Water treatment method and water treatment apparatus

Abstract

To provide a water treatment method capable of efficiently obtaining treated water having water quality satisfying a sewage discharge standard from treated water containing septic tank sludge or night soil sludge by a smaller apparatus, and a water treatment apparatus.SOLUTION: A separated liquid obtained by subjecting sludge containing at least either of septic tank sludge and night soil sludge to solid-liquid separation is supplied into an aeration treatment tank 2 housing a biological carrier. In the water treatment method, an aeration condition in the treatment tank 2 is set to at least two or more conditions of an aeration condition of nitrification promoting treatment and an aeration condition of denitrification promoting treatment with an aeration amount smaller than that of the aeration condition of the nitrification promoting treatment so that the nitrification promoting treatment for promoting nitrification and the denitrification promoting treatment for promoting denitrification are performed in the treatment tank 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water treatment method and a water treatment device, and more particularly to a water treatment method and a water treatment device suitable for application to water treatment in which septic tank sludge and human waste sludge are treated and the treated water is discharged into a sewer system. [Background technology]

[0002] In order to discharge treated water obtained by treating raw water containing septic tank sludge and human waste sludge into the sewer system, it is necessary to satisfy sewage discharge standards, which are generally 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, TN (total nitrogen) 10 mg / L, and SS (suspended solids) 10 mg / L, while standards for sewage discharge are BOD 600 mg / L, TN 240 mg / L, and SS 600 mg / L.

[0003] Conventional treatment methods include removing waste (sewage residue) from human waste and diluting it to the exclusion standard before discharging it. In this case, the dilution rate is generally about 10 to 20 times, resulting in excessive amounts of dilution water and discharge into the sewer system.

[0004] Another treatment method is to separate the solids and liquids from the human waste using a dehydrator, dilute the separated liquid, and then discharge it into the sewer system. In this case, the separated liquid has significantly reduced BOD, SS, nitrogen, and other components compared to the separated liquid after sludge removal, so the dilution ratio can generally be about 4 to 8 times. However, because the quality of the separated liquid varies, the amount of water used for dilution also varies greatly depending on the water.

[0005] Furthermore, the method of separating sewage and other waste into solids and liquids using a dehydrator ultimately results in a discharge of 6 to 9 times the amount brought in, so the effect of reducing the amount of wastewater discharged into the sewerage system is limited. Furthermore, since 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 separated liquid from the dehydrated wastewater may deteriorate, making it necessary to increase the amount of dilution water. In some cases, regulations on the amount of discharged water may make it impossible to meet the discharge standards.

[0006] Another method for more reliably reducing the amounts of dilution water and discharged water is to combine solid-liquid separation with biological treatment. For example, Japanese Patent Laid-Open Publication No. 61-50691 (Patent Document 1) describes a method in which the solid-liquid fraction obtained by solid-liquid separation of septic tank sludge is mixed with human wastewater, the mixed liquid is subjected to coagulation treatment, and the separated liquid is then subjected to biological treatment. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 61-50691 Summary of the Invention [Problem to be solved by the invention]

[0008] The method described in Patent Document 1 does not state where the biologically treated water is to be discharged, but since it describes that the treated water in Example 1 can be treated until the BOD is 10 mg / L or less, it can be said that this treatment method is intended for discharge into public water bodies.

[0009] However, treated water discharged into a sewer system does not necessarily have to meet the water quality required for discharge into a public water body, as described in Patent Document 1. On the other hand, in the water treatment that combines solid-liquid separation and biological treatment as described in Patent Document 1, there is a problem in that it is difficult to perform partial treatment to a level that meets the sewage rejection standards. For example, when nitrification-denitrification treatment is performed as biological treatment, possible methods include treating not all of the nitrogen, but about 60%, or nitrifying all of the ammoniacal nitrogen contained in the dehydrated separated liquid, and then denitrifying only 60% of that.

[0010] However, when treating about 60% of the nitrogen, about 40% of the nitrate nitrogen remains, and denitrification occurs again in the downstream settling tank when the tank becomes anaerobic, and the nitrogen gas generated causes the sludge to float, which can prevent sufficient solid-liquid separation in the settling tank.If solid-liquid separation is not possible in the settling tank, the MLSS (activated sludge concentration) in the nitrification / denitrification tank cannot be maintained, and the treatment itself will deteriorate.

[0011] If all of the ammonia nitrogen contained in the dehydrated separated liquid is nitrified, the capacity of the water tank will be excessive, the aeration air volume required for nitrification will be excessive, and it will be necessary to add hydrogen donors such as methanol or ethanol, which are necessary for denitrification, resulting in excessive equipment and operating costs compared to the required treated water quality.

[0012] Another method for efficiently treating septic tank sludge and human waste sludge is to use biological treatment using the activated sludge method, which involves roughly treating the treated water until the quality of the treated water falls below the sewage discharge standard, diluting it, and discharging it into the sewer system. However, this method requires a large tank capacity for biological treatment using the activated sludge method, and also requires an excessive amount of aeration airflow to deal with the high BOD load, so it cannot be said to be a good method in terms of treatment efficiency.

[0013] In view of the above problems, the present invention provides a water treatment method and a water treatment device that can efficiently obtain treated water of a quality that satisfies sewage discharge standards from treated water containing septic tank sludge or sewage sludge using a smaller device. [Means for solving the problem]

[0014] As a result of intensive research conducted by the present inventors to solve the above problems, it was discovered that it is effective to supply the separated liquid obtained by solid-liquid separation of sludge including septic tank sludge or sewage sludge into a treatment tank equipped with a biofilm and to treat the sludge by setting two or more aeration conditions in the treatment tank.

[0015] In one aspect, a water treatment method according to an embodiment of the present invention, which was completed based on the above findings, comprises: supplying a separated liquid obtained by solid-liquid separation of sludge containing at least one of septic tank sludge and sewage sludge into an aeration tank containing a biological carrier; setting aeration conditions in the treatment tank at least under two conditions, namely, aeration conditions for nitrification promotion treatment and aeration conditions for denitrification promotion treatment with a lower aeration volume than the aeration conditions for nitrification promotion treatment, so that a nitrification promotion treatment that promotes nitrification and a denitrification promotion treatment that promotes denitrification are carried out in the treatment tank; switching the aeration conditions to perform biological treatment so that the nitrification promotion treatment and the denitrification promotion treatment are alternately performed in the treatment tank; and diluting the biologically treated water obtained by the biological treatment so that it meets the sewage discharge standards.

