JP2006043706A - Method and apparatus for treating waste water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waste water treatment process involving solid-liquid separation after biological treatment, in which solid-liquid separation of activated sludge can be more efficiently performed. <P>SOLUTION: In the waste water treatment process, the solid-liquid separation of activated sludge mixed liquid obtained after biologically treating waste raw water is performed. Therein, the raw water is allowed to flow into a biological reaction vessel to perform biological treatment, subsequently, the activated sludge mixed liquid treated in the biological reaction vessel is introduced into a solid-liquid separation vessel in which a water-permeable filter member is immersed and arranged, thereby, a dynamic filter layer of the sludge is formed on the surface of the water-permeable filter member and filtrated water is obtained from the water-permeable filter member. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to wastewater treatment, and more particularly to solid-liquid separation of activated sludge, concentration of excess sludge, and the like. Specifically, activated sludge that can be used for treatment of organic industrial wastewater, domestic wastewater, etc. The present invention relates to a wastewater treatment method and apparatus including solid-liquid separation.

  In the water treatment by the activated sludge method, in order to obtain treated water, the activated sludge must be subjected to solid-liquid separation. Usually, for this purpose, a method has been used in which activated sludge is introduced into a sedimentation basin, the sludge is sedimented by gravity sedimentation, and the supernatant is discharged from the sedimentation basin as treated water. However, in this method, a sedimentation basin having a sufficient sedimentation area and residence time is required to settle activated sludge, which has been a factor in increasing the size of the processing apparatus and increasing the installation volume. Moreover, when activated sludge deteriorated sedimentation property by bulking etc., the sludge flowed out from the sedimentation basin and caused deterioration of treated water.

  In recent years, instead of a sedimentation basin, a method of performing solid-liquid separation of activated sludge by membrane separation is also used. In this case, a microfiltration membrane or an ultrafiltration membrane is generally used as the solid-liquid separation membrane. However, in this method, suction and pressurization by a pump is necessary as a filtration and separation main point, and since filtration is usually performed at a pressure of several tens to several hundred kPa, the power of the pump is large, which increases the running cost. It was. In addition, clear treated water having no SS (suspension material) can be obtained by membrane separation, but the permeation flux is low, and it is necessary to wash the medicine regularly in order to prevent membrane contamination.

  More recently, as a method for solid-liquid separation of activated sludge as an alternative to a sedimentation basin, a method has been proposed in which a filter body made of a breathable sheet such as a nonwoven fabric is immersed in an aeration tank to obtain filtered water at a low head pressure. The concept of such a method is shown in FIG. According to the proposed method, an aeration diffuser tube 202 and a filter body 204 are disposed in the biological reaction tank 201, and an air diffuser tube 203 for washing the filter body is disposed below the filter body. At the time of biological reaction processing (during filtration operation), raw raw water is supplied into the biological reaction tank 201 from the raw water supply pipe 205, and air is aerated from the diffuser pipe 202, so that biological treatment with activated sludge in the tank is performed. Then, the treatment liquid is filtered through the filter body 204, and treated water (filtered water) is taken out from the discharge pipe 206. At this time, the cross flow flow of the activated sludge mixed liquid that is a downward flow on the surface of the filter body is generated in the biological reaction tank 201 by aeration by the air diffusion tube 202 (FIG. 1 a). Due to the cross flow, a dynamic filtration layer of activated sludge is formed on the surface of the filter body 204, and the activated sludge mixed liquid is filtered by the formed dynamic filtration layer and taken out from the discharge pipe 206. When the filtration layer formed on the surface of the filter body 204 becomes consolidated and the filtration resistance increases and the amount of filtered water decreases, aeration from the air diffuser 202 is stopped and air is diffused from the air diffuser 203. The filtration layer on the surface of the filter body is removed by washing with air (FIG. 1b). According to this method, clear filtered water can be obtained by separating the sludge formed on the surface of the filter body by the dynamic filtration layer. Here, the “sludge dynamic filtration layer” is an adhering layer of activated sludge particles formed on the surface of the filter body by the progress of filtration. The filtration medium of the filter body used in this method has a pore diameter substantially larger than that of the activated sludge particles and allows the particles to pass therethrough. An adhering layer of activated sludge particles (sludge dynamic filtration layer) is formed on the surface of the substrate, and the passage of activated sludge particles can be prevented by this dynamic filtration layer. Usually, a nonwoven fabric, a woven fabric, a wire mesh, etc. are used as a filter body of this system. In the method using a dynamic filtration layer, a deposit layer of activated sludge particles as a filtration layer is uniformly and efficiently formed on the surface of the filtration medium so as to have a thickness and pressure density suitable for filtration of activated sludge. It is important to prevent the activated sludge particles from passing through and to obtain stable treated water with good water quality. In the proposed method, as a method for forming the dynamic filtration layer, the flow rate of activated sludge flowing through the surface of the filter body is 0.05 to 0.4 m / s on average, preferably 0.15 to 0.25 m / s. It is prescribed to control. In the proposed method, when the filter surface flow velocity is 0.2 m / s, the filtration flux is about 2 m / d and the filtration duration is 2.5 h or more, whereas the filter surface flow velocity is At 0.03 m / s, the initial filtration flux is 4.1 m / d, but after 45 minutes, the filtration flux decreases to 3.3 m / d, and the filtration flux decreases in a short time.

