Biological treatment device and method for organic wastewater

Abstract

To provide a biological treatment apparatus and biological treatment method for organic waste water capable of reducing an amount of air in aerobic biological treatment and efficiently removing organic matter with a high load while significantly reducing an amount of sludge generated, as well as to maintain stable treated water quality.SOLUTION: A first biological treatment tank 3 has a fixed bio-attachment carrier 30 and an air diffusing means 31 located below the fixed bio-attachment carrier, the second biological treatment tank 4 introduces the treated liquid from the first biological treatment tank and treats it with floating microorganisms that do not use bio-attachment carriers and has an air diffusing means 41, and a sedimentation tank 5 where the mixed liquid treated in the second biological treatment tank is divided and introduced into the sedimentation sludge and treatment water. An inflow line that distributes and introduces organic waste water into the first biological treatment tank and the second biological treatment tank, and a return line 6 that returns part of the sedimentation sludge discharged from the sedimentation tank to the second biological treatment tank, furthermore, an agitating means is provided in the second biological treatment tank to agitate the treated liquid, and denitrification is performed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a biological treatment device and a biological treatment method for organic wastewater, and more particularly to a biological treatment device and a biological treatment method for organic wastewater that can improve the treatment efficiency by using microorganisms and improve the water quality of the treated water by using floating microorganisms. [Background technology]

[0002] When treating a wide range of organic wastewater, such as sewage, domestic wastewater, and wastewater from food factories, if the BOD concentration of the organic wastewater falls below 300 mg / L, a large amount of water is required for high-load treatment, and the residence time of the wastewater in the treatment tank is also short. For this reason, when evaluating treated water, not only is the biochemical oxygen demand (BOD) of the treated water required to be low, but suspended solids (SS) must also be low.

[0003] The activated sludge process, which uses suspended microorganisms, is widely used in the biological treatment of organic wastewater. The activated sludge process produces excellent treated water quality and is easy to maintain, so it is widely used in sewage treatment and industrial wastewater treatment facilities. However, the BOD volume load in the activated sludge process is 0.2 to 0.8 kg-BOD / m 3 / d (d means one day), and there is room for technical improvement.

[0004] Another biological treatment method for organic wastewater is the fluidized bed method, which uses carriers to maintain a high concentration of microorganisms in the treatment tank. This method has a BOD volumetric load of 2 to 3 kg-BOD / m 3 Compared to the activated sludge process, this process can handle a higher organic matter load and has excellent treatment efficiency, but since the SS concentration in the treated water is high, it is common to install SS removal equipment such as filtration equipment after the fluidized bed process.

[0005] As wastewater treatment, hybrid wastewater treatment has been carried out by combining a first biological treatment using non-coagulating sludge with a second biological treatment using floating sludge, instead of the above-mentioned activated sludge method or fluidized bed method. Specifically, there are the following technologies, and the problems of the conventional technologies are listed below with reference to representative patent documents.

[0006] Patent Document 1 discloses that organic wastewater is bacterially treated in a first treatment tank that is not filled with carriers, and the organic matter contained in the wastewater is oxidized and decomposed, and converted into non-aggregated bacteria including dispersed bacteria. Thereafter, sludge is returned from a settling tank to a second treatment tank, where it is preyed upon and removed by sessile protozoa, greatly reducing the amount of excess sludge produced.

[0007] Treatment in a first treatment tank not filled with carriers is rate-limiting due to the proliferation of non-aggregating bacteria, and is not suitable for treatment with short retention times. Even in Patent Document 1, wastewater requires a long retention period of 3 to 10 days.

[0008] Furthermore, it is necessary to produce flocs that can be separated into solid and liquid in the second treatment tank, and in order to grow protozoa, which have a slow growth rate, it is necessary to extend the sludge retention time in the second treatment tank without adding a BOD source. As a result, it is necessary to increase the capacity of the second treatment tank and the settling tank.

[0009] Patent Document 2 discloses that organic wastewater is introduced into a first biological treatment tank and biologically treated with bacteria, the first biological treatment water containing dispersed bacteria from the first biological treatment tank 1 is passed through a fluidized bed type second biological treatment tank in a one-way manner to obtain second biological treatment water, the second biological treatment water is passed through a floating type third biological treatment tank to obtain third biological treatment water, and the third biological treatment water is separated into sludge and treated water in a settling tank, and a part of the separated sludge is returned to the third biological treatment tank as returned sludge. It also discloses that the first biological treatment tank is a fluidized bed type biological treatment tank with a carrier filling rate of 10% or less, and the second biological treatment tank is a fluidized bed type biological treatment tank with a carrier filling rate of 10% or more.

[0010] Patent Document 2 also shows that in order to ensure an appropriate organic load in the downstream biological treatment tank, the raw water is divided into organic wastewater and organic wastewater is dispensed into the first biological treatment tank and the third biological treatment tank. As a guideline for dispensing, it also shows an example of operation so that the sludge load due to soluble BOD in the third biological treatment tank is 0.025 kg-BOD / kg-MLSS / d or more.

[0011] In all of the embodiments disclosed in Patent Document 2, one or both of the first and second biological treatment tanks are filled with fluidized bed carriers. When filling the tanks with carriers, it is necessary to provide a carrier separation means such as a screen to separate the carriers and allow the mixed liquid to be taken out. In addition, in order to fluidize the carriers, a large amount of air is required as a power source, more than is required for biological treatment.

[0012] In this treatment method, the carriers in both the first and second treatment tanks flow with the inflow of raw water, and accumulate near the screen on the downstream side of the tank. This causes a problem that the carriers create filtration resistance near the screen, making it difficult to discharge the mixed liquid from the tank. If the accumulated carriers are not transported to the upstream side of the tank, the specified performance cannot be achieved, which hinders efficient treatment using the fluidized bed carriers.

[0013] Moreover, it has become clear that when the retention time of the raw water in the treatment tank is short, such as a few hours, the fluidized bed carriers tend to be concentrated in the downstream part of the treatment tank, preventing the proliferation of dispersed bacteria.

[0014] Patent Document 3, like Patent Document 2, discloses a fluidized bed method with added carriers for high-load treatment of organic wastewater. 3 This method allows operation at a BOD volumetric load of more than 1000 m3 / d. However, the amount of sludge generated is about 30% of the decomposed BOD, which is higher than that of the conventional activated sludge process.

[0015] Specifically, organic wastewater is introduced into a first biological treatment tank for biological treatment using bacteria, the first biologically treated water containing dispersed bacteria from the first biological treatment tank is passed through a second biological treatment tank to obtain second biologically treated water, and the second biologically treated water is subjected to solid-liquid separation. The second biological treatment tank is provided with fluidized bed carriers and rocking bed carriers as carriers for retaining microorganisms. A BOD volume load of 5 kg / m can be achieved by returning a portion of the sludge from the subsequent biological treatment tank, by configuring this first biological treatment tank as a multi-stage tank of two or more tanks, or by adding carriers. 3 It has also been shown that high-load processing of more than / d is possible.

[0016] In this treatment system, too, the carriers in both the first and second treatment tanks are fed with the inflow of the liquid to be treated and the return sludge, making this a high-load treatment method in which carriers are added to the activated sludge process.

[0017] The treatment method of Patent Document 3 also has the problem that the carrier flows and accumulates near the screen on the downstream side of the tank, as in Patent Document 2. This causes a problem that the carrier generates a filtration resistance near the screen, making it difficult to discharge the mixed liquid from the tank. In addition, there is a problem that the specified performance cannot be achieved unless the accumulated carrier is transferred to the upstream side of the tank.

[0018] In response to this, the present inventors proposed in Patent Document 4 to place fixed organism attachment carriers (referred to as "fixed contact carriers" in Patent Document 4) in the biological treatment tank. It has been confirmed that the fixed-type organism-attached carriers can eliminate the problems of the fluidized bed carriers (fluidized carriers) pointed out in Patent Documents 2 and 3, and can efficiently treat organic wastewater. However, as the amount of treatment in the biological treatment tank increases, a large amount of suspended solids (SS) is generated, and the soluble BOD is also high, causing the discharged treated water to become turbid, resulting in a significant deterioration in water quality, which is a new problem.

[0019] To remove fine suspended solids (SS) and soluble BOD, it is necessary to add a treatment process using suspended microorganisms or a sedimentation process in the downstream stage. However, in order to provide a suspended microorganism treatment tank or a sedimentation tank with a treatment capacity that matches the treatment capacity of a biological treatment tank using fixed bioattaching carriers, it is essential that the capacity is at least several times the capacity of the biological treatment tank. It was also found that in treated water treated in a biological treatment tank using fixed-type biological attachment carriers, the floating microorganisms in the downstream treatment tank do not multiply sufficiently, and the treatment effect of the floating microorganisms cannot be fully expected. [Prior art documents] [Patent documents]

[0020] [Patent Document 1] Japanese Patent Application Publication No. 55-20649 [Patent Document 2] JP 2009-202115 A [Patent Document 3] JP 2013-141640 A [Patent Document 4] JP 2017-159243 A [Non-patent literature]

[0021] [Non-Patent Document 1] "Easy Water Treatment" by Isao Muneya, (Publisher) Isao Muneya, (Printer) Tanaka Print Co., Ltd., Published on December 25, 2008 Summary of the Invention [Problem to be solved by the invention]

[0022] In view of the above-mentioned problems, the problem that the present invention aims to solve is to provide a biological treatment apparatus and a biological treatment method for organic wastewater which can reduce the amount of air used in aerobic biological treatment, and which can efficiently remove organic matter under high load while significantly reducing the amount of sludge generated, and which can maintain a stable water quality of the treated water. [Means for solving the problem]

[0023] In order to solve the above problems, the biological treatment apparatus and method for organic wastewater of the present invention have the following features. (1) A system comprising a first biological treatment tank having fixed organism-attached carriers and an aeration means disposed below the fixed organism-attached carriers, a second biological treatment tank into which the treated liquid from the first biological treatment tank is introduced and treated with floating microorganisms without using organism-attached carriers and which also has an aeration means, and a settling tank for performing solid-liquid separation of the mixed liquid from the second biological treatment tank into settled sludge and treated water, and an inlet line for distributing and introducing organic wastewater into the first biological treatment tank and the second biological treatment tank, and a return line for returning a portion of the settled sludge discharged from the settling tank to the second biological treatment tank, Also The second biological treatment tank is provided with an agitation means for agitating the treated liquid, and denitrification treatment is carried out. The apparatus further includes a first BOD measuring means for measuring the BOD value of the organic wastewater and a second BOD measuring means for measuring the soluble BOD value of the treatment liquid in the second biological treatment tank, and an adjusting means for adjusting the amount of the organic wastewater distributed to the first biological treatment tank and the second biological treatment tank based on the measurements of the first and second BOD measuring means so that the ratio of the soluble BOD value of the second biological treatment tank to the BOD value of the organic wastewater is in the range of 6.7 to 30%. The present invention relates to a biological treatment apparatus for organic wastewater.

