JP2024036698A - Wastewater treatment method and wastewater treatment apparatus - Google Patents

Abstract

To provide a wastewater treatment method and a wastewater treatment apparatus, capable of quickly detecting an indication of blockage in a separation membrane, and stably, efficiently treating wastewater while appropriately controlling fouling.SOLUTION: A wastewater treatment method that uses a membrane separation active sludge process includes: measuring an organic matter concentration of a liquid phase of raw water subjected to membrane filtration in a membrane separation activated sludge tank 1 and an organic matter concentration of a membrane-filtered water to take a difference therebetween as a monitoring index; and adjusting an operation condition so as to perform any one or more pieces of processing among increasing an amount of cleaning air supplied to the membrane separation activated sludge tank 1, shortening a filtration continuation time, and shortening a sludge retention time of the membrane separation activated sludge tank 1, when the sludge retention time of the membrane separation activated sludge tank is 6 days or longer and the monitoring index increases.SELECTED DRAWING: Figure 1

Description

The present invention relates to a wastewater treatment method and a wastewater treatment apparatus, and particularly to a wastewater treatment method and a wastewater treatment apparatus using a membrane separation activated sludge method.

In conventional human waste and septic tank sludge treatment, the main method is to directly biologically treat the sludge from which impurities have been removed using the activated sludge method to remove organic matter and nitrogen, and the membrane separation activated sludge method is one of the treatment methods. It has been adopted as one. The membrane separation activated sludge method performs solid-liquid separation by membrane separation, so it has the advantage of increasing the MLSS (Mixed Liquor Suspended Solids) concentration in the biological treatment tank and reducing the site area. have.

In addition, in recent years, methods have become mainstream to reduce the burden of biological treatment by dehydrating human waste and septic tank sludge in advance, reusing the dehydrated cake as solid fuel, and treating only the dehydrated separated liquid. It is becoming. Furthermore, even in equipment that anaerobically digests biomass such as sludge and food waste and recovers methane gas, which has been increasing in recent years, it is necessary to biologically treat the anaerobically digested sludge after dewatering it. Even in such cases, the membrane separation activated sludge method is often used for biological treatment to reduce the site area.

As a technology using the membrane separation activated sludge method, for example, Japanese Patent No. 5868217 (Patent Document 1) discloses that the water to be treated is biologically treated with activated sludge in a biological reaction tank, and the mixed liquid in the biological reaction tank is In the membrane separation activated sludge treatment method, in which solid-liquid separation is performed using a membrane separator and the membrane-filtered water that has passed through the separation membrane is taken out of the tank, COD (chemical oxygen demand), BOD (biological oxygen demand), Determine the organic matter concentration based on TOC (total oxygen demand), total sugar concentration, protein concentration, uronic acid concentration, or E260 (ultraviolet absorbance at a wavelength of 260 nm), and calculate the organic matter concentration in the liquid phase of the mixed liquid in the tank. The biological reaction tank A membrane separation activated sludge treatment method is described, which is characterized by increasing the amount of activated sludge in the biological reaction tank, and reducing the amount of activated sludge in the biological reaction tank when the adjustment index decreases, thereby suppressing fouling of the separation membrane. has been done.

Japanese Patent No. 4046661 (Patent Document 2) discloses that organic sewage is treated with activated sludge in a biological treatment tank, and an activated sludge mixture is collected using a submerged membrane separator serving as a first separation means that is submerged in the biological treatment tank. COD containing bio-derived polymers accumulated in the biological treatment tank through activated sludge treatment is timely solid-liquid separated from the activated sludge mixture by the second separation means, and the activated sludge in the biological treatment tank is separated into solid and liquid. In order to maintain the amount of biologically derived polymer in the activated sludge mixture at a low concentration while maintaining the amount of biologically derived polymer in the activated sludge mixture at a high concentration, the COD in the membrane filtrate that has passed through the submerged membrane separation device is measured, and the COD is The activated sludge mixture in the biological treatment tank is filtered using a filtration means having pores with a predetermined diameter larger than the pores of the filtration membrane of the device.The COD in the filtrate of the filtration means is measured, and the COD in the filtrate of the filtration means is measured. A sewage treatment method characterized in that when a COD difference value obtained by subtracting COD in a membrane filtrate is equal to or higher than a predetermined value, COD containing a biological polymer is separated from an activated sludge mixture by a second separation means. Are listed.

Japanese Patent No. 5822264 (Patent Document 3) discloses an aeration tank in which an aeration means for aerating a liquid to be treated in activated sludge is immersed, and a membrane separation system for obtaining a permeate from the liquid to be treated in activated sludge. A method of operating a membrane separation activated sludge treatment device equipped with a membrane separation tank in which the device is immersed, the method comprising: When the organic matter concentration is above a predetermined value and the value of BOD/SS load is above a predetermined value, the amount of air diffused per unit time of the aeration means is increased, and the value of BOD/SS load is set to the predetermined value. A method of operating a membrane separation activated sludge treatment equipment is described in which the amount of air diffused per unit time of the aeration means is adjusted so as to reduce the amount of air diffused per unit time of the aeration means when the amount of air diffused per unit time is less than There is.

Japanese Patent Laid-Open No. 2014-193452 (Patent Document 4) discloses that organic sewage is flowed into a water storage tank containing activated sludge, subjected to biological treatment, and subjected to membrane separation installed in the water storage tank or its subsequent stage. A method for treating organic sewage in which treated water is obtained by solid-liquid separation using an apparatus, wherein the amount of extracellular ATP in activated sludge or the rate of increase in the amount of extracellular ATP in activated sludge reaches a predetermined standard value. At this time, the amount of aeration supplied to the membrane separation device, the cleaning conditions of the membrane separation device, the conditions for injecting the flocculant into the water storage tank to be treated, the filtration flux of the membrane separation device, and the water storage tank to be treated A method for treating organic wastewater is described in which at least one condition selected from the following is controlled: the amount of activated sludge withdrawn from the organic wastewater.

Patent No. 5868217 Patent No. 4046661 Patent No. 5822264 Japanese Patent Application Publication No. 2014-193452

When dewatering organic sludge such as human waste, septic tank sludge, and anaerobic digestion sludge, inorganic flocculants and polymer flocculants (polymers) are added to the sludge to flocculate the sludge before dewatering. conduct. At this time, the addition rate of the polymer flocculant is determined by the condition of the flocculated flocs, etc., but if excess or deficiency occurs due to changes in the properties of the sludge, the concentration of suspended solids (SS) in the dehydrated liquid will increase and the This results in an increase in the amount of residual polymer in the liquid, and an increase in the concentration of the polymer flocculant contained in the raw water for biological treatment.

Since polymer flocculants are often difficult to decompose, they are difficult to be decomposed by microorganisms, and their molecular weight is 1 million or more. Such polymer flocculants are usually captured by the separation membrane used in the membrane separation activated sludge method, but as the concentration of polymer flocculant in the tank increases, a layer called a gel layer is formed on the separation membrane. There is a risk that fouling may occur due to the formation of dirt. Therefore, measures are required to appropriately suppress fouling.

