Wastewater treatment method and water treatment apparatus

Abstract

To provide a wastewater treatment method and a wastewater treatment apparatus capable of rapidly detecting signs of clogging of a separation membrane, while stably and efficiently performing wastewater treatment with appropriate fouling control.SOLUTION: In the wastewater treatment method using the membrane separation activated sludge method, the organic matter concentration in the liquid phase of the membrane-filtered raw water within a membrane separation activated sludge tank and the organic matter concentration in the membrane-filtered water are measured. The difference between these concentrations serves as a monitoring indicator. When the monitoring indicator increases while the sludge retention time in the membrane separation activated sludge tank is 6 days or longer, one or more of the following treatments is performed: increasing the amount of cleaning air supplied to the membrane separation activated sludge tank, shortening the filtration duration, or shortening the sludge retention time in the membrane separation activated sludge tank. When the monitoring indicator increases with a sludge retention time exceeding 35 days, the operation conditions are adjusted to shorten the sludge retention time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wastewater treatment method and a wastewater treatment device, and more particularly to a wastewater treatment method and a wastewater treatment device that utilize a membrane separation activated sludge process. [Background technology]

[0002] In conventional sewage and septic tank sludge treatment, the mainstream method is to directly biologically treat the sludge after removing impurities using methods such as the activated sludge process to remove organic matter and nitrogen, and the membrane bioreactor has also been adopted as one of the treatment methods.The membrane bioreactor has the advantage of increasing the MLSS (Mixed Liquor Suspended Solids) concentration in the biological treatment tank and reducing the site area because solid-liquid separation is performed using membrane separation.

[0003] In recent years, a method of reducing the burden of biological treatment has become mainstream: first dewatering sewage and septic tank sludge, reusing the dewatered cake as solid fuel, and limiting the biological treatment to the dewatered separated liquid. Furthermore, even in facilities that anaerobically digest biomass such as sludge and food waste, which have been increasing in number in recent years, and recover methane gas, the anaerobic digestion sludge must be biologically treated after dewatering. Even in such cases, the membrane bioreactor is often used for biological treatment, reducing the site area.

[0004] As an example of a technology utilizing the membrane bioreactor, Japanese Patent No. 5868217 (Patent Document 1) describes a membrane bioreactor in which water to be treated is biologically treated with activated sludge in a biological reactor, and the mixed liquor in the biological reactor is subjected to solid-liquid separation using a membrane separator, and the membrane-filtered water that has permeated the separation membrane is removed from the reactor. The membrane bioreactor describes a membrane bioreactor in which the organic matter concentration is determined based on one of COD (chemical oxygen demand), BOD (biological oxygen demand), TOC (total oxygen demand), total sugar concentration, protein concentration, uronic acid concentration, and E260 (ultraviolet absorbance at a wavelength of 260 nm). The difference in organic matter concentration between the liquid phase of the mixed liquor in the reactor and the membrane-filtered water, or the ratio of the organic matter concentration between the liquid phase of the mixed liquor in the reactor and the membrane-filtered water, is used as an adjustment index. When the adjustment index increases, the amount of activated sludge in the biological reactor is increased, and when the adjustment index decreases, the amount of activated sludge in the biological reactor is decreased, thereby suppressing membrane fouling.

[0005] In Japanese Patent No. 4046661 (Patent Document 2), organic wastewater is treated with activated sludge in a biological treatment tank, and a submerged membrane separator serving as a first separation means submerged in the biological treatment tank separates the activated sludge mixed liquid into solid and liquid. COD containing biological polymers accumulated in the biological treatment tank by the activated sludge treatment is separated into solid and liquid from the activated sludge mixed liquid in a timely manner by a second separation means, thereby maintaining the amount of activated sludge in the biological treatment tank at a high concentration while maintaining the amount of biological polymers in the activated sludge mixed liquid at a low concentration. The method for treating wastewater is characterized by measuring the COD in the membrane filtrate that has passed through the submerged membrane separation device, measuring the COD in the filtration means filtrate obtained by filtering the activated sludge mixed liquid in the biological treatment tank using a filtration means having pores with a predetermined diameter larger than the pores of the filtration membrane of the submerged membrane separation device, and separating COD containing biological polymers from the activated sludge mixed liquid by a second separation means when the COD difference value obtained by subtracting the COD in the membrane filtrate from the COD in the filtration means filtrate is equal to or greater than a predetermined value.

[0006] Japanese Patent No. 5822264 (Patent Document 3) describes a method for operating a membrane bioreactor activated sludge treatment device equipped with an aeration tank in which an aeration means is submerged and arranged to diffuse aeration into the liquid being treated in the activated sludge, and a membrane separation tank in which a membrane separation device is submerged and arranged to obtain a permeate from the liquid being treated in the activated sludge, in which the method adjusts the amount of air diffused per unit time of the aeration means based on the organic matter concentration in the supernatant liquid of the liquid being treated in the activated sludge and the BOD / SS load value, so that when the organic matter concentration is equal to or greater than a predetermined value, the amount of air diffused per unit time of the aeration means is increased if the BOD / SS load value is equal to or greater than the predetermined value, and the amount of air diffused per unit time of the aeration means is decreased if the BOD / SS load value is less than the predetermined value.

[0007] Japanese Patent Publication No. 2014-193452 (Patent Document 4) describes a method for treating organic wastewater, in which organic wastewater is introduced into a tank containing activated sludge, subjected to biological treatment, and treated water is obtained by solid-liquid separation using a membrane separation device installed in the tank or downstream thereof.When the amount of extracellular ATP in the activated sludge or the rate of increase in the amount of extracellular ATP in the activated sludge reaches a predetermined standard value, the method controls at least one condition selected from the amount of air diffused to the membrane separation device, the cleaning conditions of the membrane separation device, the coagulant injection conditions for injecting a coagulant into the tank containing the water to be treated, the filtration flux of the membrane separation device, and the amount of activated sludge withdrawn from the tank containing the water to be treated. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5868217 [Patent Document 2] Patent No. 4046661 [Patent Document 3] Patent No. 5822264 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-193452 Summary of the Invention [Problem to be solved by the invention]

[0009] When dewatering organic sludge such as sewage, septic tank sludge, and anaerobic digestion sludge, inorganic coagulants and polymer coagulants (polymers) are added to the sludge to cause it to flocculate before dewatering. The rate at which polymer coagulants are added is determined by the state of the flocs, but if the properties of the sludge change and there is an excess or deficiency, this will lead to an increase in the concentration of suspended solids (SS) in the dewatered separated liquid and an increase in residual polymers in the filtrate, which will increase the concentration of polymer coagulants in the raw water for biological treatment.

[0010] Polymer flocculants are often persistent, meaning they are difficult to decompose by microorganisms, and have a molecular weight of over 1 million. Such polymer flocculants are usually captured by the separation membrane used in the membrane bioreactor. However, as the concentration of polymer flocculants in the tank increases, a layer called a gel layer forms on the separation membrane, which can lead to fouling. Therefore, measures to appropriately suppress fouling are necessary.

[0011] The invention described in Reference 1 proposes to use the difference in organic matter concentration between the mixed liquor in the tank and the membrane-filtered water, and to increase the amount of activated sludge in the biological reactor when the difference in concentration increases. However, with this treatment method, the increased activated sludge or its extracellular matter and the polymer flocculant in the biological reactor may further bind together in the biological reactor, causing further deposition of a gel layer on the separation membrane, which may result in insufficient fouling control.

