JP2008200639A - Method for biologically treating organic matter-containing water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent clogging of a membrane in the case where a mixture liquid containing biologically treated microorganisms is subjected to membrane separation. <P>SOLUTION: An iron salt is allowed to coexist so as to give an iron concentration of 10 to 40% by mass based on MLSS in an activated sludge held in a biological treatment tank 10. The pH value of the mixture liquid within the biological treatment tank 10 is brought to a range of 5 to 6.5, and, in this state, biological treatment is carried out. The presence of a predetermined amount range of iron salt and the control of pH value can realize strong aggregation of microorganisms constituting the activated sludge and, at the same time, can suppress the production of mucilage and the like by the microorganisms, whereby clogging of a membrane separation apparatus such as an immersion membrane 11 can be prevented. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a biological treatment method for treating organic substance-containing water by an activated sludge method, and more particularly to a biological treatment method for obtaining treated water by membrane separation of a mixed solution in a biological treatment tank.

  Biological treatment is known as a treatment method for removing organic matter from organic matter-containing water. Among biological treatment methods, an activated sludge method using a microbial community called activated sludge is widely used because it can be applied to organic matter-containing water having various properties and can provide treated water with good water quality. Activated sludge treated water obtained by treating organic substance-containing water by the activated sludge method is also used as raw water (also referred to as raw water) for producing pure water (including ultrapure water; hereinafter the same). For example, Patent Document 1).

  By the way, in the biological treatment tank that performs the treatment by the activated sludge method, a liquid (mixed liquid) in which the organic substance-containing water introduced into the treatment tank and the microorganisms retained in the tank are mixed is held. For this reason, in order to obtain the clear processing liquid processed with the biological treatment tank, it is necessary to carry out solid-liquid separation of the liquid mixture. Since the microorganisms and the like contained in the mixed liquid in the biological treatment tank are fine, a fine solid content is aggregated by adding a flocculant to the mixed liquid prior to solid-liquid separation.

Examples of the solid-liquid separation device for clarifying the mixed solution include a sedimentation basin, a membrane separation device, and a floating separation device. In particular, the membrane separator has a higher solids separation ability than other solid-liquid separators, and clear treated water can be obtained by using the membrane separator. When a membrane separator is used as the solid-liquid separator, a flocculant that aggregates the solid content in the mixed solution may be added to the biological treatment tank (for example, Patent Document 2).
Japanese Patent Laid-Open No. 5-329477 JP-A-11-347587

  The membrane separation apparatus has a problem that the separation membrane is clogged. In particular, when the mixed solution is subjected to membrane separation, microorganisms contained in the mixed solution and mucilage produced by the microorganisms tend to adhere to the membrane surface and cause clogging.

  Therefore, the BOD (Biochemical Oxygen Consumption) for the sludge retained in the biological treatment tank that maintains the activated sludge concentration (Mixed Liquor Suspended Solid) in the biological treatment tank at a low level (for example, 10,000 mg / L or less). Measures have been taken to suppress the sludge load to about 0.1 kg-BOD / kg-MLVSS / day.

  However, the prevention of clogging by these measures is not always thorough, and the permeation flow rate of the membrane is about 0.5 m / day in the case of an immersion membrane, and about 0.7 m / day even in the case of being high. For this reason, many membrane separation apparatuses are required for solid-liquid separation.

  An object of the present invention is to provide a method for treating organic substance-containing water that improves the effect of preventing clogging of the membrane by adding a flocculant and can increase the permeation flow rate of the membrane separation device.

  The present inventor has found that the above problem can be achieved by including an iron salt so that the activated sludge retained in the aeration tank has a concentration within a predetermined range, and has completed the present invention. Specifically, the present invention provides the following.