  Further, an activated sludge method in which a filter body is immersed in at least one of a biological reaction tank and a final sedimentation basin, and treated water is drawn out from the filter body through an outlet of the filter body due to a water head pressure difference with a subsequent tank. A sewage treatment apparatus has been proposed.

  However, these proposed methods have the following problems. That is, in the proposed method, the flow of the sludge mixed liquid on the surface of the filter body is formed by causing a flow circulating in the tank by aeration. However, in this method, since the flow velocity on the surface of the filter body is not uniform, a uniform sludge dynamic filtration layer cannot be formed on the surface of the filter body, and sludge tends to accumulate on the surface of the filter body. Furthermore, since the water level in the biological reaction tank varies depending on the amount of inflow water and the amount of aeration air, the head pressure on the filter body is not constant, the amount of filtered water changes, and a stable water amount cannot be obtained. When the water head pressure is unstable and extremely high, the water passing performance of the sludge dynamic filtration layer formed on the surface of the filter body is lowered, and there is a possibility that the filtration flux is rapidly lowered. As a result, the frequency of cleaning increases, and the flux recovery rate after cleaning also decreases. Furthermore, when organic pollutants such as BOD (biological oxygen consumption) in the raw water flowing into the bioreactor remain even if they are attached directly to the filter body, the biofilm is deposited on the surface of the filter body. Will grow and cause a marked decrease in the amount of filtered water.

  Moreover, when a filter body is immersed in the final sedimentation basin, there are the following problems. That is, in the final sedimentation basin using gravity sedimentation of sludge, the sludge concentration inside the sedimentation basin is not uniform, as can be seen from the fact that concentrated sludge accumulates at the bottom and supernatant water is obtained from the top. For this reason, the sludge density | concentration of a filter body immersion part becomes non-uniform | heterogenous, formation of a favorable dynamic filtration layer is impossible, and the stable treated water cannot be obtained.

  Furthermore, as a result of examining in detail the relationship between the filtration flux of the filter body and the surface flow velocity in the filtration method using the dynamic filtration layer of the activated sludge mixed liquid, the present inventors have determined that the flow velocity on the surface of the filter body is 0.05 to 0. .4 m / s, particularly when 0.15 to 0.25 m / s, which is considered to be preferable, the sludge flow on the surface of the filter body is intense, and it is difficult to form a uniform dynamic filtration layer of sludge. An effective filtration area could not be obtained, and furthermore, in this case, the filter body surface was quickly clogged with fine sludge flocs, and it was found that the effect would be reduced even if it was washed with water or washed with water. Immediately after washing the filter body, a stable dynamic filtration layer is formed in an extremely short time of 5 minutes or less by setting the surface flow velocity to less than 0.05 m / s. In that case, the filtration flux is 5 m / d or more. It was found that the dynamic filtration layer formed on the surface of the filter body can be easily peeled off only by rinsing under the condition that the pressure can be continued for 4 hours or more and the surface flow rate is less than 0.05 m / s.

Means to solve the problem

  In view of the above problems, the present inventors have conducted extensive research to provide a method for performing solid-liquid separation of an activated sludge mixture more efficiently. As a result, the raw water is allowed to flow into the biological reaction tank to perform biological treatment. After that, the activated sludge mixed liquid treated in the biological reaction tank is introduced into a solid-liquid separation tank in which the water-permeable filter body is immersed, so that a sludge dynamic filtration layer is formed on the surface of the water-permeable filter body. It was found that the solid-liquid separation of activated sludge can be performed very efficiently by obtaining filtered water. Furthermore, the sludge dynamic filtration layer can be stably formed on the surface of the water-permeable filter by making the moving speed of the activated sludge mixed liquid with respect to the surface of the water-permeable filter less than 0.05 m / s on average. It was found. Furthermore, by arranging a rectifying device in the solid-liquid separation tank so that the activated sludge mixed solution passes through the surface of the water-permeable filter after being rectified by the rectifying device, the solid-liquid separation is further efficiently performed. I found it going. The present invention has been completed based on these findings.