[0012] In the fouling suppression method using a second separation means as described in Patent Document 2, it is necessary to consider not only the problem of the first separation means but also the problem of membrane clogging of the second separation means, which makes maintenance processing cumbersome. The method of adjusting the aeration air volume based on the organic matter concentration and BOD / SS load value in the supernatant liquid of the treated liquid in activated sludge as described in Patent Document 3, or the fouling control method based on the amount of extracellular ATP as described in Patent Document 4, like other conventional technologies, are still not sufficient in terms of quickly detecting signs of separation membrane clogging, suppressing fouling, and performing long-term stable wastewater treatment.

[0013] In view of the above problems, the present invention provides a wastewater treatment method and a wastewater treatment device that can quickly detect signs of clogging of a separation membrane and perform wastewater treatment stably and efficiently while appropriately suppressing fouling. [Means for solving the problem]

[0014] As a result of intensive research by the present inventors to solve the above problems, they have found that it is effective to use the difference between the organic matter concentration in the liquid phase of membrane-filtered raw water in a membrane bioreactor and the organic matter concentration in membrane-filtered water (membrane permeate water) obtained by membrane filtration as a monitoring index, and to carry out specific treatment based on this monitoring index.

[0015] One aspect of an embodiment of the present invention, which has been completed based on the above findings, is a wastewater treatment method using a membrane bioreactor, which comprises measuring the organic matter concentration in the liquid phase of membrane-filtered raw water in a membrane bioreactor tank and the organic matter concentration in the membrane-filtered water, using the difference as a monitoring index, and adjusting operating conditions so that, when the monitoring index increases, one or more of the following treatments are performed: increasing the amount of cleaning air supplied to the membrane bioreactor tank, shortening the filtration duration, or increasing the amount of sludge extracted from the membrane bioreactor tank.

[0016] In one embodiment, the wastewater treatment method according to an embodiment of the present invention performs a process of increasing the amount of sludge withdrawn from the membrane separation activated sludge tank when the monitoring index exceeds the first reference value, and when the monitoring index exceeds a second reference value higher than the first reference value, performs one or more processes of increasing the amount of cleaning air supplied to the membrane separation activated sludge tank or shortening the filtration duration.

[0017] In another aspect, an embodiment of the present invention is a wastewater treatment method using a membrane separation activated sludge method, which measures the organic matter concentration in the liquid phase of the membrane filtration raw water and the organic matter concentration of the membrane filtrate in the membrane separation activated sludge tank, uses the difference as a monitoring index, and when the sludge retention time in the membrane separation activated sludge tank is 6 days or more and the monitoring index increases, adjusts the operating conditions to increase the amount of sludge withdrawn from the membrane separation activated sludge tank, and when the sludge retention time in the membrane separation activated sludge tank is less than 6 days and the monitoring index increases, adjusts the operating conditions to reduce the amount of sludge withdrawn from the membrane separation activated sludge tank.

[0018] In one embodiment, the wastewater treatment method according to an embodiment of the present invention adjusts the operating conditions to perform a process of increasing the amount of sludge withdrawn from the membrane separation activated sludge tank when the sludge retention time in the membrane separation activated sludge tank is 6 days or more and the monitoring index increases, in combination with a process of performing one or more of increasing the amount of cleaning air supplied to the membrane separation activated sludge tank and shortening the filtration duration. When the sludge retention time in the membrane separation activated sludge tank is less than 6 days and the monitoring index increases, the operating conditions are adjusted to perform a process of reducing the amount of sludge withdrawn from the membrane separation activated sludge tank, in combination with a process of performing one or more of increasing the amount of cleaning air supplied to the membrane separation activated sludge tank and shortening the filtration duration.

[0019] In one embodiment, the wastewater treatment method according to an embodiment of the present invention includes an organic matter concentration including any one of COD, BOD, TOC, or the organic matter concentration fractionated to a molecular weight of 20,000 or more as a result of measurement by organic carbon detection type size exclusion chromatography.

[0020] In one embodiment, the wastewater treatment method according to an embodiment of the present invention further includes performing any one or more of ozone decomposition treatment, accelerated oxidation treatment, or activated carbon adsorption treatment on at least a part of the raw water for membrane filtration when a monitoring index increases.

[0021] In one embodiment, the raw water for membrane filtration in the wastewater treatment method according to an embodiment of the present invention is a dewatered separation liquid generated after adding a polymer flocculant to sludge containing organic matter and performing a dehydration treatment.

[0022] In yet another embodiment, the wastewater treatment method according to an embodiment of the present invention reduces the addition rate of the polymer flocculant added to the raw water for membrane filtration in the dehydration treatment before being supplied to the membrane separation activated sludge tank when the monitoring index increases.

[0023] On one side, a wastewater treatment apparatus according to an embodiment of the present invention includes a membrane separation activated sludge tank that performs membrane separation treatment on raw water for membrane filtration in the presence of activated sludge to obtain membrane-filtered water, an aeration device that aerates the membrane separation activated sludge tank, a suction pump that sucks the membrane-filtered water from the membrane separation activated sludge tank, a sludge discharge pump that draws out sludge from the membrane separation activated sludge tank, and uses the difference value between the organic matter concentration in the liquid phase of the raw water for membrane filtration in the membrane separation activated sludge tank and the organic matter concentration of the membrane-filtered water as a monitoring index. When the monitoring index increases, a control device that controls the operating conditions of the aeration device, the suction pump, and the sludge discharge pump to perform any one or more of the following treatments: increasing the amount of cleaning air supplied to the membrane separation activated sludge tank, shortening the filtration duration, or increasing the amount of sludge drawn out from the membrane separation activated sludge tank.

Advantages of the Invention

[0024] According to the present invention, it is possible to provide a wastewater treatment method and a wastewater treatment apparatus that can quickly detect signs of clogging of the separation membrane and stably and efficiently perform wastewater treatment while appropriately suppressing fouling.

Brief Description of the Drawings

[0025] [Figure 1] It is a schematic diagram showing an example of a wastewater treatment apparatus according to an embodiment of the present invention. [Figure 2] 1 is a graph showing an example of the relationship between sludge retention time (SRT) and a monitoring index (ΔS-CODMn). [Figure 3] 1 is a graph showing an example of the relationship between SRT and transmembrane pressure. [Figure 4] 1 is a graph showing an example of the relationship between SRT and 5C filter paper filtration amount. [Figure 5] 1 is a graph showing an example of the relationship between BOD-SS load and ΔS-CODMn. [Figure 6] 1 is a graph showing an example of the relationship between BOD-SS load and transmembrane pressure. [Figure 7] 1 is a graph showing an example of the relationship between BOD-SS load and 5C filter paper filtration volume. [Figure 8] 1 is a graph showing an example of the relationship between ΔS-CODMn and transmembrane pressure. [Figure 9] 1 is a graph showing an example of the relationship between ΔS-CODMn and the amount of 5C filter paper filtration. DETAILED DESCRIPTION OF THE INVENTION

[0026] A wastewater treatment device and a wastewater treatment method according to embodiments of the present invention will be described below with reference to the drawings. In the following description of the drawings, identical or similar parts are designated by identical or similar reference numerals. Note that the embodiments shown below are examples of devices and methods that embody the technical idea of ​​this invention, and the technical idea of ​​this invention does not limit the structure, arrangement, etc. of component parts to those described below.