[0024] (2) In the biological treatment apparatus for organic wastewater described in (1) above, the second biological treatment tank is characterized in that the aeration means is disposed at least either upstream or downstream of the agitation means.

[0026] ( 3 ) Above (1) Or (2) In the biological treatment apparatus for organic wastewater described in the above, the first biological treatment tank is characterized in that a baffle wall for restricting the flow of the organic wastewater is disposed in the direction of the flow of the organic wastewater.

[0027] ( 4 ) a first biological treatment process in which organic wastewater is treated with a fixed type biological attachment carrier; a second biological treatment process in which the treated liquid from the first biological treatment process is introduced and treated with floating microorganisms without using a biological attachment carrier; and a sedimentation process in which the mixed liquid from the second biological treatment process is solid-liquid separated into a settled sludge and treated water, the organic wastewater being distributed and introduced into the first biological treatment process and the second biological treatment process, and a part of the settled sludge discharged from the sedimentation process is returned to the second biological treatment process; AlsoIn the second biological treatment step, the treatment liquid is stirred by a stirring means to carry out denitrification treatment. Furthermore, the amount of organic wastewater distributed to the first biological treatment step and the second biological treatment step is adjusted so that the ratio of the soluble BOD value of the treated liquid of the second biological treatment step to the BOD value of the organic wastewater is in the range of 6.7 to 30%. The present invention relates to a biological treatment method for organic wastewater.

[0028] ( 5 ) the above( 4 ) is characterized in that the second biological treatment step comprises aeration by an aeration means at least on either the upstream side or the downstream side of the agitation means. Effect of the Invention

[0030] The biological treatment device and biological treatment method for organic wastewater of the present invention are capable of treating organic matter under high loads, and after the sedimentation process, treated water with extremely low BOD and SS can be obtained. Specifically, most of the organic wastewater is treated in a first biological treatment process consisting of a reaction tank filled with fixed-type biological attachment carriers, and a part of the organic wastewater is also introduced into a second biological treatment process consisting of a floating-type microbial treatment tank, and return sludge from the sedimentation process is introduced, whereby the soluble BOD remaining in the first biological treatment process can be biologically decomposed, and the bacteria that could not be flocculated from the first biological treatment process can be attached and captured by the floating sludge. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 is a diagram showing an outline (first embodiment) of a biological treatment device for organic wastewater according to the present invention. [Diagram 2] FIG. 1 is a diagram showing an outline of a biological treatment apparatus for organic wastewater according to the present invention (second embodiment). [Diagram 3] FIG. 1 is a diagram showing an outline of a biological treatment apparatus for organic wastewater according to the present invention (third embodiment). [Figure 4] FIG. 1 is a diagram showing an outline of a biological treatment apparatus for organic wastewater according to the present invention (fourth embodiment). [Diagram 5] FIG. 1 is a diagram showing an outline of a biological treatment apparatus for organic wastewater according to the present invention (fifth embodiment). [Figure 6] 1 is a graph showing the experimental results of Example 1. [Figure 7]FIG. 2 is a diagram showing an application example of a second biological treatment tank used in the biological treatment device for organic wastewater according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The biological treatment apparatus and method for organic wastewater according to the present invention will be specifically described below. As shown in Figures 1 and 2, the biological treatment apparatus for organic wastewater of the present invention comprises a first biological treatment tank 3 having a fixed organism attachment carrier 30 and an aeration means 31 arranged below the fixed organism attachment carrier, a second biological treatment tank 4 into which the treatment liquid treated in the first biological treatment tank is introduced and treated by floating microorganisms and which also has an aeration means 41, and a settling tank 5 in which the mixed liquid treated in the second biological treatment tank is separated into solid-liquid separation and separation into settled sludge and treated water, and further comprises inlet lines (11, 12) for distributing and introducing organic wastewater into the first biological treatment tank 3 and the second biological treatment tank 4, and a return sludge line 6 for returning a portion of the settled sludge discharged from the settling tank 5 to the second biological treatment tank 4.

[0033] In addition, with regard to the biological treatment method for organic wastewater of the present invention, the treatment carried out in the first biological treatment tank corresponds to the "first biological treatment step", the treatment carried out in the second biological treatment tank corresponds to the "second biological treatment step", and the treatment carried out in the sedimentation tank corresponds to the "sedimentation step".

[0034] In the first biological treatment tank (treatment step) used in the present invention, the BOD volume load is 0.5 kg / m 3 / d~3kg / m 3 / d, the BOD removal rate is 80% or more, and the BOD volume load is 0.75 kg / m 3 / d~1.5kg / m 3 Although a BOD removal rate of 90% or more is achieved at 1000 / d, even if a sedimentation process is provided in the latter stage, fine particles and bacteria will flow into the treated water during the sedimentation process, making further improvement of the treated water necessary for practical use. Note that the first biological treatment tank, the second biological treatment tank, and the sedimentation tank in the present invention are not limited to tanks each consisting of a single container, and also include tanks in which multiple containers are connected in series or parallel with piping.

[0035] The second biological treatment tank (treatment step) used in the present invention is a biological treatment method using normal suspended sludge, or the so-called activated sludge method, and the BOD volume load required to produce sludge with good settling properties in the sedimentation step is 0.1 kg / m 3 / d~0.5kg / m 3 / d, preferably with a BOD volumetric loading of 0.1 kg / m 3 / d~0.3kg / m 3 / d. Furthermore, in order to form good flocs of suspended sludge in the settling step and improve settling properties, the MLSS in the second biological treatment tank is preferably maintained at 1000 mg / L to 2000 mg / L, and preferably 1000 mg / L to 1500 mg / L.

[0036] In the present invention, when organic wastewater is distributed and treated in the entire system consisting of the first biological treatment tank (treatment process), the second biological treatment tank (treatment process), and the sedimentation tank (sedimentation process), the BOD volume load in the entire biological reactors of the first biological treatment process and the second biological treatment process is 0.5 kg / m 3 / d~1.5kg / m 3 / d, it is possible to achieve a BOD removal rate of 80% or more, and a BOD volumetric load of 0.6 kg / m 3 / d~0.9kg / m 3 / d, a treatment performance of more than 95% BOD removal rate can be achieved.

[0037] In this case, it is extremely important to adjust the amount of organic wastewater distributed to the first biological treatment process and the second biological treatment process. The distribution amount of the organic wastewater in the present invention is adjusted by a flow rate adjustment mechanism indicated by reference symbol 2 in Fig. 1 or 2. A supply line 1 for the organic wastewater (raw water) branches through the flow rate adjustment mechanism 2 to form distribution lines (11, 12). A sensor S1 is provided to measure the BOD concentration of raw water, and a sensor S2 is provided to measure the BOD concentration in the second biological treatment tank.

[0038] In Figure 2, in order to suppress the effect of returned sludge on sensor S2, a space is provided surrounding the confluence of treated water from the first biological treatment tank and organic wastewater (raw water) (part of the partition that forms the space has an opening that communicates with the inside of the second biological treatment tank), forming a water quality measuring section 9.

[0039] The operator can adjust the flow control mechanism 2 based on the measurement results from sensors S1 and S2, but it is also possible to input the measurement results to a control device 8 as an adjustment means and automatically control the flow control mechanism, as shown in Figures 4 and 5.

[0040] The fixed-type organism-attaching carriers 30 filled in the first biological treatment tank are an aggregate of individual carriers. As shown in Patent Document 4 or Non-Patent Document 1, the carriers are preferably in the shape of generally usable corrugated sheets, honeycomb tubes, bottles, cylinders, nets, balls, or sea urchins. Microorganisms attach to the carriers, and the microorganisms corresponding to the load of each tank multiply, making it possible to efficiently treat the organic matter in the tanks.

[0041] If the raw water contains suspended solids (SS), the fixed organism attachment carrier filling section in the tank will become clogged if too much SS adheres to and is retained on the carrier. For this reason, it is preferable to select a carrier with sufficient mesh size that is less likely to be clogged by SS. Among the above single bodies, cylindrical, net, ball, or sea urchin-shaped carriers with wide mesh sizes can be suitably selected.

[0042] In the first biological treatment step, it is necessary to devise a way to prevent the fixed biological carriers placed in the tank from flowing out due to aeration or the inflow or outflow of wastewater. Specifically, a mesh-like support part with a mesh width is provided in the reaction tank of the first biological treatment step, the fixed biological carriers are filled on the upper part of this net, and a mesh with a mesh width or a holed restraining part is provided on the upper surface of the filled part so that the fixed biological carriers do not flow out due to aeration or the like. When the technical purpose is high-load treatment, it is important that the filling ratio of the fixed biological carriers in the first biological treatment step is at least 50% or more, preferably 60% to 70%. The fixed biological carriers of the present invention include not only those fixedly placed in the biological treatment tank, but also those configured so that the carriers are densely packed together and do not easily flow.

[0043] In the first biological treatment tank, an aeration means 31 for supplying air containing oxygen is disposed below the fixed organism-attached carriers 30. The air discharged from the aeration means is prevented from diffusing upward and being easily discharged to the outside by the fixed organism-attached carriers, and a large amount of air remains in the liquid to be treated. This results in a higher oxygen dissolution efficiency than when the fluidized bed type carriers of Patent Documents 2 or 3 are used. Furthermore, when the fixed organism-attached carriers are used, air, which serves as a power source for moving the fluidized bed type carriers of Patent Documents 2 or 3, is not required, making it possible to significantly reduce the amount of air required for the treatment of organic wastewater.

