WO2004054935A1

WO2004054935A1 - Waste water treating device

Info

Publication number: WO2004054935A1
Application number: PCT/JP2003/015530
Authority: WO
Inventors: Yasuzo Sakai; Susumu Ishida
Original assignee: Maezawa Industries,Inc.
Priority date: 2002-12-05
Filing date: 2003-12-04
Publication date: 2004-07-01
Also published as: JPWO2004054935A1; AU2003289175A1

Abstract

A waste water treating device that effectively introduces a magnetic separation method thereby making it possible to realize a great reduction of surplus sludge in an activated sludge method and a great simplification of process control and that can be applied, by small-scale improvement, to the existing waste water treating plant. This waste water treating device comprises a magnetic separation means (21), installed in the rear stage of an aeration tank (12) for water treatment by activated sludge having magnetic powder added thereto, for magnetically separating, from the liquid, part of the activated sludge contained in an activated sludge suspension flowing out of the treating tank, a final settling basin (13) installed in the rear stage of the magnetic separation means for separating, from the liquid, the activated sludge in the activated sludge suspension flowing out of the magnetic separation means, and a path (14) for sending the activated sludge separated by the magnetic separation means back to the treating tank.

Description

Description Wastewater treatment equipment Technical field

The present invention relates to a wastewater treatment device, and more particularly, to a wastewater treatment device that performs a water treatment of wastewater or sewage containing organic matter as a main pollutant component by an activated sludge method to which magnetic powder is added. Background art

Activated sludge has been widely used as a treatment method for sewage and organic wastewater. This method basically decomposes organic matter contained in sewage and the like into activated sludge in a treatment tank such as an aeration tank, and then sediments and separates the activated sludge by gravity in a final sedimentation tank. The sludge is returned to the treatment tank. In such an activated sludge method, the activated sludge settles and separates in the final sedimentation tank due to the difference in density with water, so the settling property of the activated sludge is affected by the settling index and concentration of the activated sludge. In maintaining and controlling the settleability of activated sludge, process managers need to pay close attention to influential factors such as load conditions and dissolved oxygen concentration. A wide variety of organisms and specialists are required. If the activated sludge concentration exceeds 300 mg ZL (liter) in MLVSS, sedimentation and separation of activated sludge may be incomplete. For this reason, a method using membrane separation has been proposed to ensure solid-liquid separation without being affected by the settling index and concentration of activated sludge (eg, K. Yamamoto, M. Hiasa, T. Mahmood and T. Matsuo: Direct solid-liquid separation using hollow fiber membrane in an activated sludge aeration tank. Wat. Sci. Tech., 21, 43-54 (1989)). In addition, the activated sludge method removes organic matter in water, but has about half the growth of microorganisms in the removed organic matter. The microorganisms of this growth are called excess sludge, and this excess sludge cannot be discarded as it is because it contains a large amount of water. Concentrates by consuming energy. Incineration after dehydration. In addition, excess sludge is a major problem because it accounts for a large proportion of industrial waste. In order to reduce excess sludge, a method has been reported in which a part of the microorganisms grown by adding ozone is solubilized and then re-input as an organic substance to the activated sludge process (see, for example, Yasui, H.). ., Nakamura, K., Iwasaki, M., Sakai, Y,: A full-scale operating of a novel activated sludge process without excess sludge production.Wat.Sci.Tech.36 (ll), 163-36 1 (1996) )). On the other hand, it has been proposed to apply the magnetic separation method to the activated sludge method. That is, the addition of triiron or ferrite particles is ^_ ferromagnetic powder activated sludge suspension, fouling Dorofu-locking is immediately captures these ferromagnetic powders that collected sludge flocs magnetically It has been reported by Sakai et al. That an activated sludge method that does not rely on sedimentation separation is possible (eg, Sakai, Y., Fukase, T., Yasui, H., Shibata, M: An activated sludge process without excess sludge production.Wat.Sci.Tech.36 (11), 163-1705 (1997), Y.Sakai, S. Kurakata and F. Takahashi, "Magnetic Forced Sedimentation of Floes in Activated Sludge Supplemented with Ferromagnetic Powder of Iron Oxide ", J. Ferment. Bioeng" 71 (3), 208-210, (1991), Y.Sakai, K. Tani and F. Takahashi, "Sewage Treatment under Conditions of Balancing Microbial Growth and Cell Decay with a High Concentration of Activated Sludge Supplemented with Ferromagnetic ⁰ Powder ", J. Ferment. Bioeng., 74 (6), 413-415 (1992) Y. Sakai, T. Terakado and F.