[0016] In one embodiment of the water treatment method according to the present invention, the separated liquid is intermittently supplied to the treatment tank.

[0017] In another embodiment of the water treatment method according to the present invention, in the denitrification promotion treatment, the separated liquid contained in the treatment tank is caused to flow by at least one of the following: causing the separated liquid to flow from the bottom of the treatment tank, stirring with a stirrer, or aeration.

[0018] In one aspect, a water treatment device according to an embodiment of the present invention is a water treatment device comprising: a solid-liquid separation device that separates sludge, including at least one of septic tank sludge and sewage sludge, into separated sludge and separated liquid by solid-liquid separation; a treatment tank that contains a biofilm that biologically treats the separated liquid and performs a nitrification-promoting treatment that promotes nitrification and a denitrification-promoting treatment that promotes denitrification on the separated liquid; a control means that sets and controls the aeration conditions of the treatment tank to at least two conditions, i.e., aeration conditions for the nitrification-promoting treatment and aeration conditions for the denitrification-promoting treatment, so that the nitrification-promoting treatment and the denitrification-promoting treatment are performed alternately in the treatment tank; and a dilution tank that dilutes the biologically treated water treated in the treatment tank so that it meets the sewage discharge standards.

[0019] In another embodiment of the water treatment device according to the present invention, a separated liquid supply pipe is provided which is connected to the lower part of the treatment tank and is capable of supplying separated liquid into the treatment tank so as to generate a liquid flow within the treatment tank. [Effects of the Invention]

[0020] According to the present invention, a water treatment method and a water treatment device can be provided that can efficiently produce treated water of a quality that satisfies sewage removal standards from treated water containing septic tank sludge or sewage sludge using a smaller device. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic diagram illustrating a water treatment device according to an embodiment of the present invention. [Figure 2] FIG. 1 is a schematic diagram showing a process flow in a laboratory test. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below are examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the structure, arrangement, etc. of the components to those described below.

[0023] <Water treatment method> A water treatment method according to an embodiment of the present invention includes subjecting a separated liquid obtained by solid-liquid separation of sludge containing at least one of septic tank sludge and sewage sludge to biological treatment using a biofilm (biological carrier), and diluting the biologically treated water obtained by the biological treatment so that it meets sewage removal standards.

[0024] As the raw water, a separated liquid obtained by solid-liquid separation of sludge containing at least one of septic tank sludge and night soil sludge can be used. Typically, a separated liquid obtained by dehydration of septic tank sludge, night soil sludge, or a mixture thereof can be suitably used. When septic tank sludge and night soil sludge are mixed, the mixed liquid obtained by mixing the septic tank sludge and night soil sludge may be subjected to solid-liquid separation. However, it is preferable to separately separate the septic tank sludge and night soil sludge and then mix the separated liquids obtained by the solid-liquid separation.

[0025] Various solid-liquid separation devices can be used for the solid-liquid separation treatment. Among them, using a dehydrator to separate raw water into separated sludge and separated liquid is preferred in terms of equipment and operating costs. It is also preferred to subject the raw water before the solid-liquid separation treatment to a concentration treatment. Both gravity concentration and mechanical concentration are effective concentration methods.

[0026] 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, which allows for the compactness of the treatment equipment. Further dehydration of the highly concentrated concentrated sludge using a dehydrator produces dehydrated sludge (separated sludge) with a moisture content of 70% or less, resulting in a more significant sludge volume reduction effect. Because this low-moisture dehydrated sludge has a high calorie content, it can be self-burned without auxiliary fuel during incineration, resulting in energy savings and low costs.

[0027] Typical raw water qualities include, but are not limited to, a BOD of 600 to 2000 mg / L and a TN of 240 to 1000 mg / L, more typically a TN of 240 to 700 mg / L. The quality of the biologically treated water before dilution obtained by the biological treatment described below is a BOD of 200 to 1500 mg / L and a TN of 240 to 600 mg / L.

[0028] The separated liquid is supplied to a treatment tank equipped with a biofilm, which is a carrier surface on which microorganisms are attached, and biological treatment using the biofilm method is carried out in the treatment tank. Biofilm methods according to this embodiment can be broadly divided into those that require a periodic cleaning process for the carrier, and those in which the amount of biofilm is autonomously controlled during treatment. The former includes biofilm filtration methods, etc. The latter include trickling filter methods, fluidized bed methods, rotating disk methods, and fixed bed methods (contact oxidation methods). Among these, it is preferable to use a biofilm method in which the amount of biofilm is autonomously controlled during treatment as the biological treatment according to this embodiment of the present invention, which is defined in this specification as a "non-blocking biofilm method."

[0029] In particular, in this embodiment, an aerated biofilm method is preferably used, which performs biological treatment in an aeration treatment tank (hereinafter also referred to as a "treatment tank") containing biological carriers, including a contact oxidation method (fixed bed method) using fixed bed carriers or a fluidized bed method using fluidized bed carriers. The "aerated biofilm method" refers to biological treatment in which the biological carriers contained in the treatment tank are fluidized while aeration is used to diffuse air within the treatment tank using an aeration means. An example of an aerated biofilm method suitable for this embodiment is shown below.

[0030] -Catalytic oxidation method (fixed bed method)- In the contact oxidation method, fixed-bed carriers are immersed in the liquid contained in a treatment tank, and the separated liquid is passed through while aeration is performed, resulting in the formation of a biofilm on the surface of the carriers, which decomposes the organic matter in the separated liquid and produces biologically treated water. Because treatment is carried out using a biofilm attached to the carriers, there is no need to control the amount of sludge by returning it, as opposed to activated sludge methods, and maintenance is easier. The BOD volume load is 0.1 to 1.0 kg-BOD / m 3 / d is preferable, and if it is operated at a high load, the biofilm may grow and clog the contact material. In addition, the TN load should be 0.06 to 0.3 kg-N / m 3 / d is preferred.

[0031] There are no particular limitations on the material and specific shape of the carrier for the catalytic oxidation method, and any device can be used. The carrier can be made of polyethylene, plastic, or the like, and can be in any shape, such as a tube, string, net, plate, or ball.

