JP2008149226A - Wastewater treatment system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wastewater treatment system capable of suppressing the fouling of a membrane in order to enhance the maintenance properties of the membrane in the production of regenerated water by a membrane separation activated sludge process. <P>SOLUTION: The wastewater treatment system is equipped with a sensor 20a for measuring the pH of the sewage of a tank 5 in which the membrane for filtering water to be treated is installed, a pH adjusting means 11 for injecting an acid in order to adjust the pH of the sewage in the tank 5 in which the membrane is installed, and a monitor control device 10 for calculating the pH becoming a set concentration or above in the solubility of a hardness component on the basis of the pH measured by the sensor 20a to control the injection amount of the acid of the pH adjusting means 11 so as to obtain the calculated pH. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wastewater treatment system for reusing raw water including hardness, such as sewage, miscellaneous wastewater, or industrial wastewater, and more particularly to a wastewater treatment system using a membrane separation activated sludge method and a membrane filtration treatment.

  In recent years, the frequency of droughts has increased, and measures such as securing water sources are important in order to avoid droughts and ensure safety and security. In addition to the development of water storage facilities such as dams, the use of reclaimed water using sewage as a resource is spreading. The Ministry of Land, Infrastructure, Transport and Tourism has set water quality standards for using reclaimed water and promotes the recycling of water.

In general, methods for reclaiming wastewater include removal of organic substances by activated sludge, removal of suspended solids (abbreviated as “SS”) by filtration, and disinfection with a chlorine agent or the like. When higher water quality is required, membrane treatment such as ozone treatment, activated carbon treatment, reverse osmosis membrane is performed.

  Under such circumstances, in recent years, the membrane separation activated sludge method has been put into practical use by the advancement of membrane technology. The membrane-separated activated sludge method is a method for decomposing organic substances by biological treatment, and is characterized in that the activated sludge that has been conventionally performed in the final sedimentation basin is separated by a membrane. Advantages of the membrane-separated activated sludge method are prevention of activated sludge carry-over, downsizing of equipment, and reduction of sludge volume by extending SRT. Taking advantage of these advantages, it is possible to install reclaimed water production equipment on-site, that is, in a facility that is a source of sewage generation.

  In water treatment using a membrane, one of the new problems is that membrane fouling and chemical cleaning are necessary. Substances causing fouling in the raw membrane water include organic matter, manganese, aluminum, hardness (calcium and magnesium), and the like.

  In the case of clean water, water quality standards are set for these substances. In the water purification process, organic substances can be removed by coagulation sedimentation, filtration, activated carbon, and biological treatment. Manganese and aluminum can be removed by manganese sand filtration and coagulation precipitation / filtration, respectively.

  As a method for removing hardness (softening water), [Non-Patent Document 1] discloses a coagulation precipitation method, an ion exchange method, a reverse osmosis method, and a pellet method. As a specific example, Patent Document 1 discloses a water softening method using a cation exchanger. This method is a method of softening water for home appliances, in which the hardness component adsorbed on the cation exchanger is eluted using acidic water obtained by electrolysis and the resin is regenerated using alkaline water. .

  [Patent Document 2] shows an example of water softening by a pellet method. In this method, a fluidized bed crystallization reaction tank, an acid / alkali agent for pH adjustment, and pellets used as nuclei for crystallization of potassium carbonate are used. The pH in the reaction vessel is adjusted to the alkali side, and hardness components in the current water are deposited on the pellets. Treated water is neutralized with an acid such as sulfuric acid and adjusted to a range that satisfies water quality standards such as tap water.

JP-A-6-296963 JP 2001-58102 A Doi, 57th National Waterworks Research Presentation, p292 (2006)

Among the water quality standards for reclaimed water, items related to membrane fouling include organic matter (BOD,
COD), which can be removed at the stage of biological treatment with activated sludge.

  Manganese and aluminum have a sufficiently low water quality standard value, and it is presumed that the concentration of sewage does not increase greatly when used in homes and office buildings.

  On the other hand, the water quality standard value of the hardness of clean water is ≦ 300 mg / L. If the raw water of the tap water is high in hardness and is not softened by the water purification process, the hardness of the sewage is also maintained at a high concentration, which is likely to cause fouling. The water softening method is a technique established in the field of water purification treatment as in the conventional technique described above, but has not been applied to sewage and wastewater considering fouling suppression.