Takahashi, "A Sewage Treatment Process Using Highly Condensed Activated Sludge with an Apparatus for Magnetic Separation", J. Ferment. Bioeng., 78 (1), 120-122, (1994), Y.Sakai, T. Miama and Fujio Takahashi , "Simultaneous Removal of Organic and Nitrogen Compounds in Intermittently Aerated Activated Sludge Process Using Magnetic ⁵ Separation", Water Research, 31 (8), 2113-2116, (1997), Hozo Sakai, Fujio Takahashi, "Activated sludge by magnetic separation method Separation of Filamentous Fungi and Flocculating Bacteria in Water ", Japan Society on Water Environment, 22 (4), 323-326, (1999). ).

In these papers, the magnetic separation method is used alone or after the sedimentation separation and is used to completely separate the activated sludge from the treated water. By magnetic separation method For example, if MLVSS can separate up to 16 g / L of activated sludge, and if the concentration of activated sludge of MLVSS is set according to the load, the experiment using borepteptone / glucose mixed solution as a simulated drainage It has been reported that excess sludge can be reduced to almost zero by oxidization. Also, there has been proposed an invention of a device in which activated sludge provided with magnetization is magnetized by a permanent magnet and separated from treated water (see Japanese Patent Publication No. 3-57979). If 100 kg of organic matter is treated by a general activated sludge method, about 40 to 70 kg of excess sludge will be generated. In exchange for water purification, a large amount of excess sludge is released to society. In addition, since the process is not feasible if the sedimentation of activated sludge (microorganisms) deteriorates, the sedimentation of activated sludge is managed at a high cost. On the other hand, in the method of separating activated sludge by only the magnetic separation, high magnetic separation performance is required, so that the size and cost of the magnetic separation device cannot be avoided. Furthermore, there is no denying that solid-liquid separation will not be performed at all in the event of a magnetic separator failure or power outage. In addition, in order to prevent the activated sludge from leaking from the final sedimentation tank due to a temporary increase in the flow rate in rainy weather, measures such as increasing the size of the sedimentation tank have been taken in the past, but to cope with the temporary load However, the extra space that would normally be needed must be allocated to the sedimentation tank and temporary storage tank. Depending on the amount of rainfall, the space will be large. Furthermore, large-scale sewage treatment plants and the like often have methane fermentation treatment, but methane fermentation is performed by mixing surplus sludge with poor fermentability and raw sludge with good fermentability. However, there is a problem that methane fermentation efficiency is low. Therefore, the present invention can realize a significant reduction of excess sludge in the activated sludge method and a greatly simplified process control by effectively introducing the magnetic separation method. The objective is to provide wastewater treatment equipment that can be applied to wastewater treatment facilities with small-scale improvements. Disclosure of the invention

