JP3536366B2 - How to set up a biofilm filtration device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for starting a biofilm filter, and more particularly to a method for easily and efficiently starting a biofilm filter in a short period of time.

[0002]

2. Description of the Related Art A microorganism is attached to the surface of a carrier (filter material),
A biofilm filtration treatment method in which wastewater is passed through a biofilm filtration tank having a filter medium layer of this microorganism-attached carrier for treatment is a method suitable for removing soluble organic matters and SS in wastewater, and in recent years In addition, it has been applied to removal of nitrogen and phosphorus, and has become an industrially extremely useful technique.

In the biofilm filtration method, since it is necessary to form a biofilm of useful microorganisms on a carrier, in the prior art, prior to the start of the process, the equipment is started up and the waste water to be treated is treated. Alternatively, simulated wastewater according to it is passed under the design load of the biofilm filtration device to preliminarily form a biofilm on the carrier. Here, the reason for using the simulated drainage is as follows. That is, when the biofilm filtration device is started up, the state of bacteria is unstable. Therefore, when treating industrial wastewater with large fluctuations in water quality, industrial water of stable quality was used instead of treated wastewater. Start up by passing simulated drainage.

[0004]

As described above, in the biofilm filtration device, the startup operation for forming the biofilm is necessary. The period required for this startup is to improve the treatment efficiency, the amount of water used, and the amount of water used. From the viewpoint of energy cost reduction, etc., it is required to be as short as possible. In particular, when industrial water is used for startup, a large amount of industrial water is used when the startup period is long, so it is further desired to shorten the startup period.

However, the conventional method for starting up a biofilm filtration device has a problem that it takes a long time to start up. In particular, when a bacterium having a small growth rate such as nitrifying bacteria is used, the formation rate of the biofilm is slow and the startup period is often long.

In order to shorten the start-up period, it is conceivable to inoculate only useful bacteria in a large amount.
It is difficult and unrealistic to obtain a large amount of only a specific useful bacterium.

The present invention solves the above-mentioned conventional problems, and effectively grows and attaches useful microorganisms to the carrier packed in the biofilm filtration device, thereby making the device easy and efficient in a short period of time. The purpose is to provide a way to get started.

[0008]

According to a first aspect of the present invention, there is provided a method for starting up a biofilm filtration device, wherein a biofilm filtration device for treating wastewater with a biofilm is filled with a carrier carrying microorganisms. in the method and passed through launch the device raw water, as raw water for launching, while passed through the raw water of the high substrate concentration than the raw wastewater, circulating water passage a part of the effluent in the apparatus circulates Ratio of water to raw water (circulation
Ratio) than the circulation ratio during steady operation after startup
It is characterized by making it larger . The biofilm filtration device according to claim 2.
The method of starting up the equipment is to treat the wastewater to be treated with biofilm filtration.
A biofilm filtration device filled with a carrier carrying microorganisms for
Person who starts up the device by passing raw water for startup to
According to the law, as raw water for startup, rather than treated wastewater
While passing raw water with high substrate concentration,
Ratio of circulating water circulating to the equipment to raw water (circulation
Ratio) than the circulation ratio during steady operation after startup
Increase the load on the device and the linear velocity (LV)
It is characterized in that it is almost the same as during steady operation after raising.
It

It is to be noted that in the following, the process of passing raw water for startup to the biofilm filtration device to start up the device is referred to as "start-up operation", and the treated wastewater is passed through,
Performing biofilm filtration of wastewater is called "steady operation".

In addition, the ratio (volume ratio) of the circulating water that circulates through the device to the raw water (the wastewater to be treated) introduced into the biological film filtering device, out of the outflow water (the treated water) of the biological film filtering device. The circulation ratio ".

[0011]

In the biofilm filtration device, in order to efficiently grow the bacteria and smoothly attach the biofilm to the carrier, it is necessary to increase the growth rate of the bacteria and prevent the outflow of the bacteria. .

By the way, in the biofilm filter, if the load is the same, it is considered that the growth rate of the bacteria per unit time is the same regardless of the raw water concentration. On the other hand, it has been proposed that the exfoliation rate of bacteria is exfoliation rate = K ₁ Me ^K2v (where K ₁ and K ₂ are constants), where M is the ^biofilm thickness and v is the linear velocity (LV). It is known that the peeling speed increases as the linear velocity (LV) increases.

