JP5034778B2 - Membrane separation wastewater treatment method and apparatus - Google Patents

Description

  The present invention relates to a membrane separation type wastewater treatment method and apparatus for treating wastewater such as organic matter-containing water with biological sludge and membrane separation of a mixed liquid containing biological sludge to obtain treated water.

  Biological treatment is known as a method for treating wastewater containing organic matter and the like. Among biological treatment methods, an activated sludge method using a microbial community called activated sludge is widely used because it can be applied to wastewater of various properties and can provide treated water with good water quality. In the activated sludge method, wastewater containing a pollutant that becomes a substrate of the activated sludge is introduced into a biological treatment tank and brought into contact with the activated sludge to biodegrade the pollutant. Since the biologically treated water flowing out from the biological treatment tank contains biological sludge, the clarified treated water is obtained by separating the solid content with a solid-liquid separator.

  As a solid-liquid separator, a precipitation device is often used. In a precipitation apparatus, solid-liquid separation is generally performed by gravity sedimentation of activated sludge that has been flocked. Biological sludge tends to flock as the sludge residence time (SRT) increases. Therefore, a method is known in which a plurality of biological treatment tanks are provided, the biological treatment tank on the front stage is operated at a high load and microorganisms are exponentially grown, and then introduced into the biological treatment tank on the rear stage with a longer SRT. (Patent Document 1). In this method, the biological sludge in a dispersed state grown in the former-stage biological treatment tank is flocked in the latter-stage biological treatment tank, and the sedimentation property becomes high.

On the other hand, when a membrane separator is used as the solid-liquid separator, a mixed liquid containing biological sludge having poor sedimentation can also be clarified. Therefore, a membrane separation type biological treatment apparatus provided with a membrane separation apparatus in the subsequent stage of the biological treatment tank and a biological treatment method using the same are also known (for example, Patent Document 2).
Japanese Patent No. 3478241 JP 2005-74346 A

  By the way, the membrane separation apparatus has a problem that the separation membrane is clogged. In particular, when biologically treated water containing biological sludge is subjected to membrane separation, sticky substances produced by microorganisms tend to adhere to the membrane surface and easily clog.

  As a measure for preventing clogging of the membrane, a method of devising a cleaning method of the separation membrane is known in addition to a method of aggregating a viscous material with a flocculant as in the method described in Patent Document 2. Specifically, the separation membrane is back-washed with a chemical such as sodium hypochlorite about once a week or two weeks. However, such a simple cleaning method requires cleaning chemicals, and requires an alternative separation membrane to obtain treated water even while the separation membrane is being cleaned, resulting in high costs.

  As another method for preventing clogging of the membrane, there is a method of devising a water passing method to the membrane. Specifically, after performing suction filtration with a separation membrane for about 10 minutes, intermittent suction for stopping suction is performed for about 1 minute. When intermittent suction is performed, since the treated water cannot be obtained during the suction stop time, the efficiency of membrane separation is not good.

  As another method for preventing clogging of the membrane, there is a method of reducing the activated sludge suspended solid (MLSS) concentration and sludge load in the biological treatment tank. In this method, MLSS is lowered (for example, 12,000 mg / L or less) in order to reduce the amount of biological sludge adhering to the membrane. In addition, the sludge retention time (SRT: Sludge Retention Time) is reduced by reducing the BOD (organic matter expressed in terms of biochemical oxygen consumption) sludge load on the sludge retained in the biological treatment tank in order to suppress the production of mucilage. ) To be long.

  However, the effect of controlling MLSS and SRT is not always sufficient. Moreover, if the MLSS of the biological treatment tank is lowered and the SRT is lengthened, the biological treatment apparatus cannot be made compact because the load on the biological treatment tank is reduced.

  An object of the present invention is to improve the effect of preventing clogging of a film against such a problem.

