JP6899104B2 - Wastewater treatment method and wastewater treatment equipment - Google Patents

Description

The present invention relates to a wastewater treatment method and a wastewater treatment apparatus for treating wastewater containing organic matter by a membrane separation activated sludge method.

In recent years, membrane separation activated sludge treatment equipment such as immersion film activated sludge treatment equipment has been introduced in small and medium-sized wastewater treatment equipment such as septic tanks and food factories and sewage treatment plants. As a feature of the immersion membrane activated sludge treatment, the sludge concentration can be maintained at a higher concentration than that of ordinary floating activated sludge, so that the reaction tank can be made compact, and the treated water quality is filtered by the membrane treatment. Is much better than the conventional method.

However, when the immersion membrane active sludge treatment is applied, the membrane is clogged remarkably quickly depending on the conditions such as drainage and sludge properties, sludge load, membrane flux, etc., and the operation trouble due to membrane clogging (fouling) is the largest. This has become an issue, and it is desired to suppress the membrane differential pressure and perform stable operation. Normally, sludge deposited on the membrane is washed by aeration with an air diffuser installed at the bottom of the membrane, but dissolved organic substances such as biopolymers and fuminic substances, which are metabolites of microorganisms, are washed by air. It is difficult and is the main obstructive substance of the membrane. These membrane-occlusive substances should be washed in-line with a chemical such as hypochlorous acid once every few months, and in some cases, once every few days to a week, while the membrane is immersed in activated sludge. There was a problem that stable operation could not be performed because the differential pressure was recovered and the operation was carried out. If the differential pressure does not recover even after in-line cleaning, the membrane is taken out of the reaction vessel and immersed in chemicals such as hypochlorous acid and citric acid for cleaning. The timing of the immersion cleaning is usually performed when the differential pressure of the suction pressure of the membrane reaches about 30 to 50 kPa, and the frequency is at least one year or more, preferably no immersion cleaning. It is preferable in terms of operation that stable operation is possible. For these reasons, at present, there are problems such as complicated operation management and an increase in chemical cost.

As a method for eliminating the blockage of the film, a polyurethane resin carrier (see Patent Document 1), a water-absorbent gel carrier (see Patent Documents 2 and 3), a granular microbial carrier (see Non-Patent Document 1), or the like is charged into a reaction vessel. , Proposals have been made to devise a biological reaction tank.

However, the conventional carrier damages the film, and the water-absorbent gel carrier has not been put into practical use in terms of cost and strength. Further, the granular microbial carrier has problems such as a decrease in the filterability of the sludge itself and a damage to the membrane surface. Proposals have been made to make the internal structure of the biological reaction tank and the membrane module specifications other than the standard, but the cost of the membrane device is high and there is a problem in practical use.

It has been strongly demanded for the spread of membrane separation activated sludge methods such as the immersion film activated sludge method to solve these problems by a method that can be economically put into practical use and a method that can be applied to existing equipment.

Japanese Unexamined Patent Publication No. 11-221562 Japanese Unexamined Patent Publication No. 2001-062477 Japanese Unexamined Patent Publication No. 2001-104982

Journal of Membrane Science, 469 (2014), p.292-299

An object of the present invention is to provide a wastewater treatment method and a wastewater treatment apparatus that enable stable operation while suppressing membrane blockage in wastewater treatment for treating wastewater containing organic substances by a membrane separation active sludge method.

The present invention is a wastewater treatment method for treating wastewater containing organic matter by a membrane separation active sludge method, in which ^{a sponge-like carrier having a density of 35 kg / m 3} or more and a cell size of 46 cells / 25 mm or more is present in a biological reaction tank. It is a wastewater treatment method that operates while letting it operate.

In the wastewater treatment method, it is preferable that the sponge-like carrier is made of hydrophobic polyurethane.

In the wastewater treatment method, it is preferable that the material of the membrane used in the membrane separation activated sludge method is a fluororesin.

The present invention is a wastewater treatment apparatus for treating wastewater containing organic matter by a membrane separation active sludge method, in which ^{a sponge-like carrier having a density of 35 kg / m 3} or more and a cell size of 46 cells / 25 mm or more is present in a biological reaction tank. It is a wastewater treatment device that operates while operating.

