JP2021090937A - Water treatment method - Google Patents

Abstract

To provide a water treatment method for biological treatment of treated water containing calcium and organic matter by preventing calcium from scaling on the carrier and ensuring stable biological treatment.SOLUTION: A water treatment method includes a treated water containing calcium and organic matter passed through a reaction tank containing a carrier loaded with bacteria that decompose organic matter, and treated under aerobic conditions. The suspended solids concentration (mg/L) in the reaction tank is controlled to be three times or more than the calcium concentration (mg/L) of the treated water.SELECTED DRAWING: Figure 1

Description

The present invention relates to a water treatment method for stably performing biological treatment by suppressing scaling of calcium on a carrier when biologically treating water to be treated containing calcium and an organic substance.

The water to be treated that requires treatment may contain calcium. For example, when treating groundwater in which calcium leaches from soil or factory wastewater using calcium-based chemicals.

Calcium reacts with carbonate ions and precipitates as calcium carbonate. In water to be treated containing calcium, such precipitation of calcium is called scaling and can be a problem in water treatment. In particular, when a carrier is used in a reaction vessel for biological treatment, calcium may scale to this carrier, resulting in a decrease in biological treatment capacity due to blockage of the carrier surface and deterioration of fluidity due to an increase in the specific density of the carrier. is there.

As a method of suppressing calcium scaling, there is a method of removing calcium in the pre-stage of the reaction vessel.

Patent Document 1 describes a method for removing calcium by adding sodium carbonate to water to be treated and precipitating calcium carbonate under alkaline conditions at pH. However, this method has a problem that both the initial cost and the running cost are high because a tank for removing calcium is required in the front stage of the reaction tank and a chemical addition is also required.

Patent Document 2 describes a method of suppressing calcium scaling by controlling the pH of a reaction vessel for biological treatment to be low. However, the pH of the reaction vessel is closely related to the biotreatment property, and lowering the pH may reduce the biotreatment property.

Japanese Unexamined Patent Publication No. 2012-236122 JP-A-2007-296499

The present invention has been made to solve the above problems, and provides a method for suppressing the scaling of calcium on a carrier when biologically treating water to be treated containing calcium and an organic substance using the carrier. The purpose is.

By controlling the concentration of suspended solids (hereinafter sometimes referred to as SS) in the reaction vessel, the present inventors can scale calcium to SS instead of the carrier and reduce the amount of calcium adhering to the carrier. I found that.

That is, the present invention is a water treatment method in which water to be treated containing calcium and an organic substance is passed through a reaction vessel containing a carrier carrying a carrier that decomposes the organic substance to perform the treatment under aerobic conditions. This is a water treatment method in which the concentration of suspended solids (mg / L) in the reaction vessel is controlled to be three times or more the calcium concentration (mg / L) of the water to be treated.

In the present invention, it is preferable to supply suspended solids to the reaction vessel in order to control the concentration of suspended solids in the reaction vessel. At this time, in order to control the concentration of suspended solids in the reaction vessel, it is a preferable embodiment to return the suspended solids from the settling tank provided downstream of the reaction vessel to the reaction vessel. Further, in order to control the concentration of suspended solids in the reaction vessel, it is also a preferable embodiment to supply a separately prepared suspended solid to the reaction vessel.

In the present invention, the calcium concentration of the water to be treated is preferably 50 to 1000 mg / L. It is also preferable that the carrier is a polyvinyl alcohol-based gel-like carrier.

According to the present invention, when biological treatment is performed on water to be treated containing calcium and organic substances, even if calcium is contained in the water to be treated, the scaling of calcium on the carrier is suppressed and stable water is obtained. A processing method can be provided.

It is a flow chart which showed an example of the processing apparatus used in the processing method of this invention. It is a flow figure which showed the other example of the processing apparatus used in the processing method of this invention. It is a flow figure which showed the other example of the processing apparatus used in the processing method of this invention.

