JP4793635B2 - Recycling method of organic wastewater - Google Patents

Description

  The present invention relates to a method for regenerating organic sewage, and in particular, organic sewage that is reclaimed to a level that can be used as drinking water or industrial water by purifying raw water containing organic matter by biological treatment and then further advanced treatment. It relates to a reproduction method.

  A method is known in which raw water containing organic matter and nitrogen components is biologically treated and purified with activated sludge, and biologically treated water containing activated sludge at a high concentration is membrane-separated using a microfiltration membrane or ultrafiltration membrane. (For example, refer to Patent Document 1). According to this method, clear treated water can be obtained by membrane separation, and there is an advantage that a sedimentation basin for separating activated sludge from biological treated water becomes unnecessary.

  In addition, as a method for regenerating organic wastewater, a method in which the membrane separation water obtained by the above method is treated with a reverse osmosis membrane device and regenerated to a level that can be used as drinking water or industrial water has attracted attention. . However, in a reverse osmosis membrane device, a substance that inhibits membrane permeability adheres to and propagates on the membrane surface of the reverse osmosis membrane constituting the reverse osmosis membrane device, causing a so-called fouling. Problems always occur.

Usually, the FI value is used for risk assessment of fouling of water supplied to the reverse osmosis membrane device. This FI value is obtained by quantifying the turbidity in water supplied to the reverse osmosis membrane device, and is an index for predicting fouling of the reverse osmosis membrane. Since the membrane-separated water after the biological treatment described above has fine turbidity removed by membrane separation, the FI value is extremely small and the risk of fouling is considered to be relatively low.
JP 2004-243248 A

  However, even in this type of organic sewage regeneration method, rapid fouling may occur in the reverse osmosis membrane constituting the reverse osmosis membrane device.

  An object of the present invention is to provide a method for regenerating organic sewage for preventing a rapid fouling of a reverse osmosis membrane when a membrane separation water after biological treatment is supplied to a reverse osmosis membrane device to perform the reverse osmosis membrane treatment. There is.

In order to achieve the above object, a method for regenerating organic wastewater according to the present invention includes a first step of biologically treating raw water containing organic matter, and a second step of membrane-separating biologically treated water that has undergone the first step. In the method for regenerating organic wastewater comprising the third step of treating the membrane separation water in the second step with a reverse osmosis membrane device, the solubility of the biologically treated water in the first step or the membrane separation water in the second step When the organic substance concentration increases, the injection amount of the fouling inhibitor injected into the reverse osmosis membrane from the injection means of the fouling inhibitor into the reverse osmosis membrane of the reverse osmosis membrane device is increased .

The organic wastewater regeneration method according to the present invention includes a first step of biologically treating raw water containing organic matter, a second step of membrane-separating biologically treated water that has undergone the first step, and a second step of the second step. In a method for regenerating organic wastewater comprising a third step of treating membrane separation water with a reverse osmosis membrane device, when the concentration of soluble organic matter in the biologically treated water in the first step or the membrane separation water in the second step is increased. Increasing the amount of the internal liquid by increasing the degree of opening of the back pressure valve provided in the internal liquid circulation line to be circulated to the reverse osmosis membrane by the internal liquid circulation means for the reverse osmosis membrane of the reverse osmosis membrane device It is characterized by.

  In the present invention, the cause of the rapid fouling of the reverse osmosis membrane when treating the membrane separation water after biological treatment with the reverse osmosis membrane device is not the turbidity remaining in the membrane separation water but mainly the dissolution in the membrane separation water. It was created by paying attention to the fact that it is an organic material.

  In other words, the quality of raw water containing this kind of organic matter often varies with time, day, and season. Biological treatment is also greatly affected by changes in water temperature. For this reason, the quality of the membrane separation water supplied to the subsequent reverse osmosis membrane device may fluctuate greatly. Membrane separation water may contain soluble organic matter that is difficult to biodegrade by biological treatment or soluble organic matter secreted by activated sludge, which causes fouling in the reverse osmosis membrane device. Alternatively, bacteria using these soluble organic substances as nutrients grow on the surface of the reverse osmosis membrane and promote fouling.

  In the present invention, a first step of biologically treating raw water containing organic matter, a second step of membrane-separating biologically treated water that has passed through the first step, and a second step of treating the membrane-separated water of the second step with a reverse osmosis membrane device. In the method for regenerating organic wastewater comprising three steps, the operating conditions of the fouling suppression means in the reverse osmosis membrane device based on the concentration of soluble organic matter in the biologically treated water in the first step or the membrane separation water in the second step To control.

