JP2002307086A - Discharge type wastewater denitrification equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge type wastewater denitrification equipment which is simple in operation, does not need special management can be installed in a small installation area, is inexpensive and free from toxity problem, can be hardly affected by temperature, and can obtain an enough denitrification effect even in a large scale wastewater treatment such as stockbreeding wastewater treatment, while the features of a biological denitrification method are being utilized. SOLUTION: In the wastewater denitrification equipment in which air permeable soil 4 is packed in a space 2 with its upper part opened which is formed in an earth 1 by a water impermeable member 3, a water collecting pipe 5 is installed on the bottom surface of the space 2, a treatment water soaking member 6 is installed above the pipe 5, embankment 8 is carried out over the outside of the member 3 in the upper part of the space 2, and treated wastewater is supplied to the member 6, and after being denitrified by being soaked in the soil 4, is discharged from the pipe 5, a water permeable iron layer 7 is formed in the soil 4 between the member 6 and the pipe 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a denitrification apparatus used for sewage treatment of a discharge type in which water after denitrification treatment is collected and collected by a water collecting pipe, and more particularly to discharge of primary treatment water such as domestic sewage and livestock wastewater. The present invention relates to a sewage denitrification system.

[0002]

2. Description of the Related Art Various types of nitrogen oxides, including organic nitrogen, ammonia nitrogen, etc., are contained in domestic wastewater such as sewage of flush toilets and kitchen wastewater, and livestock sewage such as livestock excreta and livestock washing water. Which must be removed because they cause eutrophication of rivers and lakes. In particular, nitrate nitrogen has adverse effects on the human body, such as causing methemoglobinemia, and causes various environmental pollution. Therefore, the environmental standard of the public waters and groundwater of the Environment Agency is less than 10 mg / liter. It is stipulated that

[0003] Methods for removing nitrogen in wastewater include selective physicochemical treatment methods such as ammonia stripping and ion exchange, comprehensive physicochemical treatments such as reverse osmosis and electrodialysis, and biological methods. Biochemical treatment methods such as the denitrification method have been proposed. Among them, the biological denitrification method
Since organic nitrogen can be removed together with ammonia nitrogen,
Practical applications are being made in the field of various wastewater treatments.

[0004] Biological denitrification utilizes a group of microorganisms that live in nature and are involved in the nitrogen cycle, and ultimately convert nitrogen compounds into nitrogen gas. In this method, a reaction tank is divided into a nitrification tank and a denitrification tank, and in the nitrification tank, organic nitrogen is oxidized to ammonia nitrogen by a BOD oxidizing bacterium, and then nitrite is oxidized by an obligately aerobic nitrite and a nitrate. After oxidizing to nitric acid and nitrate nitrogen, nitrite and nitrate nitrogen are reduced by a facultative anaerobic denitrifying bacterium to nitrogen gas in a denitrification tank and released into the atmosphere.

[0005] However, in such a conventional biological denitrification method, the operation and management of sludge treatment are complicated, and a nitrification tank and a denitrification tank need to be provided with a sedimentation tank. Requires large site for installation, high construction cost, large amount of alkali for pH adjustment in nitrification tank, need for methanol in denitrification tank, causing toxicity problems, processing efficiency decreases at low temperature There were problems such as doing.

[0006] In order to solve such a problem of the conventional biological denitrification method, the present inventor first stated that "a 60 cm to 4 m wide space having an open upper part by an impermeable member was soiled. The space is filled with air-permeable soil, a water collection pipe is laid at the bottom thereof, a treated water infiltration member is provided above the water collection pipe, and the water-impermeable member is provided above the space. A sewage denitrification apparatus which fills over the outside of the member, infiltrates the treated water infiltration member with the sewage treatment water supplied into the permeable soil, performs a denitrification treatment, and discharges the sewage treatment water from the water collection pipe. (Japanese Patent No. 3105519).

With this apparatus, a sufficient denitrification effect can be obtained in the case of small-scale sewage treatment of households, shops, public facilities, etc. There was a risk that nitriding would not take place.