[0044] Next, the start-up of the biological treatment system for organic wastewater of the present invention can employ a method that makes use of the characteristics of the first biological treatment step. In the first method, the first biological treatment step is filled with raw water, and the treated liquid is kept in the tank for a period during which treatment is satisfactory. During this initial period, the entire amount of raw water is treated in the second biological treatment step via a dispensing line. As the treatment in the first biological treatment process progresses, it is advisable to gradually increase the amount of raw water on the first biological treatment process side.

[0045] In the second method, the sludge returned from the settling tank to the second biological treatment tank is returned to the first biological treatment tank as seed sludge, and the supply of raw water to the first biological treatment tank is reduced while a portion of the raw water is treated in the first biological treatment tank, while the majority of the raw water is treated in the second biological treatment tank.

[0046] When a steady state is reached, the amount of raw water dispensed should be greater in the first biological treatment process than in the second biological treatment process. The distribution rate of raw water to the first biological treatment process is preferably in the range of 70 to 95% of the total amount of raw water. The distribution rate of raw water is defined as the ratio of the amount of raw water distributed to the first biological treatment process or the ratio of the amount of raw water distributed to the second biological treatment process to the amount of raw water.

[0047] FIG. 3 shows an example in which a baffle wall 10 is installed in the first biological treatment tank. In the first biological treatment tank, there are areas filled with fixed-type biological carriers and areas without carriers, and the fluid resistance differs between the two spaces. The raw water mainly passes through the areas without carriers, which have low fluid resistance, resulting in insufficient contact between the raw water and the carriers. In order to prevent the raw water from flowing into the second biological treatment tank in an insufficiently treated state, that is, to efficiently bring the raw water into contact with the carriers in the first biological treatment tank and to sufficiently treat the water, it is important to provide a baffle wall 10 in the first biological treatment tank. In particular, when the raw water is likely to flow laterally below the fixed organism-attached carriers 30, the provision of a baffle wall is important. The flow barrier may be anything that provides resistance to the flow of raw water, etc., and may be a partition plate with an opening or a protrusion disposed on the bottom surface of the treatment tank.

[0048] In the second biological treatment tank shown in Figs. 1 to 5, an aeration means 41 is disposed in the treatment tank. If the BOD load in the second biological treatment tank is small, or if the amount of aeration is large and the dissolved oxygen concentration exceeds 2 mg / L, the ammonia nitrogen contained in the organic wastewater will be oxidized to produce NO2-N (nitrite nitrogen) and NO3-N (nitrate nitrogen), causing sludge to float in the settling tank, increasing the SS of the treated water, and the BOD concentration, which may result in the discharge standard value not being met.

[0049] In order to suppress the production of NO2-N (nitrite nitrogen) and NO3-N (nitrate nitrogen) in the second biological treatment tank, it is important to make the second biological treatment tank anoxic (a state essentially free of dissolved oxygen) and stop the oxidation of ammonia nitrogen. For this reason, as shown in Fig. 7, an agitation means 42 is placed in the treatment tank, and the microorganisms are suspended in the BOD of the dispensed organic wastewater, allowing biological denitrification treatment. In denitrification treatment, the ASRT (Aerobic Sludge Retention Time) required for the proliferation of nitrifying bacteria that produce NO2-N (nitrite nitrogen) and NO3-N (nitrate nitrogen) is shortened, preventing the generation of NO2-N and NO3-N due to the inhibition of proliferation of nitrifying bacteria. In addition, symbol (3) in Figure 7 indicates the treated liquid introduced from the first biological treatment tank 3, symbol (5) indicates the treated liquid heading toward the sedimentation tank 5, and symbol 6 indicates the return sludge line flowing into the second biological treatment tank.

[0050] In FIG. 7(a), a partition wall 43 with an opening is provided in the treatment tank, and after anoxic mixing by agitation means 42 in the upstream tank, BOD treatment is performed by aeration using aeration means 41 in the downstream tank. This is not limiting, and it is also possible to place the agitation means 42 above the aeration means 44 in the upstream tank, as shown in FIG. 7(b). In order to adjust the amount of air from the aeration means 44, it is preferable to control the rotation speed of the blower that sends air to the aeration means 44 using the value of a dissolved oxygen concentration meter (sensor S3). In this case, the concentration of dissolved oxygen is 0.5 mg / L or less, and preferably 0.3 mg / L or less. The dotted arrow pointing to the symbol (8) in FIG. 7(b) indicates that the signal of the sensor S3, which is the dissolved oxygen concentration meter, is transmitted to the control device 8.

[0051] As shown in Figure 7(c), it is also possible to perform treatment under low dissolved oxygen conditions without providing a partition wall in the second biological treatment tank by providing an aeration means 41 and an agitation means 42. The quality of the treated water will be good if the treatment time for the total amount of dispensed organic wastewater and effluent from the first biological treatment tank is set to 2 hours or more. EXAMPLES

[0052] An experiment was conducted in which the ratio of the inflow rate of organic wastewater (raw water) to the second biological treatment tank, i.e., the distribution rate of raw water to the second biological treatment tank, was changed. In this example, the BOD volume load in the entire system and the distribution rate of each raw water are shown in Figure 1. In the following examples, the raw water distribution rate to the second biological treatment tank is abbreviated to "raw water distribution rate".

[0053] The raw organic wastewater for this treatment system is 72m 3 / d, the BOD concentration is 150 mg / L. The raw water is treated in a first biological treatment process (hereinafter referred to as the first process) filled with fixed biological attachment carriers, and in a second biological treatment process (hereinafter referred to as the second process) where floating microbial treatment is carried out and sludge is returned from the sedimentation process, followed by solid-liquid separation in the sedimentation process. In the sedimentation process, the separation speed per water surface area is 20 m 3 / m 2 Solid-liquid separation was carried out in a gravity settling tank at 1000 m / d, and the quality of the treated water was evaluated. The BOD concentration and S-BOD (soluble BOD) values ​​in RUN1 to RUN7 were measured in accordance with the official method JIS-K0102:2016 edition.

[0054] The results will be evaluated based on the achievement of the target values, as follows: The estimated SS generation concentration from BOD conversion is 66% of BOD. Since the BOD is 150 mg / L, the SS generation concentration in this case was set to 100 mg / L. 1) If the BOD removal rate is 95% or more and the SS rate is 10 mg / L or less, it is evaluated as "Very satisfactory" and indicated by the symbol ○. If the SS rate is 10 mg / L or less, the estimated removal rate is 90% or more. 2) If the BOD removal rate is between 80% and 95% and the SS is 20 mg / L or less, it is evaluated as "satisfactory" and indicated by the symbol △. If the SS is 20 mg / L or less, the estimated removal rate is 80% or more. 3) If the BOD removal rate is less than 80%, regardless of the SS concentration, it is evaluated as "unsatisfactory" and indicated by the symbol x.

[0055] [Table 1]

[0056] In the experiment, the sedimentation process was not changed, but the capacity of each of the tanks in the first and second processes was changed, as shown in Table 1, and the BOD volume load of the entire treatment system relative to the total capacity of the first and second processes (hereinafter referred to as the BOD load of the entire system) was set to 0.5 kg / m 3 / d~1.5kg / m 3 Seven runs (RUN1 to RUN7) were performed with different treatment times and 7 / d. In each run, the raw water distribution ratio to the first and second processes was changed by 5 points, and the treated water was evaluated. The tank volumes for the first and second steps were adjusted according to the load, and the volumes are shown in Table 1 for each RUN. The fixed bioattached carriers for the first step had internal gaps and were cage-shaped with wide mesh, fixed with upper and lower supports. The filling capacity of the fixed bioattached carriers was 60% of the volume of the first step (reaction tank). The MLSS concentration (concentration of bacteria in the treatment tank) for the second step was adjusted to 1000 mg / L. The experimental results are also shown in Table 1.

[0057] In RUN1, the tank capacity of the first process is 11m 3 , 2nd process 11m 3 The BOD load of the entire system is 0.5 kg / m 3 / d. First, if the raw water distribution rate is set to 5%, the amount of raw water to the second process is 3.6 m 3 The BOD load in the second process is 0.05 kg / m 3 The raw water distribution ratio was 5%, and the BOD concentration of the treated water after the sedimentation process was 16.5 mg / L, with a removal rate of 89%, and the SS concentration was 17 mg / L, which was rated as "satisfactory (△)."

[0058] Next, if the raw water distribution rate is increased to 10%, 15%, 20%, 25%, and 30%, the amount of raw water to the second process is 7.2 m3 From 21.6m 3 Up to 3.6m 3 The BOD load in the second step is 0.1-0.29 kg / m depending on the distribution ratio. 3 It is / d. For raw water distribution rates of 10%, 15%, 20%, 25%, and 30%, the BOD concentration of the treated water after the sedimentation process was 6 to 7 mg / L, the BOD removal rate was 95 to 96%, and the SS concentration was 7 to 10 mg / L, and was rated as "very satisfactory (○)."

[0059] When the raw water distribution rate is increased to 35%, 40%, 45%, and 50%, the amount of raw water to the second process is 25.2 m 3 36m from 3 The BOD load in the second process is 0.35-0.50 kg / m depending on the distribution ratio. 3 It is / d. For raw water distribution rates of 35%, 40%, 45%, and 50%, the BOD concentration of the treated water after the sedimentation process was 12 to 29 mg / L, the BOD removal rate was 81 to 92%, and the SS concentration was 7 to 18 mg / L, which was rated as "satisfactory."

[0060] Furthermore, if the raw water distribution rate is set to 55%, the amount of raw water to the second process is 39.6 m 3 The BOD load in the second process is 0.55 kg / m, which is above the treatment limit. 3 The BOD concentration of the treated water after the sedimentation process with a raw water distribution rate of 55% was 38 mg / L, with a removal rate of 75%, and the SS concentration was 24 mg / L, which was rated as "not satisfactory (×)."