Among the water softening methods described in [Patent Document 1] and [Patent Document 2], the reverse osmosis method (Reverse
Osmosis (hereinafter referred to as RO method) is a treatment for relatively clear raw water. When sewage is used as raw water, the RO method has the disadvantages that the clogging of the membrane due to SS occurs, so that the maintenance becomes complicated and the running cost is further increased.

  On the other hand, the coagulation sedimentation method, the pellet method, and the ion exchange method can be used in the water and industrial water production process, but the system configuration and operation control considering the maintainability of membrane treatment such as membrane separation activated sludge method Does not mention.

  An object of the present invention is to provide a wastewater treatment system capable of suppressing membrane fouling in order to improve membrane maintainability in reclaimed water production by membrane treatment such as membrane separation activated sludge method.

  In order to achieve the above object, the wastewater treatment system of the present invention includes a measuring means for measuring water quality in a tank in which a membrane for filtering sewage is installed, and an acid is injected to adjust the pH in the tank. And a monitoring control means for controlling the acid injection amount of the pH adjusting means so that the solubility of the hardness component becomes a certain concentration or higher based on the water quality measurement result.

  In addition, water softening means is provided in the previous stage of the biological reaction tank, the water softening treatment is performed in the previous stage of the biological reaction tank, the hardness at the time of membrane separation is reduced, and a film of a compound of the remaining hardness component is installed. In this case, reprecipitation is suppressed in the tank and fouling is further reduced.

  In addition, the monitoring control means measures the flow rate of clean water, the flow rate of reclaimed water, predicts the water quality in the reaction tank using a preset inflow pattern, calculates the solubility of the hardness component using the predicted value, The injection amount of the pH adjusting means is controlled.

  In addition, the reclaimed water and the waste water generated from the facility using clean water are mixed to soften the water, thereby reducing the load on the water softening means and reducing the size of the apparatus.

  According to the wastewater treatment system of the present invention, in the sewage treatment by the membrane separation activated sludge method, fouling due to hardness is suppressed, so that the number of times of membrane chemical cleaning is reduced and the maintainability of the membrane is improved.

  Embodiments 1 to 5 of the present invention will be described with reference to the drawings.

  Embodiment 1 of the wastewater treatment system of the present invention will be described with reference to FIG.

  As shown in FIG. 1, clean water supplied from the outside, such as a water purification plant, is stored in a clean water storage tank 13, and the stored clean water is stored in a clean water utilization facility 12 connected to the clean water storage tank 13. Supplied according to the amount of clean water used. A wastewater treatment system 100 is connected to the water supply facility 12. Here, the water use facility 12 is a bath, a washroom, and a kitchen.

  The wastewater treatment system 100 decomposes and removes organic matter in the sewage by the pretreatment / regulation tank 1 in which the screen 2 is immersed, the pump 3a connected to the pretreatment / regulation tank 1, and the activated sludge connected to the pump 3a. A biological reaction tank 4, a membrane separation tank 5 provided adjacent to the biological reaction tank 4 and immersed in a plurality of membrane units 9, a sensor 20 a for measuring pH installed in the membrane separation tank 5, and a sensor A signal is input from 20a, the monitoring controller 10 for controlling the acid solution injection amount of the acid injection device 11 for injecting the acid solution into the membrane separation tank 5, and the biological reaction tank 4 and the membrane separation tank 5 are installed. The air diffuser 6 diffuses the air supplied from the blower 8 through the valve 7.

  A plurality of membrane units 9 are immersed in the membrane separation tank 5 of the wastewater treatment system 100. The pump 3b is connected to the membrane unit 9, and the regenerated water storage tank 14 is connected to the pump 3b. Reclaimed water from which activated sludge, SS, bacteria, etc. have been separated is sent to the reclaimed water storage tank 14. A disinfectant supply device 15 is connected to the reclaimed water storage tank 14 so that sodium hypozinc acid is supplied. The reclaimed water in the reclaimed water storage tank 14 is supplied to a reclaimed water utilization facility 16 such as a toilet, a watering facility, and a landscape water supply facility. Here, the landscape water is water supplied to use amenity such as pond, moat, murmuring, fountain, wall spring and the like.