  The present inventor returns a certain amount or more of the separated sludge separated by the membrane separation apparatus to the biological treatment tank and absorbs the pollutant such as the BOD component in the separated sludge, and then decomposes it to make the viscous material As a result, the present invention was completed. Specifically, the present invention provides the following.

(1) A membrane-separated wastewater treatment method in which wastewater is biologically treated with a biological treatment device, and then biologically treated water flowing out from the biological treatment device is separated into liquid and separated sludge in a membrane separation tank equipped with a separation membrane. The biological treatment apparatus is composed of a first biological treatment tank to which the separated sludge is returned, and a second biological treatment tank provided at a stage subsequent to the first biological treatment tank, and to the first biological treatment tank The return amount of the separated sludge is 10 times or more the base mass contained in the wastewater and flowing into the first biological treatment tank as the dry mass of MLVSS, and the membrane for operating the first biological treatment tank at a high load Separated wastewater treatment method.
(2) The wastewater is organic-containing water containing a BOD component as the substrate, and the first biological treatment tank is operated at a high load of BOD sludge load 4 kg-BOD / kg-MLVSS / day or higher (1) The membrane separation type wastewater treatment method according to 1.
(3) The biological treatment apparatus is composed of three or more biological treatment tanks connected in series with each other, and the sludge of the last biological treatment tank provided on the front side of the membrane separation tank and connected to the membrane separation tank. The membrane separation wastewater treatment method according to (1) or (2), wherein the residence time is 20 days or longer.
(4) A biological treatment apparatus including a first biological treatment tank in which wastewater is introduced and operated at a high load, a second biological treatment tank provided at a stage subsequent to the first biological treatment tank, and the biological treatment apparatus including a separation membrane A membrane separation tank for separating the biologically treated water flowing out from the liquid into liquid and separated sludge, and a sludge return pipe for returning the separated sludge to the first biological treatment tank, wherein the separated sludge is dried by MLVSS. A membrane-separated wastewater treatment apparatus comprising: a sludge return pipe that is returned so as to be 10 times or more the basic mass flowing into the first biological treatment tank by being contained in the wastewater as a weight.
(5) The waste water is organic-containing water containing a BOD component as the substrate, and the first biological treatment tank is a treatment tank operated at a high load of BOD sludge load 4 kg-BOD / kg-MLVSS / day or higher. The membrane separation type waste water treatment apparatus as described in (4).
(6) The biological treatment apparatus includes three or more biological treatment tanks connected in series with each other, and the last biological treatment tank provided on the front side of the membrane separation tank and connected to the membrane separation tank is sludge. The membrane separation waste water treatment apparatus according to (4) or (5), which is a treatment tank operated for a residence time of 20 days or longer.

  The wastewater to be treated according to the present invention is not limited as long as it contains a pollutant that becomes a substrate for activated sludge. The pollutant is not limited to the BOD component, and may be nitrogen such as organic nitrogen or ammonia nitrogen. Therefore, the “biological treatment tank” includes an “aeration tank” that removes BOD aerobically, a “digestion tank” that decomposes organic matter anaerobically, a “nitrification tank” that performs nitrification, and a “denitrification tank” that performs denitrification. "Nitrogen tank" shall be included. The biological treatment tank holds biological sludge that grows using the pollutant as a substrate. Examples of such biological sludge include sludge mainly composed of aerobic bacteria that decompose BOD (hereinafter referred to as “BOD sludge”), sludge mainly composed of nitrifying bacteria that oxidize ammonia (hereinafter referred to as “nitrified sludge” in particular). Sludge mainly composed of denitrifying bacteria that reduce nitric acid or nitrous acid (hereinafter, particularly referred to as “denitrified sludge”), and sludge mainly composed of methane bacteria (hereinafter, particularly referred to as “methane sludge”). Is mentioned.

  The biological treatment apparatus includes two or more biological treatment tanks connected in series. The separated sludge obtained by the membrane separation apparatus at the latter stage of the biological treatment apparatus is returned to the biological treatment tank (first biological treatment tank) into which the wastewater containing the substance that becomes the substrate of the activated sludge is introduced.