(1) Organic matter-containing water containing organic matter is introduced into a biological treatment tank, mixed with activated sludge and biologically treated, and the mixture of the organic matter-containing water and the activated sludge is subjected to membrane separation. In the biological treatment method, the iron salt is present in the biological treatment tank so that the concentration as iron is 10% by mass or more and 45% by mass or less of the activated sludge concentration, and the pH of the mixed solution is adjusted. A biological treatment method for organic-containing water that is 5 or more and 6.5 or less.
(2) The biological treatment method for organic matter-containing water according to (1), wherein MLVSS / MLSS, which is a ratio of the activated sludge organic suspended solids to the activated sludge concentration, is 0.05 or more and 0.75 or less.
(3) The biological treatment method for organic matter-containing water according to (1) or (2), wherein the mixed solution is subjected to membrane separation by an immersion membrane module immersed in the biological treatment tank.
(4) The biological treatment method for organic matter-containing water according to any one of (1) to (3), wherein the organic matter-containing water is natural water, tap water, or recovered water.

  In this specification, “biological treatment tank” includes “aeration tank” for removing BOD, “nitrification tank” mainly for nitrification, and “denitrification tank” mainly for denitrification. . The biological treatment tank holds a microbial community called “activated sludge”. In the present specification, the term “activated sludge” refers to sludge mainly composed of aerobic bacteria that decompose BOD (hereinafter, particularly “BOD sludge”). Sludge mainly composed of nitrifying bacteria that oxidize ammonia (hereinafter referred to as “nitrified sludge”) and sludge mainly composed of denitrifying bacteria that reduce nitric acid or nitrous acid (hereinafter referred to as “denitrifying”). (Referred to as “sludge”).

  The biological treatment tank is operated so as to hold activated sludge having an MLSS concentration of about 1,000 to 30,000, and an iron salt is added so that the activated sludge contains iron at a ratio of 10% by mass or more of the MLSS concentration. . Examples of the iron salt to be added include ferric chloride, ferrous chloride, and ferric sulfate. If the iron salt is excessively added, extremely fine particles derived from iron are generated. Therefore, the amount of iron salt added is preferably 40% by mass of the MLSS concentration and more preferably 35% by mass. The biological treatment tank may be a floating type, a type to which a carrier such as a sponge is added, and a fixed bed. If a carrier is added or a fixed bed type, the content of iron salt in the floating sludge Is 10 mass% or more and 40 mass% or less as iron.

  The addition amount of the iron salt may be determined based on the organic matter concentration of the organic matter-containing water introduced into the biological treatment tank. In this case, about 25 to 400% by mass of the organic matter (TOC) contained in the organic matter-containing water. It is good to add. The activated sludge in the biological treatment tank should not contain any aggregating substances other than iron salt, such as aluminum salt, but it is mixed in if it is somewhat (for example, about 10% by mass or less of iron). Also good.

  Here, the ratio of the amount of organic matter in MLSS, specifically, the activated sludge organic suspended matter (Mixed Liquor Volatile Suspended Solids) / MLSS ratio is about 0.05 to 0.75, especially 0.15 to 0.5. It should be in the range. When the organic matter concentration of organic substance-containing water introduced into the biological treatment tank is extremely low (for example, assimilar organic carbon (hereinafter referred to as “AOC” concentration is less than about 100 ng / L)), the activity in the biological treatment tank In some cases, the sludge growth is reduced and the MLVSS / MLSS ratio is outside the above range. In such a case, a small amount of organic substance may be added to the biological treatment tank, or other organic substance-containing water having a high organic substance concentration may be mixed.

  The liquid in the biological treatment tank that holds the activated sludge to which the iron salt is added (that is, the mixed liquid) has a pH of 5 to 6.5, and particularly preferably 5.5 to 6.0. For pH adjustment, an acid such as hydrochloric acid or an alkali may be used. Depending on the type and amount of the iron salt to be added, the pH may be adjusted without separately adding an acid or an alkali.

  If the pH is set in the above range in the presence of an iron salt, the activated sludge is strongly aggregated and the filterability is improved, so that clogging (fouling) when performing membrane separation can be effectively prevented. In addition, by adjusting the pH to the above range in the presence of iron salt, metabolites such as mucilage usually produced from activated sludge are hardly produced. For this reason, the risk of fouling due to sticky substances adhering to the film can be avoided. Furthermore, since it becomes difficult for the treated water flowing out from the biological treatment tank to contain the organic matter (TOC) derived from the sticky material, the treated water quality can also be improved.

