Title of Invention	A MULTISTAGED UPFLOW ANAEROBIC SLUDGE BLANKET TREATMENT APPARATUS
Abstract	The present invention provides an anaerobic treatment apparatus which can effect stabilized wastewater treatment even at a high COD load using a multistage upflow anaerobic sludge blanket (UASB) treatment apparatus which effectively uses sludge particles in the good fluidity state, that is, the entire sludge particles without interfering with the contact of sludge particles with organic substances for the treatment- As the means to achieve such an object, one embodiment of the present invention provides an apparatus for anaerobically treating organic wastewater or waste which is an upflow anaerobic sludge blanket treatment apparatus having an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed to the inner part of the treatment tank, the area taken by each baffle being not smaller than 1/2 of the cross-sectional area of the treatment tank, and having a means to feed an antifoaming agent into the treatment tank.

Title of Invention

A MULTISTAGED UPFLOW ANAEROBIC SLUDGE BLANKET TREATMENT APPARATUS

Abstract

The present invention provides an anaerobic treatment apparatus which can effect stabilized wastewater treatment even at a high COD load using a multistage upflow anaerobic sludge blanket (UASB) treatment apparatus which effectively uses sludge particles in the good fluidity state, that is, the entire sludge particles without interfering with the contact of sludge particles with organic substances for the treatment- As the means to achieve such an object, one embodiment of the present invention provides an apparatus for anaerobically treating organic wastewater or waste which is an upflow anaerobic sludge blanket treatment apparatus having an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed to the inner part of the treatment tank, the area taken by each baffle being not smaller than 1/2 of the cross-sectional area of the treatment tank, and having a means to feed an antifoaming agent into the treatment tank.