  Separated sludge absorbs substrates such as sugar, protein, and organic acids. The amount of substrate absorbed by the separated sludge is about 1/10 of that of activated sludge organic suspended solids (MLVSS). Therefore, in the present invention, the return amount of the separated sludge is set to 10 times or more of the substrate such as BOD brought into the first biological treatment tank in terms of MLVSS dry mass. If the return amount of the separated sludge is set in this way, almost the entire amount of the substrate flowing into the first biological treatment tank can be absorbed by the separated sludge. The term “10 times or more” refers to the amount required for the separated sludge to absorb the substrate brought into the treatment tank in the first biological treatment tank. However, depending on the type of substrate, the amount absorbed by the separated sludge may be larger than the above-mentioned value. In such a case, it is within the equivalent range of the present invention that the return amount of the separated sludge is an amount capable of absorbing the substrate while being less than 10 times the substrate brought into the first biological treatment tank.

  On the other hand, the rate at which these substrates are degraded by the metabolic activity of microorganisms is much slower than the absorption rate. In the present invention, the substrate is absorbed only by the separated sludge in the first biological treatment tank, and the substrate absorbed by the separated sludge is decomposed in the subsequent stage of the first biological treatment tank. By doing in this way, the activated sludge with little production amount of mucilage can be formed in the latter part of the 1st biological treatment tank.

  Moreover, the absorption rate of the substrate by the separated sludge is about 4 kg-BOD / kg-MLVSS / day as BOD. Therefore, the residence time of the first biological treatment tank may be a time that allows the separated sludge to absorb the substrate. Specifically, the BOD sludge load of the first biological treatment tank is preferably a high load of 4 kg-BOD / kg-MLVSS / day or more, which is similar to the absorption rate of the substrate by the separated sludge. By making such a high load, the first biological treatment tank can not only absorb the substrate in the separated sludge, but also the first biological treatment tank can be miniaturized. However, when the substrate is mainly composed of substances that are not easily absorbed by the separated sludge, such as polyethylene glycol (PEG), polyvinyl alcohol (PVA), and machine oil, the BOD sludge load in the first biological treatment tank is 4 kg-BOD / kg- It is better to make it lower than MLVSS / day.

  If the first biological treatment tank is operated at a high load without returning a sufficient amount of separated sludge, the amount of mucus produced by the biological sludge increases, causing clogging of the membrane, which is not preferable.

  In the present invention, the separated sludge separated in the membrane separation tank is returned to the first biological treatment tank to absorb the substrate in the waste water, and then biodegradation is performed in the biological treatment tank subsequent to the first biological treatment tank. By making it, the production | generation of a sticky substance can be suppressed. Therefore, according to this invention, the clogging at the time of carrying out membrane separation of the biologically processed liquid mixture can be avoided effectively.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Hereinafter, the same members are denoted by the same reference numerals, and description thereof is omitted or simplified.

  FIG. 1 is a schematic view of a membrane separation wastewater treatment apparatus (hereinafter simply referred to as “treatment apparatus”) 1 used in the present invention. The processing apparatus 1 includes a biological processing apparatus 10 and a membrane separation tank 21. The biological treatment apparatus 10 includes a first biological treatment tank 11 and a second biological treatment tank 12, and the first biological treatment tank 11 and the second biological treatment tank 12 are each provided with a diffuser pipe 15 as an aeration means. ing.

  A separation membrane 17 is provided in the membrane separation tank 21, and the separation membrane 17 is immersed in the liquid. The membrane separation tank 21 is also provided with an air diffuser 15. The air diffusion tube 15 is disposed at the bottom of the membrane separation tank 21 and below the separation membrane 17 so that the separation membrane 17 can be aerated and washed.

