JP2000229296A - Biological water treating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive the weight reduction of generated sludge without worsening treated water. SOLUTION: Raw water from a raw water tank 10 is treated at an immersed filter bed tank 12, and after that, the water is filtered by a filter device 18. The backward washing waste water from the filter device 18 is subjected to solubilizing treatment at a solubilizing tank 22, then returned to the raw water tank 10. Therefore, the solubilized sludge is treated again at the immersed filter bed tank 12 and subjected to the weight reduction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological treatment apparatus for organic wastewater and the like, and more particularly, to the treatment of excess sludge generated during biological treatment.

[0002]

2. Description of the Related Art In biological wastewater treatment of organic wastewater, activated sludge method and immersion filter method are two mainstreams. In the activated sludge method, water to be treated and microbial sludge are aerated and mixed in an aeration tank. Then, the aerated mixed liquid from the aeration tank is settled and separated in the settling tank to obtain treated water. In the immersion filter method, the water to be treated is biologically treated by flowing the water to be treated into a treatment tank in which a packed layer made of a filler on which microorganisms have settled is formed. obtain.

[0003] A treatment method combining the activated sludge method and the immersion filter bed method is also known. For example, raw water is treated by the immersion filter bed method, and the obtained immersion filter bed treatment water is treated by the activated sludge method, thereby maintaining good treated water quality under high volume load conditions, and reducing the amount of generated sludge. Methods for reducing this are known.

On the other hand, filtration apparatuses such as a sand filtration apparatus and a membrane filtration apparatus are known as apparatuses for separating suspended solids (SS: suspended solids). The turbid matter in the treated water obtained in the treatment can be further separated and removed.

One of such filtration devices is disclosed in, for example,
As disclosed in JP-A-315110 and JP-A-1-304011, a filter medium having a length of, for example, 0.1 mm is used.
2. Description of the Related Art An ultra-high-speed filtration device filled with a long fiber bundle made of a single fiber having a thickness of 4 to 3.0 m and a thickness of 20 to 80 μ is known. This ultra-high-speed filtration apparatus has excellent trapping power for turbid substances and can filter and separate turbid substances at high speed. Then, an apparatus for efficiently obtaining clear treated water having a low SS content by connecting an ultra-high-speed filtration device filled with the long fiber bundle to the subsequent stage of the treatment tank of the immersion filter method has been proposed.

[0006] Such a treatment apparatus combining the immersion filter bed method and the filtration treatment has an advantage that a sedimentation basin required in the activated sludge method is not required. However, the filtration device captures and removes SS using a filter medium, and when the captured turbidity reaches a predetermined amount, it is necessary to backwash. And the backwash wastewater obtained by backwashing contains high concentration turbidity (sludge). Normally, the backwash wastewater is subjected to coagulation and sedimentation to separate sludge and supernatant water.

[0007] Therefore, a new sedimentation basin is required for the treatment of the backwash wastewater of the filtration device. The sludge generated in the sedimentation basin is subjected to dehydration, etc., and is incinerated or treated as industrial waste. However, the disposal cost is increasing.

Further, regarding sludge treatment, a part of the excess sludge is reduced with an oxidizing agent such as ozone or hydrogen peroxide, thermophilic bacteria,
Alternatively, there has been proposed a method of solubilizing with an organic solubilizing agent such as an enzyme or a bactericide, and introducing into an aeration tank for aerobic treatment. Thereby, the generated sludge is further biologically treated, and the amount of sludge is reduced.

[0009]

However, operating costs are increased, such as a sludge solubilizing agent added to solubilize excess sludge and a heat source required to culture thermophilic bacteria that also solubilize excess sludge. There was a problem. In addition, equipment costs such as an ozone generator, an ozone treatment tank, or a tank for solubilizing sludge by thermophilic bacteria are required.

[0010] Furthermore, by introducing and treating the sludge solubilized and the biodegradability improved or the added sludge solubilizing agent into the aeration tank, the volume load of the aeration tank increases, resulting in insufficient aeration air volume and sludge load. There was a problem that the quality of treated water deteriorated due to the increase in water content.