The present invention relates to a water treatment method for biologically treating water to be treated containing calcium and organic substances. Hereinafter, an example of the biological treatment apparatus used in the treatment method of the present invention will be described. FIG. 1 shows an example of a biological treatment apparatus used in the present invention. Hereinafter, the processing method of the present invention will be described by taking as an example the case where processing is performed using this processing apparatus.

In the present invention, the water to be treated is supplied to the aerobic tank. For example, in the treatment apparatus shown in FIG. 1, the water to be treated is introduced into the aerobic tank 1 (reaction tank) through the water supply pipe 2 to be treated. The water to be treated contains calcium and organic substances.

In the present invention, the treated water is discharged by treating the substance to be treated, such as an organic substance in the water to be treated, with the bacteria carried on the carrier in the reaction vessel.

The concentration of calcium in the water to be treated supplied to the reaction vessel is usually preferably low, but since the present invention has an effect of suppressing calcium scaling, the effect of the present invention is 50 mg / L or more. It is prominent, more prominent at 100 mg / L and above, and even more prominent at 200 mg / L and above. On the other hand, if the calcium concentration is too high, the scaling progresses remarkably, so 1000 mg / L or less is preferable. It is assumed that the calcium contained in the water to be treated is dissolved as calcium ions.

The SS concentration in the reaction vessel is preferably controlled to be 3 times or more the calcium concentration in the water to be treated in order to suppress calcium scaling. That is, the concentration ratio (SS / Ca) is preferably 3 or more. The concentration ratio (SS / Ca) is more preferably controlled to be 5 times or more, and further preferably controlled to be 7 times or more. Further, if the SS concentration in the reaction vessel becomes too high, the number of microorganisms supported on the carrier may decrease and the biological treatment capacity may decrease. Therefore, the SS concentration in the reaction vessel should be 5000 mg / L or less. Is more preferable, and it is more preferably 3000 mg / L or less, and further preferably 2000 mg / L or less.

Here, the suspended solid (SS) is a particulate matter having a diameter of 2 mm or less that is suspended or suspended in the liquid. For example, in the case of rivers and groundwater, soil particles and the like are included, and in the case of sewage and factory wastewater, organic matter and metals are included as SS. The SS content is determined from, for example, the dry weight of the substance remaining on the filter medium when the water to be treated is passed through the filter medium of 1 μm.

The BOD (biochemical oxygen demand) of the water to be treated flowing into the reaction vessel is preferably 4000 mg / L or less, more preferably 2000 mg / L or less, still more preferably 1000 mg / L or less. Since the present invention relates to a method for biologically treating water, the BOD of the water to be treated is usually larger than 0 mg / L. Further, BOD volume load is preferably not more than 5kg ^{/ m} 3 ^/ d, more preferably not more than 4kg ^{/ m} 3 ^/ d, more preferably not more than 3kg ^{/ m} 3 ^/ d. Since the present invention relates to a method for biologically treating water, the BOD volume load of the water to be treated is usually ^{larger than 0 kg / m 3} / d.

The pH in the reaction vessel is preferably 5-9, more preferably 6-8. If the pH deviates from this range, it becomes difficult for bacteria to grow and the rate of decomposition of organic matter may decrease.

The temperature in the reaction vessel is preferably 10 to 40 ° C, more preferably 20 to 35 ° C. If the temperature falls outside this range, it becomes difficult for bacteria to grow and the rate of decomposition of organic matter may decrease.

The DO (Dissolved Oxygen) in the reaction vessel is preferably 0.5 mg / L or more. If the DO is less than 0.5 mg / L, the organic matter decomposition rate may decrease. The upper limit of DO is not particularly limited, but 9 mg / L or less is preferable in terms of operation in water treatment.

In the present invention, it is preferable to aerate the treated water in the aerobic tank 1 from the viewpoint of efficiently advancing the decomposition of organic substances. The method of aeration is not particularly limited, but as shown in FIG. 1, it is preferable that the aerobic tank 1 includes an air diffuser 6 to which an air pipe 7 is connected. The treated water in the aerobic tank 1 can be aerated by the air from the air diffuser 6, and the treated water and the carrier 4 can be sufficiently flowed. When the fluidity of the carrier 4 is further improved, the inside of the aerobic tank 1 may be agitated using a stirring device such as a stirrer.