[0061] In RUN2, the tank capacity of the first process is 9m 3 , 2nd process 9m 3 The BOD load of the entire system is 0.6 kg / m 3 / d. First, if the raw water distribution rate is set to 5%, the amount of raw water to the second process is 3.6 m 3 The BOD load in the second process is 0.06 kg / m 3The BOD concentration of the treated water after the sedimentation process in RUN2 with a raw water distribution rate of 5% was 16.5 mg / L, with a removal rate of 89%, and the SS concentration was 15 mg / L, which was rated as "satisfactory."

[0062] Next, if the raw water distribution rate is increased to 10%, 15%, 20%, and 25%, the amount of raw water to the second process is 7.2 m 3 From 18m 3 Up to 3.6m 3 The BOD load in the second step is 0.12-0.30 kg / m depending on the distribution ratio. 3 It is / d. For raw water distribution rates of 10%, 15%, 20%, and 25%, the BOD concentration of the treated water after the sedimentation process was 6 to 7 mg / L, with a BOD removal rate of 96%, and the SS concentration was 7 to 10 mg / L, earning an evaluation of "very satisfactory."

[0063] When the raw water distribution rate is increased to 30%, 35%, and 40%, the amount of raw water to the second process is 21.6 m 3 From 28.8m 3 The BOD load in the second process is 0.36-0.48 kg / m depending on the distribution ratio. 3 It is / d. For raw water distribution rates of 30%, 35%, and 40%, the BOD concentration of the treated water after the sedimentation process was 12 to 26 mg / L, with a BOD removal rate of 83 to 92%, and the SS concentration was 7 to 16 mg / L, which was rated as "satisfactory."

[0064] Furthermore, if the raw water distribution rate is set to 45%, the amount of raw water to the second process is 32.4 m 3 The BOD load in the second process is 0.54 kg / m, which is above the treatment limit. 3 The BOD concentration of the treated water after the sedimentation process with a raw water distribution rate of 45% was 39 mg / L, with a removal rate of 74%, and the SS concentration was 25 mg / L, which was rated as "not satisfactory."

[0065] In RUN3, the tank capacity of the first process is 8m 3 , 2nd process 8m 3 The BOD load of the entire system is 0.7 kg / m 3 / d. First, if the raw water distribution rate is set to 5%, the amount of raw water to the second process is 3.6 m 3 The BOD load in the second process is 0.07 kg / m 3 The BOD concentration of the treated water after the sedimentation process in RUN3 with a raw water distribution rate of 5% was 16.5 mg / L, with a removal rate of 89%, and the SS concentration was 14 mg / L, which was rated as "satisfactory."

[0066] Next, if the raw water distribution rate is increased to 10%, 15%, and 20%, the amount of raw water to the second process is 7.2 m 3 From 14.4m 3 Up to 3.6m 3 The BOD load in the second step is 0.14-0.27 kg / m depending on the distribution ratio. 3 It is / d. For raw water distribution rates of 10%, 15%, and 20%, the BOD concentration of the treated water after the sedimentation process was 5-6 mg / L, with a BOD removal rate of 96%, and the SS concentration was 6-8 mg / L, earning an evaluation of "very satisfactory."

[0067] Furthermore, if the raw water distribution rate is set to 25%, 30%, or 35%, the amount of raw water to the second process will be 18 to 25.2 m 3 The BOD load in the second process is 0.36 to 0.48 kg / m 3 In RUN3, with raw water distribution ratios of 25%, 30%, and 35%, the BOD concentration of the treated water after the sedimentation process was 12-24 mg / L, with a removal rate of 84-92%, and the SS concentration was 7-15 mg / L, which was rated as "satisfactory."

[0068] Furthermore, if the raw water distribution rate is set to 40%, the amount of raw water to the second process is 28.8 m 3 The BOD load in the second process is 0.55 kg / m, which is above the treatment limit. 3 The BOD concentration of the treated water after the sedimentation process with a raw water distribution rate of 40% was 39 mg / L, with a removal rate of 74%, and the SS concentration was 25 mg / L, which was rated as "not satisfactory."

[0069] In RUN4, the tank capacity of the first process was 6.8m 3 , 2nd process 6.8m 3 The BOD load of the entire system is 0.8 kg / m3 / d. First, if the raw water distribution rate is set to 5%, the amount of raw water to the second process is 3.6 m 3 The BOD load in the second process is 0.09 kg / m 3 The BOD concentration of the treated water after the sedimentation process in RUN3 with a raw water distribution rate of 5% was 16.5 mg / L, with a removal rate of 89%, and the SS concentration was 14 mg / L, which was rated as "satisfactory."

[0070] Next, if the raw water distribution rate is increased to 10% or 15%, the amount of raw water to the second process will be 7.2m 3 From 10.8m 3 Up to 3.6m 3 The BOD load in the second step is 0.17-0.26 kg / m depending on the distribution ratio. 3 It is / d. The raw water distribution rate was 10% and up to 15%, after the sedimentation process the BOD concentration of the treated water was 5-6 mg / L with a BOD removal rate of 96% and the SS concentration was 10 mg / L, which was rated as "very satisfactory."

[0071] When the raw water distribution rate is set to 20%, 25%, or 30%, the amount of raw water to the second process is 14.4 to 21.6 m 3 The BOD load in the second process was 0.34-0.5 kg / m3 / d. In RUN4, the BOD concentration of the treated water after the sedimentation process at raw water distribution rates of 20%, 25%, and 30% was 10.5-29.5 mg / L, with a removal rate of 80-93%, and the SS concentration was 10-20 mg / L, which was rated as "satisfactory."

[0072] Furthermore, if the raw water distribution rate is set to 35%, the amount of raw water to the second process is 25.2 m 3 The BOD load in the second process is 0.56 kg / m, which is above the treatment limit. 3 The BOD concentration of the treated water after the sedimentation process with a raw water distribution rate of 35% was 42 mg / L, with a removal rate of 72%, and the SS concentration was 27 mg / L, which was rated as "not satisfactory."

[0073] In RUN5, the tank capacity of the first process is 6m 3 , 2nd process 6m 3The BOD load of the entire system is 0.9 kg / m 3 / d. First, if the raw water distribution rate is set to 5%, the amount of raw water to the second process is 3.6 m 3 The BOD load in the second process is 0.09 kg / m 3 The BOD concentration of the treated water after the sedimentation process in RUN3 with a raw water distribution rate of 5% was 16.5 mg / L, with a removal rate of 89%, and the SS concentration was 12 mg / L, which was rated as "satisfactory."

[0074] Next, if the raw water distribution rate is increased to 10% or 15%, the amount of raw water to the second process will be 7.2m 3 From 10.8m 3 The BOD load in the second process is 0.18-0.27 kg / m depending on the distribution ratio. 3 It is / d. The BOD concentration of the treated water after the sedimentation process with a raw water distribution rate of 10% and 15% was 6 mg / L, the BOD removal rate was 96%, and the SS concentration was 9 to 10 mg / L, and was rated as "very satisfactory."

[0075] Furthermore, if the raw water distribution rate is set to 20% or 25%, the amount of raw water to the second process is 14.4 to 18 m 3 The BOD load in the second process is 0.36 to 0.45 kg / m 3 In RUN5, with raw water distribution ratios of 20% and 25%, the BOD concentration of the treated water after the sedimentation process was 23-28 mg / L, with a removal rate of 81-85%, and the SS concentration was 10 mg / L, which was rated as "satisfactory."

[0076] When the raw water distribution rate is set to 30%, the amount of raw water to the second process is 21.6 m 3 The BOD load in the second process is 0.54 kg / m 3 The BOD concentration of the treated water after the sedimentation process was 31 mg / L, with a removal rate of 79%, and the SS concentration was 15 mg / L, which was rated as "not satisfactory."

[0077] As mentioned above, the second biological treatment tank (treatment step) used in the present invention is a biological treatment method using normal suspended sludge, or the so-called activated sludge method, and the BOD volume load required to produce sludge with good settling properties in the sedimentation step is 0.1 kg / m 3 / d~0.5kg / m 3 / d, preferably with a BOD volumetric loading of 0.1 kg / m 3 / d~0.3kg / m 3 / d.

[0078] BOD load in the second process is 0.5kg / m 3 If the BOD load in the second process exceeds 0.5 kg / m3, the treatment capacity will be exceeded. 3 It is also important to set it below / d.

[0079] In RUN6, the tank capacity of the first process is 5.4m 3 , 2nd process 5.4m 3 The BOD load of the entire system is 1.0 kg / m 3 / d. First, if the raw water distribution rate is set to 5%, the amount of raw water to the second process is 3.6 m 3 The BOD load in the second process is 0.1 kg / m 3 / d. After the sedimentation process in RUN6, where the raw water distribution rate was 5%, the BOD concentration of the treated water was 22 mg / L, with a removal rate of 85%, and the SS concentration was 14 mg / L, which was rated as "satisfactory."

[0080] Next, if the raw water distribution rate is increased to 10%, 15%, 20%, and 25%, the amount of raw water to the second process is 7.2 m 3 From 18m 3 The BOD load in the second process is 0.2-0.5 kg / m depending on the distribution ratio. 3 It is / d. For raw water distribution rates of 10%, 15%, 20%, and 25%, the BOD concentration of the treated water after the sedimentation process was 21-28 mg / L, the BOD removal rate was 81-86%, and the SS concentration was 14-18 mg / L, which was rated as "satisfactory."

[0081] Furthermore, if the raw water distribution rate is set to 30%, the amount of raw water to the second process is 21.6 m 3 The BOD load in the second process is 0.6 kg / m, which is above the treatment limit. 3 In RUN6, the BOD concentration of the treated water after the sedimentation process with a raw water distribution rate of 30% was 32 mg / L, with a removal rate of 79%, and the SS concentration was 25 mg / L, which was rated as "not satisfactory."