  The water supplied from the outside such as a water purification plant is stored in the water storage tank 13 and supplied according to the amount of water used in the water supply facility 12. A portion of the sewage discharged from the water use facility 12 is discharged into the sewage, the rest flows down into the pretreatment / regulation tank 1, and a relatively large solid is separated by the screen 2. The sewage from which the solid matter is separated is sent to the biological reaction tank 4 by the pump 3a, and the organic substances in the sewage are decomposed and removed by the activated sludge in the biological reaction tank 4. The treated sewage flows into the membrane separation tank 5 together with some activated sludge.

In the membrane separation tank 5, sewage is sucked by the pump 3 b, activated sludge, SS, bacteria, etc. are separated by the membrane unit 9 and stored in the reclaimed water storage tank 14. Part of the air supplied from the blower 8 is supplied to the surface of the membrane unit 9 by the air diffuser 6, and activated sludge and SS adhering to the membrane surface due to the shear force generated by the flow of sewage generated by the rise of air bubbles and air. Etc. are removed from the film surface. Thereby, blockage of the film surface is prevented.

  Sodium hypochlorite is supplied from the disinfectant supply device 15 to the reclaimed water storage tank 14 to disinfect the reclaimed water. Reclaimed water is supplied from the reclaimed water storage tank 14 in accordance with the amount of reclaimed water used at the reclaimed water utilization facility 16. The reclaimed water used in the reclaimed water utilization facility 16 is discharged into sewage.

  The pH of the sewage is measured by a pH meter installed in the membrane separation tank 5, and the measurement result is sent to the monitoring controller 10. In the monitoring control device 10, the injection amount of the acid solution is controlled by the acid injection device 11 using pH measurement data. The type of acid to be injected from the acid injection device 11 is not particularly limited, but an organic acid that is decomposed by biological treatment is desirable in order to reduce the concentration of the soluble substance in the reclaimed water.

  The main component of the scale, which is derived from hardness and causes fouling, is calcium carbonate. The carbonate is dissolved by the reaction shown in Formula 1.

From the reaction formula of Equation 1, it can be seen that the higher the H ⁺ concentration, the more the equilibrium shifts to the right. That is, the lower the pH, the more CaCO ₃ is precipitated. Therefore, the monitoring control device 10 measures the pH value of the sensor 20a, calculates the difference between the acquired actual measurement value and the set value, and adjusts the injection amount in proportion to the difference. For this injection amount control, a general control method such as PI control can be employed.

  Thus, since the water quality in the tank in which the membrane for filtering the treated water is installed is measured and the pH in the tank is adjusted, the compound of the hardness component in the tank in which the membrane is installed is deposited. To suppress the occurrence of fouling.

  A second embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a block diagram showing the wastewater treatment system of the present embodiment, which is composed of a pretreatment / conditioning tank 31, a biological reaction tank 4, and a membrane separation tank 5 as in the first embodiment.

  In the present embodiment, a portion for injecting sodium hydroxide from the alkali agent injection device 21 is provided at the subsequent stage of the pretreatment / adjustment tank 31 and controlled by a signal from the monitoring control device 10 so as to be stirred by the rotary blades. It has become. A sensor 20b for measuring the pH after crystallization treatment by adding sodium hydroxide is provided on the outlet side of the rear stage of the pretreatment / regulation tank 31.

  An acid injection device 11 that is controlled by a signal from the monitoring control device 10 and injects acid into a pipe that connects the pump 3a and the biological reaction tank 4 is provided, and the pipe between the acid injection unit and the biological reaction tank 4 has a pH. A sensor 20c is provided for measuring. The sensor 20d installed in the membrane separation tank 5 measures water temperature, pH, and alkalinity.

  The clean water stored in the clean water storage tank 13 is supplied according to the amount of clean water used in the clean water utilization facility 12. A portion of the sewage discharged from the water use facility 12 is discharged into the sewage, the rest flows down into the pretreatment / regulation tank 1, and a relatively large solid is separated by the screen 2.