That is, the present invention has the following configuration.
1. Wastewater treatment method for solid-liquid separation of the activated sludge mixture obtained after biological treatment of raw wastewater, biological treatment was performed by flowing raw water into the biological reaction tank, and then treated in the biological reaction tank The activated sludge mixed liquid is introduced into a solid-liquid separation tank in which the water-permeable filter body is immersed, and a sludge dynamic filtration layer is formed on the surface of the water-permeable filter body. A method for treating wastewater, characterized in that filtered water is obtained.

  2. Wastewater treatment method for solid-liquid separation of the activated sludge mixture obtained after biological treatment of raw wastewater, biological treatment was performed by flowing raw water into the biological reaction tank, and then treated in the biological reaction tank The activated sludge mixed liquid is introduced into a solid-liquid separation tank in which the water-permeable filter body is immersed, and a sludge dynamic filtration layer is formed on the surface of the water-permeable filter body. A method of treating waste water, wherein filtered water is obtained by sucking the water with a pump.

3. 3. The method according to the above item 1 or 2, wherein the moving speed of the activated sludge mixed liquid relative to the surface of the water-permeable filter body is less than 0.05 m / s on average.
4). Any of the above-mentioned items 1 to 3, wherein a rectifying device is installed in the solid-liquid separation tank, and the activated sludge mixed liquid passes through the surface of the water-permeable filter after passing through the rectifying device. The method of crab.

  5. A wastewater treatment device for solid-liquid separation of an activated sludge mixed liquid obtained after biological treatment of raw wastewater, a biological reaction tank for conducting biological treatment by inflowing raw water, and a water-permeable filter body are immersed. A solid-liquid separation tank that introduces an activated sludge mixed solution treated in a biological reaction tank to perform solid-liquid separation, and a dynamic filtration layer of sludge is formed on the surface of the water-permeable filter, and the water-permeable filter A wastewater treatment apparatus characterized in that filtered water can be obtained at a higher water head pressure.

  6). A wastewater treatment device for solid-liquid separation of an activated sludge mixed liquid obtained after biological treatment of raw wastewater, a biological reaction tank for conducting biological treatment by inflowing raw water, and a water-permeable filter body are immersed. A solid-liquid separation tank that introduces an activated sludge mixed solution treated in a biological reaction tank to perform solid-liquid separation, and a dynamic filtration layer of sludge is formed on the surface of the water-permeable filter, and the water-permeable filter An apparatus for treating waste water, wherein filtered water is obtained by sucking the permeate side of the water with a pump.

  7). Item 5 or item 5 above, characterized in that a rectifier is installed in the solid-liquid separation tank, and that the activated sludge mixed liquid passes through the surface of the water-permeable filter after passing through the rectifier. 7. The apparatus according to item 6.

  According to the present invention, a solid-liquid separation tank is installed after the biological reaction tank, and a water-permeable filter body is immersed in the solid-liquid separation tank so that clear filtration can be performed with less filtration pressure than in the conventional method. You can get water.

  In the method of the present invention, as the driving pressure for obtaining filtered water from the filter body, either water head pressure or suction pressure by a pump can be used. Filtration by water head pressure is filtration driving pressure by natural gravity, so there is an advantage that power is not necessary and low filtration pressure that forms a dynamic filtration layer can be easily constructed. There is a drawback that the amount of filtered water tends to decrease due to the conversion. On the other hand, filtration by pump suction pressure has the disadvantages that power is required and that it is difficult to stably maintain a low filtration pressure at which a dynamic filtration layer is formed, but the amount of filtered water is reduced. There is an advantage that it hardly occurs. In the present invention, any preferable method can be adopted in consideration of the disadvantages and advantages of both.

  As the water-permeable filter that can be used in the present invention, the same effect can be obtained by using any water-permeable filter known in the prior art such as a nonwoven fabric, a filter cloth, and a metal net. Moreover, the shape of a filter body can also use arbitrary shapes well-known in prior arts, such as a plane type, a cylinder type, and a hollow type, and it can also bundle and use as a module filter body.