Full Text	ANAEROBIC TREATMENT APPARATUS TECHNICAL FIELD The present invention relates to an upflow anaerobic sludge blanket treatment apparatus to be used for the treatment of the organic wastewater discharged from various plants, sewage treatment facilities, night soil treatment facilities, livestock production facilities and the like, and more specifically, it relates to an upflow anaerobic sludge blanket treatment apparatus having a multistage gas-solid separator (hereinafter referred to as "GSS"). BACKGROUND ART Organic wastewater, organic waste or the like is sometimes subjected to separation treatment by anaerobic treatment. As such a decomposition treatment method, there is, for example, an upflow anaerobic sludge blanket process (hereinafter referred to as "UASB process"). This method has spread in recent years, and is to biologically decompose organic substances in wastewater under anaerobic conditions by allowing organic wastewater to flow as an upflow within a reactor into which a sludge (sludge particles) comprising granulated microorganisms mainly having anaerobic bacteria such as methane bacteria is packed. The UASB process can characteristically maintain methane bacteria at a high concentration in the reactor by granulating anaerobic bacteria to granules. As a result, the wastewater having a remarkably high concentration of organic substance can be efficiently treated. For example, the apparatus which embodies this method can be characteristically operated with good efficiently even with the wastewater/waste having a volume load of CODCr (hereinafter referred to as "COD"), measured by using potassium bichromate as the oxidizing agent, of 10 to 15 kg/m3/d. The anaerobic bacteria to be used for the anaerobic treatment aimed at organic wastewater and organic waste are roughly classified into two types by the ambient temperature. For example, there are medium temperature anaerobic bacteria having an optimum temperature in the medium temperature region of 30 to 35°C and high temperature anaerobic bacteria having an optimum temperature in the high temperature region of 50 to 55°C. In the UASB process utilizing the action of these anaerobic bacteria, with increased loads (for example, a COD volume load of not smaller than of 15 kg/m3/d) of organic substances to be decomposed, the amount of a gas to be generated is increased. In this instance, unless gas drainage from the reactor is surely carried out from time to time, effluence of the sludge particles in the form of granules becomes conspicuous by blow-off on gas drainage or the like, and it is difficult to retain the sludge particles in the reactor. As a treatment measure in this case, a method of forming a multistage UASB apparatus and dispersing and discharging the generated gas out of the system is proposed. Fig. 1 is a schematic view of an anaerobic treatment apparatus using a multistage the UASB apparatus[G. Lettinga (1995), Anaerobic digestion and wastewater treatment system, Antonie van Leeuwenhoek 67:3-28]. In the apparatus as shown in Fig. 1# a plurality of baffles 3 downwardly inclined are alternately provided inside a cylindrical reactor 2 connected to a raw water inlet pipe 1 at its lower end to form sectional sludge zones 4a to 4e by dividing multistagewise the inside of the reactor at respective positions. The corners (clogging parts to be formed by baffles) of respective upper ends of the sectional zones 4a to 4e form GSS 5. Sludge particles in the form of granules are packed in the reactor. When organic wastewater (raw water) is introduced from the lower end of such an apparatus, the organic substances in the raw water are decomposed by the action of the anaerobic bacteria present in the sludge particles in the form of granules placed in the reactor, and a gas is generated. Since a large amount of the gas is generated in the lower part of the reactor due to the state of a high load, the generated gas adheres to the sludge particles to reduce their apparent specific density, and simultaneously the adhered gas entrains the sludge particles and flows upward along an upward water flow together with the sludge particles. The sludge particles entrained by the gas are trapped by GSS 5 formed by the baffle 3 and come to air bubbles at the water surface to form an air bubble layer 5b. The air bubbles soon break and a gas accumulates in the GSS 5 to form a gas phase layer 5a. Generated gas recovery piping 6 is connected to each place where the gas phase layer 5a is formed to recover the gas. The generated gas recovery piping 6 is connected to an external water-sealed tank 7, and the gas is trapped in the water-sealed tank 7. On breakage of air bubbles, the gas is separated from the sludge particles. The sludge particles regain the original specific gravity and settle by gravity. The sludge particles which settle on the baffles 3 further settle while sliding on the baffles 3 to fall. The settled sludge particles are again brought into contact with the organic substances in the raw water to decompose the organic substances with the anaerobic microorganisms in the sludge particles. Thus, gas is generated, and the sludge particles are entrained by the gas and flow upwardly. The above described cyclic motion of the sludge particles occurs in the reactor. As the gas generated in the lower part of the reactor is recovered in GSS in the lower part of the reactor, the influence of the gas generated in the lower part of the reactor on the fluidity of sludge particles is reduced at higher position in the reactor. Therefore, at higher position in the reactor, the load of organic substances is slowly reduced, and thus the amount of the generated gas is decreased to increase the apparent specific gravity of the sludge particles to be flown with the generated gas, and the velocity of the upflow sludge particles entrained by the gas is decreased, that is, the flow of sludge particles becomes slower. The treated water thus obtained by subjecting organic substances to anaerobic treatment overflows the upper end of the reactor 2 and is discharged through treated water piping 9. As described above, the flow of sludge particles becomes slower in proportion at higher position in the reactor, that is, approximates standing state, and accordingly the overflow from the upper end of the reactor does not contain sludge particles to give a clean water. However, the multi-staged UASB apparatus still has the following problems. (1) Depending on the properties of wastewater to be treated, foaming is caused in the GSS to invite clogging of the inside of the GSS or the generated gas trapping piping, and trapping of the generated gas becomes difficult. (2) Depending on the properties of wastewater to be treated, scum is formed in the GSS to make trapping of the generated gas difficult. Above all, when the load is low and the amount of the generated gas is small, the effect of destroying and removing scum by the generated gas is small and scum is easy to form. (3) As the result of the above described problems (1) and (2), the effect of diffusing the generated gas to discharge it out of the system which is the characteristic feature of the multistage UASB apparatus is lost and invites a large amount of effluent sludge to cause the deterioration of treatment. (4) When the angle of installing a baffle constituting the GSS is obtuse, sludge deposits on the baffle to cause a dead space of sludge and as a result, the entire sludge particles within the reactor are sometimes not effectively used. (5) When each GSS is formed even in the lower part of the reactor, good fluidity of sludge particles is obstructed, and the contact of sludge particles with organic substances sometimes becomes insufficient or fails. (6) When the velocity of the water passed in a reactor is low, a short circuiting flow is caused and, inversely when that is high, effluence of sludge is caused and as a result, the treatment result is sometimes deteriorated. In view of such actual circumstances, the object of the present invention is to provide an anaerobic treatment apparatus capable of carrying out stabilized wastewater treatment even with a high COD load by stably recovering the generated gas in the GSS in the multistage UASB apparatus which effectively uses the entire sludge particles for treatment without disturbing good flow of sludge particles, that is, good contact of the sludge particles with organic substances. DISCLOSURE OF THE INVENTION The present invention provides an anaerobic treatment apparatus relating to each of the following embodiment as the means to solve the above described problems. The invention of claim 1 of the present invention relates to an upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed in the treatment tank, the area taken up by each baffle being not smaller than 1/2 of the cross-sectional area of the treatment tank, and further has a means to feed an antifoaming agent into the treatment tank. The invention of claim 2 of the present invention relates to an upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed in the treatment tank, each baffle being fixed so as to render the angle to the inner wall of the treatment tank not larger than 35 degrees and, simultaneously, the area taken up by each baffle being not smaller than 1/2 of the cross-sectional area of the treatment tank. The invention of claim 3 of the present invention relates to an apparatus of claim 2 further having a means to feed an antifoaming agent into the treatment tank. The invention of claim 4 relates to an upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed in the treatment tank, each baffle being fixed so as to render the angle to the inner wall of the treatment tank not larger than 35 degrees, and further has a means to feed an antifoaming agent into the treatment tank. The invention of claim 5 relates to the apparatus of any one of claims 1 to 4, wherein a gas feed pipe for blowing an oxygen-free gas into the inside or below each of the gas-solid separators is installed. The invention of claim 6 relates to the apparatus of any one of claims 1 to 5, wherein the gas-solid separators are formed at a position in the range of upper 50% of the treatment tank. The invention of claim 7 relates to the apparatus of any one of claims 1 to 6, wherein the amount of the raw water passed in the treatment tank is regulated to 1 to 5 m/h. BRIEF EXPLANATION OF THE DRAWINGS Fig. 1 is a diagram showing a constitution example of the conventional multistage UASB apparatus. Fig. 2 is a diagram showing a constitution example of the multistage UASB apparatus relating to one embodiment of the present invention. Fig. 3 is a diagram showing a constitution example of the multistage UASB apparatus relating to another embodiment of the present invention. Fig. 4 is a diagram showing the constitution of the multistage UASB apparatus relating to one embodiment of the present invention used in Example 2. Fig. 5 is a diagram showing the constitution of the multistage UASB apparatus used in Example 2 for comparison. Fig. 6 is graphs showing the change in the COD treatment results with time in Example 2. Fig. 7 is diagrams showing the constitutions of various types of multistage UASB apparatus used in Example 3. Fig. 8 is graphs showing the change in the COD treatment results with time in the experiment (Run 1) using soft drink wastewater in Example 3. Fig. 9 is graphs showing the change in the COD treatment results with time in the experiment (Run 2) using food production wastewater in Example 3. BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will now be explained but the present invention is not to be limited thereto. Fig. 2 is a diagram showing one example of the multistage UASB apparatus relating to a first embodiment of the present invention. In the accompanying drawings, the same reference numbers are given to the same constitutional elements. In the multistage UASB apparatus relating to one embodiment of the present invention as shown in Fig. 2f by providing a plurality of baffles 3 in a cylindrical reactor 2 to the lower end of which a raw water inlet pipe 1 is connected, the inside of the reactor 2 is divided to form sectional sludge zones in multistage. One end of each baffle 3 is fixed to the inner wall of the reactor 2 and the other end extends downwardly inclined toward the direction of the opposite inner wall. Fig. 2 shows a constitution example in which two sludge zones 4a and 4b are formed in multistage by arranging two sheets of downwardly inclined baffles 3. GSS 5 is formed in the upper end corner (clogged part formed by the baffle 3) of each of the sectional sludge zones 4a and 4b. Sludge particles in the form of granules are packed in the reactor. Organic wastewater (raw water) is first conditioned in a raw water conditioning tank/acid fermentor 23 through a feed pipe 25, and then introduced into the reactor 2 from its lower end through a raw water inlet pipe 1. The raw water conditioning tank/acid fermentor 23 is not necessarily installed and the raw water may be directly fed to the reactor 2. Unless particularly required, the raw water may not be conditioned in the tank 23. In the reactor 2f granule sludge particles containing anaerobic bacteria are packed. The anaerobic treatment according to the present invention includes anaerobic treatments of all temperature ranges such as medium temperature methane fermentation treatment having an optimum temperature of 30°C to 35°C and high temperature methane fermentation treatment having an optimum temperature of 50°C to 55°C. Into the lower end of the reactor 2 packed with the granule sludge particles containing anaerobic bacteria, raw water containing organic waste and the like is introduced through the raw water feed pipe 1. If necessary, the raw water can be suitably diluted with the circulating liquor of the treated water, diluting water to be fed from outside the system or the like, and then fed to the reactor. The amount of the influent raw water is preferably regulated in such a manner that the velocity of the water passed in the reactor 2 is rendered 1 to 5 m/h. In the reactor 2, organic waste is decomposed in the presence of the granule sludge particles containing anaerobic bacteria to generate a decomposed gas. The generated gas is separately collected in GSS 5 at the upper end of each of the sectional sludge zones 4a and 4b to form an air bubble layer 5b and a gas phase layer 5a in each of the sectional sludge zones, and recovered to a water-sealed tank 7 from the gas phase layer 5a through generated gas recovery piping 6. Discharge amount of the recovered generated gas is recorded by a gas meter 8. Part of the gas generated in the reactor adheres to the granule sludge particles in each of the sectional sludge zones 4a and 4b to reduce their apparent specific density, and simultaneously entrains the granule sludge particles and reaches the water surface of GSS 5 with the particles. Thus, the generated gas forms air bubbles and temporarily stays in the water surface air bubble layer 5b. The air bubbles collected in the water surface air bubble layer 5b soon break and separates into generated gas and granule sludge particles. The granule sludge particles regain their original specific density and settle in water, while the generated gas forms the gas phase layer 5a and