The wastewater treatment apparatus of the present invention comprises a treatment tank for performing water treatment with activated sludge to which magnetic powder has been added, and a part of activated sludge contained in the activated sludge suspension flowing out of the treatment tank. Magnetic separation means for separating from the liquid by force, solid-liquid separation means for separating the activated sludge in the activated sludge suspension flowing out of the magnetic separation means from the liquid, and activated sludge separated by the magnetic separation means And a magnetic separation sludge return route for returning to the treatment tank. Further, in the wastewater treatment apparatus of the present invention, in the above-described configuration, the magnetic separation sludge return path includes a solubilization treatment unit that solubilizes at least a part of the activated sludge separated by the magnetic separation unit. The solid-liquid separation means is a final sedimentation tank for separating activated sludge by sedimentation separation by gravity, and the MLVSS concentration in the activated sludge suspension flowing out of the magnetic separation means and flowing into the final sedimentation basin is low. 300 Omg ZL or less; the magnetic separation means is provided at an outflow portion of the treatment tank; and the magnetic separation means is provided at an inflow portion of the solid-liquid separation means. The magnetic separation means separates 50 to 99.5% of the activated sludge in the effluent of the treatment tank, and the ratio between the activated sludge and the magnetic powder is such that the MLVSS of the activated sludge is 1 Magnetic powder at a concentration of 0.01 to 10 It is characterized. Further, in the above configuration, a settling separated sludge return path for returning at least a part of the activated sludge separated by the solid-liquid separation means to the treatment tank after treating it in a sterilization treatment section is provided. A settling separation sludge return route for returning at least a part of the activated sludge separated by the solid-liquid separation means to the treatment tank after treating it in the solubilization treatment section; Solid-liquid separation means, methane fermentation means for performing methane fermentation using the initial settled sludge separated by the preliminary solid-liquid separation means, and solubilization and sterilization treatment of excess sludge after methane fermentation by the methane fermentation means. A sterilization treatment means, and an excess sludge introduction path for introducing the excess sludge treated by the solubilization / sterilization treatment means into the treatment tank, wherein the magnetic powder has a size of 0.05 to 2X. m Wherein the coercive force is 0 to 200 eO3 iron oxide powder, and the magnetic separation means includes a magnet having N poles and S poles alternately provided at an interval of 2 to 20 mm. It is characterized by having. The water treatment by the activated sludge method in the present invention is not limited to the standard activated sludge method using an aeration tank as a treatment tank, but may be applied to various water treatment facilities that perform water treatment using activated sludge. it can. For example, the method can be applied to a long-time air-rate method, an OD method, an A〇 method, an A2〇 method, and the like, and can also be applied to a water treatment for removing nitrogen and phosphorus. A general sedimentation tank or sedimentation tank can be used as the solid-liquid separation means for finally separating the activated sludge.However, a filtration device, a membrane separation device, a flotation separation device, or a combination thereof must be used. You can also. Further, when a solid-liquid separation means for separating coarse solids or the like is provided at the preceding stage of the treatment tank, a floating separation device or a fine screen can be used in addition to a general first settling tank. ADVANTAGE OF THE INVENTION According to the wastewater treatment apparatus of this invention, in the water treatment by the activated sludge method, the activated sludge is separated in two stages of magnetic separation by magnetic force and ordinary solid-liquid separation, and activated sludge in magnetic separation By not requiring a separation rate of 100%, the size of the magnetic separation means can be significantly reduced while reliably separating the activated sludge. In other words, if the activated sludge separation rate in the magnetic separation means is in the range of 50 to 99.5%, the required activated sludge can be separated in several seconds to several tens of seconds. Of the final sedimentation basin can be reduced to about 110 to 1/1000. Therefore, it can be easily applied to existing water treatment facilities. In addition, by completely oxidizing organic substances to reduce excess sludge to zero, the activated sludge method can achieve zero emission of excess sludge and eliminate the need for disposal of excess sludge as industrial waste. And greatly contribute to the global environment. Furthermore, since the activated sludge concentration is stabilized by the balance between the growth of the activated sludge itself and the auto-oxidation, the maintenance and management of the activated sludge process is simplified. Since the magnetic separation means has a simple principle, the management of the equipment is easy, and even non-experts can ask questions. Operation management can be performed without any problems. As a result, cost reduction and the spread of the activated sludge method can be expected, which can contribute to the improvement of the water environment. In addition, the problems of the conventional activated sludge method, such as measures against bulking and rainwater, can be solved. In addition, since the efficiency of methane fermentation can be expected to increase, more energy can be created with compact equipment, which can contribute to reducing fossil fuel consumption. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a system diagram of a wastewater treatment apparatus showing one embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating an example of the magnetic separation device.

FIG. 3 is a diagram showing the relationship between the suspension residence time in the magnetic separation device and the MLVSS concentration in the magnetic separation device effluent in Example 1.