  In the subsequent stage of the pretreatment / adjustment tank 1, sodium hydroxide is injected from the alkali agent injection device 21, and the hardness component is removed by crystallization to become alkaline. The pH after the crystallization treatment is measured by the sensor 20b, and the measurement result is sent to the monitoring control device 10 and fed back to the control of the injection amount of the alkaline agent to adjust the pH in the tank to be alkaline (about pH 9 to 11). . As a result of this adjustment, the reaction formula (1) proceeds to the right, and the main hardness component calcium is precipitated as calcium carbonate. At this time, in order to sufficiently mix the alkali agent and promote crystal growth of calcium carbonate, inflowing water is introduced from a communication hole provided in the lower part of the partition plate, and the inside of the tank is stirred by the rotary blade. The settled precipitate is periodically withdrawn from the lower part of the pretreatment / regulation tank 1 and discharged to an appropriate treatment facility such as sewage.

  Acid is injected from the acid injection device 11 into the sewage after the crystallization treatment, and the pH of the sewage is adjusted so that the water quality is suitable for biological treatment and the set solubility of calcium is obtained. The acid injection amount from the acid injection device 11 is determined by the sensor 20c at the outlet of the pH adjustment tank and the sensor 2d that measures the quality of the membrane filtration treated water.

  The alkali and acid injection control flow will be described in more detail with reference to FIG. The frequency of this injection control is preferably carried out at least about every hour in consideration of daily fluctuations in the quality of the influent water and the amount of recycled water used, but may be set as appropriate.

In step S201, the measured values of the sensors 20b, 20c, and 20d are captured. In step S202, it is diagnosed whether the acquired actual measurement value is abnormal. For example, if there is a difference greater than a set ratio compared to the previous actual measurement value, the actual value reading process is performed again.

In step S203, a set value that is a condition to be satisfied at each of the installation locations of the sensors 20b, 20c, and 20d is read. In the sensor 20b in the pretreatment / regulation tank 1, a lower limit value of pH at which calcium carbonate is precipitated and the hardness in the sewage can be sufficiently reduced is set as a crystallization condition. The sensor 20c at the outlet of the pretreatment / regulation tank 31 sets a pH range in which microorganisms can act well in the biological reaction tank 4. In the membrane separation tank 5 the outlet of the sensor 20d, to set the lower limit of the Ca ²⁺ concentration required to inhibit fouling.

  In step S204, in order to control the injection amount of the alkaline agent, the set value is compared with the actual measurement value, and the difference between the actual measurement value and the set value is calculated. In step S205, the increase / decrease amount of the injection amount is calculated from the calculated difference value. calculate.

  In step S211, the set value is compared with the actual measured value of the pH of the sensor 20c for controlling the injection amount of the acid agent.

  In step S212, the pH range is determined by calculating a pH value that satisfies the set value using an evaluation index relating to the solubility of calcium carbonate, which is the main component of hardness. In this embodiment, a Langeria index is used as an evaluation index. The definition formula of the Langeria index is Equation 2, which is the difference between the pH when calcium carbonate is in the equilibrium state shown in Equation 1 and the actual pH of water. When this index is greater than 0, calcium carbonate precipitates, and when it is less than 0, calcium carbonate dissolves.

Here, [Ca ²⁺ ] is the calcium ion amount (me / L), [Alk] is the total alkalinity (me / L), and S is a correction term relating to the soluble substance concentration.

  In the present embodiment, the pH at which the Langeria index is less than 0 is calculated using the measured values of the water temperature and alkalinity, the set value of the target calcium ion amount, and S = 0.2. Although the correction term S depends on the soluble substance concentration, a constant value is used because it is assumed that the sensitivity to the soluble substance concentration is low and the soluble substance concentration in the sewage is always at a high level.

FIG. 4 shows an example of the correlation between pH and Langeria index. The calculation conditions of this example are Ca ²⁺ = 50 mg / L, Alk = 100 mg / L, T = 25 ° C., S = 0.2. The pH range to be satisfied under this condition is pH <7.81.

  In step S213, the pH evaluated from the Langeria index is compared with the actual pH. In step S214, an acid injection amount is calculated from the comparison result in step S211 and the comparison result in step S213. As in the first embodiment, a general control method such as PI control can be applied to the injection amount control.

  In this example, Langerian index was used as an index of calcium carbonate precipitation, but other indices such as Ryzner stability index, Momentary Excess, Driving force Index, erodibility index, and calcium carbonate scale formation ability were also used. Can also be used.

  Ryzner's stability index RI is expressed by Equation 3, and when the RI is 7 or more, the scale protective film of calcium carbonate does not develop.

  The stability index ME of Momentary Excess is expressed by Equation 4, ME is greater than 0, and no scale is generated.