[0027] As shown in FIG. 1, a wastewater treatment device according to an embodiment of the present invention includes a membrane bioreactor activated sludge tank 1 for treating wastewater using a membrane bioreactor activated sludge method to obtain treated sludge and membrane-filtered water, an aeration device 2 for aerating the membrane bioreactor activated sludge tank 1, a suction pump 3 for sucking the membrane-filtered water from the membrane bioreactor activated sludge tank 1, a wastewater pump 4 for extracting sludge from the membrane bioreactor activated sludge tank 1, and a control device 8 for controlling the operating conditions of the membrane bioreactor activated sludge tank 1.

[0028] The target of treatment is not particularly limited as long as it is organic wastewater containing organic matter. In particular, dehydrated separated liquid of organic sludge, including one or more of sewage / septic tank sludge, primary sewage sludge, excess sewage sludge, food waste, and anaerobic digestion sludge of biomass, can be used as raw water for membrane filtration in the membrane bioreactor activated sludge tank 1. Because the dehydrated separated liquid contains a polymer flocculant, over a long period of treatment in the membrane bioreactor activated sludge tank 1, the polymer flocculant contained in the dehydrated separated liquid aggregates to form a gel layer, which adheres to the separation membrane 10 in the membrane bioreactor activated sludge tank 1 and is prone to fouling. By performing biological treatment using the wastewater treatment device according to an embodiment of the present invention, stable treatment can be achieved over a long period of time while suppressing fouling.

[0029] The dehydrated separated liquid is composed of suspended solids (SS), soluble COD (COD Cr , COD Mn The dehydrated separated liquid may contain, but is not limited to, SS of 100 to 3000 mg / L, more typically 500 to 2000 mg / L. The dehydrated separated liquid may contain COD Cr Contains 500 to 10,000 mg / L, more typically 1,000 to 5,000 mg / L, and COD Mn The dehydrated effluent contains 100 to 5000 mg / L, more typically 500 to 3000 mg / L of BOD. The dehydrated effluent contains 500 to 5000 mg / L, more typically 1000 to 3000 mg / L of BOD, and 250 to 4000 mg / L, more typically 500 to 2000 mg / L of TOC. The dehydrated effluent contains 10 to 500 mg / L of total nitrogen (TN), more typically 50 to 300 mg / L of total phosphorus (TP), and 5 to 200 mg / L, more typically 10 to 100 mg / L of total phosphorus. The dehydrated effluent contains a mixture of organic nitrogen (TN) and inorganic nitrogen (NO). x -N, NH4-N) is 5 to 300 mg / L, more typically 50 to 200 mg-N / L.

[0030] In particular, if the dewatered separated liquid contains 500 mg / L or more of SS, the polymer flocculant adsorbed to the SS will have a greater effect of flowing into the membrane bioreactor activated sludge tank 1, making fouling more likely to progress. Also, if the dewatered separated liquid contains 50 mg / L or more of organic nitrogen, polymeric organic matter will be produced during the protein decomposition process, making it more likely that a gel layer will form.

[0031] In addition, the BOD / COD in the dehydrated separated liquid Cr When the ratio is 0.7 or less, the proportion of persistent and slowly degradable organic matter increases, and they tend to combine with the polymer flocculant in the membrane bioreactor tank to form a gel layer. Furthermore, when the types of sludge to be dewatered include sludge from primary sedimentation tanks, human waste sludge, food waste, and other sludge that has not undergone biological treatment, the sludge properties tend to fluctuate. Pre-dewatering such sludge can result in an excess or insufficient polymer addition rate, which can lead to the polymer flocculant easily leaking into the filtrate.

[0032] When using dehydrated separated liquid as membrane filtration raw water, the organic sludge undergoes the following pretreatment before being supplied to the membrane bioreactor activated sludge tank 1. For example, the pretreatment involves adding a polymer flocculant and, if necessary, an inorganic flocculant to the organic sludge, followed by stirring to perform flocculation treatment. Because the surface of organic sludge is generally negatively charged, it is preferable to use a cationic polymer as the polymer flocculant. The molecular weight of the polymer flocculant is preferably 1 to 15 million, preferably 1 to 10 million, and more preferably 1 to 7.5 million. The addition rate of the polymer flocculant is typically 0.2 to 4 w / w% relative to TS, more preferably 0.5 to 3 w / w%. The selection and addition rate of the polymer flocculant are preferably determined by flocculation tests or laboratory-scale dehydration tests.

[0033] Inorganic coagulants that can be used include polyferric sulfate, ferric chloride, aluminum sulfate, and polyaluminum chloride (PAC). Among these, polyferric sulfate is preferred from the standpoint of chemical costs and corrosion prevention. The addition rate of the inorganic coagulant should also be determined by coagulation tests, laboratory-scale dehydration tests, etc.

[0034] Methods for adding inorganic flocculants include a pre-addition method in which inorganic flocculants are added before sludge concentration, a post-addition method in which inorganic flocculants are added after sludge concentration, and a dual-addition method in which inorganic flocculants are added both before and after sludge concentration. Among these, the post-addition method or dual-addition method is preferred from the viewpoints of improving dewaterability and supplying phosphorus necessary for subsequent biological treatment to the separated liquid side.

[0035] The flocculated sludge obtained by the above flocculation treatment can be thickened before dehydration to improve the treatment speed during dehydration and reduce the moisture content of the dehydrated sludge. Mechanical thickening can be used for the thickening treatment, and the thickener may be of any type, including rotary, gravity, or pressure.

[0036] The concentrated sludge obtained by the concentration treatment is further dehydrated to obtain dehydrated sludge and dehydrated separated liquid. The dehydrator may be a centrifugal dehydrator, a belt press dehydrator, a filter press dehydrator, a screw press dehydrator, a rotary press dehydrator, an electroosmotic dehydrator, or the like.

[0037] In particular, a screw press dehydrator is preferred because it can achieve a low moisture content with low power consumption. A screw press dehydrator is provided with a cylindrical outer cylinder, a screw shaft concentric with the cylindrical outer cylinder, and screw blades, and is formed with a thickening section on the mixed sludge supply side and a squeezing section on the dehydrated cake discharge side in which the space between the cylindrical outer cylinder and the screw shaft gradually narrows in the direction of movement of the mixed sludge, and the cylindrical outer cylinder is provided with a plurality of openings for discharging separated liquid.

[0038] Among these, the shaft-sliding screw press dehydrator has a mechanism in which the screw shaft moves parallel to the direction of the dehydrated sludge outlet, forcibly discharging the dehydrated sludge. The use of a screw press dehydrator can significantly reduce the moisture content of the dehydrated cake. Furthermore, in addition to dehydration devices that combine an independent screen and dehydrator, dehydration devices that include a thickening section in the front stage that performs the function of a screen and a pressing section in the rear stage, where the screen and dehydrator are integrated, are preferred because they do not require a separate screen and therefore have a simpler device configuration.

[0039] In the membrane bioreactor tank 1, the membrane-filtered raw water flowing into the tank 1 undergoes biological treatment using activated sludge, where organic matter is removed by microbial reaction using activated sludge, and nitrogen is removed by nitrification-denitrification, and activated sludge and treated water are separated by membrane separation.

[0040] The biological treatment in the membrane bioreactor tank 1 may be any method capable of removing organic matter and nitrogen, such as a circulating nitrification-denitrification method or a step-flow nitrification-denitrification method. The sludge concentration (MLSS) of the activated sludge is typically 4,000 to 18,000 mg / L, more preferably 6,000 to 15,000 mg / L, and is desirably adjusted according to the treatment conditions. For example, a sludge concentration meter 7 for measuring the MLSS in the membrane bioreactor tank 1 may be installed in the membrane bioreactor tank 1.