  The solid content (separated sludge) separated from the liquid by the membrane separator is partially returned to the biological treatment tank as return sludge as necessary, and the sludge residence time in the biological treatment tank is about 2 to 50 days, In particular, it is preferable to extract the sludge so as to be about 5 to 20 days. The extracted sludge may be discharged as excess sludge, or may be reduced in volume by a volume reducing means such as an ozone reaction layer or a digester.

  According to the present invention, treated water that is highly clarified and has a low TOC concentration is obtained. For this reason, the present invention treats recovered water obtained by treating natural water such as groundwater, river water, lake (including dam lake) water, tap water, or wastewater as raw water, and treating the obtained treated water. It can be suitably used when used for pure water production.

  These waters originally have an organic substance concentration as low as about 0.1 to 10 mg / L. When these waters are used for producing pure water, organisms mainly composed of microorganisms called oligotrophic bacteria such as Pseudomonas After biological treatment with activated carbon or the like, solid-liquid separation is performed with an ultrafiltration (UF) membrane or a membrane having a pore size of about 0.2 μM or less. The membrane used for the treatment of pure water production water is likely to be clogged because of its small pore size. In particular, natural water contains humic substances and urea that tend to clog the membrane, and the concentration of insoluble suspension (SS) may be high. However, according to the present invention, since a high filing-preventing effect can be obtained, the raw water may contain one or both of high-concentration humic substances and urea exceeding 1 mg / L. It may be contained in the range of about 30 mg / L.

  In the present invention, the activated sludge in the biological treatment tank can be made to contain iron salt, and the coagulability of the activated sludge can be enhanced by setting the pH within a predetermined range. Moreover, the production of metabolites by activated sludge can be suppressed. For this reason, the clogging at the time of carrying out membrane separation of the liquid mixture in a biological treatment tank can be avoided effectively, and the quality of treated water can be improved.

  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 biological treatment apparatus (hereinafter simply referred to as “treatment apparatus”) 1 for organic substance-containing water used in the present invention. The treatment apparatus 1 includes a biological treatment tank 10, an immersion membrane 11 as a membrane separation device, an iron salt addition unit 12, and a pH adjustment unit 13 as a pH adjustment unit. The immersion film 11 is immersed in the biological treatment tank 10. The iron salt addition means 12 includes an iron salt storage tank 15 and an iron salt addition path 16, and the pH adjustment means 13 includes a pH adjuster storage tank 17 and a pH adjuster addition path 18. Hereinafter, the processing method in the case of processing organic substance containing water using this processing apparatus 1 is demonstrated.

  A raw water pipe 31 is connected to the biological treatment tank 10, and organic substance-containing water is introduced into the biological treatment tank 10 through the raw water pipe 31. The biological treatment tank 10 of the present embodiment is configured for the purpose of treating pure water production water, and BOD sludge mainly composed of oligotrophic aerobic bacteria such as Pseudomonas is MLSS concentration of about 1,000 to 30,000 mg / L. Hold on.

  The activated sludge in the biological treatment tank 10 contains an iron salt, and the MLVSS / MLSS is preferably about 0.05 to 0.75, particularly about 0.15 to 0.5. In order to maintain the MLSS concentration and the MLVSS / MLSS ratio in the biological treatment tank 10 within the above ranges, when the organic matter concentration in the raw water is low, the biological treatment tank 10 contains organic substance-containing water having a BOD concentration of about 1 to 10 mg / L. It is preferable to introduce. The biological treatment tank 10 is operated with a BOD sludge load of 0.01 to 0.2 kg-BOD / kg-MLVSS / day and a sludge residence time of about 2 to 50 days, and the BOD is aerobically activated with activated sludge. Biodegradable.

  Iron salt is added from the iron salt reservoir 15 to the biological treatment tank 10 via the iron salt addition path 16. An iron salt having an aggregating action is added to the biological treatment tank 10, and the kind thereof is as described above. The biological treatment tank 10 is preferably provided with an MLSS meter as shown in FIG. 1, and the amount of iron salt added is 10 to 40% by mass of the MLSS concentration of the biological treatment tank 10 as described above.