  In the present invention, in order to stably form the dynamic filtration layer on the surface of the water-permeable filter body, the average flow rate of the sludge mixed liquid introduced into the solid-liquid separation tank with respect to the filter body surface is 0.05 m / It is preferable to be less than s. By doing so, a good dynamic filtration layer can be easily formed on the surface of the filter body, regardless of whether the sludge mixed solution passes through the surface of the filter body in a downward flow or an upward flow. Moreover, since the average flow velocity of the sludge mixed liquid with respect to the filter body surface is less than 0.05 m / s, the decrease in the filtration flux is small and a high flux can be stably obtained. Therefore, the processing apparatus can be made compact. In the present invention, for example, the sludge mixed liquid (concentrated sludge mixed liquid) treated in the solid-liquid separation tank is taken out by a pump or the like on the side opposite to the introduction site of the sludge mixed liquid in the solid-liquid separation tank. A flow in a certain direction with respect to the filter body surface of the sludge mixed liquid can be formed. For example, when the activated sludge mixed liquid treated in the biological treatment tank is introduced into the solid / liquid separation tank from the top of the solid / liquid separation tank, the concentrated sludge mixed liquid is pumped from the bottom of the solid / liquid separation tank. By taking out, the flow of the sludge mixed liquid with respect to the filter body surface can be formed in a certain direction. Accordingly, the flow rate of the sludge mixed liquid with respect to the filter body surface is adjusted by controlling the sludge mixed liquid take-out speed from the solid-liquid separation tank. The extracted concentrated sludge mixed liquid can be returned to a biological reaction tank, a sludge concentration tank, a sludge digestion tank or the like, or taken out as excess sludge.

  In addition, when the average flow velocity of the sludge mixed liquid passing through the filter body surface is equal to or lower than the sedimentation speed of the sludge particles, the sludge mixed liquid flows downward with respect to the filter body surface, that is, the upper part of the solid-liquid separation tank. It is preferable to introduce from the bottom toward the bottom. If comprised in this way, even if inflow sludge settles, since it always passes the filter body surface, a favorable sludge dynamic filtration layer is formed.

  In a further preferred aspect of the present invention, it is preferable that a rectifier is installed inside the solid-liquid separation tank so that the activated sludge mixed liquid passes through the filter body surface after passing through the rectifier. With such a configuration, the flow direction in the solid-liquid separation tank is constant, and a sludge dynamic filtration layer can be uniformly formed on the surface of the filter body.

  In addition, in the apparatus concerning this invention, it is preferable to install a washing | cleaning apparatus in the filter body lower part of a solid-liquid separation tank. The sludge layer formed on the surface of the filter body can be easily peeled off by periodically stopping filtration and cleaning the filter body using this cleaning device. As the washing method, one or both of washing with air and washing with water can be used. In addition, it is preferable to adjust the air washing air volume so that the ascending flow rate of air bubbles during air washing is at least 0.2 m / s. As the air washing tube installed at the lower part of the filtration module, a porous tube having a larger ventilation hole than the conventional diffuser tube is desirable. If a perforated tube is used, it is possible to obtain a higher rising speed than that of the air diffusing tube with an equivalent aeration amount, and the rising bubbles are large, so that the sludge layer on the surface of the filter body can be easily peeled off. In addition, it is preferable that the air hole diameter of a porous tube is 2 mm or more.

  In the apparatus according to the present invention, sludge enters the filtration module before the sludge dynamic filtration layer is formed on the surface of the filter body. For this reason, in order to eliminate the accumulation of sludge in the filtration module, it is desirable to periodically drain the mud. As this mud draining method, it is preferable to provide a mud drain pipe penetrating from the lower part of the filtration module and to connect the discharged sludge to the biological reaction tank. The discharge power is preferably natural flow due to the water head pressure, and the discharge water head pressure is preferably about the same as the head pressure of filtration. However, in particular, when a pump is used as the filtration driving pressure, the pump can be used as the sludge discharge power.

  In the apparatus according to the present invention, it is preferable to return the concentrated sludge formed in the solid-liquid separation tank to the biological reaction tank. If it does in this way, the BOD load in a biological reaction tank can be managed appropriately, and it becomes possible to perform stable biological treatment. In addition, as the activated sludge mixed liquid passes along the filter body surface, the filtered water is gradually filtered and concentrated. The concentrated sludge mixed liquid thus formed is preferably returned to the biological reaction tank as return sludge. Moreover, when making sludge flow in from the upper part of a solid-liquid separation tank by a downward flow, it is preferable to return sludge mixed liquid with a high density | concentration from the lower part of a solid-liquid separation tank to a biological reaction tank as return sludge.