In the wastewater treatment apparatus, it is preferable that the sponge-like carrier is made of hydrophobic polyurethane.

In the wastewater treatment apparatus, it is preferable that the material of the membrane used in the membrane separation activated sludge method is a fluororesin.

In the present invention, in the wastewater treatment in which the wastewater containing organic substances is treated by the membrane separation active sludge method, the membrane is blocked by operating while a sponge-like carrier having ^{a density of 35 kg / m 3 or more is present in the biological reaction tank.} Suppressed stable operation becomes possible.

It is a schematic block diagram which shows an example of the wastewater treatment apparatus which concerns on embodiment of this invention. It is a schematic block diagram which shows another example of the wastewater treatment apparatus which concerns on embodiment of this invention. It is a schematic block diagram which shows another example of the wastewater treatment apparatus which concerns on embodiment of this invention. It is a schematic block diagram which shows another example of the wastewater treatment apparatus which concerns on embodiment of this invention. It is a figure which shows the processing day (d) and the differential pressure (kPa) of a film in an Example.

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

An outline of an example of the wastewater treatment apparatus according to the embodiment of the present invention is shown in FIG. 1, and the configuration thereof will be described. The wastewater treatment device 1 may include a biological reaction tank 12, a raw water tank 10, and a treatment water tank 14.

In the wastewater treatment device 1 of FIG. 1, a raw water pipe 26 is connected to the inlet of the raw water tank 10. The outlet of the raw water tank 10 and the inlet of the biological reaction tank 12 are connected by a raw water supply pipe 28 via a pump 20. An immersion membrane 16 is installed as a membrane inside the biological reaction tank 12, and the treated water outlet of the immersion membrane 16 is connected to the treated water tank 14 by a treated water pipe 30 via a suction pump 22. The inside of the biological reaction tank 12 is filled with a sponge-like carrier 18 having ^{a density of 35 kg / m 3 or more in a predetermined filling amount.} An aeration pipe 32 is connected to the vicinity of the central portion of the lower part of the biological reaction tank 12 and below the immersion film 16, and is aerated by an aeration device (not shown). An air volume meter 24 is installed in the middle of the aeration pipe 32 connected below the immersion film 16.

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

The organic matter-containing wastewater containing organic matter, which is raw water, is stored in the raw water tank 10 through the raw water pipe 26 as needed, and then sent to the biological reaction tank 12 through the raw water supply pipe 28 by the pump 20. Aerobic activated sludge is present in the biological reaction tank 12, and the sponge-like carrier 18 is filled with a predetermined filling amount. On the other hand, oxygen-containing gas such as air is sent from the aeration blower or the like through the aeration pipe 32 from the vicinity of the central portion below the biological reaction tank 12 and below the immersion membrane 16. In the biological reaction tank 12, the activated sludge is used to decompose organic substances in the raw water (activated sludge treatment step). The inside of the immersion film 16 is sucked by the suction pump 22 to perform solid-liquid separation (solid-liquid separation step). The solid-liquid separated treated water is sent to the treated water tank 14 through the treated water pipe 30 by the pump 22.

In the wastewater treatment method and the wastewater treatment apparatus 1 according to the present embodiment, the operation is performed while the sponge-like carrier 18 having ^{a density of 35 kg / m 3 or more is present in the biological reaction tank 12.} Conventionally, in the operation of a wastewater treatment device by the membrane separation activated sludge method, the blockage of the membrane due to the continuation of the operation has been a big problem. The present inventors have been studying the stable operation of the wastewater treatment apparatus by the membrane separation activated sludge method, and have found that the increase in the differential pressure is suppressed by adding the granular carrier to the biological reaction tank. .. However, the conventional granular carrier has problems in terms of damage to the membrane surface, deterioration of the filterability of the sludge itself due to damage to the flocs of biological sludge, and economic efficiency due to a large amount of filling. The present inventors focused on a sponge-like carrier as a carrier to be filled inside a biological reaction vessel, and investigated the effect of the carrier by changing the density, size, cell size, etc. of the sponge-like carrier. As a result, it has been found that, in particular, by filling the inside of the biological reaction tank with a sponge-like carrier having a high density of 35 kg / m ^{3 or more, stable operation with suppressed membrane blockage is possible.} It was found that by adding such a sponge-like carrier having an appropriate density and openness to the biological reaction tank, there is almost no damage to the membrane and sludge, and the effect of suppressing the increase in the differential pressure of the membrane is high.