  For this reason, when the concentration of the soluble organic matter in the biologically treated water in the first step or the membrane separation water in the second step is increased, the operating conditions of the fouling suppression means are enhanced, thereby increasing the rapid fouling of the reverse osmosis membrane device. Rings can be suppressed.

  FIG. 1 is a system diagram showing an embodiment of a method for regenerating organic sewage according to the present invention. The biological treatment apparatus 10 includes a denitrification tank 12 and a nitrification tank 14. A stirrer 16 is installed at the bottom of the denitrification tank 12. By driving the stirrer 16, the biologically treated water in the denitrification tank 12 is mixed and stirred and maintained in an anaerobic state. The denitrification tank 12 and the nitrification tank 14 communicate with each other through a water channel 18. A membrane separation unit 20 is immersed in the nitrification tank 14. A diffuser tube 22 is disposed below the membrane separation unit 20, and the compressed air supplied from the blower 24 is diffused from the diffuser tube 22 into the nitrification tank 14. The biologically treated water in the nitrification tank 14 is maintained in an aerobic state by diffusing from the diffusing tube 22.

  The membrane separation unit 20 is configured by a flat membrane or a hollow fiber membrane made of a microfiltration membrane or an ultrafiltration membrane, and activated sludge in biologically treated water in the nitrification tank 14 is membrane-separated by the membrane separation unit 20. The Membrane separation water 26 that has passed through the membrane material of the membrane separation unit 20 is sent to a subsequent adjustment tank 30 by a membrane filtration pump 28. A circulation pump 32 is connected to the nitrification tank 14, a part of the biologically treated water containing activated sludge extracted at a high concentration extracted by the circulation pump 32 is discharged out of the system as surplus sludge 34, and the remainder is sent to the denitrification tank 12. Circulated.

  A supply pump 38 is connected to the adjustment tank 30, and the internal liquid 40 in the adjustment tank 30 is supplied to the reverse osmosis membrane device 42 by the supply pump 38. The treated water 46 that has passed through the reverse osmosis membrane 44 of the reverse osmosis membrane device 42 is effectively used as reclaimed water. A flow meter 48 is disposed in a pipeline for supplying the treated water 46, and the flow rate of the treated water 46 detected by the flow meter 48 is transmitted to the first controller 50. The first controller 50 controls the rotation speed of the supply pump 38 so that the flow rate of the treated water 46 transmitted from the flow meter 48 maintains a set value.

  Most of the concentrated liquid 52 concentrated by the reverse osmosis membrane device 42 is circulated to the adjustment tank 30 as the circulating liquid 56 through the first back pressure valve 54. The remaining portion of the concentrated liquid 52 is returned to the denitrification tank 12 via the second back pressure valve 58. A concentrated liquid 52 discharge line 78 is branched into the concentrated liquid 52 transport line, and the concentrated liquid 52 is periodically discharged via a third back pressure valve 80 provided in the discharged line 78, so that Prevents excessive increase in salt concentration.

  The adjusting tank 30 is connected to a fouling inhibitor injection means 60. That is, the chemical solution (fouling inhibitor) for suppressing fouling of the reverse osmosis membrane 44 is adjusted to a predetermined concentration and stored in the chemical solution storage tank 62. A chemical solution injection pump 64 is connected to the chemical solution storage tank 62, and a fouling inhibitor 66 having a predetermined flow rate is injected into the adjustment tank 30 continuously or intermittently by the chemical solution injection pump 64.

  A sensor 68 capable of detecting the dissolved organic matter concentration of biologically treated water is connected to the nitrification tank 14. The detection value of the sensor 68 is transmitted to the second controller 70. The second controller 70 controls the operating condition of the chemical solution injection pump 64 based on the dissolved organic substance concentration of the biologically treated water transmitted from the sensor 68. The second controller 70 can also control the opening degree of the first back pressure valve 54 and the second back pressure valve 58 based on the dissolved organic matter concentration of the biologically treated water transmitted from the sensor 68.

  As the sensor 68 for detecting the concentration of soluble organic matter in biologically treated water, for example, a COD meter capable of continuous automatic analysis or an ultraviolet absorbance meter is preferably used. However, the biologically treated water contains high-concentration activated sludge as an insoluble organic substance. If the biologically treated water is directly applied to the sensor 68, the insoluble organic substance is also detected as the organic substance concentration. An error occurs. Therefore, when detecting the dissolved organic substance concentration of biologically treated water, it is important to separate the biologically treated water as a pretreatment with a filter paper or the like and detect only the separated liquid by the sensor 68.