  In the processing apparatus 1, since the immersion film 11 is provided in the biological treatment tank 10, the solid content and the liquid content are separated into membranes by the immersion film 11 in the biological treatment tank 10. Part of the separated solid content (separated sludge) is discharged from the separated sludge pipe 34 connected to the biological treatment tank 10, and the remainder is held in the biological treatment tank 10. The separated sludge may be periodically withdrawn from the biological treatment tank 10 so that the sludge residence time in the biological treatment tank 10 is in the above-described range. Thus, in the processing apparatus 1, since the iron salt added to the biological treatment tank 10 is taken out from the biological treatment tank 10 with the extraction of the separated sludge, the amount of iron salt added is from the raw water pipe 31 to the biological treatment tank. What is necessary is just to determine on the basis of the organic substance density | concentration of the organic substance containing water introduce | transduced into 10. FIG.

  The biological treatment tank 10 is preferably provided with a pH meter H as shown in FIG. And the pH of the liquid in a tank is made into the said range by adding the acid or alkali stored by the pH adjuster storage tank 17 as a pH adjuster via the pH adjuster addition path 18. FIG.

  An acid air pipe 14 is provided in the biological treatment tank 10 as a diffuser. From the acid air pipe 14, aeration is also performed on the immersion membrane 11 provided in the biological treatment tank 10, and membrane separation is performed while cleaning the immersion membrane 11 by aeration.

  The immersion film 11 is not particularly limited as long as it is a film 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.

  A treated water pipe 32 is attached to the immersion film 11. A pump P is provided in the middle of the treated water pipe 32, and the inside of the immersion membrane 11 is sucked by the pump P to separate the mixed liquid in the biological treatment tank 10 into a membrane. The liquid separated from the solid content by membrane separation and clarified is taken out from the biological treatment tank 10 through the treated water pipe 32 as treated water. On the other hand, as described above, the separated sludge is held in the biological treatment tank 10 and a part thereof may be discharged from the separated sludge pipe 34 as excess sludge.

  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 an apparatus suitable for treating organic substance-containing water having an organic substance concentration of about 20 to 100 mg / L and generating a large amount of excess sludge. The treatment apparatus 2 further includes an ozone reaction tank 19 as a sludge volume reducing means. Have. The ozone reaction tank 19 is connected to the biological treatment tank 10 via the separated sludge pipe 34 and solubilizes excess sludge discharged from the biological treatment tank 10 with ozone.

  A sludge pipe 35 is connected to the ozone reaction tank 19 to take out the solubilized sludge. The return pipe 34 is branched from the sludge pipe 35 and the return pipe 34 is connected to the biological treatment tank 10 to return the solubilized sludge to the biological treatment tank 10. On the other hand, in order to maintain the MLVSS / MLSS ratio in the above range, the sludge in which inorganic substances are accumulated is appropriately discharged from the mud pipe 35.

  In the processing method using this processing apparatus 2, the amount of excess sludge generated can be reduced by solubilizing excess sludge and returning it to the biological treatment tank 10. Moreover, since excess sludge is returned to the biological treatment tank 10, the amount of iron salt taken out of the system of the treatment apparatus 2 is reduced. For this reason, in the processing method using the processing apparatus 2, an iron salt may be appropriately added as necessary so that the iron salt concentration with respect to the MLSS concentration in the biological treatment tank 10 falls within a predetermined range. Thus, in the processing method using the processing apparatus 2, since it is not necessary to add an iron salt continuously on the basis of the organic substance density | concentration of organic substance containing water like the processing apparatus 1, it can reduce the usage-amount of iron salt. it can.

  Although the treatment method for performing the membrane separation with the immersion membrane 11 has been described so far, the treatment device 3 including the pressure type membrane module 21 shown in FIG. 3 as the membrane separation device may be used instead of the immersion membrane 11. The type of membrane used in the membrane module 21 may be an MF membrane or a UF membrane, and the module type may be a spiral membrane other than a hollow fiber membrane or a flat membrane.