FIG. 4 is a diagram showing the change over time of the MLVSS concentration in the aeration tank in Example 1. BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a system diagram showing one embodiment of the wastewater treatment apparatus of the present invention. This wastewater treatment system basically treats sewage by the standard activated sludge method that has been widely used in the past. Preliminary solid-liquid separation means (first sedimentation basin 1 1) equipped with a screen for separating coarse solids, etc., from the activated sludge suspension mixed with activated sludge A treatment tank (aeration tank) 12 for aeration by aeration and a solid-liquid separation means (final sedimentation tank) 13 for sedimentation and separation of activated sludge by gravity and discharge of treated water In addition to these, a magnetic separation means 21 for separating activated sludge by magnetic separation treatment is provided between the aeration tank 12 and the final sedimentation tank 13. That is, the activated sludge in the activated sludge suspension that has been aerated in the aeration tank 12 is separated in two stages: the magnetic separation means 21 and the final sedimentation basin 13. In the magnetic separation means 21, magnetically separated activated sludge is supplied to the aeration tank 12 There is provided a magnetic separation sludge return route 14 for returning the sludge to the facility. The final sedimentation tank 13 is provided with a sedimentation-separated sludge return path 15 for returning the settled-separated activated sludge to the aeration tank 12. The settling separated sludge return path 15 is provided with a sterilization section 16 and a bypass path 17 bypassing the sterilization section 16, and at least a part of the activated sludge is provided to the sterilization section 16. And sterilized. The magnetic separation sludge return path 14 is provided with a solubilization treatment means 18 and a bypass path 19 bypassing the solubilization treatment means 18 as necessary, and the activated sludge separated by the magnetic separation means is provided. At least part of the solution can be solubilized. In order to make the activated sludge magnetically separable by the magnetic separation means 21, magnetic powder is added to the activated sludge in advance, and the activated sludge must be adsorbed and held on the activated sludge. There is. Appropriate magnetic powder can be selected, but magnetic powder with a size of 10 m or more is too heavy for activated sludge, and is often separated from activated sludge by gravity. For this reason, smaller ones are preferable, and usually ones in the range of 0.05 to 2 / im are optimal. Although it is possible to use ultrafine magnetic powder, it is not preferable because the cost of the magnetic powder increases. In addition, the coercive force of the magnetic powder is appropriately 0 to 200 Oe, and the magnetic powder having a large coercive force has a defect that it is aggregated by its own magnetic force, separated from the activated sludge, and settles. . Further, in consideration of long-term use, it is preferable to use an oxide-based magnetic powder that hardly dissolves in water at room temperature or is hardly deteriorated. Iron oxide powder of 1 to 1.0 m, for example, about 0.4 ^ m is most suitable. If the concentration (mixing amount) of the magnetic powder is too low, a strong magnet such as a superconducting magnet is required to separate the activated sludge. Conversely, if the concentration is too high, the cost of the magnetic powder increases. However, it is preferable that the MLVSS of the activated sludge be in the concentration range of 0.01 to 10 with respect to 1.In general, if the concentration is set so as to be approximately the same as the MLVSS of the activated sludge. Good. When such a magnetic powder is put into the activated sludge suspension at an appropriate position such as an aeration tank 12, the activated sludge is immediately adsorbed and held by the activated sludge, and is attracted to a magnet. It becomes. Since most or all of the activated sludge containing magnetic powder circulates together with the returned sludge, addition and mixing of the activated magnetic sludge into the activated sludge suspension is usually performed only once before starting magnetic separation. However, it can be added as appropriate according to the situation of the water treatment facility. Also, it is preferable to add an appropriate amount of magnetic powder at appropriate intervals while circulating the activated sludge so that the magnetic powder is evenly adsorbed on the entire activated sludge circulating in the system. Since the separation of the treated water and the activated sludge is performed by the magnetic separation means 21 and the final sedimentation tank 13, the magnetic separation means 21 does not need to magnetically separate the entire amount of the activated sludge containing the magnetic powder. Depending on the concentration of the activated sludge containing magnetic powder and the load on the final sedimentation basin 13, more than half of the activated sludge containing magnetic powder present in the liquid, that is, 50 to 99.5%, can be separated. You should leave it. As the magnetic separation means 21 for separating the activated sludge containing magnetic powder from the suspension, various types of methods proposed so far can be used. For example, as shown in the cross-sectional view of FIG. 2, a magnetic separation tank 22 having an inflow portion 22a and an outflow portion 22b of the activated sludge suspension, and a rotating drum 2 having magnets arranged on the outer peripheral surface thereof. 