is discharged out of the system by the generated gas recovery piping 6 through the water-sealed tank 7. The clarified treated water after decomposition of organic substances overflows the upper end of the reactor and is discharged out of the system through treated water piping 9. Further, as shown in Fig. 2, the treated water piping 9 may branch off to constitute treated water circulating piping 21, through which the treated water may be circulated to the raw water conditioning tank/acid fermented 23 through piping 24 and then recirculated to the reactor 2 after reconditioning if necessary. Or, bypass piping 22 may be placed, through which the treated water may be recirculated to the reactor 2 without any treatment. Since the gas pressure in the gas phase layer 5a of each GSS 5 is different, its differential pressure may preferably be regulated in the water-sealed tank 7. It is necessary to maintain the water sealing pressure higher on the side near to the raw water feeding side (that is, higher pressure at lower GSS). This can be achieved by lowering the position of the opening in the water-sealed tank 7 of the generated gas recovery piping 6 connected to lower GSS (refer to Fig. 2). As the pressure control of gas recovery, there are many methods other than the method using the water-sealed tank 7 and, for example, a pressure valve or the like may be used. In the anaerobic treatment of the present invention, since the generated gas generated in every sectional sludge zone can be recovered separately. the amount of the generated gas per unit cross-sectional area of the reactor will be reduced. Particularly, in the part nearest the treated water piping 9 which allows the treated water to flow out, the gas amount per unit cross-sectional area of the reactor becomes very small. Thus, the amount of effluent granule sludge particles out of the system can be extremely reduced. Herein, it is preferred that the baffles 3 to be installed in the reactor 2 are made to have a size such that the cross-sectional area taken up by each of the baffles is not smaller than 1/2 of the cross-sectional area of the treatment tank. When the area taken up by the baffles 3 is smaller than 1/2 of the cross-sectional area of the treatment tank, trapping of the generated gas in the reactor by the baffles is insufficient to cause failure of gas-solid separation. In other words, the generated gas passes through upwardly at the center of the reactor, and thus GSS 5 ceases to sufficiently accumulates the gas. Further, when the raw water to be treated is effervescent, it is possible that the gas phase layer 5a in GSS 5 and the generated gas recovery piping 6 are blocked to make recovery of the generated gas difficult. Accordingly, in one embodiment of the present invention, by feeding an antifoaming agent into the reactor 2, foaming in GSS 5 can be inhibited to smoothly effect treatment. As the means to feed the antifoaming agent into the reactor 2, as shown in Fig. 2, antifoaming agent feed piping 10 can be connected to the raw water feed pipe 1 to previously add the antifoaming agent into raw water. Further, in other embodiments, the antifoaming agent can be fed to the raw water conditioning tank/acid fermentor 23 by dropwise addition or spraying ((2) in Fig. 2); to the treated water circulating piping (®, (6) or (7) in Fig. 2); introduced into the reactor 2 by direct dropwise addition or spraying (® in Fig. 2); or to GSS 5 of the reactor 2 by dropwise addition or spraying ((3) in Fig. 2). As the antifoaming agent, a preferred one has an antifoaming effect in accordance with the properties of the raw water and can be used at medium temperatures (30°C to 35°C) or at high temperatures (50°C to 55°C) which are suited for use in antifoaming a fermented liquor without losing the antifoaming effect. As the antifoaming agent which can be used in the present invention, any of a silicone-containing antifoaming agent and an alcohol-containing antifoaming agent can be applied. A first embodiment of the present invention relates to an anaerobic treatment apparatus having the above described characteristic features. Namely, the first embodiment of the present invention relates to an upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-liquid separators formed by a plurality of baffles fixed in the treatment tank, the area taken up by each baffle being not smaller than 1/2 of the cross-sectional area of the treatment tank, and further has a means to feed an antifoaming agent into the treatment tank. Further, a second embodiment of the present invention is characterized by fixing the baffles so as to make the angle to the inner wall of the treatment tank not larger than 35 degrees. Namely, the second embodiment of the present invention relates to an upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-liquid separators formed by a plurality of baffles fixed in the treatment tank, each baffle being fixed so as to make the angle to the inner wall of the treatment tank not larger than 35 degrees, and simultaneously the area taken up by each baffle being not smaller than 1/2 of the cross-sectional area of the treatment tank. The second embodiment of the present invention is explained by reference to Fig. 2. In the second embodiment, by fixing the baffle downwardly inclined toward the opposite inner wall with an angle (G) formed between the inner wall of the reactor 2 and each baffle 3 of not larger than 35 degrees, such a problem that granule sludge particles settling from above are deposited on to the baffles 3 forming sludge zones 4a and 4b, and their flowability accordingly becomes insufficient to cause dead spaces of sludge particles ceases to exist. When angles formed between the inner wall of the reactor 2 and each baffle 3 are larger than 35 degrees, sludge particles are deposited as described above to easily form a dead space of sludge particles, and thus the treatment with a high load of 30 kg/m3/d or higher becomes difficult. When angles formed between the inner wall of the reactor 2 and each baffle 3 are not larger than 35 degrees, an inclination of larger than repose angle of the sludge particles is formed, and the sludge particles settled on the baffles slide on the surface of the baffles to flow down, and thus there is no deposition of sludge on the baffles. The angle formed between the baffle and the inner wall of the reactor is preferably not larger than 30 degrees, more preferably not greater than 27 degrees. Further, also in the second embodiment of the present invention, the baffles 3 to be arranged in the inner part of the reactor 2 preferably have such a size that the area to be taken up by each baffle comes to not smaller than 1/2 of the cross-sectional area of the treatment tank. When the area taken up by each baffle 3 is smaller than 1/2, trapping of the gas generated by the baffles in the reactor is insufficient to cause failure of gas-liquid separation. In other words, the gas passes through upward from the center of the reactor, and accordingly GSS 5 cannot sufficiently collect the gas. It is not essential in the second embodiment of the present invention to add an antifoaming agent. However, as in the first embodiment of the present invention, it is more preferred that an antifoaming agent is fed to the reactor to inhibit foaming in GSS 5. In addition, a third embodiment of the present invention relates to an upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-liquid separators formed by a plurality of baffles fixed in the treatment tank, each baffle being fixed so as render the angle to the inner wall of the treatment tank not larger than 35 degrees, and further has a means to feed an antifoaming agent into the treatment tank. Further, when scum is easily formed due to the high concentration of SS in raw water or the like, scum is sometimes formed on the surface of the air bubble layer 5b in the inner part of GSS 5 to make recovery of the generated gas difficult. In such a case, by arranging a gas feed pipe inside or below the GSS 5 to feed a gas, the scum can be destroyed or the formation of the scum can be inhibited. As the gas which can be used for this purpose, an oxygen-free gas such as a nitrogen gas which does not affect the biological treatment such as methane fermentation can be used. Further, the gas generated by the anaerobic treatment can be used as the gas for destroying scum or preventing formation of the scum. A constitution example of such an embodiment of the anaerobic treatment apparatus is shown in Fig. 3. In the apparatus as shown in Fig. 3, the generated gas recovered through generated gas recovery piping 6 and a water-sealed tank 7 is stored in a gas holder 11, and is fed to a diffusion pipe 12 installed below each of the GSS through generated gas feed piping 13 as air bubbles, or is fed to the generated gas recovery piping 6 to directly feed the gas to the inside of the GSS. Thus, the destruction of scum in GSS or the prevention of forming scum therein can be achieved- When the generated gas feed piping 13 is connected to the generated gas recovery piping 6 in each GSS to destroy and remove the scum in GSS 5-1, by closing a valve 14a, blowing the generated gas into the GSS 5-1 and making the entire inside of GSS gas phase layer 5-la to push down the air bubble layer 5-lb, the scum can be discharged from GSS 5-1. Since this discharged scum is trapped in GSS 5-2 above the GSS 5-1, the valve 14b may then be closed and the generated gas may be blown into the GSS 5-2 in the same manner to make the entire inside of GSS 5-2 gas phase layer 5-2a, and the air bubble layer 5-2b may be pushed down to discharge scum from the GSS 5-2. The discharged scum may be flown out together with the treated water. When the generated gas feed piping 13 is connected to the diffusion pipe 12 arranged below each GSS, scum is destroyed by air bubbles to be blown from the diffusion pipe 12, and the destroyed scum is discharged with the flowing of the liquor in the reactor 2 as the treated water. This technique is independent of opening and closing of the valves 14a and 14b. When the above described operation is performed with the valves 14a and 14b opened, the gas blown from the diffusion pipe 12 is recovered through the generated gas recovery piping 6. When the above described operation is performed with the valves 14a and 14b closed, in addition to the scum destruction effect by the air bubbles to be blown from the diffusion pipe 12, a scum discharge effect can be also expected by directly feeding a gas into the inside of GSS through the generated gas feed piping 13. The frequency of feeding a gas into the inside of GSS 5 or into the diffusion pipe 12 for the purpose of destruction of scum and prevention of forming scum depends on the properties of the wastewater to be treated and may be typically once a day to once a week, and this frequency has an effect of destruction and removal of scum inside GSS 5. In the multistage UASB apparatus relating to the present invention, it is more preferred that the gas-liquid separator is formed only in the upper part of the treatment tank. This is because that, when the gas-liquid separator is formed even in the lower part of the treatment tank, good flowability of sludge particles in the treatment tank is obstructed and the contact of sludge with organic substances fails to sometimes render the treatment unstable. From this viewpoint, in the multistage UASB apparatus relating to the present invention, the gas-liquid separator is preferably formed at a position in the range of upper 70% of the treatment tank, preferably in the range of upper 50%, more preferably in the range of upper 30% of the treatment tank. In the multistage UASB apparatus of the present invention, the amount of the raw water passed in the treatment tank is preferably regulated to 1 to 5 m/h. With too small amounts of the water passed in the tank, a short circuiting flow is caused in the sludge layer in the tank and sometimes the entire sludge layer ceases to be effectively used. With too large amounts of the water passed in the tank, the upflow velocity of the liquor becomes higher than the settling velocity of granule sludge particles, and the granule sludge particles flows out together with treated water, and thus sludge cannot be stably retained in the tank to sometimes render the treatment unstable. From this viewpoint, the amount of the raw water passed in the treatment tank is preferably regulated to 1 to 5 m/h, more preferably 2 to 3 m/h. Various embodiments of the present invention will now be more concretely explained by examples but the present invention is not to be limited thereto. Example 1 With the use of the apparatus as shown in Fig. 2, wastewater was subjected to anaerobic treatment. Two sheets of baffles 3 were fixed downwardly inclined in a cylindrical reactor 2 having a cross-sectional area of 0.16 m2 and a height of 6.25 m (a tank volume of 1 m2) so as to render the area taken up by each baffle 0,112 m2 (70% of the cross-sectional area of the reactor). The angle (0) of fixing each of the baffles 3 was 45 degrees. The water temperature in the reactor 2 was regulated to 35°C. Sludge particles in the form of granules were packed into the reactor 2. As the raw water, the treated water (COD=10,000 mg/L; SS=500 mg/L) by acid fermentation of effervescent soft drink wastewater was used. By allowing the treated water overflowing the upper end of the reactor 2 as the circulating water together with the raw water to flow into the reactor 2, the velocity of the water to be passed in the reactor was set at 2 m/h. The ratio of the flow rate of the raw water to the amount of the circulating treated water were set depending on the COD load. From the antifoaming agent introduction piping 10 connected to the raw water feed pipe 1, a silicone-containing antifoaming agent was introduced at a ratio of 10 mg/L per amount of the influent into the reactor. For the control data, the same experiment as described above was carried out without introducing the antifoaming agent. The results of the treatments in the stationary state are shown in Table 1. From the above described Table it would be found that by feeding an antifoaming agent into the treatment tank in the multistage UABS treatment apparatus according to the present invention, excellent treatment performance could be obtained. With the antifoaming agent not fed, foaming was caused inside GSS by the rise in load to reduce the treatment performance. Example 2 Experiments was carried out by using reactors 2 having structures as shown in Fig. 4 and Fig. 5 in the anaerobic treatment apparatus as shown in Fig. 2. In the reactor 2 as shown in Fig. 4, two inclined baffles 2 were fixed and the angle (0) formed between the side wall of the apparatus and each of the baffles 3 was set at 30 degrees. The baffles 3 were arranged only at the positions in the range of upper 50% of the reactor 2. In the reactor 2 as shown in Fig. 5, five inclined baffles 3 were fixed over the entire height of the reactor 2, and the angle (0) formed between the side wall of the apparatus and each of the baffles 3 was set at 45 degrees. In both cases, the experiments were carried out with the use of the reactors having a cross-sectional area of 0.16 m2 and a height of 6.25 m (a volume of 1 m3), and each baffle to form the