JP4241143B2 - Organic wastewater filtration method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel filtration method and apparatus that can accurately prevent the generation of bad odors such as hydrogen sulfide that accompany the filtration of organic sewage such as sewage. INDUSTRIAL APPLICABILITY The present invention is a particularly suitable new technique as a filtration technique for sewage flowing into a sewage treatment facility or rainwater overflowing water (abbreviated as CSO) in a combined sewer containing organic suspended particles. .
[0002]
[Prior art]
In recent years, the pollution load of rainwater overflowing water (CSO) in public water bodies in a combined sewer has become a major problem.
In addition, the sewage flowing into the sewage treatment facility is first separated and separated in the settling basin, and then treated with activated sludge. However, since the SS removal rate of the first settling basin is poor, a coagulant is added and coagulated and settled. Examples are prevalent in Scandinavia. However, there are disadvantages that a large amount of sludge is generated, the coagulation sedimentation rate is small, and a large sedimentation basin is required. Therefore, a new technology that can separate CSO and sewage into solid-liquid separation with as compact a facility as possible is awaited.
[0003]
Conventionally, the technology for filtering and removing SS from a suspension is known as deep bed filtration using particulate materials such as sand and anthracite as a filter medium, but when attempting to remove organic SS such as sewage Clogging was severe and impractical. Therefore, in recent years, as disclosed in “Upward Flow Filtration Device” (Patent Document 1), an upward flow filtration method for sewage using a large particle size granular plastic having a particle size of several centimeters as a filter medium has been put into practical use. .
[0004]
[Patent Document 1]
Japanese Examined Patent Publication No. 6-77651
[Problems to be solved by the invention]
However, this technology has the following problems. That is, when sewage is filtered, a large amount of septic SS accumulates in the filtration layer. This decays, the filtration layer becomes anaerobic, and the oxidation-reduction potential (ORP) at which sulfate-reducing bacteria are actively active, that is, −200 mV or less. As a result, a large amount of harmful odor gas (mainly hydrogen sulfide) is generated. For this reason, it is indispensable to suck harmful odor gas with a suction fan and duct, send it to the deodorization equipment, and remove the harmful odor gas, and the harmful odor gas removal equipment requires a very large cost. It is a fact.
[0006]
The present invention has been made in view of such a conventional situation, and is a new technology capable of preventing generation of the above-mentioned harmful malodorous gas from a filtering device for organic wastewater such as sewage by an extremely simple facility. The purpose is to provide.
[0007]
[Means for Solving the Problems]
The present invention has solved the above-described problems by the following means.
(1) Organic sewage supplied with oxygen-containing microbubbles having a bubble diameter of 1 mm or less in a method of filtering organic sewage flowing into a sewage treatment facility by an upflow filtration method using a large particle size granular plastic as a filter medium When the flow rate of oxygen-containing microbubbles is controlled so that the oxidation-reduction potential in the packed bed becomes positive with respect to −100 mV when flowing into the packed bed of filter medium, harmful odors from the packed bed A method for filtering organic sewage characterized by preventing gas generation .
(2) The method for filtering organic wastewater according to (1), wherein the filter medium is washed when the trapping capacity of the packed bed reaches a limit .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment for sewage treatment of the filtration technique of the present invention. The inside of the filtration tower 2 provided with the raw water inflow part in the lower part and the filtered treated water outflow part in the upper part was filled with, for example, many hollow cylindrical particles (particle size is about 2 to 3 cm) floating in water. A packed layer 4 (with a porosity of about 90%) is provided.
[0009]
The sewage and “oxygen-containing microbubbles (air bubble diameter: 1 mm or less) such as air and oxygen-enriched gas” are allowed to flow into the packed bed 4 having a large porosity from the lower side in the sewage. Organic SS (suspended particles) is trapped in the voids of the filler and filtered off. The oxygen-containing microbubbles are generated from a microbubble generator 5 provided below the packed bed 4. The filtered water 3 from which SS has been removed flows out from the upper part of the apparatus.
Since the microbubbles generated from the microbubble generator 5 have a fine diameter, the bubble floating speed is very small. (The rising speed of bubbles with a diameter of 500 μm is about 0.1 m / sec). For this reason, the filler is not disturbed by the upward movement of the bubbles. As a result, there is an important characteristic that the SS filtration effect is not deteriorated. The microbubbles generated here are preferably those in which 50% or more of the bubbles are 1000 μm or less, and when the ratio of those having a fine diameter is small, the action on the filter medium is reduced. When most of the bubbles having a bubble diameter of 1000 μm or more are introduced, the rising speed of the bubbles is large, the filter layer is disturbed, and the SS filtration effect is deteriorated. Therefore, the bubble diameter is preferably 1000 μm or less.
[0010]
The inside of the packed bed 4 can be maintained at an ORP (a value on the positive side of about −100 mV) that can inhibit the activity of sulfate-reducing bacteria. For this reason, in the present invention, the microbubble supply flow rate is controlled so that the ORP of the filtrate 3 that is the effluent of the filtration tank has a value on the plus side of −100 mV.
Since air microbubbles have a very small bubble diameter, the oxygen absorption efficiency of bubbles having a bubble diameter of 1000 μm or less is as large as 35% or more. As a result, the ORP can be set with a relatively small amount of air microbubbles.
[0011]