  As described above, the apparatus according to the present invention includes a biological treatment tank and a solid-liquid separation tank. These tanks are, for example, as shown in Example 1 and FIG. Two tanks may be formed by dividing a single tank by a partition, and the two tanks may be in liquid communication by providing an opening at the bottom of the partition, or, for example, the following Example 2 and FIG. As shown in FIG. 7, you may comprise by forming two tanks separately and connecting these with piping.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples. In the following description, COD _Mn is chemical oxygen consumption by potassium permanganate at 100 ° C .; S-COD _Mn is soluble chemical oxygen consumption by potassium permanganate at 100 ° C .; BOD ₅ is 5 days S-BOD ₅ is the soluble biochemical oxygen consumption in 5 days.

Example 1
In FIG. 2, an example of the waste water treatment method by this invention with respect to collective groundwater is shown with a flow sheet. In the apparatus shown in FIG. 2, the biological reaction tank 2 and the solid-liquid separation tank 6 are integrally formed. The biological reaction tank 2 and the solid-liquid separation tank 6 are separated by a partition wall 15. The liquid is communicated by an opening 4 opened at the bottom of the liquid crystal. The influent raw water 1 is first introduced into the biological reaction tank 2. In the biological reaction tank 2, air is supplied by the blower 3 through the diffusion pipe 13, and aerobic treatment is performed by the action of microorganisms in the activated sludge accommodated in the tank. The activated sludge liquid flowing out from the biological reaction tank 2 is supplied to the bottom of the solid-liquid separation tank 6 through the opening 4 formed at the bottom of the partition wall 15. A water-permeable filter body 7 is disposed in the solid-liquid separation tank 6, and a rectifier 5 is disposed below the water-permeable filter body. The activated sludge liquid that has passed through the opening 4 is supplied to the bottom of the rectifier 5. The activated sludge mixed liquid that has passed through the rectifier 5 flows uniformly upward in the solid-liquid separation tank 6 and is solid-liquid separated by the water-permeable filter 7. The treated water 9 is obtained from the water intake pipe 8 of the water-permeable filter 7 due to the water head pressure difference. Cleaning of the filter body 7 is performed by periodically stopping the filtration and blowing air through the air diffuser 14 from the cleaning device 10 installed in the lower part of the rectifier. The concentrated sludge mixed liquid in the solid-liquid separation tank 6 is returned to the biological reaction tank 2 by the concentrated sludge mixed liquid return pump 11. Excess sludge is periodically discharged out of the system from the sludge pipe 12.

  The treatment conditions of the biological reaction tank 2 and the treatment conditions of the solid-liquid separation tank 6 in the wastewater treatment experiment conducted using the system shown in FIG. 2 are shown in Table 1 and Table 2, respectively.

As shown in Table 1, the amount of raw water inflow into the biological reaction tank 2 was 10 m ³ / d, and the amount of concentrated sludge mixed liquid returned from the solid-liquid separation tank 6 was 5 m ³ / d. The MLSS in the biological reaction tank 2 was about 2500 mg / L. In this case, the BOD load of the entire tank was about 0.15 kg / kg.d.

The mixed liquid from the biological reaction tank 2 was collected at the opening 4 at the bottom of the partition wall 15 (that is, the biological reaction tank outlet) 4 and the residual BOD _{5 of the} treated liquid was measured. It was found that the activated sludge mixed solution flowing into the solid-liquid separation tank 6 was almost completely decomposed and removed, and no undecomposed BOD remained at all. For this reason, in the solid-liquid separation tank 6, it was possible to suppress the biological contamination of the filter body surface accompanying filtration separation. As a result, the life of the filter body was prolonged, and a stable amount of filtered water could be secured over a long period of time. In addition, in order to acquire the above-mentioned process effect, it is preferable that the BOD load of the biological reaction tank 2 shall be 0.3 kg / kg.d or less. Further, not only a method of removing BOD such as anaerobic / aerobic method and nitrification / denitrification method but also a biological method of removing N and P can be used.

As shown in Table 2, the solid-liquid separation tank 6 having an effective area of 0.04 m ² and an effective volume of 0.06 m ³ was used for the solid-liquid separation process in this example. As the water-permeable filter body 7, the solid-liquid separation tank 6 is composed of 8 flat nonwoven fabric filter bodies having an effective area of 0.4 m ² made from a polyester nonwoven fabric having a thickness of 0.4 mm and openings of 20 to 30 μm as filter modules. Installed inside. The average head pressure during filtration was about 10 cm. The amount of filtered water was 10 m ³ / d, and the activated sludge mixed liquid flow rate on the surface of the filter body was about 0.006 m / s. Further, the filtration body was washed by stopping the filtration for 3 minutes every 6 hours of filtration and aeration of air from the washing machine 10. The amount of aeration was adjusted so that the flow velocity of the filter surface of air bubbles during washing was 0.5 m / s on average.

