JP7654121B2 - Water treatment equipment - Google Patents

Description

The present invention relates to a water treatment device, and in particular to a water treatment device suitable for use in water treatment for treating septic tank sludge and sewage sludge and discharging treated water into a sewer system.

In order to discharge treated water obtained by treating raw water containing septic tank sludge and human waste sludge into a sewer system, it is necessary for the treated water to satisfy sewage discharge standards, but sewage discharge standards are generally known to be more lenient than standards for discharge into public water bodies. For example, standards for discharge into public water bodies are BOD (biochemical oxygen demand) 10 mg/L, N (nitrogen) 10 mg/L, and SS (suspended solids) 10 mg/L, while sewage discharge standards are BOD 600 mg/L, T-N 240 mg/L, and SS 600 mg/L.

A conventional method for treating effluent from a sewer system is, for example, to remove waste (screen waste) contained in human waste and dilute the water to the sewage discharge standard before discharging it. In this case, the dilution rate is generally about 10 to 20 times, which results in excessive amounts of diluted water and effluent from the sewer system.

Another treatment method is to separate the sewage and other waste into solids and liquids using a dehydrator, dilute the separated liquid, and then discharge it into the sewer system. In this case, the separated liquid contains significantly less BOD, SS, nitrogen, and other components than the sludge-removed sewage, so the dilution ratio can generally be about 3 to 8 times. However, there is a problem in that the water quality of the separated liquid varies, and so the amount of dilution water also varies greatly depending on the water quality.

Furthermore, the method of separating sewage and other waste into solid and liquid form using a dehydrator ultimately results in discharging 4 to 9 times the amount brought in, so its effectiveness in reducing the amount discharged into the sewer system is limited. Because soluble components are difficult to remove with solid-liquid separation, if the sewage and other waste contains a large amount of soluble components, the quality of the dehydrated separated liquid may deteriorate, making it necessary to increase the amount of dilution water. There are also cases where regulations on the amount of discharged water make it impossible to meet sewage removal standards.

As another method for more reliably reducing the amount of dilution water and discharge water, a method that combines solid-liquid separation and biological treatment can be considered. For example, JP 61-50691 A (Patent Document 1) describes a method in which the solids obtained by solid-liquid separation of septic tank sludge are mixed with human wastewater and subjected to coagulation treatment, and the separated liquid is then subjected to biological treatment.

Japanese Unexamined Patent Publication No. 61-50691

The method described in Patent Document 1 does not state where the biologically treated water is discharged, but since the BOD of the treated liquid in Example 1 can be reduced to 10 mg/L or less, it can be inferred that this treatment method is intended for discharge into public water areas.

However, as mentioned above, sewage discharge standards tend to be looser than standards for discharge into public water bodies, so the water quality mentioned in Patent Document 1 is not required for treated water to be discharged into sewers. Therefore, it is desirable to propose a more efficient and appropriate treatment method that meets the water quality standards for discharge into sewers.

On the other hand, in water treatment that combines solid-liquid separation and biological treatment as described in Reference 1, there is a problem in that it is difficult to perform partial treatment to the extent that it meets the sewage discharge standards.

For example, when nitrification-denitrification is used as a biological treatment, it is possible to treat only about 60% of the nitrogen rather than the entire amount, or to nitrify all of the ammonia nitrogen contained in the dehydration separation liquid and then denitrify only 60% of it.

However, when treating about 60% of the nitrogen, about 40% of the nitrate nitrogen remains, and denitrification will occur again in the downstream settling tank where the anaerobic conditions are created, and the nitrogen gas generated will cause the sludge to float, which may prevent sufficient solid-liquid separation in the settling tank. If solid-liquid separation cannot be achieved in the settling tank, the MLSS (activated sludge concentration) of the nitrification/denitrification tank cannot be maintained, and the treatment itself will deteriorate.

If all of the ammonia nitrogen contained in the dehydration separation liquid is nitrified, the tank capacity will be too large, the aeration air volume required for nitrification will be too large, and hydrogen donors such as methanol and ethanol, which are necessary for denitrification, will need to be added, resulting in excessive equipment and operating costs compared to the required treated water quality.

Another method is to use biological treatment using the activated sludge method to roughly treat the treated water until the water quality falls below the sewage discharge standard, then dilute the water and discharge it into the sewer. In this case, it is possible to solve the above-mentioned problems caused by incomplete biological treatment using nitrification/denitrification by treating the water with a high BOD load that does not cause nitrification, but this requires an appropriate tank capacity for biological treatment using the activated sludge method, and the aeration air volume to deal with the high BOD load is also excessive, so this is not an efficient method of treatment.

In consideration of the above problems, the present invention provides a water treatment device that can more efficiently obtain treated water that meets sewage removal standards with a smaller amount of dilution water.

As a result of intensive research conducted by the present inventors to solve the above problems, it was discovered that it is effective to subject at least a portion of the dehydrated separated liquid obtained by separating solids and liquids from water to be treated, which contains at least one of septic tank sludge and sewage sludge, using a dehydrator, to a specific biological treatment and then dilution treatment.

In one aspect, the water treatment method according to the embodiment of the present invention, which was completed based on the above findings, is a water treatment method that includes using a dehydrator to separate water to be treated, which contains at least either septic tank sludge or sewage sludge, into separated sludge and dehydrated separated liquid, subjecting at least a portion of the dehydrated separated liquid to biological treatment using a non-blocking biofilm method that includes at least any one of the trickling filter method, fluidized carrier method, rotating disk method, and fixed bed method, and diluting the biologically treated water obtained by the biological treatment so as to meet the sewage removal standards.