Although the detailed mechanism is unknown, the membrane is due to the effect of a sponge-like carrier of appropriate density cleaning the sludge adhering to the membrane surface and the effect of adsorbing and decomposing biopolymers, which are considered to be substances that clog the membrane. It is considered that the blockage of the membrane was suppressed and the differential pressure of the membrane could be suppressed. As a result, stable operation with suppressed membrane blockage is possible, and it is possible to reduce the chemical cost and the labor of operation management associated with the chemical cleaning.

As described above, in the wastewater treatment apparatus 1 of FIG. 1, by filling the inside of the biological reaction tank 12 with a sponge-like carrier 18 having a high ^{density of 35 kg / m 3 or more, stable operation in which blockage of the immersion film 16 is suppressed is suppressed.} Is possible. The membrane separation activated sludge method can be adopted for wastewater and sludge, which have been difficult to apply until now, and is effective in reducing the burden of operation management by reducing the frequency of chemical cleaning and cost reduction by reducing chemical costs. In addition, it is possible to plan wastewater treatment at a value higher than the conventional standard permeation flow velocity (flux), which is an effective method for reducing the initial cost.

[Sponge-like carrier]
The density of the sponge-like carrier 18 is 35 kg / ^{m 3} or more, 35 kg / ^{m 3} or more, is preferably in the range of 100 kg / ^{m 3} or less. If the density of the sponge-like carrier 18 ^{is less than 35 kg / m 3} , the effect of suppressing membrane blockage is low, and if ^{it exceeds 100 kg / m 3} , air bubbles are difficult to escape from the carrier, resulting in poor levitation and fluidity. There is. In addition, the price increases as the density of the carrier increases, which poses a practical problem.

The shape of the sponge-like carrier 18 is not particularly limited, and examples thereof include a polygonal pillar shape such as a square pillar shape such as a cube shape, a cylindrical shape, a spherical shape, and the like. Is preferable.

As for the size of the sponge-like carrier 18, for example, a square pillar-shaped carrier having a side of 3 mm or more and 10 mm or less may be used. If the size of the sponge-like carrier 18 is smaller than 3 mm, the carrier may be worn over time and the effect of suppressing film blockage may be reduced. If the size of the sponge-like carrier 18 is smaller than 3 mm, if the membrane is a hollow fiber type, it may enter the membrane module. On the other hand, when the size of the sponge-like carrier 18 is larger than 10 mm, the specific surface area becomes small, and the effects of both cleaning and adsorption may be low.

The cell size of the sponge-like carrier 18 is preferably 15 pieces / 25 mm or more, preferably 46 pieces / 25 mm or more, and the upper limit is, for example, less than 80 pieces / 25 mm. If the cell size of the sponge-like carrier 18 is less than 15 cells / 25 mm, the surface area inside the sponge-like carrier may become small and the retention amount of microorganisms may decrease. Since each of the sponge-like carriers has small pores, the pores may be filled with the biological film, and the permeation and diffusion of the substrate (organic matter) into the pores may be hindered.

The filling amount of the sponge-like carrier 18 in the biological reaction tank 12 is preferably in the range of about 3% to 40% with respect to the internal volume of the biological reaction tank 12, and is 5% to 30 in terms of economy, fluidity and the like. The% range is more preferred. If the filling amount of the sponge-like carrier 18 in the biological reaction tank 12 is less than 3%, the effect of suppressing the blockage of the membrane may be lowered, and if it exceeds 40%, the sponge-like carrier becomes difficult to flow and the sponge-like carrier becomes difficult to flow for a long period of time. During operation, sludge may adhere to the sponge-like carrier, which may reduce its fluidity and cause clogging, reduce the contact area between the raw water and the sponge-like carrier, and deteriorate the quality of the treated water.