[0082] The relationship between the raw water distribution rate and the BOD volumetric load in Table 1 is shown in the graph in Figure 6. The symbols "○", "△", and "×" in the graph reflect the evaluation in Table 1. From FIG. 6, it can be seen that the water quality of the treated water can be set to “△ (satisfactory)” or better by adjusting the ratio Y (%) of the amount of organic wastewater supplied to the second biological treatment tank to the total amount of organic wastewater supplied so that it satisfies the following formula 1 within the range of 0.5 or more and less than 0.814, and so that X satisfies the following formula 2 within the range of 0.814 or more and 1.5 or less. (Formula 1) 5≦Y<-63X+82.5 (Formula 2) 5≦Y<-20X+47.5

[0083] The two straight lines (dotted lines) at the top of Figure 6 are linear approximations of the boundary between the evaluations of "△" and "×" in order to specify the upper limit of the ratio Y (%) of the amount of organic wastewater supplied to the second biological treatment tank to the total amount of organic wastewater supplied. The intersection point of the two lines is (X, Y) = (0.814, 31.2), as shown in Figure 6.

[0084] In addition, from the results of Example 1, in order to maintain the water quality of the treated water at a level that can be evaluated as "satisfactory" in terms of BOD concentration and SS concentration, the BOD volume load on the second biological treatment tank using suspended microorganisms should be set to 0.05 kg / m 3 / d (5% distribution rate to the second step of RUN1) to 0.5 kg / m 3It is understood that it is preferable to set the distribution rate in the range of up to 0.025 kg-BOD / kg-MLSS / d (50% distribution rate in RUN1 and 25% distribution rate in RUN6). This value corresponds to a range of 2 to 20 times the guideline for sludge load of "0.025 kg-BOD / kg-MLSS / d" as disclosed in Patent Document 2. In a biological treatment device using a fixed-type biological attachment carrier such as that of the present invention, it is understood that in order to improve the water quality of the treated water, a high sludge load is required in the second biological treatment tank using suspended microorganisms. EXAMPLES

[0085] In the present invention, the first step can handle a high volume load, and the maximum volume load that can be handled is 3 kg / m as shown in RUN 7 of Example 1. 3 / d. On the other hand, the second step is 0.5 kg / m 3 / d is the maximum treatment load. From a technical standpoint, it is rational to place a load on the first process as a whole system, and a minimum load on the second process within the acceptable range of treated water quality. In Example 2, the raw water distribution ratio was verified when the BOD concentration of the raw water increased in RUN 8. In addition, the change in the final treated water when the capacity of the second process was increased relative to that of the first process was verified in RUN 9. The MLSS concentration in the second process was set to 1000 mg / L.

[0086] The results of RUN8 are shown in Table 2. The raw organic wastewater in RUN8 was 24 m 3 / d, and the BOD concentration is 450mg / L. We investigated whether the distribution rate to the second process is reproducible even when the BOD concentration is high. The load on the entire system is 0.9kg / m 3 / d, which is equivalent to the load in RUN5 of Example 1. The capacity of the first process is 6m 3 , the capacity of the second process is 6m 3 The distribution rate of the raw water was examined as the separation speed per water surface area of ​​20 m 3 / m 2 Solid-liquid separation was carried out in a gravity settling tank at 1000 m / d, and the quality of the treated water was evaluated.

[0087] The results will be evaluated based on the achievement of the target values, as follows: The estimated SS generation concentration from BOD conversion is 66% of BOD. Since the BOD is 450 mg / L, the SS generation concentration in this case was set at 300 mg / L. 1) If the BOD removal rate is 95% or more and the SS is 30 mg / L or less, it is evaluated as "Very satisfactory" and indicated by the symbol ○. If the SS is 30 mg / L or less, the estimated removal rate is 90% or more. 2) If the BOD removal rate is between 80% and 95% and the SS is 60 mg / L or less, it is evaluated as "satisfactory" and indicated by the symbol △. If the SS is 60 mg / L or less, the estimated removal rate is 80% or more. 3) If the BOD removal rate is less than 80%, regardless of the SS concentration, it is evaluated as "unsatisfactory" and indicated by the symbol x.

[0088] [Table 2]

[0089] The BOD concentration of RUN8 is three times higher than that of Example 1. Under these conditions, the results of the treated water from RUN8 are compared with those of RUN5 in Example 1. At a distribution rate of 5-25%, the treatment was evaluated as "satisfactory (△)" and "very satisfactory (○)", and RUN8 was evaluated as RUN5 in Example 1. In this RUN8, the volumetric load of the second step was 0.5 kg / m 3 When the distribution rate exceeded 30% / d, the water quality was rated as “unsatisfactory.”

[0090] It can be seen that even if the BOD concentration of the raw water increases (fluctuations) as in RUN8, the water quality of the treated water can be set to “satisfactory (△)” or higher by adjusting the ratio of the amount of organic wastewater supplied to the second biological treatment tank to the total amount of organic wastewater supplied within the numerical range defined by the above-mentioned formula 1 or formula 2.

[0091] In RUN9, the capacity of the first process is 6m 3 , the capacity of the second process is 12m 3The raw water volume and raw water BOD sedimentation concentration were the same as in RUN8. In the sedimentation process, the separation speed per water surface area was 20 m 3 / m 2 Solid-liquid separation was carried out in a gravity settling tank at 1000 m / d, and the quality of the treated water was evaluated. The capacity of the second process is 12m 3 The load on the entire system increased to 0.6 kg / m 3 / d, and the volume load in the second process is limited to 0.5 kg / m 3 The treated water has a BOD removal rate of over 95% and SS of 30 mg / L or less, which is within the "very satisfactory" evaluation range.

[0092] Based on the above results, regardless of the BOD of the raw water, the BOD load of the entire system was set, and the volumetric load of the second process of the second process was set at a limit of 0.5 kg / m 3 The distribution ratio of the raw water should be adjusted so that the BOD concentration of the raw water, the volumetric load of the entire system, and the volumetric load of the second process are deemed reproducible from the limit values ​​in the application range shown in Example 1.

[0093] Furthermore, in cases where the capacity of the second step can be made larger relative to the capacity of the first step, as in RUN9, it is easily understood that the quality of the treated water can be improved even if the ratio of the amount of organic wastewater supplied to the second biological treatment tank to the total amount of organic wastewater supplied is set in a wide numerical range exceeding the upper limit value defined by formula 1 or formula 2. However, simply increasing the capacity of the second step is problematic in terms of both space and cost, so it is preferable to set the upper limit of the capacity of the second step to twice that of the first step, as in RUN9.

[0094] Conversely, the case where the capacity of the second step is made smaller relative to the capacity of the first step will be considered. For example, in RUN2 of Example 1, the capacity of the first step is set to 9 m 3 , the capacity of the second process is 4.5m 3 In this case, the BOD volume load of the entire system is 0.8 kg / m 3If the ratio of the organic wastewater supply to the second process (raw water distribution rate) is set to 5% and 10%, the BOD volume load in the second process is 0.12 kg / m 3 / d and 0.24 kg / m 3 / d. The BOD volumetric loading in the second step of Example 1 is 0.1 to 0.3 kg / m 3 Since the water quality was "very satisfactory" within the range of / d, an improvement in the water quality of the treated water can be expected in this case as well.

[0095] When the capacity of the second step is made smaller relative to the capacity of the first step, it is generally necessary to further reduce the amount of raw water distributed to the second step in order to optimize the BOD volume load of the second step. However, when the raw water distribution rate to the second step is made lower than 5%, the range for adjusting the raw water distribution rate is narrow when the amount of raw water treated or the BOD concentration of the raw water changes, making it difficult to maintain the BOD volume load of the second step at an optimal state. For this reason, it is preferable to set the ratio of the volume of the second step to the volume of the first step to 0.5 or more.

[0096] For the above reasons, it is preferable to set the capacity of the second step in the range of 0.5 to 2 times the capacity of the first step. In the present invention, the first step has a high BOD treatment capacity, but the SS concentration is also likely to be high. The second step is expected to play a role in reducing this SS concentration. For this reason, it is necessary to maintain a treatment speed slower in the second step than in the first step, and it is more preferable to set the capacity of the second step in the range of 1 to 2 times the capacity of the first step. EXAMPLES

[0097] The raw organic wastewater for RUN11 is 72m 3 / d. The organic wastewater concentration and the total system load are 0.6 kg / m 3 Based on / d, the capacity of the first process is set at 9m 3 , the capacity of the second process is 9m 3The amount of returned sludge was changed for each run so that the MLSS in the second process was 1000 mg / L. In the sedimentation process, the separation speed per water surface area was 20 m 3 / m 2 Solid-liquid separation was carried out in a gravity settling tank at 1000 m / s, and the quality of the treated water was evaluated.

[0098] The results will be evaluated based on the achievement of the target values, as follows: The estimated SS generation concentration from BOD conversion is 66% of BOD. Since the BOD is 150 mg / L, the SS generation concentration in this case was set to 100 mg / L. 1) If the BOD removal rate is 95% or more and the SS rate is 10 mg / L or less, it is evaluated as "Very satisfactory" and indicated by the symbol ○. If the SS rate is 10 mg / L or less, the estimated removal rate is 90% or more. 2) If the BOD removal rate is between 80% and 95% and the SS is 20 mg / L or less, it is evaluated as "satisfactory" and indicated by the symbol △. If the SS is 20 mg / L or less, the estimated removal rate is 80% or more. 3) If the BOD removal rate is less than 80%, regardless of the SS concentration, it is evaluated as "unsatisfactory" and indicated by the symbol x.

[0099] Specifically, a detector capable of measuring organic matter concentration was installed in the raw water line and in the water quality measurement section where the outflow of the first process and the raw water to the second process join in the second process, and these two signals (soluble BOD value) were introduced into the calculation mechanism, and the flow rate adjustment mechanism was adjusted so that the soluble BOD value of the water quality measurement section of the second process would be a specified ratio to the soluble BOD value of the raw water, and the raw water flow rate to the second process was adjusted. As a result, the flow rate of the first process also changes. Note that the soluble BOD value is the BOD concentration excluding SS, and since the MLSS in the second process is 1000 mg / L, there is a large error in the BOD measurement, so the soluble BOD value excluding MLSS by filtration was used as the control index.