In the invention described in Cited Document 1, the concentration difference between the organic matter concentration in the mixed liquid in the tank and the organic matter concentration in membrane-filtered water is applied, and when the concentration difference increases, the amount of activated sludge in the biological reaction tank is increased. It is proposed to perform processing to However, with such a treatment method, there is a risk that the activated sludge or its extracellular substances increased in the biological reaction tank and the polymer flocculant will further combine in the biological reaction tank, causing a gel layer to be further deposited on the separation membrane. As a result, fouling may not be properly suppressed.

In the fouling suppression method using the second separation means as described in Patent Document 2, it is necessary to consider not only the problem of membrane clogging of the first separation means but also the second separation means, so maintenance processing is required. It becomes complicated. A method of adjusting the aeration air volume based on the organic matter concentration in the supernatant liquid of the liquid to be treated in activated sludge and the value of BOD/SS load as described in Patent Document 3, or a cell method as described in Patent Document 4 Similar to other conventional technologies, the fouling control method based on the amount of external ATP can quickly detect signs of separation membrane clogging, suppress fouling, and provide stable wastewater treatment over a long period of time. cannot be said to be a sufficient process.

In view of the above-mentioned problems, the present invention provides a wastewater treatment method and a wastewater treatment apparatus that can quickly detect signs of separation membrane blockage and perform wastewater treatment stably and efficiently while appropriately suppressing fouling. provide.

As a result of intensive studies by the present inventors to solve the above problems, we found that the organic matter concentration in the liquid phase of the membrane-filtered raw water of the membrane separation activated sludge equipment and the organic matter concentration in the membrane-filtered water (membrane permeated water) obtained by membrane filtration. We have found that it is effective to use the difference between the two as a monitoring index and to perform specific processing based on this monitoring index.

One aspect of the embodiment of the present invention, which was completed based on the above knowledge, is that in a wastewater treatment method using a membrane separation activated sludge method, the concentration of organic matter in the liquid phase of membrane filtration raw water in a membrane separation activated sludge tank and the The organic matter concentration of the filtrate is measured and the difference is used as a monitoring index, and when the monitoring index increases, the amount of cleaning air supplied to the membrane separation activated sludge tank is increased, the filtration duration is shortened, or the membrane separation activated sludge tank is changed. This wastewater treatment method includes adjusting operating conditions so as to perform one or more of the following treatments: increasing the amount of sludge drawn from the wastewater treatment plant.

In one embodiment of the wastewater treatment method according to the embodiment of the present invention, when the monitoring index exceeds the first reference value, the amount of sludge drawn from the membrane separation activated sludge tank is increased, and the monitoring index is increased. When the second standard value, which is higher than the first standard value, is exceeded, one or more of the following steps is performed: increasing the amount of cleaning air supplied to the membrane separation activated sludge tank or shortening the filtration duration time.

In another aspect of the embodiment of the present invention, in a wastewater treatment method using a membrane separation activated sludge method, the organic matter concentration of the liquid phase of the membrane filtration raw water in the membrane separation activated sludge tank and the organic matter concentration of the membrane filtration water are controlled. The operating conditions are set such that when the monitoring index increases when the sludge retention time in the membrane separation activated sludge tank exceeds 6 days, the amount of sludge drawn from the membrane separation activated sludge tank is increased. This includes adjusting operating conditions to reduce the amount of sludge drawn from the membrane-separated activated sludge tank when the monitoring index increases when the sludge retention time in the membrane-separated activated sludge tank is less than 6 days. This is a wastewater treatment method.

In one embodiment of the wastewater treatment method according to the embodiment of the present invention, when the sludge retention time in the membrane separation activated sludge tank increases for 6 days or more and the monitoring index increases, the amount of sludge drawn from the membrane separation activated sludge tank increases. Adjusting the operating conditions so as to perform a combination of a process that increases the amount of cleaning air supplied to the membrane separation activated sludge tank and a process that increases the amount of cleaning air supplied to the membrane separation activated sludge tank and shortens the filtration duration time,
A process that reduces the amount of sludge drawn from the membrane-separated activated sludge tank when the sludge retention time in the membrane-separated activated sludge tank is less than 6 days and the monitoring index increases, and the amount of cleaning air supplied to the membrane-separated activated sludge tank. The operating conditions are adjusted so as to perform a combination of one or more of increasing the filtering time and shortening the filtration duration time.

In one embodiment of the wastewater treatment method according to the embodiment of the present invention, the organic matter concentration is fractionated into those having a molecular weight of 20,000 or more as measured by COD, BOD, TOC, or organic carbon detection size exclusion chromatography. Contains any organic matter concentration.

In one embodiment of the wastewater treatment method according to the embodiment of the present invention, when a monitoring index increases, at least a portion of the membrane-filtered raw water is subjected to ozonolysis treatment, accelerated oxidation treatment, or activated carbon adsorption treatment. The method further includes performing any one or more of the processes.

In one embodiment of the wastewater treatment method according to the embodiment of the present invention, the membrane filtration raw water is a dehydrated separated liquid generated after dehydration treatment is performed by adding a polymer flocculant to sludge containing organic matter.

In yet another embodiment of the wastewater treatment method according to the embodiment of the present invention, when a monitoring index increases, high Reduce the addition rate of molecular flocculant.

In one aspect, the wastewater treatment apparatus according to the embodiment of the present invention includes a membrane separation activated sludge tank for obtaining membrane filtrate water by subjecting membrane filtration raw water to membrane separation treatment in the presence of activated sludge, and a membrane separation activated sludge tank for aeration. a suction pump that sucks membrane-filtered water from the membrane-separated activated sludge tank, a sludge pump that pulls out sludge from the membrane-separated activated sludge tank, and organic matter in the liquid phase of the membrane-filtered raw water in the membrane-separated activated sludge tank. The difference value between the concentration and the organic matter concentration of membrane-filtered water is used as a monitoring index, and when the monitoring index increases, the amount of cleaning air supplied to the membrane-separated activated sludge tank is increased, the filtration duration is shortened, or the membrane-separated activated sludge is increased. This wastewater treatment device includes a control device that controls operating conditions of an aeration device, a suction pump, and a sludge pump so as to increase the amount of sludge drawn from the tank.

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 separation membrane blockage and perform wastewater treatment stably and efficiently while appropriately suppressing fouling.