[0041] When nitrogen is removed from membrane-filtered water, if alkalinity is insufficient during nitrification, an alkaline agent such as sodium hydroxide solution (NaOH) can be added by a chemical addition means (not shown), and if organic matter is insufficient during denitrification, an organic matter such as methanol (CHOH) can be added.

[0042] A separation membrane 10 is housed in the membrane bioreactor activated sludge tank 1. The separation membrane 10 may be a microfiltration (MF) membrane or an ultrafiltration (UF) membrane. In particular, using a membrane with a pore size of 0.2 μm or more or a molecular weight cutoff of 1 million or more enables stable operation over the long term while suppressing fouling.

[0043] As for membrane materials, organic membranes such as PSF (polysulfone), PE (polyethylene), CA (cellulose acetate), PAN (polyacrylonitrile), PP (polypropylene), PVDF (polyvinylidene fluoride), and PTFE (polytetrafluoroethylene) can be used, while inorganic membranes can be made of ceramic. The filtration method can be either dead-end filtration or cross-flow filtration, but cross-flow filtration is preferable from the perspective of suppressing fouling. There are no particular restrictions on the type of membrane module, and hollow fiber, flat membrane, spiral, tubular, monolithic, and other types can be used.

[0044] The aeration device 2 can include an aeration device 21 housed in the membrane bioreactor activated sludge tank 1 and a blower 22 that supplies a gas such as air to the aeration device 21. The aeration device 2 is arranged so that air bubbles hit the membrane surface of the separation membrane 10. Typically, the aeration device 2 is arranged below or at the bottom of the separation membrane 10, and is configured to send gas into the membrane bioreactor activated sludge tank 1 to remove deposits (gel layer) that have accumulated on the membrane surface and clean the membrane. The amount of aeration air used during membrane cleaning is not limited to the following, but is typically 6 to 30 L / m 2 / min, more preferably 9 to 25 L / m 2 / min.

[0045] The aeration device 2 may be of a continuous aeration type, or may be of an intermittent aeration type in which a predetermined rest period is provided between one aeration period and the next. When intermittent aeration is performed, the operating conditions are set so that membrane cleaning by aeration using the aeration device 2 is performed during the rest period when the suction pump 3, which sucks membrane-filtered water from the membrane bioreactor activated sludge tank 1, is turned off (suction is stopped), thereby making it possible to more effectively obtain the membrane cleaning effect of the aeration device 2.

[0046] From the viewpoint of suppressing fouling of the separation membrane 10, it is desirable to provide an intermittent timer to perform intermittent suction of the membrane-filtrated water by the suction pump 3. During membrane filtration, organic matter is adsorbed onto the membrane surface of the separation membrane 10, making fouling more likely to progress. Therefore, particularly when progress of fouling is expected, it is desirable to increase the flux and reduce the ratio of suction time as much as possible. Specifically, if one cycle is defined as one ON time and one OFF time, the ratio of ON / OFF time of the intermittent timer per cycle is desirably 59:1 to 4:1, and more desirably 29:1 to 9:1.

[0047] The sludge discharge pump 4 is connected to an extraction pipe 41 connected to the lower part of the membrane bioreactor activated sludge tank 1, and extracts treated sludge generated in the membrane bioreactor activated sludge tank 1 as excess sludge. The amount of sludge extracted by the sludge discharge pump 4 can be adjusted appropriately in accordance with the operating conditions input from the control device 8.

[0048] As shown in FIG. 1, an organic substance concentration measuring device 5 for measuring the organic substance concentration of the membrane-filtered raw water contained in the membrane bioreactor activated sludge tank 1, and an organic substance concentration measuring device 6 for measuring the organic substance concentration of the membrane-filtered water sucked from the inside of the membrane bioreactor activated sludge tank 1 to the outside of the membrane bioreactor activated sludge tank 1 via the suction pump 3 may be provided.

[0049] Organic matter measuring devices such as a COD meter, a BOD meter, a TOC meter, and a size exclusion chromatography with organic carbon detection (LC-OCD) can be used as the organic matter concentration measuring devices 5 and 6. Of course, it is also possible to manually or automatically sample the membrane-filtered raw water and membrane-filtered water without using the organic matter concentration measuring devices 5 and 6, and measure the organic matter concentrations of the membrane-filtered raw water and membrane-filtered water in equipment other than the wastewater treatment device of Figure 1.

[0050] The measurement results of the organic matter concentrations of the membrane-filtered raw water and the membrane-filtered water are input to the control device 8. The membrane bioreactor activated sludge tank 1 may be further provided with measuring devices including a thermometer for measuring the temperature of the membrane-filtered raw water and a pressure gauge for measuring the transmembrane pressure difference of the separation membrane 10, and the measurement results from each measuring device may be input to the control device 8.

[0051] The mechanism of membrane clogging of the separation membrane 10 is believed to be that membrane-clogging substances, such as polymer flocculants contained in the membrane-filtered raw water, flow into the biological treatment system, bind to activated sludge or its extracellular substances, form a polymeric, persistent complex, and form a gel layer on the membrane surface. Furthermore, once this gel layer is formed, the presence of the gel layer makes it easier for membrane-clogging substances to be captured on the membrane surface, rapidly progressing fouling. Therefore, in order to prevent fouling, it is important to monitor the behavior of organic substances that cause membrane clogging.

[0052] In the wastewater treatment device and wastewater treatment method according to the embodiment of the present invention, the difference between the organic matter concentration in the liquid phase of the membrane-filtered raw water and the organic matter concentration in the membrane-filtered water is used as an indicator of substances that cause membrane blockage. This is because this difference significantly affects the concentration of organic matter captured by the separation membrane 10, i.e., the concentration of organic matter that forms a gel layer that accumulates on the surface of the separation membrane 10. Another indicator of fouling can be measured using a filter paper with a specified pore size (e.g., 5C) over a specified time period (e.g., 5 minutes). However, this method can be affected by measurement conditions such as water temperature and how the filter paper is folded, as well as operating conditions such as MLSS during measurement. Measuring the organic matter concentration difference as described above reduces error and is superior in terms of quantitative accuracy.

[0053] The membrane-filtered raw water in the membrane bioreactor tank 1 typically contains high-concentration activated sludge. Therefore, when measuring the organic matter concentration in the liquid phase of the membrane-filtered raw water as a monitoring index, the membrane-filtered raw water collected from the membrane bioreactor tank 1 is filtered to remove the activated sludge from the membrane-filtered raw water before analysis. When collecting the membrane-filtered raw water, readily biodegradable organic matter in the raw water and methanol added during denitrification may remain in the upstream portion of the membrane bioreactor tank 1, which may affect the measurement of the difference in organic matter concentration. Therefore, it is desirable to collect the sludge immediately before it is subjected to membrane separation downstream of the membrane bioreactor tank 1. When filtering, it is desirable to use a filter with a pore size equal to or larger than the pore size of the membrane used in the membrane bioreactor tank 1, typically with a pore size of approximately 0.45 to 1 μm.

[0054] As mentioned above, COD, BOD, TOC, etc. can be used as monitoring indicators for measuring organic matter concentrations. However, COD is a more appropriate indicator for measuring organic matter that causes gel layer formation and for properly measuring persistent polymers. Mn , COD Cr , the use of TOC is more preferable.