Further, it was observed that particularly fine bubbles having a bubble diameter of 500 μm or less were trapped and stayed in the voids of the filler because the ascending speed was very low. Since oxygen was supplied to the liquid from the fine staying bubbles, it was confirmed that the inside of the packed bed 4 can be maintained in an oxidation-reduction potential (ORP) state in which generation of hydrogen sulfide is suppressed very effectively.
On the other hand, unlike the present invention, without using microbubbles having a fine bubble diameter, when an oxygen-containing gas having a bubble diameter of several millimeters is aerated from a diffuser plate, a diffuser tube, etc. As a result, the SS filtration effect is greatly deteriorated, and the purpose of filtration cannot be achieved.
[0012]
In order to generate microbubbles having a fine bubble diameter of 1000 μm or less, which is important in the present invention, a diffuser plate using a special polyurethane film having fine pores (for example, the literature 7-2000 Annual Report on Sewerage Research Presentation) 23; Aeration characteristics of the ultrafine bubble diffuser) Or, a republished patent: International Publication No. WO00 / 69550, “Swivel Microbubble Generator” described in “Swivel Microbubble Generator” may be applied.
[0013]
As a method of installing this microbubble generator in a filtration tower having a packed bed, when organic sewage (raw water) is passed through the filter tower in an upward flow, the apparatus is installed below the packed bed. Thus, such an arrangement is usually adopted, but when organic sewage is passed in a downward flow, the apparatus can be installed above the packed bed. Oxygen-containing microbubbles generated from a microbubble generator installed below the packed bed are mixed with organic sewage when organic sewage is supplied to the lower part of the filtration tower and passed in an upward flow. Passes through the packed bed, and fine bubbles are trapped in the voids of the filler to perform the action. The microbubble generator may be provided outside the filtration tower, and a liquid flow containing oxygen-containing microbubbles may be introduced therefrom.
[0014]
Therefore, when the operation of the apparatus of FIG. 1 is continued, the SS trapping capacity of the packed bed 4 reaches the limit, the SS of the treated water 3 increases rapidly, or the filtration resistance reaches a predetermined value. Wash the filter media.
The filter medium cleaning is performed as follows, for example. That is, air having a coarse particle diameter is diffused vigorously from the air diffuser 6 at the lower part of the tank for several minutes, and the filter medium is strongly disturbed to separate turbidity adhering to the floating particles. Thereafter, the water in the tank is rapidly discharged from the discharge pipe of the cleaning waste water 7. As a result, the suspended matter trapped in the filler is discharged, and the packed bed 4 is almost cleaned. Thereafter, the raw water 1 is supplied again, and filtration is started.
[0015]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
[0016]
Example 1 (sewage filtration test)
A sewage filtration test was conducted using a 1 m high packed bed (94% porosity of the packed bed) filled with a large number of hollow cylindrical fillers (diameter 20 mm, length 20 mm) in a 30 cm diameter square cylindrical container. .
Sewage (SS 130 mg / liter) was passed in an upward flow at a high filtration rate of 1000 m / d. The sewage flow rate is 62.5 liters / minute. In addition, air microbubbles having an average bubble diameter of 500 μm generated by the microbubble generator were allowed to flow into the filtration tank at a flow rate of 8 liters / minute.
[0017]
As a result, the filtrated water SS was 31 to 38 mg / liter for 2 hours after the start of operation. However, the filtered water SS deteriorated to 81 mg / liter after 2 hours and 10 minutes. Therefore, after operating for 2 hours, the raw water supply was stopped and the operation was performed in a cycle in which cleaning was performed. The cleaning was performed by aeration for 3 minutes and draining all the water in the apparatus in 1 minute. As a result, even if the operation was continued for one month, the generation of hydrogen sulfide was several ppm or less. The filtered water was ORP (the redox potential was −40 to −75 mV).
The filtrate water SS was 28 mg / liter of filtrate water SS with respect to the raw water average SS of 157 mg / liter, and good SS removal and malodor prevention were performed.
[0018]
Comparative Example 1
In Example 1, parallel operation with Example 1 was performed on the same conditions except having stopped supplying microbubbles.
As a result, hydrogen sulfide having a concentration of 630 ppm was always detected from the upper part of the filter bed after 10 days from the start of operation. The ORP of the washing waste water was very anaerobic at -186 mV.
[0019]
【The invention's effect】
According to the present invention, when wastewater containing perishable organic SS such as sewage is filtered, generation of harmful malodorous gases such as hydrogen sulfide, which has been a major problem, is eliminated, and the working environment is improved. In addition, deodorization equipment is not required, and construction costs and maintenance costs can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the structure of an upflow filtration device for introducing oxygen-containing microbubbles according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Raw water 2 Filtration tower 3 Filtration water 4 Packing bed 5 Microbubble generator 6 Coarse bubble diffuser pipe 7 for washing filter media Washing drainage

Claims (2)

In a method of filtering organic sewage flowing into a sewage treatment facility by an upflow filtration method using a large particle size granular plastic as a filter medium, the organic sewage supplied with oxygen-containing microbubbles having a bubble diameter of 1 mm or less is used as a filter medium. Generation of harmful odorous gas from the packed bed by controlling the flow rate of the oxygen-containing microbubbles so that the redox potential in the packed bed is on the plus side of -100 mV when flowing into the packed bed A method for filtering organic sewage, characterized by preventing water. The method for filtering organic wastewater according to claim 1, wherein the filter medium is washed when the trapping capacity of the packed bed reaches a limit .

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