GSS taking an effective cross-sectional area of 0.112 m2 (70% of the cross-sectional area of the reactor). In the reactor 2, sludge particles in the form of granules were packed, and raw water was allowed to flow thereinto through the raw water feed pipe 1 connected to the lower end of the reactor 2, and treated water was obtained from a treated water pipe 9 in the upper part of the reactor 2. In the reactor 2, each GSS 5 where the gas generated in decomposing and clarifying the organic substances is collected by the baffles was formed, and at its upper end, a discharge outlet of a generated gas recovery pipe 6 communicating with the outside was provided. The amount of the generated gas from each GSS 5 was measured by a gas meter installed in a water-sealed tank 7. The water temperature in the reactor 2 was controlled to 35°C. As the raw water, acid fermentation treated water (COD=7,000 mg/L) of sugar-containing wastewater added with inorganic nutrient salts (nitrogen, phosphorus and the like) was used. By allowing the treated water as the circulating water together with the raw water to flow into the reactor 2, the velocity of the water passed in the reactor was set at 2 m/h. The ratio of the flow rate of the raw water to the amount of the circulating treated water was set depending on the COD load. By taking the results obtained by using the reactor 2 in which the angle of fixing each of the baffles is 30 degrees shown in Fig. 4 as system B and those obtained by using the reactor 2 in which the angle of fixing each of the baffles is 45 degrees shown in Fig. 5 as system A , the following is reported. Fig. 6 shows the course of the experiments and the change in the COD treatment results. In both systems, the load amount of organic substances was slowly increased while observing the COD concentration in the treated water. In the course of the experiments, the treatment could be conducted with almost the same load amount till about 120th day. When the COD load came to 30 kg/m3/d or more on and after about 120th day, the COD concentration in the treated water was increased in system A. In system A where five inclined baffles were fixed and the angle formed between the inner wall of the reactor 2 and each of the baffles 3 was set at 45 degrees as shown in Fig. 5, dead spaces were formed on the baffles 3 by deposited sludge, and the entire sludge particles were not effectively used to render the treatment unstable. Accordingly, the COD load was decreased to 25 kg/m3/d. In system B with a COD load of 25 kg/m3/d, stable treatment was carried out. Table 2 shows comparison of the treatment results in the stationary state. In system B where the angle of fixing each of the baffles is set at 30 degrees, the COD load was 35 kg/m3/d; the COD removal ratio was 90%; and the VSS concentration in the treated water was 300 to 400 mg/L. On the other hand, in the system A where the angle of fixing each of the baffles was set at 45 degrees, the COD load was 25 kg/m3/d; the COD removal ratio was 90%; and the VSS concentration of the treated water was 300 to 400 mg/L. Thus, by rendering the angle of fixing baffles not larger than 35 degrees, a higher COD removal ratio could be obtained compared to the set angle of fixing the baffles of 45 degrees. In the process of system B# in spite of the operation with a high COD load, the treatment result of the COD concentration in the treated water was stabilized. Further, the VSS concentration in the treated water was nearly equal to that in the process of system A, and even when the number of GSS is smaller than in the process of system A, the amount of the granule sludge in the tank in the upflow anaerobic sludge blanket (UASB) process was also stabilized. This is due to a smaller gas amount per unit cross-sectional area of the reactor at the position nearest to the treated water piping 9 for allowing the treated water to flow out and the resulting small amount of the granule sludge flowing out of the system. Next, the treatment results in the stationary state when the treatment was carried out with the use of system B with a COD concentration of the raw water of 7,000 g/L and a COD load of 30 kg/m3/d at a velocity of the water passed of 0.5 to 7 m/h are shown in Table 3 for comparison. In the system B where the angle formed between each baffle and the inner wall of the reactor was made 30 degrees, in order to carry out stabilized treatment with a COD removal ratio of not less than 85%, when the velocity of the water passed is set at 1 to 5 m/h and preferably the COD removal ratio is set at not less than 90%, it has been found that it is preferred to set the velocity of the water passed in the reactor at 2 to 3 m/h. This is due to the formation of a short circuiting flow of the sludge layer to make it impossible to effectively utilize the entire sludge layer when the velocity of the water passed is lower than 1 m/h. Further, when the velocity of the water passed is higher than 5 m/h, the VSS concentration comes to 1,500 mg/L or more and the amount of the sludge in the reactor 2 cannot be stably maintained and as a result, the treatability is deteriorated. Example 3 As the reactor 2, various types of reactors as shown in Fig. 7 were used. In system A, two inclined baffles were fixed and the angle formed between each of the baffles and the inner wall of the reactor 2 was set at 30 degrees. In system B# antifoaming agent introduction piping 10 was connected to the raw water feed pipe 1 in the reactor 2 of system Af and a silicone-containing antifoaming agent was added to the raw water in an amount of 10 mg per liter of water flowing into the reactor. In system C, diffusion pipes 12 were further fixed to the reactor 2 of system B and by feeding a generated gas through generated gas feed piping 13, the scum in each GSS was destroyed and removed. In each system, each GSS was arranged at a position in the range of upper 50% of the reactor 2. In the experiments, the apparatus as shown in Fig. 3 was used. Granule sludge particles were packed in the reactor 2. Raw water was fed through the raw water feed pipe 1 connected to the lower end of the reactor 2 and treated water was obtained from the treated water pipe 9 in the upper part of the reactor 2. In the reactor 2, GSSs were formed in the reactor 2, where a gas generated in decomposing and clarifying organic substances was collected. To the upper end of each GSS, generated gas recovery piping 6 was connected (refer to Fig. 3). In any of the systems, the reactor had a cross-sectional area of 0.16 m2 and a height of 6.25 m (a volume of m3), and each baffle forming GSS had an effective cross-sectional area of 0.112 m2 (70% of the cross-sectional area of the reactor). The amount of the gas generated in each GSS section was measured by a gas meter installed in the water-sealed tank 7. The temperature in the reactor 2 was controlled to 35°C. As the raw water, the acid fermentation treated water (Run 1; COD=10,000 mg/L and SS=500 mg/L) of effervescent soft drink wastewater and the acid fermentation treated water (Run 2; COD=10,000 mg/L and SS=300 mg/L) of food production wastewater which easily forms scum added with inorganic nutrient salts (nitrogen, phosphorus and the like) were used. By allowing the treated water as the circulating water together with the raw water to flow into the reactor 2, the velocity of the water passed in the reactor was set at 2 m/h. The ratio of the flow rate of the raw water to the amount of the circulating treated water was set depending on the COD load. In Fig. 8 and Fig. 9, the course of the experiment and the change in the COD treatment results are shown. In both systems, the load of organic substances was gradually increased while observing the COD concentration in the treated water. In Run 1 (Fig. 8) using the soft drink wastewater, the treatment was carried out with nearly the same load till about 80th day in the course of the experiment. When the COD load came to 20 kg/m3/d on and after about 80th day, the COD concentration in the treated water according to system A was increased. In system A with the antifoaming agent not added, the amount of a generated gas was increased by the rise in load to cause foaming in GSS 5, and the GSS 5 and the generated gas recovery piping 6 were clogged. Accordingly, the generated gas was not recovered in GSS and was discharged to the air from the upper part of the reactor 2. As a result, a large amount of the granule sludge in the reactor flowed out and the sludge in the reactor 2 could not be stably retained to deteriorate the treatment performance. Thus, the COD load was increased to 15 kg/m3/d to remove foaming but scum was retained in GSS 5 to make recovery of the generated gas difficult in GSS 5, and the treatment performance was still kept low as described above. On the other hand, in systems B and C with the antifoaming agent added, stabilized treatment was possible even with a COD load of 35 kg/m3/d. When the wastewater is comparatively hard to form scum, addition of an antifoaming agent enables a high load treatment and due to the increase in the amount of a generated gas, this generated gas had an effect of preventing formation of scum inside GSS. Thus, the treatment performance was the same in systems B and C. The comparison of the treatment results in the stationary state is shown in Table 4. In system B with the antifoaming agent added, the COD load was 35 kg/m3/d; the COD removal ratio was 90%; and the VSS concentration in the treated water was 300 to 400 mg/L. On the other hand, in system A with the antifoaming agent not added, the COD load was 15 kg/m3/d; the COD removal ratio was 90%; and the VSS concentration in the treated water was 300 to 400 mg/L. Thus, by addition of an antifoaming agent, a higher COD removal ratio could be obtained compared to the case where the antifoaming agent was not added- In system B where the antifoaming agent was added, the treatment result of the COD concentration in the treated water was stabilized in spite of the operation with a high COD load. Further, the VSS concentration in the treated water was almost equal to that in the case of the antifoaming agent not added. Next, in Run 2 (Fig. 9) using the food production wastewater, when the COD load came to 15 kg/m3/d or more on and after 80 days in the course of the experiment, in system A with the antifoaming agent not added, the COD concentration in the treated water was increased. This can be thought due to the result that foaming and scum formation were caused in GSS to render recover of the generated gas insufficient as described above, and thus the sludge amount in the reactor 2 could not be stably retained to deteriorate the treatment performance. Accordingly, the COD load was reduced to 10 kg/m3/d to remove foaming but due to presence of scum inside GSS 5, the treatment performance was still kept low. In system B with the antifoaming agent added, the COD load on about 110th day in the course of the experiment was set at 20 kg/m3/d. On 110th day to 120th day, scum started forming inside GSS to gradually deteriorate the treatment, and on and after 120th day, the COD concentration was increased. This could be thought due to the result that foaming inside GSS could be inhibited but scum gradually formed and the recovery of the generated gas became insufficient as described above, and thus the amount of the sludge in the reactor 2 could not be stably retained to deteriorate the treatment performance. In system C with a gas fed from beneath GSS, stabilized treatment could be carried out with a COD load of 35 kg/m3/d. When the wastewater easily forms scum, it becomes possible to carry out a high load treatment by adding an antifoaming agent and blowing the generated gas into GSS to destroy and remove the scum therein. Comparison of the treatment results at the stationary state is shown in Table 5. In system B with the antifoaming agent added, the COD load was 35 kg/m3/d; the COD removal ratio was 90%; and the VSS concentration in the treated water was 300 to 400. On the other hand, in system A where the antifoaming agent was not added, the COD load was 10 kg/m3/d; the COD removal ratio was 90%; and the VSS concentration in the treated water was 300 to 400. Furthermore, in system C with the formation of scum prevented, the treatment result of the COD in the treated water was stabilized in spite of the operation with a high COD load. Further the VSS concentration of the treated water was almost the same as in the conventional process. INDUSTRIAL APPLICABILITY According to a first embodiment of the present invention, in the upflow anaerobic sludge blanket treatment apparatus having multistage gas-solid separators formed by baffles in a treatment tank, stabilized anaerobic treatment can be carried out even with a high COD load by feeding an antifoaming agent into the treatment tank. Further, according to a second embodiment of the present invention, by rendering the angle formed between each of the baffles to form each gas-liquid separator and the inner wall of the reactor not larger than 35 degrees, formation of dead spaces by deposition of sludge particles on the baffles is prevented to maintain a good flowing state of the sludge particles, and the entire sludge particles can be effectively utilized in the treatment. Furthermore, by rendering the angle formed between each of the baffles and the inner wall of the treatment tank not larger than 35 degrees and, simultaneously, feeding an antifoaming agent into the treatment tank, more stabilized treatment can be effected. In addition, by further installing a scum-forming prevention means, more stabilized treatment even with a high COD load can be carried out. CLAIMS 1. An upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed in the treatment tank, the area taken up by each baffle being not smaller than 1/2 of the cross-sectional area of the treatment tank, and further has a means to feed an antifoaming agent into the treatment tank in the apparatus. 2. An upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed in the treatment tank, each baffle being fixed so as to render the angle to the inner wall of the treatment tank not larger than 35 degrees and, simultaneously, the area taken up by each baffles being not smaller than 1/2 of the cross-sectional area of the treatment tank. 3. The apparatus of claim 2 further having a means to feed an antifoaming agent into the treatment tank. 4. An upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed in the treatment tank, each baffle being fixed so as to render the angle to the inner wall of the treatment tank not larger than 35 degrees, and further has a means to feed an antifoaming agent into the treatment tank. 5. The apparatus of any one of claims 1 to 4, wherein a gas feed pipe for blowing an oxygen-free gas into the inside or below each of the gas-solid separators is installed. 6. The apparatus of any one of claims 1 to 5, wherein the gas-solid separators are formed at a position in the range of upper 50% of the treatment tank. 7. The apparatus of any one of claims 1 to 6, wherein the amount of the raw water passed in the treatment tank is regulated to 1 to 5 m/h. 8. An upflow anaerobic sludge blanket treatment apparatus substantially as herein above described with reference to the accompanying drawings.