As shown in FIG. 1, it is preferable that the aerobic tank 1 is provided with a carrier capturing means such as a screen 5 at the discharge port of the aerobic tank 1 in order to prevent the carrier 4 from flowing out.

The method for controlling the SS concentration in the reaction vessel is not particularly limited, but a method of supplying suspended solids to the reaction vessel is preferable. In one aspect thereof, a separately prepared suspended solid is supplied to the reaction vessel in order to control the concentration of suspended solids in the reaction vessel. For example, in the treatment apparatus of FIG. 1, the activated sludge as SS stored in the activated sludge storage tank 9 is supplied to the aerobic tank 1 via the activated sludge addition pipe 8, and is contained in the aerobic tank 1. The suspended solids concentration is controlled to be three times or more the calcium concentration of the water to be treated.

Further, for example, in the treatment apparatus of FIG. 2, the activated sludge settled at the bottom of the settling tank 10 provided downstream of the aerobic tank 1 via the treated water pipe 3 passes through the activated sludge addition pipe 8 to the aerobic tank. Returned to No. 1, the concentration of suspended solids in the aerobic tank 1 is controlled to be three times or more the concentration of calcium in the water to be treated. As a result, it is not necessary to procure SS separately, and the activated sludge used in the apparatus can be reused.

Further, in the treatment apparatus of FIG. 3, an activated sludge tank 11 is provided downstream of the aerobic tank 1 via a treatment water pipe 3, and a settling tank 10 is further provided downstream of the activated sludge tank 11 via a treatment water pipe 3. In the activated sludge tank 11, the treatment liquid containing the activated sludge is aerated by the air from the air diffuser 6.

The volume ratio (filling rate) of the carrier added to the reaction tank to the tank volume can be appropriately determined according to the properties of the water to be treated. The filling rate is preferably 5 to 60% in terms of volume, more preferably 5 to 40%, further preferably 5 to 30%, and particularly preferably 8 to 20%. The higher the filling rate of the carrier, the more efficiently the decomposition reaction of the organic matter can proceed. However, if the filling rate is too high, the fluidity of the carrier may decrease, and the reaction efficiency may decrease.

The carrier used in the present invention preferably has holes (communication holes) that communicate from the surface to the inside. Here, the term "holes communicating" means that the holes do not exist independently of each other, but that the holes communicate with each other.

The pore size of the communication holes of the carrier is preferably 30 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less. By using a carrier having a communication hole having a pore size of 30 μm or less, bacteria can be efficiently supported on the carrier. Further, the pore diameter is preferably 0.1 μm or more. If the pore size is less than 0.1 μm, bacteria may not be able to invade the inside of the carrier. Here, the pore diameter of 30 μm or less or the pore diameter of 0.1 μm or more means that 50% or more of the fine pores of the carrier have a pore diameter of 30 μm or less or 0.1 μm or more. The pore diameter at this time is the diameter of the hole seen when observing the cross section of the carrier with an electron microscope, and if the hole is not a perfect circle, the diameter of the perfect circle having the same area as the hole is defined as the pore diameter.

The pore size on the surface of the carrier is preferably 0.5 μm or more within the observable range. On the other hand, when the pore size on the surface of the carrier exceeds 30 μm, large organisms other than bacteria easily enter, and the decomposition rate of organic substances may decrease. The pore size of the surface of the carrier is more preferably 20 μm or less, and further preferably 10 μm or less. The surface of a carrier is a range that can be seen when the surface of the carrier is observed with an electron microscope without being cut. The definition of the hole diameter is the same as when observing the cross section.

The water content of the carrier used in the present invention is preferably 50% or more, more preferably 70% or more, and further preferably 85% or more in terms of mass. When the water content is at least a certain value, the growing environment of the bacterium can be improved, and the bacterium is easily grown and supported. On the other hand, the water content is preferably 96% or less. When the water content is below a certain value, the carrier is not easily damaged, so that it is not necessary to add an additional carrier and long-term operation is possible. The water content can be calculated from the mass ratio before and after drying when the carrier in a water-containing state is completely dried.