In the present invention, raw water having a substrate concentration higher than that of the wastewater to be treated is used as the raw water for start-up, and a part of the outflow water is circulated and the circulation ratio during the start-up operation is constant.
Prevent the outflow of bacteria by making it larger than that during operation
And efficiently grow the bacteria in the biofilm filtration device.
Promotes the attachment and growth of the biofilm on the carrier. The load and the linear velocity of the biological membrane filtering device (LV) is substantially the same in the up operation at the time of steady operation start, the growth rate and the release rate of the bacteria at startup operation, the same as during normal operation To do .

That is, the method of the present invention is performed under the following start-up operating conditions with respect to the biofilm filtration device (the cross-sectional area of the filtration layer is S and the volume is V) set to the following steady-state operating conditions. Perform start-up operation.

Steady operating conditions Treated wastewater substrate concentration: C Treated wastewater treatment amount: Q Circulation ratio: r Circulating water amount: rQ Load: CQ / V Linear velocity (LV): (Q + rQ) / S = (1 + r) Q / S Start-up operating conditions Start-up raw water substrate concentration: KC Start-up raw water treatment amount: Q / K Circulation ratio: K (1 + r) -1 Circulating water amount: {K (1 + r) -1} Q / K Load: KCx Q / K ÷ V = CQ / V Linear velocity (LV): [Q / K + {K (1 + r) -1} × Q
/ K] ÷ S = (1 + r) Q / S Under the above-mentioned start-up operating conditions, since the load and the linear velocity are the same as those in the steady operation, the bacterial growth rate and the peeling rate per unit thickness of the biofilm are Are the same.

However, since the circulation ratio is different between the startup operation and the steady operation, the outflow rate is different. That is, as the outflow rate of bacteria, the amount of water discharged from the biofilm filtration device to the outside of the system (the amount of treated water, that is, this amount of water is equal to the amount of treated water or raw water) is introduced into the biofilm filtration device. It is shown as a value divided by the amount of water (total amount of treated water and circulating water).

[0017]

[Equation 1]

[0018]

On the other hand, the outflow rate of bacteria during start-up operation is

[0020]

[Equation 2]

[0021] Therefore, the outflow rate of the bacteria can be reduced to 1 / K of that in the steady operation.

By the way, as compared with a biofilm filtration device that operates at a circulation ratio r = 2 during steady operation, a raw water for start-up that has a substrate concentration 10 times that of the wastewater to be treated (that is, K = 10) is used. When the startup operation is performed under the above startup operation conditions, the outflow rate of bacteria during steady operation

[0023]

[Equation 3]

On the other hand, the outflow rate of bacteria during start-up operation is

[0025]

[Equation 4]

Thus, the outflow rate of bacteria is reduced to 1/10.

Therefore, the growth of the bacteria in the device can be promoted to accelerate the growth of the biofilm, and the outflow of the bacteria that have grown in the device can be suppressed, so that an efficient start-up operation can be performed.

Particularly, the substrate concentration of the raw water for start-up is 50 to 100 times the substrate concentration of the wastewater to be treated (that is, K = 50 to 1).
When high-concentration raw water such as 00) is used, the amount of raw water used for start-up operation can be reduced and the amount of industrial water used for preparing raw water can be reduced, which is extremely advantageous.

In the present invention, when raw water for start-up having a high substrate concentration is used, the concentration of the substrate and by-products resulting from the biological treatment of the substrate should be adjusted so as not to inhibit the biological reaction in the apparatus. It is important to set the circulation ratio.

Incidentally, nitrifying bacteria have an ammonia concentration of 1
When it is more than 00 ppm, the activity decreases. Therefore, it is necessary to set the circulation ratio so that the concentration of NH ₄ —N flowing into the filter bed in the apparatus does not exceed 100 ppm by diluting the raw water for start-up with the circulating water.

Further, in order to prevent the osmotic pressure change due to the inflow of high-concentration salt from adversely affecting the bacteria due to the passage of the raw water for startup, the substrate concentration of the raw water for startup is gradually increased. It is preferable to go.

A method of setting the startup operation conditions suitable for the present invention will be described below.

(I) Substrate concentration of raw water for start-up If the substrate concentration of raw water for start-up is low, the effect of the present invention cannot be sufficiently obtained. On the contrary, if it is excessively high, it may adversely affect bacteria. Therefore, 2 to 100 times, especially 5 to 50 times, the substrate concentration C of the wastewater to be treated during the steady operation, that is, at the substrate concentration KC of the raw water for start-up, K = 20 to 10
It is preferably 0, sometimes 5 to 50.

(Ii) Treating amount of raw water for start-up In order to equalize the load CQ / V for steady operation, the treating amount is Q / K with respect to the above substrate concentration KC.