  The stability index DFI of the driving force index is expressed by Equation 5, where the DFI is less than 1 and the scale dissolves.

Stability index CCPP (Calcium Carbonate)
Precipitation Potential) is expressed by Equation 6, and CCPP is less than 0 and is not saturated.

  The biological treatment after the biological reaction tank 4, the membrane separation treatment, and the use of reclaimed water are the same as in the first embodiment.

  In this way, water softening treatment is performed in the previous stage of the biological reaction tank, the hardness at the time of membrane separation is reduced, and reprecipitation is suppressed in the tank in which the film of the remaining hardness component compound is installed. In addition, fouling can be further reduced.

  A third embodiment of the present invention will be described with reference to FIG. FIG. 5 is a configuration diagram of the wastewater treatment system of this embodiment.

  This embodiment is configured in the same manner as the embodiment shown in FIG. 2, but in this embodiment, the sensor 20b is not provided, and an ion exchange tower of a fluidized bed is provided at the rear stage of the pretreatment / regulation tank 41. A desorption liquid tank 42 which is provided and controlled by a signal from the monitoring control apparatus 10 and supplies a desorption liquid such as an NaCl solution to the ion exchange tower of the pretreatment and adjustment tank 41; and a reclaimed water storage tank 14 by a signal from the monitoring control apparatus 10 A valve 43 is provided when the reclaimed water from is supplied to and shut off from the ion exchange tower of the pretreatment / regulation tank 41.

  The clean water stored in the clean water storage tank 13 is supplied according to the amount of clean water used in the clean water utilization facility 12. A part of the sewage discharged from the water use facility 12 flows down to the pretreatment / regulation tank 41, and a relatively large solid is separated by the screen 2. The subsequent stage of the pretreatment / regulation tank 41 is a fluidized bed ion exchange tower, which is configured to remove hardness components with a cation exchange resin.

In the ion exchange treatment of the ion exchange tower of the fluidized bed, the adsorbed Ca ^{2+ and the} like are periodically desorbed from the exchange capacity of the resin, the quality of the influent water and the amount of treated water. Desorption is performed by closing the gate of the pretreatment / adjustment tank 41 and stopping the inflow of sewage, and then supplying a desorption liquid such as an NaCl solution from the desorption liquid tank 42. The used desorption liquid is discharged into sewage. Subsequently, the valve 43 is opened, the reclaimed water is supplied from the reclaimed water storage tank 14, and the ion exchange resin is washed.

  The sewage softened by the ion exchange treatment is transferred to the biological reaction tank 4 by the pump 3a. At this time, using the measurement results of the sensors 20c and 20d, the amount of acid injected is calculated and the pH of the sewage is adjusted in the same manner as in Example 2. The biological treatment after the biological reaction tank 4, membrane separation treatment and use of reclaimed water are the same as in the second embodiment.

  In this example, an example of the ion exchange method was shown as a softening treatment method other than the crystallization method, but softening treatment was performed by electrodialysis, electrodialysis and diffusion dialysis using a dialysis membrane such as an ion exchange membrane. May be. In electrodialysis using an ion exchange membrane, sewage and NaCl solution are alternately supplied side by side, and if a NaCl solution is used for the anode side polar solution and water is used for the cathode side extreme solution, hypochlorite by the diaphragm method is used. Sodium acid production becomes possible and can be used for disinfection of reclaimed water.

  In this way, water softening treatment is performed in the previous stage of the biological reaction tank, the hardness at the time of membrane separation is reduced, and reprecipitation is suppressed in the tank in which the film of the remaining hardness component compound is installed. In addition, fouling can be further reduced.

  In addition, because the Langeria index is used as an indicator of solubility of hardness components, fouling is possible because water quality management takes into account not only the relationship between pH and solubility of hardness components, but also the influence of other components in wastewater. Can be further reduced.

  A fourth embodiment of the present invention will be described with reference to FIGS. FIG. 6 is a configuration diagram of the wastewater treatment system of this embodiment.

  This embodiment is configured in the same manner as the embodiment shown in FIG. 2, but in this embodiment, the sensors 20b, 20c, and 20d are not provided, and the water storage tank 13 and the water utilization facility 12 are connected. A sensor 20e for measuring the amount of clean water used in the pipe, and a sensor 20f for measuring the amount of reclaimed water used in the pipe connecting the reclaimed water storage tank 14 and the reclaimed water use facility 16 are provided. Signals from the sensors 20e and 20f Is fed back to the monitoring control device 10.