[0032] The specific surface area of ​​the carrier for contact oxidation is 50 to 200 m2 in terms of the adhesion of microorganisms. 2 / m 3 , preferably 70 to 150 m 2 / m 3 The porosity of the carrier is preferably 97 to 99.5%, more preferably 97.5 to 99%, from the viewpoint of preventing clogging and achieving the above-mentioned specific surface area.

[0033] Generally, when using contact oxidation for treatment, continuous aeration is the norm, and switching to low aeration airflow is not performed. This is because low aeration airflow weakens agitation within the tank, potentially causing short-passing of raw water and resulting in the outflow of untreated wastewater. In contrast, the water treatment method according to an embodiment of the present invention utilizes contact oxidation as a method for pre-treating the separated liquid, which is obtained by solid-liquid separation of sludge to reduce the load on biological treatment, for discharge into a sewer system. Therefore, the intended treatment can be fully achieved even if the water in the tank is insufficiently mixed during periods of low aeration airflow or no aeration. Furthermore, to further improve mixing within the tank, at least one of the following can be implemented: inflow of raw water from the bottom of the treatment tank, stirring with an agitator, or aeration. This can also promote the flow of separated liquid contained in the treatment tank within the tank, thereby achieving even more stable treatment.

[0034] -Floating Carrier Method- The fluidized carrier method is a method in which carriers are placed in a treatment tank and allowed to flow within the liquid in the treatment tank, thereby bringing microorganisms into contact with organic matter and oxygen in the water to be treated, thereby obtaining biologically treated water. A treatment tank using the fluidized carrier method may be newly constructed, or carriers and an aeration device may be installed in an existing storage tank. There are no particular restrictions on the carriers used in fluidized carriers, but typical examples include the following:

[0035] The carrier used may be any carrier that can accommodate microorganisms and that can be fluidized by aeration. The carrier material may be any carrier that can be fluidized by aeration, such as plastics (polyurethane (PU), polyethylene (PE), polyethylene glycol (PEG), polyvinyl alcohol (PVA)), wood chips, sand, etc. The carrier may be in the form of a sponge, gel, solid, etc.

[0036] The shape of the carrier can be any shape, such as spherical, cubic, cylindrical, honeycomb, etc. Among these, by using a bonded immobilization carrier that attaches microorganisms to the outer surface of the carrier, it is possible to attach microorganisms that are suitable for the environment in the treatment tank to the carrier, and it is possible to perform more stable biological treatment that is less susceptible to fluctuations in the properties of the influent water.

[0037] The carrier preferably has a structure that takes into consideration the contact efficiency between the carrier and raw water in both the nitrification promotion treatment that promotes nitrification and the denitrification promotion treatment that promotes denitrification in the treatment tank. For example, in order to efficiently promote nitrification promotion treatment, it is preferable to use a carrier with a large specific surface area to increase the contact efficiency between nitrifying bacteria and oxygen. On the other hand, since denitrification treatment does not require contact with oxygen, in order to promote denitrification promotion treatment, it is preferable to have a carrier structure in which microorganisms are filled into the voids inside the carrier.

[0038] Therefore, the specific surface area of ​​the carrier suitable for nitrification promotion treatment and denitrification promotion treatment is 50 to 5000 m 2 / m 3 , preferably 100 to 3000 m 2 / m 3It is preferable that the pores of the carrier are filled with sludge and that the pores of the carrier are filled with sludge. 2 / m 3 It is preferable that the carrier has a structure capable of maintaining a specific surface area of ​​at least 100%. The porosity of the carrier (i.e., the volume of the voids in the carrier divided by the outer dimensions of the carrier) is preferably 50 to 99%, and more preferably 70 to 99%. The effective diameter of the carrier is preferably 3 to 10 mm, which allows stable separation using a screen for separating the carrier.

[0039] The specific gravity of the carrier is 1.00 to 1.10 g / cm, which allows the carrier to flow quickly and uniformly in the treatment tank even when intermittent aeration or micro-aeration is performed in the treatment tank. 3 It is preferable that the density is 1.01 to 1.05 g / cm. 3 It is preferable to set the following.

[0040] The carrier packing rate is preferably 10 to 50% by volume (V%), which allows the carrier to be uniformly mixed and flowable, and more preferably 20 to 40% by volume (V%). A packing rate of 20% by volume or more allows a large amount of microorganisms to be retained in the tank, while a packing rate of 40% by volume or less allows for the creation of appropriate voids, thereby maintaining good fluidity.

[0041] It is also possible to pack two types of carriers in the treatment tank, one for nitrification promotion treatment and one for denitrification promotion treatment. In this case, it is preferable to pack a carrier with a relatively large specific surface area for the nitrification promotion treatment, and a carrier with a relatively high porosity and packing rate for the denitrification promotion treatment. Although not limited to the following, for example, a carrier with a specific surface area of ​​100 m2 for the nitrification promotion treatment is suitable. 2 / m 3 More than 300m, preferably 300m 2 / m 3The above carriers are preferably packed in an amount of 20 to 35% by volume of the tank, and carriers for denitrification promotion treatment, for example, with a porosity of 70% or more, preferably 85% or more, are preferably packed in an amount of 5 to 20% by volume of the tank. By using such carriers, the carriers can be fluidized in the treatment tank by micro-aeration, intermittent aeration, or by supplying a separated liquid into the treatment tank, allowing the denitrification treatment to proceed optimally.

[0042] The BOD volume load is 0.1 to 2.0 kg-BOD / m 3 / d, preferably 0.2 to 1.0 kg-BOD / m 3 The TN load is preferably 0.03 to 0.7 kg-N / m 3 / d, preferably 0.06 to 0.3 kg-N / m 3 / d is preferred. The fluidized bed carrier method is less likely to clog under high loads than the contact oxidation method. Activated sludge may be added to the treatment tank in addition to the fluidized bed carrier. By adding activated sludge to the treatment tank, fluctuations in the properties of the biologically treated water due to fluctuations in the properties of the raw water can be suppressed, allowing for more stable treatment.