In one embodiment of the water treatment method according to the present invention, the biological treatment includes treating the water by connecting in parallel or in series a biological treatment tank for removing BOD from the dehydrated separated liquid and a biological treatment tank for removing nitrogen from the dehydrated separated liquid.

In another embodiment of the water treatment method according to the present invention, the biological treatment includes stepwise inflow of the dewatered separated liquid into biological treatment tanks connected in series in two or more stages.

In yet another embodiment of the water treatment method according to the present invention, the biological treatment includes supplying the dehydrated separated liquid to a trickling filter to aerobicly decompose the BOD in the dehydrated separated liquid and nitrify the ammonia nitrogen to obtain biologically treated water, circulating the biologically treated water to the trickling filter, and disposing carriers in a circulation tank that contains the circulating water to be circulated to the trickling filter, and allowing the denitrification reaction to proceed by microorganisms attached to the carriers.

In one aspect, the water treatment device according to the embodiment of the present invention is a water treatment device that includes a dehydrator that dehydrates the water to be treated, which contains at least one of septic tank sludge and sewage sludge, and separates it into separated sludge and dehydrated separated liquid, a biological treatment tank that performs biological treatment on at least a portion of the dehydrated separated liquid using a non-blocking biofilm method that includes at least one of the trickling filter method, the fluidized carrier method, the rotating disk method, and the fixed bed method, and a dilution tank that dilutes the biologically treated water obtained by the biological treatment so that it meets the sewage removal standards.

In another embodiment of the water treatment device according to the present invention, a membrane carrier having a structure in which the dehydrated separated liquid and oxygen permeate in opposing directions across the membrane surface is disposed in the biological treatment tank.

In yet another embodiment of the water treatment device according to the present invention, the membrane carrier includes a support and a membrane supported by the support, the membrane has a loop shape that covers the support, the dehydrated separated liquid permeates from the outer surface of the membrane, oxygen permeates from a space formed on the inner surface of the membrane to the outer surface of the membrane, and an opening is formed in the membrane for discharging sludge peeling off from the inner surface of the membrane to the outside of the space.

In yet another embodiment, the water treatment device according to the present invention includes an inflow means for inflowing the dehydrated separated liquid in steps into each of the biological treatment tanks, which include two or more treatment tanks connected in series, and a control means for controlling the step ratio of the dehydrated separated liquid to be inflowed into the biological treatment tank based on the volume load of the biological treatment tank and the water quality of the dehydrated separated liquid or the biological treatment water.

The present invention provides a water treatment device that can more efficiently obtain treated water that meets sewage removal standards with a smaller amount of dilution water.

1 is a schematic diagram illustrating a water treatment device according to a first embodiment. FIG. 11 is a cross-sectional view showing an example of a membrane carrier provided in a water treatment device according to a second embodiment. FIG. 11 is a side view showing an example of a membrane carrier included in a water treatment device according to a second embodiment. FIG. 11 is a schematic diagram illustrating a water treatment device according to a third embodiment. FIG. 13 is a schematic diagram illustrating a water treatment device according to a fourth embodiment. FIG. 13 is a schematic diagram illustrating a water treatment device according to a fifth embodiment. FIG. 13 is a schematic diagram illustrating a water treatment device according to a sixth embodiment. FIG. 13 is a schematic diagram illustrating a water treatment device according to a seventh embodiment. FIG. 23 is a schematic diagram illustrating a water treatment device according to a modified example of the seventh embodiment. 1 is a graph showing the results of confirming the transition of the BOD set load in each tank when the water treatment method of the embodiment is used.

<Water treatment method>
A water treatment method according to an embodiment of the present invention includes subjecting water to solid-liquid separation, which contains at least either septic tank sludge or sewage sludge, to separated sludge and separated liquid, subjecting at least a portion of the separated liquid to biological treatment using a non-blocking biofilm method which includes at least any one of a trickling filter method, a fluidized carrier method, a rotating disc method, and a fixed bed method, and diluting the biologically treated water so that it meets the sewage removal standards.

(Water to be treated)
The water to be treated is not particularly limited as long as it contains at least one of septic tank sludge and human waste sludge. For example, in the case of using a mixture of human waste sludge and septic tank sludge as the water to be treated, it is preferable to separate the human waste sludge and the septic tank sludge from each other in solid-liquid separation.

(Solid-liquid separation)
For the solid-liquid separation treatment, various solid-liquid separation devices can be used, but for example, it is preferable to separate the separated sludge and the separated liquid using a dehydrator in terms of equipment and operation costs. Furthermore, it is more preferable to perform a concentration treatment on the water to be treated before solid-liquid separation. As a concentration method, both gravity concentration and mechanical concentration are effective concentration methods.

By performing a concentration process in which a polymer flocculant is added before solid-liquid separation, the sludge concentration (TS) of the concentrated sludge can be increased to a maximum of approximately 10-12% by mass. If the concentrated sludge is further dehydrated using a dehydrator, dehydrated sludge (separated sludge) with a low moisture content of 70% or less can be obtained, resulting in a more significant sludge volume reduction effect. As this dehydrated sludge with a low moisture content has a high calorie content, it can be spontaneously combusted without auxiliary fuel during incineration, resulting in energy savings and low costs.

