JP2009189943A - Water treatment method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treatment method which is free from generation of clogging of an immersed membrane in water treatment using an immersed membrane activated sludge process and sudden generation of clogging of an RO membrane when treatment using the RO membrane is performed at the subsequent stage, and can perform water treatment of low concentration organic matter-containing raw water, or stable water recovery. <P>SOLUTION: In the water treatment method, activated sludge treatment of organic matter-containing raw water having a TOC concentration of 50 mgC/L or less is carried out by the immersed membrane activated sludge process using a backwashable hollow fiber immersed membrane, and a residence time in the activated sludge treatment is in a range of 1-24 hours. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a water treatment method and a water treatment apparatus for treating low-concentration organic material-containing raw water by immersion membrane activated sludge treatment.

  In recent years, submerged membrane activated sludge treatment devices have begun to be introduced in small- and medium-sized wastewater treatment facilities such as septic tanks and food factories and overseas sewage treatment plants. In these cases, as the concentration of raw water to be treated, many achievements are being made in the drainage of BOD 200 mg / L or more to several thousand mg / L. As a feature of submerged membrane activated sludge treatment, the sludge concentration can be maintained at a higher concentration than ordinary floating activated sludge, so the reaction tank can be made compact and filtered by membrane treatment, so the quality of treated water Is much better than the conventional method.

  However, when applying the submerged membrane activated sludge treatment, there is a possibility that an operation trouble accompanying the clogging of the membrane may occur. In particular, regarding sludge load (BOD-SS load), it has been pointed out that if it is too high, the amount of permeated water (flux) of the submerged membrane will decrease due to the increase of dispersal bacteria that do not form flocs and the adhesion of excessive sludge concentration It has been proposed to operate in a certain sludge load range, for example, 0.15 to 0.40 kg BOD / kg VSS / day (see Patent Document 1).

  On the other hand, by increasing the sludge concentration for the purpose of reducing excess sludge, etc., it is also considered to reduce the sludge load and perform the immersion membrane activated sludge treatment, but even in operation with low sludge load, Since sludge disperses, especially in the self-oxidation state of fungi, sludge flocs dismantle and membrane separation is difficult, and countermeasures have been studied and proposed (for example, see Patent Document 2). However, in the method of Patent Document 2, it is necessary to perform monitoring with complicated operations such as culture of specific bacteria (CFB group) in sludge, which is a main dispersal bacterium, and detection at a gene level. .

  In recent years, large quantities of production water, pure water, ultrapure water, etc. have been used in electronic manufacturing factories such as semiconductor manufacturing processes and liquid crystal panel manufacturing factories, chemical factories, automobile factories, etc., limiting the intake of industrial water and securing water resources Consideration is being made to collect and reuse wastewater in the factory due to the environmental impact on the wastewater discharge destination and soaring sewage charges. However, unlike food wastewater etc., a large amount of inorganic wastewater is also discharged in addition to organic wastewater, so the organic matter concentration of the target wastewater is often in the low concentration range of about TOC 10 to 50 mgC / L. Yes.

  Currently, as a wastewater recovery process in the above-mentioned factory, there is an increasing number of cases where water is recovered and reused by performing reverse osmosis membrane (RO membrane) treatment after biological treatment. In this treatment method, RO due to microorganisms or metabolites is increasing. The problem is that the film is clogged quickly and the flux rapidly decreases. When the RO membrane is clogged, it is necessary to frequently perform alkali cleaning or the like, which is a big problem in terms of operation management and running cost. Therefore, a method of operating RO membrane water with alkali has been proposed (see Patent Document 3). However, the running cost is always increased by performing alkaline operation, the life of RO membrane, and even in this method, chemicals are used. It is necessary to perform cleaning, which is an operational issue.