  The membrane module 21 is connected to the biological treatment tank 10 via the liquid feeding pipe 36. The pump P is provided in the middle of the liquid feeding pipe 36. The mixed liquid is taken out from the biological treatment tank 10 and contains activated sludge that contains iron salt and agglomerated, and is sent to the membrane module 21 by the pump P in a state where the pH is in the above range, and is pressure filtered.

  A treated water pipe 32 and a separated sludge pipe 33 are connected to the membrane module 21, and the treated water 32 separated from the solid content by the membrane module 21 is taken out from the treated water pipe 32, and the separated sludge is taken out from the separated sludge pipe 33. A part of the separated sludge 33 is returned to the biological treatment tank 10 by branching the return pipe 34 from the separated sludge pipe 33 and connecting the return pipe 34 to the biological treatment tank 10. A part of the separated sludge may be pulled out from the separated sludge pipe 33 as excess sludge. When using this processing apparatus 3, the sludge residence time, MLSS concentration, and MLVSS / MLSS ratio of the biological treatment tank 10 may be adjusted by adjusting the return amount and withdrawal amount of the separated sludge.

  In the case of using the processing apparatus 3, when the separated sludge is continuously extracted from the separated sludge 33 as excess sludge, the organic substance concentration of the organic substance-containing water introduced into the biological treatment tank 10 is used as a standard, as in the case of using the processing apparatus 1. As a result, an iron salt may be added. On the other hand, when the separated sludge pipe 33 is connected to the volume reducing means to solubilize the excess sludge and return it to the biological treatment tank 10, the iron salt is biologically used as necessary, as in the case of using the treatment apparatus 2. What is necessary is just to add to the processing tank 10.

  Thus, the said embodiment can be changed suitably, for example, can be applied also when hold | maintaining the nitrification sludge which has nitrifying bacteria as a main body in a biological treatment tank. Alternatively, it can also be performed when denitrifying sludge mainly composed of denitrifying bacteria is retained in the biological treatment tank. In these cases, the iron salt may be added so as to be in the above range with respect to the MLSS concentration in the biological treatment tank, and the pH may be set in the above range.

  According to the knowledge of the present inventor, among these various aspects, in the case where organic substance-containing water is treated with activated sludge mainly composed of aerobic bacteria that remove BOD, the above numerical values are obtained at the MLSS concentration within the above numerical range. When the pH is in the above range in the presence of the iron salt in the range, a high antifouling effect is obtained. Further, as the membrane separation device, a submerged membrane type having a low risk of floc breakage during liquid feeding by a pump is preferable.

[Comparative Example 1]
Hereinafter, examples and comparative examples will be described. First, as Comparative Example 1, river water (organic water containing BOD concentration of 1.2 mg / L, SS concentration of 3 mg / L with addition of 1 potassium phosphate to a phosphorus concentration of 0.3 mg / L was treated. In order to grasp the content of humic substances in the river water, the ultraviolet absorbance E260 at a wavelength of 260 nm, which has a high correlation with the humic substances, was measured, and the value of E260 was 0.42.

In Comparative Example 1, an experimental apparatus simulating the processing apparatus 1 shown in FIG. 1 was used. The size of the biological treatment tank was 0.2 m ³ , and an immersion film was immersed therein. As the immersion film, a flat film type having a size of 4 m ³ and a pore diameter of 0.1 μmM F (manufactured by Mitsubishi Rayon Co., Ltd.) were used.

The organic substance-containing water was supplied to the biological treatment tank at a flow rate of ³ m ³ / day. The treated water was taken out from the treated water pipe by reducing the pressure with a vacuum pump provided in the middle of the treated water pipe connected to the immersion membrane. In Comparative Example 1, the membrane was clogged in one day from the start of the experiment, and the treated water could not be drawn. The TOC concentration of the treated water at this time was 2.2 mg / L, and the properties of the mixed solution in the tank were as follows.