[0055] Although not limited to the following examples, COD is used as a monitoring indicator. Mn The difference value (ΔCOD Mn) when using ΔCOD Mn The standard for the above is set to 70 mg / L or less, further 60 mg / L or less, and further 40 mg / L or less, and if the measured value exceeds the predetermined standard, the operating conditions of the membrane bioreactor activated sludge tank 1 are changed, thereby making it possible to suppress membrane clogging in the membrane bioreactor activated sludge tank 1 for a long period of time.

[0056] When circulating nitrification and denitrification is performed in the membrane bioreactor tank 1 to remove nitrogen, easily degradable organic matter may remain in the membrane-filtered water depending on the nitrification and denitrification conditions. If easily degradable organic matter remains, it becomes difficult to quantitatively evaluate the substances that cause membrane clogging of the separation membrane 10. In such cases, it is preferable to measure persistent organic matter as an indicator of the organic matter concentration to be measured. Here, persistent organic matter is defined as organic matter that remains after aerating the wastewater to be measured for a certain period of time (e.g., 1 to 8 hours). Measuring the concentration of such organic matter enables more rapid detection of signs of clogging of the separation membrane 10.

[0057] Another method for measuring organic substances that cause membrane clogging is to use size exclusion chromatography with organic carbon detection (LC-OCD: Liquid Chromatography-Organic Carbon Detector), an analytical device that combines molecular weight fractionation and organic substance concentration distribution. Organic substances that cause membrane clogging are known to be substances that are fractionated by LC-OCD to have a molecular weight of 20,000 or more, and by measuring the concentrations in the liquid phase of the membrane-filtered raw water and the membrane-filtered water, it is possible to narrow down and quantify them.

[0058] LC-OCD is a liquid chromatograph organic carbon analyzer equipped with a size exclusion column. Dissolved organic matter in a sample is fractionated into the following molar mass fractions (1) to (5) using a liquid chromatograph equipped with a size exclusion column, and each fraction is then measured with an organic carbon analyzer to quantify the organic carbon. (1) Biopolymers: Biopolymers, fractions with a molar mass of 20,000 g / mol or more (2) Humic Substances: Humic substances, fraction with a molar mass of 500 to 20,000 g / mol (3) Building Blocks: Building blocks (basic elements), fractions with molar masses of 300 to 500 g / mol (4) LMW Acids: Low molecular weight organic acids, a fraction of organic acids with a molar mass of 350 g / mol or less (5) LMW Neutrals: Low molecular weight neutral substances, fractions other than organic acids with a molar mass of 350 g / mol or less

[0059] Analysis using LC-OCD can be performed, for example, as follows. First, the collected sample is filtered through a 0.45 μm pore size PTFE membrane filter and diluted with ultrapure water (Milli-Q water) to a TOC concentration of 1-2 mg / L to prepare an analytical sample. The water is then passed through a size exclusion column in the LC-OCD instrument. The sample is fractionated into four fractions: molar mass ≥ 20,000 g / mol, molar mass 500-20,000 g / mol, molar mass 300-500 g / mol, and molar mass ≤ 350 g / mol, and the organic carbon concentration of each fraction is measured. Phosphate buffer (pH 6.58) is used as the mobile phase. The LC-OCD analyzer that can be used is, for example, the LC-OCD Model 8 from DOC-Labor.

[0060] After fractionation using a size exclusion column, the analytical sample for each fraction is placed in a thin-film reactor (Glanzel thin-film reactor, DOC-Labor) where inorganic carbon is removed using an acidifying solution (phosphoric acid, pH 1.5) and a nitrogen gas purge. The sample is then oxidized using an ultraviolet lamp (DOCOX lamp, DOC-Labor) and detected as CO2 using an NDIR (non-dispersive infrared) detector. The analytical results are analyzed using dedicated software (ChromCALC, DOC-Labor). Specifically, peaks are divided based on the shape of the chromatogram, and the concentration is calculated from the area of ​​each peak. This allows the quantification of organic matter fractionated into molecular weights of 20,000 or greater using LC-OCD.

[0061] -How to improve your driving- In this embodiment, when the monitoring index increases, the following three measures are implemented as an operation improvement method for reducing fouling: (1) reducing the inflow of substances that cause membrane blockage, (2) promoting the removal of the gel layer that adheres to the membrane, and (3) decomposing or discharging the membrane blockage substances in the membrane bioreactor activated sludge tank 1. Of course, if the following improvement measures are implemented appropriately so that the monitoring index falls within an appropriate range, the treatment conditions may be returned to normal conditions.

[0062] (1) Reduction of the inflow of substances that cause membrane blockage If the raw water from membrane filtration contains excessive amounts of polymer flocculants, for example, in the dewatered separated liquid, the concentration of polymer flocculants in the separated liquid increases, binding to the activated sludge and its extracellular substances to form complexes that make membrane clogging more likely. Therefore, if the monitoring index increases, check the optimal addition rate of additives such as polymer flocculants added to the raw water from membrane filtration before it flows into the membrane bioreactor activated sludge tank 1, for example, during pretreatment operations, and adjust the operating conditions to reduce the amount of substances that cause membrane clogging by reducing the additive addition rate if possible to maintain stable operation.

[0063] For example, when using dehydrated separated liquid as raw water for membrane filtration, if the measured value of the monitoring index exceeds a preset standard, the operating conditions are adjusted to reduce the addition rate of polymer flocculant for dehydration treatment. The optimal addition rate of polymer flocculant can be confirmed by flocculation tests or analysis of the colloidal charge of the dehydrated separated liquid. Other methods that can be taken when the monitoring index increases include reselecting the type of polymer flocculant, adjusting the addition rate of inorganic flocculant, or reducing the amount of food waste, etc., that is accepted.

[0064] (2) Promotes the removal of the gel layer attached to the membrane One method for promoting the detachment of the gel layer adhering to the separation membrane 10 contained in the membrane bioreactor activated sludge tank 1 is to use an intermittent timer to adjust the timing of suction of membrane-filtrated water by the suction pump 3, thereby adjusting the duration of filtration of the separation membrane 10. When the monitoring index increases, the ratio of the ON / OFF time of the intermittent timer per cycle can be adjusted within an appropriate range of 59:1 to 4:1, preferably 29:1 to 9:1, so that the filtration duration (ON time) is shortened and the filtration pause time (OFF time) is lengthened, thereby lengthening the time that air bubbles are applied to the membrane surface during the OFF time, thereby promoting the detachment of the gel layer.

[0065] Another method for promoting the detachment of the gel layer adhering to the separation membrane 10 contained in the membrane bioreactor tank 1 is to adjust the aeration time in the membrane bioreactor tank 1 using the aeration device 2. For example, when the monitoring index increases, the aeration air volume is adjusted to 6 to 30 L / m. 2 / min, more preferably 9 to 25 L / m 2 / min, by increasing the amount of cleaning air supplied to the membrane bioreactor activated sludge tank 1 by about 5 to 50% compared to normal operation, it is possible to promote the detachment of the gel layer adhering to the membrane surface of the separation membrane 10.

[0066] (3) Decomposition or discharge of membrane-blocking substances in membrane bioreactor activated sludge tank 1 Even if the gel layer adhering to the membrane of the separation membrane 10 is peeled off, the substances that cause the gel layer are difficult to decompose and decompose slowly, have large molecular weights, and tend to be captured on the membrane surface. Therefore, as long as the easily captured substances remain in the tank, they may adhere to the membrane surface again, and the state in which fouling tends to progress may continue. Therefore, the following methods are preferably used as measures to promote the decomposition or discharge of membrane-clogging substances in the membrane bioreactor activated sludge tank 1.