Full Text

ANAEROBIC TREATMENT APPARATUS
TECHNICAL FIELD The present invention relates to an upflow anaerobic sludge blanket treatment apparatus to be used for the treatment of the organic wastewater discharged from various plants, sewage treatment facilities, night soil treatment facilities, livestock production facilities and the like, and more specifically, it relates to an upflow anaerobic sludge blanket treatment apparatus having a multistage gas-solid separator (hereinafter referred to as "GSS").
BACKGROUND ART Organic wastewater, organic waste or the like is sometimes subjected to separation treatment by anaerobic treatment. As such a decomposition treatment method, there is, for example, an upflow anaerobic sludge blanket process (hereinafter referred to as "UASB process"). This method has spread in recent years, and is to biologically decompose organic substances in wastewater under anaerobic conditions by allowing organic wastewater to flow as an upflow within a reactor into which a sludge (sludge particles) comprising granulated microorganisms mainly having anaerobic bacteria such as methane bacteria is packed. The UASB process can characteristically maintain methane bacteria at a high concentration in the reactor by

granulating anaerobic bacteria to granules. As a result, the wastewater having a remarkably high concentration of organic substance can be efficiently treated. For example, the apparatus which embodies this method can be characteristically operated with good efficiently even with the wastewater/waste having a volume load of CODCr (hereinafter referred to as "COD"), measured by using potassium bichromate as the oxidizing agent, of 10 to 15 kg/m3/d.
The anaerobic bacteria to be used for the anaerobic treatment aimed at organic wastewater and organic waste are roughly classified into two types by the ambient temperature. For example, there are medium temperature anaerobic bacteria having an optimum temperature in the medium temperature region of 30 to 35°C and high temperature anaerobic bacteria having an optimum temperature in the high temperature region of 50 to 55°C. In the UASB process utilizing the action of these anaerobic bacteria, with increased loads (for example, a COD volume load of not smaller than of 15 kg/m3/d) of organic substances to be decomposed, the amount of a gas to be generated is increased. In this instance, unless gas drainage from the reactor is surely carried out from time to time, effluence of the sludge particles in the form of granules becomes conspicuous by blow-off on gas drainage or the like, and it is difficult to retain the sludge particles in the reactor.
As a treatment measure in this case, a method of

forming a multistage UASB apparatus and dispersing and discharging the generated gas out of the system is proposed. Fig. 1 is a schematic view of an anaerobic treatment apparatus using a multistage the UASB apparatus[G. Lettinga (1995), Anaerobic digestion and wastewater treatment system, Antonie van Leeuwenhoek 67:3-28]. In the apparatus as shown in Fig. 1# a plurality of baffles 3 downwardly inclined are alternately provided inside a cylindrical reactor 2 connected to a raw water inlet pipe 1 at its lower end to form sectional sludge zones 4a to 4e by dividing multistagewise the inside of the reactor at respective positions. The corners (clogging parts to be formed by baffles) of respective upper ends of the sectional zones 4a to 4e form GSS 5. Sludge particles in the form of granules are packed in the reactor. When organic wastewater (raw water) is introduced from the lower end of such an apparatus, the organic substances in the raw water are decomposed by the action of the anaerobic bacteria present in the sludge particles in the form of granules placed in the reactor, and a gas is generated. Since a large amount of the gas is generated in the lower part of the reactor due to the state of a high load, the generated gas adheres to the sludge particles to reduce their apparent specific density, and simultaneously the adhered gas entrains the sludge particles and flows upward along an upward water flow together with the sludge particles. The sludge particles entrained by the gas are trapped by GSS 5 formed by the baffle 3 and come to air

bubbles at the water surface to form an air bubble layer 5b. The air bubbles soon break and a gas accumulates in the GSS 5 to form a gas phase layer 5a. Generated gas recovery piping 6 is connected to each place where the gas phase layer 5a is formed to recover the gas. The generated gas recovery piping 6 is connected to an external water-sealed tank 7, and the gas is trapped in the water-sealed tank 7. On breakage of air bubbles, the gas is separated from the sludge particles. The sludge particles regain the original specific gravity and settle by gravity. The sludge particles which settle on the baffles 3 further settle while sliding on the baffles 3 to fall. The settled sludge particles are again brought into contact with the organic substances in the raw water to decompose the organic substances with the anaerobic microorganisms in the sludge particles. Thus, gas is generated, and the sludge particles are entrained by the gas and flow upwardly. The above described cyclic motion of the sludge particles occurs in the reactor. As the gas generated in the lower part of the reactor is recovered in GSS in the lower part of the reactor, the influence of the gas generated in the lower part of the reactor on the fluidity of sludge particles is reduced at higher position in the reactor. Therefore, at higher position in the reactor, the load of organic substances is slowly reduced, and thus the amount of the generated gas is decreased to increase the apparent specific gravity of the sludge particles to be flown with the generated gas, and the velocity of the

upflow sludge particles entrained by the gas is decreased, that is, the flow of sludge particles becomes slower.
The treated water thus obtained by subjecting organic substances to anaerobic treatment overflows the upper end of the reactor 2 and is discharged through treated water piping 9. As described above, the flow of sludge particles becomes slower in proportion at higher position in the reactor, that is, approximates standing state, and accordingly the overflow from the upper end of the reactor does not contain sludge particles to give a clean water.
However, the multi-staged UASB apparatus still has the following problems.
(1) Depending on the properties of wastewater to be treated, foaming is caused in the GSS to invite clogging of the inside of the GSS or the generated gas trapping piping, and trapping of the generated gas becomes difficult.
(2) Depending on the properties of wastewater to be treated, scum is formed in the GSS to make trapping of the generated gas difficult. Above all, when the load is low and the amount of the generated gas is small, the effect of destroying and removing scum by the generated gas is small and scum is easy to form.
(3) As the result of the above described problems (1) and (2), the effect of diffusing the generated gas to discharge it out of the system which is the characteristic feature of the multistage UASB apparatus is lost and invites a large amount of effluent sludge to cause the deterioration of treatment.

(4) When the angle of installing a baffle constituting the GSS is obtuse, sludge deposits on the baffle to cause a dead space of sludge and as a result, the entire sludge particles within the reactor are sometimes not effectively used.
(5) When each GSS is formed even in the lower part of the reactor, good fluidity of sludge particles is obstructed, and the contact of sludge particles with organic substances sometimes becomes insufficient or fails.
(6) When the velocity of the water passed in a reactor is low, a short circuiting flow is caused and, inversely when that is high, effluence of sludge is caused and as a result, the treatment result is sometimes deteriorated.
In view of such actual circumstances, the object of the present invention is to provide an anaerobic treatment apparatus capable of carrying out stabilized wastewater treatment even with a high COD load by stably recovering the generated gas in the GSS in the multistage UASB apparatus which effectively uses the entire sludge particles for treatment without disturbing good flow of sludge particles, that is, good contact of the sludge particles with organic substances.
DISCLOSURE OF THE INVENTION
The present invention provides an anaerobic treatment apparatus relating to each of the following embodiment as the means to solve the above described problems.
The invention of claim 1 of the present invention

relates to an upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed in the treatment tank, the area taken up by each baffle being not smaller than 1/2 of the cross-sectional area of the treatment tank, and further has a means to feed an antifoaming agent into the treatment tank.
The invention of claim 2 of the present invention relates to an upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed in the treatment tank, each baffle being fixed so as to render the angle to the inner wall of the treatment tank not larger than 35 degrees and, simultaneously, the area taken up by each baffle being not smaller than 1/2 of the cross-sectional area of the treatment tank.
The invention of claim 3 of the present invention relates to an apparatus of claim 2 further having a means to feed an antifoaming agent into the treatment tank.
The invention of claim 4 relates to an upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed in the treatment tank, each baffle being fixed so as to

render the angle to the inner wall of the treatment tank not larger than 35 degrees, and further has a means to feed an antifoaming agent into the treatment tank.
The invention of claim 5 relates to the apparatus of any one of claims 1 to 4, wherein a gas feed pipe for blowing an oxygen-free gas into the inside or below each of the gas-solid separators is installed.
The invention of claim 6 relates to the apparatus of any one of claims 1 to 5, wherein the gas-solid separators are formed at a position in the range of upper 50% of the treatment tank.
The invention of claim 7 relates to the apparatus of any one of claims 1 to 6, wherein the amount of the raw water passed in the treatment tank is regulated to 1 to 5 m/h.
BRIEF EXPLANATION OF THE DRAWINGS
Fig. 1 is a diagram showing a constitution example of the conventional multistage UASB apparatus.
Fig. 2 is a diagram showing a constitution example of the multistage UASB apparatus relating to one embodiment of the present invention.
Fig. 3 is a diagram showing a constitution example of the multistage UASB apparatus relating to another embodiment of the present invention.
Fig. 4 is a diagram showing the constitution of the multistage UASB apparatus relating to one embodiment of the present invention used in Example 2.