  In the above background, the use of submerged membrane activated sludge treatment has been started for wastewater collection in the factory, but since the concentration of raw water is low, the sludge concentration is always higher than in the case where a conventional submerged membrane was applied. , BOD volumetric load and sludge load will be operated in a lower situation than before. However, at present, there are almost no reports of submerged membrane activated sludge treatment under such conditions of low raw water concentration, low sludge concentration, and low sludge load, clogging of membranes due to sludge floc dismantling, appearance of dispersal bacteria, sludge If the concentration is low, there is a concern that fine particle components that are not adsorbed by activated sludge cause clogging of the membrane (for example, see Non-Patent Document 1). Although studies have been conducted to reduce the aeration operation power at a low sludge concentration (for example, 6,000 mg / L), the progress of film clogging due to the influence of a decrease in water temperature or the like has been confirmed (see Non-Patent Document 1). ).

  If the submerged membrane becomes clogged, in-line cleaning is performed by injecting hypochlorous acid or the like while immersed in activated sludge, or the submerged membrane is taken out from the biological reaction tank and immersed in hypochlorous acid or citric acid. It is necessary to wash. The timing of chemical cleaning is generally performed when the differential pressure of the suction pressure of the immersion film reaches about 30 to 50 kPa, and the frequency is at least 3 months or more, preferably 6 months to 1 Once a year is preferable for operation.

JP 2003-53363 A JP 2006-212470 A JP 2005-81268 A Proceedings of the 10th Japan Water Environment Society Symposium, p. 97-98 (September 2007)

  In the water treatment by the submerged membrane activated sludge treatment, the present invention does not cause the clogging of the submerged membrane, and the RO membrane is not clogged suddenly when the treatment with the RO membrane is performed at a later stage. A water treatment method and a water treatment apparatus capable of stably performing treatment or water recovery are provided.

  The present invention performs an activated sludge treatment of raw water containing organic matter having a TOC concentration of 50 mgC / L or less by a submerged membrane activated sludge treatment using a backwashable hollow fiber type immersion membrane, and the residence time in the activated sludge treatment is 1 It is the water treatment method which is the range of time to 24 hours.

  Moreover, in the said water treatment method, it is preferable that the BOD-SS load in the said activated sludge process is the range of 0.005-0.15 kgBOD / kgSS / day.

  Moreover, in the said water treatment method, it is preferable that the sludge density | concentration in the said activated sludge process is 10,000 mg / L or less.

  Moreover, it is preferable to perform the separation process using a reverse osmosis membrane in the latter stage of the activated sludge process in the water treatment method.

  The present invention also includes an immersion membrane unit including a back-washable hollow fiber type immersion membrane, a biological reaction tank for performing an activated sludge treatment of raw material water containing organic matter having a TOC concentration of 50 mgC / L or less, and the immersion membrane. And a backwashing means for backwashing, wherein the residence time in the activated sludge treatment is in the range of 1 to 24 hours.

  Moreover, it is preferable that the said water treatment apparatus is equipped with the separation means which has a reverse osmosis membrane in the back | latter stage of the said biological reaction tank.

  In the present invention, by using a hollow fiber type submerged membrane that can be back-washed, the submerged membrane is clogged by performing the activated sludge treatment of the organic material-containing raw water having a TOC concentration of 50 mgC / L or less for a predetermined residence time. Further, when the treatment with the RO membrane is performed in the subsequent stage, the RO membrane is not clogged rapidly, and the water treatment or the water recovery of the low concentration organic substance-containing raw water can be stably performed.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

  The present inventors examined the application of the submerged membrane activated sludge treatment to the low concentration organic substance-containing raw water. As a result, as will be described later in the examples, a flat membrane type immersion membrane made of polyethylene (PE), which has a proven track record in the world, generates suction pressure in a very short period of time. On the other hand, by applying a backwashable hollow fiber type immersion membrane made of polyvinylidene fluoride (PVDF), etc., the flux (0.4 m / day) that has been applied in the conventional wastewater treatment is secured while being stable. Clarified that good processing can be performed. As a result, operation management has been solved by solving clogged immersion membranes, operational troubles due to clogged RO membranes, and increased costs associated with alkaline operation, which have been problematic in conventional low-concentration organic substance-containing raw water treatment and recovery systems. However, it became possible to carry out easy and stable water treatment.