[0067] -SRT control- The substances that cause the gel layer are likely to be captured by the membrane and remain in the tank along with the sludge. Therefore, the longer the SRT, the more the substances that cause the gel layer become concentrated, and the more likely fouling will progress. For this reason, it is desirable to lower the SRT within the range that does not deteriorate the nitrification, denitrification, etc. treatment, and discharge the substances that cause the gel layer out of the tank.

[0068] As described in Patent Document 1, the presence of extracellular substances in activated sludge is known to be one of the causes of fouling, and measures to prevent fouling are sometimes taken to increase the SRT and reduce the sludge load. However, when raw water, such as dehydrated separated liquid, contains persistent gel layer-causing substances and the SRT is already within an appropriate range, increasing the SRT may actually promote the concentration of fouling-causing substances. For this reason, in this embodiment, it is preferable to adopt a method of preventing the concentration of gel layer-causing substances by deliberately lowering the SRT while maintaining an appropriate SRT.

[0069] By adjusting the amount of extracted sludge so that the SRT is typically 35 days or less, more typically 30 days or less, it becomes possible to carry out wastewater treatment stably and efficiently over a long period of time while appropriately suppressing fouling. On the other hand, if the SRT is too short, the transmembrane pressure difference of the separation membrane 10 increases, and stable treatment may not be possible. Typically, the SRT is preferably controlled to 6 days or more, and more preferably 10 days or more. This allows for stable treatment while appropriately suppressing fouling of the separation membrane 10 in the membrane bioreactor activated sludge tank 1.

[0070] -Physical and chemical treatment- If the monitoring index increases, at least a portion of the membrane-filtered raw water is subjected to one or more of the following treatments: ozone decomposition treatment, advanced oxidation treatment, or activated carbon adsorption treatment, to decompose and remove the substances that cause the gel layer.

[0071] -Adjusting the volume of activated sludge in membrane bioreactor tank 1 based on the measured values ​​of monitoring indicators- Even if the SRT is adjusted appropriately, there are cases where the conditions in the membrane bioreactor activated sludge tank 1 temporarily become conditions that promote the formation of a gel layer due to fluctuations in the membrane-filtered raw water, etc. In this embodiment, when the monitoring index increases, it is preferable to control the operating conditions for adjusting the sludge pump 4 so that the amount of sludge extracted from the membrane bioreactor activated sludge tank 1 is increased to reduce the amount of activated sludge in the membrane bioreactor activated sludge tank 1, thereby discharging the substances that cause the gel layer adhering to the separation membrane 10 out of the tank.

[0072] Although not limited to the following, if the monitoring index increases during a first sludge retention time (typically, an SRT of 6 to 35 days) during which the transmembrane pressure of the separation membrane 10 is maintained within a preset allowable range and biological treatment using the membrane bioreactor can be stably performed, the amount of sludge extracted from the membrane bioreactor tank 1 is increased. If the monitoring index increases during a second sludge retention time (typically, less than 6 days) during which the transmembrane pressure of the separation membrane 10 exceeds the allowable range, it is preferable to reduce the amount of sludge extracted from the membrane bioreactor tank 1. If the monitoring index increases when the SRT exceeds 35 days, reducing the amount of extracted sludge may lengthen the SRT and affect treatment. If the monitoring index increases when the SRT exceeds 35 days, the amount of sludge extracted from the membrane bioreactor tank 1 is increased.

[0073] The control device 8 is electrically connected to the blower 22 of the aeration device 2, the waste sludge pump 4, the suction pump 3, the organic matter concentration measuring devices 5 and 6, and the sludge concentration meter 7, and controls the operating conditions of the aeration device 2, the suction pump 3, and the waste sludge pump 4 so that, when the monitoring index increases, one or more of the following processes are performed: increasing the amount of cleaning air supplied to the membrane bioreactor activated sludge tank 1, shortening the filtration duration, or increasing the amount of sludge extracted from the membrane bioreactor activated sludge tank 1.

[0074] A wastewater treatment method according to an embodiment of the present invention can be carried out using the wastewater treatment equipment shown in Fig. 1. That is, the wastewater treatment method according to the embodiment includes measuring the organic matter concentration in the liquid phase of membrane-filtered raw water in the membrane bioreactor activated sludge tank 1 and the organic matter concentration in the membrane-filtered water, using the difference between the two as a monitoring index, and adjusting the operating conditions so that, when the monitoring index increases, one or more of the following treatments are performed: increasing the amount of cleaning air supplied to the membrane bioreactor activated sludge tank 1, shortening the filtration duration, or increasing the amount of sludge extracted from the membrane bioreactor activated sludge tank 1.

[0075] As described above, according to the wastewater treatment equipment and wastewater treatment method of the embodiment of the present invention, the organic matter concentration in the liquid phase of the membrane-filtered raw water in the membrane bioreactor activated sludge tank 1 and the organic matter concentration in the membrane-filtered water are measured, and the difference between them is used as a monitoring index. If the monitoring index increases, at least one of the following measures is carried out: reducing the inflow of substances that cause membrane blockage; promoting the removal of the gel layer adhering to the membrane; and decomposing or discharging the membrane-blocking substances in the membrane bioreactor activated sludge tank 1. This makes it possible to quickly detect signs of separation membrane blockage and perform stable and efficient wastewater treatment while appropriately suppressing fouling.

[0076] (Variation) As a method for suppressing clogging of the separation membrane 10 in the membrane bioreactor activated sludge tank 1, when the monitoring index increases, it is preferable to optimize at least one of the timing of increasing the amount of cleaning air supplied to the membrane bioreactor activated sludge tank 1, shortening the filtration duration, or increasing the amount of sludge extracted from the membrane bioreactor activated sludge tank, or the treatment time, for each treatment.

[0077] For example, increasing the amount of scrubbing air supplied to the membrane bioreactor activated sludge tank 1 and shortening the filtration duration are processes for physically removing the gel layer adhering to the separation membrane 10, and as measures for suppressing fouling, they tend to be effective in a relatively short period of time. On the other hand, controlling the sludge pump 4 to increase the amount of sludge extracted from the membrane bioreactor activated sludge tank 1 is a process for adjusting the concentration in the membrane bioreactor activated sludge tank 1 so as not to increase the concentration of substances that tend to form a gel layer on the surface of the separation membrane 10, and as a measure for suppressing fouling, it is necessary to continue this process for a relatively long period of time to achieve an effect. Therefore, it is preferable to combine short-term and long-term measures for suppressing fouling, depending on the degree of contamination of the separation membrane 10 and the concentrations of sludge and influent polymer flocculant in the membrane bioreactor activated sludge tank 1.

[0078] While increasing the amount of scrubbing air can suppress fouling in the short term, it also raises issues such as increased running costs due to increased power consumption by the blower 22 and the need to dismantle activated sludge. Increasing the filtration duration can suppress fouling in the short term, but it also limits the amount of filtration per hour. Furthermore, SRT control takes several days to several tens of days for the sludge to be replaced, so it takes time for the effects to be seen. Therefore, this embodiment combines a process of increasing the amount of scrubbing air and shortening the filtration duration, which achieves short-term effects, with a process of adjusting the amount of extracted sludge, which achieves long-term effects. For example, in the early stages of fouling, short-term and long-term measures are implemented simultaneously. After the sludge replacement progresses and the monitoring index decreases, the short-term measures are returned to their pre-treatment state. This immediately suppresses fouling, reduces running costs over the long term, and enables stable operation.