The type of carrier used in the present invention is not particularly limited, but it is preferable that the carrier is a polymer gel carrier because it has a high affinity with bacteria and is excellent in bacterial habitatability, and is a polyvinyl alcohol-based gel-like carrier. (PVA gel carrier) is more preferable. Since the PVA gel carrier is a hydrogel carrier and can carry many bacteria, stable treatment is possible with a short hydraulic residence time. Among them, a PVA gel carrier having communication holes is preferably adopted.

The PVA gel carrier may be a PVA gel carrier in which at least a part of the contained hydroxyl groups is acetalized.

The equivalent sphere diameter of the carrier is preferably 1 to 10 mm. If the equivalent diameter of the sphere is too small, the mesh of the screen to prevent the outflow of the carrier must be made small, which may cause clogging. It is more preferable that the equivalent diameter of the sphere is 2 mm or more. On the other hand, if the equivalent diameter of the sphere exceeds 10 mm, the fluidity of the carrier may decrease. The sphere-equivalent diameter of the carrier is more preferably 6 mm or less. Here, the sphere-equivalent diameter is the diameter of a sphere having a volume equal to the volume of the carrier. The shape of the carrier is not particularly limited, and any shape such as a spherical shape, a cube, a rectangular parallelepiped, and a columnar shape can be taken. Among these, a spherical shape is preferable in consideration of contact efficiency with bacteria.

It is preferable that the specific density of the carrier is slightly larger than that of water and can be easily swung in the aerobic tank. The specific gravity of the carrier is preferably 1.001 or more, and more preferably 1.005 or more. On the other hand, the specific gravity is preferably 1.2 or less, more preferably 1.1 or less, and even more preferably 1.05 or less.

Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Example 1]
Using the treatment apparatus shown in FIG. 1, water to be treated containing calcium was passed through and treated under aerobic conditions. At that time, an organic source that generates carbon dioxide during biological treatment was added to the water to be treated, and a biological treatment test was carried out.

(Water to be treated containing organic substances)
The following BOD water was used as the water to be treated biologically.
BOD5: 1000mg / L

(SS concentration in the reaction tank)
The SS concentration in the reaction vessel was controlled at 1000 mg / L.

(Carrier)
0.1 L (filling rate: 10%) of the carrier 4 was charged into the aerobic tank 1 (volume 1 L). The loaded carrier 4 was a polyvinyl alcohol gel carrier. The carrier 4 was spherical, had a spherical equivalent diameter of 4 mm, and had a specific gravity of 1.015. When the surface and the inside of this carrier were observed using an electron microscope, pores communicating with each other were confirmed. Further, when the pore diameters on the surface and inside of the carrier were measured using the obtained observation image with an electron microscope, most of the pore diameters were included in the range of 0.5 to 10 μm, which was out of the range. There were only a few, and it was clear that more than 50% was within this range. The water content of the carrier was 94% on a mass basis.

(Processing device)
An air diffuser 6 is attached to the bottom of the aerobic tank 1, and the treated water in the tank is aerated by the air sent through the air pipe 7. A screen 5 for preventing the outflow of the carrier 4 is attached to the outlet of the aerobic tank 1. Further, in order to control the SS concentration in the aerobic tank 1, active sludge is added to the aerobic tank 1 from the active sludge storage tank 9 through the active sludge addition pipe 8 as SS.

The BOD of the water to be treated supplied to the aerobic tank 1 through the water supply pipe 2 to be treated is lowered by the decomposition of organic substances by bacteria carried on the carrier 4 in the aerobic tank 1. The treated water in which the organic matter has been decomposed is discharged to the outside of the aerobic tank 1 through the treated water pipe 3.