  An example of a water treatment apparatus according to an embodiment of the present invention is schematically shown in FIG. The water treatment apparatus 1 includes a raw water tank 10, a biological reaction tank 12, a submerged membrane unit 14 including a hollow fiber type submerged membrane, a biological treatment water tank 16, and a backwash pump 18 serving as a backwash means. And an RO membrane separation device 20 which is a separation means having a reverse osmosis membrane (RO membrane).

  In the water treatment apparatus 1 of FIG. 1, the outlet of the raw water tank 10 is connected to the lower part of the biological reaction tank 12 by a raw water pipe 24 via a raw water pump 22. An immersion membrane unit 14 is installed in the biological reaction tank 12, and the hollow fiber type immersion membrane of the immersion membrane unit 14 is connected to the biological treatment water tank 16 by a biological treatment water pipe 28 via a suction pump 26. The outlet of the biological treatment water tank 16 is connected to the inlet of the RO membrane separation device 20 through a filter 30 and a pump 32 through a biological treatment water pipe 34. A treated water pipe 36 is connected to the outlet of the RO membrane separation device 20. Further, the lower part of the biological treatment water tank 16 is connected to the downstream side of the suction pump 26 in the middle of the biological treatment water pipe 28 by the backwash pipe 38 via the backwash pump 18. A compressor 40 serving as aeration means is connected to the bottom of the biological reaction tank 12 by an aeration pipe 42.

  The operation of the water treatment method and the water treatment apparatus 1 according to this embodiment will be described.

  In the water treatment apparatus 1 of FIG. 1, organic substance-containing raw water containing organic substances (hereinafter sometimes simply referred to as “raw water”) flows into the raw water tank 10 and then passes through the raw water pipe 24 by the raw water pump 22 to the biological reaction tank. 12 is fed. In the biological reaction tank 12, aerobic activated sludge exists. On the other hand, air from the compressor 40 is fed from the bottom of the biological reaction tank 12 through the aeration pipe 42. In the biological reaction tank 12, the organic matter in the raw water is decomposed by the activated sludge (activated sludge treatment step). The hollow fiber type immersion membrane of the immersion membrane unit 14 is sucked by the suction pump 26, and solid-liquid separation is performed (solid-liquid separation step). The biologically treated water subjected to solid-liquid separation is sent to the biologically treated water tank 16 through the biologically treated water pipe 28. When the biologically treated water is collected and reused, the liquid is further sent to the RO membrane separation device 20 through the biological treatment water pipe 34 via the filter 30 by the pump 32, and the RO membrane separation device 20 uses the RO membrane to return the RO. Membrane treatment is performed (RO membrane treatment step). The treated water subjected to the RO membrane treatment is discharged out of the system through the treated water pipe 36. Further, at a predetermined interval, at least a part of the biologically treated water in the biologically treated water tank 16 is backwashed water, and the hollow fiber type immersion of the submerged membrane unit 14 is passed by the backwash pump 18 through the backwash pipe 38 and the biologically treated water pipe 28. The solution is fed to the membrane and the hollow fiber type immersion membrane is backwashed.

<Raw water for treatment>
In this embodiment, the TOC density | concentration of the organic substance containing raw | natural water used as a process target is 50 mgC / L or less. The organic material-containing raw water having a low TOC concentration of 50 mgC / L or less is subjected to a submerged membrane activated sludge treatment using a submerged submerged submerged membrane.

  Moreover, it is preferable to apply this method to organic substance containing raw water whose BOD concentration is 150 mg / L or less.

  The raw water to be treated is, for example, organic waste water discharged from semiconductor factories, liquid crystal factories, and other fields. Mainly, 2-aminoethanol, 2-propanol, TMAH (tetramethylammonium hydroxide), DMSO (dimethyl sulfoxide), N-methyl-2-pyrrolidone, acetic acid, oxalic acid and other organic acids, surfactants, etc. However, it is not limited to these substances.

<Immersion membrane activated sludge treatment conditions>
As the treatment conditions of the biological reaction tank 12 in the immersion membrane activated sludge treatment, the sludge concentration is 10,000 mg / L or less, preferably in the range of 3,000 to 8,000 mg / L, and the sludge viscosity is 60 mPa · s or less, preferably Is 50 mPa · s or less, and the biological reaction tank 12 is operated at a load of 1.5 kg BOD / m ³ / day or less, preferably 0.4 to 1.0 kg BOD / m ³ / day.