[0043] As with the contact oxidation process described above, continuous aeration is generally the norm when using the fluidized bed carrier process, and switching to low aeration airflow is generally not performed. This is because low aeration airflow weakens agitation within the tank, potentially resulting in short-passing of raw water and the resulting discharge of untreated wastewater. In contrast, the water treatment method according to an embodiment of the present invention utilizes the fluidized bed carrier process as a method for pre-treating the separated liquid, which is obtained by solid-liquid separation of sludge to reduce the load on biological treatment, for discharge into a sewer system. Therefore, even if insufficient mixing of the water in the tank occurs during periods of low aeration airflow or no aeration, resulting in settling of the carriers, the intended treatment can still be achieved. Furthermore, to further improve mixing within the tank, at least one of the following can be implemented: inflow of raw water from the bottom of the treatment tank, agitation with an agitator, or aeration. This can promote the flow of the separated liquid contained in the treatment tank within the tank, thereby achieving even more stable treatment.

[0044] Furthermore, in general, in treatments using flow-through carriers, the single-tank system is rarely adopted because the treatment speed can be increased by separating the nitrification tank and denitrification tank, with nitrifying bacteria predominating in the nitrification tank carrier and denitrifying bacteria predominating in the denitrification tank carrier, compared to when both nitrifying and denitrifying bacteria are attached to a single carrier.In contrast, the water treatment according to the embodiment of the present invention aims to roughly treat treated water containing septic tank sludge or human waste sludge so that the water quality satisfies the sewage discharge standards.By adopting a single-tank system with a system that switches between the nitrification process and the denitrification process, a water treatment method and water treatment device can be provided that can efficiently produce treated water using a smaller device.

[0045] According to the water treatment method of the present invention, by using an aerated biofilm process containing fixed-bed or fluidized bed carriers in the treatment tank, the settling tank installed downstream of the biological treatment can be omitted or downsized, thereby achieving a more compact treatment system. Omitting the settling tank eliminates the need to consider the problem of poor sludge settling due to the residual BOD or TN components of the biologically treated water in the settling tank, thereby improving treatment efficiency. Even if a settling tank is installed downstream of the treatment tank, a compact settling tank is sufficient because only an auxiliary tank is required. Even if some activated sludge flows out due to poor settling, sufficient carriers are retained within the treatment tank, ensuring stable treatment at all times. Furthermore, while conventional batch activated sludge processes require a certain amount of settling time to settle MLSS, maintain microorganisms, and obtain clear treated water, this method uses biological carriers, which eliminates or shortens the settling time, thereby enabling a higher treatable load than activated sludge treatment.

[0046] In biofilm processes where biological treatment is performed using fixed-bed or fluidized bed carriers housed in a treatment tank, oxygen is supplied by aeration, which also functions as agitation within the tank, to ensure the fluidity of the carriers and the contact efficiency between the raw water and the carriers. However, when nitrification and denitrification are performed in the same tank, it is generally difficult to keep the aeration volume during denitrification low enough to be suitable for denitrification. In this embodiment, since the biological treatment only requires the production of treated water in which some of the BOD and TN components remain, BOD removal and nitrogen removal from raw water can be easily and efficiently performed in a single tank by simply adjusting the aeration volume within the treatment tank. This allows treated water of the desired quality (for sewage discharge) to be efficiently obtained using a compact facility.

[0047] In the biological treatment of this embodiment, two or more aeration conditions are set in the treatment tank so that a nitrification-promoting treatment that promotes nitrification and a denitrification-promoting treatment that promotes denitrification are alternately performed in the treatment tank. By setting two or more aeration conditions in the treatment tank and performing both the nitrification-promoting treatment and the denitrification-promoting treatment in a single treatment tank, the water treatment method of this embodiment can be applied even when only one treatment tank is available due to modifications to existing facilities, etc., so the economic burden of modifications can be reduced and treated water suitable for discharge into a sewerage system can be obtained more efficiently and stably.

[0048] The aeration conditions in the treatment tank should be at least two, one for the nitrification promotion treatment and one for the denitrification promotion treatment, with the aeration condition for the nitrification promotion treatment and the aeration condition for the denitrification promotion treatment having a lower aeration volume than the aeration condition for the nitrification promotion treatment. However, it goes without saying that three or more or four or more conditions may be set as necessary.

[0049] -Nitrification promotion treatment- In the nitrification promotion treatment, it is preferable to set the aeration conditions so that the dissolved oxygen (DO) in the tank is 1.0 to 5.0 mg / L, preferably 2.5 to 4.0 mg / L. This allows the ammonia nitrogen (NH4-N) contained in the raw water to be converted into nitrate nitrogen (NO x -N) can be oxidized to promote the nitrification reaction.

[0050] The aeration volume is 0.2 to 0.6 m to move the carrier throughout the tank. 3 / m 2 / min, preferably 0.3-0.5m 3 / m 2 / min is preferred. This allows the carrier to flow throughout the entire tank, increasing the reaction efficiency. Preferably, while confirming that the carrier flows throughout the entire tank at the above-mentioned aeration air volume, fine adjustment of the aeration air volume is made so that the set DO is within the above-mentioned range, thereby enabling the nitrification promotion treatment according to the present invention to be carried out more efficiently.

[0051] When the fluidized carrier method is used as the biofilm method, the nitrification promotion treatment causes the carriers to flow throughout the tank due to aeration, thereby increasing the contact efficiency with the raw water and increasing the nitrification capacity. Note that since the purpose of the nitrification promotion treatment in this embodiment is to roughly remove BOD and TN, it is not necessary to nitrify the entire amount, and it is sufficient that nitrification is completed to the target concentration.

[0052] According to the studies of the present inventors, it is preferable to adjust the pH so that the free ammonia concentration of the ammoniacal nitrogen-containing wastewater in the tank is maintained at 1.0 to 10 mg / L, more preferably 2.0 to 10 mg / L. This allows ammonia-oxidizing bacteria to preferentially attach to the carrier while suppressing the growth of nitritizing bacteria, thereby achieving stable nitritation treatment.

[0053] In nitritation treatment, where NH4-N is normally nitrified to NO3-N, the reaction can be stopped at NO2-N, which increases the efficiency of oxygen use and reduces the amount of oxygen supplied. Furthermore, under the latter stage of denitrification conditions, in addition to dependent denitrification using BOD and other substances in the raw water as electron donors, denitrification by anaerobic ammonium oxidation reactions involving NO2-N and NH4-N also progresses in part, increasing the efficiency of nitrogen removal. The free ammonia concentration can be calculated using equation (1).