Fig. 5 is a diagram showing the constitution of the multistage UASB apparatus used in Example 2 for comparison.
Fig. 6 is graphs showing the change in the COD treatment results with time in Example 2.
Fig. 7 is diagrams showing the constitutions of various types of multistage UASB apparatus used in Example 3.
Fig. 8 is graphs showing the change in the COD treatment results with time in the experiment (Run 1) using soft drink wastewater in Example 3.
Fig. 9 is graphs showing the change in the COD treatment results with time in the experiment (Run 2) using food production wastewater in Example 3.
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will now be explained but the present invention is not to be limited thereto. Fig. 2 is a diagram showing one example of the multistage UASB apparatus relating to a first embodiment of the present invention. In the accompanying drawings, the same reference numbers are given to the same constitutional elements.
In the multistage UASB apparatus relating to one embodiment of the present invention as shown in Fig. 2f by providing a plurality of baffles 3 in a cylindrical reactor 2 to the lower end of which a raw water inlet pipe 1 is connected, the inside of the reactor 2 is divided to form sectional sludge zones in multistage. One end of each

baffle 3 is fixed to the inner wall of the reactor 2 and the other end extends downwardly inclined toward the direction of the opposite inner wall. Fig. 2 shows a constitution example in which two sludge zones 4a and 4b are formed in multistage by arranging two sheets of downwardly inclined baffles 3. GSS 5 is formed in the upper end corner (clogged part formed by the baffle 3) of each of the sectional sludge zones 4a and 4b. Sludge particles in the form of granules are packed in the reactor. Organic wastewater (raw water) is first conditioned in a raw water conditioning tank/acid fermentor 23 through a feed pipe 25, and then introduced into the reactor 2 from its lower end through a raw water inlet pipe 1. The raw water conditioning tank/acid fermentor 23 is not necessarily installed and the raw water may be directly fed to the reactor 2. Unless particularly required, the raw water may not be conditioned in the tank 23.
In the reactor 2f granule sludge particles containing anaerobic bacteria are packed. The anaerobic treatment according to the present invention includes anaerobic treatments of all temperature ranges such as medium temperature methane fermentation treatment having an optimum temperature of 30°C to 35°C and high temperature methane fermentation treatment having an optimum temperature of 50°C to 55°C. Into the lower end of the reactor 2 packed with the granule sludge particles containing anaerobic bacteria, raw water containing organic waste and the like is introduced through the raw water feed

pipe 1. If necessary, the raw water can be suitably diluted with the circulating liquor of the treated water, diluting water to be fed from outside the system or the like, and then fed to the reactor. The amount of the influent raw water is preferably regulated in such a manner that the velocity of the water passed in the reactor 2 is rendered 1 to 5 m/h.
In the reactor 2, organic waste is decomposed in the presence of the granule sludge particles containing anaerobic bacteria to generate a decomposed gas. The generated gas is separately collected in GSS 5 at the upper end of each of the sectional sludge zones 4a and 4b to form an air bubble layer 5b and a gas phase layer 5a in each of the sectional sludge zones, and recovered to a water-sealed tank 7 from the gas phase layer 5a through generated gas recovery piping 6. Discharge amount of the recovered generated gas is recorded by a gas meter 8. Part of the gas generated in the reactor adheres to the granule sludge particles in each of the sectional sludge zones 4a and 4b to reduce their apparent specific density, and simultaneously entrains the granule sludge particles and reaches the water surface of GSS 5 with the particles. Thus, the generated gas forms air bubbles and temporarily stays in the water surface air bubble layer 5b. The air bubbles collected in the water surface air bubble layer 5b soon break and separates into generated gas and granule sludge particles. The granule sludge particles regain their original specific density and settle in water, while

the generated gas forms the gas phase layer 5a and is discharged out of the system by the generated gas recovery piping 6 through the water-sealed tank 7. The clarified treated water after decomposition of organic substances overflows the upper end of the reactor and is discharged out of the system through treated water piping 9.
Further, as shown in Fig. 2, the treated water piping 9 may branch off to constitute treated water circulating piping 21, through which the treated water may be circulated to the raw water conditioning tank/acid fermented 23 through piping 24 and then recirculated to the reactor 2 after reconditioning if necessary. Or, bypass piping 22 may be placed, through which the treated water may be recirculated to the reactor 2 without any treatment.
Since the gas pressure in the gas phase layer 5a of each GSS 5 is different, its differential pressure may preferably be regulated in the water-sealed tank 7. It is necessary to maintain the water sealing pressure higher on the side near to the raw water feeding side (that is, higher pressure at lower GSS). This can be achieved by lowering the position of the opening in the water-sealed tank 7 of the generated gas recovery piping 6 connected to lower GSS (refer to Fig. 2). As the pressure control of gas recovery, there are many methods other than the method using the water-sealed tank 7 and, for example, a pressure valve or the like may be used. In the anaerobic treatment of the present invention, since the generated gas generated in every sectional sludge zone can be recovered separately.

the amount of the generated gas per unit cross-sectional area of the reactor will be reduced. Particularly, in the part nearest the treated water piping 9 which allows the treated water to flow out, the gas amount per unit cross-sectional area of the reactor becomes very small. Thus, the amount of effluent granule sludge particles out of the system can be extremely reduced.
Herein, it is preferred that the baffles 3 to be installed in the reactor 2 are made to have a size such that the cross-sectional area taken up by each of the baffles is not smaller than 1/2 of the cross-sectional area of the treatment tank. When the area taken up by the baffles 3 is smaller than 1/2 of the cross-sectional area of the treatment tank, trapping of the generated gas in the reactor by the baffles is insufficient to cause failure of gas-solid separation. In other words, the generated gas passes through upwardly at the center of the reactor, and thus GSS 5 ceases to sufficiently accumulates the gas.
Further, when the raw water to be treated is effervescent, it is possible that the gas phase layer 5a in GSS 5 and the generated gas recovery piping 6 are blocked to make recovery of the generated gas difficult. Accordingly, in one embodiment of the present invention, by feeding an antifoaming agent into the reactor 2, foaming in GSS 5 can be inhibited to smoothly effect treatment. As the means to feed the antifoaming agent into the reactor 2, as shown in Fig. 2, antifoaming agent feed piping 10 can be connected to the raw water feed pipe 1 to previously add

the antifoaming agent into raw water. Further, in other embodiments, the antifoaming agent can be fed to the raw water conditioning tank/acid fermentor 23 by dropwise addition or spraying ((2) in Fig. 2); to the treated water circulating piping (®, (6) or (7) in Fig. 2); introduced into the reactor 2 by direct dropwise addition or spraying (® in Fig. 2); or to GSS 5 of the reactor 2 by dropwise addition or spraying ((3) in Fig. 2). As the antifoaming agent, a preferred one has an antifoaming effect in accordance with the properties of the raw water and can be used at medium temperatures (30°C to 35°C) or at high temperatures (50°C to 55°C) which are suited for use in antifoaming a fermented liquor without losing the antifoaming effect. As the antifoaming agent which can be used in the present invention, any of a silicone-containing antifoaming agent and an alcohol-containing antifoaming agent can be applied.
A first embodiment of the present invention relates to an anaerobic treatment apparatus having the above described characteristic features.
Namely, the first embodiment of the present invention relates to an upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-liquid separators formed by a plurality of baffles fixed in the treatment tank, the area taken up by each baffle being not smaller than 1/2 of the cross-sectional area of the treatment tank, and further has a

means to feed an antifoaming agent into the treatment tank.
Further, a second embodiment of the present invention is characterized by fixing the baffles so as to make the angle to the inner wall of the treatment tank not larger than 35 degrees. Namely, the second embodiment of the present invention relates to an upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-liquid separators formed by a plurality of baffles fixed in the treatment tank, each baffle being fixed so as to make the angle to the inner wall of the treatment tank not larger than 35 degrees, and simultaneously the area taken up by each baffle being not smaller than 1/2 of the cross-sectional area of the treatment tank.
The second embodiment of the present invention is explained by reference to Fig. 2. In the second embodiment, by fixing the baffle downwardly inclined toward the opposite inner wall with an angle (G) formed between the inner wall of the reactor 2 and each baffle 3 of not larger than 35 degrees, such a problem that granule sludge particles settling from above are deposited on to the baffles 3 forming sludge zones 4a and 4b, and their flowability accordingly becomes insufficient to cause dead spaces of sludge particles ceases to exist. When angles formed between the inner wall of the reactor 2 and each baffle 3 are larger than 35 degrees, sludge particles are deposited as described above to easily form a dead space of

sludge particles, and thus the treatment with a high load of 30 kg/m3/d or higher becomes difficult. When angles formed between the inner wall of the reactor 2 and each baffle 3 are not larger than 35 degrees, an inclination of larger than repose angle of the sludge particles is formed, and the sludge particles settled on the baffles slide on the surface of the baffles to flow down, and thus there is no deposition of sludge on the baffles. The angle formed between the baffle and the inner wall of the reactor is preferably not larger than 30 degrees, more preferably not greater than 27 degrees.
Further, also in the second embodiment of the present invention, the baffles 3 to be arranged in the inner part of the reactor 2 preferably have such a size that the area to be taken up by each baffle comes to not smaller than 1/2 of the cross-sectional area of the treatment tank. When the area taken up by each baffle 3 is smaller than 1/2, trapping of the gas generated by the baffles in the reactor is insufficient to cause failure of gas-liquid separation. In other words, the gas passes through upward from the center of the reactor, and accordingly GSS 5 cannot sufficiently collect the gas.
It is not essential in the second embodiment of the present invention to add an antifoaming agent. However, as in the first embodiment of the present invention, it is more preferred that an antifoaming agent is fed to the reactor to inhibit foaming in GSS 5.
In addition, a third embodiment of the present

invention relates to an upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-liquid separators formed by a plurality of baffles fixed in the treatment tank, each baffle being fixed so as render the angle to the inner wall of the treatment tank not larger than 35 degrees, and further has a means to feed an antifoaming agent into the treatment tank.
Further, when scum is easily formed due to the high concentration of SS in raw water or the like, scum is sometimes formed on the surface of the air bubble layer 5b in the inner part of GSS 5 to make recovery of the generated gas difficult. In such a case, by arranging a gas feed pipe inside or below the GSS 5 to feed a gas, the scum can be destroyed or the formation of the scum can be inhibited. As the gas which can be used for this purpose, an oxygen-free gas such as a nitrogen gas which does not affect the biological treatment such as methane fermentation can be used. Further, the gas generated by the anaerobic treatment can be used as the gas for destroying scum or preventing formation of the scum. A constitution example of such an embodiment of the anaerobic treatment apparatus is shown in Fig. 3.
In the apparatus as shown in Fig. 3, the generated gas recovered through generated gas recovery piping 6 and a water-sealed tank 7 is stored in a gas holder 11, and is fed to a diffusion pipe 12 installed below each of the GSS