(Biological treatment)
Biological treatment using the biofilm process can be roughly divided into those that require a periodic cleaning process for the carrier, and those in which the amount of biofilm is autonomously controlled during the treatment. The former includes the biofilm filtration method, while the latter includes the trickling filter method, the fluidized carrier method, the rotating disk method, and the fixed bed method (contact oxidation method).

Among these, it is preferable to use a biofilm process in which the amount of biofilm is autonomously controlled during the treatment as the biological treatment according to the embodiment of the present invention, and this is defined in this specification as a "non-blocking biofilm process." In particular, among the non-blocking biofilm processes, the trickling filter process and the fluidized carrier process can be operated stably even with a BOD volume load of 1 kg-BOD/ ^m3 /d or more, and are effective when the site area is limited. Specific examples of biological treatments included in this "non-blocking biofilm process" are described below.

-Trickling filter method-
The trickling filter method is one of the aerobic biochemical treatment methods, in which the action of microorganisms attached to the surface of the filter media decomposes organic matter in the treated water (separate liquid) that is sprayed to obtain biologically treated water. It is generally known that the surface of the biofilm becomes aerobic and the inside of the biofilm becomes anaerobic in the trickling filter method. For this reason, when the trickling filter is operated with a load that allows nitrification to proceed, the nitrification reaction proceeds on the surface of the biofilm and the denitrification reaction proceeds inside the biofilm, which is characterized by its excellent nitrogen removal efficiency.

There are no particular limitations on the specific configuration of the carrier, the trickling part, etc. used in the trickling filter. Any material may be used for the carrier as long as microorganisms can adhere to it, and representative examples include plastic and crushed stone. The shape of the carrier may be any shape, such as a plate, sphere, cylinder, rectangular parallelepiped, hollow, etc. The carrier filling rate relative to the volume of the reaction vessel is preferably 40 to 80%, and more preferably 50 to 70%. In the case of a membrane carrier, it is preferable to fill the membrane so that the surface area of the membrane relative to the volume of the reaction vessel is 0.05 to 0.15 ^m2 / ^m3 .

In order to carry out biological treatment more efficiently and stably, it is preferable to place a membrane carrier in the trickling filter that has a structure in which the separated liquid after solid-liquid separation that is supplied to the trickling filter and the oxygen in the trickling filter permeate opposite each other across the membrane surface.

The membrane carrier has an area rich in BOD and poor in oxygen on the separated liquid supply side, while the oxygen supply side is an area poor in BOD and rich in oxygen. Therefore, it is possible to create conditions suitable for the denitrification reaction to proceed on the supply side of the water to be treated (separated liquid), while creating conditions suitable for the nitrification reaction on the oxygen supply side, making it more suitable than other carriers in terms of its excellent nitrogen removal performance.

In contrast, in the case of normal granular carriers, BOD, nitrogen, and oxygen are supplied to the biofilm on the carrier surface from the same direction, so at a load of 1 to 1.5 kg-BOD/ ^m3 / ^d , the oxygen is consumed by the oxidation of BOD, and the nitrification-denitrification reaction may not proceed easily. In addition, compared to treatment methods that use carriers of other shapes, membrane carriers have the advantage that they can be operated stably without clogging even under high load conditions of 1.5 kg-BOD/m3/d or more. This is because in membrane carriers, the carriers are arranged vertically, and biofilms that peel off from the carriers are discharged outside the tank without clogging between the carriers.

The separated liquid after solid-liquid separation is transferred to the upper part of the trickling filter bed using a siphon or the like before it is introduced into the trickling filter bed. When sprinkling, it is sufficient that the separated liquid is sprinkled over the entire filter bed, and any sprinkling device can be used, such as a perforated plate, a sprinkler-type or spiral-type nozzle, or a self-propelled rotating sprinkler.

- Fluid carrier method -
The floating carrier method is a method in which carriers are placed in a biological treatment tank and the carriers are allowed to flow within the biological treatment tank, thereby bringing microorganisms into contact with organic matter and oxygen in the water to be treated, thereby obtaining biologically treated water. A biological treatment tank using the floating carrier method may be newly constructed, or carriers, an aeration device, etc. may be installed in an existing storage tank, etc. There are no particular limitations on the carriers used as floating carriers, but the following are some typical examples.

The carrier to be used may be any carrier that can be attached to microorganisms and can be fluidized by aeration. The material of the carrier may be any carrier that can be fluidized by aeration, for example, plastic (polyurethane (PU), polyethylene (PE), polyethylene glycol (PEG), polyvinyl alcohol (PVA)), wood chips, sand, etc. are used. The carrier may have a sponge-like, gel-like, solid, etc. shape. The carrier may have any shape, such as a spherical, cubic, cylindrical, honeycomb, etc. Among them, by using a bonded immobilized carrier that attaches microorganisms to the outer surface of the carrier, microorganisms suitable for the environment in the biological treatment tank can be attached to the carrier, and the biological treatment can be performed more stably without being affected by fluctuations in the properties of the inflow water. The filling rate of the carrier is preferably 20 to 40% from the viewpoint of fluidity and performance. A filling rate of 20% or more can hold a large amount of microorganisms in the tank, and a filling rate of 40% or less can create appropriate voids to maintain good fluidity. The BOD load in the fluidized carrier process is preferably 0.5 to 5.0 kg-BOD/m ³ /d, more preferably 1.0 to 3.0 kg-BOD/m ³ /d. The fluidized carrier process is suitable for cases where an existing aeration tank for activated sludge is utilized.