[0100] In RUN11, the raw water BOD concentration was 150 mg / L, and the total system BOD load was 0.6 kg / m 3 / d. The capacity of the first process is 9m 3 , the capacity of the second process is 9m 3 The results of RUN11 are shown in Table 3. In RUN11, the BOD concentration and S-BOD value were measured using a submersible water quality measuring instrument, a Spectrolyzer BOD meter (model Sp1-005-pO-sNO-075, manufactured by Ebara Jitsugyo Co., Ltd.).

[0101] [Table 3]

[0102] In Table 3, the soluble BOD value from the water quality measurement section of the second process is referred to as the S-BOD value. In test 11, the amount of raw water distributed to the second process was 5m 3 The S-BOD value was 10mg / L, which is 6.7% of the raw water BOD concentration. In this test 11, the BOD concentration of the treated water after the sedimentation process was 15mg / L, with a removal rate of 90%, and the SS concentration was 10mg / L, which was rated as "satisfactory (△)."

[0103] In test 12, the amount of raw water distributed to the second process was adjusted to 7 m 3 / d, the S-BOD value was 15 mg / L, 10% of the raw water BOD concentration. In this test 12, the treated water BOD concentration after the sedimentation process was 3 mg / L, a significant increase to a removal rate of 98%, and the SS concentration was 8 mg / L. Based on the BOD removal rate and SS concentration, the treatment result of test 12 was rated as "Very Satisfactory (○)."

[0104] In test 13, the raw water distribution volume was 11m 3 / d, and in test 14, the raw water distribution volume was 14m 3 / d, the S-BOD value and the ratio to the raw water BOD concentration were 23 mg / L, or 15.3%, in Test 13, and 30 mg / L, or 20% in Test 14. Even under these conditions, the treated water BOD concentration after the sedimentation process was 3 mg / L, maintaining a removal rate of 98%. The SS concentration was 5 mg / L. Based on the BOD removal rate and SS concentration, the treatment results of Tests 13 and 14 were rated as "very satisfactory."

[0105] In test 15, the raw water distribution volume was adjusted to 18m 3 / d, the S-BOD value and the ratio to the raw water BOD concentration were 38 mg / L and 25.3%, respectively. Under these conditions, the BOD concentration of the treated water after the sedimentation process was 9 mg / L, with a removal rate of 94%, a decrease from Test 14. The SS concentration was 15 mg / L. Based on the BOD removal rate and SS concentration, the treatment result of Test 15 was rated "satisfactory." From the results of Tests 12 to 14, it was determined that the range in which the treatment results were "very satisfactory" was an S-BOD value of 10% to 20% relative to the raw water BOD concentration.

[0106] The raw water distribution volume was adjusted to 19m in test 16. 3 / d, 22m in test 17 3 / d. The S-BOD value and its ratio to the raw water BOD concentration were 40 mg / L and 26.7%, while in test 17, the S-BOD value and its ratio to the raw water BOD were 45 mg / L and 30%, which were higher than the set value of 10% to 20% for the ratio to the raw water BOD. In test 16, the treated water after the sedimentation process had a BOD concentration of 15 mg / L, a removal rate of 90%, and an SS concentration of 18 mg / L, and in test 17, the BOD concentration was 21 mg / L, a removal rate of 86%, and an SS concentration of 20 mg / L. Based on the BOD removal rate and SS concentration, the treatment results of Tests 16 and 17 were rated as "satisfactory."

[0107] In test 18, the raw water distribution volume was adjusted to 24m 3 / d. In this case, the S-BOD value and its ratio to the raw water BOD concentration were 50 mg / L, and the ratio to the raw water BOD was 33.3%. In the case of Test 18, the treated water BOD concentration after the sedimentation process was 33 mg / L, with a removal rate of 78%, and the SS concentration was 25 mg / L. Based on the BOD removal rate and SS concentration, the treatment result of Test 18 was rated "unsatisfactory (x)."

[0108] After the completion of Test 18, the S-BOD value of the water quality measurement section in the second process was set to 23 mg / L, and the ratio to the raw water BOD concentration was adjusted to 15.3% by operating the calculation mechanism and adjusting the flow rate adjustment mechanism, and the raw water distribution volume was reduced. The BOD concentration of the treated water after the sedimentation process was 3 mg / L, and the removal rate was 98%, which was a significant increase. The raw water distribution volume at this time was 11 m 3 / d.

[0109] From the above results, if the flow rate control mechanism is adjusted so that the ratio of the S-BOD value in the second process to the raw water BOD concentration is in the range of 6.7% to 30%, the evaluation will be ``satisfactory (△)'' or higher. Furthermore, if the flow rate control mechanism is adjusted so that the ratio of the S-BOD value in the second process to the raw water BOD concentration is in the range of 10% to 20%, the evaluation will be ``very satisfactory (○)''. From these findings, it was found that the water quality of this system can be controlled by setting the ratio of the S-BOD value in the second process to the raw water BOD concentration.

[0110] From the above tests, it can be seen that the system can be easily maintained in an optimal operating condition by setting the S-BOD value as a ratio to the raw water BOD concentration at 6.7 to 30%, preferably 10% to 20%, operating the calculation mechanism at this value, adjusting the flow control mechanism, and adjusting the raw water flow rate to the second process. EXAMPLES

[0111] In RUN12, the raw water BOD concentration was 300 mg / L, and the total system BOD load was 0.6 kg / m 3 / d. The capacity of the first process is 18m 3 , the capacity of the second process is 18m 3 and the MLSS in the second step was 1000 mg / L. In RUN12, BOD concentration and S-BOD value were measured using a submersible water quality measuring device, a Spectrolyzer BOD meter (model Sp1-005-pO-sNO-075, manufactured by Ebara Jitsugyo Co., Ltd.). The results are shown in Table 4. Here, the soluble BOD value from the water quality measurement section of the second process is referred to as the S-BOD value.

[0112] The results will be evaluated based on the achievement of the target values, as follows: The estimated SS generation concentration from BOD conversion is 66% of BOD. Since the BOD is 300 mg / L, the SS generation concentration in this case was set to 200 mg / L. 1) If the BOD removal rate is 95% or more and the SS is 20 mg / L or less, it is evaluated as "Very satisfactory" and indicated by the symbol ○. If the SS is 20 mg / L or less, the estimated removal rate is 90% or more. 2) If the BOD removal rate is between 80% and 95% and SS is 40 mg / L or less, it is evaluated as "satisfactory" and indicated by the symbol △. If the SS is 40 mg / L or less, the estimated removal rate is 80% or more. 3) If the BOD removal rate is less than 80%, regardless of the SS concentration, it is evaluated as "unsatisfactory" and indicated by the symbol x.

[0113] [Table 4]

[0114] Because the raw water BOD concentration in RUN12 was high at 300 mg / L, the method used was as shown in Figure 4. Instead of collecting water from the water quality measurement section, water was collected from the point where the outflow of the first process and the raw water to the second process join in the second process, and analyzed immediately.

[0115] In test 21, the amount of raw water distributed to the second process was 5m 3 The S-BOD value was 20mg / L, which is 6.7% of the raw water BOD concentration. After the sedimentation process, the treated water BOD concentration was 30mg / L, with a removal rate of 90%, and the SS concentration was 20mg / L, so the treated water was rated as "satisfactory (△)".

[0116] In test 22, the raw water distribution to the second process was 7m 3 / d, the S-BOD value was 30 mg / L, which was 10% of the raw water BOD concentration. In this test 22, the BOD concentration of the treated water after the sedimentation process was 9 mg / L, with a removal rate of 97%, and the SS concentration was 16 mg / L, and the treated water was rated "Very Satisfactory (○)", indicating a significant improvement in water quality.

[0117] The raw water distribution volume was adjusted to 11m in Test 23. 3 / d, 14m in test 24 3 / d, the S-BOD value and the ratio to the raw water BOD were 45 mg / L and 15.0% in Test 23, and 60 mg / L and 20% in Test 24. Even under these conditions, the treated water BOD concentration after the sedimentation process was 9 mg / L, with a removal rate of 97%, and the SS concentration was 10 mg / L, and the evaluation of this treated water was maintained at "very satisfactory."

[0118] In test 25, the raw water distribution volume was adjusted to 18m by adjusting the flow rate adjustment mechanism. 3 / d, the S-BOD value and the ratio to the raw water BOD were 75mg / L and 25.0%. In this state, the treated water BOD concentration after the sedimentation process was 30mg / L, with a removal rate of 90%, and the SS concentration was 20mg / L, and the treated water was evaluated as "satisfactory."

[0119] In tests 26 and 27, the flow rate control mechanism was adjusted to distribute the raw water to 19m 3 / d, test 27 is 22m 3 / d. The S-BOD value and the ratio to the raw water BOD concentration were 80 mg / L and 26.7% in Test 26, and 90 mg / L and 30% in Test 27, which were higher than the set value of 10% to 20% for the ratio to the raw water BOD concentration. In this state, the treated water after the sedimentation process had a BOD concentration of 36 mg / L, a removal rate of 88%, and a SS concentration of 30 mg / L in Test 26, and a BOD concentration of 58 mg / L, a removal rate of 81%, and a SS concentration of 30 mg / L in Test 27, and the evaluation of the treated water was "satisfactory."

[0120] In test 28, the flow rate control mechanism was adjusted to distribute the raw water to 24 m 3 / d. The S-BOD value and the ratio to the raw water BOD concentration were 100 mg / L and 33.3%, which were higher than the set value of 10% to 20% for the ratio to the raw water BOD concentration. In this state, the treated water after the sedimentation process had a BOD concentration of 64 mg / L, a removal rate of 78%, and an SS concentration of 45 mg / L, and the evaluation of the treated water was "unsatisfactory (x)".

[0121] The results of Tests 21 to 28 show that the ratio of the S-BOD value of the second process to the raw water BOD concentration is in the range of 6.7% to 30%, the BOD removal rate is 90% or more, the SS is 40 mg / L or less, and it is 20% or less of the estimated BOD conversion SS generation concentration, which is evaluated as being "satisfactory" or better. Furthermore, as can be seen from the results of Tests 22 to 24, when the ratio of the S-BOD value of the second process to the raw water BOD concentration is in the range of 10% to 20%, the BOD removal rate is 95% or more, the SS is 20 mg / L or less, and it is 10% or less of the estimated BOD conversion SS generation concentration, which is evaluated as being in a "very satisfactory" state.