[Mixed liquid in biological treatment tank]
Iron content ratio: 4.8% by mass of MLSS (as iron)
MLSS concentration: 490 mg / L
MLVSS concentration: 180 mg / L
pH: 7.1

[Example 1]
(First stage)
The biological treatment tank in which treated water could not be pulled out in Comparative Example 1 was emptied, and activated sludge was added to the biological treatment tank to an MLSS concentration of 100 mg / L, and ferric chloride was added as an iron salt to this mixed solution. Iron was added at a rate of 1,000 mg / L. In addition, a pH meter was provided in the biological treatment tank, pH was adjusted with sodium hydroxide, and the pH was maintained at 6. Then, ferric chloride was added at 4 mg / L to the organic substance-containing water to be treated in Comparative Example 1 and supplied to the biological treatment tank at a flow rate of 1.2 m ³ / day. Therefore, the increase in the differential pressure of the immersion film disappeared. The TOC concentration of treated water at this time was 145 ng / L, and the properties of the mixed solution in the biological treatment tank were as follows.
[Mixed liquid in biological treatment tank]
Iron content ratio: 35% by mass of MLSS (as iron)
MLSS concentration: 1940 mg / L
MLVSS concentration; 110 mg / L
pH: 6

(Second stage)
Therefore, the first stage was terminated, and the supply amount of organic substance-containing water to the biological treatment tank was set to 3 m ³ / day as the second stage. In the second stage, sludge in the tank was extracted from the biological treatment tank at 20 L / day. Other conditions were the same as in the second stage, and the organic treatment water to which ferric chloride was added at 4 mg / L was supplied to the biological treatment tank, and the pH in the biological treatment tank was also maintained at 6. In the second stage, no increase in the differential pressure of the immersion film was observed for 2 months, and the TOC concentration of the treated water was stabilized at 20 ng / L or less. The properties of the mixed solution in the biological treatment tank in the second stage were as follows.
[Mixed liquid in biological treatment tank]
Iron content ratio: 22% by mass of MLSS (as iron)
MLSS concentration: 3,700 mg / L
MLVSS concentration: 1,670 mg / L
pH: 6

(3rd stage)
Subsequent to the second stage, the treatment was continued for one month in the same manner as in the second stage except that the supply amount of organic substance-containing water to the biological treatment tank was changed to 4 m ³ / day as the third stage. During the third stage of one month, no increase in the differential pressure of the immersion film was observed, and the TOC concentration of the treated water was stable at 100 ng / L or less. The properties of the mixed solution in the biological treatment tank in the third stage were as follows.
[Mixed liquid in biological treatment tank]
Iron content ratio: 19.7% by mass of MLSS (as iron)
MLSS concentration: 4,900 mg / L
MLVSS concentration: 2,350 mg / L
pH: 6

(Fourth stage)
Following the third stage, isopropyl alcohol (IPA) was further added at 8 mg / L to the organic substance-containing water supplied to the biological treatment tank as the fourth stage. The treatment was continued for one month in the same manner as in the third stage except that IPA was added to the organic substance-containing water. During the fourth stage period of one month, no increase in the differential pressure of the immersion film was observed, and the TOC concentration of the treated water was 133 ng / L. The properties of the mixed solution in the biological treatment tank in the fourth stage were as follows.
[Mixed liquid in biological treatment tank]
Iron content ratio: 15.3% by mass of MLSS (as iron)
MLSS concentration: 5,690 mg / L
MLVSS concentration: 2,810 mg / L
pH: 6

(5th stage)
Subsequent to the fourth stage, as the fifth stage, the amount of IPA added to the organic substance-containing water was increased to 10 mg / L, and the amount of organic substance-containing water supplied to the biological treatment tank was 3 m ³ / day. The treatment was continued for one week in the same manner as in the fourth step except that the amount of IPA added to the organic substance-containing water was increased and the water flow rate was lowered. During the fifth phase of one week, the differential pressure of the immersion film hardly increased and the TOC concentration of the treated water was 274 ng / L. The properties of the mixed solution in the biological treatment tank in the fifth stage were as follows.
[Mixed liquid in biological treatment tank]
Iron content ratio: 12.9% by mass of MLSS (as iron)
MLSS concentration: 2700 mg / L
MLVSS concentration: 1377 mg / L
pH: 6