through generated gas feed piping 13 as air bubbles, or is fed to the generated gas recovery piping 6 to directly feed the gas to the inside of the GSS. Thus, the destruction of scum in GSS or the prevention of forming scum therein can be achieved-
When the generated gas feed piping 13 is connected to the generated gas recovery piping 6 in each GSS to destroy and remove the scum in GSS 5-1, by closing a valve 14a, blowing the generated gas into the GSS 5-1 and making the entire inside of GSS gas phase layer 5-la to push down the air bubble layer 5-lb, the scum can be discharged from GSS 5-1. Since this discharged scum is trapped in GSS 5-2 above the GSS 5-1, the valve 14b may then be closed and the generated gas may be blown into the GSS 5-2 in the same manner to make the entire inside of GSS 5-2 gas phase layer 5-2a, and the air bubble layer 5-2b may be pushed down to discharge scum from the GSS 5-2. The discharged scum may be flown out together with the treated water.
When the generated gas feed piping 13 is connected to the diffusion pipe 12 arranged below each GSS, scum is destroyed by air bubbles to be blown from the diffusion pipe 12, and the destroyed scum is discharged with the flowing of the liquor in the reactor 2 as the treated water. This technique is independent of opening and closing of the valves 14a and 14b. When the above described operation is performed with the valves 14a and 14b opened, the gas blown from the diffusion pipe 12 is recovered through the generated gas recovery piping 6. When the above described

operation is performed with the valves 14a and 14b closed, in addition to the scum destruction effect by the air bubbles to be blown from the diffusion pipe 12, a scum discharge effect can be also expected by directly feeding a gas into the inside of GSS through the generated gas feed piping 13. The frequency of feeding a gas into the inside of GSS 5 or into the diffusion pipe 12 for the purpose of destruction of scum and prevention of forming scum depends on the properties of the wastewater to be treated and may be typically once a day to once a week, and this frequency has an effect of destruction and removal of scum inside GSS 5.
In the multistage UASB apparatus relating to the present invention, it is more preferred that the gas-liquid separator is formed only in the upper part of the treatment tank. This is because that, when the gas-liquid separator is formed even in the lower part of the treatment tank, good flowability of sludge particles in the treatment tank is obstructed and the contact of sludge with organic substances fails to sometimes render the treatment unstable. From this viewpoint, in the multistage UASB apparatus relating to the present invention, the gas-liquid separator is preferably formed at a position in the range of upper 70% of the treatment tank, preferably in the range of upper 50%, more preferably in the range of upper 30% of the treatment tank.
In the multistage UASB apparatus of the present invention, the amount of the raw water passed in the

treatment tank is preferably regulated to 1 to 5 m/h. With too small amounts of the water passed in the tank, a short circuiting flow is caused in the sludge layer in the tank and sometimes the entire sludge layer ceases to be effectively used. With too large amounts of the water passed in the tank, the upflow velocity of the liquor becomes higher than the settling velocity of granule sludge particles, and the granule sludge particles flows out together with treated water, and thus sludge cannot be stably retained in the tank to sometimes render the treatment unstable. From this viewpoint, the amount of the raw water passed in the treatment tank is preferably regulated to 1 to 5 m/h, more preferably 2 to 3 m/h.
Various embodiments of the present invention will now be more concretely explained by examples but the present invention is not to be limited thereto. Example 1
With the use of the apparatus as shown in Fig. 2, wastewater was subjected to anaerobic treatment. Two sheets of baffles 3 were fixed downwardly inclined in a cylindrical reactor 2 having a cross-sectional area of 0.16 m2 and a height of 6.25 m (a tank volume of 1 m2) so as to render the area taken up by each baffle 0,112 m2 (70% of the cross-sectional area of the reactor). The angle (0) of fixing each of the baffles 3 was 45 degrees. The water temperature in the reactor 2 was regulated to 35°C. Sludge particles in the form of granules were packed into the reactor 2.

As the raw water, the treated water (COD=10,000 mg/L; SS=500 mg/L) by acid fermentation of effervescent soft drink wastewater was used. By allowing the treated water overflowing the upper end of the reactor 2 as the circulating water together with the raw water to flow into the reactor 2, the velocity of the water to be passed in the reactor was set at 2 m/h. The ratio of the flow rate of the raw water to the amount of the circulating treated water were set depending on the COD load.
From the antifoaming agent introduction piping 10 connected to the raw water feed pipe 1, a silicone-containing antifoaming agent was introduced at a ratio of 10 mg/L per amount of the influent into the reactor. For the control data, the same experiment as described above was carried out without introducing the antifoaming agent. The results of the treatments in the stationary state are shown in Table 1.

From the above described Table it would be found that by feeding an antifoaming agent into the treatment tank in the multistage UABS treatment apparatus according to the present invention, excellent treatment performance could be

obtained. With the antifoaming agent not fed, foaming was caused inside GSS by the rise in load to reduce the treatment performance. Example 2
Experiments was carried out by using reactors 2 having structures as shown in Fig. 4 and Fig. 5 in the anaerobic treatment apparatus as shown in Fig. 2. In the reactor 2 as shown in Fig. 4, two inclined baffles 2 were fixed and the angle (0) formed between the side wall of the apparatus and each of the baffles 3 was set at 30 degrees. The baffles 3 were arranged only at the positions in the range of upper 50% of the reactor 2. In the reactor 2 as shown in Fig. 5, five inclined baffles 3 were fixed over the entire height of the reactor 2, and the angle (0) formed between the side wall of the apparatus and each of the baffles 3 was set at 45 degrees.
In both cases, the experiments were carried out with the use of the reactors having a cross-sectional area of 0.16 m2 and a height of 6.25 m (a volume of 1 m3), and each baffle to form the GSS taking an effective cross-sectional area of 0.112 m2 (70% of the cross-sectional area of the reactor).
In the reactor 2, sludge particles in the form of granules were packed, and raw water was allowed to flow thereinto through the raw water feed pipe 1 connected to the lower end of the reactor 2, and treated water was obtained from a treated water pipe 9 in the upper part of the reactor 2.

In the reactor 2, each GSS 5 where the gas generated in decomposing and clarifying the organic substances is collected by the baffles was formed, and at its upper end, a discharge outlet of a generated gas recovery pipe 6 communicating with the outside was provided. The amount of the generated gas from each GSS 5 was measured by a gas meter installed in a water-sealed tank 7. The water temperature in the reactor 2 was controlled to 35°C. As the raw water, acid fermentation treated water (COD=7,000 mg/L) of sugar-containing wastewater added with inorganic nutrient salts (nitrogen, phosphorus and the like) was used. By allowing the treated water as the circulating water together with the raw water to flow into the reactor 2, the velocity of the water passed in the reactor was set at 2 m/h. The ratio of the flow rate of the raw water to the amount of the circulating treated water was set depending on the COD load. By taking the results obtained by using the reactor 2 in which the angle of fixing each of the baffles is 30 degrees shown in Fig. 4 as system B and those obtained by using the reactor 2 in which the angle of fixing each of the baffles is 45 degrees shown in Fig. 5 as system A , the following is reported.
Fig. 6 shows the course of the experiments and the change in the COD treatment results. In both systems, the load amount of organic substances was slowly increased while observing the COD concentration in the treated water.
In the course of the experiments, the treatment could be conducted with almost the same load amount till about

120th day. When the COD load came to 30 kg/m3/d or more on and after about 120th day, the COD concentration in the treated water was increased in system A.
In system A where five inclined baffles were fixed and the angle formed between the inner wall of the reactor 2 and each of the baffles 3 was set at 45 degrees as shown in Fig. 5, dead spaces were formed on the baffles 3 by deposited sludge, and the entire sludge particles were not effectively used to render the treatment unstable. Accordingly, the COD load was decreased to 25 kg/m3/d.
In system B with a COD load of 25 kg/m3/d, stable treatment was carried out. Table 2 shows comparison of the treatment results in the stationary state.

In system B where the angle of fixing each of the baffles is set at 30 degrees, the COD load was 35 kg/m3/d; the COD removal ratio was 90%; and the VSS concentration in the treated water was 300 to 400 mg/L. On the other hand, in the system A where the angle of fixing each of the baffles was set at 45 degrees, the COD load was 25 kg/m3/d; the COD removal ratio was 90%; and the VSS concentration of

the treated water was 300 to 400 mg/L. Thus, by rendering the angle of fixing baffles not larger than 35 degrees, a higher COD removal ratio could be obtained compared to the set angle of fixing the baffles of 45 degrees.
In the process of system B# in spite of the operation with a high COD load, the treatment result of the COD concentration in the treated water was stabilized. Further, the VSS concentration in the treated water was nearly equal to that in the process of system A, and even when the number of GSS is smaller than in the process of system A, the amount of the granule sludge in the tank in the upflow anaerobic sludge blanket (UASB) process was also stabilized. This is due to a smaller gas amount per unit cross-sectional area of the reactor at the position nearest to the treated water piping 9 for allowing the treated water to flow out and the resulting small amount of the granule sludge flowing out of the system.
Next, the treatment results in the stationary state when the treatment was carried out with the use of system B with a COD concentration of the raw water of 7,000 g/L and a COD load of 30 kg/m3/d at a velocity of the water passed of 0.5 to 7 m/h are shown in Table 3 for comparison.

In the system B where the angle formed between each baffle and the inner wall of the reactor was made 30 degrees, in order to carry out stabilized treatment with a COD removal ratio of not less than 85%, when the velocity of the water passed is set at 1 to 5 m/h and preferably the COD removal ratio is set at not less than 90%, it has been found that it is preferred to set the velocity of the water passed in the reactor at 2 to 3 m/h. This is due to the formation of a short circuiting flow of the sludge layer to make it impossible to effectively utilize the entire sludge layer when the velocity of the water passed is lower than 1 m/h. Further, when the velocity of the water passed is higher than 5 m/h, the VSS concentration comes to 1,500 mg/L or more and the amount of the sludge in the reactor 2 cannot be stably maintained and as a result, the treatability is deteriorated. Example 3
As the reactor 2, various types of reactors as shown in Fig. 7 were used. In system A, two inclined baffles were fixed and the angle formed between each of the baffles and the inner wall of the reactor 2 was set at 30 degrees.

