Title of Invention: Method and apparatus for wastewater treatment Abstract: Phosphorus in wastewater is removed by using an apparatus including a settling tank, an anaerobic tank, an aerobic tank, and a final settling tank. Nitrogen in wastewater is removed by using an apparatus including a settling tank, an anaerobic tank, a nitrification tank, and a final settling tank. Summary of Invention: BACKGROUND OF THE INVENTION &lsqb;0001&rsqb; 1. Field of the Invention &lsqb;0002&rsqb; The present invention relates to methods for treating wastewater and apparatuses therefor, and more particularly, to methods for removing phosphorus and nitrogen from wastewater and apparatuses therefor. &lsqb;0003&rsqb; 2. Description of the Related Art &lsqb;0004&rsqb; The activated sludge process is a typical treatment process for removing organic substances from wastewater, and an anaerobic-aerobic activated sludge process is used as a conventional method for simultaneously removing phosphorus anions and organic substances from wastewater. &lsqb;0005&rsqb; An example of a wastewater treatment apparatus by the anaerobic-aerobic activated sludge process is shown in FIG. 6. This wastewater treatment apparatus includes a primary settling tank 2, an anaerobic tank 3 in which activated sludge releases phosphoric acid ion from cells into wastewater by a biological phosphorus-releasing reaction, an aerobic tank 4 in which activated sludge takes up phosphoric acid ion into cells by a biological phosphorus-uptake reaction, and a final settling tank 6. The amount of phosphorus taken up at the aerobic stage is greater than the amount of phosphorus released at the anaerobic stage, and a difference between these amounts corresponds to the amount of phosphorus removed. &lsqb;0006&rsqb; In the primary settling tank 2, relatively large and heavy solids contained in wastewater 1 are removed. After being subjected to the biological phosphorus-releasing reaction at the anaerobic stage and the biological phosphorus-uptake reaction at the aerobic stage, phosphorus in the wastewater is transformed into a constituent of the sludge, and is finally discharged as excess sludge from the wastewater treatment apparatus. Meanwhile, organic substances in the wastewater are removed both at the anaerobic stage and at the aerobic stage. &lsqb;0007&rsqb; The phosphorus removal from wastewater using a wastewater treatment apparatus by means of the anaerobic-aerobic activated sludge process has the following drawbacks. That is, when the organic substance concentration in the wastewater is decreased, for example, by the influx of rainwater, since the wastewater is diluted while being supplied with oxygen, the organic substances in the wastewater, which have been oxidized and diluted, are fed to the anaerobic stage. As a result, since the organic substance concentration is decreased in comparison with the phosphoric acid ion concentration, the rate of the phosphorus-releasing reaction at the anaerobic stage and the rate of the phosphorus-uptake reaction at the aerobic stage are decreased, resulting in deterioration in the quality of treated water. &lsqb;0008&rsqb; Since solid waste components of the wastewater are subjected to sedimentation in the primary settling tank, the wastewater supplied to the anaerobic tank from the primary settling tank containing mainly soluble pollutants. Therefore, when the ratio of the organic substance concentration to the phosphoric acid ion concentration is low with respect to the soluble pollutants in the wastewater to be fed to the anaerobic stage, the rate of the phosphorus-releasing reaction at the anaerobic stage and the rate of the phosphorus-uptake reaction at the aerobic stage are also decreased, resulting in deterioration in the quality of treated water. &lsqb;0009&rsqb; In order to cope with such problems, a method may be employed in which an organic chemical agent such as methanol, together with the wastewater, is supplied to the anaerobic stage, and thus, by compensating for the shortage of the organic substance concentration in the wastewater, decreases in the rate of the phosphorus-releasing reaction at the anaerobic stage and the rate of the phosphorus-uptake reaction at the aerobic stage are prevented. &lsqb;0010&rsqb; In the conventional method of adding an organic chemical agent to the anaerobic stage, although in general, relatively inexpensive methanol is used, the cost for the chemical agent still increases operating expenses. Moreover, since methanol is a Class IV hazardous substance, safety must be taken into consideration in handling and storage facilities, and facilities for receipt and supply must be prepared, resulting in an increased cost of equipment and difficulty in handling. &lsqb;0011&rsqb; With respect to both the phosphorus-releasing reaction at the anaerobic stage and the phosphorus-uptake reaction at the aerobic stage, substantially large amounts of organic substances are required. In the phosphorus removal treatment by the anaerobic-aerobic activated sludge process, if there is a shortage of organic substances, satisfactory phosphorus removal cannot be achieved. Therefore, it is effective for improving the results of phosphorus removal treatment to introduce the organic substances contained in the wastewater fed into the primary settling tank and removed in the primary settling tank, that is, organic substances mainly composed of solids, to the anaerobic stage or both the anaerobic stage and the aerobic stage. &lsqb;0012&rsqb; As a conventional method of operating facilities having such an effect, there is a method in which by decreasing the number of primary settling tanks used in wastewater treatment facilities having a plurality of treatment lines, operation is performed at increased water surface loading with respect to the primary settling tanks so that suspended solid (SS) concentration in the primary settling tank effluent is increased, and thus organic substances flowing into the anaerobic stage are increased. &lsqb;0013&rsqb; However, it is difficult to accurately control the amount of solid organic substances that flow into the anaerobic stage by changing the number of primary settling tanks in operation. &lsqb;0014&rsqb; In order to solve the problems described above, the inventor has already applied for patents which disclose techniques for satisfactory phosphorus removal treatment by increasing an amount of organic substances to be supplied to anaerobic tanks. One such method for removing phosphorus from wastewater, in which at least a portion of sediment in a primary settling tank is fed to an anaerobic tank, and a method for removing phosphorus from wastewater, in which the