1 is a schematic diagram showing an example of a wastewater treatment device according to an embodiment of the present invention. It is a graph showing an example of the relationship between sludge retention time (SRT) and monitoring index (ΔS-COD _Mn ). It is a graph showing an example of the relationship between SRT and transmembrane differential pressure. It is a graph showing an example of the relationship between SRT and 5C filter paper filtration amount. It is a graph showing an example of the relationship between BOD-SS load and ΔS-COD _Mn . It is a graph showing an example of the relationship between BOD-SS load and transmembrane differential pressure. It is a graph showing an example of the relationship between BOD-SS load and 5C filter paper filtration amount. 7 is a graph showing an example of the relationship between ΔS-COD _Mn and transmembrane pressure. It is a graph showing an example of the relationship between ΔS-COD _Mn and the amount of 5C filter paper filtration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 description of the drawings below, the same or similar parts are denoted by the same or similar symbols. The embodiments shown below are intended to exemplify devices and methods for embodying the technical idea of this invention. It is not specific to

As shown in FIG. 1, a wastewater treatment apparatus according to an embodiment of the present invention includes a membrane-separated activated sludge tank 1 that processes wastewater using a membrane-separated activated sludge method to obtain treated sludge and membrane-filtered water; An aeration device 2 that aerates the separation activated sludge tank 1, a suction pump 3 that sucks membrane filtrate water from the membrane separation activated sludge tank 1, a drainage pump 4 that pulls out sludge from the membrane separation activated sludge tank 1, and a membrane separation activated sludge tank 1. A control device 8 that controls the operating conditions of the sludge tank 1 is provided.

The object to be treated is not particularly limited as long as it is organic wastewater containing organic matter. In particular, the dehydrated separated liquid of organic sludge containing one or more of human waste/septic tank sludge, sewage initial settling sludge, sewage surplus sludge, food waste, and biomass anaerobic digested sludge is transferred to the membrane separation activated sludge tank 1. It can be used as filtered raw water. Since the dehydrated separated liquid contains a polymer flocculant, as it is treated in the membrane separation activated sludge tank 1 for a long period of time, the polymer flocculant contained in the dehydrated separated liquid aggregates and forms a gel layer. It forms, adheres to the separation membrane 10 in the membrane separation activated sludge tank 1, and tends to cause fouling. By performing biological treatment using the wastewater treatment apparatus according to the embodiment of the present invention, the treatment can be performed stably for a long period of time while suppressing fouling.

The dehydrated separated liquid may contain suspended solids (SS), soluble COD (COD _Cr , COD _Mn ), BOD, TOC, nitrogen, phosphorus, calcium (Ca), and the like. Although not limited to the following, the dehydrated separation solution typically contains 100 to 3000 mg/L of SS, more typically 500 to 2000 mg/L. The dehydrated separate contains COD _Cr at 500-10000 mg/L, more typically 1000-5000 mg/L, and COD _Mn at 100-5000 mg/L, more typically 500-3000 mg/L. The dehydrated separate contains 500-5000 mg/L BOD, more typically 1000-3000 mg/L, and 250-4000 mg/L, more typically 500-2000 mg/L TOC. The dehydrated separated liquid contains 10 to 500 mg/L of total nitrogen (TN), more typically 50 to 300 mg/L, and 5 to 200 mg/L of total phosphorus (TP), more typically Contains 10 to 100 mg/L. The dehydrated separated liquid contains organic nitrogen (concentration determined by subtracting inorganic nitrogen (NO _x -N, NH ₄ -N) from TN) of 5 to 300 mg/L, more typically 50 to 200 mg/L. Including N/L.

In particular, if the dehydrated separated liquid contains 500 mg/L or more of SS, the influence of the polymer flocculant adsorbed by the SS flowing into the membrane-separated activated sludge tank 1 becomes large, and fouling tends to progress. . Furthermore, if the dehydrated separated liquid contains 50 mg/L or more of organic nitrogen, high-molecular organic substances are generated during the protein decomposition process, and a gel layer is likely to be formed.

Furthermore, when the BOD/COD _Cr in the dehydrated separated liquid becomes 0.7 or less, the proportion of persistent and slowly decomposable organic matter increases, and in the membrane-separated activated sludge tank, it combines with the polymer flocculant and forms a gel layer. becomes easier to form. Furthermore, when the type of sludge to be subjected to dewatering treatment includes sludge that has not undergone biological treatment, such as sewage primary sedimentation tank sludge, human waste sludge, and garbage, the sludge properties tend to change. By pre-dehydrating such sludge, the addition rate of polymer becomes excessive or insufficient, and the polymer flocculant tends to flow out to the filtrate side.

When using a dehydrated separated liquid as raw water for membrane filtration, the following pretreatment operation is performed on the organic sludge before it is supplied to the membrane-separated activated sludge tank 1. As a pretreatment operation, for example, a polymer flocculant and, if necessary, an inorganic flocculant are added to organic sludge, and the mixture is stirred to perform flocculation treatment. Since 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 million to 15 million, preferably 1 million to 10 million, more preferably 1 million to 7.5 million. The addition rate of polymeric flocculant is typically 0.2-4% w/w to TS, more preferably 0.5-3% w/w. It is desirable that the selection and addition rate of the polymer flocculant be determined by a flocculation test, a laboratory-scale dehydration test, or the like.

As the inorganic flocculant, polyferric sulfate, ferric chloride, aluminum sulfate, polyaluminum chloride (PAC), etc. can be used. Among these, it is desirable to use polyferric sulfate from the viewpoint of chemical costs and corrosion prevention. The addition rate of the inorganic flocculant is also preferably determined by a flocculation test, a laboratory-scale dehydration test, etc.

The inorganic flocculant can be added using a pre-addition method in which the inorganic flocculant is added before sludge concentration, a post-addition method in which the inorganic flocculant is added after sludge concentration, or an inorganic flocculant is added before and after sludge concentration. There are two types of addition methods. Among these, the post-addition method or both addition methods are desirable from the viewpoint of improving dewatering performance and supplying phosphorus necessary for subsequent biological treatment to the separated liquid side.

By concentrating the flocculated sludge obtained by the above flocculation treatment before the dewatering treatment, it is possible to improve the processing speed during the dewatering treatment and reduce the water content of the dehydrated sludge. Mechanical concentration can be used as the concentration process, and the concentrator may be of any type, such as a rotary type, a gravity type, or a pressurized type.

By further dehydrating the thickened sludge obtained through the concentration treatment, dehydrated sludge and dehydrated separated liquid can be obtained. As the dehydrator, 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 can be used.

In particular, a screw press dehydrator is preferable because it can achieve a low water content with low power. The screw press dehydrator is equipped with a screw shaft and screw blades concentric with the cylindrical outer cylinder inside the cylindrical outer cylinder, and a space between the thickening section on the mixed sludge supply side and the cylindrical outer cylinder and the screw shaft. The cylindrical outer cylinder is provided with a squeeze part on the dewatered cake discharge side that gradually becomes narrower in the direction of movement of the mixed sludge, and the cylindrical outer cylinder is provided with a plurality of openings for discharging the separated liquid.

Among them, the shaft-sliding type screw press dehydrator has a mechanism in which the screw shaft moves in parallel to the dewatered sludge outlet direction and forcibly discharges the dehydrated sludge. By using a screw press dehydrator, the water content of the dehydrated cake can be significantly reduced. In addition to dehydration equipment that combines an independent screen and dehydrator, we also offer dehydration equipment that integrates a screen and dehydrator, including a concentration section in the front stage that functions as a screen, and a compression section in the latter stage. This is preferable because there is no need to separately provide a screen and the device configuration is simplified.