On the other hand, a technique for treating nitrate-nitrogen-containing wastewater with metallic iron to reduce nitric acid and convert it to nitrogen gas (32nd Annual Meeting of Japan Society on Water Environment, p. 84 (1998)
)), And a technology for purifying wastewater by using iron scrap for nitric acid decomposition (Chunichi Shimbun, page 1, June 29, 2000). However, in these methods, the reduction rate is high under acidic conditions of pH 4 or less, but the reduction rate is low under neutral or alkaline conditions exceeding pH 4, and the conversion rate of the reaction product to nitrogen gas (the denitrification effect). ) Is reduced. Furthermore, according to the experiment of the present inventor, simply treating the treated wastewater with iron reduces nitrate nitrogen, but increases nitrite nitrogen and ammonia nitrogen, and eventually the total nitrogen amount does not decrease much. Further, it has been found that the biochemical oxygen demand (BOD) and the chemical oxygen demand (COD) increase.

[0009]

SUMMARY OF THE INVENTION Accordingly, the present invention solves the above-mentioned problems of the prior art, makes use of the excellent characteristics of the biological denitrification method, is simple in operation, and does not require any special management. A discharge type denitrification device that requires a small installation area, is low-cost, has no toxicity problems, is not easily affected by cold and heat, and has a sufficient denitrification effect even in large-scale wastewater treatment such as livestock wastewater treatment. It is an object to provide

[0010]

The inventor of the present invention has made further improvements based on the denitrification apparatus of the discharge type using the breathable soil proposed in Japanese Patent No. 3105519.
By using metallic iron which cannot exert a sufficient denitrification effect in its sole use in the permeable soil of the discharge type denitrification device, a sufficient denitrification effect can be obtained even in large-scale sewage treatment, In particular, they have found that contamination of harmful nitrate nitrogen can be reduced to a level that does not cause any problem, and have completed the present invention.

That is, according to the present invention, (1) air-permeable soil is filled in an open space formed in the soil by a water-impermeable member, and a water collecting pipe is laid at the bottom thereof. A treated water infiltration member is provided above the water collection pipe, and the embankment is laid over the outside of the water impermeable member in the upper part of the space, and the sewage treated water supplied to the treated water infiltration member is infiltrated into the breathable soil. After the denitrification treatment, the discharge type sewage denitrification device discharged from the water collection pipe is characterized in that a permeable metal iron layer is provided in the permeable soil between the treated water infiltration member and the water collection pipe. Discharge type sewage denitrification apparatus, (2) The discharge type sewage denitrification apparatus of (1), wherein the metal iron layer is a layer made of pig iron spheres, (3) The metal iron layer is formed of a metal iron wire. (1) the discharge type sewage denitrification apparatus of (1), and (4) the treated water immersion The discharge type sewage denitrification apparatus according to (1), (2) or (3), wherein the member is formed by projecting a plurality of wing pieces made of a water-absorbent sheet on the side surface of the tubular body of the water-absorbent sheet. Provided.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a schematic vertical sectional view showing an example of a sewage treatment system using a discharge type sewage denitrification apparatus of the present invention, and FIG.
1 is a cross-sectional view of the discharge type sewage denitrification apparatus of the present invention shown in FIG.

1 and 2, A is a sewage supply pipe, B is a first digestion chamber containing a permeable soil B1 and gravels B2, C is a second digestion chamber containing a permeable soil C1 and gravels C2, D is a digestive filtration room filled with breathable soil D1 and gravel D2, and E is a pump room provided with a pump E1. F is a discharge type sewage denitrification apparatus of the present invention, which is an impermeable member 3 forming a space 2 having an open top in soil 1, a permeable soil 4 filled in the space 2, and laid on the bottom thereof. Drainage pipe 5,
A treated water infiltration member 6 provided in the permeable soil 4 above the water collecting pipe 5, a permeable metallic iron layer provided in the permeable soil 4 between the treated water infiltrating member 6 and the water collecting pipe 5. 7 and an embankment 8 formed above the space 2 over the impermeable member 3, that is, over the soil 1. Reference numeral 9 denotes a drainage storage tank for temporarily storing wastewater collected by the water collection pipe 5.