sediment is subjected to ultrasonic treatment before being fed to the anaerobic tank, are disclosed in Japanese Patent Application No. 9-133989. Another such method for removing phosphorus from wastewater, in which the sediment is subjected to ozone treatment before being fed to the anaerobic tank, is disclosed in Japanese Patent Application No. 9-133988. However, when the sediment in the primary settling tank is introduced to the anaerobic tank as it is, since particles of solids contained in the sedimented sludge are relatively large and have a small surface area per unit weight, the rate of decomposition/treatment in a biological reactor such as an anaerobic tank is relatively low. When the sediment in the primary settling tank is fed to the anaerobic tank after ultrasonic treatment, solids, as the sediment, contain microorganisms enclosed by cell walls and/or cell membranes, and cellulose, which are relatively rigid and are not easily broken by vibration treatment. Therefore, the particle size of the solids introduced to the anaerobic tank is not sufficiently reduced. Furthermore, when the sediment in the primary settling tank is fed to the anaerobic tank after ozone treatment, a portion of organic substances contained in the sediment is oxidized and mineralized, and thus loses effectiveness as organic substances. Since a relatively large amount of electric power, approximately 10 to 15 kWh/kg O3, is also consumed for the generation of ozone, operating expenses increase. &lsqb;0015&rsqb; As a conventional method for simultaneously removing nitrogen compounds and organic substances, a biological nitrification-denitrification process is used. &lsqb;0016&rsqb; An example of a wastewater treatment apparatus by the biological nitrification-denitrification process is shown in FIG. 14. This wastewater treatment apparatus includes a primary settling tank 2, a nitrification tank 4 for oxidizing (nitrifying) nitrogen compounds contained in wastewater to nitrate nitrogen or to nitrite nitrogen, a denitrification tank 3 for reducing (denitrifying) nitrate nitrogen or nitrite nitrogen to nitrogen gas, and a final settling tank 7. After relatively large and heavy solids are removed from wastewater 1 in the primary settling tank 2, nitrification and denitrification are performed, and nitrogen is released into the atmosphere as nitrogen gas, and thus nitrogen is removed from wastewater. Meanwhile, organic substances in the wastewater are removed both at the denitrification stage and at the nitrification stage. &lsqb;0017&rsqb; The nitrogen removal from wastewater using a wastewater treatment apparatus by the biological nitrification-denitrification process has the following drawbacks. That is, when the organic substance concentration in the wastewater is decreased, for example, by the influx of rainwater, since the wastewater is diluted while being supplied with oxygen, the organic substances in the wastewater, which have been oxidized and diluted, are fed to the denitrification stage. As a result, since the organic substance concentration is further decreased in comparison with the nitrogen concentration, the rate of denitrification reaction at the denitrification stage is decreased, resulting in deterioration in the quality of treated water. &lsqb;0018&rsqb; Since solid particles are subjected to sedimentation in the primary settling tank, the wastewater fed to the denitrification stage through the primary settling tank is mainly composed of soluble pollutants. Therefore, when the ratio of the organic substance concentration to the nitrogen concentration is low with respect to the soluble wastes in the wastewater to be fed to the denitrification stage, the rate of nitrogen removal reaction at the denitrification stage is also decreased, resulting in deterioration in the quality of treated water. &lsqb;0019&rsqb; In order to cope with such problems, a method is used, in which an organic chemical agent such as methanol, together with the wastewater, is fed to the denitrification stage, and thus, by compensating for the shortage of the organic substance concentration in the wastewater, a decrease in the rate of denitrification reaction is prevented. &lsqb;0020&rsqb; In the conventional method of adding an organic chemical agent to the denitrification stage, although in general methanol, which is relatively inexpensive, is used, the cost for the chemical agent still increases operating expenses. Moreover, since methanol is a Class IV hazardous substance, safety must be taken into consideration in handling, and storage facilities and facilities for receipt and supply must be prepared, resulting in increased cost of equipment and difficulty in handling. &lsqb;0021&rsqb; When the ratio of the organic substance concentration to the nitrogen concentration is low with respect to the wastewater supplied to the denitrification stage, it is difficult to cause satisfactory nitrogen removal reactions, in particular, denitrification reactions, because of a shortage of organic substances, and thus satisfactory nitrogen removal cannot be achieved. Therefore, it is effective in improving the results of nitrogen removal treatment to introduce the organic substances contained in the wastewater fed into the primary settling tank and removed in the primary settling tank, that is, organic substances mainly composed of solids, to the denitrification stage. &lsqb;0022&rsqb; As a conventional method for operating facilities for producing such effects, there is a method in which, by decreasing the number of primary settling tanks used in wastewater treatment facilities having a plurality of treatment lines, operation is performed at increased water surface loading with respect to the primary settling tanks so that suspended solids (SS) concentration in the primary settling tank effluent is increased, and thus the amount of organic substances flowing into the denitrification stage is increased. &lsqb;0023&rsqb; However, it is difficult to accurately control the amount of solid organic substances that flow into the denitrification stage by changing the number of primary settling tanks in operation. &lsqb;0024&rsqb; In order to solve the problems described above, the inventor has already applied for patents which disclose techniques for satisfactory nitrogen removal treatment by increasing the amounts of organic substances to be supplied to denitrification tanks or anaerobic tanks. One such method for removing nitrogen from wastewater, in which at least a portion of sediment in a primary settling tank is fed to a denitrification tank or an anaerobic tank, and a method for removing nitrogen from wastewater, in which the sediment is subjected to