3, a scraper 25 for scraping off activated sludge containing magnetic powder 24 attached to the rotating drum 23, and a sludge collection trough 2 for collecting activated sludge containing magnetic powder 24 scraped off by the scraper 25 A magnetic separation device 27 including the above 6 can be used. The rotary drum 23 is connected to a not-shown driving motor or the like, and the sludge collection trough 26 is connected to the magnetic separation sludge return path 14. As the magnet provided on the rotating drum 23, a special magnet such as a superconducting magnet or an electromagnet can be employed, but since it is not necessary to separate all of the magnetic powder-containing activated sludge from the suspension, a general magnet is used. Thus, permanent magnets that can be obtained at low cost, for example, ferrite magnets can be used. The arrangement of magnetic poles on the drum peripheral surface is 2 to 20 mm. It is preferable that N poles and S poles are alternately arranged at intervals. When the magnetization interval is narrow, the amount of the activated sludge containing the magnetic powder becomes saturated, and when the magnetization interval is wide, the adhesion of the activated sludge containing the magnetic powder is weakened. The size (diameter and length) of the rotating drum 23 and the number of rotations during magnetic separation processing are arbitrary, and can be selected according to the processing amount, taking into account installation space, manufacturing costs, operating costs, etc. And set it. The activated sludge containing magnetic powder separated from the suspension by the magnetic force can be collected by any method according to the structure and shape of the magnet, and it can be collected in various shapes such as plate, disk, and rod. Although it is possible to combine sludge collecting means according to the shape of these magnets and the like, the combination of the rotating drum 23 and the scraper 25 facilitates the continuous separation of the magnetically separated activated sludge 24 containing magnetic powder. Can be recovered. In addition, by using a rotating drum-shaped magnet, the device configuration can be simplified, and not only can the manufacturing cost of the magnetic separator 27 be reduced, but also maintenance and inspection can be performed easily. The wastewater that flows into the wastewater treatment system with such a structure first flows into the aeration tank 12 through the sedimentation basin 11, and returns through the magnetic separation sludge return route 14 and the sedimentation separation sludge return route 15. It is aerated when mixed with sludge (activated sludge containing magnetic powder). The activated sludge suspension after the aeration treatment flows out of the aeration tank 12 and flows into the magnetic separation means 21, and a part of the activated sludge containing the magnetic powder in the suspension is magnetically separated. The amount of activated sludge separated in the magnetic separation means 21 is set according to the balance between the amount of activated sludge multiplied in the aeration tank 12 and autoxidation, and the load on the final sedimentation tank 13. Usually, the activated sludge concentration in the activated sludge suspension flowing into the final sedimentation basin 13 is 300 mg / L or less, preferably 200 mg / L or less, and especially 150 mg / L It is preferable to set L or less. On the other hand, if the activated sludge concentration is too low, sludge blanket is less likely to be generated in the final sedimentation basin 13 and the clarity of the treated water may be reduced. Therefore, the activated sludge concentration should be 50 Omg / L or more. Generally, the BOD concentration of sewage flowing into the aeration tank 12 of a sewage treatment plant is about 100 to 20 OmgZL. In the aeration tank 12 under these load conditions, when the activated sludge concentration is in the range of 5000 to 1000 Omg / L, the amount of the activated sludge and the auto-oxidation are balanced and almost no excess sludge is generated. . Therefore, by separating 80% of the activated sludge by the magnetic separation means 21, the concentration of the activated sludge flowing into the final sedimentation basin 13 can be made 1000 to 2000 mg / L. Within this activated sludge concentration range, it is possible to perform sufficient sedimentation and separation in the final sedimentation basin 13. At this time, even if the entire amount of the activated sludge separated in the magnetic separation means 21 and the final sedimentation basin 13 is returned to the aeration tank 12, the activated sludge concentration increases due to the balance between the proliferated amount of the activated sludge itself and the auto-oxidation. The automatic stop of the activated sludge makes it unnecessary to maintain the activated sludge concentration. At this time, the activated sludge concentration in the equilibrium state naturally fluctuates with load fluctuation, but the activated sludge concentration in the magnetic separation means 21 does not exceed the allowable sludge concentration of the final sedimentation tank 13 even at the maximum load. By setting the amount of sludge separation, water treatment can be continued regardless of load fluctuation. Furthermore, by separating most of the activated sludge by the magnetic separation means 21, even if the activated sludge concentration in the aeration tank 12 is increased to some extent, it is possible to prevent the final sedimentation tank 13 from exceeding the allowable sludge concentration. Negative emission is also possible in which the excess sludge is injected into the aeration tank 12 and autooxidized. Among the microorganisms that make up the activated sludge, the filamentous fungi and the dispersible microorganisms cannot retain magnetic powder by themselves, so most of them pass through the magnetic separation means 21 and flow into the final sedimentation basin 13 where they settle. Will be separated. On the other hand, most of the floc-forming bacteria that easily hold the magnetic powder are separated by the magnetic separation means 21 and returned to the aeration tank 12 through the magnetic separation sludge return path 14. Therefore, by returning only the activated sludge separated and collected by the magnetic separation means 21 to the aeration tank 12, the activated sludge in the aeration tank 12 is returned. The mud can be mainly composed of floc-forming bacteria, and the occurrence of bulking can be prevented. However, in this case, excess sludge will be generated from the final sedimentation basin 13, so in order to prevent excess sludge from being generated, the activated sludge separated in the final sedimentation basin 13 must also be returned to the aeration tank 12. There is. When the activated sludge containing the filamentous fungi and the dispersible microorganisms is returned to the aeration tank 12, the occurrence of bulking cannot be completely prevented. Therefore, the activated sludge is transferred from the final sedimentation tank 13 to the aeration tank 12. Until the wastewater is returned, for example, as shown in Fig. 1, a sterilization treatment unit 16 is installed in the sedimentation / separation sludge