[0122] After the completion of test 28, the S-BOD value of the water quality measurement section in the second process was set to 45 mg / L, i.e., the ratio to the raw water BOD concentration was set to 15% by operating the calculation mechanism and adjusting the flow rate adjustment mechanism, and the raw water distribution volume was reduced. The BOD concentration of the treated water after the sedimentation process was 9 mg / L, and the removal rate was 97%, which was a significant increase. The raw water distribution volume at this time was 11 m 3 In addition, when the S-BOD value was controlled to 30-60 mg / L so that the ratio to the raw water BOD concentration would be 10%-20%, the treated water BOD concentration after the sedimentation process was 9 mg / L, a significant increase to a removal rate of 97%, which was a "very satisfactory" state, and the effectiveness of the control was verified.

[0123] From the above results, when the raw water BOD concentration is made higher than in Example 3 (however, the BOD load of the entire system is the same as in Example 3), if the flow control mechanism is adjusted so that the ratio of the S-BOD value of the second process to the raw water BOD concentration is in the range of 6.7% to 30%, the evaluation will be ``satisfactory (△)'' or higher. Furthermore, if the flow rate control mechanism is adjusted so that the ratio of the S-BOD value in the second process to the raw water BOD concentration is in the range of 10% to 20%, the evaluation will be ``very satisfactory (○)''. From these findings, it was found that even if the BOD concentration of the raw water changes, it is possible to control the water quality of this system by setting the ratio of the S-BOD value in the second process to the BOD concentration of the raw water. From the above tests, it has been shown that the ratio of the S-BOD value in the second process to the raw water BOD concentration should be 6.7 to 30%, preferably 10% to 20%, and by operating the calculation mechanism at this value, adjusting the flow control mechanism, and adjusting the raw water flow rate to the second process, the system can easily be maintained in an optimal operating state. EXAMPLES

[0124] RUN13 was carried out as Example 5. The amount of organic wastewater used as raw water in RUN13 was 72 m 3 / d. In RUN13, the BOD concentration of the raw water is 150 mg / L, and the BOD load of the entire system is 0.9 kg / m 3 Designed with / d. The capacity of the first process is 6m 3 , the capacity of the second process is 6m 3 The results are shown in Table 5. Here, the soluble BOD value from the water quality measurement section of the second process is referred to as the S-BOD value. The experiment was carried out according to the method shown in FIG. In RUN13, BOD concentration and S-BOD value were measured using a submersible water quality measuring device, a Spectrolyzer BOD meter (model Sp1-005-pO-sNO-075, manufactured by Ebara Jitsugyo Co., Ltd.).

[0125] The results will be evaluated based on the achievement of the target values, as follows: The estimated SS generation concentration from BOD conversion is 66% of BOD. Since the BOD is 150 mg / L, the SS generation concentration in this case was set to 100 mg / L. 1) If the BOD removal rate is 95% or more and the SS rate is 20 mg / L or less, it is evaluated as "Very satisfactory" and indicated by the symbol ○. If the SS rate is 10 mg / L or less, the estimated removal rate is 90% or more. 2) If the BOD removal rate is between 80% and 95% and the SS is 40 mg / L or less, it is evaluated as "satisfactory" and indicated by the symbol △. If the SS is 20 mg / L or less, the estimated removal rate is 80% or more. 3) If the BOD removal rate is less than 80%, regardless of the SS concentration, it is evaluated as "unsatisfactory" and indicated by the symbol x.

[0126] [Table 5]

[0127] The raw water BOD concentration in RUN13 was 150mg / L, and the method of implementation was as shown in Figure 4. Instead of the water quality measurement section, water was collected from the point where the outflow of the first process into the second process and the raw water to the second process join, and the method of analysis was adopted immediately.

[0128] In test 31, the amount of raw water distributed to the second process was 5m 3 The S-BOD value was 10mg / L, which is 6.7% of the raw water BOD concentration. After the sedimentation process, the treated water BOD concentration was 15mg / L, with a removal rate of 90%, and the SS concentration was 12mg / L, so the treated water was rated as "satisfactory (△)".

[0129] In test 32, the raw water distribution to the second process was 7m 3 / d, the S-BOD value was 15 mg / L, which was 10% of the raw water BOD concentration. In this test 32, the BOD concentration of the treated water after the sedimentation process was 4.5 mg / L, with a removal rate of 97%, and the SS concentration was 10 mg / L, and the treated water was rated "Very Satisfactory (○)", indicating a significant improvement in water quality.

[0130] The raw water distribution volume was adjusted to 11m in Test 33. 3 / d, 14m in test 34 3 / d, the S-BOD value and the ratio to the raw water BOD were 23 mg / L and 15.0% in Test 33, and 30 mg / L and 20% in Test 34. Even under these conditions, the treated water BOD concentration after the sedimentation process was 4.5 mg / L, with a removal rate of 97%, and the SS concentration was 7 mg / L, and the evaluation of this treated water was maintained at "very satisfactory."

[0131] In test 35, the raw water distribution volume was adjusted to 18m by adjusting the flow rate adjustment mechanism. 3 / d, the S-BOD value and the ratio to the raw water BOD were 38mg / L, 25.0%. In this state, the treated water BOD concentration after the sedimentation process was 15mg / L, with a removal rate of 90%, and the SS concentration was 12mg / L, and the treated water was evaluated as "satisfactory".

[0132] In tests 36 and 37, the flow rate control mechanism was adjusted to distribute the raw water to 19m 3 / d, test 37 is 22m 3 / d. The S-BOD value and the ratio to the raw water BOD concentration were 40 mg / L and 26.7% in Test 36, and 45 mg / L and 30% in Test 37, which were higher than the set value of 10% to 20% for the ratio to the raw water BOD concentration. In this state, the treated water after the sedimentation process had a BOD concentration of 18 mg / L, a removal rate of 88%, and a SS concentration of 17 mg / L in Test 36, and a BOD concentration of 27 mg / L, a removal rate of 82%, and a SS concentration of 20 mg / L in Test 37, and the evaluation of the treated water was "satisfactory."

[0133] In test 38, the flow control mechanism was adjusted to distribute the raw water to 24 m 3 / d. The S-BOD value and the ratio to the raw water BOD concentration were 50 mg / L and 33.3%, which were higher than the set value of 10% to 20% for the ratio to the raw water BOD concentration. In this state, the treated water after the sedimentation process had a BOD concentration of 38 mg / L, a removal rate of 75%, and an SS concentration of 28 mg / L, and the evaluation of the treated water was "unsatisfactory (x)".

[0134] The results of Tests 31 to 38 show that when the ratio of the S-BOD value of the second process to the raw water BOD concentration is in the range of 6.7% to 30.0%, the BOD removal rate is 90% or more, the SS is 20 mg / L or less, and is 20% or less of the estimated BOD conversion SS generation concentration, which is evaluated as being "satisfactory" or better. Furthermore, as can be seen from the results of Tests 32 to 34, when the ratio of the S-BOD value of the second process to the raw water BOD concentration is in the range of 10% to 20%, the BOD removal rate is 95% or more, the SS is 10 mg / L or less, and it is 10% or less of the estimated BOD conversion SS generation concentration, which is evaluated as being in a "very satisfactory" state.

[0135] After the end of test 38, the S-BOD value of the water quality measurement section in the second process was set to 23 mg / L, i.e., the ratio to the raw water BOD concentration was set to 15% by operating the calculation mechanism and adjusting the flow rate adjustment mechanism, and the raw water distribution volume was reduced. The BOD concentration of the treated water after the sedimentation process was 4.5 mg / L, and the removal rate was significantly increased to 97%, and the SS concentration was also 7 mg / L. The raw water distribution volume at this time was 11 m 3 In addition, when the S-BOD value was controlled to 15-30 mg / L so that the ratio to the raw water BOD concentration would be 10%-20%, the treated water BOD concentration after the sedimentation process was 4.5 mg / L, a significant increase to a removal rate of 97%, and the SS concentration also rose to 7 mg / L-10 mg / L, maintaining a "very satisfactory" state, verifying the effectiveness of the control.

[0136] From the above results, even if the BOD load of the entire system is increased (changed), if the flow control mechanism is adjusted so that the ratio of the S-BOD value of the second process to the raw water BOD concentration is in the range of 6.7% to 30%, the evaluation will be ``satisfactory (△)'' or higher. Furthermore, if the flow rate adjustment mechanism is adjusted so that the S-BOD value in the second process relative to the raw water BOD concentration is in the range of 10% to 20%, the evaluation will be "very satisfactory (○)". From these findings, it was found that even when the BOD load of the entire system was varied, the water quality of this system could be controlled by setting the S-BOD value of the second process to a predetermined ratio relative to the raw water BOD concentration. From the above tests, it has been shown that the ratio of the S-BOD value in the second process to the raw water BOD concentration should be 6.7 to 30%, preferably 10% to 20%, and by operating the calculation mechanism at this value, adjusting the flow control mechanism, and adjusting the raw water flow rate to the second process, the system can easily be maintained in an optimal operating state. EXAMPLES

[0137] RUN14 was carried out as Example 6. The raw organic wastewater in RUN14 was 72 m 3 / d. In RUN14, the BOD concentration of the raw water is 300 mg / L, and the BOD load of the entire system is 0.9 kg / m 3 Designed with / d. The capacity of the first process is 12m 3 , the capacity of the second process is 12m 3 The results are shown in Table 6. Here, the soluble BOD value from the water quality measurement section of the second process is referred to as the S-BOD value. In RUN14, BOD concentration and S-BOD value were measured using a submersible water quality measuring device, a Spectrolyzer BOD meter (model Sp1-005-pO-sNO-075, manufactured by Ebara Jitsugyo Co., Ltd.).