(Startup method, management method)
The control conditions for the aerobic tank 1 were a pH of 6.0 to 8.0, a DO of 2 to 8 mg / L, and a temperature inside the aerobic tank 1 of 25 ° C. Activated sludge was added to the aerobic tank 1 into which the carrier (carrier on which the bacteria was not supported) was charged in advance, and the BOD volume load was finally 2.5 kg / m ³ It was supplied while gradually increasing the inflow amount of the water to be treated so as to be / d.

(Evaluation method)
In evaluating the state of scaling, the mass of the inorganic component adhering to the carrier was measured. The carrier was placed in a crucible, dried in a dryer for 1 day, then incinerated in an electric furnace, and the mass of the obtained ash was divided by the bulk volume of the hydrous carrier and adhered to 1 liter of the carrier. The inorganic content mass was calculated.

Using the treatment apparatus described above, biological treatment was performed on the water to be treated containing the above-mentioned organic substances. After the treatment was stabilized at a removal rate of 95% or more with respect to the BOD volume load of 2.5 kg / m ³ / d, the addition of calcium chloride was started so that the calcium concentration of the water to be treated became 200 mg / L.

(result)
Thirty days after the start of adding calcium chloride, the amount of inorganic content attached to the carrier was measured, and 34 mg of inorganic content was attached per 1 L of the carrier.

[Example 2]
Biological treatment was carried out in the same manner as in Example 1 except that the SS concentration in the tank was set to 2000 mg / L. As a result, 20 mg of inorganic content per 1 L of the carrier was attached 30 days after the start of addition of calcium chloride.

[Example 3]
Biological treatment was carried out in the same manner as in Example 1 except that the calcium concentration to be added was set to 300 mg / L. As a result, 62 mg of an inorganic component was attached per 1 L of the carrier 30 days after the addition of calcium chloride was started.

[Comparative Example 1]
Biological treatment was carried out in the same manner as in Example 1 except that the SS concentration in the tank was set to 100 mg / L. As a result, 30 days after the start of adding calcium, the amount of the inorganic component adhering to the carrier was 3500 mg per 1 L of the carrier.

[Comparative Example 2]
Biological treatment was carried out in the same manner as in Example 1 except that the calcium concentration of the water to be treated was 300 mg / L and the SS concentration in the tank was 100 mg / L. As a result, 30 days after the start of adding calcium, the amount of the inorganic component adhering to the carrier was 5000 mg per 1 L of the carrier.

The results of Examples and Comparative Examples are shown in the table. As shown in Examples 1, 2 and 3, the scaling of calcium to the carrier can be suppressed by increasing the SS concentration in the reaction vessel to 3 times or more the concentration of calcium contained in the water to be treated. It was. On the other hand, as shown in Comparative Examples 1 and 2, when the SS concentration in the reaction vessel was less than 3 times the calcium concentration contained in the water to be treated, the scaling of calcium to the carrier proceeded remarkably. ..

1 aerobic tank 2 treated water supply pipe 3 treated water pipe 4 carrier 5 screen 6 air diffuser 7 air pipe 8 activated sludge addition pipe 9 activated sludge storage tank 10 settling tank 11 activated sludge tank

Claims (6)

A water treatment method in which water to be treated containing calcium and an organic substance is passed through a reaction vessel containing a carrier carrying a carrier that decomposes the organic substance and treated under aerobic conditions, and is suspended in the reaction vessel. A water treatment method in which the substance concentration (mg / L) is controlled to be three times or more the calcium concentration (mg / L) of the water to be treated. The water treatment method according to claim 1, wherein the suspended solids are supplied to the reaction tank in order to control the concentration of suspended solids in the reaction tank. The water treatment method according to claim 2, wherein the suspended solids are returned to the reaction tank from a settling tank provided downstream of the reaction tank in order to control the concentration of suspended solids in the reaction tank. The water treatment method according to claim 2, wherein a suspended solid prepared separately is supplied to the reaction tank in order to control the concentration of suspended solids in the reaction tank. The water treatment method according to any one of claims 1 to 4, wherein the calcium concentration of the water to be treated is 50 to 1000 mg / L. The water treatment method according to any one of claims 1 to 5, wherein the carrier is a polyvinyl alcohol-based gel-like carrier.

Images