return route 15 where sterilization treatment is performed using ozone / chlorine and hydrogen peroxide. By doing so, it is possible to eliminate filamentous fungi and the like that cause bulking. Thereby, it is possible to prevent the generation of excess sludge from the final sedimentation basin 13 while suppressing the generation of bulking. The sterilization treatment in the sterilization treatment section 16 may be performed continuously with an appropriate strength, but may be performed according to the occurrence of bulking.In general, when returning from a bulking dog state to a normal state, It is sufficient to perform the sterilization treatment for several times to about 10 times the residence time in the aeration tank. In addition, a solubilization treatment section can be provided instead of, or together with, the sterilization treatment section 16 shown in FIG. In the solubilization processing unit, a mechanical processing device such as an ozone treatment device, an ultrasonic treatment device, a heat treatment device, an alkali treatment device, or a crusher and a ball mill is installed. The main purpose of the solubilization treatment section is to improve the biodegradability of returned sludge that is difficult to biodegrade as it is. However, depending on the mode of the processing apparatus (for example, an ozone processing apparatus), the sterilization processing can be expected, and therefore, a single processing unit can also be used. Since it is necessary to return the microorganisms to the aeration tank 12, it may be better to treat only a part of the returned sludge instead of the entire amount. Therefore, the solubilization treatment unit or the sterilization treatment unit 16 may be used. It is preferable that the bypass route 17 is provided in the route where is disposed. Further, as shown in FIG. 1, the magnetically separated sludge from the magnetically separated sludge return route 14 is returned to the upstream side of the aeration tank 12 with a high organic matter concentration, and the sedimentation separated sludge return route Γ5 The sedimentation-separated activated sludge is returned to the downstream side of the aeration tank 12 having a low organic matter concentration, so that the floc-forming bacteria in the magnetic separation sludge can be preferentially grown in the aeration tank 12. In addition, by providing the solubilization treatment means 18 in the magnetic separation sludge return route 14 and performing the solubilization treatment as described above, an improvement in the biodegradability as described above can be expected. Also in this case, the bypass 19 may be provided to process only a part of the returned sludge. Even when the amount of water flowing into the final sedimentation basin 13 increases due to the inflow of rainwater, the activated sludge capturing the magnetic powder has a higher specific gravity than normal activated sludge and has good sedimentation properties. However, since the floc-forming bacteria can be preferentially grown as described above, sufficient sedimentation and separation can be performed in the final sedimentation basin 13. For example, if the capacity of the magnetic separation means 21 is set so that the MLVSS concentration flowing into the final sedimentation basin 13 becomes about 100 Omg / L even when the flow rate increases due to rainwater, usually 3 to 4 Even if the residence time of the final sedimentation basin 13 set to about the time is reduced to about half, the adverse effect on the sedimentation separation can be almost eliminated. Conventionally, when performing methane fermentation in such a wastewater treatment facility, excess sludge extracted from the first sedimentation basin 11 and the final sedimentation basin 13 was used as a raw material, but the surplus sludge from the final sedimentation basin 13 Since sludge generation can be eliminated, only fermentable primary sludge can be used as a raw material for methane fermentation. This can improve the efficiency of methane fermentation and reduce the amount of excess sludge after methane fermentation. Further, after the excess sludge is subjected to solubilization and sterilization treatment, and then charged into the aeration tank 12, the generation of excess sludge from the first sedimentation basin 11 can be eliminated. That is, as shown in Fig. 1, the methane fermentation means 31 using only the primary sediment sludge of the primary sedimentation basin 11 as a raw material, and the excess sludge generated by the methane fermentation means 31 By providing a solubilization / sterilization treatment means 32 for performing reprocessing, etc., and an excess sludge introduction route 33 for introducing the excess sludge treated by the solubilization / sterilization treatment means 32 into the aeration tank 12 It is possible to eliminate the generation of excess sludge from the first settling tank This makes it possible to implement water treatment by the activated sludge method, which completely eliminates the generation of excess sludge from the entire water treatment facility. In addition, since the magnetic separation means 21 does not need to separate the entire amount of the activated sludge containing the magnetic powder, the required amount of the activated sludge can be separated in a very short time. Even when the rate is 99.5%, the magnetic separation can be performed in several seconds to several tens of seconds, so that the processing can be performed with a volume of about 1/100 to 1/10000 of the volume of the final sedimentation basin 13. Therefore, not only between the aeration tank 12 and the final sedimentation basin 13 in the existing water treatment facility, but also as shown in FIG. Since it is possible to install the magnetic separation means 21 in the inflow section 13a of 13 with a small modification, it can be applied not only to new water treatment facilities but also to existing water treatment facilities. Easy. Further, in the present embodiment, the final sedimentation tank 13 that sediments and separates activated sludge by gravity is exemplified as the solid-liquid separation means subsequent to the magnetic separation means, but even when membrane separation is adopted as this solid-liquid separation means, Since clogging of the membrane can be suppressed and the interval between cleaning operations can be made longer than before, the life of the membrane can be extended, and the cost for membrane separation can be reduced. Example 1