In the membrane-separated activated sludge tank 1, the membrane-filtered raw water flowing into the membrane-separated activated sludge tank 1 is subjected to organic matter removal using microbial reactions using activated sludge and nitrogen removal through nitrification-denitrification. Biological treatment is performed using the membrane separation activated sludge method, which separates activated sludge and treated water by membrane separation.

The biological treatment in the membrane-separated activated sludge tank 1 may be any method as long as it can remove organic matter and nitrogen, and for example, a circulating nitrification-denitrification method, a step flow-type nitrification-denitrification method, etc. can be adopted. The sludge concentration (MLSS) of activated sludge can typically be 4,000 to 18,000 mg/L, more preferably 6,000 to 15,000 mg/L, and adjusted according to the treatment situation. It is desirable to do so. For example, a sludge concentration meter 7 for measuring MLSS in the membrane-separated activated sludge tank 1 may be disposed within the membrane-separated activated sludge tank 1.

When removing nitrogen from membrane-filtered water, if alkalinity is insufficient during nitrification, an alkaline agent such as sodium hydroxide solution (NaOH) is added using a chemical addition means (not shown) to prevent a lack of organic matter during denitrification. If necessary, an organic substance such as methanol (CH ₃ OH) may be added.

A separation membrane 10 is accommodated in the membrane separation activated sludge tank 1 . As the type of membrane for the separation membrane 10, either a MF (microfiltration) membrane or a UF (ultrafiltration) membrane may be used. In particular, by using a membrane with a pore diameter of 0.2 μm or more or a molecular weight cut-off of 1 million or more, stable operation can be achieved over a long period of time while suppressing fouling.

Membrane materials include organic membranes such as PSF (polysulfone), PE (polyethylene), CA (cellulose acetate), PAN (polyacrylonitrile), PP (polypropylene), PVDF (polyvinylidene fluoride), and PTFE (polytetrafluoroethylene). ) etc. can be used, and as the inorganic membrane, a membrane using ceramic can be used. The filtration method may be either total volume filtration or cross-flow filtration, but from the viewpoint of suppressing fouling, it is desirable to adopt cross-flow filtration. There is no particular restriction on the format of the membrane module, and hollow fiber types, flat membrane types, spiral types, tube types, monolith types, etc. can be adopted.

The aeration device 2 can include an aeration device 21 housed in the membrane-separated activated sludge tank 1 and a blower 22 that supplies 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 placed below or at the bottom of the separation membrane 10, and sends gas into the membrane separation activated sludge tank 1 to peel off deposits (gel layer) deposited on the membrane surface and remove the membrane. It is configured to perform cleaning. The amount of aerated air 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.

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 an aeration period and the next aeration period. When intermittent aeration is performed, the operation of the suction pump 3 that sucks membrane-filtered water from the membrane-separated activated sludge tank 1 is during the OFF (suction stop) period, during which the aeration is performed using the aeration device 2. By setting the operating conditions so that membrane cleaning is performed, the membrane cleaning effect of the aeration device 2 can be obtained more effectively.

From the viewpoint of suppressing fouling of the separation membrane 10, it is preferable that an intermittent timer be provided to perform intermittent suction of the membrane-filtered water by the suction pump 3. During membrane filtration, organic matter is adsorbed onto the membrane surface of the separation membrane 10, making it easier for fouling to proceed. Therefore, especially when fouling is expected to progress, it is desirable to increase the flux and reduce the suction time ratio as much as possible. Specifically, when one cycle is defined as an operation performed once each during ON time and OFF time, it is desirable that the ratio of ON and OFF times of the intermittent timer per cycle is 59:1 to 4:1. More preferably, the ratio is 29:1 to 9:1.

The sludge pump 4 is connected to a withdrawal pipe 41 connected to the lower part of the membrane separation activated sludge tank 1, and extracts the treated sludge generated in the membrane separation activated sludge tank 1 as surplus sludge. The amount of sludge drawn by the sludge pump 4 can be adjusted as appropriate according to the operating conditions input from the control device 8.

As shown in FIG. 1, an organic matter concentration measuring device 5 for measuring the organic matter concentration of the membrane-filtered raw water contained in the membrane-separated activated sludge tank 1 and a suction pump 3 are used to measure the organic matter concentration from the inside of the membrane-separated activated sludge tank 1. An organic matter concentration measuring device 6 may be provided for measuring the organic matter concentration of the membrane-filtered water sucked into the outside of the membrane separation activated sludge tank 1.

As the organic matter concentration measuring devices 5 and 6, organic matter measuring instruments such as a COD meter, a BOD meter, a TOC meter, and an organic carbon detection size exclusion chromatography (LC-OCD) can be used. Membrane filtration raw water and membrane filtrate water are sampled manually or automatically without using the organic matter concentration measuring devices 5 and 6, and the organic matter concentration of membrane filtration raw water and membrane filtrate water is measured in a separate facility other than the wastewater treatment equipment shown in Figure 1. Of course, it is also possible to measure.

The measurement results of the organic matter concentrations of the membrane-filtered raw water and membrane-filtered water are input to the control device 8 . The membrane separation activated sludge tank 1 may further be provided with a measuring device, etc., 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. , the measurement results from each measuring device may be input to the control device 8.

The mechanism of membrane clogging of the separation membrane 10 is that substances that cause membrane clogging, such as polymeric flocculants contained in the membrane-filtered raw water, flow into the biological treatment and combine with activated sludge or its extracellular substances, resulting in polymeric and difficult-to-decompose substances. It is presumed that the membrane forms a complex and forms a gel layer on the membrane surface. Furthermore, once this gel layer is formed, the presence of the gel layer makes it easier for substances that cause membrane clogging to be captured on the membrane surface, and fouling progresses rapidly. Therefore, in order to prevent the occurrence of fouling, it is important to monitor the behavior of organic substances that cause membrane clogging.

In the wastewater treatment device and wastewater treatment method according to the embodiments 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 index of membrane clogging-causing substances. do. This is because this difference greatly affects the concentration of organic matter captured by the separation membrane 10, that is, the concentration of organic matter that forms the gel layer deposited on the surface of the separation membrane 10. In addition, as an indicator of fouling, it is also possible to measure the amount of filtration in a predetermined time (e.g., 5 minutes) using a filter paper with a predetermined pore size (e.g., 5C), but this method uses water temperature, the way the filter paper is folded, The measurement conditions such as MLSS and other operating conditions at the time of measurement may have an influence. Measuring the organic matter concentration difference as described above can reduce errors and is superior in terms of quantitative performance.