An object of the present invention is to provide a biological water treatment apparatus capable of reducing excess sludge by a simple method without deteriorating the quality of treated water.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a submerged filter bed tank for circulating water to be treated and biologically treating the water to be treated in a packed bed composed of a filler on which microorganisms have settled on the surface. A filtration device for filtering immersion filter bed treated water by the immersion filter tank,
And a return means for returning backwash wastewater generated when the filtration device is backwashed to the immersion filter bed tank.

As described above, according to the present invention, the sludge in the backwash drainage is introduced into the immersion filter bed tank. As a result, a part of the returned sludge is decomposed by the microorganisms held in the immersion filter tank.

Conventionally, it has been known that the amount of sludge generated in an immersion filter bed tank is extremely small. It is said that this is because the biota food chain is formed in a higher order. In other words, in the immersion filter tank, bacteria that decompose organic matter in wastewater and protozoa that feed on bacteria, as well as metazoans that feed on protozoa are mixed, so that the amount of sludge generated is low. Become.

Here, when the returned sludge is decomposed by microorganisms existing in the packed bed of the immersion filter bed tank, the consumption of oxygen increases accordingly. However, the immersion filter bed processing apparatus is filled with a filler, and bubbles pass through the filler. For this reason, the rising speed of the bubbles is lower than that of the empty tower, the oxygen dissolving efficiency can be increased, and the shortage of oxygen can be prevented. In particular, when a cylindrical mesh filler is used as the filler, bubbles can be subdivided by this filler and the gas-liquid contact area can be increased, thereby significantly improving the oxygen dissolving efficiency and securing sufficient dissolved oxygen. can do.

Various types of organic wastewater, such as sewage and industrial wastewater, are used as the water to be treated by the apparatus of the present invention, but also raw water used for water treatment, such as river water.

Further, it is preferable that a solubilization means for solubilizing the sludge contained in the backwash water is provided, and the sludge after the solubilization treatment is returned to the immersion filter tank.

By solubilizing the sludge in the backwash wastewater with an oxidizing agent such as ozone or hydrogen peroxide, a thermophilic bacterium, an enzyme or a bactericide, the decomposition rate of the sludge in the immersion filter tank is improved, Sludge generation is further reduced. Therefore, by performing the optimal treatment, it is possible to ultimately reduce the generation of sludge to zero. In addition, what is necessary is just to perform solubilization conditions on the optimal conditions in the solubilization method to be adopted.

Further, there is provided an air washing means for washing the packed bed in the immersion filter bed tank with air. Even when the air washing means is performing the air washing, the flow of the water to be treated to the packed bed is not stopped. Is preferred.

By this air washing, microbial sludge excessively attached to the filler can be removed. Then, the separated sludge is captured by the filtration device, returned to the immersion filter bed tank again, and further decomposed. Further, sludge separated by washing is filtered by a filtration device, so that no special treatment is required. Further, since the flow of the water to be treated is continued, it is not necessary to switch the flow path.

[0021]

Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 is a view showing a configuration of an embodiment of a biological water treatment apparatus according to the present invention. Raw water such as organic waste water is introduced into a raw water tank 10 and stored therein. Raw water in the raw water tank 10 is introduced into the immersion filter tank 12. The immersion filter bed tank 12 has a filling material filled therein to form a filling layer 14. Although various materials and shapes can be used as the filler for the filling layer 14, a cylindrical mesh filler is used in the present embodiment. The cylindrical mesh filler is a pipe made of a plastic mesh material, and the filling layer 14 is formed by stacking the filler cylinders in a cross-girder shape such that the directions of the filler cylinders are sequentially orthogonal. That is, in one layer, the cylinders are arranged so as to face in the same direction, and in the layer above, the cylinders are arranged so as to face in a direction perpendicular to the cylinder.

Below the packed bed 14, an air diffuser 16 is provided.
Is provided, and the inside of the immersion filter bed tank 12 is aerated by ejecting air therefrom. The air bubbles ejected from the air diffuser 16 rise inside the packed bed 14. For this reason, the rising speed of the bubbles is lower than that of the empty tower, and the oxygen dissolving efficiency increases. In particular, a cylindrical mesh filler is used as the filler, and the filler can divide the air bubbles, increase the gas-liquid contact area, and significantly increase the oxygen dissolving efficiency.