In system B# antifoaming agent introduction piping 10 was connected to the raw water feed pipe 1 in the reactor 2 of system Af and a silicone-containing antifoaming agent was added to the raw water in an amount of 10 mg per liter of water flowing into the reactor. In system C, diffusion pipes 12 were further fixed to the reactor 2 of system B and by feeding a generated gas through generated gas feed piping 13, the scum in each GSS was destroyed and removed. In each system, each GSS was arranged at a position in the range of upper 50% of the reactor 2.
In the experiments, the apparatus as shown in Fig. 3 was used. Granule sludge particles were packed in the reactor 2. Raw water was fed through the raw water feed pipe 1 connected to the lower end of the reactor 2 and treated water was obtained from the treated water pipe 9 in the upper part of the reactor 2. In the reactor 2, GSSs were formed in the reactor 2, where a gas generated in decomposing and clarifying organic substances was collected. To the upper end of each GSS, generated gas recovery piping 6 was connected (refer to Fig. 3).
In any of the systems, the reactor had a cross-sectional area of 0.16 m2 and a height of 6.25 m (a volume of m3), and each baffle forming GSS had an effective cross-sectional area of 0.112 m2 (70% of the cross-sectional area of the reactor). The amount of the gas generated in each GSS section was measured by a gas meter installed in the water-sealed tank 7. The temperature in the reactor 2 was controlled to 35°C. As the raw water, the acid fermentation

treated water (Run 1; COD=10,000 mg/L and SS=500 mg/L) of effervescent soft drink wastewater and the acid fermentation treated water (Run 2; COD=10,000 mg/L and SS=300 mg/L) of food production wastewater which easily forms scum added with inorganic nutrient salts (nitrogen, phosphorus and the like) were used. By allowing the treated water as the circulating water together with the raw water to flow into the reactor 2, the velocity of the water passed in the reactor was set at 2 m/h. The ratio of the flow rate of the raw water to the amount of the circulating treated water was set depending on the COD load.
In Fig. 8 and Fig. 9, the course of the experiment and the change in the COD treatment results are shown. In both systems, the load of organic substances was gradually increased while observing the COD concentration in the treated water.
In Run 1 (Fig. 8) using the soft drink wastewater, the treatment was carried out with nearly the same load till about 80th day in the course of the experiment. When the COD load came to 20 kg/m3/d on and after about 80th day, the COD concentration in the treated water according to system A was increased. In system A with the antifoaming agent not added, the amount of a generated gas was increased by the rise in load to cause foaming in GSS 5, and the GSS 5 and the generated gas recovery piping 6 were clogged. Accordingly, the generated gas was not recovered in GSS and was discharged to the air from the upper part of the reactor 2. As a result, a large amount of the granule

sludge in the reactor flowed out and the sludge in the reactor 2 could not be stably retained to deteriorate the treatment performance. Thus, the COD load was increased to 15 kg/m3/d to remove foaming but scum was retained in GSS 5 to make recovery of the generated gas difficult in GSS 5, and the treatment performance was still kept low as described above. On the other hand, in systems B and C with the antifoaming agent added, stabilized treatment was possible even with a COD load of 35 kg/m3/d. When the wastewater is comparatively hard to form scum, addition of an antifoaming agent enables a high load treatment and due to the increase in the amount of a generated gas, this generated gas had an effect of preventing formation of scum inside GSS. Thus, the treatment performance was the same in systems B and C. The comparison of the treatment results in the stationary state is shown in Table 4.

In system B with the antifoaming agent added, the COD load was 35 kg/m3/d; the COD removal ratio was 90%; and the

VSS concentration in the treated water was 300 to 400 mg/L. On the other hand, in system A with the antifoaming agent not added, the COD load was 15 kg/m3/d; the COD removal ratio was 90%; and the VSS concentration in the treated water was 300 to 400 mg/L. Thus, by addition of an antifoaming agent, a higher COD removal ratio could be obtained compared to the case where the antifoaming agent was not added- In system B where the antifoaming agent was added, the treatment result of the COD concentration in the treated water was stabilized in spite of the operation with a high COD load. Further, the VSS concentration in the treated water was almost equal to that in the case of the antifoaming agent not added.
Next, in Run 2 (Fig. 9) using the food production wastewater, when the COD load came to 15 kg/m3/d or more on and after 80 days in the course of the experiment, in system A with the antifoaming agent not added, the COD concentration in the treated water was increased. This can be thought due to the result that foaming and scum formation were caused in GSS to render recover of the generated gas insufficient as described above, and thus the sludge amount in the reactor 2 could not be stably retained to deteriorate the treatment performance. Accordingly, the COD load was reduced to 10 kg/m3/d to remove foaming but due to presence of scum inside GSS 5, the treatment performance was still kept low.
In system B with the antifoaming agent added, the COD load on about 110th day in the course of the experiment was

set at 20 kg/m3/d. On 110th day to 120th day, scum started forming inside GSS to gradually deteriorate the treatment, and on and after 120th day, the COD concentration was increased. This could be thought due to the result that foaming inside GSS could be inhibited but scum gradually formed and the recovery of the generated gas became insufficient as described above, and thus the amount of the sludge in the reactor 2 could not be stably retained to deteriorate the treatment performance.
In system C with a gas fed from beneath GSS, stabilized treatment could be carried out with a COD load of 35 kg/m3/d. When the wastewater easily forms scum, it becomes possible to carry out a high load treatment by adding an antifoaming agent and blowing the generated gas into GSS to destroy and remove the scum therein. Comparison of the treatment results at the stationary state is shown in Table 5.

In system B with the antifoaming agent added, the COD load was 35 kg/m3/d; the COD removal ratio was 90%; and the VSS concentration in the treated water was 300 to 400. On the other hand, in system A where the antifoaming agent was not added, the COD load was 10 kg/m3/d; the COD removal ratio was 90%; and the VSS concentration in the treated water was 300 to 400. Furthermore, in system C with the formation of scum prevented, the treatment result of the COD in the treated water was stabilized in spite of the operation with a high COD load. Further the VSS concentration of the treated water was almost the same as in the conventional process.
INDUSTRIAL APPLICABILITY According to a first embodiment of the present invention, in the upflow anaerobic sludge blanket treatment apparatus having multistage gas-solid separators formed by baffles in a treatment tank, stabilized anaerobic treatment can be carried out even with a high COD load by feeding an antifoaming agent into the treatment tank. Further, according to a second embodiment of the present invention, by rendering the angle formed between each of the baffles to form each gas-liquid separator and the inner wall of the reactor not larger than 35 degrees, formation of dead spaces by deposition of sludge particles on the baffles is prevented to maintain a good flowing state of the sludge particles, and the entire sludge particles can be effectively utilized in the treatment. Furthermore, by

rendering the angle formed between each of the baffles and the inner wall of the treatment tank not larger than 35 degrees and, simultaneously, feeding an antifoaming agent into the treatment tank, more stabilized treatment can be effected. In addition, by further installing a scum-forming prevention means, more stabilized treatment even with a high COD load can be carried out.

CLAIMS
1. An upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed in the treatment tank, the area taken up by each baffle being not smaller than 1/2 of the cross-sectional area of the treatment tank, and further has a means to feed an antifoaming agent into the treatment tank in the apparatus.
2. An upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed in the treatment tank, each baffle being fixed so as to render the angle to the inner wall of the treatment tank not larger than 35 degrees and, simultaneously, the area taken up by each baffles being not smaller than 1/2 of the cross-sectional area of the treatment tank.
3. The apparatus of claim 2 further having a means to feed an antifoaming agent into the treatment tank.
4. An upflow anaerobic sludge blanket treatment apparatus for anaerobically treating organic wastewater or waste, which apparatus has an anaerobic treatment tank and multistage gas-solid separators formed by a plurality of baffles fixed in the treatment tank, each baffle being

fixed so as to render the angle to the inner wall of the treatment tank not larger than 35 degrees, and further has a means to feed an antifoaming agent into the treatment tank.
5. The apparatus of any one of claims 1 to 4, wherein a gas feed pipe for blowing an oxygen-free gas into the inside or below each of the gas-solid separators is installed.
6. The apparatus of any one of claims 1 to 5, wherein the gas-solid separators are formed at a position in the range of upper 50% of the treatment tank.
7. The apparatus of any one of claims 1 to 6, wherein the amount of the raw water passed in the treatment tank is regulated to 1 to 5 m/h.

8. An upflow anaerobic sludge blanket treatment apparatus substantially as herein above described with reference to the accompanying drawings.

Documents:

150-chenp-2004 claims granted.pdf

150-chenp-2004 correspondence others.pdf

150-chenp-2004 correspondence po.pdf

150-chenp-2004 form-1.pdf

150-chenp-2004 form-18.pdf

150-chenp-2004 form-2.pdf

150-chenp-2004 form-3.pdf

150-chenp-2004 petition.pdf

150-chenp-2004 power of attorney.pdf

150-chenp-2004-abstract.pdf

150-chenp-2004-claims.pdf

150-chenp-2004-correspondnece-others.pdf

150-chenp-2004-correspondnece-po.pdf

150-chenp-2004-description(complete).pdf

150-chenp-2004-drawings.pdf

150-chenp-2004-form 1.pdf

150-chenp-2004-form 3.pdf

150-chenp-2004-form 5.pdf

150-chenp-2004-pct.pdf

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Patent Number

234585

Indian Patent Application Number

150/CHENP/2004

PG Journal Number

29/2009

Publication Date

17-Jul-2009

Grant Date

09-Jun-2009

Date of Filing

23-Jan-2004

Name of Patentee

EBARA CORPORATION

Applicant Address

11-1, HANEDA ASAHI-CHO, OHTA-KU, TOKYO 144-8510,

Inventors:

#	Inventor's Name	Inventor's Address
1	HONMA, YASUHIRO	2-1-29-412, ZENGYOZAKA, FUJISAWA-SHI, KANAGAWA 251-0876,
2	TANAKA, TOSHIHIRO	181-18-1011, KAWANA, FUJISAWA-SHI, KANAGAWA 251-0015,

PCT International Classification Number

C02F 3/28

PCT International Application Number

PCT/JP02/11880

PCT International Filing date

2002-11-14

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2001-350063	2001-11-15	Japan