The water-impermeable member 3 forming the open space 2 in the soil 1 is not particularly limited as long as it is stable in the soil and can prevent water permeation.
Examples include synthetic resin sheets, fiber-reinforced plastics, and reinforced concrete.

The space 2 formed in the soil 1 usually has a width of 1 to 1.
The space 2 is 2 m long, 10 to 30 m long and 0.4 to 1 m deep. As the breathable soil 4, those usually used for soil treatment can be used, for example, a clay content of 15 to 25% and a silt content of 20.
Soil corresponding to clay loam having a sand content of ~ 45% and a sand content of 3 to 65% is considered to be suitable.
Soil mixed with perlite or the like can also be used. Also, incinerated ash of sludge discharged from papermaking and pulp mills, clinker from coal-fired power plants and the like can be suitably used.

The water collecting pipe 5 is, for example, a synthetic resin pipe having an appropriate number of water holes or a pipe formed by braiding a synthetic resin monofilament into a tubular shape and having a diameter of 5 to 10 mm with a nonwoven fabric. Can be mentioned.

A treated water infiltration member 6 is provided in the permeable soil 4 above the water collecting pipe 5. As the treated water infiltrating member 6, any material can be used as long as it can infiltrate treated water into the soil in an unsaturated state. For example, a structure as shown in FIG. 3 is preferably used. . In the treated water infiltration member 5 shown in FIG. 3, a plurality of wing pieces 12 and 12 ′ also made of a water-absorbent sheet are formed on the side surface of a tubular body 11 made of a water-absorbent sheet.
The tubular body 11 is filled with bristle-like fibers 13, and a water-permeable pipe 14 is provided at the center thereof. The outside of the lower surface of the tubular body 11 is covered with a water-impermeable sheet 15. As the water-absorbing sheet constituting the tubular body 11 and the wing pieces 12, 12 ', a polyester fiber nonwoven fabric having a thickness of about 1 to 10 mm is suitably used. In addition, the space between the water collecting pipe 5 and the treated water infiltration member 6 is usually sufficient if it is 20 to 30 cm.

Further, a water-permeable metallic iron layer 7 is provided in the water-permeable soil 4 between the treated water infiltrating member 6 and the water collecting pipe 5. As the metallic iron, any material having a reducing property can be used, such as iron pieces, iron powder, striatum, slag, a water-permeable sheet, and an arbitrary shape such as a net. Pig iron spheres of about 10 mm are preferably used.
Further, it may be used by mixing with soil or other organic or inorganic substances. Further, it is also preferable to lay a plurality of metal iron wire strips such as reinforcing bars in parallel, since the denitrification effect is large and the laying work is easy. In this case, the diameter of the striatum is 10
20 mm, preferably 13 to 17 mm, and the laying interval is suitably 5 to 20 cm, preferably 8 to 15 cm.
Further, in order to maintain and fix the interval between the plurality of filaments, another filament made of metal, synthetic resin, or the like may be woven in the lateral direction. It is effective that the wire woven in the lateral direction is also made of metallic iron. The metallic iron layer 7 reduces nitric acid in the treated water infiltrated into the permeable soil 4 from the treated water infiltrating member 6 to reduce the amount of nitric acid mixed into the wastewater. 5 to 50 mm is appropriate. Further, the metal iron layer 7 includes the treated water infiltration member 6 and the water collecting pipe 5.
For example, if metallic iron is placed in the drainage storage tank 9 and treated, nitrate nitrogen is reduced, but nitrite nitrogen and ammonia nitrogen The total nitrogen amount does not decrease so much, and the biochemical oxygen demand (BOD) and the chemical oxygen demand (COD) increase.