[0054]

number

[0055] As can be seen from equation (1), the free ammonia concentration is affected by changes in pH, NH4-N concentration, and water temperature. Stable nitritation treatment can be achieved by measuring changes in the pH, NH4-N concentration, and water temperature of the separated liquid in the treatment tank and adjusting the pH based on the measurement results so that the free ammonia concentration is 1.0 to 10 mg / L.

[0056] -Denitrification promotion treatment- In denitrification promotion treatment, it is preferable to set aeration conditions so that the DO in the treatment tank is less than 1.0 mg / L, preferably 0.5 mg / L or less, to promote the denitrification reaction. Under denitrification conditions, aeration can be completely stopped and fluidization can be performed using mechanical agitation, or micro-aeration can be performed to maintain a DO of less than 1.0 mg / L, or a combination of mechanical agitation and micro-aeration can be used. By using such aeration conditions, the nitrification rate will be slower than under nitrification conditions, but nitrification and denitrification are expected to proceed simultaneously.

[0057] When using fluidized carriers in the biological treatment according to the embodiment of the present invention, the agitation for denitrification conditions can be such that the water in the tank flows rather than the carriers flowing throughout the tank, thereby increasing the contact efficiency between the carriers and the water to be treated, and some of the fluidized carriers may remain submerged. In the case of conventional general fluidized carrier methods, it is ideal to have the fluidized carriers flow uniformly throughout the tank in order to properly proceed with the treatment. On the other hand, the water treatment method according to the present embodiment aims to perform rough treatment of septic tank sludge or sewage sludge, so it is sufficient if the target reaction proceeds rather than the degree of fluidized carrier flow within the tank that is generally required in the fluidized carrier method. The progress of the reaction can be confirmed using an ORP meter or NO meter, as described below. x This can be confirmed with a sensor such as a -N meter. To simplify operation and reduce running costs, it is preferable not to add electron donors such as methanol from the outside, but methanol may be added depending on the target treated water quality.

[0058] When stirring by aeration, the aeration air volume is set to, for example, 0.2 m because there is no need to move the biological carriers due to the reasons mentioned above. 3 / m2 / min or less.

[0059] When controlling the aeration air volume for micro-aeration conditions, inverter control has a lower control limit due to the discharge pressure, and precise control may not be possible. Therefore, it is preferable to perform intermittent aeration using the aeration blower timer, which allows for more precise adjustment of the air volume.

[0060] When adjusting the operation time ratio using a timer, if both the on (aeration operation) time and off (aeration stop) time are set to less than 1 minute, the blower will be burdened and stable operation over a long period of time may be difficult. In order to reduce the burden on the blower and perform stable treatment so that the conditions are suitable for denitrification, it is preferable to set the off time to 5 minutes or more.

[0061] The off-time is preferably adjusted so that the DO in the tank is 0.5 mg / L or less, thereby ensuring that the progress of nitrification can be stopped. For example, although this depends on the blower capacity and the size of the tank, by setting the off-time to more preferably 5 minutes or more, and even more preferably 10 minutes or more, it is possible to keep the DO in the tank at 0.5 mg / L or less and provide a period suitable for denitrification.

[0062] On the other hand, if the off time is set too long, scale is likely to adhere to the aeration device, carriers, etc. in the tank during the aeration stop period if mechanical stirring is not performed. The aeration stop time in the nitritation treatment is 60 minutes or less, more preferably 45 minutes or less, and even more preferably 30 minutes or less. There are no particular restrictions on the on-time as long as it is 1 minute or more. During the on-time, it is preferable to set the DO to 1 mg / L or more, and if a flow carrier is used, it is even more preferable to set the DO to 2.5 mg / L or more. Furthermore, if the dehydrator is not operated on holidays and there is no inflow of raw water, it is possible to promote endogenous denitrification by extending the ratio of aeration stop time under micro-aeration conditions.

[0063] In the denitrification treatment, it is preferable to generate a liquid flow in the raw water contained in the treatment tank and move the carriers in the treatment tank by at least one of the following methods: introducing raw water into the treatment tank from the bottom, stirring with a stirrer, or aeration. This increases the contact efficiency between the flowing carriers and the raw water, thereby accelerating the nitrogen removal treatment.

[0064] The raw water is preferably supplied to the treatment tank intermittently with a predetermined supply suspension period. "Intermittently" refers to, for example, a supply suspension period of several hours (e.g., 1 to 20 hours) or several days (e.g., 1 to 7 days). For example, when treating septic tank sludge and sewage sludge, raw water inflow occurs between 9:00 AM and 5:00 PM on weekdays, depending on the operating conditions of the treatment facility, and there are periods when raw water does not inflow during weekday nights and early mornings, weekends, and holidays. By intermittently supplying raw water to the treatment tank in accordance with the operating conditions of the treatment facility, such as the raw water inflow time, a storage tank for storing raw water can be omitted, contributing to the miniaturization of the entire system. Furthermore, by controlling the aeration conditions in the treatment tank to switch between aeration conditions for nitrification-promoting treatment and aeration conditions for denitrification-promoting treatment in accordance with the timing of the raw water inflow, nitrification and denitrification of raw water can be more efficiently performed in a single treatment tank. For example, by supplying raw water under denitrification-promoting conditions, and then confirming that denitrification has been completed using a set time, ORP, or other sensors (described below), the supply of raw water can be stopped and the system can be switched to nitrification-promoting conditions. This will allow the BOD components in the raw water to be effectively denitrified, and also reduce the amount of oxygen used for BOD oxidation.

[0065] In biological treatment, it is preferable to switch aeration conditions so that nitrification promotion treatment and denitrification promotion treatment are alternately performed in one treatment tank. By switching aeration conditions and repeatedly performing nitrification promotion treatment and denitrification promotion treatment alternately, BOD and TN of raw water can be roughly removed efficiently in one treatment tank.

[0066] The aeration conditions may be switched manually by an operator or automatically controlled using a timer, a sensor, etc. As a switching method, for example, the following method can be adopted.