(6th stage)
Following the fifth stage, as the sixth stage, the amount of IPA added to the organic substance-containing water was increased to 50 mg / L. The treatment was continued for one week in the same manner as in the fifth stage except that the amount of IPA added to the organic substance-containing water was increased. In the sixth stage, the differential pressure of the submerged membrane starts to increase, and at the end of the sixth stage one week later, there is a 40 kP differential pressure increase compared to the start of the sixth stage, and the TOC concentration of treated water is 1.6 mg. / L. The properties of the mixed solution in the biological treatment tank at the end of the sixth stage were as follows.
[Mixed liquid in biological treatment tank]
Iron content ratio: 9.4% by mass of MLSS (as iron)
MLSS concentration: 5700 mg / L
MLVSS concentration; 3477 mg / L
pH: 6

(7th stage)
Before starting the seventh stage, the immersion membrane was removed from the biological treatment tank and washed with a solution of sodium hydroxide, citric acid, and sodium hypochlorite. Further, half of the activated sludge in the biological treatment tank was pulled out, and ferric chloride was added to the biological treatment tank so that the content of iron salt relative to MLSS was 15% by mass. After that, as the seventh stage, the amount of IPA added to the organic substance-containing water was reduced to 10 mg / L, and otherwise, the treatment was continued for one week in the same manner as in the sixth stage. During the seventh stage of one week, the differential pressure of the immersion film did not increase, and the TOC concentration of the treated water was 192 ng / L. The properties of the mixed solution in the biological treatment tank in the seventh stage were as follows.
[Mixed liquid in biological treatment tank]
Iron content ratio: 15.1% by mass of MLSS (as iron)
MLSS concentration: 2,840 mg / L
MLVSS concentration: 1,510 mg / L
pH: 6

(Eighth stage)
Following the seventh stage, the pH of the mixed solution in the biological treatment tank was maintained at 5 as the eighth stage. The treatment was continued for one week in the same manner as in the seventh step except that the pH of the mixed solution was lowered. As a result, the differential pressure of the immersion film did not increase, and the TOC concentration of the treated water was 222 ng / L. The properties of the mixed solution in the biological treatment tank in the eighth stage were as follows.
[Mixed liquid in biological treatment tank]
Iron content ratio: 16.7% by mass of MLSS (as iron)
MLSS concentration: 3,160 mg / L
MLVSS concentration: 1,630 mg / L
pH: 5

(9th stage)
Following the eighth stage, the pH of the mixed solution in the biological treatment tank was maintained at 5.5 as the ninth stage. When the treatment was continued for one week in the same manner as in the eighth step except that the pH of the mixed solution was raised, the differential pressure of the immersion film did not rise, and the TOC concentration of the treated water was 197 ng / L. The properties of the mixed solution in the biological treatment tank in the ninth stage were as follows.
[Mixed liquid in biological treatment tank]
Iron content ratio: 18.4% by mass of MLSS (as iron)
MLSS concentration: 3,360 mg / L
MLVSS concentration: 1,690 mg / L
pH; 5.5

(10th stage)
Subsequent to the ninth stage, as the tenth stage, the pH of the mixed solution in the biological treatment tank was raised to 7. Except for raising the pH of the mixed solution, the same procedure as in the ninth stage was performed. As a result, the differential pressure of the immersion film increased from the day after the start of the tenth stage, and the treatment could not be continued in two days. The TOC concentration of the treated water 2 hours before the treatment stop was 910 ng / L, and the properties of the mixed solution in the biological treatment tank at this time were as follows.
[Mixed liquid in biological treatment tank]
Iron content ratio: 19.5% by mass of MLSS (as iron)
MLSS concentration: 3,660 mg / L
MLVSS concentration: 1,720 mg / L
pH: 7

[Comparative Example 2]
In Comparative Example 2, tap water (TOC concentration 0.3 mg / L, SS concentration 1 mg / L or less) was treated as organic matter-containing water. In Comparative Example 2, a processing apparatus having the same configuration as Comparative Example 1 and Example 1 was used.