  In the treatment system having the above-described configuration, organic sewage 72 containing organic matter and a nitrogen component as raw water flows into the denitrification tank 12. In the denitrification tank 12, nitrate nitrogen in the biologically treated water is denitrified by denitrifying bacteria constituting the activated sludge under anaerobic conditions, and released to the atmosphere as nitrogen gas. Along with this denitrification reaction, most of the organic matter in the organic sewage 72 that has flowed in is also biodegraded and removed. The biologically treated water that has undergone the denitrification process in the denitrification tank 12 flows into the nitrification tank 14 via the water channel 18. In the nitrification tank 14, ammonia nitrogen in the biologically treated water is nitrified by nitrifying bacteria constituting the activated sludge under aerobic conditions to become nitrate nitrogen. In the nitrification tank 14, organic matter remaining in the biologically treated water is biodegraded and removed by organic matter-decomposing bacteria constituting the activated sludge. The air diffused from the air diffuser 22 maintains the inside of the nitrification tank 14 in an aerobic state, and cleans the membrane surface of the membrane material in the process in which the diffused bubbles rise along the membrane material of the membrane separation unit 20. Helps prevent dirt and clogging of the membrane surface.

  In the nitrification tank 14, membrane separation is performed by the membrane separation unit 20 immersed therein, and the membrane separation water 26 that has passed through the membrane material of the membrane separation unit 20 is sent to the subsequent adjustment tank 30 by the membrane filtration pump 28. By the membrane separation by the membrane separation unit 20, the activated sludge in the biologically treated water in the nitrification tank 14 is concentrated and kept at a high concentration. A part of biologically treated water containing activated sludge extracted at a high concentration by the circulation pump 32 is discharged out of the system as surplus sludge 34, and the remainder is circulated to the denitrification tank 12. As described above, nitrate nitrogen in the circulated biological treated water is denitrified by denitrifying bacteria and released into the atmosphere as nitrogen gas.

  The adjustment tank 30 is supplied with the membrane separation water 26 from the membrane separation unit 20, the circulating fluid 56 circulating through the reverse osmosis membrane device 42, and the fouling inhibitor from the fouling inhibitor injection means 60, and is mixed by the stirrer 74. Is done. The internal liquid 40 of the adjustment tank 30 in which these liquids are mixed is supplied to the reverse osmosis membrane device 42 by the supply pump 38, and the treated water 46 that has permeated the reverse osmosis membrane 44 of the reverse osmosis membrane device 42 is discharged out of the system as reclaimed water. Is done. The flow rate of the treated water 46 passing through the reverse osmosis membrane 44 depends on the back pressure acting on the primary side of the reverse osmosis membrane 44. The back pressure valves 54 and 58 described above are provided in order to set the flow rate of the treated water 46 to a predetermined level. Further, in order to maintain the flow rate of the treated water 46 at the set value, the rotation speed control of the supply pump 38 is performed by the first controller 50. That is, when the membrane permeation performance of the reverse osmosis membrane 44 is deteriorated due to fouling or the like, the rotation speed of the supply pump 38 is increased and the flow rate of the internal liquid 40 supplied to the primary side of the reverse osmosis membrane 44 is increased. As a result, the back pressure on the primary side of the reverse osmosis membrane 44 increases and the flow rate of the treated water 46 is recovered.

  Most of the concentrated liquid 52 discharged from the primary side of the reverse osmosis membrane 44 is circulated to the adjustment tank 30 as the circulating liquid 56 through the first back pressure valve 54. The remaining portion of the concentrated liquid 52 is returned to the denitrification tank 12 via the second back pressure valve 58. The flow rate of the circulating fluid 56 can be adjusted by increasing or decreasing the opening degree of the first back pressure valve 54. Increasing the flow rate of the circulating liquid 56 means increasing the flow rate of the internal liquid 40 supplied to the primary side of the reverse osmosis membrane 44 by the supply pump 38. When the flow rate of the internal liquid 40 is increased, the flow rate of the internal liquid 40 flowing along the reverse osmosis membrane 44 increases, and the cleaning action on the membrane surface of the reverse osmosis membrane 44 increases, contributing to suppression of fouling of the reverse osmosis membrane 44. To do. In addition, by returning a part of the concentrated liquid 52 to the denitrification tank 12 through the second back pressure valve 58, it is possible to prevent salt and organic substances and excessive concentration in the internal liquid 40, and to adjust the salt concentration and the like. It balances to a certain level and helps to suppress fouling of the reverse osmosis membrane 44. When the salt concentration of the organic waste water 72 that is the inflow raw water is high, the opening degree of the second back pressure valve 58 is increased, and the flow rate of the concentrated liquid 52 returned to the denitrification tank 12 is increased. The return destination of the concentrate 52 is not limited to the denitrification tank 12 and may be returned to the nitrification tank 14. The salt concentration can also be adjusted by opening and closing the third back pressure valve 80 provided in the discharge line 78.