The material of the sponge-like carrier 18 is not particularly limited, and examples thereof include hydrophobic polyurethane, hydrophilic polyurethane, and polyvinyl alcohol (PVA). In the membrane separation active sludge method, the membrane may be washed with a chemical such as sodium hypochlorite or hydrochloric acid. Therefore, hydrophobic polyurethane is preferable from the viewpoint of chemical resistance and strength.

[film]
The wastewater treatment method and wastewater treatment apparatus according to the present embodiment can be applied to the immersion membrane activated sludge method, which is a membrane separation active sludge method, the out-of-tank type membrane separation activated sludge method, and the like. Further, as the membrane (separation membrane) to be used, any of a flat membrane, a hollow fiber membrane, a cross-flow membrane and the like can be applied.

The material of the film is not particularly limited, and examples thereof include fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyethylene (PE), polyvinyl chloride (PVC), and ceramics. From the viewpoint of strength, chemical resistance and the like, a fluororesin or ceramic is preferable.

The pore size of the film is not particularly limited, but is preferably 0.5 μm or less, and more preferably 0.01 μm or more and 0.1 μm or less.

The permeation flow velocity of the membrane during operation may be, for example, about 0.1 to 1.0 m / h, and preferably 0.2 to 0.6 m / h.

[Biological treatment conditions]
As the treatment conditions of the biological reaction tank 12 in the membrane separation activated sludge method, the sludge concentration may be, for example, 15,000 mg / L or less, preferably in the range of 3,000 to 8,000 mg / L. The load of the aerobic biological reaction tank 12 may be, for example, operated at 1.5 kgBOD / m ³ / d or less, preferably in the range of ^{0.4 to 1.0 kgBOD / m 3 / d.} ..

The sludge load (BOD-SS load) in the biological reaction tank 12 may be, for example, in the range of 0.05 to 0.15 kg BOD / SS / day.

The pH in the biological reaction vessel 12 may be adjusted to be, for example, in the range of 6.0 to 8.5, and preferably in the range of 6.5 to 7.5.

The DO (dissolved oxygen) concentration in the biological reaction tank 12 may be, for example, 0.5 mg / L or more, preferably in the range of 1.5 to 3.5 mg / L.

In the biological reaction vessel 12, at least one of a nutrient source, a nitrogen source and a phosphorus source may be added. As a nutrient source, in order for microorganisms to decompose and proliferate organic substances, in addition to nitrogen and phosphorus, trace metals such as alkali metals such as sodium, potassium, calcium and magnesium, and metals such as iron, manganese and zinc At least one of the types and the like can be mentioned. As the nitrogen source, urea, an ammonia salt or the like may be added from the outside. As the phosphorus source, phosphate or phosphoric acid may be added from the outside.

[Disposal target wastewater]
The wastewater to be treated by the wastewater treatment method and the wastewater treatment apparatus according to the present embodiment contains organic substances discharged from sewage treatment, food factories, chemical factories, semiconductor factories / liquid crystal factories, paper and pulp factories, and other fields. It may be wastewater as long as biological treatment and membrane separation active sludge method can be applied. The wastewater treatment method and the wastewater treatment apparatus according to the present embodiment are also effective for the membrane separation activated sludge method of the wastewater recovery system.

<Other Embodiments>
FIG. 2 shows an outline of another example of the wastewater treatment apparatus according to the embodiment of the present invention. The wastewater treatment device 3 includes a membrane separation tank 38 after the biological reaction tank 36 in addition to the raw water tank 34, the biological reaction tank 36, and the treatment water tank 40.

In the wastewater treatment device 3 of FIG. 2, a raw water pipe 58 is connected to the inlet of the raw water tank 34. The outlet of the raw water tank 34 and the inlet of the biological reaction tank 36 are connected by a raw water supply pipe 60 via a pump 48. A screen 42 is installed inside the biological reaction tank 36, and the biological treatment water outlet of the biological reaction tank 36 and the inlet of the membrane separation tank 38 are connected by a biological treatment water pipe 62. An immersion membrane 44 is installed as a membrane inside the membrane separation tank 38, and the treated water outlet of the immersion membrane 44 is connected to the treated water tank 40 by a treated water pipe 64 via a suction pump 50. The inside of the biological reaction tank 36 is filled with a sponge-like carrier 46 having ^{a density of 35 kg / m 3 or more in a predetermined filling amount.} An aeration pipe 68 is connected near the center of the lower part of the biological reaction tank 36 and below the screen 42, and near the center of the lower part of the membrane separation tank 38 and below the immersion membrane 44, by an aeration device (not shown). It is supposed to be aerated. Air volume meters 54 and 56 are installed in the middle of the aeration pipe 68 connected to the lower part of the screen 42 and the lower part of the immersion film 44, respectively. The sludge outlet of the membrane separation tank 38 and the sludge inlet of the biological reaction tank 36 are connected by a sludge circulation pipe 66 via a pump 52.