The membrane-filtered raw water in the membrane-separated activated sludge tank 1 is usually highly concentrated activated sludge. Therefore, when measuring the organic matter concentration in the liquid phase of membrane-filtered raw water as a monitoring index, filter the membrane-filtered raw water collected from membrane separation activated sludge tank 1, remove the activated sludge in the membrane-filtered raw water, and then Perform analysis. When collecting membrane-filtered raw water, easily decomposable organic matter in the undecomposed raw water and methanol added during denitrification remain in the upstream part of the membrane-separated activated sludge tank 1, which may affect the measurement of the difference in organic matter concentration. It may be harmful. Therefore, regarding the collection location, it is desirable to collect the sludge immediately before being subjected to membrane separation downstream of the membrane separation activated sludge tank 1. When filtering, it is desirable to use a pore size that is equal to or larger than the pore size of the membrane used in the membrane separation activated sludge tank 1, and typically has a pore size of about 0.45 to 1 μm. .

As mentioned above, COD, BOD, TOC, etc. can be adopted as the organic matter concentration to be measured as a monitoring index, but it is necessary to more appropriately measure the organic matter that causes the formation of the gel layer, and to properly measure the persistent polymer. It is more desirable to use COD _Mn , COD _Cr , and TOC as indicators for this purpose.

Although not limited to the following examples, for example, when using the difference value of COD _Mn (ΔCOD _Mn ) as a monitoring index, the standard for ΔCOD _Mn is set to 70 mg/L or less, further 60 mg/L or less, or 40 mg/L or less, and by changing the operating conditions of the membrane separation activated sludge tank 1 when the measured value exceeds a preset standard, it is possible to suppress membrane clogging of the membrane separation activated sludge tank 1 for a long period of time. can.

When performing circulating nitrification and denitrification for nitrogen removal in the membrane-separated activated sludge tank 1, easily decomposable organic matter may remain in the membrane-filtered water depending on the nitrification and denitrification conditions. If easily decomposable organic substances remain, it becomes difficult to quantitatively evaluate the substances that cause membrane clogging of the separation membrane 10. In such a case, it is preferable to measure persistent organic matter as an indicator of the concentration of organic matter to be measured. Here, the persistent organic matter is defined as the organic matter that remains after aerating the wastewater to be measured for a certain period of time (for example, 1 to 8 hours). By measuring such an organic matter concentration, signs of clogging of the separation membrane 10 can be detected more quickly.

Another method for measuring organic substances that cause membrane clogging is LC-OCD (Liquid Chromatography-Organic Carbon Detector), which is an analytical device that combines molecular weight fractionation and organic substance concentration distribution. There is a method to analyze it. The organic substances that cause membrane clogging are known to be fractionated by LC-OCD into molecules with a molecular weight of 20,000 or more, and by measuring the concentration of the liquid phase of membrane-filtered raw water and membrane-filtered water, It becomes possible to narrow down the target and quantify it.

LC-OCD is a liquid chromatograph organic carbon analyzer equipped with a size exclusion column, which converts dissolved organic matter in a sample into molar mass fractions (1) to (5) below using a liquid chromatograph equipped with a size exclusion column. After fractionation, each fraction is measured with an organic carbon meter and quantified as organic carbon.
(1) Biopolymers: Biopolymers, fractions with a molar mass of 20,000 g/mol or more (2) Humic Substances: Humic substances, fractions with a molar mass of 500 to 20,000 g/mol (3) Building Blocks: Building blocks (basic (4) LMW Acids: Low-molecular organic acids, fractions of organic acids with a molar mass of 350 g/mol or less (5) LMW Neutrals: Low-molecular neutral substances, mol Fractions other than organic acids with a mass of 350 g/mol or less

Analysis using LC-OCD can be performed, for example, by the following procedure. First, the collected sample was filtered through a PTFE membrane filter with a pore size of 0.45 μm, and an analysis sample was prepared by diluting it with ultrapure water (Milli-Q water) so that the TOC was 1 to 2 mg/L. Water is passed through the size exclusion column. It is fractionated into four fractions with a molar mass of 20,000 g/mol or more, a molar mass of 500 to 20,000 g/mol, a molar mass of 300 to 500 g/mol, and a molar mass of 350 g/mol or less, and the organic carbon concentration of each fraction is determined. Measure. Phosphate buffer (pH 6.58) is used as the mobile phase. As the LC-OCD analyzer, for example, LC-OCD Model 8 manufactured by DOC-Labor can be used.

After fractionation using the size exclusion column, each fraction was analyzed in a thin film reactor (Glanzel thin film reactor, DOC-Labor) using an acidifying solution (phosphoric acid, pH 1.5) and nitrogen gas purge to remove inorganic carbon. After being removed, it is oxidized with an ultraviolet lamp (DOCOX lamp, DOC-Lavor) and detected as CO ₂ with an NDIR (non-dispersive infrared absorption) detector. The obtained analysis results are analyzed using dedicated software (ChromCALC, DOC-Labor). Specifically, by dividing the peaks based on the shape of the chromatogram and calculating the concentration from the area of each peak, it is possible to quantify organic substances that are fractionated into molecules with a molecular weight of 20,000 or more using LC-OCD. can.

-How to improve driving-
In this embodiment, when the monitoring index increases, the following three measures are taken as an operation improvement method to reduce fouling: (1) reducing the inflow amount of substances that cause membrane clogging, and (2) adhering to the membrane. At least one of the following processes is carried out: (3) decomposition or discharge of membrane-clogging substances in the membrane-separated activated sludge tank 1; Of course, the processing conditions may be returned to normal conditions if the following improvement measures are appropriately taken so that the monitoring index falls within the appropriate range.

(1) Reducing the inflow amount of substances that cause membrane clogging If there is an excess of substances that cause membrane clogging in the membrane filtration raw water, for example, polymer flocculants in the dehydrated separation liquid, the concentration of polymer flocculants contained in the dehydrated separation liquid becomes high, combines with activated sludge and its extracellular substances, forms a complex, and becomes more likely to cause membrane clogging. Therefore, when the monitoring index increases, the optimum addition rate of additives such as polymer flocculants to be added to the membrane filtration raw water before it flows into the membrane separation activated sludge tank 1, for example in the pretreatment operation, can be determined. If possible to maintain stable operation, adjust operating conditions to reduce the amount of substances that cause membrane clogging by reducing the additive addition rate. do.

For example, when using a dehydrated separated liquid as raw water for membrane filtration, operating conditions may be changed to reduce the addition rate of polymer flocculant for dehydration treatment if the measured value of a monitoring index exceeds a preset standard. adjust. The optimum addition rate of the polymer flocculant can be confirmed by a flocculation test or by analyzing the colloidal charge of the dehydrated separated liquid. Other methods include reselecting the type of polymer flocculant, adjusting the addition rate of inorganic flocculant, and reducing the amount of garbage received if the monitoring index increases. You can take this approach.

(2) Promoting peeling of the gel layer adhering to the membrane One method for promoting the destruction of the gel layer adhering to the membrane of the separation membrane 10 housed in the membrane separation activated sludge tank 1 is to use an intermittent timer. A conceivable method is to adjust the filtration duration time of the separation membrane 10 by adjusting the timing of suction of membrane-filtrated water by the suction pump 3. If the monitoring index increases, the filtration duration ( By adjusting the ratio of ON and OFF times and lengthening the time when air bubbles are exposed to the membrane surface during the OFF time, the gel layer is Peeling can be promoted.