  A raw water pipe 30 is connected to the first biological treatment tank 11, and wastewater is introduced into the biological treatment apparatus 10 through the raw water pipe 30. The first biological treatment tank 11 and the second biological treatment tank 12 are connected in series via the first treatment liquid pipe 31. The second biological treatment tank 12 is connected to the membrane separation tank 21 via the second treatment liquid pipe 32. The membrane separation tank 21 is further connected to a sludge extraction pipe 35 from which separated sludge separated by the separation membrane is taken out and a separation water pipe 36 from which separated water (treated water) is taken out. A sludge return pipe 37 is branched from the sludge extraction pipe 35, and the sludge return pipe 37 is connected to the first biological treatment tank 11. The separated sludge separated in the membrane separation tank 21 is returned to the first biological treatment tank 11 through the sludge extraction pipe 35 and the sludge return pipe 37.

  The wastewater contains substances that serve as microbial substrates, such as BOD components and nitrogen. Hereinafter, the biological treatment method according to the present invention in the case where the organic substance-containing water containing the BOD component is treated as wastewater using the treatment apparatus 1 will be described.

  Wastewater containing a BOD component is introduced into the first biological treatment tank 11 and mixed with the separated sludge sent from the membrane separation tank 21. The return amount of the separated sludge is such that the dry mass as MLVSS is 10 times or more the BOD amount included in the wastewater and brought into the first biological treatment tank 11.

For example, when the BOD concentration of the organic substance-containing water flowing into the first biological treatment tank 11 is 1,000 mg / L and the inflow amount is 100 m ³ / day, the BOD amount brought into the first biological treatment tank 11 is 100 kg. / Day. Therefore, the return amount of the separated sludge may be 1,000 kg-MLVSS / day or more as MLVSS (dry mass).

  According to the knowledge of the present inventor, the returned separated sludge absorbs the BOD component serving as a substrate into the microorganism at a rate of 4 kg-BOD / kg-MLVSS / day or more. The absorption rate of the substrate by the separated sludge is the fastest under aerobic conditions, but the absorption rate does not decrease so much even under anaerobic conditions or under anaerobic conditions. In addition, there is no significant difference depending on the type of sludge (difference between BOD sludge and nitrified sludge, etc.) and the difference in substrate (difference between BOD component and nitrogen, etc.).

  In the present invention, in the first biological treatment tank 11, the separated sludge and the waste water are mixed and the substrate (BOD component) in the waste water is absorbed by the separated sludge. That is, in Patent Document 2, the biological sludge is propagated in the first biological treatment tank using the pollutant in the wastewater as a substrate. In the present invention, the biological sludge is not propagated, but the separated sludge returned from the membrane separation tank 21 is contaminated. Absorb material in separated sludge. Therefore, in the present invention, the return amount of the separated sludge is set as described above.

The separated sludge is taken out from the first biological treatment tank when the substrate is absorbed. For this reason, in the 1st biological treatment tank 11, what is necessary is just to apply the sludge load equivalent to or more than the absorption rate of the substrate by separation sludge, and to shorten hydraulic residence time (HRT). Specifically, the BOD sludge load of the first biological treatment tank 11 is preferably 4 kg-BOD / kg-MLVSS / day or more. For example, when the MLVSS concentration of the separated sludge is 15,000 mg / L and the MLVSS concentration of the first biological treatment tank 11 is 10,000 mg / L under the above conditions, the BOD sludge load of the first biological treatment tank 11 is 5 kg- As BOD / kg-MLVSS / day, HRT is set to 36 minutes or less. In this case, if it is the separation sludge having the above-mentioned MLVSS concentration, the return amount may be 67 m ³ / day (return rate 67%) or more.

  Operating the first biological treatment tank 11 with such a high load and shortening the HRT also leads to miniaturization of the biological treatment apparatus 10. If the load of the first biological treatment tank 11 is lowered, the apparatus is increased in size, and the effect of suppressing the generation of mucilage by biological sludge cannot be obtained satisfactorily.