The organic matter-containing wastewater containing organic matter, which is raw water, is stored in the raw water tank 34 through the raw water pipe 58 as needed, and then sent to the biological reaction tank 36 through the raw water supply pipe 60 by the pump 48. Aerobic activated sludge is present in the biological reaction tank 36, and the sponge-like carrier 46 is filled with a predetermined filling amount. On the other hand, oxygen-containing gas such as air is sent from the aeration blower or the like through the aeration pipe 68 from the vicinity of the central portion below the biological reaction tank 36 and from the lower part of the screen 42. In the biological reaction tank 36, the activated sludge is used to decompose organic substances in the raw water (activated sludge treatment step). By installing the screen 42 having a size capable of separating the carrier in the biological reaction tank 36, it is possible to prevent the sponge-like carrier 46 from moving to the membrane separation tank 38. In the membrane separation tank 38, the inside of the immersion membrane 44 is sucked by the suction pump 50, and solid-liquid separation is performed (solid-liquid separation step). Oxygen-containing gas such as air is sent from the aeration blower or the like through the aeration pipe 68 from the vicinity of the central portion below the membrane separation tank 38 and below the immersion film 44. The solid-liquid separated treated water is sent to the treated water tank 40 through the treated water pipe 64 by the pump 50. The sludge in the membrane separation tank 38 is circulated to the biological reaction tank 36 by the pump 52 through the sludge circulation pipe 66 (sludge circulation step).

In the wastewater treatment apparatus 3 of FIG. 2, the operation is performed while the sponge-like carrier 46 having ^{a density of 35 kg / m 3 or more is present in the biological reaction tank 36.} This enables stable operation in which the immersion film 44 of the membrane separation tank 38 is suppressed from being blocked. In this way, when the biological reaction tank 36 and the membrane separation tank 38 are separated, the sponge-like carrier 46 is placed only in the biological reaction tank 36 in the previous stage to circulate the sludge, thereby adsorbing the biopolymer and the biopolymer. It is possible to form a microbial phase suitable for decomposition and suppress an increase in the differential pressure of the immersion film 44.

FIG. 3 shows an outline of another example of the wastewater treatment apparatus according to the embodiment of the present invention. The wastewater treatment device 5 has almost the same configuration as that shown in FIG. 2, but the inside of the membrane separation tank 38 is also filled with a sponge-like carrier 46 having ^{a density of 35 kg / m 3 or more in a predetermined filling amount.}

In the wastewater treatment apparatus 5 of FIG. 3, the ^{operation is performed while the sponge-like carrier 46 having a density of 35 kg / m 3} or more is present in both the biological reaction tank 36 and the membrane separation tank 38. This enables stable operation in which the immersion film 44 of the membrane separation tank 38 is suppressed from being blocked. In this way, when the biological reaction tank 36 and the membrane separation tank 38 are separated, the sponge-like carrier 46 is placed in both the biological reaction tank 36 in the front stage and the membrane separation tank 38 in the rear stage to circulate the sludge. It is possible to form a microbial phase suitable for biopolymer adsorption and biopolymer decomposition, and to further suppress an increase in the differential pressure of the immersion film 44.

FIG. 4 shows an outline of another example of the wastewater treatment apparatus according to the embodiment of the present invention. The wastewater treatment device 7 includes a membrane separation device 76 having a membrane after the biological reaction tank 74, in addition to the raw water tank 72, the biological reaction tank 74, and the treatment water tank 78.