-Rotating disk method-
The rotating disk method is a method in which a part of a rotating disk is exposed to the water to be treated and the outside air, forming a biofilm on the surface of the disk, and decomposing the organic matter in the water to be treated (separate liquid) to obtain biologically treated water. Since aeration is not performed, there is no need to install a blower that requires air volume adjustment, and there is no need to supply return sludge as in the activated sludge method, so it is advantageous in that simpler equipment can be provided. The BOD load for the rotating disk method is preferably 0.1 to 1.5 kg-BOD/ ^m3 /d, and if an excessive load is applied, excessive microorganisms may adhere to the disk, causing problems such as damage to the rotating shaft.

There are no particular limitations on the material or specific shape of the disk, and any device can be used. For example, the disk can be made of polystyrene foam, plastic, polyvinyl chloride, waterproof plywood, or metal plates such as aluminum, and can be made into a disk shape with a diameter of 1 to 3 m and a thickness of 0.7 to 20 mm.

-Fixed bed method (catalytic oxidation method)-
In the contact oxidation method, a fixed bed carrier is immersed in a reaction tank, and aeration is performed while the water to be treated is passed through the tank, forming a biofilm on the surface of the carrier, which decomposes the organic matter in the water to be treated (separate liquid) to obtain biologically treated water. Since treatment is performed using a biofilm attached to the carrier, there is no need to control the amount of sludge by returning it, as in the activated sludge method, making maintenance and management easier. The BOD load is preferably 0.1 to 1.0 kg-BOD/ ^m3 /d, and operation at a high load may cause the biofilm to swell and clog the contact material.

There are no particular restrictions on the material or specific shape of the carrier for the contact oxidation method, and any device can be used. The carrier can be made of polyethylene, plastic, etc., and can be in any shape, such as a tube, string, net, plate, ball, etc.

(Dilution ratio)
The biologically treated water obtained by the above biological treatment is sent to a dilution tank and mixed with dilution water to be diluted to meet the sewage discharge standard. According to this embodiment, the dilution rate is typically 1 to 4 times, more typically 1 to 3 times, or even 1 to 2 times, so that the amount satisfies the sewage discharge standard. Dilution may be performed continuously, or may be performed only when necessary to meet the sewage discharge standard. This allows more efficient and appropriate treatment in accordance with the water quality standard for discharge into the sewer system to be performed with a smaller amount of dilution water than in the conventional method.

According to this embodiment, by carrying out the above-mentioned biological treatment, the biologically treated water may be treated to such an extent that dilution of the biologically treated water is not necessary. In such a case, it goes without saying that the biologically treated water after biological treatment using a non-blocking biofilm method, including either the trickling filter method or the fluidized bed method, on at least a portion of the separated liquid may be discharged directly into the sewer without dilution.

According to the water treatment method of the embodiment of the present invention, water to be treated, which contains at least one of septic tank sludge and sewage sludge, is subjected to biological treatment using the non-blocking biofilm method described above, and then diluted, so that treated water that can be discharged into the sewer system can be obtained more efficiently and stably with a small amount of dilution water.

In addition, according to the water treatment method of this embodiment, biological treatment is used to treat the separated liquid obtained by solid-liquid separation, so by supplying the amount of phosphorus necessary for the growth of microorganisms in the biological treatment tank, the water quality of the treated water by biological treatment can be maintained at a higher level and stabilized.

In general, in biological treatment, about 1 mg/L of phosphorus is required for a BOD of 100 mg/L. For this reason, it is desirable to supply phosphorus so that this ratio is satisfied for the BOD of the influent (separate liquid). If treatment is good, the phosphorus concentration may be reduced to 1 mg/L or less, preferably 0.7 mg/L or less, and more preferably 0.5 mg/L or less before supplying it.

In particular, when iron- or aluminum-based coagulants are used in the dewatering process of septic tank sludge and sewage sludge, phosphorus is absorbed into the sludge and the phosphorus concentration in the dewatered separated liquid decreases, so adding phosphorus produces treated water with more stable quality. In crude treatment, the supply of nutrients such as phosphorus tends to be overlooked, but a phosphorus deficiency can make it almost impossible to remove BOD, so in fact, even in crude treatment, it is often important to supply phosphorus.

Below, the first to seventh embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are given the same or similar reference numerals. Note that the embodiments shown below are examples of devices and methods for embodying the technical idea of this invention, and the technical idea of this invention does not specify the structure, arrangement, etc. of the components as described below. Furthermore, it is of course possible to combine each configuration described in each of the embodiments shown below with a water treatment device according to another embodiment.

(First embodiment)
As shown in FIG. 1, the water treatment device according to the first embodiment includes a solid-liquid separation device 1 that performs solid-liquid separation of water to be treated, which contains at least one of septic tank sludge and sewage sludge, into separated sludge and separated liquid, a biological treatment tank 2 that performs biological treatment on the separated liquid using a non-blocking biofilm method, i.e., any of the trickling filter method, fluidized carrier method, rotating disk method and fixed bed method, and a dilution tank 3 that dilutes the biologically treated water so that it meets the sewage removal standards.