The clean water stored in the clean water storage tank 13 is supplied according to the amount of clean water used in the clean water utilization facility 12. At this time, the amount of clean water used is measured by the sensor 20e, and the measurement result is sent to the monitoring control device 10. The sewage flows down to the pretreatment / regulation tank 31 and then is supplied to the biological reaction tank 4 through the screen 2 and the crystallization treatment as described above. During this time, an alkali agent is injected for crystallization treatment and an acid is injected for pH adjustment.

  Biological treatment after the biological reaction tank 4, membrane separation treatment and use of reclaimed water are performed in the same manner as in the first embodiment. The amount of reclaimed water used is measured by the sensor 20 f and the measurement result is sent to the monitoring control device 10.

  The monitoring control device 10 uses the alkaline agent injection device 21 and the acid injection by using the usage amount of clean water and reclaimed water, the daily fluctuation pattern of the sewage water quality set in advance, and the target value of the water quality in the crystallization treatment and the membrane separation tank 5. A control signal is transmitted to the apparatus 11 to control the injection amount of the alkaline agent and the acid, respectively.

  FIG. 7 shows a control flow of the monitoring control apparatus 10. The frequency of injecting the alkaline agent and the acid is preferably carried out at a frequency of, for example, every hour in consideration of daily fluctuations in the quality of the influent water and the amount of recycled water used, but this frequency can be changed as appropriate.

  In step S301, the daily fluctuation pattern of the quality of the inflow water to the pretreatment / regulation tank 31 input in advance to the monitoring control apparatus 10 is acquired. The water quality items are pH, alkalinity, hardness, and water temperature. The daily fluctuation pattern of the influent water quality depends not only on the use of the facility where the waste liquid treatment system is installed, but also on weekdays or holidays. Therefore, each pattern is recorded and can be called as appropriate.

  In step S302, the usage amounts of clean water and reclaimed water that change with time are acquired. The amount of water used is the capacity of the pretreatment / regulation tank 31, and the water quality at the time of entering the crystallization process of sewage is calculated. Get past data. In step S303, the reclaimed water production plan water amount is acquired.

  In step S304, the acquired data is used to determine the alkalinity, hardness, pH, and inflow water amount at the entrance of the crystallization process. For the evaluation of the concentration, an extrusion flow or a mixing tank model can be used in consideration of the actual shape of the pretreatment / adjustment tank 31 and the residence time.

  In step S305, the injection amount of the alkaline agent necessary for performing the crystallization process at an appropriate pH is obtained using the information in step S304.

In step S306, evaluation is performed in consideration of a decrease in alkalinity due to crystallization and a change in pH during biological treatment. In crystallization, since CaCO ₃ is removed as a precipitate, the alkalinity after the crystallization treatment is taken into consideration. On the other hand, in biological treatment with activated sludge, a decrease in pH due to nitrification of ammonia nitrogen, that is, an increase in pH due to consumption of alkalinity or denitrification occurs. Therefore, the amount of change in pH is corrected in consideration of whether the treatment process carried out in the biological reaction tank is a process for nitrification or denitrification.

In step S307, the range of pH satisfying the condition is evaluated using the target value of the evaluation index regarding the alkalinity and pH correction value, the amount of treated water, the variation pattern of the water temperature, and the solubility of CaCO ₃ , and the pH satisfying the condition. The amount of acid injection required to satisfy the above range is obtained. As the evaluation index, the index described in the second embodiment such as the Langeria index is used.

  In this example, control was performed in consideration of daily fluctuation patterns such as alkalinity and hardness of the influent water. However, when the fluctuations of these water quality items are small, these are regarded as constant and fluctuation patterns of other necessary parameters are considered. It is also possible to set the injection rate of the chemical solution more easily by using the amount of clean water and reclaimed water.

  As described above, the water quality in the reaction tank is predicted using the inflow pattern set in advance with respect to the quality and amount of the inflow raw water, and the pH is adjusted by calculating the solubility of the hardness component using the predicted value. The number of monitoring devices used in the processing system can be reduced, and in addition to suppressing fouling, maintenance and management of the entire system can be simplified.