[0067] -Time-based switching- Since the ratio of nitrification rate to denitrification rate is about 1:1 to 1:5, it is possible to maintain appropriate nitrification time and denitrification time by setting the time ratio of nitrification promotion treatment to denitrification promotion treatment to be 1:1 to 5:1, preferably 2:1 to 4:1. When using a flow-through carrier in biological treatment, it is possible to manually or automatically set the optimal ratio of nitrification time and denitrification time depending on the adhesion state of microorganisms by sampling the acclimatized carrier and determining the nitrification rate and denitrification rate, for example, by performing the following batch test.

[0068] (Nitrification batch test) For example, 20 vol% of the carrier collected from the treatment tank is added to a 1-liter measuring cylinder, and the raw water is diluted to a total volume of 1 liter. Sodium carbonate is then added so that the alkalinity (mg-CaCO3 / L) is 7 times the ammonia concentration (mg-N / L) of the raw water. Aeration is then started, and samples are taken at regular intervals (e.g., 0, 30, 60, 90, and 120 minutes) to perform water quality analysis. x The nitrification rate per carrier volume (mg-N / L-carrier / h) is calculated from the change in N concentration.

[0069] (Denitrification batch test) For example, 20 vol% of the carrier collected from the treatment tank is placed in a 1 L sealable container, and the raw water is diluted to a total volume of 1 L. NaNO3 is then added so that the NO3-N concentration is 50-100 mg / L. After replacing the gas in the container with nitrogen gas, stirring is started, and samples are taken at regular intervals (e.g., 0, 30, 60, 90, and 120 minutes) to analyze the water quality. x From the change in -N concentration, the denitrification rate per carrier volume (mg-N / L-carrier / h) is calculated.

[0070] -Sensor-based control 1 (feedback control)- Sensor-based control methods include pH control, alkalinity control, ORP control, DO control, NH4-N control, and NO x -N control, etc., and their combinations. For the reasons described below, ORP control, NO x -N control is preferred.

[0071] (pH, alkalinity control) In nitrification promotion treatment, alkalinity decreases and pH drops as the nitrification reaction progresses. If nitrification is carried out using only the alkalinity in the raw water without adding alkali, the nitrification process will stop once the alkalinity falls below a certain value, and the pH will also stop decreasing. Therefore, by checking the change in pH or alkalinity over time, the point at which the change per hour falls below a certain value can be considered the point at which nitrification is complete and the process can be switched to denitrification promotion treatment.

[0072] In denitrification promotion treatment, alkalinity increases as the denitrification reaction progresses, causing the pH to rise. Therefore, by checking the change in pH or alkalinity over time, the point at which the change per hour falls below a certain value can be considered the point at which denitrification is complete, and the system can be switched to nitrification promotion treatment.

[0073] (ORP control) In nitrification promotion treatment, ORP increases with the oxidation of organic matter and the nitrification of ammonia. The slope of the change in ORP over time differs during the period when organic matter oxidation and nitrification are proceeding simultaneously, the period when organic matter oxidation is complete and only nitrification is proceeding, and after nitrification is complete. Therefore, by checking the amount of change and determining when the change per hour falls below a certain value, nitrification can be considered complete and the treatment can be switched to denitrification promotion treatment.

[0074] In the denitrification treatment, the inflow of raw water and NO xORP decreases as -N is denitrified, and the rate of change becomes smaller when denitrification is complete. Therefore, the point at which the rate of change per hour falls below a certain value is considered to be the point at which nitrification is completed, and it is possible to switch to nitrification promotion treatment. Compared to pH and DO, ORP control has a wider range of possible values ​​and higher resolution (generally -400mV to +400mV), allowing for more accurate control. In addition, NH4-N and NO x Unlike -N, it is an index that can comprehensively evaluate the state of organic matter, nitrogen compounds, etc. in the system, rather than the concentration of a single substance. Therefore, in cases like this, where the purpose is to roughly remove BOD and nitrogen and BOD and nitrogen remain in the tank, it is an appropriate index for evaluating the state inside the tank.

[0075] (DO control) In nitrification promotion treatment, if the same amount of air is blown in, after the oxidation and nitrification of organic matter in the tank is complete, DO will be higher than when the reaction was in progress. By checking the change in DO over time, nitrification can be considered complete when DO increases, and the process can be switched to denitrification promotion treatment.

[0076] (NH4-N control) In nitrification promotion treatment, the change in NH4-N concentration over time increases in the following order: the period when nitrification is complete, the period when organic matter oxidation and nitrification are proceeding simultaneously, and the period when organic matter oxidation is complete and nitrification is proceeding. By checking this change over time and determining when the change in NH4-N becomes small, nitrification can be considered complete and treatment can be switched to denitrification promotion treatment.

[0077] (NO x -N) In nitrification promotion treatment, NO x The time-dependent change in NO concentration increases in the following order: the period when nitrification is complete, the period when oxidation of organic matter and nitrification are proceeding simultaneously, and the period when oxidation of organic matter is complete and nitrification is proceeding. x When the change in -N becomes small, nitrification is considered to be complete and denitrification treatment can be started.

[0078] In the denitrification promotion treatment, the amount of change is large while denitrification is progressing, and the amount of change becomes smaller when denitrification is completed. x When the change in -N becomes small, denitrification is considered complete and the process can be shifted to nitrification promotion treatment. x Control based on the -N concentration is preferable to this embodiment in that the completion time of the denitrification promotion treatment can be confirmed with one sensor, compared to DO control or NH4 -N control.

[0079] -Sensor-based control 2 (combined with feedforward)- Since most of the nitrogen components in raw water are NH4-N, the nitrogen concentration in raw water can be measured with an NH4-N meter. Therefore, if the target value of the nitrogen concentration in the treated water is determined, it is possible to calculate the required amount of nitrification and denitrification based on the relationship between the NH4-N concentration in the raw water and the target TN concentration in the treated water. The nitrification rate and denitrification rate per hour are determined by the NH4-N concentration in the treatment tank or the NO x Since it can be calculated from the -N concentration, the time required for nitrification and denitrification conditions to reach the target concentration can be calculated by the computer and the blower can be controlled accordingly. This makes it possible to keep nitrification time to the minimum necessary and reduce the aeration air volume.