  The operating condition of the first biological treatment tank 11 is sufficient if the ratio of the inflow BOD amount and the return amount of the separated sludge satisfies the above condition, and further satisfies the above load condition. Other conditions (oxygen) The concentration is not limited. However, the absorption of the substrate by the separated sludge is an effect caused by microbial activity, and is therefore affected by pH and temperature. For this reason, the pH of the solution in the tank of the first biological treatment tank 11 is near neutral (about 6 to 8.5), and the temperature is preferably about 10 to 40 ° C.

  The liquid in the tank of the first biological treatment tank 11 is taken out from the first treatment liquid pipe 31 and introduced into the second biological treatment tank 12. In the present invention, most of the organic matter flowing into the biological treatment apparatus 10 is absorbed by the separated sludge in the first biological treatment tank 11, so that the substrate absorbed in the separated sludge is biodegraded in the second biological treatment tank 12. Just do it. Specifically, in the second biological treatment tank 12, the load is reduced and the SRT is increased (20 days or more). By doing so, it is possible to biodegrade the substrate absorbed by the separated sludge and to obtain activated sludge with a small amount of mucilage produced.

  The operating conditions of the second biological treatment tank 12 are not particularly limited, except that it is preferable to lengthen the SRT, and may be any conditions as long as the absorbed substrate is decomposed. In the present invention, in the first biological treatment tank 11, most of the BOD contained in the raw water is absorbed by the separated sludge, so that the BOD sludge load of the second biological treatment tank 12 is reduced.

  The solution in the tank taken out from the second biological treatment tank 12 is sent to the membrane separation tank 21 via the second treatment liquid pipe 32. In the activated sludge contained in the tank liquid (biologically treated water) sent to the membrane separation tank 21, the production of mucilage is suppressed. Therefore, in the membrane separation tank 21, it is not necessary to perform intermittent suction in order to prevent the separation membrane 17 from being clogged. However, intermittent suction is not excluded. The separated sludge separated from the liquid by membrane separation is extracted from the sludge extraction pipe 35, and the necessary amount described above is sent to the first biological treatment tank 11 through the sludge return pipe 37 by the pump P provided in the middle thereof. Excess extracted sludge may be discharged out of the system from the sludge extraction pipe 35. The separated water may be taken out from the separated water pipe 36 as treated water.

  The separation membrane 17 is not particularly limited as long as it is a membrane generally used for solid-liquid separation. Specifically, a microfiltration (MF) membrane or an ultrafiltration (UF) membrane may be used, and the shape of the membrane module may be a hollow fiber or a flat membrane.

  The present invention is not limited to the above method. Next, as another embodiment of the present invention, a processing method using the processing apparatus 2 shown in FIG. 2 will be described. The treatment apparatus 2 is different from the treatment apparatus 1 according to the first embodiment in that the biological treatment apparatus 10B includes three biological treatment tanks connected in series. The three biological treatment tanks are referred to as a first biological treatment tank 11B, a second biological treatment tank 12B, and a third biological treatment tank 13 from the front side.

  The first biological treatment tank 11B is the same as the first biological treatment tank 11 of the treatment apparatus 1 of the first embodiment in that separated sludge is returned and wastewater containing a substrate is introduced. However, in the processing apparatus 2, the first biological treatment tank 11 </ b> B does not include an aeration tube, and instead includes a stirrer 16 so as to perform anaerobic biological treatment. In the treatment apparatus 2 as well, the first biological treatment tank 11B is preferably returned to the separation sludge 10 times or more of the substrate (for example, protein) flowing into the first biological treatment tank 11B from the membrane separation tank 21 and operated at a high load.

  The 2nd biological treatment tank 12B is comprised as an anaerobic biological treatment tank provided with the stirrer 16 without the aeration pipe | tube with the structure similar to the 1st biological treatment tank 11B. The third biological treatment tank 13 corresponds to the second biological treatment tank 12 in the treatment apparatus 1 of the first embodiment, and is operated with a low SRT by extending the SRT.