  A fifth embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a configuration diagram of the wastewater treatment system of this embodiment.

Although this embodiment is configured in the same manner as the embodiment shown in FIG. 6, in this embodiment, after the crystallization treatment by adding sodium hydroxide to the outlet side of the rear stage of the pretreatment / regulation tank 31. The sensor 20b for measuring pH, the sensor 20c for measuring pH in the pipe between the acid injection part and the biological reaction tank 4, and the sensor 20d for the membrane separation tank 5 are sensors for measuring water temperature, pH and alkalinity. 20d, and the signals of the sensors 20b, 20c, and 20d are fed back to the monitoring control device 10. The reclaimed water utilization facility 16 is connected to piping on the downstream side of the clean water utilization facility 12.

  The discharged sewage used in the water use facility 12 and the reclaimed water use facility 16 flows down to the pretreatment / regulation tank 31. The amounts of clean water and reclaimed water used are measured by the sensors 20e and 20f, respectively, and the measurement results are sent to the monitoring control device 10.

  The sewage flows down to the pretreatment / regulation tank 31, and then is supplied to the biological reaction tank 4 through the screen 2 and the crystallization treatment. During this time, an alkali agent is injected for crystallization treatment and an acid is injected for pH adjustment. The biological treatment after the biological reaction tank 4, membrane separation treatment and use of reclaimed water are performed in the same manner as in the first embodiment.

  The monitoring control device 10 transmits a control signal to the alkaline agent injection device 21 and the acid injection device 11 by using the amounts of clean water and reclaimed water used, the crystallization process, and the target value of the water quality in the membrane separation tank 5, and the alkaline agent. And the amount of acid injected are controlled respectively.

  FIG. 9 shows a control flow of the monitoring control apparatus 10. The frequency of injecting the alkaline agent and the acid is preferably carried out at a frequency of, for example, every hour in consideration of daily fluctuations in the quality of the influent water and the amount of recycled water used, but this frequency can be changed as appropriate.

  In step S401, the measured values of the sensors 20b, 20c, 20d, 20e, and 20f are captured. In step S402, it is diagnosed whether the acquired value is abnormal. In step S403, a set value that is a condition that should be satisfied at each of the installation locations of the sensor 20c and the sensor 20d is read.

  In step S404, the water supply ratio is calculated. The ratio of clean water is defined as the ratio of sewage that takes into account the clean water newly added to the reclaimed water after the crystallization treatment. Clean water is newly supplied from the outside and causes hardness. On the other hand, reclaimed water has been softened and has a lower hardness than clean water. Therefore, assuming that the regular crystallization treatment is one cycle, the water supply ratio is the lowest immediately after the crystallization treatment, and the hardness is also low. With the use of clean water and reclaimed water, the ratio of clean water increases and the hardness gradually increases.

  In step S405, crystallization conditions are set in accordance with the R value (abbreviation of the Ratio value) which is the water supply ratio. When the R value is smaller than the set value, crystallization treatment is not performed, and acid injection for adjusting the pH of the membrane separation tank 5 is performed. On the other hand, when the R value is equal to or greater than the set value, the pH at the outlet of the pretreatment / regulation tank 31 is set to a sufficiently high value as shown in FIG.

  Regarding the injection of the alkaline agent, the processing of Steps S406 to S408 is performed, and regarding the injection of the acid agent, the processing of Step S411 to Step S415 is performed.

  In this way, since the mixed water of the reclaimed water and the waste water generated from the facility using the clean water is softened, in addition to the suppression of fouling, the load of the softening means is reduced at sites with a relatively high regeneration rate. Further, the apparatus can be miniaturized.

  According to the above embodiment, in a reclaimed water production facility using a membrane such as a membrane separation activated sludge method, since the device configuration is capable of suppressing fouling caused by hardness, the number of times of membrane chemical cleaning is reduced, and the membrane The maintainability can be improved.

It is an apparatus block diagram of the wastewater treatment system which is Example 1 of this invention. It is an apparatus block diagram of the waste water treatment system which is Example 2 of this invention. It is a flowchart which shows an example of the processing flow of a monitoring control apparatus. It is explanatory drawing which shows the example of evaluation of the water quality conditions in a membrane separation tank. It is an apparatus block diagram of the wastewater treatment system of Example 3 of this invention. It is an apparatus block diagram of the waste water treatment system of Example 4 of this invention. It is a flowchart which shows an example of the processing flow of a monitoring control apparatus. It is an apparatus block diagram of the waste water treatment system of Example 5 of this invention. It is a flowchart which shows an example of the processing flow of a monitoring control apparatus. It is explanatory drawing which shows an example of the setting method of the water quality conditions of a crystallization tank.

