JP2916134B1 - Biofilm filtration - Google Patents

Abstract

An object of the present invention is to provide a biofilm filtration method capable of increasing the recovery rate of treated water by increasing the duration of filtration as compared with conventional techniques, and improving the quality of treated water and reducing running costs. SOLUTION: In a biofilm filtration method in which an organic pollutant is decomposed and SS is trapped by a biofilm attached to the surface of a filter medium 3, aeration for supplying oxygen is intermittently performed from the lower part of the filter bed 2. To do. When aeration is stopped, sewage preferentially passes through a portion with a small amount of blocking substance formed by contact with air, and filtration is performed. For this reason, the whole filter bed 2 is utilized, and clogging hardly occurs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biofilm filtration method suitable for treating wastewater having a BOD of 50 mg / L or less, such as secondary sewage water, industrial wastewater, river water, and the like.

[0002]

2. Description of the Related Art Biological membranes in which sewage is passed through a filter bed filled with filter media, and a biofilm adhered to the surface of the filter media during the passage between the filter media decomposes organic pollutants and captures SS. Filtration methods have been widely known. For example, 199
According to the “Guidelines and Explanation of Sewerage Facility Planning and Design” issued for 4 years, the filter media has a particle size of 3 to 5 mm, and aeration is performed continuously from the lower part of the filter bed.

[0003] However, in such a conventional biofilm filtration method, the flow path of wastewater and the rising path of air in the filter medium are likely to be fixed as if they had a path. Therefore, the portion where the SS is trapped in the sewage or the organic matter is decomposed is biased to a specific portion in the filter medium, and the filter medium is easily blocked.
Therefore, as a result, there is a problem in that the duration of filtration becomes shorter, the frequency of washing becomes higher, and the recovery rate of the treated water becomes lower. In addition, there is a problem that the substantial filtration medium passage time (the contact time between the wastewater and the biofilm) is shortened and the quality of the treated water is deteriorated. Further, there is a problem that the operation cost of the blower increases due to continuous aeration.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the prior art, and increases the recovery time of the treated water by making the filtration duration longer than before, thereby improving the quality of the treated water and reducing the running cost. The purpose of the present invention is to provide a biofilm filtration method that can achieve the following.

[0005]

Means for Solving the Problems The biofilm filtration method of the present invention made to solve the above-mentioned problems has a particle diameter of 2-3 m.
thick filled with filter material m is a dirty water filter bed of 0.6~2m
This is a biofilm filtration method in which organic pollutants are decomposed and SS is captured by a biofilm attached to the surface of the filter medium while water is passed through the filter medium while passing between the filter media. Supply of air containing oxygen necessary for metabolism and oxidative decomposition of organic matter at every set time while giving priority to dissolved oxygen in treated water
Or in response to changes in the pressure loss of the filter material, intermittently have rows from the bottom of the filter bed, the rise path of the air in the filter medium layer during its
And the air is supplied uniformly to the entire filter bed .

According to the biological membrane filtration method [0006] The present invention, intermittently have line the supply of oxygen by aeration, increasing air path in the filter medium is changed each time, Ru be uniformly supplied to the entire air Oroyuka . For this reason, the portion where the SS is trapped in the sewage or the organic matter is decomposed is not specified, and the sewage treatment is performed more uniformly in the entire filter bed than before. Therefore, the filtration continuation time is extended, and the recovery rate of treated water and the quality of treated water can be improved. Further, since continuous aeration is not performed as in the related art, it is possible to reduce the operating cost of the blower.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. In FIG. 1, 1 is a treatment tank, and 2 is a filter bed filled with a filter medium 3. As the filter medium 3, an anthracite having a particle diameter of 2 to 3 mm, bituminous coal, activated carbon, or the like having a relatively low specific gravity is used. This particle size is considerably smaller than the particle size of the filter media used in the conventional biofilm filtration method. Aerobic microorganisms adhere to the surface of the filter medium 3 to form a biofilm. Conventionally, the thickness of the filter bed 2 required 2 m or more, but in the present invention, since the entire filter bed 2 is utilized, the thickness may be 0.6 to 2 m.

[0008] The sewage is preferably passed from the upper part of the treatment tank 1 to the filter bed 2 as a downward flow, and by a biofilm adhered to the surface of the filter medium 3 while passing between the fine particles of the filter medium 3 as in the prior art. Decomposition of organic pollutants and capture of SS are performed. An air diffuser 4 is provided below the filter bed 2, and pressurized air supplied from a blower 5 is aerated into the processing tank 1 to recycle oxygen required for respiration of microorganisms, metabolism of organic matter, and oxidative decomposition. Supply. The reason why the downward flow is preferable is that the wastewater and the oxygen come into countercurrent contact, and the contact between the two is sufficiently performed. However, the present invention is also applicable to a case where sewage is passed through the filter bed 2 in an upward flow.