Another method for promoting the destruction of the gel layer adhering to the membrane of the separation membrane 10 housed in the membrane separation activated sludge tank 1 is to adjust the aeration time in the membrane separation activated sludge tank 1 by the aeration device 2. There is a method. For example, when the monitoring index increases, the amount of cleaning air supplied to the membrane separation activated sludge tank 1 is in the range of 6 to 30 L/m ² /min, more preferably in the range of 9 to 25 L/m ² /min. By increasing the amount by about 5 to 50% compared to normal operation, peeling of the gel layer adhering to the membrane surface of the separation membrane 10 can be promoted.

(3) Decomposition or discharge of membrane clogging substances in the membrane separation activated sludge tank 1 Even if the gel layer attached 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, and the molecular weight is It is large and has the property of being easily captured on the membrane surface. Therefore, as long as substances that are easily captured remain in the tank, they may adhere to the membrane surface again and continue to be in a state where fouling tends to progress. The following methods are preferably used as measures to promote emissions.

-SRT control-
The substances that cause the gel layer are likely to be captured by the membrane and remain in the tank together with the sludge. Therefore, the longer the SRT, the more concentrated the causative substance is, and the more likely fouling is to progress. For this reason, it is desirable to lower the SRT within a range that does not deteriorate processes such as nitrification and denitrification, and to discharge substances that cause the gel layer to the outside of the tank.

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 in order to prevent fouling, the SRT is lengthened and the sludge load is Measures may be taken to reduce the However, if the raw water contains substances that cause a persistent gel layer, such as dehydrated separated liquid, and the SRT is already within an appropriate range, lengthening the SRT will conversely promote the concentration of the substances that cause fouling. It may lead to doing so. For this reason, in this embodiment, it is preferable to adopt a method of maintaining an appropriate SRT and intentionally lowering the SRT to prevent concentration of the causative substance of the gel layer.

For SRT, by adjusting the amount of sludge extracted so that it is typically 35 days or less, more typically 30 days or less, wastewater treatment can be performed stably and efficiently over a long period of time while appropriately suppressing fouling. It becomes possible to do this. On the other hand, if the SRT is made too short, the transmembrane pressure difference of the separation membrane 10 increases, and stable processing may not be possible. Typically, SRT is preferably controlled to be 6 days or more, and preferably 10 days or more. Thereby, stable treatment can be performed while appropriately suppressing fouling of the separation membrane 10 in the membrane separation activated sludge tank 1.

-Physical chemical treatment-
When the monitoring index increases, at least a portion of the membrane-filtered raw water is treated with one or more of ozone decomposition treatment, accelerated oxidation treatment, and activated carbon adsorption treatment to eliminate the substances that cause the gel layer. Decompose and remove.

- Adjustment of activated sludge amount in membrane separation activated sludge tank 1 based on measured values of monitoring indicators -
Even if the SRT is adjusted appropriately, the condition inside the membrane-separated activated sludge tank 1 may temporarily become a state that promotes the formation of a gel layer due to changes in the membrane-filtered raw water or the like. In this embodiment, the sludge pump 4 is configured to increase the amount of sludge drawn from the membrane separation activated sludge tank 1 and reduce the amount of activated sludge in the membrane separation activated sludge tank 1 when the monitoring index increases. It is preferable that the causative substance of the gel layer adhering to the separation membrane 10 is discharged out of the tank by controlling the operating conditions for adjustment.

Although not limited to the following, the first sludge is capable of maintaining the transmembrane pressure difference of the separation membrane 10 within a preset allowable range and stably performing biological treatment by the membrane separation activated sludge method. If the monitoring index increases during the residence time (typically SRT is 6 to 35 days), the amount of sludge drawn from the membrane separation activated sludge tank 1 is increased. If the monitoring index increases during the second sludge retention time (typically less than 6 days) when the transmembrane pressure difference of the separation membrane 10 exceeds the above-mentioned allowable range, the membrane separation activated sludge tank 1 will be withdrawn. It is preferable to reduce the amount of sludge. Note that if the monitoring index increases when the SRT exceeds 35 days, reducing the amount of sludge drawn may lengthen the SRT and affect the treatment. Note that if the monitoring index increases when the SRT exceeds 35 days, the amount of sludge drawn from the membrane separation activated sludge tank 1 is increased.

The control device 8 is electrically connected to the blower 22 of the aeration device 2, the sludge pump 4, the suction pump 3, the organic matter concentration measuring devices 5 and 6, and the sludge concentration meter 7, and when the monitoring index increases, The aeration device is configured to perform one or more of the following: increasing the amount of washed air supplied to the membrane-separated activated sludge tank 1, shortening the filtration duration time, or increasing the amount of sludge drawn from the membrane-separated activated sludge tank 1. 2. Control the operating conditions of the suction pump 3 and the sludge pump 4.

The wastewater treatment method according to the embodiment of the present invention can be carried out using the wastewater treatment apparatus shown in FIG. That is, the wastewater treatment method according to the embodiment measures the organic matter concentration of the liquid phase of the membrane-filtered raw water and the organic matter concentration of the membrane-filtered water in the membrane separation activated sludge tank 1, and uses the difference as a monitoring index, and the monitoring index is When the amount of sludge increases, one or more of the following treatments are performed: increasing the amount of washed air supplied to the membrane-separated activated sludge tank 1, shortening the filtration duration time, or increasing the amount of sludge drawn from the membrane-separated activated sludge tank 1. including adjusting operating conditions to

As described above, according to the wastewater treatment apparatus and the wastewater treatment method according to the embodiment of the present invention, the organic matter concentration of the liquid phase of the membrane-filtered raw water in the membrane separation activated sludge tank 1 and the organic matter concentration of the membrane-filtered water are measured. The difference is used as a monitoring index, and when the monitoring index increases, the amount of inflow of substances that cause membrane clogging is reduced, the peeling of the gel layer adhering to the membrane is promoted, and the membrane clogging substances in the membrane separation activated sludge tank 1 are decomposed. Alternatively, by performing at least one or more treatment of discharge, signs of clogging of the separation membrane can be quickly detected, and wastewater treatment can be performed stably and efficiently while appropriately suppressing fouling.

(Modified example)
As a method of suppressing clogging of the separation membrane 10 in the membrane separation activated sludge tank 1, when the monitoring index increases, increasing the amount of cleaning air supplied to the membrane separation activated sludge tank 1, shortening the filtration duration time, or increasing the amount of cleaning air supplied to the membrane separation activated sludge tank 1, or It is preferable to optimize at least either the timing of increasing the amount of sludge drawn from the separated activated sludge tank or the treatment time for each treatment.