A magnetic separator having the structure shown in FIG. 2 was prepared. That is, N poles and S poles are alternately provided at intervals of about 10 mm on the outer peripheral surface of a rotating drum having a diameter of 20 cm and a length of 35 cm, and a scraper for removing activated sludge adhering to the rotating drum. The lower half of the rotating drum was inserted into a magnetic separation tank and rotated, and the activated sludge attached to the magnet of the rotating drum was scraped off with a scraper every rotation. Prepare an activated sludge suspension containing magnetic powder of MLVSS: 600 Omg / L and triiron tetroxide: 600 Omg / L as the activated sludge, and rotate the rotating drum at 10 rpm. And magnetic separation was performed. The effective volume of the magnetic separation tank is 580ml. Figure 3 shows the relationship between the suspension residence time in the magnetic separator and the ML VSS concentration in the effluent of the magnetic separator. From these results, when the residence time was 14 seconds or more, the MLVSS concentration in the effluent was reduced to 5 mgZL or less, showing a sludge separation rate of nearly 100%. The MLVS S in the effluent at a residence time of 7 seconds is about 5 Omg / L, but the sludge residual rate is only 0.8%. When the residence time is 2 seconds, the MLVS S concentration in the effluent is 1180 mgZL, and the sludge separation rate is approximately 80%. The throughput of this magnetic separator was about lm3 / h at 80% sludge separation rate. This magnetic separation device is installed on the upper part of the aeration tank of a sewage treatment experimental plant using the ordinary activated sludge method, which treats 20 m3 per day, and the effluent from the aeration tank flows into the final sedimentation tank through this magnetic separation device. Was. As a result, the concentration of activated sludge in the aeration tank stopped increasing at MLVSS of 6000 mg / L, and a stable operating state was achieved without performing bow I removal of excess sludge. Figure 4 shows the time-dependent changes in the MLVSS concentration in the aeration tank at this time. During the operation, activated sludge with MLVS S of 500-1500 mgZL flowed into the final sedimentation basin through the magnetic separator, and complete solid-liquid separation was achieved. Example 2