  Table 3 below shows the quality of the treated water after continuous drainage treatment for about 2 months under these conditions, together with the quality of the raw water.

As shown in Table 3, raw water has pH = 7.1, turbidity = 150 degrees, and SS = 86 mg / L, whereas in treated water, pH = 7.6, turbidity = 5. 0 degree, SS = 4.6 mg / L, and it was recognized that the filtered water obtained by the dynamic filtration layer of sludge formed on the nonwoven fabric filter body was clear. In addition, COD _Mn and S-COD _Mn , BOD ₅ and S-BOD ₅ are 75 mg / L and 42 mg / L and 110 mg / L and 65 mg / L for raw water, respectively, while 12 for treated water. .5 mg / L and 11.0 mg / L, 6.3 mg / L and 5 mg / L or less, and the treated water quality was recognized to be good.

  The time-dependent change of the filtration flux in Example 1 is shown in FIG. As is clear from FIG. 3, in the continuous treatment for about 1500 hours, the average filtration flux was about 3.2 m / d, and a stable treatment was obtained. Moreover, the turbidity change of treated water is shown in FIG. From FIG. 4, in the continuous treatment for about 1500 hours, the turbidity of the treated water is always around 5 degrees, no significant fluctuation is observed, the sludge dynamic filtration layer is stably formed, and stable treated water quality is obtained. You can see that

Comparative Example 1
Using the same processing apparatus as in Example 1, the flow rate of the sludge mixed liquid on the surface of the filter body is set to 85 m ³ / d by returning the concentrated sludge mixed liquid from the solid-liquid separation tank 6 to the biological treatment tank 2. A continuous wastewater treatment experiment was performed under the same conditions as in Example 1, except that the speed was 0.1 m / s, which was about 17 times faster than that in Example 1.

  The time-dependent change of the filtration flux in the comparative example 1 is shown in FIG. 5, and the turbidity change of the treated water is shown in FIG. As shown in FIG. 5, when the sludge mixed liquid flow rate on the surface of the filter body is 0.1 m / s, the filtration flux is only 2.7 m / d even at the start of the treatment, and the sludge mixed liquid flow rate is 0. Compared with Example 1 which is 006 m / d, it is lower by about 10% or more. Further, in Comparative Example 1, the filtration flux decreased rapidly with the passage of time, and the filtration flux became 2 m / d or less after about 170 hours, and became 1 m / d or less after about 500 hours. From the treatment time of 500 hours, the washing interval for the filter body was reduced from 3 minutes of air washing every 6 hours of filtration to 3 minutes of air washing every 2 hours of filtration, but no increase in filtration flux was observed, It gradually decreased. From these results, when the flow rate of the sludge mixed liquid with respect to the filter body surface is 0.05 m / s or more, a decrease in the filtration flux accompanying fine sludge adhesion on the filter body surface was recognized. Further, even if the cleaning frequency is increased, there is no effect in maintaining the filtration flux. Therefore, it is considered that there is a high possibility that the filter pore diameter will be clogged due to clogging by these adhered sludge.

  Moreover, as FIG. 6 shows, the filtration water turbidity is as high as 10 degree | times until 200 hours after a process start, and it is thought that the dynamic filtration layer of sludge is not well formed in the filter body surface. The reason why the filtered water turbidity gradually decreased after 200 hours is thought to be that the filtration flux decreased due to clogging of the filter body, and the sludge intrusion into the filter body also decreased.