[0009] In the conventional biofilm filtration method, the supply of oxygen by this aeration was performed continuously.
In the present invention, aeration is performed intermittently. As described above, when continuous aeration is performed, a path of air is formed inside the filter bed 2, and the clogging material such as SS is reduced in that portion, but the clogging material is rapidly deposited in many other portions. Easy to clog. On the other hand, in the present invention, since the supply of oxygen by aeration is performed intermittently, sewage preferentially passes through a portion with a small amount of blocking substance formed by contact with air, that is, a portion with low resistance when aeration is stopped. Then, oxidative decomposition of organic matter, removal of SS, and filtration are performed. This phenomenon is repeated each time aeration is performed intermittently.

Therefore, according to the present invention, the plugging material is deposited uniformly over almost the entire filter bed 2 instead of accumulating the plugging material on a specific portion of the filter bed 2 as in the prior art. As a result, the duration of filtration is lengthened and the recovery rate of the treated water is improved. Further, the quality of the treated water can be improved by substantially extending the contact time. In addition, in the present invention, since the aeration is performed intermittently, the operating cost of the blower 5 can be reduced, and the thickness of the filter bed 2 can be made thinner than before, so that the output of the blower 5 can be reduced. And equipment costs can be reduced.

Although the method of determining the timing of intermittent aeration is not particularly limited, it can be performed, for example, every set time determined empirically.
However, the BOD concentration of incoming sewage is high and DO of treated water is high.
When the (dissolved oxygen content) becomes, for example, 0.5 mg / L or less, aeration is basically performed even before the set time has elapsed. Should be determined. In addition, a method of detecting a change in the pressure loss of the filter medium 3 and starting aeration when the pressure loss exceeds a predetermined level can be adopted. Raw water BOD
When the concentration is low and the DO of the treated water is 2 to 3 mg / L or more,
Aeration in the sense of supplying oxygen is not required. As described above, methods for determining the timing of aeration include a method performed at set time intervals, a method performed in accordance with a change in pressure loss of the filter medium, a method performed in accordance with the dissolved oxygen amount of treated water, and a method in which treated water is dissolved. It is also possible to adopt a method in which the amount of oxygen is prioritized, and the method is performed every set time or in response to a change in pressure loss of the filter medium.

[0012]

Next, examples of the present invention will be described. Particle size 2-3m
Using a filter bed having a thickness of 1 m filled with m of anthracite, biofilm filtration of sewage secondary treatment water was performed by the method of the present invention. The water flow rate is 120m / day, and wastewater (raw water)
SS was 17 mg / L and BOD was 19 mg / L. The aeration was performed intermittently for a time equivalent to 2/3 of the whole.
For comparison, biofilm filtration was also performed by a conventional method in which aeration was continuously performed using the same apparatus over the entire time.

As a result, the SS of the treated water is 3.
Although it decreased to 5 mg / L, it was 4.5 in the conventional method, and the BOD of the treated water was reduced to 5.2 mg / L in the present invention, but was 7.8 in the conventional method.

When the pressure loss of the filter bed was continuously measured, the results as shown in FIG. 2 were obtained. In the conventional method in which continuous aeration is performed, SS is captured only in a specific portion, and the pressure loss of the filter bed rises sharply. Therefore, it is necessary to perform backwashing frequently. Because of the gentleness, the number of times of backwashing could be reduced to about 1/2 of the conventional one.

[0015]

As described above, according to the biofilm filtration method of the present invention, the trapping of SS and the decomposition of organic substances are performed more uniformly in the entire filter bed than in the past. Therefore, the duration of filtration is extended, and the recovery rate of treated water and the quality of treated water can be improved. In addition, since continuous aeration is not performed, the operating cost of the blower can be reduced. .

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a graph showing a change in pressure loss of a filter bed in an example.

[Explanation of symbols]

1 treatment tank, 2 filter beds, 3 filter media, 4 diffuser tubes, 5 blowers 5

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-23390 (JP, A) JP-A-5-169077 (JP, A) JP-A-57-177391 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) C02F 3/02-3/10

Claims (1)

(57) [Claims] 1. A thickness particle size filled with filter media 2~3mm
So There was passed through the sewage in downflow in filter bed of 0.6～2M, perform a capture of degradation and SS of organic pollutants by biofilm deposited on the surface of the filter media while passing between filter media In biofilm filtration , the supply of air containing oxygen necessary for respiration of microorganisms, metabolism of organic matter, and oxidative decomposition is determined by the amount of dissolved oxygen in treated water.
Pressure loss of the filter media every set time or
Depending on the change, intermittently have rows from the bottom of the filter bed, the filter material layer
Change the rising path of the air in the
A biofilm filtration method characterized by uniformly feeding the entire filter bed .