  The injection of the fouling inhibitor by the fouling inhibitor injection means 60 is literally performed to suppress the fouling of the reverse osmosis membrane 44. That is, as described above, the membrane separation water 26 contains a soluble organic material that is difficult to biodegrade by biological treatment or a soluble organic material secreted by activated sludge that permeates the membrane material of the membrane separation unit 20. These soluble organic substances cause the fouling of the reverse osmosis membrane 44. Alternatively, bacteria that use these soluble organic substances as nutrients grow on the surface of the reverse osmosis membrane 44 and promote fouling. Therefore, in the fouling inhibitor injection means 60, a fouling inhibitor for disassembling or peeling off or sterilizing the causative substance that has adhered and proliferated on the membrane surface of the reverse osmosis membrane 44 or sterilized is continuously provided in the adjustment tank 30. Inject intermittently or intermittently. In FIG. 1, a single fouling inhibitor injection means 60 is illustrated, but in this embodiment, a plurality of different types of fouling inhibitor injection means may be provided.

  As described above, main means for suppressing fouling of the reverse osmosis membrane 44 include adjustment of the opening of the back pressure valves 54 and 58 and injection of a fouling inhibitor. However, these methods have limitations mainly from the economic aspect. That is, increasing the flow rate of the circulating fluid 56 (in other words, the internal fluid 40) by maximizing the opening degree of the first back pressure valve 54 is effective in suppressing fouling, but the operating power is correspondingly increased. Increased and uneconomical driving. Further, increasing the flow rate of the concentrated liquid 52 returned to the denitrification tank 12 with the opening degree of the second back pressure valve 58 being maximized is also effective for suppressing fouling. As a result, the facility scale of the entire processing system increases, and initial and running costs rise. Further, if the injection amount of the fouling inhibitor is maximized, it is effective for suppressing fouling, but the injection cost of the fouling inhibitor increases, and the excess inhibitor causes contamination of the treated water 46. Therefore, standard operating conditions are set for fouling suppression measures mainly from an economic point of view, and fouling suppression is only temporarily performed when fouling progresses or fouling progress is predicted. It is advisable to increase the operating conditions of the means.

  However, the fouling phenomenon in the reverse osmosis membrane 44 often proceeds abruptly when the causative substance increases due to some factor, and recovery becomes difficult when the degree of fouling exceeds a certain level. It causes a situation that cannot be continued. Therefore, in the present embodiment, forward control described below is executed in order to prevent such an unexpected situation.

  That is, the dissolved organic matter concentration of the biologically treated water is detected by the sensor 68 connected to the nitrification tank 14. The soluble organic matter in the biologically treated water passes through the membrane material of the membrane separation unit 20 as it is and is contained in the membrane separation water, which may cause fouling in the reverse osmosis membrane 44. Therefore, the second controller 70 controls the operation of the chemical solution injection pump 64 and sends it to the adjustment tank 30 from the injection means 60 when the dissolved organic matter concentration detected by the sensor 68 increases. Increase injection volume of 66. Then, the fouling inhibitor concentration of the internal liquid 40 in the adjustment tank 30 increases, and fouling of the reverse osmosis membrane 44 in the reverse osmosis membrane device 42 is suppressed. As a method of increasing the injection amount of the fouling inhibitor 66, the injection flow rate is increased when the injection is continuous, and the injection frequency is increased when the injection is intermittent.