(Iii) Circulation ratio In order to equalize the linear velocity (LV) = (1 + r) Q / S in steady operation, the circulation ratio is set as follows with respect to the above processing amount Q / K. That is, the linear velocity is as follows when the throughput is Q / K and the circulation ratio is r ′.

(Processed amount + circulated water amount) ÷ cross-sectional area = (Q / K
+ R '· Q / K) / S Since this is made equal to (1 + r) Q / S,
r'is as follows.

(Q / K + r ′ · Q / K) / S = (1 + r) Q / S Q / K + r ′ · Q / K = (1 + r) Q 1 / K + r ′ / K = 1 + r r ′ / K = 1 + r− 1 / Kr '= K (1 + r) -1 In the present invention, the model of the biofilm filtration device is not particularly limited, and an upward flow type using a levitation filter medium as shown in Fig. 1 described later is used. It may be a biofilm filtration device or a downflow type biofilm filtration device using a sedimentary filter medium.

[0038]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below.

Example 1 As shown in FIG. 1, a flotation filter medium (particle size: 3.5 mm) was filled in a biofilm filtration device having a diameter of 400 mm and a height of 3000 mm to form a filtration layer 1A. This biofilm filtration device
NH ₄ -N of treated wastewater: 50 mg / l, circulation ratio r = 3
It is operated under the steady operation condition of.

In this biofilm filtration device, firstly, night soil nitrification sludge was inoculated at 3000 mg / l per volume of the filter medium layer 1A, and then ammonium sulfate was added as a substrate to the starting raw water having the concentration shown in Table 1 to pipe. From 11, the water was circulated at the flow rates shown in Table 1 and circulated, and the rest was discharged from the system through the pipe 13. The ammonium sulfate concentration was gradually increased in accordance with the increase in nitrification rate, and after 7 days, 1300 mg /
It was set to l.

As a result, the daily change in nitrification rate was as shown in FIG.

Comparative Example 1 A biofilm filtration apparatus was started up in the same manner as in Example 1 with the substrate concentration, water flow rate and circulation ratio of the raw water for start-up set as shown in Table 1.

As a result, the daily change in nitrification rate was as shown in FIG.

[0044]

[Table 1]

From FIG. 2, in comparison with Comparative Example 1 in which NH ₄ -N: 50 mg / l of raw water was used, in Example 1, the change in nitrification increased about twice as fast, and 1 week after 1 kg-. It is clear that it will reach N / m ³ · day. In Comparative Example 1, 14
It was 0.9 kg-N / m ³ · day per day.

When the number of startup days in Example 1 is 7 days and the number of startup days in Comparative Example 1 is 14 days, the amount of water used for the startup operation is as follows. According to the present invention, the amount of water used is It is clear that can be reduced by 98% or more.

Example 1: 2.02 m ³ Comparative Example 1: 104.8 m ³

[0048]

As described in detail above, according to the method for starting up a biofilm filtration device of the present invention, it is possible to efficiently grow bacteria and prevent the outflow thereof to promote the growth of biofilm. As a result, the period required to start up the biofilm filtration device can be significantly shortened, and the amount of water required for startup can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a system diagram showing a biofilm filtration device started up in Example 1.

FIG. 2 is a graph showing the results of Example 1 and Comparative Example 1.

[Explanation of symbols]

1 Biofilm filtration device 1A filtration layer

Front page continuation (56) References JP-A-61-216688 (JP, A) JP-A-3-123687 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C02F 3 / 06 ZAB

Claims (2)

(57) [Claims] 1. A method for starting raw water for start-up by passing the raw water for start-up to a bio-film filtration device, which is filled with a carrier supporting microorganisms, for performing a bio-film filtration treatment of wastewater to be treated, As raw water for use, raw water having a substrate concentration higher than that of the wastewater to be treated is passed, and the ratio (circulation ratio) of the circulating water that circulates a part of the effluent to the equipment to the raw water
Raising of the biological membrane filtering device, wherein the this <br/> be greater than the circulation ratio at the time of steady state operation after raising. 2. A biofilm filtration treatment of the wastewater to be treated.
, A biofilm filtration device filled with a carrier supporting microorganisms
The method of starting up the device by passing raw water for starting up
At this time, as raw water for start-up,
Allows raw water to pass through and circulates part of the effluent to the equipment.
The ratio (circulation ratio) of circulating water to raw water
Set it higher than the circulation ratio during steady operation after raising,
The load on the device and the linear velocity (LV) are steady after the startup.
Biofilm filtration device characterized by being almost the same as during operation
How to set up the table.