ultrasonic treatment before being fed to the denitrification tank or the anaerobic tank, are disclosed in Japanese Patent Application No. 9-133989. Another such method for removing nitrogen from wastewater, in which the sediment is subjected to ozone treatment before being fed to the denitrification tank or the anaerobic tank, is disclosed in Japanese Patent Application No. 9-133988. However, when the sediment in the primary settling tank is introduced to the denitrification tank or the anaerobic tank as it is, since particles of solids contained in the sedimented sludge are relatively large and have a small surface area per unit weight, the rate of decomposition/treatment in a biological reactor, such as a denitrification tank or an anaerobic tank, is relatively low. When the sediment in the primary settling tank is fed to the denitrification tank or the anaerobic tank after ultrasonic treatment, solids, as the sediment, contain microorganisms enclosed by cell walls and/or cell membranes, and cellulose, which are relatively rigid and are not easily broken by vibration treatment. Therefore, the particle size of the solids introduced to the denitrification tank or the anaerobic tank is not sufficiently reduced. Furthermore, when the sediment in the primary settling tank is fed to the denitrification tank or the anaerobic tank after ozone treatment, a portion of organic substances contained in the sediment is oxidized and mineralized, and thus loses effectiveness as organic substances. Since a relatively large amount of electric power, approximately 10 to 15 kWh/kg O3, is also consumed for the generation of ozone, operating expenses increase. SUMMARY OF THE INVENTION &lsqb;0025&rsqb; It is an object of the present invention to provide methods for treating wastewater and apparatuses therefor, in which effective wastewater treatment can be performed in an economical manner. &lsqb;0026&rsqb; According to a first aspect of the present invention, a method for treating wastewater includes the steps of: removing phosphorus from wastewater, using a wastewater treatment apparatus including a settling tank, an anaerobic tank, and an aerobic tank; crushing at least a portion of sediment in the settling tank; and supplying the crushed sediment to the anaerobic tank. &lsqb;0027&rsqb; According to a second aspect of the present invention, a wastewater treatment apparatus includes: a settling tank for removing solids contained in wastewater; an anaerobic tank, in which effluent from the settling tank is introduced and activated sludge releases phosphoric acid ion from cells into the wastewater by a biological phosphorus-releasing reaction; an aerobic tank in which effluent from the anaerobic tank is introduced and activated sludge takes up phosphoric acid ion into cells by a biological phosphorus-uptake reaction; a line for withdrawing sediment from the settling tank; a crushing device for crushing the withdrawn sediment; and a line for supplying the crushed sediment to the anaerobic tank. &lsqb;0028&rsqb; According to a third aspect of the present invention, a method for treating wastewater includes the steps of: removing phosphorus from wastewater, using a wastewater treatment apparatus including a primary settling tank, an anaerobic tank, an aerobic tank, and a final settling tank; returning effluent from the aerobic tank to the primary settling tank; returning sludge withdrawn from the final settling tank to the primary settling tank; and sending sludge withdrawn from the primary settling tank to the anaerobic tank or the aerobic tank. &lsqb;0029&rsqb; According to a fourth aspect of the present invention, a method for treating wastewater includes the steps of: removing phosphorus from wastewater, using a wastewater treatment apparatus including a primary settling tank, an anaerobic tank, an aerobic tank, and a final settling tank; returning effluent from the aerobic tank to the primary settling tank; and sending sludge withdrawn from the primary settling tank to the anaerobic tank or the aerobic tank. &lsqb;0030&rsqb; According to a fifth aspect of the present invention, a method for treating wastewater includes the steps of: removing phosphorus from wastewater, using a wastewater treatment apparatus including a primary settling tank, an anaerobic tank, an aerobic tank, and a final settling tank; returning sludge withdrawn from the final settling tank to the primary settling tank; and sending sludge withdrawn from the primary settling tank to the anaerobic tank or the aerobic tank. &lsqb;0031&rsqb; According to a sixth aspect of the present invention, a wastewater treatment apparatus includes: a primary settling tank for removing solids contained in wastewater; an anaerobic tank, in which effluent from the settling tank is introduced and activated sludge releases phosphoric acid ion from cells into the wastewater by a biological phosphorus-releasing reaction; an aerobic tank in which effluent from the anaerobic tank is introduced and activated sludge takes up phosphoric acid ion into cells by a biological phosphorus-uptake reaction; a final settling tank for settling wastewater treated in the aerobic tank; a line for returning effluent from the aerobic tank to the primary settling tank; a line for returning sludge withdrawn from the final settling tank to the primary settling tank; and a line for sending sludge withdrawn from the primary settling tank to the anaerobic tank or the aerobic tank. &lsqb;0032&rsqb; According to a seventh aspect of the present invention, a wastewater treatment apparatus includes: a primary settling tank for removing solids contained in wastewater; an anaerobic tank, in which effluent from the settling tank is introduced and activated sludge releases phosphoric acid ion from cells into the wastewater by the biological phosphorus-releasing reaction; an aerobic tank in which effluent from the anaerobic tank is introduced and activated sludge takes phosphoric acid ion into cells by the biological phosphorus-uptake reaction; a final settling tank for settling wastewater treated in the aerobic tank; a line for returning effluent from the aerobic tank to the primary settling tank; and a line for sending sludge withdrawn from the primary settling tank to the anaerobic tank or the aerobic tank. &lsqb;0033&rsqb; According to an eighth aspect of the present invention, a wastewater treatment apparatus includes: a primary settling tank for removing solids contained in wastewater; an anaerobic tank, in which effluent from the settling tank is introduced and activated sludge releases phosphoric acid ion from cells into the wastewater by a biological phosphorus-releasing reaction; an aerobic tank in which