For example, the process of increasing the amount of cleaning air supplied to the membrane separation activated sludge tank 1 and shortening the filtration duration is a process for physically removing the gel layer attached to the separation membrane 10, and suppressing fouling. As a treatment for this, it tends to be effective in a relatively short period of time. On the other hand, the control of the sludge pump 4 to increase the amount of sludge drawn from the membrane separation activated sludge tank 1 is carried out to prevent the membrane separation activation from increasing the concentration of substances that tend to form a gel layer on the membrane surface of the separation membrane 10. This is a measure to adjust the concentration in the sludge tank 1, and as a measure to suppress fouling, it can be effective by continuing for a relatively long time. Therefore, depending on the degree of contamination of the separation membrane 10 and the concentration of sludge and inflow polymer flocculant in the membrane-separated activated sludge tank 1, short-term measures and long-term measures for suppressing fouling may be combined. is preferred.

Although an increase in the amount of cleaning air can suppress fouling in the short term, there are problems such as an increase in running costs due to an increase in the power consumption of the blower 22 and the disassembly of activated sludge. Furthermore, while increasing the filtration duration can suppress fouling in the short term, there is a limit to the amount of filtration per hour. Furthermore, SRT control requires a period of several days to several tens of days for sludge to be replaced, and it takes time for it to become effective. Therefore, in this embodiment, the process of increasing the amount of washed air and shortening the filtration duration time, which is effective in the short term, is combined with the process of adjusting the amount of drawn sludge, which is effective in the long term. For example, in the early stages of fouling, short-term and long-term measures are taken at the same time, and after sludge replacement progresses and monitoring indicators decline, short-term measures can be returned to the pre-treatment level to prevent fouling. While immediately suppressing the ring, running costs can be suppressed over a long period of time, and stable operation can be achieved.

As a specific example, but not limited to, for example, a first reference value and a second reference value larger than the first reference value are set in advance for a monitoring index. When the monitoring index increases and exceeds the first standard value, processing to increase the amount of sludge drawn from the membrane-separated activated sludge tank 1 is started, and when the monitoring index exceeds the second standard value, the membrane separation starts. The operating conditions can be adjusted so as to start the first process that increases the amount of washed air supplied to the activated sludge tank 1 and shortens the filtration duration time.

Specifically, the membrane separation activated sludge tank 1 has a first sludge retention time (typically 6 to 35 days) during which the transmembrane pressure difference of the separation membrane 10 falls within the standard range and stable biological treatment is performed. ), when the monitoring index increases, a first process of increasing the amount of cleaning air supplied to the membrane separation activated sludge tank 1 and shortening the filtration duration time; The operating conditions can be adjusted so as to perform at least one of the second process of increasing the amount of sludge drawn from the sludge.

In addition, if the monitoring index increases during the second sludge retention time (typically less than 6 days) where the transmembrane pressure difference of the separation membrane 10 exceeds the above reference range, the sludge is supplied to the membrane separation activated sludge tank 1. Perform at least one of a first process that increases the amount of washed air and shortens the filtration duration, and a third process that reduces the amount of sludge drawn from the membrane-separated activated sludge tank 1. The operating conditions can be adjusted accordingly. In addition, if the monitoring index increases when the SRT exceeds 35 days, a first treatment is performed in which one or more of increasing the amount of washed air supplied to the membrane separation activated sludge tank 1 and shortening the filtration duration time is performed. The operating conditions can be adjusted so as to perform at least one of the following:

As a result, the biological treatment in the membrane separation activated sludge tank 1 can proceed more stably, and while the treated water that meets the standard values can be stably and continuously obtained, rapid changes in the properties of the membrane-filtered raw water can be avoided. Even in such a case, it is possible to quickly detect signs of clogging of the separation membrane 10 and perform wastewater treatment stably and efficiently for a long period of time while appropriately suppressing fouling.

If the above measures are taken and a decrease in the monitoring index is confirmed, the first treatment will be carried out to increase the amount of washed air supplied to the membrane separation activated sludge tank 1 and shorten the filtration duration. By returning to the previous state in stages, it is possible to stabilize processing while reducing running costs.

Examples of the present invention will be shown below along with comparative examples, but these examples are provided to better understand the present invention and its advantages, and are not intended to limit the invention.

(Test 1) SRT control Dehydrated separated liquid of human waste and septic tank sludge is used as the membrane filtration raw water supplied to the membrane separated activated sludge tank equipped with a denitrification tank and a nitrification tank (membrane separation tank), and MLSS of the dehydrated separated liquid is used. 3,000 to 20,000 mg/L, SRT, TN-SS load of the nitrification tank (hereinafter referred to as "TN-SS load") and total tank BOD-SS load (hereinafter referred to as "BOD-SS load"). Table 1 shows the treatment test conditions and measurement results for examining membrane filtration performance due to changes in . Note that the BOD-SS load represents the total BOD-SS load of the denitrification tank and the nitrification tank.

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 degree of contamination of the membrane was evaluated based on the change in the pressure difference between the membranes, the difference in organic matter concentration (ΔS- _CODMn ), and the amount of 5C filter paper filtration. The 5C filter paper filtration amount is the result of measuring the amount of filtrate that can filter 50 ml of sludge mixture in 5 minutes using a 150 mmφ 5C filter paper. ΔS-COD _Mn represents the difference between the soluble COD _Mn (S-COD _Mn ) in the membrane separation tank mixture and the COD _Mn of the membrane-separated water. The higher this ΔS-COD _Mn , the higher the degree of contamination of the membrane surface, indicating that it is difficult to filter. Δ transmembrane pressure difference, ΔS-COD _Mn , and 5C filter paper filtration amount are all measured values after 3 months of continuous treatment.

Figures 2 to 4 show the relationship between the SRT obtained in Test 1, ΔS- _CODMn , which is an indicator of the degree of membrane contamination, the transmembrane pressure difference, and the amount of 5C filter paper filtration. When SRT was 10 to 30 d, ΔS-COD _Mn was relatively stable at 22 to 40 mg/L, and it was judged that there was little membrane contamination. On the other hand, when the SRT was as short as 6d, ΔS-COD _Mn was as high as 82 mg/L, and it was determined that there was a lot of membrane contamination. Furthermore, when the SRT was as long as 40 d, ΔS-COD _Mn was as high as 90 mg/L, indicating that there was a lot of membrane contamination.

From the relationship between SRT and transmembrane differential pressure shown in Figure 3, in order to keep the transmembrane differential pressure below 25 KPa, which is a guideline for stabilizing treatment, and preferably below 20 KPa, SRT should be 6 to 35 d, and more preferably 10 to 30 d. It is assumed that it is reasonable. From the relationship between SRT and 5C filter paper filtration amount shown in FIG. It is judged that it is preferable to set the distance between 10 and 30 d.