In an embodiment of treatment (BOD removal type) in which the BOD in the biologically treated water is the basis for determining the dilution ratio, it is preferable to provide a dehydrator as the solid-liquid separation device 1 and a trickling filter bed as the biological treatment tank 2. Treatment conditions for the trickling filter can be, for example, a BOD volumetric loading of 0.5 to 7.5 kg-BOD/ ^m3 /d, and in another embodiment, 1.0 to 5.0 kg-BOD/ ^m3 /d.

The water to be treated is separated into solids and liquids by the solid-liquid separator 1, and a separated liquid and separated sludge, for example, with a BOD of 600 to 10,000 mg/L, more typically 1,000 to 5,000 mg/L, are obtained. The separated liquid is then introduced into the biological treatment tank 2, where the BOD is roughly removed, and biologically treated water with a BOD of about 600 to 3,000 mg/L is obtained. The biologically treated water is mixed with dilution water in the dilution tank 3, and is diluted until it meets the sewage removal standards, after which it is discharged into the sewer system. Note that instead of a trickling filter bed, a fluidized bed carrier tank, a contact oxidation tank, or a rotating disk device can also be used as the biological treatment tank 2.

According to the water treatment device and water treatment method of the first embodiment, biologically treated water that has been biologically treated using trickling filters, fluidized beds, contact oxidation tanks, rotating disk devices, etc., which have traditionally been used as biological treatment tanks 2 for septic tank sludge and sewage sludge, is diluted with dilution water. This makes it possible to omit the power required for aeration compared to treatment using the activated sludge method, etc., and also in terms of equipment, it is possible to efficiently obtain treated water for discharge into the sewerage system using simpler equipment.

Second Embodiment
The water treatment device of the second embodiment includes a membrane carrier 20 (see Figures 2 and 3) arranged in the biological treatment tank 2 of Figure 1, the membrane carrier 20 having a structure in which the separated liquid and oxygen permeate in opposing directions across the membrane surface.

As shown in FIG. 2, the membrane carrier 20 includes a support 21 and a membrane 22 supported by the support 21. The membrane 22 has a loop shape that covers the support 21. The separated liquid permeates from the outer surface of the loop-shaped membrane 22, and oxygen permeates from a space 23 formed on the inner surface of the loop-shaped membrane 22 to the outer surface of the membrane. The membrane 22 includes a curved portion 22a that curves on the outside of the support 21, and extension portions 22b and 22c that extend approximately parallel to each other from both ends of the curved portion 22a. An opening 22d is formed on the lower end side of the membrane 22, i.e., on the side of the membrane 22 facing the bottom surface of the biological treatment tank 2, for discharging sludge (not shown) that accumulates on the inner surface of the membrane 22 and is subsequently peeled off, out of the space 23.

When the membrane carrier 20 having the structure shown in Figures 2 and 3 is housed in a trickling filter bed serving as a biological treatment tank 2, the outside of the membrane 22 of the membrane carrier 20, which is the separated liquid supply side, becomes an area rich in BOD and poor in oxygen, while the oxygen supply side inside the membrane 22 becomes an area poor in BOD and rich in oxygen. Therefore, it is possible to create conditions suitable for the denitrification reaction to proceed on the separated liquid supply side, while creating conditions suitable for the nitrification reaction on the oxygen supply side.

According to the water treatment device and water treatment method of the second embodiment, by using the membrane carrier 20 having the structure shown in Figures 2 and 3, it is possible to reliably form oxygen-poor areas and oxygen-rich areas within a certain area, compared to when sand or stones are used as a filter medium. Therefore, it is possible to create an environment in which the nitrification-denitrification reaction is more likely to proceed than when sand or stones are used as a filter medium. In addition, since the sludge accumulated on the inner surface of the membrane 22 can be discharged from the opening 22d, it is possible to perform stable treatment for a longer period of time. Since much of the discharged sludge is detached from living organisms and this sludge has good settling properties, it is recommended that solid-liquid separated water be supplied to the dilution tank via a solid-liquid separation device such as a sedimentation tank. The separated sludge is returned to the receiving tank before the dehydration equipment for septic tank sludge and sewage sludge, dehydrated, and discharged outside the facility as dehydrated cake.

Third Embodiment
As shown in FIG. 4, the water treatment device of the third embodiment includes a biological treatment tank 2, which is a biological treatment tank (high-load biological treatment tank) 2a for removing BOD from the separated liquid and a biological treatment tank (low-load biological treatment tank) 2b for removing nitrogen from the separated liquid, connected in parallel to each other.

The BOD load condition in the biological treatment tank 2a is not limited to the following, but may be, for example, 3.0 to 10.0 kg-BOD/ ^m3 /d, in another embodiment 3.0 to 8.0 kg-BOD/ ^m3 /d, and in yet another embodiment 3.0 to 5.0 kg-BOD/ ^m3 /d. In the biological treatment tank 2a, treatment is carried out with the aim of roughly removing the BOD from the separated liquid.

The BOD load condition of the biological treatment tank 2b is desirably lower than that of the biological treatment tank 2a, and is not limited to the following, but may be, for example, 0.5 to 2.0 kg-BOD/m ³ /d, in another embodiment 0.5 to 1.5 kg-BOD/m ³ /d, and in yet another embodiment 0.5 to 1.0 kg-BOD/m ³ /d. In the biological treatment tank 2b, treatment is carried out with the aim of removing TN (total nitrogen) from the separated liquid.