[0080] -Addition of nutrients (phosphorus)- In the water treatment method according to the embodiment of the present invention, biological treatment is used to treat the separated liquid (raw water), and it may be necessary to supply phosphorus in an amount sufficient for the growth of organisms. Generally, in biological treatment, approximately 1 mg / L of phosphorus is required for a BOD of 100 mg / L, and it is desirable to supply phosphorus so as to satisfy this ratio relative to the raw water BOD. If the treatment is satisfactory, 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.

[0081] In particular, when dewatering septic tank sludge and sewage sludge as a solid-liquid separation process, using iron- or aluminum-based coagulants can result in phosphorus being incorporated into the sludge, lowering the phosphorus concentration in the separated liquid and making it necessary to add phosphorus. In crude treatment for BOD and TN removal, the supply of nutrients such as phosphorus tends to be overlooked, but a phosphorus deficiency can make it almost impossible to remove BOD, so it is preferable to supply phosphorus even in crude treatment. There are no particular restrictions on the form of phosphorus to be added, but methods include adding chemicals such as phosphoric acid or potassium dihydrogen phosphate, or adding a portion of sewage sludge.

[0082] (Dilution ratio) The biologically treated water obtained by the above biological treatment is sent to a dilution tank, where it is mixed with dilution water and diluted to meet the sewage discharge standards. The biologically treated water can be diluted typically by 1 to 4 times, more typically by 1 to 3 times, even by 1 to 2 times, or even by 1 to 1.5 times to meet the sewage discharge standards. Dilution can be performed continuously or only when necessary to meet the sewage discharge standards. This allows for more efficient and appropriate treatment that meets the water quality standards for sewerage discharge using a smaller amount of dilution water than conventional methods.

[0083] According to this embodiment, the biological treatment may be performed to such an extent that dilution of the biologically treated water is no longer necessary. In such a case, the biologically treated water after the biological treatment using the biofilm method may be discharged directly into a sewer system without dilution.

[0084] According to the water treatment method of the embodiment of the present invention, the separated liquid obtained by solid-liquid separation of sludge containing at least one of septic tank sludge and sewage sludge is subjected to a nitrification promotion treatment and a denitrification promotion treatment, and two or more aeration conditions are set in the treatment tank, and the BOD and nitrogen are roughly removed and then diluted, thereby making it possible to more efficiently and stably obtain treated water suitable for discharge into the sewerage system using a small amount of dilution water and a small and simple device.

[0085] <Water treatment equipment> As shown in FIG. 1, a water treatment device according to an embodiment of the present invention includes a solid-liquid separation device 1 that separates sludge, including at least one of septic tank sludge and sewage sludge, into separated sludge and separated liquid by solid-liquid separation; a treatment tank (aeration treatment tank) 2 that contains a biofilm that biologically treats the separated liquid and performs a nitrification-promoting treatment that promotes nitrification and a denitrification-promoting treatment that promotes denitrification on the separated liquid; control means 4 that sets and controls the aeration conditions of the treatment tank 2 to at least two conditions so that the nitrification-promoting treatment and the denitrification-promoting treatment are performed alternately in the treatment tank 2; and a dilution tank 3 that dilutes the biologically treated water treated in the treatment tank 2 so that it meets the sewage discharge standards.

[0086] Various devices can be used for the solid-liquid separation device 1, and among them, it is preferable to use a dehydrator as the solid-liquid separation device 1 in terms of equipment and operation costs. It is also preferable to use a concentration machine (not shown) upstream of the solid-liquid separation device 1 to perform concentration treatment on the raw water before solid-liquid separation.

[0087] The treatment tank 2 contains a biofilm with microorganisms attached to the surface of carriers. Typically, a contact oxidation tank containing fixed-bed carriers or a fluidized bed carrier tank containing fluidized bed carriers can be suitably used as the treatment tank 2 according to this embodiment. The treatment tank 2 may be provided with an agitator 21 for agitating the separated liquid supplied to the treatment tank 2. The agitator 21 may be omitted. An aeration means 22 for aerating the treatment tank 2 is connected to the bottom of the treatment tank 2. The aeration means 22 can be composed of a pump and an aeration pipe (not shown) for sending gas into the treatment tank 2. Aeration by the aeration means 22 generates a liquid flow in the separated liquid in the treatment tank 2, which causes the biofilm (fluidized bed carriers or fixed-bed carriers) in the treatment tank to flow.

[0088] A measuring means 23 for measuring the water quality of the separated liquid in the treatment tank 2 may be disposed in the treatment tank 2. Examples of the measuring means 23 include a pH meter, an ORP meter, a DO meter, an NH4-N concentration meter, and a NO xA measuring means 24 for measuring the water quality of the separated liquid flowing into the treatment tank 2 may be provided. Examples of the measuring means 24 include a pH meter, an ORP meter, a DO meter, an NH4-N concentration meter, a NO x -N densitometers and combinations thereof are available.

[0089] For example, the measurement means 24 measures the NH4-N concentration of the separated liquid, and the measurement means 23 measures the NH4-N concentration or NO x By measuring the -N concentration and setting a target value for the nitrogen concentration in the biological treatment water, the required amount of nitrification and denitrification can be calculated from the relationship between the NH4-N concentrations in the separated liquid and the biological treatment water.By determining the nitrification promotion treatment time and denitrification promotion treatment time based on the calculation results and setting the aeration conditions for each treatment, it is possible to efficiently remove BOD and TN from the separated liquid.

[0090] The treatment tank 2 preferably includes a separation liquid supply pipe 11 connected to the bottom of the treatment tank 2 and capable of supplying a separation liquid into the treatment tank 2 so as to generate a liquid flow within the treatment tank 2. By connecting the separation liquid supply pipe 11 to the bottom of the treatment tank 2 and configuring it so that the separation liquid is supplied from the bottom to the top of the treatment tank 2, sedimentation of the fluidized carrier or fixed-bed carrier contained in the treatment tank 2 to the bottom of the treatment tank 2 can be suppressed, the fluidity of the carrier can be increased, and the contact efficiency between the carrier and the separation liquid can be improved. By connecting the separation liquid supply pipe 11 at a height that is relatively 0 (tank bottom) to 0.5, more preferably 0 to 0.3, when the height of the treatment tank 2 is 1, the efficiency of generating a liquid flow within the tank due to the supply of separation liquid can be improved.

