 Reaction tank 2A, 2B Reaction tank 3 Upstream compartment 4 Downstream compartment 5 Partition wall (partition)
5a Notch 6 Air diffuser 8 Filter 11a Top 14 Downstream compartment 15 Support (support)
15a Notch 16 Air diffuser 17 Microbial adhesion carrier 18 Filter (another filter)
19 Partition wall (another partition wall)
21 First section (stirring tank)
22 Second section (upstream section)
23 Third section (downstream section)
26 Return pump 30 First stage reaction tank (second reaction tank)
31 First section (second upstream section)
32 Second section (second downstream section)
33 Post-stage reaction tank (reaction tank)
35 Slow sand filter 36 Return pump 37 Partition wall (second partition)
38 Filter section (second filter)
39 Filter section (filter)
40 Press plate 41 Perforated portion 42 Non-perforated portion 50 Press plate 51 Perforated portion 52 Non-perforated portion 60 Press plate 61 Perforated portion 62 Non-perforated portion L5, L6 Return line S Wastewater treatment system SA, SB, SC Wastewater treatment system

Claims (11)

An activated sludge method is applied in which a mixed solution containing microorganisms and wastewater contained in a reaction tank is aerated through an air diffuser provided in at least a part of the reaction tank to treat an object to be treated in the wastewater. The wastewater treatment equipment used
The reaction tank
An upstream section provided on the upstream side based on the drainage flow,
The downstream section provided on the downstream side of the upstream section and the downstream section
A partition that separates the upstream section from the downstream section,
Including at least the air diffuser provided in the upstream section,
A filter made of woven fabric is provided between the upstream section and the downstream section.
The partition and the filter are configured so that the mixed solution flowing down from the upstream section to the downstream section passes through the filter .
The partition portion is provided with a U-shaped notch that is open upward from above the water surface to below the water surface of the mixed solution.
The filter is installed along the U-shaped edge of the notch, extends in a U-shaped cross section at a height including the water surface in the upstream section and the downstream section, and is above the water surface. A wastewater treatment device that is open only at the upper surface located in and the downstream end located in the downstream section. An activated sludge method is applied in which a mixed solution containing microorganisms and wastewater contained in a reaction tank is aerated through an air diffuser provided in at least a part of the reaction tank to treat an object to be treated in the wastewater. The wastewater treatment equipment used
The reaction tank
An upstream section provided on the upstream side based on the drainage flow,
The downstream section provided on the downstream side of the upstream section and the downstream section
A partition that separates the upstream section from the downstream section,
Including at least the air diffuser provided in the upstream section,
A filter made of woven fabric is provided between the upstream section and the downstream section.
The partition and the filter are configured so that the mixed solution flowing down from the upstream section to the downstream section passes through the filter.
The partition portion is provided with a U-shaped notch that is open upward from above the water surface to below the water surface of the mixed solution.
The notch is fitted with a holding plate having a U-shaped cross section that extends at a height including the water surface and has a large number of holes through which the mixed solution can pass.
The filter is attached to the outside of the holding plate and installed along the U-shaped edge of the notch, and has a U-shaped cross section at a height including the water surface in the upstream section and the downstream section. Wastewater treatment equipment that extends like a letter. An activated sludge method is applied in which a mixed solution containing microorganisms and wastewater contained in a reaction tank is aerated through an air diffuser provided in at least a part of the reaction tank to treat an object to be treated in the wastewater. The wastewater treatment equipment used
The reaction tank
An upstream section provided on the upstream side based on the drainage flow,
The downstream section provided on the downstream side of the upstream section and the downstream section
A partition that separates the upstream section from the downstream section,
Including at least the air diffuser provided in the upstream section,
A filter made of woven fabric is provided between the upstream section and the downstream section.
The partition and the filter are configured so that the mixed solution flowing down from the upstream section to the downstream section passes through the filter.
A wastewater treatment device in which the volume of the downstream section is smaller than the volume of the upstream section, and the downstream section is a non-stirring tank. The wastewater treatment apparatus according to any one of claims 1 to 3, wherein the opening of the filter is within the range of 10 μm or more and 200 μm or less. The wastewater treatment apparatus according to any one of claims 1 to 4, wherein at least a part of the filter is installed above the air diffuser. A support portion provided in the upstream section for supporting the holding plate is further provided.
The support portion is provided with a U-shaped notch that is open upward from above the water surface to below the water surface of the mixed solution.
The holding plate is bridged between the support portion and the partition portion, the upstream end portion is fitted into the notch of the support portion, and the downstream end portion is the partition portion. The wastewater treatment apparatus according to claim 2 , which is fitted in a notch. The wastewater treatment apparatus according to claim 6, wherein the holding plate includes at least a perforated portion located in the upstream section and a non-perforated portion located in at least the downstream section. The wastewater treatment apparatus according to claim 1, 2, 6, or 7 , wherein the air diffuser and a microbial adhesion carrier are provided in the downstream section. The reaction vessel is further provided on the upstream side of the upstream compartment and further includes a stirrer without forced oxygen supply.
A return pump is provided in the downstream section.
The wastewater treatment apparatus according to claim 3 , further comprising a return line including one end connected to the return pump and the other end opening toward the inside of the stirring tank. Another partition and another filter made of woven cloth are provided between the stirring tank and the upstream section, and the other partition and the other filter are provided from the stirring tank. The mixed solution flowing down to the upstream compartment is configured to pass through the filter, and the opening of the other filter is the mesh of the filter between the upstream compartment and the downstream compartment. The wastewater treatment apparatus according to claim 9, which is larger than the opening. A second reaction tank provided on the upstream side of the reaction tank is further provided.
Note that the second reaction tank is
A second upstream section provided on the upstream side based on the drainage flow,
The second downstream side section provided on the downstream side of the second upstream side section,
Includes a second partition that separates the second upstream compartment from the second downstream compartment.
A second filter made of woven fabric is provided between the second upstream side section and the second downstream side section.
The second partition and the second filter are configured such that the mixed liquid flowing down from the second upstream section to the second downstream section passes through the second filter.
A slow sand filter is provided in the second upstream section.
A return pump is provided in the downstream section of the reaction vessel.
The wastewater treatment apparatus according to claim 3 , further comprising a return line including one end connected to the return pump and the other end opening toward the inside of the second upstream section.

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