The inflow ratio of the separated liquid to the biological treatment tank 2a and the biological treatment tank 2b can be adjusted according to the water quality (BOD, T-N) of the separated liquid. Although not shown, a control means may be provided to control the inflow ratio of the separated liquid to the biological treatment tank 2a and the biological treatment tank 2b based on the water quality of the separated liquid. Note that FIG. 4 shows an example in which the biological treatment tank 2a and the biological treatment tank 2b are connected in parallel as two biological treatment tanks 2, but it goes without saying that two or more biological treatment tanks may be provided.

According to the water treatment device and water treatment method of the third embodiment, more appropriate treatment can be performed using multiple biological treatment tanks 2 depending on the purpose of removing organic matter from the separated liquid, so that treated water that meets the sewage removal standards can be produced more efficiently.

(Fourth embodiment)
5, the water treatment device according to the fourth embodiment includes a biological treatment tank 2 connected in series with a biological treatment tank (high-load biological treatment tank) 2a for removing BOD from the separated liquid and a biological treatment tank (low-load biological treatment tank) 2b for removing nitrogen from the separated liquid, as the biological treatment tank 2. The biologically treated water finally obtained by the treatment in the biological treatment tanks 2a and 2b is circulated to the front stage of the biological treatment tanks 2a and 2b via a return means 4.

According to the water treatment device and water treatment method of the fourth embodiment, BOD removal is performed in the biological treatment tank 2a at the front stage, and the nitrification reaction can be advanced in the biological treatment tank 2b at the rear stage. Furthermore, by returning the biologically treated water using the return means 4, circulating nitrification and denitrification can be further promoted, so that more stable water treatment can be performed for discharge into the sewer system.

Fifth embodiment
As shown in FIG. 6, the water treatment device of the fifth embodiment has two or more stages of biological treatment tanks 2a, 2b, ..., 2n connected in series, and is equipped with an inflow means 5 for inflowing separated liquid in steps into each of the biological treatment tanks 2a, 2b, ..., 2n.

The inflow rate (step ratio) into each biological treatment tank 2a, 2b, ..., 2n can be changed as desired, but from the standpoint of nitrogen removal, it is desirable to include one or ^{more biological treatment tanks 2a, 2b, ..., 2n with a BOD volume load of 1.0 to 4.0 kg-BOD/m 3 /} d, preferably 1.5 to 3.0 kg-BOD/m ³ /d, and a TN volume load of 0.5 to 2.0 kg-N/m ³ /d, preferably 0.7 to 1.5 kg-N/m 3 /d, and to determine each step ratio so that the number of such tanks is further increased.

Table 1 shows examples of treated water quality in terms of BOD and T-N when the flow rate of the water to be treated is 12 ^m3 /d, BOD is 2000 mg/L, _NH4 -N is 700 mg/L, three biological treatment tanks 2 are connected in series, the volume of each biological treatment tank 2 is ² m3, and the step inflow amount of separated liquid supplied from the inflow means 5 is changed. Among cases A to C in Table 1, the example showing the best treated water quality is indicated with ◎, the example showing the second best treated water quality with ○, and the example showing the third best treated water quality with △.

As shown in Table 1, when the inflow rate to the previous step is reduced as in case A, the T-N treatment performance improves, while when the inflow rate to the previous step is increased as in case C, the BOD treatment performance tends to improve. This is because adjusting the load to allow nitrification to proceed in the previous step, where it is possible to reduce the amount of treated water, contributes to nitrogen removal throughout the entire process.

According to the water treatment device of the fifth embodiment, the inflow means 5 can adjust the distribution ratio of the amount of water flowing into each biological treatment tank 2a, 2b, ..., 2n. Therefore, for example, the inflow amount on the upstream side of the biological treatment tanks 2a, 2b, ..., 2n can be reduced to promote nitrification and increase the NO ₃ -N concentration in the treated water, and in the downstream side, a denitrification reaction can be promoted between the NO ₃ -N generated in the upstream side and the BOD components contained in the separation liquid flowing in at the step, thereby efficiently removing BOD and T-N from the treated water.

In addition, the water treatment device according to the fifth embodiment does not circulate the treated water as in the circulating nitrification-denitrification method, so it is possible to reduce pump power compared to the circulating nitrification-denitrification method.

Sixth embodiment
As shown in FIG. 7, the water treatment device of the sixth embodiment includes an inflow means 5 for inflowing the separated liquid into each biological treatment tank 2a, 2b, ..., 2n in steps, and a control means 6 for controlling the step ratio of the separated liquid to be inflowed into the biological treatment tanks 2a, 2b, ..., 2n.

The step ratio of the separated liquid by the inflow means 5 can be controlled by the control means 6 shown in FIG. 7 so that the treatment in each biological treatment tank 2a, 2b, ... 2n is carried out more stably depending on the volume load of each biological treatment tank 2a, 2b, ... 2n and the water quality of the separated liquid obtained from the solid-liquid separation device 1 or the biological treatment water obtained from the biological treatment tanks 2a, 2b, ... 2n.