The same sewage treatment experimental plant as in Example 1 was installed and operated with the same two magnetic separators as in Example 1. At normal loading, the MLVSS concentration in the final sedimentation basin influent was 100-20 OmgZL. Assuming rainwater inflow, the supernatant of the final sedimentation basin was returned 10 m3 / day, and the amount of inflow water into the aeration tank was increased 1.5 times. As a result, the MLVSS concentration in the influent of the final sedimentation basin increased to about 300 to 400 mg / L, but due to the sufficiently low activated sludge concentration and the capture of magnetic powder, the sedimentation Therefore, solid-liquid separation in the final sedimentation basin was sufficiently performed, and no outflow of SS due to increased flow rate was observed.

Claims

The scope of the claims

1. A treatment tank that performs water treatment with activated sludge to which magnetic powder has been added, and a magnet that separates a part of the activated sludge contained in the activated sludge suspension flowing out of the treatment tank from the liquid by magnetic force Separation means, solid-liquid separation means for separating activated sludge in the activated sludge suspension flowing out of the magnetic separation means from the liquid, and magnetism for returning the activated sludge separated by the magnetic separation means to the treatment tank. Wastewater treatment equipment including a separated sludge return route.

2. The wastewater treatment apparatus according to claim 1, wherein the magnetic separation sludge return path includes a solubilization treatment means for solubilizing at least a part of the activated sludge separated by the magnetic separation means.

3. The solid-liquid separation means is a final sedimentation tank for separating activated sludge by gravity sedimentation separation, and the MLVSS concentration in the activated sludge suspension flowing out of the magnetic separation means and flowing into the final sedimentation basin is reduced. 3. The wastewater treatment device according to claim 1, wherein the concentration is not more than 300 Omg / L.

4. The wastewater treatment apparatus according to claim 1, wherein the magnetic separation means is provided at an outlet of the treatment tank.

5. The wastewater treatment apparatus according to claim 1, wherein the magnetic separation unit is provided at an inflow portion of the solid-liquid separation unit.

6. The wastewater treatment apparatus according to claim 1, wherein the magnetic separation means separates 50 to 99.5% of the activated sludge in the effluent of the treatment tank.

7. The wastewater treatment apparatus according to claim 1, wherein the ratio of the activated sludge to the magnetic powder is such that the MLVSS of the activated sludge is 1 and the magnetic powder has a concentration of 0.01 to 10%.

8. The wastewater treatment apparatus according to claim 1, further comprising a sedimentation separation sludge return path for returning at least a part of the activated sludge separated by the solid / night separation means to the treatment tank after treating it in a sterilization treatment section. .

9. The wastewater treatment apparatus according to claim 1, further comprising a sedimentation separation sludge return path for returning at least a part of the activated sludge separated by the solid-liquid separation means to the treatment tank after treating in the solubilization treatment section. .

10. Preliminary solid-liquid separation means provided in the preceding stage of the treatment tank, methane fermentation means for performing methane fermentation using the primary sludge separated by the preliminary solid-liquid separation means as a raw material, and methane fermentation means Solubilization and sterilization means for solubilizing and sterilizing surplus sludge after methane fermentation; 2. The wastewater treatment device according to 1.

11. The wastewater treatment apparatus according to claim 1, wherein the magnetic powder is iron trioxide powder having a size of 0.05 to 2 m and a coercive force of 0 to 200 Oe.

12. The wastewater treatment apparatus according to claim 1, wherein the magnetic separation unit includes a magnet in which N poles and S poles are alternately provided at an interval of 2 to 20 mm.