Example 2
In FIG. 7, the waste water treatment method which concerns on the other aspect of this invention with respect to group groundwater is shown with a flow sheet. The inflow raw water 101 is first introduced into the biological reaction tank 102 and subjected to aerobic treatment by the action of microorganisms in the activated sludge accommodated in the tank. The effluent from the biological reaction tank 102 flows down to the sludge stationary tank 104 through the line 103. In the sludge stationary tank 104, sludge flocs are formed and homogenized while being slowly stirred by the stirrer 105. The sludge mixed liquid is supplied from the sludge stationary tank 104 to the upper part of the solid-liquid separation tank 107 by the sludge supply pump 106. The sludge mixed liquid is filtered by the filtration module 108 disposed in the solid-liquid separation tank 107, and filtered water 112 is obtained from the intake pipe at the top of the filtration module, and flows into the treated water tank 113 through the electromagnetic valve 111. The treated water in the treated water tank 113 is appropriately discharged out of the system through the drain pipe 123. The sludge passing through the solid-liquid separation tank 107 is taken out from the bottom of the solid-liquid separation tank 107 as return sludge 118 and returned to the biological reaction tank 102. The water head pressure for the filtration module during filtration can be set by raising and lowering the filtered water level adjustment valve 109 and opening the electromagnetic valve 110. The air washing outside the filtration module is usually performed by closing the electromagnetic valve 111, starting the air washing blower 119, closing the electromagnetic valve 121, and opening the electromagnetic valve 122 to supply air to the diffuser pipe 120. . In addition, air filtration inside the filtration module is performed by supplying air from the blower 119 with the electromagnetic valve 122 closed and the electromagnetic valve 121 opened. In addition, water backwashing inside the filtration module is performed by closing the solenoid valves 110 and 111 and starting the water backwash pump 116 with the solenoid valve 115 opened, so that the filtered water in the treated water tank enters the module from the top of the filtration module. Do by introducing. The water backwash wastewater that has passed through the inside of the filtration module is discharged from the discharge pipe at the bottom of the module to the sludge stationary tank 104 through the electromagnetic valve 115. Note that the water level of the water backwash drainage is set by adjusting the water level control valve 114 so that the backwash head pressure is equivalent to the filtration head pressure. Thus, the operation can be automated by switching the solenoid valve in the order of air washing → water backwash → water backwash drainage → filtration.

  A continuous operation experiment of wastewater treatment was conducted using the system shown in FIG. The processing conditions of the biological reaction tank 102 were the same as those in Example 1. Table 4 below shows the processing conditions of the solid-liquid separation tank 107.

In this example, a set of five flat woven fabric filter bodies having an effective area of 1 m ² was installed in the solid-liquid separation tank 117 as a filtration module. As a material for the woven fabric, a polyester material having a thickness of 0.1 mm, 200 mesh and a pore diameter of about 72 μm was used. The head pressure at the time of filtration and the head pressure at the time of water backwash drainage were both 10 cm, and the average flow rate of the activated sludge mixed liquid passing through the filtration module surface was 0.01 m / s. The amount of air washed at the time of external washing of the filtration module was 150 L / min, and the amount of air washed at the time of internal washing was 30 L / min. The amount of water at the time of water backwashing was 140 L / min.

  Table 5 below shows a time chart for continuous operation. The filtration module was continuously operated with a cycle of 3 minutes of air washing, 30 seconds of water backwashing, and 2 minutes of water backwash drainage discharge every 120 minutes of filtration. In addition, air washing was normally performed by aeration to the outside of the filtration module, and air washing inside the filtration module was performed once in 50 cycles.

  FIG. 8 shows the change over time of the filtration flux of the filtration module in Example 2. As is clear from FIG. 8, in the continuous processing for about 1500 hours, the average filtration flux of the filtration module was about 3 m / d, and a stable treatment was obtained. FIG. 9 shows changes in turbidity of treated water. From FIG. 9, in the continuous treatment for about 1500 hours, the turbidity of the treated water was about 5 degrees, and no significant fluctuation was observed, so the sludge dynamic filtration layer was stably formed in the filtration module, It was recognized that good treated water quality was stably obtained.

Industrial applicability

  According to the present invention, it is possible to obtain clear filtrated water with a small filtration pressure by installing a solid-liquid separation tank after the biological reaction tank and immersing the water-permeable filter in the solid-liquid separation tank. it can. In a preferred embodiment of the present invention, the activated sludge mixed liquid flows in a fixed direction along the filter body surface at a flow rate of less than 0.05 m / s, so that a good sludge dynamic filtration layer is easily formed. Since the decrease in filtration flux is small and a high flux can be obtained stably, the volume of the solid-liquid separation tank can be made significantly smaller than that of a conventional sedimentation basin, and the processing apparatus can be made compact. . Furthermore, in a preferred embodiment of the present invention, a rectifier is installed in the solid-liquid separation tank so that the activated sludge mixed liquid passes through the filter body after passing through the rectifier. The average speed of the activated sludge mixed liquid in is uniform, and a sludge dynamic filtration tank is uniformly formed on the surface of the filter body. Furthermore, in a preferred embodiment of the present invention, by providing a cleaning device at the lower part of the filter body, by periodically stopping the filtration and performing cleaning, the sludge tank formed on the surface of the filter body is easily peeled off. be able to. Furthermore, in a preferred embodiment of the present invention, the BOD load of the biological reaction tank can be appropriately managed by returning the concentrated sludge from the solid-liquid separation tank to the biological reaction tank, and stable biological treatment can be performed. It becomes possible.