If the sludge concentration exceeds 10,000 mg / L, the viscosity of the sludge increases rapidly and the immersion membrane may be clogged. If it is less than 3,000 mg / L, the BOD load per sludge increases and the quality of the treated water It may get worse. If the sludge viscosity exceeds 60 mPa · s, the viscosity of the sludge increases rapidly and the immersion film may be clogged. Further, when the load of the biological reaction tank 12 exceeds 1.5 kg BOD / m ³ / day, the quality of the treated water may be deteriorated and the immersion film may be clogged. If the load is less than 0.4 kg BOD / m ³ / day, the immersion film Clogging may occur, and the biological reaction tank may be greatly uneconomical.

  The residence time in the biological reaction tank 12 is in the range of 1 hour to 24 hours, and preferably in the range of 2 to 5 hours. If the residence time is less than 1 hour, the treatment cannot be performed sufficiently. If it exceeds 24 hours, the processing cost increases. In addition, flocs are dispersed.

  About the sludge load (BOD-SS load) in the biological reaction tank 12, the range of 0.005-0.15 kgBOD / SS / day is preferable. If the sludge load is less than 0.005 kg BOD / SS / day, the sludge may be in a dispersed state due to a low load and the immersion membrane may be clogged. If the sludge load exceeds 0.15 kg BOD / SS / day, the treated water quality deteriorates due to the high load. In addition, the immersion membrane may be clogged due to an increase in bacterial metabolites.

  The pH of the liquid in the biological reaction tank 12 is preferably adjusted to be in the range of 6.0 to 8.5, particularly in the range of 6.5 to 7.5. When the pH is less than 6.0 or exceeds 8.5, the biological treatment performance may deteriorate.

  The DO (dissolved oxygen) concentration in the biological reaction tank 12 is preferably 0.5 mg / L or more, particularly preferably in the range of 1.5 to 3.5 mg / L. When the DO concentration is less than 0.5 mg / L, the biological treatment performance may be deteriorated, and when it exceeds 3.5 mg / L, flocs are dispersed, and the processing cost increases, which may be uneconomical. is there.

  As nutrient sources in the biological reaction tank 12, in order for microorganisms to decompose and grow organic matter, in addition to nitrogen and phosphorus, alkali metals such as sodium, potassium, calcium, magnesium, iron, manganese, zinc, etc. Trace metals such as these metals are required. As the nitrogen source, urea, ammonia salt or the like can be added from the outside. As the phosphorus source, phosphate and phosphoric acid can be added from the outside. Moreover, as a nitrogen source / phosphorus source, it is not necessary to add from the outside if the raw water contains a sufficient amount, and it is also possible to add other waste water containing nitrogen / phosphorus to the organic material-containing raw water. Can do. Trace metals are often deficient in organic material-containing raw water at semiconductor factories and liquid crystal factories. For this reason, it can be replenished by a method such as introducing water containing trace metals such as tap water or industrial water, or adding a preparation containing trace elements.

<Immersion film>
The immersion membrane can be immersed in the biological reaction tank 12 and biologically treated water can be obtained by suction filtration of the immersion membrane. A separate membrane separation tank is provided after the biological reaction tank 12, and the immersion membrane is immersed therein. You can also In this embodiment, a form that can be backwashed periodically, that is, a hollow fiber membrane is used. The flat membrane is difficult to backwash because there is a risk of damage to the edges. As the immersion membrane, a microfiltration membrane or an ultrafiltration membrane can be used. The material of the immersion film can be, for example, a fluorine resin such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), etc. PVDF is preferred. The pore diameter of the membrane is preferably 0.1 μm or less. The membrane can be operated at a permeation flow rate of about 0.1 to 0.8 m / hr, more preferably 0.2 to 0.6 m / hr.