In the wastewater treatment device 7 of FIG. 4, a raw water pipe 90 is connected to the inlet of the raw water tank 72. The outlet of the raw water tank 72 and the inlet of the biological reaction tank 74 are connected by a raw water supply pipe 92 via a pump 84. A screen 80 is installed inside the biological reaction tank 74, and the biological treatment water outlet of the biological reaction tank 74 and the inlet of the membrane separation device 76 are connected by a biological treatment water pipe 94 via a pump 86. The inside of the biological reaction tank 74 is filled with a sponge-like carrier 82 having ^{a density of 35 kg / m 3 or more in a predetermined filling amount.} The treated water (permeated water) outlet of the membrane separation device 76 is connected to the treated water tank 78 by a treated water pipe 96. An aeration pipe 100 is connected to the vicinity of the central portion of the lower part of the biological reaction tank 74 and below the screen 80, and is aerated by an aeration device (not shown). An air volume meter 88 is installed in the middle of the aeration pipe 100 connected below the screen 80. The concentrated water outlet of the membrane separation device 76 and the concentrated water inlet of the biological reaction tank 74 are connected by a concentrated water circulation pipe 98.

The organic matter-containing wastewater containing organic matter, which is raw water, is stored in the raw water tank 72 through the raw water pipe 90 as needed, and then sent to the biological reaction tank 74 through the raw water supply pipe 92 by the pump 84. Aerobic activated sludge is present in the biological reaction tank 74, and the sponge-like carrier 82 is filled with a predetermined filling amount. On the other hand, oxygen-containing gas such as air is sent from the aeration blower or the like through the aeration pipe 100 from the vicinity of the central portion below the biological reaction tank 74 and from the lower part of the screen 80. In the biological reaction tank 74, the activated sludge is used to decompose organic substances in the raw water (activated sludge treatment step). The activated sludge-treated biologically treated water is sent to the membrane separation device 76 through the biologically treated water pipe 94 by the pump 86. By installing the screen 80 having a size capable of separating the carrier in the biological reaction tank 74, it is possible to prevent the sponge-like carrier 82 from moving to the membrane separation device 76. In the membrane separation device 76, solid-liquid separation is performed by the membrane (solid-liquid separation step). The solid-liquid separated treated water (permeated water) is sent to the treated water tank 78 through the treated water pipe 96. The concentrated water is sent to the biological reaction tank 74 through the concentrated water circulation pipe 98, and sludge is circulated (sludge circulation step).

In the wastewater treatment apparatus 7 of FIG. 4, the operation is performed while the sponge-like carrier 82 having ^{a density of 35 kg / m 3 or more is present in the biological reaction tank 74.} This enables stable operation in which the membrane of the membrane separation device 76 is suppressed from being blocked. In this way, when the membrane separation device 76 is installed outside the biological reaction tank 74, the sponge-like carrier 82 is placed in the biological reaction tank 74 in the previous stage to circulate the sludge, thereby adsorbing the biopolymer and the biopolymer. It is possible to form a microbial phase suitable for decomposition and suppress an increase in the differential pressure of the membrane of the membrane separation device 76.

When an immersion type flat membrane is used as the membrane, it can be applied to the forms shown in FIGS. 1, 2, and 3.

When a hollow fiber type membrane module is applied as a membrane, the sponge-like carrier 46 is charged into the biological reaction tank 36 in the previous stage instead of the membrane separation tank 38 as shown in FIG. 2, and the organism into which the sponge-like carrier 46 is charged. By circulating the sludge of the membrane separation tank 38 in the reaction tank 36, it is possible to suppress the clogging of the membrane while suppressing the carrier from being trapped in the hollow fiber type membrane module. The hollow fiber type membrane module can also be applied to the forms shown in FIGS. 1 and 3.

When a cross-flow type membrane module is applied as a membrane, it can be applied by charging the sponge-like carrier 82 into the biological reaction tank 74 in the previous stage of the membrane separation device 76 as shown in FIG. When the sponge-like carrier 82 may be clogged in the membrane module, it is more appropriate to install a screen 80 having a size capable of separating the carrier in the biological reaction tank 74.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

<Examples 1 and 2 and Comparative Examples 1 and 2>
[Water flow conditions]
Experiments were conducted using artificial sewage having the composition and concentration shown in Table 1 (raw water TOC concentration: 100 mg / L, TN concentration: 50 mg / L) as raw water.