It is a figure which shows the concept of the solid-liquid separation method of the activated sludge liquid mixture of a prior art. It is a flow sheet of one example of a processing method of waste water concerning the present invention. 3 is a graph showing a change with time of an average filtration flux in Example 1. 3 is a graph showing the change with time of the filtered water turbidity in Example 1. 6 is a graph showing a change with time of an average filtration flux in Comparative Example 1. 6 is a graph showing a change with time of filtered water turbidity in Comparative Example 1. It is a flow sheet of other examples of the processing method of the drainage concerning the present invention. 6 is a graph showing the change with time of the average filtration flux in Example 2. It is a graph which shows the time-dependent change of the filtration water turbidity in Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inflow raw water 2 Biological reaction tank 3 Blower 4 Opening of biological reaction tank exit 5 Rectifier 6 Solid-liquid separation tank 7 Water-permeable filter body 8 Intake pipe 9 Treated water 10 Washing apparatus 11 Concentrated sludge mixed liquid return apparatus 12 Waste mud line 13 Aeration pipe 14 Aeration pipe 15 Bulkhead 101 Inflow raw water 102 Biological reaction tank 103 Biological reaction tank effluent 104 Sludge stationary tank 105 Stirrer 106 Sludge supply pump 107 Solid-liquid separation tank 108 Filtration module 109 Filtration water level adjustment valve 110 Solenoid valve 111 Electromagnetic Valve 112 Filtration water 113 Treated water tank 114 Water backwash drainage water level adjustment valve 115 Solenoid valve 116 Water backwash pump 117 Check valve 118 Return sludge 119 Air washing blower 120 Aeration pipe 121 Solenoid valve 122 Solenoid valve 123 Filtration water discharge pipe 201 Biology Reaction tank 202 Aeration tube 203 Aeration tube 204 Filter body 205 Raw water supply tube 206 Filtration Discharge pipe

Claims (7)

Wastewater treatment method for solid-liquid separation of the activated sludge mixture obtained after biological treatment of raw wastewater, biological treatment was performed by flowing raw water into the biological reaction tank, and then treated in the biological reaction tank The activated sludge mixed liquid is introduced into a solid-liquid separation tank in which the water-permeable filter body is immersed, and a sludge dynamic filtration layer is formed on the surface of the water-permeable filter body. A method for treating wastewater, characterized in that filtered water is obtained. Wastewater treatment method for solid-liquid separation of the activated sludge mixture obtained after biological treatment of raw wastewater, biological treatment was performed by flowing raw water into the biological reaction tank, and then treated in the biological reaction tank The activated sludge mixed liquid is introduced into a solid-liquid separation tank in which the water-permeable filter body is immersed, and a sludge dynamic filtration layer is formed on the surface of the water-permeable filter body. A method of treating waste water, wherein filtered water is obtained by sucking the water with a pump. The method according to claim 1 or 2, wherein the moving speed of the activated sludge mixed liquid with respect to the surface of the water-permeable filter is less than 0.05 m / s on average. The rectifier is installed in the solid-liquid separation tank, and the activated sludge mixed liquid passes through the surface of the water-permeable filter after passing through the rectifier. the method of. A wastewater treatment device for solid-liquid separation of an activated sludge mixed liquid obtained after biological treatment of raw wastewater, a biological reaction tank for conducting biological treatment by inflowing raw water, and a water-permeable filter body are immersed. A solid-liquid separation tank that introduces an activated sludge mixed solution treated in a biological reaction tank to perform solid-liquid separation, and a dynamic filtration layer of sludge is formed on the surface of the water-permeable filter, and the water-permeable filter A wastewater treatment apparatus characterized in that filtered water can be obtained at a higher water head pressure. A wastewater treatment device for solid-liquid separation of an activated sludge mixed liquid obtained after biological treatment of raw wastewater, a biological reaction tank for conducting biological treatment by inflowing raw water, and a water-permeable filter body are immersed. A solid-liquid separation tank that introduces an activated sludge mixed solution treated in a biological reaction tank to perform solid-liquid separation, and a dynamic filtration layer of sludge is formed on the surface of the water-permeable filter, and the water-permeable filter An apparatus for treating waste water, wherein filtered water is obtained by sucking the permeate side of the water with a pump. The rectifier is installed in the solid-liquid separation tank, and the activated sludge mixed liquid is configured to pass through the surface of the water-permeable filter body after passing through the rectifier. apparatus.

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