In Comparative Example 2, ferric chloride was added to the organic substance-containing water at an addition amount of 3 mg / L and supplied to the biological treatment tank at a flow rate of ³ m ³ / day. The treated water was taken out by decompressing the submerged membrane by depressurizing with a vacuum pump provided in the middle of the treated water pipe. In Comparative Example 2, the differential pressure of the submerged membrane began to increase soon after the start of the treatment, and the membrane was clogged 10 days after the start of the experiment, making it impossible to draw the treated water. The TOC concentration of the treated water at this time was 234 ng / L, and the properties of the mixed solution in the tank were as follows.
[Mixed liquid in biological treatment tank]
Iron content ratio: 46% by mass of MLSS (as iron)
MLSS concentration: 1,160 mg / L
MLVSS concentration: 71 mg / L
pH: 6.8

[Comparative Example 3]
The immersion film was taken out of the biological treatment tank in which the treated water could not be pulled out in Comparative Example 2, washed with citric acid, and immersed again in the biological treatment tank. Further, a pH meter was provided in the biological treatment tank, and the pH was maintained in the range of 5.8 to 6.2 by adding sulfuric acid having a concentration of 1% by mass. In other cases, the experiment was performed under the same conditions as in Comparative Example 2. As a result, the differential pressure of the immersion film gradually increased, and the treated water could not be drawn out in one month from the start of the experiment. The TOC concentration of treated water at this time was 0.266 mg / L, and the properties of the mixed solution in the biological treatment tank were as follows.
[Mixed liquid in biological treatment tank]
Iron content ratio: 49% by mass of MLSS (as iron)
MLSS concentration: 1,740 mg / L
MLVSS concentration; 49 mg / L
pH: 5.8-6.2

[Example 2]
The immersion film was taken out from the biological treatment tank in which the treated water could not be pulled out in Comparative Example 3, washed with citric acid, and immersed again in the biological treatment tank. Further, IPA was further added to the tap water treated in Comparative Example 3 so that the concentration was 1 mg / L with 2 mg / L of IPA and N of diammonium phosphate as N. Other than that, the experiment was performed under the same conditions as in Comparative Example 3. As a result, no increase in the differential pressure of the immersion film was observed over one month. The TOC concentration of treated water one month after the start of the experiment in Example 2 was 217 ng / L, and the properties of the mixed solution in the biological treatment tank were as follows.
[Mixed liquid in biological treatment tank]
Iron content ratio: 38% by mass of MLSS (as iron)
MLSS concentration: 2,920 mg / L
MLVSS concentration; 674 mg / L
pH: 5.8-6.2

  From the above, it was shown that the fouling of the membrane can be effectively prevented and the treatment can be performed at a high permeation flow rate by setting the ratio of the iron salt to the MLSS in the biological treatment tank within a predetermined range.

  The present invention can be used for the treatment of organic substance-containing water.

The schematic diagram of the 1st biological treatment apparatus used for this invention. The schematic diagram of the 2nd biological treatment apparatus used for this invention. The schematic diagram of the 3rd biological treatment apparatus used for this invention.

Explanation of symbols

1-3 biological treatment apparatus 10 biological treatment tank 11 immersion film 12 iron salt addition means 13 pH adjustment means 14 acid pipe 15 iron salt storage tank 16 iron salt addition path 17 pH adjustment agent storage path 18 pH adjustment agent addition path 19 ozone reaction tank

Claims (4)

Biological treatment method for organic matter-containing water, wherein organic matter-containing water containing organic matter is introduced into a biological treatment tank and mixed with activated sludge to be biologically treated, and the mixed liquid in which the organic matter-containing water and the activated sludge are mixed is subjected to membrane separation In
An iron salt is present in the biological treatment tank so that the concentration of iron is 10% by mass or more and 45% by mass or less of the activated sludge concentration, and the pH of the mixed solution is 5 or more and 6.5. Biological treatment method of organic substance-containing water as follows.   The biological treatment method for organic matter-containing water according to claim 1, wherein MLVSS / MLSS, which is a ratio of the activated sludge organic suspended solids to the activated sludge concentration, is 0.05 or more and 0.75 or less.   The biological treatment method for organic matter-containing water according to claim 1 or 2, wherein the mixed solution is subjected to membrane separation by a submerged membrane module immersed in the biological treatment tank.   The biological treatment method for organic matter-containing water according to any one of claims 1 to 3, wherein the organic matter-containing water is natural water, tap water, or recovered water.

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