The raw water flows into the lower part of the immersion filter tank 12, rises in the packed bed 14, and the immersion filter treatment water is discharged from the upper part. Therefore, the raw water always passes through the packed bed 14, where it is treated by microorganisms that have settled on the surface of the filler. The flow of raw water into the immersion filter bed tank is not limited to such as rising flowing water, but it is possible to flow raw water from the upper part of the tank and descending flowing water to discharge treated water from the lower part, or the length of a rectangular tank. The raw water may flow in from one end in the direction, and may be horizontal flow water that discharges treated water from the other end. The immersion filter bed treatment water treated in the immersion filter tank 12 is taken out from the upper part of the immersion filter tank 12 and introduced into the filtration device 18. In this filtration device 18, a large number of long fiber bundles 20 made of a single fiber having a length of, for example, about 0.4 to 3.0 m and a thickness of about 20 to 80 μ are used as a filter medium.
And is filled with the upper end being a free end. By passing between the long fiber bundles 20, the immersion filter treatment water in the immersion filter tank 12 is further filtered to form SS (turbidity). Quality) is further removed. In addition, this filtration device 18
The water to be treated is circulated in a descending flow, and the long fibers 20 are filled with a filling amount such that the whole fiber stands upright when the water to be treated flows in the descending flow. Then, the filtered water of the filtration device 18 is discharged as treated water.

Here, the filtering device 18 is used for the long fiber bundle 2
0 captures the turbidity and gradually causes clogging.
Therefore, backwashing is performed periodically to eliminate clogging of the long fiber bundle 20. In this backwash, usually, filtered water and air are used in combination. Then, the backwash wastewater is introduced into the solubilization tank 22.

The solubilization tank 22 is for solubilizing sludge contained in the backwash wastewater, and for example, adds a bactericide containing a quaternary ammonium salt as a bactericide to perform solubilization. In this case, the germicide is 0.01 to 0.05.
An addition amount of about g / gSS is preferable. The pH is preferably 7 or more, and more preferably 9 or more.

Here, the solubilization treatment does not have to be performed with a bactericide. For example, ozone treatment can be adopted. At this time, the added amount of ozone is 0.03 to 0.05 g.
O ₃ / gSS is preferred, and the pH is preferably 5 or less. Further, the pressure of the reaction tank of the solubilization treatment tank 22 is set to a gauge pressure of 0.1.
It is good to be 5 to ² kgf / cm ² . Furthermore, 40-8
Heating to 0 ° C. increases the reaction rate. Further, addition of hydrogen peroxide can also be adopted. In this case, 0.1% for hydrogen peroxide
０．００0.001 gH ₂ O ₂ / gSS is preferred, and 0.2 to 10 gFe / gH ₂ O ₂ is preferably added as an iron ion as a catalyst. The pH is preferably 4 or less, and the water temperature is preferably 40 to 80 ° C. Further, it is also preferable to perform treatment with thermophilic bacteria, addition of sodium hypochlorite, UV irradiation treatment, ultrasonic treatment, mechanical destruction, or a combination thereof.

If the existing equipment is to be modified and a backwash drainage tank already exists, the solubilization treatment tank 22 is used.
You may also be used.

The sludge that has been solubilized and has improved biodegradability is
Return to the immersion filter tank 12 via the raw water tank 10 (you may return directly to the immersion filter tank 12 without passing through the raw water tank 10)
Then, it is decomposed by microorganisms held in the immersion filter bed. In the immersion filter tank 12, bacteria that decompose organic matter in the wastewater, protozoa that prey on the bacteria, and metazoans that prey on the protozoa are mixed, and the food chain of the biota is formed at a higher level. Therefore, the amount of generated sludge is reduced.

The returned sludge and BOD derived from chemicals
(Biochemical oxygen demand), B of the immersion filter tank 12
Although the OD load increases, the immersion filter bed tank 12 can maintain the sludge at a high concentration and maintain a high oxygen dissolving efficiency, so that the quality of the immersion filter bed treatment water does not deteriorate.