[Experimental device]
It was carried out using the experimental equipment as shown in FIG. 1 and using the carriers shown in Table 2 under the test conditions shown below. A water flow test was carried out for 50 days, and the differential pressure (kPa) of the membrane was measured. The results are shown in FIG. The arrows in the figure indicate that the sludge on the film surface was physically washed when the differential pressure increased. The density of the sponge-like carrier was measured according to JIS K7222.
(Test condition)
Flat membrane (Material: PVDF, nominal pore size 0.1 μm)
Biological reaction tank: Capacity 7.5L
Water retention time (HRT): 7 hours pH: Neutral water temperature: 20 ° C
MLSS: 3,000-4,000 mg / L
Aeration amount: 17 L / min Permeation flow velocity of immersion membrane: 0.45 m / day

[result]
In Comparative Example 1 in which no carrier was used, the differential pressure of 30 kPa or more, which required washing, was reached about 7 days after the start of water flow. After that, the sludge on the membrane surface was physically washed and water was passed again, but the differential pressure increased at intervals of about 3 to 14 days, and physical washing was required. Further, in Comparative Example 2 using a sponge-like carrier having a density lower than 35 kg / m ³ , the effect of suppressing the differential pressure was observed at the initial stage, but after the differential pressure increased once, it was different from Comparative Example 1. Similarly, the differential pressure increased, and the result was that the differential pressure suppressing effect was not observed. On the other hand, in Examples 1 and 2 using the sponge-like carrier having a density of 35 kg / m ³ or more, the effect of suppressing the increase in the differential pressure was high, and the difference pressure increase was hardly observed during the test period and was stable. It was possible to drive.

Table 3 shows the water quality (TOC concentration, TN concentration) of the treated water. The treated water quality was good in both Examples and Comparative Examples.

In the example in which the sponge-like carrier having a density of 35 kg / m ³ or more was operated while being present in the biological reaction tank as described above, stable operation was possible while suppressing the blockage of the membrane. Membrane separation Activated sludge treatment has been a major issue for membrane clogging, and stable operation with suppressed increase in differential pressure has become possible, and it has been found that this is an effective method for reducing the burden of operation management and cleaning chemical costs. .. In addition, this method is also an effective method for improving the existing membrane separation activated sludge treatment.

1,3,5,7 Wastewater treatment equipment 10,34,72 Raw water tank, 12,36,74 Biological reaction tank, 14,40,78 Treatment water tank, 16,44 Immersion membrane, 18,46,82 Sponge-like carrier , 20,48,52,84,86 pumps, 22,50 suction pumps, 24,54,56,88 air flow meters, 26,58,90 raw water pipes, 28,60,92 raw water supply pipes, 30,64,96 Treated water piping, 32,68,100 air exposure piping, 38 film separation tank, 42,80 screen, 62,94 biologically treated water piping, 66 sludge circulation piping, 76 film separation device, 98 concentrated water circulation piping.

Claims (6)

It is a wastewater treatment method that treats wastewater containing organic matter by the membrane separation activated sludge method.
A wastewater treatment method characterized in that a sponge-like carrier having a density of 35 kg / m ³ or more and a cell size of 46 cells / 25 mm or more is operated while being present in a biological reaction tank. The wastewater treatment method according to claim 1, wherein the sponge-like carrier is made of hydrophobic polyurethane. The wastewater treatment method according to claim 1 or 2, wherein the material of the membrane used in the membrane separation activated sludge method is a fluororesin. A wastewater treatment device that treats wastewater containing organic matter by the membrane separation activated sludge method.
A wastewater treatment apparatus characterized in that a sponge-like carrier having a density of 35 kg / m ³ or more and a cell size of 46 cells / 25 mm or more is operated while being present in a biological reaction tank. The wastewater treatment apparatus according to claim 4, wherein the sponge-like carrier is made of hydrophobic polyurethane. The wastewater treatment apparatus according to claim 4 or 5, wherein the material of the membrane used in the membrane separation activated sludge method is a fluororesin.

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