[0138] The results are evaluated based on the achievement of the target value. Specifically, it is as follows. The estimated SS generation concentration from BOD conversion is set to 66% of BOD. Since the BOD is 300 mg / L, the SS generation concentration in this case is set to 200 mg / L. 1) If the BOD removal rate is 95% or more and the SS is 20 mg / L or less, it is evaluated as "Very satisfactory" and indicated by the symbol ○. If the SS is 20 mg / L or less, the estimated removal rate is 90% or more. 2) If the BOD removal rate is between 80% and 95% and SS is 40 mg / L or less, it is evaluated as "satisfactory" and indicated by the symbol △. If the SS is 40 mg / L or less, the estimated removal rate is 80% or more. 3) If the BOD removal rate is less than 80%, regardless of the SS concentration, it is evaluated as "unsatisfactory" and indicated by the symbol x.

[0139] [Table 6]

[0140] The raw water BOD concentration in RUN14 was 300 mg / L, and the method of implementation was as shown in Figure 4. Water was collected not from the water quality measurement section, but from the point in the second process where the outflow of the first process and the raw water to the second process join, and immediately analyzed using a submersible water quality measuring device, a Spectrolyzer BOD meter (model Sp1-005-pO-sNO-075, manufactured by Ebara Jitsugyo Co., Ltd.).

[0141] In test 41, the amount of raw water distributed to the second process was 5m 3 The S-BOD value was 20mg / L, which is 6.7% of the raw water BOD concentration. After the sedimentation process, the treated water BOD concentration was 30mg / L, with a removal rate of 90%, and the SS concentration was 17mg / L, so the treated water was rated as "satisfactory (△)".

[0142] In test 42, the raw water distribution to the second process was 7m 3 / d, the S-BOD value was 30 mg / L, which was 10% of the raw water BOD concentration. In this test 42, the treated water BOD concentration after the sedimentation process was 9 mg / L, with a removal rate of 97%, and the SS concentration was 14 mg / L, and the treated water was rated "Very Satisfactory (○)", indicating a significant improvement in water quality.

[0143] The raw water distribution volume was adjusted to 11m in Test 43. 3 / d, 14m in test 44 3 / d, the S-BOD value and the ratio to the raw water BOD were 45 mg / L and 15.0% in Test 43, and 60 mg / L and 20% in Test 44. Even under these conditions, the treated water BOD concentration after the sedimentation process was 9 mg / L, with a removal rate of 97%, and the SS concentration was 10 mg / L, and the evaluation of this treated water was maintained at "very satisfactory."

[0144] In test 45, the raw water distribution volume was adjusted to 18m by adjusting the flow rate adjustment mechanism. 3 / d, the S-BOD value and the ratio to the raw water BOD were 75mg / L and 25.0%, respectively. Under these conditions, the BOD concentration of the treated water after the sedimentation process was 30mg / L, with a removal rate of 90%, and the SS concentration was 25mg / L, with the treated water being rated as "satisfactory."

[0145] In tests 46 and 47, the flow rate control mechanism was adjusted to distribute the raw water to 19m 3 / d, test 47 is 22m 3 / d. The S-BOD value and the ratio to the raw water BOD concentration were 80 mg / L and 26.7% in Test 46 and 90 mg / L and 30% in Test 47, which were higher than the set value of 10% to 20% for the ratio to the raw water BOD concentration. In this state, the treated water after the sedimentation process had a BOD concentration of 36 mg / L, a removal rate of 88%, and a SS concentration of 32 mg / L in Test 46, and a BOD concentration of 54 mg / L, a removal rate of 82%, and a SS concentration of 35 mg / L in Test 47, and the evaluation of the treated water was "satisfactory."

[0146] In test 48, the flow control mechanism was adjusted to distribute the raw water to 24 m 3 / d. The S-BOD value and the ratio to the raw water BOD concentration were 100 mg / L and 33.3%, which were higher than the set value of 10% to 20% for the ratio to the raw water BOD concentration. In this state, the treated water after the sedimentation process had a BOD concentration of 81 mg / L, a removal rate of 73%, and an SS concentration of 40 mg / L, and the evaluation of the treated water was "unsatisfactory (x)".

[0147] The results of Tests 41 to 48 show that the ratio of the S-BOD value of the second process to the raw water BOD concentration is in the range of 6.7% to 30%, the BOD removal rate is 90% or more, the SS is 40 mg / L or less, and it is 20% or less of the estimated BOD conversion SS generation concentration, which is evaluated as being "satisfactory" or better. Furthermore, as can be seen from the results of Tests 42 to 44, when the ratio of the S-BOD value of the second process to the raw water BOD concentration is in the range of 10% to 20%, the BOD removal rate is 95% or more, the SS is 20 mg / L or less, and it is 10% or less of the estimated BOD conversion SS generation concentration, which is evaluated as being in a "very satisfactory" state.

[0148] After the completion of Test 48, the S-BOD value of the water quality measurement section in the second process was set to 45 mg / L, and the ratio to the raw water BOD concentration was adjusted to 15% by operating the calculation mechanism and adjusting the flow rate adjustment mechanism, and the raw water distribution volume was reduced. The BOD concentration of the treated water after the sedimentation process was 9 mg / L, a significant increase in removal rate to 97%, and the SS concentration was 10 mg / L. The raw water distribution volume at this time was 11 m 3 In addition, when the S-BOD value in the second process was controlled to 30-60 mg / L so that the ratio to the raw water BOD concentration would be 10%-20%, the treated water BOD concentration after the sedimentation process increased significantly to 9 mg / L with a removal rate of 97%, and the SS concentration also reached a "very satisfactory" level of 10-14 mg / L, verifying the effectiveness of the control.

[0149] From the above results, even if the BOD concentration of the raw water or the BOD load of the entire system is increased, if the flow control mechanism is adjusted so that the ratio of the S-BOD value of the second process to the raw water BOD concentration is in the range of 6.7% to 30%, the evaluation will be "satisfactory" or higher. Furthermore, if the flow rate control mechanism is adjusted so that the ratio of the S-BOD value in the second process to the raw water BOD concentration is in the range of 10% to 20%, the evaluation will be "very satisfactory." From these findings, it was found that the water quality of this system can be controlled by setting the S-BOD value in the second process to a specified ratio relative to the raw water BOD concentration. The above tests have shown that even if the BOD concentration of the raw water or the BOD load of the entire system fluctuates, the system can be easily maintained in an optimal operating state by setting the ratio of the S-BOD value of the second process to the raw water BOD concentration at 6.7 to 30%, preferably 10% to 20%, operating the calculation mechanism at this value, adjusting the flow control mechanism, and adjusting the raw water flow rate to the second process. [Industrial Applicability]

[0150] As described above, according to the present invention, it is possible to provide a biological treatment apparatus and a biological treatment method for organic wastewater that can reduce the amount of air used in aerobic biological treatment, efficiently remove organic matter under high load while significantly reducing the amount of sludge generated, and maintain a stable water quality of the treated water. [Explanation of symbols]

[0151] 1. Organic wastewater line 2 Flow rate adjustment mechanism (organic wastewater volume distribution mechanism) 3. First biological treatment tank 4. Second biological treatment tank 5 Sedimentation tank 6 Return sludge line 7 Treated water outflow line 8 Control device 9. Water Quality Measurement Section 10. Baffle 11 Raw water inlet line to the first biological treatment tank 12 Raw water inlet line to the second biological treatment tank 30 Fixed bioadhesive carriers 31, 41, 44 Aeration means 42 Mixing means 43 Partition Wall S1, S2, S3 sensors

Claims

1. A first biological treatment tank having a fixed type organism attachment carrier and an aeration means disposed below the fixed type organism attachment carrier; a second biological treatment tank into which the treated liquid from the first biological treatment tank is introduced and treated by floating microorganisms without using biological carriers, and which has an aeration means; a sedimentation tank for separating the mixed liquid treated in the second biological treatment tank into solid-liquid and sedimented sludge and treated water; an inflow line for distributing and introducing organic wastewater into the first biological treatment tank and the second biological treatment tank; a return line for returning a portion of the settled sludge discharged from the settling tank to the second biological treatment tank; In addition, a stirring means for stirring the treatment liquid is provided in the second biological treatment tank, and denitrification treatment is performed. Further, a first BOD measuring means for measuring the BOD value of the organic wastewater and a second BOD measuring means for measuring the soluble BOD value of the treatment liquid in the second biological treatment tank are provided, This biological treatment device for organic wastewater is characterized by having an adjustment means for adjusting the amount of organic wastewater distributed to the first biological treatment tank and the second biological treatment tank so that the ratio of the soluble BOD value of the second biological treatment tank to the BOD value of the organic wastewater is in the range of 6.7 to 30% based on the measurements of the first and second BOD measuring means.

2. 2. The biological treatment apparatus for organic wastewater according to claim 1, wherein the second biological treatment tank has an aeration means disposed at least either upstream or downstream of the agitation means.

3. 3. The biological treatment apparatus for organic wastewater according to claim 1 or 2, wherein the first biological treatment tank is provided with a baffle wall for suppressing the flow of the organic wastewater in the direction of the flow of the organic wastewater.

4. A first biological treatment step in which organic wastewater is treated using a fixed biological carrier; A second biological treatment process in which the treated liquid from the first biological treatment process is introduced and treated with floating microorganisms without using a biological attachment carrier; A sedimentation process for separating the mixed liquid treated in the second biological treatment process into solid-liquid and treated water, The organic wastewater is distributed and introduced into the first biological treatment step and the second biological treatment step, A portion of the settled sludge discharged from the settling step is returned to the second biological treatment step, In the second biological treatment step, the treatment liquid is stirred by a stirring means to perform denitrification treatment, The biological treatment method for organic wastewater is further characterized in that the amount of organic wastewater distributed to the first biological treatment step and the second biological treatment step is adjusted so that the ratio of the soluble BOD value of the treated liquid from the second biological treatment step to the BOD value of the organic wastewater is in the range of 6.7 to 30%.

5. 5. The method for biologically treating organic wastewater according to claim 4, wherein the second biological treatment step comprises aeration by an aeration means at least on either the upstream side or the downstream side of the agitation means.

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