The amount of sludge returned to the immersion filter tank 12 is preferably equal to or greater than the amount of excess sludge originally generated by treating raw water in the immersion filter tank 12. In particular, in order to reduce the generation of sludge in the entire system to zero, the amount of returned sludge must be made larger than the amount of surplus sludge in anticipation of excess sludge being decomposed and newly forming sludge. In addition, the inorganic sludge must be withdrawn, but if the amount of inorganic substances contained in the filtered water matches the amount generated, the amount of generated sludge can be completely reduced to zero.

In the conventional sludge reduction method using the solubilization treatment of sludge, the sludge amount of excess sludge or more is also decomposed and returned to the aeration tank. However, the activated sludge treatment was adopted in the conventionally proposed treatment method. Activated sludge had a very high sludge conversion rate of 40 to 60% on a BOD basis, and it was necessary to add an oxidizing agent and chemicals and to cope with the size of the solubilization treatment tank.

In the present invention, since the sludge conversion rate is extremely low, 5 to 20%, by employing the immersion filter bed, the amount of the oxidizing agent and chemicals added is small, and the solubilization tank 22 is used.
Can be small.

Further, in the immersion filter bed tank 12, the amount of sludge in the packed bed 14 increases with the treatment. Therefore, it is necessary to periodically remove and remove sludge. In the present embodiment, the filling layer 14 is cleaned by periodically increasing the amount of air from the air diffuser 16 from the amount of air during normal processing. Here, at the time of this air cleaning, the inflow of raw water continues. Therefore, the immersion filter bed treatment water containing the exfoliated sludge is discharged from the immersion filter bed tank 12. However, a filtration device 18 is provided downstream of the immersion filter tank 12. Thus, the separated sludge is trapped and removed in the filtration device 18 and has no adverse effect on the quality of the filtered water. Then, the separated sludge is introduced into the solubilization tank 22 as backwash wastewater by the backwashing of the filtration device 18 and processed.

At the time of air cleaning, the flow of raw water may be temporarily stopped, and cleaning water may be separately introduced from the lower part of the immersion filter tank 12 to wash the packed bed 14. This is uneconomical since a separate water storage tank and cleaning water pump must be provided.

With such a configuration, it is not necessary to separately treat the washing and drainage of the immersion filter tank 12. Therefore, the apparatus can be simplified as a whole. In addition, filtration device 1
8, the wastewater from the immersion filter tank 12 can be concentrated and the sludge can be treated efficiently. Further, there is no need to stop the flow of the raw water into the immersion filter bed tank 12, so that there is an advantage that the management of the treatment process is facilitated.

The supply source of oxygen to the immersion filter tank 12 may use not only air but also high-concentration oxygen gas.

Further, there is a concern that the returned sludge may block the space between the fillers in the packed bed 14, but this is solved by using a filler having a porosity of 90% or more, such as a cylindrical mesh filler. Is done. Further, by using the filler having a high void, the retention amount of the sludge is increased, and as a result, the residence time of the sludge in the treatment system is prolonged, and the effect of further decomposing the sludge is obtained.

The backwash drainage from the filtration device may be temporarily stored in a drainage tank, or may be sent to the raw water tank if there is room in the raw water tank. Further, it is preferable that the backwashing of the filter is performed with both the air and the filtered water.

It is preferable that the backwash wastewater from the filtration device that is not returned to the immersion filter bed tank 12 is coagulated and settled and separated into sludge and supernatant water. In this case, the coagulation sedimentation basin becomes smaller and the cost of the coagulant to be added can be reduced as compared with the case where the whole amount of the reverse drainage is treated. The supernatant water obtained by coagulation and precipitation may be mixed with raw water or, depending on the quality of the water, may be mixed with filtered water.

The present biological water treatment apparatus is suitable for treating various kinds of organic wastewater, and can be used for treating water such as river water.

In the above-described embodiment, the solubilizing tank 22 is provided, but the solubilizing tank 22 may not be necessarily provided.

[0043]

EXAMPLES Next, examples performed using the apparatus of this embodiment will be described.