  As described above, when three or more biological treatment tanks are connected in series, the separated sludge of 10 times or more in terms of MLVSS dry mass is returned to the first biological treatment tank into which the wastewater containing the substrate is introduced. . Moreover, the load of the first biological treatment tank to which the separated sludge is returned is increased. On the other hand, the biological treatment tank (last biological treatment tank) disposed immediately before the membrane separation tank is preferably operated with a longer SRT.

[Example 1]
As waste water, food factory waste water (BOD concentration 1,900 mg / L) was treated with an apparatus having the same configuration as the processing apparatus 1 shown in FIG. Both the first biological treatment tank 11 and the second biological treatment tank 12 are aerobic treatment tanks operated under aerobic conditions. The membrane separation tank 21 was aerated by immersing a microfiltration membrane made of polyethylene (module type: hollow fiber membrane, manufactured by Mitsubishi Rayon Co., Ltd., trade name “Sterapore LFM”). The membrane area was 4 m ² . The other operating conditions of each tank are described below.

[First biological treatment tank]
MLVSS: 8,300-8,900 mg / L
HRT: 1.1 hours BOD sludge load: 4.4-4.7 kg-BOD / kg-MLVSS / day
[Second biological treatment tank]
MLVSS: 8,400-9,000mg / L
HRT: 24 hours [membrane separation tank]
MLVSS: 15,500mg / L
Membrane flux: 0.4 m / day
HRT: 1 hour

  In Example 1, the return amount of the separated sludge from the membrane separation tank 21 was set to 125% of the raw water inflow amount to the first biological treatment tank 11. This return amount is about 10.2 times the inflow BOD amount to the first biological treatment tank 11 as the dry mass of MLVSS.

  As a result of treating the wastewater for 10 days under the above conditions, the pressure loss of the separation membrane hardly increased. The water quality of the separated water (treated water) obtained after membrane separation was a total organic matter (TOC) concentration of 34 mg / L, and the soluble TOC concentration of the membrane separation tank was 35 mg / L.

[Example 2]
As Example 2, the processing was performed by an apparatus having the same configuration as the processing apparatus 2 shown in FIG. In Example 2, the first biological treatment tank 11B and the second biological treatment tank 12B are both anaerobic treatment tanks operated under anaerobic conditions. The configuration and operating conditions of the second biological treatment tank 12B were the same as those of the first biological treatment tank 11B, but the HRT was 8 hours. The third biological treatment tank 13 has the same configuration and operating conditions as the second biological treatment tank 12 of Example 1, and the membrane separation tank 21 also has the same configuration and operating conditions as in Example 1.

  In Example 2, the same waste water as Example 1 was processed on the same conditions as Example 1 except having made the 1st biological treatment tank 11B and the 2nd biological treatment tank 12B into the anaerobic treatment tank. As a result of treating wastewater for 10 days under these conditions, the pressure loss of the separation membrane hardly increased. The water quality of the separated water (treated water) obtained after the membrane separation was a TOC concentration of 32 mg / L, and the soluble TOC concentration of the membrane separation tank was also 32 mg / L.

[Comparative Example 1]
As Comparative Example 1, an experiment was performed in Example 1 in which the load of the first biological treatment tank 11 was reduced. Specifically, the BOD sludge load was lowered by setting the HRT of the first biological treatment tank 11 to 2 hours. Except for reducing the load on the first biological treatment tank 1, the same waste water as in Example 1 was treated with the same configuration and operating conditions as in Example 1. As a result, the pressure loss of the separation membrane began to increase immediately after operation, and increased by 16 kPa over 4 days. The quality of the treated water at this time was a TOC concentration of 30 mg / L, and the soluble TOC concentration of the membrane separation tank was 58 mg / L.