The embankment 8 formed above the space 2 over the water-impermeable member 3 prevents rainwater from flowing into the apparatus as a surface flow, and prevents the water-impermeable member 3 from entering the apparatus.
By keeping the inside and outside communicating with each other, the inside of the water-impermeable member 3 is maintained at a negative pressure by a siphon phenomenon, and a capillary unsaturated water zone and a capillary saturated water zone separated by a hydrodynamic gradient line described later are formed. This is provided so that the oxidation treatment and the reduction treatment can be sequentially performed, and is usually formed to have a thickness of 10 cm or more from the surface of the soil 1.

Now, the sewage supplied via the sewage supply pipe A is supplied to the first digestion chamber B containing the permeable soil B1 and the gravel B2, and the second digestion chamber C containing the permeable soil C1 and the gravel C2. In the digestive filtration chamber D filled with the permeable soil D1 and the gravels D2, it is digested and filtered by a conventional method, and sent to the sewage denitrification apparatus F of the present invention by the pump E1 in the pump chamber E. The digestion and filtration steps are not limited to those described above, and any generally used sewage treatment method can be used. In addition, if there is a gradient allowing natural flow between the digestive filtration chamber D and the sewage denitrification apparatus F, the pump chamber E and the pump E1 need not be provided.

The primary treated water sent to the sewage denitrification apparatus F of the present invention is infiltrated from the treated water infiltrating member 5 into the permeable soil 3 in an evenly unsaturated state. As shown in FIG. 2, parabolic hydrodynamic gradient lines A and A ′ are formed on the left and right of the water collecting pipe 5 in the permeable soil 3. The upper side of the hydrodynamic gradient lines A and A 'becomes a capillary unsaturated water zone, the negative pressure of pore water in the soil is high, aerobicity is maintained, active oxidation by aerobic bacteria is performed, and the primary treated water Is oxidized to nitrite and nitrate nitrogen.
In particular, the primary treated water supplied after digestion treatment has dissolved oxygen near zero, but when the treated water infiltrate into the soil 3 due to the siphon phenomenon and the unsaturated flow from the treated water infiltration member 5, Oxygen can be taken in efficiently. On the other hand, the lower side of the hydrodynamic gradient lines A and A 'becomes a capillary saturated water zone,
As the time elapses, the negative pressure of the pore water in the soil decreases, and the state becomes oxygen-deficient. Accordingly, nitrite and nitrate nitrogen generated by oxidation in the capillary unsaturated water zone are reduced by facultative anaerobic bacteria in this zone to become nitrogen gas.

At this time, the reduction of nitrate nitrogen in the treated water is further promoted by the water-permeable metallic iron layer 7 provided between the treated water infiltrating member 6 and the water collecting pipe 5, and the nitric acid mixed into the wastewater is reduced. The amount of nitrogen can be greatly reduced to a level that is not problematic. The treated water thus denitrified is discharged from the collecting pipe 5 to the drainage storage tank 9.

[0023]

Example 1 Primary treatment in which urine discharged from a piggery and separated from manure and solid and liquid and washing water of the piggery were digested in a multi-compartment digester (B) to (D) shown in FIG. The water was treated in the discharge type sewage denitrification apparatus F of the present invention shown in FIGS. The sewage denitrification apparatus F was designed such that the space 2 had a width of 1 m and a depth of 0.6 m, and a water load of 80 liter / m · day.

Treated water infiltration member 6 used for sewage denitrification device F
As shown in FIG. Pig iron spheres having an average particle size of 5.3 mm were spread to a thickness of 3 mm. After the operation for one month, the inspection results of the denitrification-treated water collected from the drainage storage tank 9 were as shown in Table 1.

Example 2 As the metal iron layer 7, instead of the pig iron spheres of Example 1,
Eleven metal iron wires (reinforcing bars for concrete reinforcement) having a diameter of 15 mm were laid in the longitudinal direction of the space 2 at intervals of 10 cm, and the others were treated in the same manner as in Example 1. After the operation for one month, the inspection results of the denitrification-treated water collected from the drainage storage tank 9 were as shown in Table 1.