Example An experiment was conducted using wastewater for producing waste paper as water to be treated (raw water). First, as Comparative Example 1, an immersion filter bed and an ultra-high-speed filtration device (filter) filled with long fibers
Was performed in combination with the above. The backwash wastewater from the filtration device was excluded outside the system. In Examples 1 and 2, the backwash wastewater from the ultrahigh-speed filtration device was returned to the immersion filter bed tank. Here, in Example 1, sludge was not solubilized in the backwash wastewater, and in Example 2, solubilization treatment was performed and then the sludge was returned to the immersion filter tank. Note that a cylindrical mesh filler having a diameter of 7 cm and an aperture of 1 cm was used as a filler for the immersion filter bed.

The filter medium of the filtration device has a thickness of 35 mm.
μ, using a long fiber bundle consisting of acrylic fiber of 1 m in length,
The long fiber bundle was packed in a filter at a packing density of 75 kg / m ² .

In any of the examples, the aeration LV for the immersion filter bed tank during normal operation is 20 m ³ / m ² / H, the cleaning air LV for air cleaning is 50 m ³ / m ² / H, and the number of cleaning times is 4 times. /
The washing time was set to 15 minutes / time, and the inflow of the water to be treated was continued during the air washing of the immersion filter tank.

As a solubilization treatment, a bactericide containing a quaternary ammonium salt was used and added to a concentration of 0.05 g / g SS. The pH of the solubilization treatment was 9, and the reaction time was 6 hours.

The amount of excess sludge withdrawn and the amount of sludge returned to the immersion filter bed tank were adjusted until a steady state was reached.

Table 1 shows the experimental conditions.

[0050]

[Table 1] Table 2 shows each treatment condition and treated water quality in the steady state.

[0051]

[Table 2] To return the backwash wastewater, the volume load of the immersion filter tank was increased in Examples 1 and 2 as compared with Comparative Example 1. Along with this, the quality of the immersion filter bed treatment water of the immersion filter tank of Example 2 slightly deteriorated, which is considered to be due to the effect of the solubilizing agent.

In Example 1, the solubilization was not performed, but the sludge conversion rate was reduced to 1/4 of that in Comparative Example 1 by setting the amount of sludge returned to the immersion filter tank to 0.0245 m ³ / d. I was able to. In addition, the amount of backwash wastewater transferred to the coagulation treatment without being returned can also be reduced to about 1/4, and it has become clear that the running cost of the coagulant can be reduced.

In Example 2, the sludge generation rate could be reduced to zero by solubilization. Therefore, chemicals such as a flocculant and sludge treatment necessary for coagulating the washing wastewater from the immersion filter tank are not required at all. In addition, since the solubilized sludge was returned to the immersion filter bed tank, the volume load increased, but the quality of the immersion filter treatment water hardly deteriorated.

[0054]

As described above, according to the present invention,
The sludge contained in the backwash wastewater can be treated by returning the backwash wastewater from the filtration device to the immersion filter bed tank. Then, it became possible to reduce the amount of excess sludge by a simple method without deteriorating the quality of the treated water. Further, the amount of generated sludge can be further reduced by solubilizing the sludge. Furthermore, by performing air cleaning in the immersion filter tank and introducing immersion filter treatment water containing exfoliated sludge to the filtration device, it is not necessary to treat the washing wastewater from the immersion filter tank.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a biological water treatment apparatus according to an embodiment.

[Explanation of symbols]

10 raw water tank, 12 immersion filter bed tank, 14 packed bed, 16
Aeration device, 18 filtration device, 20 long fiber bundle, 22
Solubilization tank.

Claims (3)

[Claims] 1. An immersion filter tank for circulating water to be treated and biologically treating the water to be treated in a packed bed comprising a filler on which microorganisms have settled on the surface, and immersion in the immersion filter tank. A biological water treatment comprising: a filtration device for filtering treated water from a filter bed; and return means for returning backwash wastewater generated when the filter device is backwashed to the immersion filter bed tank. apparatus. 2. The apparatus according to claim 1, further comprising solubilizing means for solubilizing the sludge contained in the backwash water, and returning the sludge after the solubilization treatment to the immersion filter tank. A biological water treatment apparatus, characterized in that: 3. The apparatus according to claim 1, further comprising air cleaning means for air-cleaning the packed bed in the immersion filter tank, wherein air cleaning is performed by the air cleaning means.
A biological water treatment apparatus characterized by not stopping the flow of the water to be treated to the packed bed.