effluent from the anaerobic tank is introduced and activated sludge takes up phosphoric acid ion into cells by a biological phosphorus-uptake reaction; a final settling tank for settling wastewater treated in the aerobic tank; a line for returning sludge withdrawn from the final settling tank to the primary settling tank; and a line for sending sludge withdrawn from the primary settling tank to the anaerobic tank or the aerobic tank. &lsqb;0034&rsqb; According to a ninth aspect of the present invention, a method for treating wastewater includes the steps of: removing nitrogen from wastewater, using a wastewater treatment apparatus including a settling tank and a denitrification tank; crushing at least a portion of sediment in the settling tank; and supplying the crushed sediment to the denitrification tank. &lsqb;0035&rsqb; According to a tenth aspect of the present invention, a method for treating wastewater includes the steps of: removing nitrogen from wastewater, using a wastewater treatment apparatus including a settling tank and an anaerobic tank, and a nitrification tank; crushing at least a portion of sediment in the settling tank; and supplying the crushed sediment to the anaerobic tank. &lsqb;0036&rsqb; According to an eleventh aspect of the present invention, a wastewater treatment apparatus includes: a settling tank for removing solids contained in wastewater; a denitrification tank, in which effluent from the settling tank is introduced and nitrate nitrogen or nitrite nitrogen in wastewater is reduced to nitrogen gas; a line for withdrawing sediment in the settling tank; a crushing device for crushing the withdrawn sediment; and a line for supplying the crushed sediment to the denitrification tank. &lsqb;0037&rsqb; According to a twelfth aspect of the present invention, a wastewater treatment apparatus includes: a settling tank for removing solids contained in wastewater; an anaerobic tank, in which effluent from the settling tank is introduced, nitrate nitrogen or nitrite nitrogen in the wastewater is reduced to nitrogen gas, and activated sludge releases phosphoric acid ion from cells into the wastewater by a biological phosphorus-releasing reaction; a line for withdrawing sediment from the settling tank; a crushing device for crushing the withdrawn sediment; and a line for supplying the crushed sediment to a denitrification tank. &lsqb;0038&rsqb; According to a thirteenth aspect of the present invention, a wastewater treatment apparatus includes: a primary settling tank for removing solids contained in wastewater; a denitrification tank, in which effluent from the primary settling tank is introduced, and nitrate nitrogen or nitrite nitrogen in the wastewater is reduced to nitrogen gas; a nitrification tank, in which effluent from the denitrification tank is introduced, and nitrogen compounds in the wastewater are oxidized to nitrate nitrogen or nitrite nitrogen; a final settling tank for settling effluent from the nitrification tank; and a line for returning a portion of effluent from the nitrification tank or a portion of effluent from the final settling tank to the primary settling tank. Detailed Description: DESCRIPTION OF THE PREFERRED EMBODIMENT &lsqb;0056&rsqb; Embodiment 1 &lsqb;0057&rsqb; In embodiment 1, the deterioration of phosphorus removal performance in an anaerobic-aerobic activated sludge process due to low organic substance concentration in wastewater, in particular, a shortage of the soluble organic substance concentration, is overcome. In accordance with embodiment 1, methods and apparatuses for effectively and economically removing phosphorus are provided, in which sludge containing solid organic substances generated in a primary settling tank are supplied to an anaerobic tank, and thus by compensating for the shortage of the organic substance concentration of the wastewater flowing into the anaerobic tank, organic substances generated in the waste treatment facilities are effectively used and the deterioration of phosphorus removal performance is avoided. &lsqb;0058&rsqb; Embodiment 1 relates to methods for removing phosphorus from wastewater and apparatuses therefor, in which phosphorus in wastewater is removed using an apparatus including at least a settling tank for wastewater to be treated, an anaerobic tank, and an aerobic tank, and at least a portion of the sediment from the wastewater in the settling tank is crushed or ground before being supplied to the anaerobic tank. &lsqb;0059&rsqb; In accordance with the method for biologically removing phosphorus from wastewater and the apparatus therefor in embodiment 1, at least a portion of the sediment in the primary settling tank, which contains abundant solid organic substances, that is, at least a portion of the solid organic substances, is fed into the anaerobic tank in order to secure an organic substance concentration required for the phosphorus-releasing reaction at the anaerobic stage. By crushing or grinding at least a portion of the sediment in the primary settling tank, solid organic substances contained in the sediment in the primary settling tank are particulated or solubilized so that microorganisms can effectively and promptly use the solid organic substances for the phosphorus-releasing reaction. The present inventors have found through experimentation that when the organic substance concentration in wastewater is low and the organic substance concentration required for the phosphorus-releasing reaction at the anaerobic stage is insufficient, the oxidation-reduction potential (ORP) at the anaerobic stage is −100 mV or more. Accordingly, an ORP at the anaerobic stage is measured, and only when the ORP is −100 mV or more, that is, only when the organic substance concentration required for the phosphorus-releasing reaction is insufficient at the anaerobic stage, sediment from the primary settling tank which has been crushed or ground is fed into the anaerobic tank. Thus, by supplying organic substances originating from the solids, the organic substance concentration required for the phosphorus-releasing reaction will be sufficient. &lsqb;0060&rsqb; An example of a biological phosphorus removal apparatus based on embodiment 1 is shown in FIG. 1. &lsqb;0061&rsqb; The biological phosphorus removal apparatus based on embodiment 1 mainly includes a primary settling tank 2, an anaerobic tank 3, an aerobic tank 4, and a final settling tank 6. In the anaerobic tank 3, only agitation is performed, and in the aerobic tank 4, oxygen is supplied by an. air diffuser 5 and agitation is performed by flow caused by the air diffusion. &lsqb;0062&rsqb; In the biological phosphorus removal apparatus shown in FIG. 1, wastewater 