For example, the control means 6 includes a measuring means 11 for measuring the water quality of the separated liquid obtained in the solid-liquid separation device 1, and a monitoring means 7 for monitoring the measurement results of the measuring means 12, 13, and 14 for measuring the water quality of the biological treatment water obtained in each biological treatment tank 2a, 2b, ..., 2n, and based on the monitoring results of the monitoring means 7, the control means 6 adjusts the step ratio of the separated liquid flowing into each biological treatment tank 2a, 2b, ..., 2n from the inflow means 5 so that the flow rate ratio is more optimal according to the volume load of each biological treatment tank 2a, 2b, ..., 2n.

There are no particular limitations on the items monitored by the monitoring means 7, but for example, flow rate, water temperature, pH, ORP, BOD, COD, TOC, ammonia nitrogen, nitrate nitrogen, etc. can be monitored. The locations monitored by the monitoring means 7 are not limited to the example in Figure 7, and it is also possible to pick out and monitor any of the representative biological treatment tanks 2a, 2b, ... 2n.

The control means 6 includes a calculation means (not shown) that calculates the step ratio of the separated liquid to be flowed into each of 2a, 2b, ..., 2n based on the items monitored by the monitoring means 7, and adjusts the flow rate of the separated liquid flowing in from the inflow means 5 with a flow adjustment device based on the calculation result by the calculation means. Examples of the flow adjustment device include a solenoid valve, a manual valve, etc.

According to the water treatment device of the sixth embodiment, the water quality of the separated liquid obtained from the solid-liquid separation device 1 or the biologically treated water obtained from the biological treatment tanks 2a, 2b, ... 2n can be grasped in real time, so that even if the water quality of the water to be treated fluctuates, the step ratio of the separated liquid can be set so that more appropriate biological treatment can be performed in each biological treatment tank 2a, 2b, ... 2n, and more stable treatment can be performed.

Seventh embodiment
In the water treatment device according to the seventh embodiment, as shown in Fig. 8, a biological treatment tank 2a and a biological treatment tank 2b are connected in parallel. The biological treatment tank 2a includes a trickling filter bed 201a for aerobic decomposition of BOD in the separated liquid and nitrification of ammonia nitrogen to obtain biologically treated water, a circulation line 203a for circulating the biologically treated water obtained in the trickling filter bed 201a to the trickling filter bed 201a, and a circulation tank 202a for accommodating the circulating water to be circulated to the trickling filter bed 201a. The biological treatment tank 2b includes a trickling filter bed 201b for aerobic decomposition of BOD in the separated liquid and nitrification of ammonia nitrogen to obtain biologically treated water, a circulation line 203b for circulating the biologically treated water obtained in the trickling filter bed 201b to the trickling filter bed 201b, and a circulation tank 202b for accommodating the circulating water to be circulated to the trickling filter bed 201b.

After solid-liquid separation of the water to be treated, which contains at least one of septic tank sludge and sewage sludge, the separated liquid is stored in the storage tank 2x and then supplied to the circulation tanks 202a and 202b of the biological treatment tanks 2a and 2b, respectively. In the dehydration treatment of septic tank sludge and sewage sludge, if a metal salt (polyiron, aluminum sulfate, etc.) is used as a flocculant, phosphorus in the raw water is chemically fixed to iron or aluminum, so the phosphorus concentration in the separated liquid decreases. For this reason, phosphorus supply means 2y are connected to the front stage of the circulation tanks 202a and 202b, respectively, to supply the amount of phosphorus necessary for the growth of microorganisms in the trickling filter beds 201a and 201b. There are no particular restrictions on the form of phosphorus supplied from the phosphorus supply means 2y, but there are methods such as adding chemicals such as phosphoric acid and potassium dihydrogen phosphate, or a portion of sewage sludge or septic tank sludge. When using septic tank sludge and sewage sludge, the sludge can be dispensed into the separated liquid storage tank after dehydration depending on the amount of phosphorus that is lacking.

As shown in FIG. 9, the circulation tank 202 can also be filled with carriers. In this case, by housing the carriers with microorganisms attached to their surfaces in the 10-40% V/V circulation tank 202, the denitrification reaction proceeds with the microorganisms housed in the circulation tank 202. After the denitrification reaction proceeds in the circulation tank 202 housing the carriers with the microorganisms attached, the circulating water can be circulated to the trickling filter bed 201, and the treated water can be returned to the circulation tank 202.

According to the water treatment device shown in Figure 9, carriers with microorganisms attached to their surfaces are contained in the circulation tank 202, so that the organic matter (BOD) and nitrogen (T-N) contained in the separated liquid can be efficiently and roughly removed stably regardless of fluctuations in the water to be treated.

The water treatment device according to the seventh embodiment does not require sludge concentration control by return or the like, and can be easily maintained without problems such as sludge re-floating, making it possible to efficiently remove the organic matter (BOD) and nitrogen (T-N) contained in the separated liquid. This makes it possible to reduce the amount of dilution water required to meet sewage discharge standards and reduce the operating costs of the facility.

The following examples of the present invention are presented together with comparative examples, but these examples are provided to provide a better understanding of the present invention and its advantages, and are not intended to limit the invention.

As the separated liquid, the dehydrated separated liquid from a sewage treatment facility was supplied to the water treatment device shown in Figure 8 to obtain treated water. Nutrients (monopotassium phosphate ( _KH2PO4 )) were added to _the separated liquid. Table 2 shows the properties of typical separated liquids during the experiment.