Comparative Examples 1 and 2 On the other hand, for comparison, in the sewage denitrification apparatus F of the above embodiment, a denitrification treatment was carried out in the same manner as in the above embodiment without using a metallic iron layer. Comparative example 1). Comparative Example 1
, 20 g / ton of metallic iron (the pig iron sphere) was put into the treated water in the drainage storage tank 9 and left at 25 ° C. for 5 days (Comparative Example 2). The inspection results of each denitrification treatment water were as shown in Table 1.

[0027]

[Table 1]

As is clear from Table 1, when the sewage denitrification apparatus of the present invention is used (Examples 1 and 2), the amount of nitrate nitrogen is reduced to a level at which there is no problem even if it is mixed into the wastewater. However, in Comparative Example 1 in which the metallic iron layer was not used, the amount of nitrate nitrogen was large, and there was a possibility of wastewater contamination. On the other hand, Comparative Example 1
In Comparative Example 2 in which the denitrification-treated water obtained in Step 2 was further treated with metallic iron in a wastewater storage tank, although nitrate nitrogen decreased, nitrite nitrogen and ammonia nitrogen increased, resulting in total nitrogen However, there is a problem that BOD and COD are increased. In the embodiment using the sewage denitrification apparatus of the present invention in which metallic iron is used in soil, the total nitrogen amount is greatly reduced, the nitrogen is reliably removed, and the BOD and COD are increased. There is no such thing. The reason for this is unclear at present, and must be elucidated in the future. Although a large-scale livestock wastewater treatment has been described in the above embodiment, it goes without saying that the wastewater can be effectively used for human waste and washing water, and domestic living wastewater including miscellaneous wastewater such as kitchens, baths, and laundry.

[0029]

According to the sewage denitrification apparatus of the present invention, while utilizing the excellent features of the biological denitrification method, the operation is simple, no special management is required, and a vast area for installing a sedimentation basin is provided. And no costly site, no toxicity problems,
It is hardly affected by the cold and warm weather,
A sufficient denitrification effect can be achieved even in large-scale wastewater treatment such as livestock wastewater treatment, and in particular, the amount of nitrate nitrogen can be reduced to a level at which there is no problem even if mixed into wastewater. Does not increase.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view showing an example of a sewage treatment system using a discharge type sewage denitrification device of the present invention.

FIG. 2 is a cross-sectional view of the discharge type sewage denitrification apparatus of the present invention shown in FIG.

FIG. 3 is a cross-sectional view showing an example of a treated water infiltration member used in the present invention.

[Explanation of symbols]

 F Discharge type sewage denitrification equipment 1 Soil 2 Space 3 Water-impermeable member 4 Breathable soil 5 Water collecting pipe 6 Treated water infiltration member 7 Metal iron layer 8 Embankment

Claims (4)

[Claims] An air-permeable soil is filled in an open space formed in the soil by an impermeable member, and a water collecting pipe is laid at a bottom thereof, and a treated water infiltrating member is provided above the water collecting pipe. And embankment is provided over the outside of the water-impermeable member in the upper part of the space, and the sewage treated water supplied to the treated water infiltrating member is infiltrated into the permeable soil to perform a denitrification treatment. A discharge type sewage denitrification apparatus, wherein a permeable metallic iron layer is provided in a permeable soil between a treated water infiltration member and a water collection pipe. 2. The discharge type sewage denitrification apparatus according to claim 1, wherein the metal iron layer is a layer made of pig iron spheres. 3. The discharge type sewage denitrification apparatus according to claim 1, wherein the metal iron layer is a layer made of a metal iron wire. 4. The water-infiltrating member according to claim 1, wherein a plurality of wings made of the water-absorbent sheet are formed on the side surface of the tubular body of the water-absorbent sheet.
4. The discharge type sewage denitrification apparatus according to 2 or 3.