1 is subjected to the solid-liquid separation in the primary settling tank 2, and is then passed to the anaerobic tank 3 and to the aerobic tank 4 in that order. Effluent from the aerobic tank 4 flowing into the final settling tank 6 is separated into treated water 7 and activated sludge in the final settling tank 6. At least a portion of the activated sludge separated and thickened in the final settling tank 6 is sent to the anaerobic tank 3 as return sludge 8. &lsqb;0063&rsqb; Sediment 9 settled in the primary settling tank is subjected to crushing or grinding treatment by a crushing device or a grinding device 10, and is then directly sent to the anaerobic tank 3 as crushed or ground sediment 11 from the primary settling tank, or is sent to the anaerobic tank 3 through the effluent channel of the primary settling tank 2. Alternatively, the crushed or ground sediment 11 is fed to the primary settling tank 2 through the influx channel of the primary settling tank 2, and a portion, excluding those which are settled again in the primary settling tank 2, is sent to the anaerobic tank 3 through the effluent channel of the primary settling tank 2. &lsqb;0064&rsqb; In the anaerobic tank 3, by using organic substances mainly constituting soluble components in the wastewater 1 and organic substances originating from the sediment 9 in the primary settling tank, activated sludge releases phosphoric acid ion accumulated in cells in the activated sludge into the wastewater (the phosphorus-releasing reaction). In the aerobic tank 4, activated sludge takes up phosphoric acid ion in the wastewater into cells in the activated sludge (the phosphorus-uptake reaction), and simultaneously, organic substances are removed by oxidizing decomposition. &lsqb;0065&rsqb; After solid organic substances contained in the sediment 9 are treated by the crushing device or the grinding device 10, at least a portion thereof is finely particulated and at least a portion thereof becomes soluble components. That is, when the grain sizes of the solids are reduced by crushing or grinding treatment, the surface area increases with respect to solids having the same weight. Microorganisms, animals, plants, and the like are contained in the sediment 9, and these organisms are composed of cells enclosed by cell membranes and/or cell walls. When these membranous structures are broken by crushing or grinding treatment, since cell fluids are released from the cells, the soluble organic substance concentration of the wastewater into which the crushed or ground sediment 11 is fed is increased. &lsqb;0066&rsqb; In general, when microorganisms propagate by decomposing and using organic substances, organic substances having higher molecular weights take longer time to be decomposed and become useful. Organic substances having lower molecular weights are easier to be used, and the rate of the decomposing reaction is higher. In comparison with soluble organic substances, solid organic substances generally have larger molecular weights, and thus the solid organic substances are more difficult to be used by microorganisms. This is because of the fact that when microorganisms take up organic substances through cell membranes and/or cell walls, the organic substances must have enough low molecular weights. In order for microorganisms to use organic substances having high molecular weights, the organic substances having high molecular weights must be decomposed into organic substances having lower molecular weights, thus requiring time for decomposition to usable states. In organisms, reactions for decomposing organic substances having high molecular weights into organic substances having lower molecular weights are mainly performed by the enzymatic reactions. In such reactions, as the surface on which an enzyme acts is increased, that is, as the grain sizes of solid organic substances having comparable weights are decreased, the reaction rate increases. Consequently, in embodiment 1, by subjecting the sediment 9 to crushing or grinding treatment so that the grain sizes of solids are reduced, enzymatic reactions which allow microorganisms to decompose and use solid organic substances are enhanced, the rate of decomposition and use of solid organic substances is increased, and the microbial reactions may be efficiently completed in a reactor of limited capacity. When the soluble organic substances generated by crushing or grinding the sediment 9 are introduced to the anaerobic tank 3, they are also effectively and promptly used for the phosphorus-releasing reaction and the denitrification reaction in the anaerobic tank 3 and for the subsequent phosphorus-uptake reaction in the aerobic tank 4. This happens at least in the treatment of municipal wastewater. Sediments 9 for a municipal wastewater treatment include microbial bodies or plant cells or animal cells, which are enveloped by cell walls, or cell membrane and cell fluids including organic components leak out by breaking the cell structure. In this respect also, the crushing or grinding treatment to the sediment 9 contributes to increase in the rate of decomposition and use of the organic substances contained in solids in the influent wastewater 1 by microorganisms in the reaction tank, and this is effective to complete the microbial reaction in a reactor of limited capacity. &lsqb;0067&rsqb; The crushed or ground sediment 11 may be directly fed into the anaerobic tank 3, or may be fed into the effluent channel of the primary settling tank 2 at any point from the weir to the anaerobic tank 3. When such a method is used, all the crushed or ground sediment 11 can be fed into the anaerobic tank 3. Since the capacity of the channel from the supply point of the crushed or ground sediment 11 to the anaerobic tank 3 is relatively small and the residence time is relatively short, by changing the feed amount of the crushed or ground sediment 11, the reaction in the anaerobic tank 3 may be controlled over relatively short periods of time. Whether the crushed or ground sediment 11 is directly fed into the anaerobic tank 3 or is fed into the effluent channel of the primary settling tank 2 at any point from the weir to the anaerobic tank 3 can be determined depending on the distance between the installation position of the crushing device or grinding device 10 and the supplying position of the crushed or ground sediment 11, waterhead difference, or the like. &lsqb;0068&rsqb; The crushed or ground sediment 11 may be fed into the influx channel of the primary settling tank 2 at any point, and after removing the solids settled again in the primary settling tank 2, components of the crushed or ground sediment 11 which