As for the treatment flow, one trickling filter bed 201a in FIG. 8 was connected in parallel as a high-load type (No. 1), and the other trickling filter bed 201b was connected in parallel as a low-load type (No. 2), and the dehydrated separated liquid was flowed into each of them. The set load of each tank was gradually increased, and the treated water quality at each load was confirmed (see FIG. 10). The outer diameter dimensions of the trickling filter bed 201a and the trickling filter bed 201b were 0.05 mW x 1.15 mD x 2.42 mH, and the effective volume was 2 ^m3 . The membrane carrier shown in FIG. 2 and FIG. 3 was used as the filter bed for the trickling filter bed 201a and the trickling filter bed 201b. The surface area of the membrane carrier was 246 ^m2 . During the experiment, no sludge was returned from the treatment tank, and no sludge amount was controlled. The experimental results are shown in Table 3.

Under high load conditions (3.0-10 kg-BOD/ ^m3 /d), the T-N removal rate was low at 18% or less, but the BOD removal rate was 38-62%, indicating that rough removal of BOD is possible. Under low load conditions (0.5-2.0 kg-BOD/ ^m3 /d), the BOD removal rate was high at 80% or more, and the T-N removal rate was 30-70%, indicating that rough removal of T-N is also possible. Furthermore, under any load conditions, there were no problems such as sludge outflow or blockage due to clogging.

The relationship between the load and the amount of nitrification obtained from the above experiment is shown in Table 4. The amount of nitrification was maximum at about 2.5 kg-BOD/ ^m3 /d. From these results, it was found that when the purpose is to remove nitrogen, the nitrogen removal efficiency can be increased by operating under a BOD load condition of 1.5 to 6.0 kg-BOD/ ^m3 /d, further 1.5 to 4.0 kg-BOD/ ^m3 /d, and even further 2.0 to 3.0 kg/ ^m3 /d.

Table 5 shows the calculated dilution ratios obtained from the removal rates of each load when the sewage discharge standards are BOD 600 mg/L and T-N 380 mg/L. Without biological treatment, a 3.8-fold dilution was necessary, but this example shows that the dilution ratio can be reduced to 1.0 to 1.7 times. Note that the calculations below assume that the entire amount of dehydrated filtrate is introduced into biological treatment, but it is self-evident that the amount of dilution water can be reduced even if only a portion of the dehydrated filtrate is biologically treated due to limitations in site area, etc.

Reference Signs List 1: Solid-liquid separation device 2, 2a to 2n: Biological treatment tank 3: Dilution tank 4: Return means 5: Inflow means 6: Control means 7: Monitoring means 11 to 14: Measurement means 20: Membrane carrier 21: Support 22: Membrane 23: Space 201, 201a, 201b: Trickling filter bed 202, 202a, 202b: Circulation tank 203a, 203b: Circulation line

Claims (8)

a dehydrator that dehydrates water to be treated, the water including at least one of septic tank sludge and sewage sludge, and separates the water into separated sludge and a dehydrated separated liquid;
a phosphorus supplying means for supplying phosphorus to at least a portion of the dehydrated separated liquid so that the phosphorus concentration is 0.7 mg/L or less per BOD of 100 mg/L;
a biological treatment tank for subjecting the dehydrated separated liquid after the phosphorus supply to a biological treatment using a non-blocking biofilm method including at least one of a trickling filter method, a fluidized carrier method, a rotating disk method, and a fixed bed method;
and a dilution tank for diluting the biologically treated water obtained by the biological treatment so that the biologically treated water meets sewage removal standards. The water treatment device according to claim 1, further comprising a storage tank for storing the dehydrated separated liquid obtained after dehydrating the water to be treated, the water containing at least one of the septic tank sludge and the sewage sludge, and the phosphorus supplying means dispenses the septic tank sludge and the sewage sludge into the dehydrated separated liquid in the storage tank. The water treatment device according to claim 1 or 2, further comprising supplying an iron-based or aluminum-based coagulant during the dehydration process of the water to be treated. 4. The water treatment device according to claim 1, wherein the biological treatment tank is a biological treatment tank using a fluidized carrier method in which the biological treatment is performed at a BOD load of 0.5 to 5.0 kg-BOD/m ³ /d. The water treatment device according to any one of claims 1 to 4, characterized in that a membrane carrier having a structure in which the dehydrated separated liquid and oxygen permeate opposite each other across a membrane surface is disposed in the biological treatment tank in which the biological treatment is performed using the trickling filter biofilm method, the membrane carrier comprises a support and a membrane supported by the support, the membrane has a loop shape that covers the support, the dehydrated separated liquid permeates from the outer surface of the membrane, the oxygen permeates from a space formed on the inner surface of the membrane to the outer surface of the membrane, and an opening is formed in the membrane for discharging sludge peeling off from the inner surface of the membrane to the outside of the space. An inflow means for inflowing the dewatered separated liquid stepwise into each of the biological treatment tanks including two or more stages of treatment tanks connected in series;
The water treatment device according to any one of claims 1 to 5, further comprising: a control means for controlling a step ratio of the dehydration separated liquid to be flowed into the biological treatment tank based on a volume load of the biological treatment tank and a water quality of the dehydration separated liquid or the biological treatment water. The water treatment device according to any one of claims 1 to 6, characterized in that the dilution tank dilutes the biologically treated water obtained in the biological treatment tank as is without performing solid-liquid separation. The water treatment device according to any one of claims 1 to 7, characterized in that the dehydrator separates the separated sludge having a moisture content of 70% or less from the dehydrated separated liquid.