[0079] As a specific example, although not limited to the following, for example, a first reference value and a second reference value greater than the first reference value are set in advance for a monitoring index, and when the monitoring index increases and exceeds the first reference value, a process of increasing the amount of sludge extracted from the membrane bioreactor activated sludge tank 1 is initiated, and when the monitoring index further exceeds the second reference value, the operating conditions can be adjusted so as to initiate a first process of increasing the amount of cleaning air supplied to the membrane bioreactor activated sludge tank 1 and / or shortening the filtration duration.

[0080] Specifically, when the transmembrane pressure difference of the separation membrane 10 in the membrane bioreactor tank 1 falls within the standard range and the monitoring index increases during the first sludge retention time (typically 6 to 35 days) during which stable biological treatment is carried out, the operating conditions can be adjusted so that at least one of a first process is carried out, which involves increasing the amount of cleaning air supplied to the membrane bioreactor tank 1 and / or shortening the filtration duration, and a second process is carried out, which involves increasing the amount of sludge extracted from the membrane bioreactor tank 1.

[0081] Furthermore, if the monitoring index increases during a second sludge retention time (typically less than 6 days) when the transmembrane pressure of the separation membrane 10 exceeds the above-mentioned reference range, the operating conditions can be adjusted to perform at least one of a first process, which involves increasing the amount of scrubbing air supplied to the membrane bioreactor activated sludge tank 1 and / or shortening the filtration duration, and a third process, which involves reducing the amount of sludge extracted from the membrane bioreactor activated sludge tank 1. If the monitoring index increases when the SRT exceeds 35 days, the operating conditions can be adjusted to perform at least one of a first process, which involves increasing the amount of scrubbing air supplied to the membrane bioreactor activated sludge tank 1 and / or shortening the filtration duration, and a second process, which involves increasing the amount of sludge extracted from the membrane bioreactor activated sludge tank 1.

[0082] This allows biological treatment in the membrane bioreactor tank 1 to proceed more stably, and treated water that meets the standard values ​​can be obtained stably and continuously. Even if there is a sudden change in the properties of the membrane-filtered raw water, signs of clogging of the separation membrane 10 can be quickly detected, and fouling can be appropriately suppressed, allowing for stable and efficient wastewater treatment over a long period of time.

[0083] If the above measures are taken and a decrease in the monitoring index is confirmed, the first process, which involves increasing the amount of cleaning air supplied to the membrane bioreactor tank 1 or shortening the filtration duration, can be gradually restored to the state before the measures were taken, thereby reducing running costs and stabilizing the process. [Example]

[0084] Examples of the present invention will be described below together with comparative examples. These examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0085] (Test 1) SRT control The dewatered separated liquid from sewage and septic tank sludge was used as the membrane-filtered raw water to be supplied to a membrane bioreactor tank equipped with a denitrification tank and nitrification tank (membrane separation tank), and the MLSS of the dewatered separated liquid was varied from 3,000 to 20,000 mg / L to examine membrane filtration performance depending on changes in SRT, TN-SS load in the nitrification tank (hereafter referred to as "TN-SS load"), and total tank BOD-SS load (hereafter referred to as "BOD-SS load"), as well as the measurement results are shown in Table 1. Note that the BOD-SS load represents the combined BOD-SS load of the denitrification tank and nitrification tank.

[0086] [Table 1]

[0087] In Test 1, an organic flat membrane with a pore size of 0.4 μm was used. The filtration flux was kept constant at 0.4 m / d, and the change in the transmembrane pressure difference and the difference in organic matter concentration (ΔS-COD MnThe degree of membrane contamination was evaluated by the ΔS-COD and the 5C filter paper filtration volume. The 5C filter paper filtration volume is the result of measuring the amount of filtrate that can be filtered in 5 minutes using 5C filter paper with a diameter of 150 mm. Mn is the soluble COD in the membrane separation tank mixture Mn (S-COD Mn ) and COD of membrane separated water Mn This shows the difference between ΔS-COD Mn The higher the value, the more contaminated the membrane surface is, and the more difficult it is to filter. Mn The filtration volume on the 5C filter paper was measured after three months of continuous treatment.

[0088] Figures 2 to 4 show the SRT and ΔS-COD obtained in Test 1, which are indicators of the membrane fouling level. Mn The relationship between the transmembrane pressure and the 5C filter paper filtration volume is shown. When the SRT is 10 to 30 days, ΔS-COD Mn On the other hand, when the SRT was short at 6 days, ΔS-COD Mn The ΔS-COD was 82 mg / L, which was considered to be a high level of membrane fouling. Mn was as high as 90 mg / L, indicating a high level of membrane fouling.

[0089] From the relationship between SRT and transmembrane pressure shown in Figure 3, it is estimated that an SRT of 6 to 35 d, and even more preferably 10 to 30 d, is appropriate to maintain a transmembrane pressure of 25 KPa or less, and preferably 20 KPa or less, which is a benchmark for stable treatment.From the relationship between SRT and 5C filter paper filtration volume shown in Figure 4, it is determined that an SRT of 6 to 35 d, and even more preferably 10 to 30 d, is preferable to maintain a 5C filter paper filtration volume of 8 ml or more, and preferably 10 ml or more, which is a benchmark for good filtration performance.

[0090] Figures 5 to 7 show the BOD-SS load and ΔS-COD of the entire reactor obtained in the test. Mn Figure 8 shows the relationship between ΔS-COD, transmembrane pressure, and 5C filter paper filtration volume. In terms of BOD-SS load, it is considered appropriate to set the BOD-SS load at 0.05 to 0.2 kg / kg / d in order to suppress membrane fouling.Mn and transmembrane pressure, and Fig. 9 shows the relationship between ΔS-COD Mn The relationship between ΔS-COD and the amount of 5C filter paper filtration is shown. Mn A good correlation was observed between the ΔS-COD and the transmembrane pressure. Mn It is preferable to operate and manage ΔS-COD at 40 mg / L or less. Mn A good correlation was also observed between ΔS-COD and the 5C filter paper filtration volume. Mn It is preferable to operate and control the concentration at about 70 mg / L or less.

[0091] From the above results, according to one embodiment of the present invention, in order to suppress membrane fouling and maintain stable filtration performance, it is necessary to reduce ΔS-COD Mn It was found that it is preferable to control the operating conditions so that the SRT and BOD-SS are at least 70 mg / L or less, preferably 40 mg / L or less, and to adjust the SRT and BOD-SS appropriately.

[0092] (Test 2) Examination of aeration air volume under appropriate SRT conditions and appropriate suction time conditions Using the same equipment as in Test 1, the dehydrated separated liquid from human waste and septic tank sludge was used as the raw water for membrane filtration, and the MLSS of the dehydrated separated liquid was varied from 3,000 to 20,000 mg / L to examine the membrane filtration performance depending on the amount of cleaning air and the duration of filtration (suction timer). The results are shown in Table 2.