<RO membrane>
As the RO membrane, a polyether amide composite membrane, a polyvinyl alcohol composite membrane, an aromatic polyamide membrane or the like can be used, and a charge neutralization membrane made of polyamide (for example, Application of Nitto Denko LF-10) or the like is preferable. The module shape of these RO membranes can be any shape such as a spiral type, a hollow fiber type, and a tubular type.

  In addition, when the organic matter-containing raw water contains a nonionic surfactant, polyethylene glycol, or the like, the RO membrane is likely to be clogged. In such a case, as shown in FIG. It is preferable to install an activated carbon treatment device 44 as an activated carbon treatment means on the front side. Further, it is preferable to install a filter 30 having a pore diameter of about 10 μm as a pretreatment of the RO membrane.

  In the case where there is a possibility that scale is generated due to an inorganic component such as calcium, it is preferable to install a dispersing agent adding means or a softening device in the RO membrane separation device 20. Furthermore, for the purpose of preventing clogging due to generation of slime caused by microorganisms in long-term operation, addition of slime control agent (such as isothiazoline), acid shock with sulfuric acid, alkaline operation (pH 9.5 or more), etc. It can be performed.

  The treated water can be reused as cooling water for factories or the like, water for production, pure water, ultrapure water, or the like.

  As described above, by using the hollow fiber type immersion membrane that can be backwashed in the immersion membrane by the water treatment method and the water treatment apparatus according to the present embodiment, the immersion membrane activated sludge having lower concentration of organic substance-containing raw water than the conventional one. Stable operation including processing and stable operation including subsequent RO processing is possible. Therefore, it becomes an effective method especially in the wastewater recovery system combined with the RO membrane. In the future, water treatment and recovery of raw water containing low-concentration organic matter will be highly desired from the viewpoint of securing water resources and draining water, including domestic and overseas, and the water treatment method and water treatment apparatus according to this embodiment Is considered very useful.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

(Example 1, Comparative Example 1)
Using the immersion membrane material, backwashing with water, and immersion membranes with different membrane pore diameters, we conducted an evaluation of immersion membrane application for low-concentration organic substance-containing raw water using actual wastewater on site. Two typical types of membranes (Example 1: PVDF hollow fiber type immersion membrane (pore size 0.1 μm), Comparative Example 1: PE flat membrane type immersion membrane (pore size 0.4 μm)) were used for the test. Evaluation of the suction pressure of the immersion membrane, the quality of the treated water, and the clogging of the subsequent RO membrane was performed. The experimental apparatus used is shown in FIGS.

<Water flow conditions>
Raw water: effluent TOC concentration of electronics industry factory 25-50mgC / L (raw water BOD concentration: 20-120mg / L)

<Experimental equipment>
The biological reaction tank (MBR tank), the immersion membrane unit, and the RO membrane were implemented using the following experimental apparatus (see FIG. 3).
[Bioreaction tank]
Capacity: 1.3m ³
Controlled by pH: 6-7 Water temperature: 20-25 ° C
Residence time: 22 hours Sludge concentration (MLSS): 4,000 to 8,000 mg / L
BOD-SS load: 0.01 to 0.03 kg BOD / kgSS / day
DO: 1-2 mg O / L
Air supply: 5 Nm ³ / hr
[Immersion membrane unit (see Table 1)]
Example 1: PVDF hollow fiber type immersion membrane (pore diameter 0.1 μm)
Comparative Example 1: PE flat membrane type immersion membrane (pore diameter 0.4 μm)
Immersion film flux: 0.4 m / day
[RO membrane]
Membrane: LF-10 2-inch module manufactured by Nitto Denko 70% water recovery rate

<Result>
In Comparative Example 1, a differential pressure of 30 kPa, which required chemical cleaning in 2 days, was reached at a flux of 0.4 m / day, which was normally put to practical use, but in Example 1, it was stable without sudden clogging for about 5 months. (See FIG. 5).