[0091] The control means 4 is composed of a general-purpose computer or the like, and is connected to the aeration means 22. The control means 4 controls the aeration conditions so that nitrification promotion treatment and denitrification promotion treatment are alternately performed in the treatment tank 2. The control means 4 may be connected to the agitator 21, and can also control the agitation conditions of the agitator 21. Furthermore, the control means 4 may be connected to the measurement means 23, 24, and can measure the water quality (pH, ORP, DO, NH4-N concentration, NO concentration) of the measurement means 23, 24. xThe aeration by the aeration means 22 may be controlled based on the measurement results of water quality (such as -N concentration). The control means 4 controls the aeration in the treatment tank 2 by the aeration means 22 based on the water quality measurement results from the measuring means 23 and 24, thereby enabling more stable biological treatment that can follow fluctuations in the water quality of the raw water. The biologically treated water treated in the treatment tank 2 is stored in the dilution tank 3, where it is diluted with dilution water to obtain treated water.

[0092] According to the water treatment device of the embodiment of the present invention, a control means 4 is provided for setting and controlling the aeration conditions of the treatment tank 2 under at least two conditions so that nitrification promotion treatment and denitrification promotion treatment are alternately performed in the treatment tank 2. This allows for rough removal of BOD and TN from the solid-liquid separated liquid of sludge containing septic tank sludge or sewage-related sludge in one treatment tank 2, thereby enabling treated water of a quality that meets sewage discharge standards to be efficiently obtained from sludge containing septic tank sludge or sewage-related sludge using a small-sized device. [Example]

[0093] The following examples of the present invention are provided for a better understanding of the present invention and its advantages, but are not intended to limit the invention.

[0094] According to the flow chart shown in Figure 2, water treatment according to the Example (experimental system), water treatment according to the Example, and water treatment according to a Reference Example (control system) for comparing the effects of the water treatment according to the Example were carried out. The raw water used was dehydrated separated liquid from an actual sewage treatment facility. Nutrients (monopotassium phosphate (KH2PO4)) were added to the raw water as appropriate. Representative examples of the raw water conditions during the experiment are shown in Table 1.

[0095] [Table 1]

[0096] The raw water is treated with a BOD volume load of 0.6 kg-BOD / m 3 / d, TN load 0.23kg-N / m 3Water was passed through each test system so that the water flow rate was 1 / d. Figure 2 shows the treatment flow of the laboratory test. In addition, a control system was used for comparison with a system in which constant aeration was performed. The carrier was a polyethylene honeycomb carrier (φ25 mm, thickness 4 mm, specific surface area 800 m 2 / m 3 ) was filled in each tank at 30% by volume.

[0097] The raw water inflow conditions and aeration conditions were set for weekdays (Monday to Friday) and holidays (Saturday and Sunday) as shown in Table 2. Note that for "nitrification conditions" in Table 2, the aeration volume was set so that the DO in the treatment tank was set to 4.0 mg / L, and mechanical agitation was not performed, and for "denitrification (micro-aeration) conditions," the aeration volume was set so that the DO in the treatment tank was set to 0.2 mg / L, and mechanical agitation was performed.

[0098] [Table 2]

[0099] The experimental results are shown in Table 3. A sample of treated water mixed with one day's worth of treated water was analyzed. The required dilution ratio was calculated based on discharge standards of BOD: 600 mg / L and TN: 240 mg / L. In the experimental system in which the aeration conditions were switched, the BOD concentration was slightly higher than in the control system, but the TN concentration averaged 320 mg-N / L, resulting in a nitrogen removal rate of 52.2%. In the control system in which the aeration conditions were not switched, the TN concentration of the treated water averaged 648 mg / L, with almost no nitrogen being removed. The dilution ratio of the dilution water used for sewerage discharge was also reduced to 1.3 times in the experimental system.

[0100] [Table 3]

[0101] From the above results, it was confirmed that stable nitrogen removal and a reduction in the dilution ratio can be achieved by setting and switching between at least two aeration conditions to alternate between nitrification and denitrification. [Explanation of symbols]

[0102] 1...Solid-liquid separator 2...Treatment tank (aeration treatment tank) 3...Dilution tank 4. Control means 11...Separated liquid supply pipe 21...Agitator 22...Aeration means 23...Measuring means 24...Measuring Instruments

Claims

1. A separated liquid obtained by solid-liquid separation of sludge containing at least one of septic tank sludge and sewage sludge is supplied into an aeration treatment tank containing a biological carrier; In the treatment tank, aeration conditions are set to at least two conditions, including aeration conditions for the nitrification promotion treatment and aeration conditions for the denitrification promotion treatment, the aeration conditions having an aeration amount smaller than that of the aeration conditions for the nitrification promotion treatment, so that a nitrification promotion treatment for promoting nitrification and a denitrification promotion treatment for promoting denitrification are carried out; By performing biological treatment while switching the aeration conditions so that the nitrification promotion treatment and the denitrification promotion treatment are alternately switched in the treatment tank, biologically treated water that meets the sewage discharge standards can be obtained. A water treatment method comprising the steps of:

2. 2. The water treatment method according to claim 1, wherein the separated liquid is supplied to the treatment tank intermittently.

3. 3. The water treatment method according to claim 1, wherein in the denitrification promotion treatment, the separated liquid contained in the treatment tank is caused to flow by at least one of the following: causing the separated liquid to flow into the treatment tank from a lower part thereof, stirring the separated liquid with an agitator, or aerating the separated liquid.

4. a solid-liquid separator that separates sludge containing at least one of septic tank sludge and sewage sludge into separated sludge and separated liquid; a treatment tank that accommodates a biofilm that biologically treats the separated liquid, and subjects the separated liquid to a nitrification promotion treatment that promotes nitrification and a denitrification promotion treatment that promotes denitrification, thereby obtaining biologically treated water that meets sewage removal standards; a control means for controlling the aeration conditions of the treatment tank by setting at least two conditions, i.e., aeration conditions for the nitrification promotion treatment and aeration conditions for the denitrification promotion treatment, so that the nitrification promotion treatment and the denitrification promotion treatment are alternately performed in the treatment tank; A water treatment device comprising:

5. 5. The water treatment device according to claim 4, further comprising a separated liquid supply pipe connected to a lower portion of the treatment tank and capable of supplying the separated liquid into the treatment tank so as to generate a liquid flow within the treatment tank.

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