Explanation of symbols

1,31,41 Pretreatment / regulation tank 2 Screen 3a, 3b Pump 4 Biological reaction tank 5 Membrane separation tank 6 Air diffuser 7, 43 Valve 8 Blower 9 Membrane unit 10 Monitoring controller 11 Acid injection device 12 Facility for using water 13 Water Supply Tank 14 Reclaimed Water Storage Tank 15 Disinfectant Supply Device 16 Reclaimed Water Utilization Facility 19 Bubbles 20a to 20f Sensor 21 Alkaline Agent Injection Device 42 Desorption Solution Tank 100 Wastewater Treatment System

Claims (9)

  A sensor for measuring the pH of sewage in a tank in which a membrane for filtering treated water is installed; pH adjusting means for injecting acid to adjust the pH of sewage in the tank in which the membrane is installed; and A wastewater treatment system comprising a monitoring control device for controlling an acid injection amount of the pH adjusting means so that a solubility of a hardness component becomes a pH equal to or higher than a set concentration based on a pH measured by a sensor.   The 1st sensor which measures the pH of the treated water of the membrane filtration tank in which the membrane for filtering treated water was installed, the biological treatment tank provided in the preceding paragraph of the membrane filtration tank, and the sewage in the membrane filtration tank PH adjusting means for injecting acid to adjust the pH of the water, softening means for removing the hardness component of the sewage provided in the front stage of the pH adjusting means, and measuring the pH of the sewage of the water softening means The biological treatment in the biological treatment tank is performed based on the second sensor and the pH measured by the first sensor and the second sensor so that the solubility of the hardness component becomes a pH equal to or higher than the set concentration. And a wastewater treatment system comprising a monitoring control device for controlling the amount of acid injected by the pH adjusting means.   The water softening means comprises an alkaline agent injection device for injecting an alkaline agent into the sewage in the tank, and a third sensor for measuring the pH of the sewage at the tank outlet, and the sewage measured by the third sensor. The wastewater treatment system according to claim 2, wherein the pH adjusting means controls the sewage in the tank to be alkaline based on the pH.   The wastewater treatment system according to claim 2 or 3, wherein the pH is calculated by calculating a Langlia index.   The wastewater treatment system according to claim 2, wherein the water softening means is constituted by an ion exchange resin tower having a fluidized bed.   The wastewater treatment system according to claim 2, wherein the water softening means is a crystallization method, an ion exchange method, or a dialysis method.   A fourth sensor that measures the amount of clean water used, a fifth sensor that measures the amount of recycled water used, a membrane filtration tank in which a membrane for filtering sewage is installed, and a front stage of the membrane filtration tank A biological treatment tank, pH adjusting means for injecting acid to adjust the pH of the treated water in the membrane filtration tank, and soft water for removing the hardness component of sewage provided in the preceding stage of the pH adjusting means , Means for use of clean water and reclaimed water measured by the fourth sensor and the fifth sensor, preset daily fluctuation patterns of sewage water quality, water quality targets for soft water treatment and membrane filtration tanks A wastewater treatment system comprising a monitoring controller for controlling the water softening means and the acid injection amount of the pH adjusting means based on the value.   A first sensor for measuring the pH of the sewage in the membrane filtration tank, and a pH of the sewage in the water softening means, which are combined with the water used for the reclaimed water and the water used for the reclaimed water. The wastewater treatment system according to claim 7, further comprising: a second sensor configured to control the measurement value measured by the first and second sensors to be a set value.   A pretreatment / conditioning tank that separates solids from sewage from a water supply facility, a biological reaction tank connected to the subsequent stage of the pretreatment / adjustment tank, and a subsequent stage of the biological reaction tank, A wastewater treatment system comprising a membrane separation tank in which a membrane for filtration is installed, and a pH adjusting means for controlling the amount of acid injected so that the solubility of hardness components in the membrane separation tank has a pH equal to or higher than a set concentration.

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