  Thus, as a test condition, when operating with a flux of 0.4 m / day, which is performed in normal wastewater treatment, the method of increasing the suction pressure, which is an index of clogging of the two submerged membranes, is It became clear that there was a significant difference beyond common sense. Regarding the PE flat membrane of Comparative Example 1, which has a proven track record in the world, it reached 30 kPa, which is the timing of chemical cleaning, in just 2 days, and practical operation was not possible. In the hollow fiber type immersion membrane, stable operation was possible for 5 months or more and 30 kPa or less despite using the same raw water and the same sludge (type, concentration, sludge load). The results of this time are thought to be influenced by the membrane material and the pore size, but it is thought that the presence or absence of backwashing in water caused a large difference in the suction pressure.

  Moreover, although the typical value of raw | natural water and a treated water is shown in Table 2, both were 5-10 mgC / L of treated water after stabilization treatment in both systems, but the water quality of the hollow fiber type immersion membrane of Example 1 is Somewhat good.

  As a result of examining the sludge concentration and the sludge viscosity (see FIG. 6), it was found that the viscosity rapidly increases when the sludge concentration is 10,000 mg / L or more. In general, when the viscosity increases, it is considered that the differential pressure of the membrane is affected. Therefore, it was found that stable operation is possible by operating at a sludge concentration of 10,000 mg / L or less and a sludge viscosity of 50 mPa · s or less. .

  In addition, FIG. 7 shows the RO membrane flux and the differential pressure change when the RO treatment is performed in the latter stage of the submerged membrane activated sludge. It was confirmed that the RO membrane in the latter stage can be stably treated with almost no clogging. . Moreover, about RO process water quality, it was confirmed that it is 0.5 mgC / L and it is a favorable water quality as collection | reuse water.

  Thus, it became clear that selection of the immersion membrane and operating conditions are more important for stable operation of the low-concentration organic substance-containing raw water treatment than expected by those skilled in the art.

It is a schematic structure figure showing an example of the water treatment equipment concerning the embodiment of the present invention. It is a schematic block diagram which shows the other example of the water treatment apparatus which concerns on embodiment of this invention. It is a schematic block diagram which shows the water treatment apparatus used in the Example of this invention. It is a schematic block diagram which shows the water treatment apparatus used in the Example of this invention. It is a graph which shows the suction pressure change of an immersion film in the Example of this invention. It is a graph which shows the examination result of sludge density | concentration (MLSS) and the sludge viscosity in the Example of this invention. It is a graph which shows the flux of RO membrane, and a differential pressure change in the Example of this invention.

Explanation of symbols

  1,3 Water treatment apparatus, 10 Raw water tank, 12 Biological reaction tank, 14 Immersion membrane unit, 16 Biological treatment water tank, 18 Backwash pump, 20 RO membrane separation device, 22 Raw water pump, 24 Raw water piping, 26 Suction pump, 28 Biologically treated water piping, 30 Filter, 32 Pump, 34 Biologically treated water piping, 36 Treated water piping, 38 Backwash piping, 40 Compressor, 42 Aeration piping, 44 Activated carbon device.

Claims (6)

By the immersion membrane activated sludge treatment using a hollow fiber type immersion membrane capable of backwashing, the activated sludge treatment of raw water containing organic matter having a TOC concentration of 50 mgC / L or less is performed.
The water treatment method characterized in that the residence time in the activated sludge treatment is in the range of 1 hour to 24 hours. The water treatment method according to claim 1,
The BOD-SS load in the activated sludge treatment is in the range of 0.005 to 0.15 kg BOD / kgSS / day. The water treatment method according to claim 1 or 2,
A water treatment method, wherein a sludge concentration in the activated sludge treatment is 10,000 mg / L or less. The water treatment method according to any one of claims 1 to 3,
A water treatment method comprising performing a separation treatment using a reverse osmosis membrane in a subsequent stage of the activated sludge treatment. An immersion membrane unit comprising a backwashable hollow fiber type immersion membrane;
A biological reaction tank for performing an activated sludge treatment of organic matter-containing raw water having a TOC concentration of 50 mgC / L or less;
Backwashing means for backwashing the immersion film;
With
The water treatment apparatus characterized in that the residence time in the activated sludge treatment is in the range of 1 hour to 24 hours. The water treatment device according to claim 5,
A water treatment apparatus comprising a separation means having a reverse osmosis membrane in the subsequent stage of the biological reaction tank.

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