[Comparative Example 2]
In Comparative Example 2, the return amount of the separated sludge to the first biological treatment tank 11 in Example 1 was reduced. Specifically, the return amount of the separated sludge to the first biological treatment tank 1 was set to 80% of the raw water inflow amount to the first biological treatment tank 11. Except for reducing the amount of sludge returned, the same waste water as in Example 1 was treated under the same configuration and operating conditions as in Example 1. As a result, the pressure loss of the separation membrane started to increase immediately after the operation, and increased by 21 kPa in 7 days. The quality of the treated water at this time was a TOC concentration of 44 mg / L, and the soluble TOC concentration of the membrane separation tank was 87 mg / L.

  From the above, it was shown that according to the present invention, the production of mucilage by microorganisms can be suppressed to prevent clogging of the film. In general, the activated sludge method generally produces about 2 to 3% of metabolites of organic substances that are decomposed into biological sludge. According to the present invention, the amount of metabolites produced is decomposed. It is suppressed to 1-2% of the organic matter. In particular, as shown in Example 2, if the biological treatment apparatus is constituted by three or more biological treatment tanks connected in series and processed, the amount of metabolite produced itself is about 1 to 2%. It is possible to reduce the amount of polymer material that is a major cause of clogging.

  The present invention can be used for membrane separation biological treatment of wastewater containing organic matter and the like.

The schematic diagram of the waste water treatment equipment concerning the 1st embodiment used for the present invention. The schematic diagram of the waste water treatment equipment concerning the 2nd embodiment used for the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2, Waste water treatment apparatus 10, 10B Biological treatment apparatus 11, 11B 1st biological treatment tank 12, 12B 2nd biological treatment tank 13 3rd biological treatment tank 15 Aeration pipe 16 Stirrer 17 Separation membrane 21 Membrane separation tank

Claims (6)

A membrane-separated wastewater treatment method in which biologically treated water discharged from the biological treatment device is separated into liquid and separated sludge in a membrane separation tank equipped with a separation membrane after biological treatment of the wastewater with the biological treatment device,
The biological treatment apparatus is composed of a first biological treatment tank to which the separated sludge is returned, and a second biological treatment tank provided at a stage subsequent to the first biological treatment tank,
The amount of return of the separated sludge to the first biological treatment tank is at least 10 times the base mass contained in the wastewater and flowing into the first biological treatment tank in terms of dry weight of MLVSS,
A membrane-separated wastewater treatment method for operating the first biological treatment tank with a high load. The waste water is an organic substance-containing water containing a BOD component as the substrate,
The membrane-separated wastewater treatment method according to claim 1, wherein the first biological treatment tank is operated at a high load of BOD sludge load 4 kg-BOD / kg-MLVSS / day or higher. The biological treatment apparatus is composed of three or more biological treatment tanks connected in series with each other,
The membrane separation wastewater treatment method according to claim 1 or 2, wherein a sludge residence time of a last biological treatment tank provided on the front side of the membrane separation tank and connected to the membrane separation tank is 20 days or more. A biological treatment apparatus comprising a first biological treatment tank in which wastewater is introduced and operated at a high load, and a second biological treatment tank provided at a stage subsequent to the first biological treatment tank;
A membrane separation tank comprising a separation membrane and membrane-separating biologically treated water flowing out of the biological treatment apparatus into a liquid component and the separated sludge;
A sludge return pipe for returning the separated sludge to the first biological treatment tank, wherein the separation sludge, a dry weight basis of MLVSS, the substrate amount flowing in the first biological treatment tank included in the waste water And a sludge return pipe that returns the pipe so as to be 10 times or more of the above. The waste water is an organic substance-containing water containing a BOD component as the substrate,
5. The membrane separation wastewater treatment apparatus according to claim 4, wherein the first biological treatment tank is a treatment tank operated at a high load of BOD sludge load 4 kg-BOD / kg-MLVSS / day or higher. The biological treatment apparatus includes three or more biological treatment tanks connected in series with each other,
The membrane separation according to claim 4 or 5, wherein the last biological treatment tank provided on the front side of the membrane separation tank and connected to the membrane separation tank is a treatment tank operated with a sludge residence time of 20 days or longer. Type wastewater treatment equipment.

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