are not settled may be fed into the anaerobic tank 3 together with the overflow from the primary settling tank 2. In such a method, although all of the crushed or ground sediment 11 is not fed into the anaerobic tank 3, since the capacity of the channel from the supply point of the crushed or ground sediment 11 to the anaerobic tank 3 is large and the residence time is increased, the components, excluding solids which readily settle out, originating from the crushed or ground sediment 11 can be fed into the anaerobic tank 3 at relatively stable concentrations. &lsqb;0069&rsqb; Depending on conditions, such as the phosphorus concentration in the effluent from the primary settling tank 2 after sedimentation and the residence time in the anaerobic tank 3 and the aerobic tank 4, the phosphorus-uptake reaction must be accelerated in comparison with the phosphorus-releasing reaction. In such a case, the crushed or ground sediment 11 may be introduced to the aerobic tank 4 in addition to the anaerobic tank 3. &lsqb;0070&rsqb; The withdrawal of the sediment 9 from the primary settling tank 2 is performed by opening an outlet provided on the lower section or the bottom of the primary settling tank 2. The sediment 9 may be naturally discharged in accordance with the position of the primary settling tank 2 or a pump may be used. &lsqb;0071&rsqb; The sediment treated by the crushing device or grinding device is in the form of a suspension or a slurry, and has a concentration of approximately 3,000 to 12,000 mg/l, and normally approximately 5,000 to 10,000 mg/l. &lsqb;0072&rsqb; The timing of adding the crushed or ground sediment is determined, for example, by measuring the oxidation-reduction potential (ORP) of the anaerobic tank, and when the ORP is −100 mV or more, the addition is performed. When the ratio of the organic substance concentration to the phosphoric acid ion concentration in the soluble components of wastewater 1 is always rather low, it is therefore practical to continuously add the crushed or ground sediment during operation. &lsqb;0073&rsqb; The pump used for withdrawing the sediment 9 from the primary settling tank is generally a slurry pump which does not easily clog, and thus the pump is not very effective for crushing or grinding the sediment. Therefore, in order to crush or grind the sediment, a crushing device or a grinding device must be provided. The crushing device or the grinding device 10 may be of various types, such as a gear type and a multiple spindle disk type. In order to control the degree of crushing or grinding, it is effective to appropriately select the mesh of a screen in which the crushed or ground sediment is to be passed. If the screen mesh is too small, clogging easily occurs, and if it is too large, solids having a large grain size easily pass therethrough, and thus the screen mesh size is preferably chosen to be approximately 1 to 5 mm. Although the crushing device or the grinding device 10 may be installed in-line or in an open channel, since the sediment 9 may be a source of unpleasant odors, the in-line installation is preferred. Since a general-purpose device can be used as such a crushing device or grinding device 10, the cost of equipment as well as the operating expenses, which mainly cover the cost of powering motors, will be relatively low, and the grain size reduction effect with respect to solids will be relatively large. &lsqb;0074&rsqb; The amount of the crushed or ground sediment added is, preferably, approximately 0.1 to 1.5% on the volume of the wastewater 1, and normally approximately 0.5 to 1.0%. The addition may be continuously or intermittently performed. &lsqb;0075&rsqb; The addition is preferably terminated when the ORP reaches approximately −150 to −250 mV, and depending on the result, continuous addition may be effective. &lsqb;0076&rsqb; FIG. 2 shows another example of a biological phosphorus removal apparatus in accordance with embodiment 1. With respect to the biological phosphorus removal apparatus based on the conventional technique shown in FIG. 6, in accordance with the results of the inventors' experimentation, when the soluble organic substance concentration in the wastewater 1 is high and the organic substance concentration required for the phosphorus-releasing reaction in the anaerobic tank 3 is obtained, the ORP in the anaerobic tank 3 is −100 mV or less, and when the organic substance concentration in the wastewater 1 is low and the organic substance concentration required for the phosphorus-releasing reaction in the anaerobic tank 3 is not satisfactory, the ORP in the anaerobic tank 3 is −100 mV or more. &lsqb;0077&rsqb; Based on the above, in the biological phosphorus removal apparatus in accordance with embodiment 1, shown in FIG. 2, the operation of the apparatus is controlled so that when the measured value by an ORP meter 12 mounted on an anaerobic tank 3 is approximately −150 to −250 mV or less, the influent of crushed or ground sediment 11 from a primary settling tank is halted or the operation of a crushing device or a grinding device 10 is halted, and when the measured value is −100 mV or more, the influx of the crushed or ground sediment 11 is started. These controls are performed by a control device 13. &lsqb;0078&rsqb; The phosphorus removal method in the present invention is also applicable to a wastewater treatment apparatus including an anaerobic stage, a denitrification stage (an anoxic stage), and a nitrification stage (an aerobic stage), in addition to the wastewater treatment apparatus including the anaerobic stage and the aerobic stage. &lsqb;0079&rsqb; FIG. 3 shows another example of a biological phosphorus removal apparatus in accordance with embodiment 1. In the biological phosphorus removal apparatus in accordance with embodiment 1 shown in FIG. 3, a denitrification tank 14 is added to the biological phosphorus removal apparatus in accordance with embodiment 1 shown in FIG. 1. The apparatus shown in FIG. 3 mainly includes a primary settling tank 2, an anaerobic tank 3, the denitrification tank 14, an aerobic tank 4, and a final settling tank 6. &lsqb;0080&rsqb; In the biological phosphorus removal apparatus shown in FIG. 3, in the denitrification tank 14, only agitation is performed, and effluent from the anaerobic tank 3 and a nitrification circulating liquid 15 are fed into the denitrification tank 14. In the denitrification tank 14, nitrate nitrogen or nitrite nitrogen contained in the nitrification circulating liquid 15 is reduced to nitrogen gas (a denitrification reaction), using organic substances in the wastewater, and thus denitrification treatment is performed. &lsqb;0081&rsqb; Additionally, in