  Further, the second controller 70 increases the opening degree of at least one of the first back pressure valve 54 and the second back pressure valve 58 when the dissolved organic matter concentration transmitted from the sensor 68 increases. It can also be controlled. When the opening degree of these back pressure valves is increased, the back pressure on the primary side of the reverse osmosis membrane 44 decreases. Then, since the flow rate of the treated water 46 that passes through the reverse osmosis membrane 44 decreases, the first controller 50 performs control so as to increase the rotation speed of the supply pump 38 in order to maintain the flow rate of the treated water 46. As a result, the flow rate of the internal liquid 40 supplied to the primary side of the reverse osmosis membrane 44 by the supply pump 38 is increased, and the cleaning action on the membrane surface of the reverse osmosis membrane 44 is enhanced, contributing to suppression of fouling of the reverse osmosis membrane 44. To do. In addition, when the opening degree of the second back pressure valve 58 is increased, the flow rate of the concentrated liquid 52 returned to the denitrification tank 12 increases. Therefore, the salts and organic substances in the internal liquid 40 circulated through the reverse osmosis membrane 44 are used. This contributes to the suppression of fouling.

  In the above description, the case where the operating condition of the fouling suppression means in the reverse osmosis membrane device is controlled by the sensor 68 connected to the nitrification tank 14 based on the dissolved organic matter concentration of the biologically treated water has been described. According to such a method, it is possible to detect the concentration of soluble organic substances that cause fouling at an early stage of biological treatment, and to control the operating conditions of the fouling suppression means, so that safe and reliable forward control is executed. be able to.

  However, the present invention is not limited to such a method. As shown in FIG. 1, a sensor 76 is attached to the supply line of the membrane separation water 26, and the fouling suppressing means in the reverse osmosis membrane device is based on the dissolved organic substance concentration of the membrane separation water 26 detected by the sensor 76. The operating conditions may be controlled. According to this method, non-soluble organic substances such as activated sludge are removed by the membrane separation unit 20, and the membrane separation water 26 does not contain non-soluble organic substances. For this reason, when detecting the soluble organic substance concentration, there is an advantage that the solid-liquid separation operation as the pretreatment can be omitted.

  As described above, according to the organic wastewater regeneration method of the present embodiment, the concentration of soluble organic matter in the biologically treated water of the biological treatment apparatus 10 in the first step or the membrane separation water of the membrane separation unit 20 in the second step is set. Based on this, the operating conditions of the fouling suppression means in the reverse osmosis membrane device 42 are controlled. For this reason, the rapid fouling of a reverse osmosis membrane apparatus can be suppressed.

It is a systematic diagram which shows embodiment of the regeneration method of the organic wastewater which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ......... Biotreatment apparatus, 12 ......... Denitrification tank, 14 ......... Nitrification tank, 16 ......... Stirrer, 20 ......... Membrane separation unit, 22 ......... Air diffuser, 24 ...... Blower, 26 ......... Membrane separation water, 28 ......... Membrane filtration pump, 30 ......... Regulation tank, 32 ......... Circulating pump, 34 ...... Excess sludge, 38 ......... Supply pump, 40 ......... Internal liquid, 42 ......... Reverse osmosis membrane device, 44 ......... Reverse osmosis membrane, 46 ......... Treatment water, 48 ......... Flow meter, 50 ......... First controller, 52 ......... Concentrated liquid, 54 ... ...... First back pressure valve, 56 ......... Circulating fluid, 58 ......... Second back pressure valve, 60 ......... Fouling inhibitor injection means, 62 ......... Medium solution storage tank, 64 ...... Medium solution Infusion pump, 66 ......... Fouling inhibitor, 68 ......... Sensor, 70 ......... Second controller, 72 ...... Organic sewage, 74 ......... Stir Machine, 76 ......... sensor, 78 ......... discharge line, 80 ......... third back pressure valve.

Claims (2)

A first step of biologically treating raw water containing organic matter, a second step of membrane-separating biologically treated water that has undergone the first step, and a third step of treating the membrane-separated water of the second step by a reverse osmosis membrane device In the method for recycling organic sewage comprising
Injected into the reverse osmosis membrane from the injection means of the fouling inhibitor for the reverse osmosis membrane of the reverse osmosis membrane device when the concentration of soluble organic matter in the biologically treated water in the first step or the membrane separation water in the second step is increased A method for regenerating organic sewage characterized by increasing the amount of the fouling inhibitor injected . A first step of biologically treating raw water containing organic matter, a second step of membrane-separating biologically treated water that has undergone the first step, and a third step of treating the membrane-separated water of the second step by a reverse osmosis membrane device In the method for recycling organic sewage comprising
The internal liquid circulated through the reverse osmosis membrane by the internal liquid circulation means for the reverse osmosis membrane of the reverse osmosis membrane device when the concentration of soluble organic matter in the biologically treated water in the first step or the membrane separation water in the second step is increased. A method for regenerating organic sewage characterized in that the amount of circulation of the internal liquid is increased by increasing the opening of a back pressure valve provided in the circulation line .

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