[0093] [Table 2]

[0094] SRT18d, 9 minutes of suction followed by 1 minute of suction stop, cleaning air volume 7-18L / m 2 At a rate of 4 L / m², the transmembrane pressure remained low at 17-23 Kpa, and the 5C filter paper filtration volume was also high at 15-21 mL, showing good conditions (No. 11-13). 2 When the speed was reduced to / min, the transmembrane pressure rose to 26 Kpa, and the filtration volume with the 5C filter paper was only 9.2 mL, indicating signs of membrane blockage (No. 14).

[0095] SRT18d, cleaning air volume 18L / m 2 Under conditions of suction rate of 1 / min, by stopping suction for 1 minute every 20 to 40 minutes, the transmembrane pressure remained low at 24 to 32 kPa, and the 5C filter paper filtration volume was high at 16 to 20 mL, which was in good condition (No. 15, 16). However, when suction was stopped for 1 minute every 60 minutes, the transmembrane pressure rose to 31 kPa, and the 5C filter paper filtration volume was low at 8.4 mL, showing signs of membrane blockage (No. 17).

[0096] (Test 3) Control based on monitoring indicators Continuous operation was carried out under the following three conditions, and the number of days until the transmembrane pressure reached 30 kPa or more was investigated. (1) Comparative Example 1: Normal operation, no control based on monitoring indicators (Cleaning air volume 7L / m 2 / min, suction timer On:Off=12:1, SRT 18 days) (2) Example 1: Control based on monitoring indicators (short-term treatment only) (ΔS-COD Mn If the concentration is 40 mg / L or higher, the cleaning air volume will be reduced from normal operation to 9 L / m 2 / min, and the suction timer is changed to On:Off=9:1. Mn When the concentration drops below 30 mg / L, the system returns to normal operation. (3) Example 2: Control based on monitoring indicators (combination of short-term and long-term treatments) ΔS-COD Mn If the concentration is 40 mg / L or higher, the cleaning air volume will be reduced from normal operation to 9 L / m 2 / min, suction timer On:Off=9:1, operate the sludge pump to change SRT to 14 days, ΔS-COD Mn When the S-COD level drops below 30 mg / L, the system returns to normal operation. Mn When the concentration is 30 mg / L or less, the cleaning air volume is 7 L / m 2 / min, suction timer On:Off=12:1, SRT 14 days, S-COD Mn Control was carried out to return to normal operating conditions when the distance was below 20m.

[0097] [Table 3]

[0098] When only short-term treatment was performed in Example 1, the operating time was 234 days, and when short-term treatment and long-term treatment were combined in Example 2, the operating time was 381 days, confirming that the plant could operate stably for a longer period of time than in Comparative Example 1, where no control was performed. [Explanation of symbols]

[0099] 1...Membrane separation activated sludge tank 2...Aeration device 3...Suction pump 4...Sludge discharge pump 5, 6...Organic substance concentration measuring device 7...Sludge concentration meter 8...Control device 10...Separation membrane 21...Air diffuser 22...Blower 41...Pulling piping

Claims

1. A wastewater treatment method using a membrane bioreactor, comprising: measuring the organic matter concentration in the liquid phase of membrane-filtered raw water in a membrane bioreactor tank and the organic matter concentration in the membrane-filtered water, using the difference between the measured organic matter concentrations as a monitoring index; when the sludge retention time in the membrane bioreactor tank is 6 days or more and the monitoring index increases, performing one or more of the following: increasing the amount of cleaning air supplied to the membrane bioreactor tank, shortening the filtration duration, or shortening the sludge retention time in the membrane bioreactor tank; and adjusting operating conditions so as to shorten the sludge retention time when the sludge retention time exceeds 35 days and the monitoring index increases.

2. A wastewater treatment method using a membrane bioreactor, comprising: measuring the organic matter concentration in the liquid phase of membrane-filtered raw water in a membrane bioreactor tank and the organic matter concentration in the membrane-filtered water, using the difference between the measured organic matter concentrations as a monitoring index; and, when the sludge retention time in the membrane bioreactor tank is 6 days or more and the monitoring index increases, performing one or more of the following: increasing the amount of scrubbing air supplied to the membrane bioreactor tank, shortening the filtration duration, or shortening the sludge retention time in the membrane bioreactor tank; and adjusting operating conditions so as to perform a treatment to reduce the addition rate of a polymer flocculant added to the membrane-filtered raw water in a dehydration treatment before the water is supplied to the membrane bioreactor tank.

3. a membrane separation activated sludge tank for subjecting membrane-filtered raw water to membrane separation treatment in the presence of activated sludge to obtain membrane-filtered water; an aeration device for aerating the membrane separation activated sludge tank; a suction pump that sucks the membrane-filtered water from the membrane separation activated sludge tank; a sludge discharge pump for extracting sludge from the membrane bioreactor activated sludge tank; a control device that controls the operating conditions of the aeration device, the suction pump, and the sludge pump so that a difference value between the organic matter concentration in the liquid phase of the membrane-filtered raw water in the membrane bioreactor tank and the organic matter concentration in the membrane-filtered water is used as a monitoring index, and when the sludge retention time in the membrane bioreactor tank is 6 days or more and the monitoring index increases, one or more of the following is performed: increasing the amount of cleaning air supplied to the membrane bioreactor tank, shortening the filtration duration, or shortening the sludge retention time in the membrane bioreactor tank; and when the sludge retention time is more than 35 days and the monitoring index increases, the sludge retention time is shortened. A wastewater treatment device comprising:

4. a membrane separation activated sludge tank for subjecting membrane-filtered raw water to membrane separation treatment in the presence of activated sludge to obtain membrane-filtered water; an aeration device for aerating the membrane separation activated sludge tank; a suction pump that sucks the membrane-filtered water from the membrane separation activated sludge tank; a sludge discharge pump for extracting sludge from the membrane bioreactor activated sludge tank; a control device that controls operating conditions of the aeration device, the suction pump, and the discharge sludge pump so that a difference value between the organic matter concentration in the liquid phase of the membrane-filtered raw water in the membrane bioreactor tank and the organic matter concentration in the membrane-filtered water is used as a monitoring index, and when the sludge retention time in the membrane bioreactor tank is 6 days or more and the monitoring index increases, one or more of the following is performed: increasing the amount of cleaning air to be supplied to the membrane bioreactor tank, shortening the filtration duration, or shortening the sludge retention time in the membrane bioreactor tank; and performing a process to reduce the addition rate of a polymer flocculant to be added to the membrane-filtered raw water in a dehydration process before the water is supplied to the membrane bioreactor. A wastewater treatment device comprising:

5. a membrane separation activated sludge tank for subjecting membrane-filtered raw water to membrane separation treatment in the presence of activated sludge to obtain membrane-filtered water; an aeration device for aerating the membrane separation activated sludge tank; a suction pump that sucks the membrane-filtered water from the membrane separation activated sludge tank; a sludge discharge pump for extracting sludge from the membrane bioreactor activated sludge tank; a control device that controls the operating conditions of the aeration device, the suction pump, and the discharge sludge pump so that a difference value between the organic matter concentration in the liquid phase of the membrane-filtered raw water in the membrane bioreactor tank and the organic matter concentration in the membrane-filtered water is used as a monitoring index, and when the sludge retention time in the membrane bioreactor tank is 6 days or more and the monitoring index increases, one or more of increasing the amount of cleaning air supplied to the membrane bioreactor tank, shortening the filtration duration, or shortening the sludge retention time in the membrane bioreactor tank is performed, and when the sludge retention time is less than 6 days and the monitoring index increases, the sludge retention time is not shortened; and A wastewater treatment device comprising:

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