the biological phosphorus removal apparatus shown in FIG. 3, a portion of crushed or ground sediment 11 from the primary settling tank may be fed into the denitrification tank 14. EXAMPLE OF THE INVENTION &lsqb;0082&rsqb; An example of the biological phosphorus removal method in accordance with embodiment 1 will be described below. FIG. 4 shows an experimental device. In the example, a mixture of return sludge, wastewater, and primary settling tank sediment taken from a wastewater treatment apparatus having a flow pattern as shown in FIG. 6 as a sample was fed into the device shown in FIG. 4, and characteristics of the phosphorus-releasing reaction of activated sludge under anaerobic conditions were measured. Table 1 shows the composition of samples. The wastewater taken from the wastewater treatment apparatus having a flow shown in FIG. 6 had a BOD concentration of 42 mg/L, and the return sludge had an MLSS concentration of 4,200 mg/L. In order to determine if the wastewater treatment apparatus having a flow shown in FIG. 1 functioned effectively, the primary settling tank sediment having an MLSS concentration of 3,200 mg/L taken from the primary settling tank in the wastewater treatment apparatus having a flow shown in FIG. 6 was ground for 3 minutes by a Potter-type glass homogenizer having a capacity of 10 ml, and its effectiveness as an organic substance source was investigated. 1 TABLE 1 Sample and Volume Sample A Sample B Return sludge (ml) 1,000 1,000 Wastewater (ml) 2,000 2,000 Ground sediment 20 0 from primary settling tank (ml) &lsqb;0083&rsqb; FIG. 5 shows a change in the phosphoric acid ion concentration in the sample wastewater over time. A sample A in which the phosphorus-releasing reaction was performed with the ground primary settling tank sediment being added was compared with a sample B in which the phosphorus-releasing reaction was performed without the ground primary settling tank sediment. The rate of increase of phosphoric acid ion in the wastewater was higher when the phosphorus-releasing reaction was performed with the ground sediment being added. That is, it has been confirmed that by adding the primary settling tank sediment, which had been subjected to grinding treatment in order to reduce the grain size of solids and to solubilize a portion of organic substances, to the sample wastewater, the rate of the phosphorus-releasing reaction was increased. &lsqb;0084&rsqb; Since crushing treatment is similar to grinding treatment, the crushing treatment is also considered to be effective in reducing the grain size of solids in the primary settling tank sediment and in solubilizing a portion of the organic substances. &lsqb;0085&rsqb; In embodiment 1, the primary settling tank sediment which has been crushed or ground is fed into an anaerobic stage, and in some cases, to an anaerobic stage of a biological phosphorus removal apparatus having an anoxic stage and an aerobic stage, so that the organic substance concentration required for the phosphorus-releasing reaction at the anaerobic stage is secured. &lsqb;0086&rsqb; Accordingly, either when the quality of treated water is deteriorated by the decreased rate of phosphorus-releasing reaction at the anaerobic stage because the concentration of organic substances supplied to the anaerobic stage is decreased more than the phosphoric acid ion concentration is decreased, such as in a case of the influx of rainwater, or when the quality of treated water is deteriorated by the decreased rate of the phosphorus-releasing reaction at the anaerobic stage because soluble pollutants in wastewater entering the anaerobic stage after being subjected to solid-liquid separation treatment in the primary settling tank have a low ratio of organic substance concentration to phosphoric acid ion concentration, the supply of the organic substances required for the phosphorus-releasing reaction is secured. Thus, a decrease in the rate of the phosphorus-releasing reaction at the anaerobic stage can be prevented, and the rate of the phosphorus-uptake reaction at the subsequent aerobic stage is effectively increased. &lsqb;0087&rsqb; In embodiment 1, the ORP at the anaerobic stage is measured and only when the ORP is −100 mV or more, the primary settling tank sediment which has been subjected to crushing or grinding treatment is fed into the anaerobic stage. Thus, organic substances can be supplied only when the organic substance concentration in the wastewater is decreased and the organic substance concentration required for the phosphorus-releasing reaction is not secured. By such control, the cost of power required for crushing or grinding the primary settling tank sediment or the cost of power required to transport the primary settling tank sediment after crushing or grinding to the anaerobic stage can be minimized, and the organic substance load at the anaerobic stage and the aerobic stage can be minimized. &lsqb;0088&rsqb; The primary settling tank sediment is subjected to crushing or grinding treatment so that the grain size of organic solids contained in the primary settling tank sediment is reduced and the organic solids are partially solubilized, and the crushed or ground sediment is then introduced to the anaerobic stage, and in some cases, further to the aerobic stage or to the denitrification stage. Thus, the crushed or ground sediment is promptly and effectively used in microbial reactions which mainly include phosphorus-releasing reactions and phosphorus-uptake reactions. &lsqb;0089&rsqb; Since a general-purpose device can be used for crushing or grinding treatment, the cost of equipment can be minimized, the operating expenses, which mainly cover the cost of powering motors can be relatively low, and large solids can be effectively broken up. &lsqb;0090&rsqb; Embodiment 2 &lsqb;0091&rsqb; In embodiment 2, two problems are overcome. The first problem is that due to low organic substance concentration in wastewater, and in particular, a shortage of the soluble organic substance concentration, the phosphorus removal performance at a wastewater treatment plant using the anaerobic-aerobic activated sludge process is deteriorated. The second problem is that the residence time at reaction tanks in the plant using an activated sludge process represented by the conventional activated sludge process is not sufficient for the phosphorus removal performance in a plant using the anaerobic-aerobic activated sludge process. When the operating expenses such as for the addition of methanol are low and the existing activated sludge facilities for removing BOD are converted to wastewater treatment facilities using the anaerobic-aerobic activated sludge process, the