Figures 5 to 7 show the relationship between the BOD-SS load of the entire reaction tank, ΔS- _CODMn , transmembrane pressure difference, and 5C filter paper filtration amount obtained in the test. In terms of BOD-SS load, it is considered appropriate to set the BOD-SS load to 0.05 to 0.2 kg/kg/d in order to suppress membrane contamination. FIG. 8 shows the relationship between ΔS-COD _Mn and the transmembrane pressure difference, and FIG. 9 shows the relationship between ΔS-COD _Mn and the amount of 5C filter paper filtration. A good correlation was observed between ΔS-COD _Mn and transmembrane pressure. In order to keep the transmembrane pressure differential at 20 KPa or less, which is a standard for stable treatment, it is preferable to operate and manage the ΔS-COD _Mn at 40 mg/L or less. A similarly good correlation was observed between ΔS-COD _Mn and the amount of 5C filter paper filtration. In order to maintain the 5C filter paper filtration amount to 10 ml or more, which is a guideline for good filtration performance, it is preferable to operate and manage the ΔS-COD _Mn at about 70 mg/L or less.

From the above results, according to one embodiment of the present invention, in order to suppress membrane contamination and maintain stable filtration performance, ΔS-COD _Mn should be at least 70 mg/L or less, preferably 40 mg/L or less. It has been found that it is preferable to manage the operating conditions and make appropriate adjustments to SRT and BOD-SS to ensure that the conditions are met.

(Test 2) Examination of aeration air volume under appropriate SRT conditions and appropriate suction time conditions Using the same equipment as in Test 1, using dehydrated separated liquid of human waste and septic tank sludge as membrane filtration raw water, the MLSS of the dehydrated separated liquid was 3,000 ~ The concentration was changed to 20,000 mg/L, and the membrane filtration performance was examined by changing the amount of washed air and the filtration duration (suction timer). The results are shown in Table 2.

Under the conditions of SRT18d, where suction is repeated for 9 minutes and suction stopped for 1 minute, the transmembrane pressure remains as low as 17 to 23 Kpa, and the amount of 5C filter paper filtration is maintained at a low value of 15 to 18 L/m ² /min. The volume was 21 mL and in good condition (Nos. 11 to 13). When the amount of cleaning air was reduced to 4 L/m ² /min, the transmembrane pressure difference increased to 26 Kpa, and the amount of 5C filter paper filtration was as small as 9.2 mL, showing signs of membrane clogging (No. 14).

By stopping suction for 1 minute every 20 to 40 minutes under the conditions of SRT18d and cleaning air volume of 18 L/m ² /min, the transmembrane differential pressure is maintained at a low value of 24 to 32 Kpa, and the amount of 5C filter paper filtration is reduced. The volume was 16 to 20 mL and 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 amount of 5C filter paper filtration was as small as 8.4 mL, showing signs of membrane clogging (No. 17).

(Test 3) Control based on monitoring index Continuous operation was performed under the following three conditions, and the number of days until the transmembrane differential pressure reached 30 kPa or more was investigated.
(1) Comparative example 1: Normal operation, no control based on monitoring index (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)
(If ΔS-COD _Mn is 40 mg/L or more, control is performed to change the cleaning air volume from normal operation to 9 L/m ² /min and suction timer On: Off = 9:1, and ΔS-COD _Mn is 30 mg/L. /L or less, control was performed to return to normal operation)
(3) Example 2: Control based on monitoring indicators (combination of short-term and long-term treatments)
If ΔS-COD _Mn is 40 mg/L or more, change the cleaning air amount from normal operation to 9 L/m ² /min, suction timer On: Off = 9:1, operate the sludge pump, and change SRT to 14 days. Change, when ΔS-COD _Mn is below 30mg/L, control is performed to return to normal operation, and when S-COD _Mn is below 30mg/L, the amount of cleaning air is set to 7L/m ² /min, and the suction timer is turned on. :Off=12:1, SRT was set to 14 days, and control was performed to return to normal operating conditions when S-COD _Mn was 20 m or less.

When only the short-term treatment of Example 1 is performed, the operation time is 234 days, and when the combination of short-term treatment and long-term treatment of Example 2 is performed, it is 381 days, which is a longer period of stable operation than in Comparative Example 1 where no control is performed. It was confirmed that it can be done.

1... Membrane separation activated sludge tank 2... Aeration device 3... Suction pump 4... Sludge pumps 5, 6... Organic matter concentration measuring device 7... Sludge concentration meter 8... Control device 10... Separation membrane 21... Diffusion device 22... Blower 41 …Pull-out piping

Claims (7)

In a wastewater treatment method using the membrane separation activated sludge method, the organic matter concentration of the liquid phase of the membrane filtration raw water in the membrane separation activated sludge tank and the organic matter concentration of the membrane filtration water are measured and the difference is used as a monitoring index. When the sludge retention time in the activated sludge tank is 6 days or more and the monitoring index increases, the amount of cleaning air supplied to the membrane-separated activated sludge tank is increased, the filtration continuation time is shortened, or the sludge retention time in the membrane-separated activated sludge tank is increased. A wastewater treatment method comprising adjusting operating conditions to perform one or more of the following: shortening sludge retention time. When the sludge retention time in the membrane separation activated sludge tank is 6 days or more and the monitoring index exceeds a preset standard, in addition to increasing the amount of cleaning air supplied to the membrane separation activated sludge tank or shortening the filtration continuation time. The wastewater treatment method according to claim 1, further comprising adjusting operating conditions so as to shorten the sludge retention time in the membrane-separated activated sludge tank. 2. The method according to claim 1, wherein the concentration of organic matter includes measuring any one of COD, BOD, TOC, or the concentration of organic matter fractionated to have a molecular weight of 20,000 or more as measured by size exclusion chromatography using organic carbon detection. The wastewater treatment method described in . Claims 1 to 3, further comprising subjecting at least a portion of the membrane-filtered raw water to one or more of ozonolysis treatment, accelerated oxidation treatment, and activated carbon adsorption treatment when the monitoring index increases. 3. The wastewater treatment method according to any one of 3. The wastewater treatment method according to any one of claims 1 to 4, wherein the membrane filtration raw water is a dehydrated separated liquid generated after dehydrating sludge containing organic matter by adding a polymer flocculant. A claim comprising performing a process of reducing the addition rate of a polymer flocculant added to the membrane-filtered raw water in a dehydration process before being supplied to the membrane-separated activated sludge tank when the monitoring index increases. The wastewater treatment method according to any one of items 1 to 5. a membrane separation activated sludge tank for obtaining membrane filtration water by subjecting membrane filtration raw water to membrane separation treatment in the presence of activated sludge;
an aeration device for aerating the membrane-separated activated sludge tank;
a suction pump that sucks the membrane-filtered water from the membrane-separated activated sludge tank;
a sludge pump that extracts sludge from the membrane-separated activated sludge tank;
The difference value between the organic matter concentration of the liquid phase of the membrane-filtered raw water in the membrane-separated activated sludge tank and the organic matter concentration of the membrane-filtered water is used as a monitoring index, and if the sludge retention time in the membrane-separated activated sludge tank is 6 days or more, When the monitoring index increases, any one or more of increasing the amount of cleaning air supplied to the membrane-separated activated sludge tank, shortening the filtration duration time, or shortening the sludge retention time in the membrane-separated activated sludge tank. A wastewater treatment device comprising: a control device that controls operating conditions of the aeration device, the suction pump, and the sludge pump so as to perform the following steps.