BOD removal and the phosphorus removal can be performed by maximizing the utilization of volume and capacity of the existing facilities. Moreover, when a new plant is opened, it is possible to make the residence time at the entire reactor as compact as that in the plant using the conventional activated sludge process. &lsqb;0092&rsqb; Embodiment 2 relates to an apparatus for removing phosphorus from wastewater including at least a settling tank in which wastewater to be treated is settled (a primary settling tank), an anaerobic tank, an aerobic tank, and a settling tank in which wastewater treated in these tanks is settled (a final settling tank). The apparatus is provided with a line for returning at least a portion of effluent from the aerobic tank or sludge withdrawn from the final settling tank to the primary settling tank, and a line for feeding at least a portion of the sludge from the primary settling tank to the anaerobic tank or the aerobic tank. &lsqb;0093&rsqb; In the biological phosphorus removal apparatus in accordance with embodiment 2, by returning at least a portion of the mixed liquor flowing from the aerobic tank, at least a portion of the sludge withdrawn from the final settling tank, or both to the primary settling tank, organic substances contained in sediment and suspended solids in the primary settling tank, and microorganisms in the activated sludge returned to the primary settling tank are brought into contact with each other under the anaerobic conditions in the primary settling tank. By effectively utilizing the solid substances in the primary settling tank and the sludge retention time, phosphorus-releasing reactions proceed. By feeding at least a portion of the sludge withdrawn from the primary settling tank to the anaerobic stage, the anoxic stage, or the aerobic stage, the sludge settled in the primary settling tank, containing the activated sludge in which the phosphorus-releasing reactions have proceeded and solid organic substances, is fed to the anaerobic stage, the anoxic stage, or the aerobic stage. Thus, further phosphorus-releasing reactions at the anaerobic stage, phosphorus-uptake reactions, and in some cases, denitrification reactions, at the anoxic stage, or phosphorus-uptake reactions at the aerobic stage proceed. &lsqb;0094&rsqb; That is, in the apparatuses of embodiment 2, since the mixed liquor containing activated sludge flowing from the aerobic tank or the sludge withdrawn from the final settling tank is returned to the primary settling tank, activated sludge is present in the primary settling tank. There are also solid organic substances as sediment and suspended solids and soluble organic substances originating from wastewater in the primary settling tank, and the activated sludge in the primary settling tank is brought into contact with these organic substances. Since the primary settling tank is not aerated and the wastewater normally has a large oxygen demand, the primary settling tank is anaerobic. That is, in the primary settling tank, activated sludge releases phosphoric acid ion accumulated in activated sludge cells into wastewater (the phosphorus-releasing reaction), using the organic substances. Subsequently, by feeding at least a portion of the sediment in the primary settling tank to the anaerobic tank or the aerobic tank, further phosphorus-releasing reactions in the anaerobic tank or phosphorus-uptake reactions in the aerobic tank are caused. &lsqb;0095&rsqb; When the sludge withdrawn from the final settling tank is returned to the primary settling tank, since the sludge withdrawn from the final settling tank has a higher activated sludge concentration than that of the mixed liquor flowing from the aerobic tank, the required return volume is smaller with respect to the same amount of activated sludge, which is advantageous. When the mixed liquor flowing from the aerobic tank is returned to the primary settling tank, differing from the case when the sludge withdrawn from the final settling tank is returned to the primary settling tank, a water load to the final settling tank is not increased, which is also advantageous. When both the method for returning the sludge withdrawn from the final settling tank to the primary settling tank and the method for returning the mixed liquor flowing from the aerobic tank to the primary settling tank are combined, an intermediate merit between the two advantages described above can be obtained. &lsqb;0096&rsqb; In the anaerobic tank, activated sludge releases phosphorus using organic substances mainly composed of soluble components in the wastewater, and in some cases, organic substances originating from the sediment in the primary settling tank. When at least a portion of the sediment in the primary settling tank is introduced to the anaerobic tank, differing from the conventional method, the activated sludge which has released phosphorus in the primary settling tank may be introduced to the anaerobic tank, together with organic solids originating from sediment in the primary settling tank, to perform a further phosphorus-releasing reaction, and thus the phosphorus-releasing reaction can be strengthened in comparison with the conventional method. &lsqb;0097&rsqb; In the aerobic tank, activated sludge takes up phosphoric acid ion in the wastewater into activated sludge cells (the phosphorus-uptake reaction), using organic substances mainly composed of soluble components in the wastewater, and in some cases, organic substances originating from the sediment in the primary settling tank, and simultaneously, organic substances are oxidized, decomposed and removed. When at least a portion of the sediment in the primary settling tank is introduced to the aerobic tank, differing from the conventional method, since a phosphorus-uptake reaction is performed using even organic solids originating from the sediment in the primary settling tank, the phosphorus-uptake reaction can be strengthened in comparison with the conventional method. In such a case, in order to maintain the sufficient activated sludge concentration in the anaerobic tank, preferably, a portion of the sludge withdrawn from the final settling tank is returned to the anaerobic tank. &lsqb;0098&rsqb; The method for removing phosphorus in accordance with the present invention is also applicable to a wastewater treatment apparatus including an anaerobic stage, a denitrification stage (an anoxic stage), and a nitrification stage (an aerobic stage), in addition to
{'app_number': '10073467', 'application_number': None, 'doc_number': '20020104798', 'publication_number': None, 'source_file': './application/2002/pa020808.xml', 'source_data': 'USPTO-Application'}