JPH1015589A - High-degree purification of organic sewage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain an extremely high nitrogen removing ratio by oxidizing a part of activated sludge of biological nitrification and denitrification treatment by ozone to subject the same to solidliquid separation and subjecting the separated water to flocculation separation and subsequently supplying the flocculated separated water to a granular filter material packed bed to which denitrifying bacteria are bonded to perform denitrification and SS filtering. SOLUTION: Org. sewage 1 is denitrified and oxidized in a biological nitration and denitrification tank A and a part of the oxidized and nitrated slurry is transferred to a sedimentation tank B as an outflow slurry 2. Herein, the outflow slurry is subjected to solid-liquid separation to be circulated to the denitrification part of the nitration and denitrification tank A as return sludge and a part thereof is transferred to an ozone oxidation tank D. An inorg. flocculant 11 is added to the separated water formed from the soluble sludge 6 oxidized by ozone in the ozone oxidizing tank D and sedimented and separated in a second sedimentation tank E to flocculate phosphorus and these flocs are separated as flocculated sludge 12 in a third sedimentation tank G. Separated sludge 8 is biologically treated in an aeration tank F to be reduced in amt. to elute phosphorus and the remainder is refluxed to the ozone oxidizing tank D as circulating sludge 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for highly purifying ammonia-containing wastewater such as sewage, and more particularly to a technique capable of removing nitrogen components at a significantly higher removal rate than conventional techniques.
The present invention also relates to a new technology that can significantly reduce the amount of excess sludge generated without deteriorating the quality of treated water.

[0002]

2. Description of the Related Art The most typical technique for removing nitrogen components in wastewater such as sewage is a nitrification liquid circulation type biological nitrification denitrification method. This technology supplies organic wastewater to a biological denitrification unit, supplies the denitrification solution to a nitrification unit to nitrify ammonia, circulates a part of the nitrification solution to the denitrification unit,
The other part is supplied to a sedimentation tank to separate activated sludge and obtain treated water.

A technique of coexisting a particulate carrier such as a gel in which nitrifying bacteria are immobilized in a nitrification portion has recently been put to practical use. In this method, when sewage is treated, a nitrogen removal rate of about 80% is obtained, and little ammonia remains and small amounts of nitrate nitrogen and SS remain in the treated water. In this method, nitrate nitrogen remains in the treated water (in the case of sewage treatment, the amount of nitrate nitrogen is 10 m
g / liter), and the nitrogen removal rate is 9
It was impossible in principle to make the content more than 0%, and it was insufficient to prevent eutrophication of the discharge water area.

In the conventional method, in order to increase the nitrogen removal rate, a second denitrification section must be provided after the nitrification section, and an expensive organic carbon source such as methanol must be added.
This was difficult to implement because the tank volume and chemical cost increased significantly. In addition, the amount of sludge generated is large, and sludge treatment and disposal has been the biggest issue.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the problems of the conventional nitrification liquid circulation type biological nitrification denitrification method, and uses a stable and extremely high nitrogen without using an organic carbon source such as methanol. It is an object of the present invention to provide a new organic sewage purification system that can obtain a removal rate and does not generate excess sludge.

[0006]

Means for Solving the Problems The present inventor has changed the structure of a conventional nitrification liquid circulation type biological nitrification denitrification process, and has proposed an organic carbon source for denitrifying bacteria by ozone oxidation of activated sludge. It has been found that the above object can be achieved by combining the production of (BOD), biological denitrification by a granular filter media packed bed in a novel manner. That is, (1) In a method of treating organic sewage such as sewage by a biological nitrification denitrification method, a part of the activated sludge of the biological nitrification denitrification treatment is withdrawn and ozone oxidized by an ozone oxidation unit. Solid-liquid separation, an inorganic coagulant is added to the separated water to perform coagulation separation, and the separated water from the coagulation separation is added to the separated water from the biological nitrification denitrification treatment, and denitrifying bacteria are attached. The biological treatment step of supplying the granular filter medium packed bed with denitrification and SS filtration to obtain highly treated water, and the solid-liquid separation of the ozone oxidized sludge coming out of the ozone oxidizing section, A method for advanced purification of organic wastewater, comprising a step of reducing excess sludge which is circulated to an ozone oxidation unit after aeration of the obtained separated sludge.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the flow of the biological nitrification and denitrification process of the organic sewage of the present invention described in (1) above. The operation will be described. Although the biological nitrification denitrification tank A is shown as a single tank in FIG. 1, it is composed of a denitrification section and a nitrification section. Organic wastewater (hereinafter also referred to as “raw water”) 1 such as sewage is supplied to a denitrification section of a biological nitrification denitrification tank A and denitrified, and then the nitrification section oxidizes ammoniacal nitrogen to nitrate nitrogen. Is done. Most of the nitrification slurry flowing out of the biological nitrification section is circulated to the denitrification section, but a part is transferred to the settling tank B as the outflow slurry 2. The nitrate nitrogen in the nitrification slurry circulated to the denitrification section is biologically denitrified using the BOD of the sewage 1. First from the nitrification section of nitrification denitrification tank A
Since nitrate nitrogen remains in the outflow slurry 2 (a part of the nitrification slurry) flowing out to the precipitation tank B, nitrate nitrogen inevitably remains in the outflow water 3 of the precipitation tank. . In order to remove the nitrate nitrogen and reduce the amount of excess sludge, the present invention performs the processing described below. That is,

[0008] From the nitrification section of the nitrification denitrification tank A to the first settling tank B
The slurry 2 flowing out to the tank is separated into solid and liquid in the first sedimentation tank B, and the separated sludge is circulated to the denitrification part of the nitrification denitrification tank A as the return sludge 4. A part of the returned sludge 4 is transferred to the ozone oxidation tank D so that the MLSS in the concentration range is maintained. Alternatively, the excess sludge amount 5 in the nitrification denitrification tank A may be transferred to the ozone oxidation tank D. The sludge transferred to the ozone oxidation tank D is solubilized by ozone oxidation in the ozone oxidation tank D, and elutes soluble BOD components. The appropriate amount of ozone for ozone oxidation is 50 to 100 g ozone per 1 kg of sludge SS. The solubilized sludge 6 flowing out of the ozone oxidation tank D is settled and separated in the second settling tank E. The separated water 8 that has been separated by precipitation contains soluble BOD (organic carbon source) and phosphorus that are easily used by denitrifying bacteria. An inorganic coagulant 11 is added to this liquid to coagulate what can coagulate, such as phosphorus, and the coagulate is precipitated and separated in the third settling tank G to remove phosphorus and the like as coagulated sludge 12. Here, when lime is used as a coagulant, phosphorus can be recovered as a calcium phosphate compound usable for fertilizer.

The separated sludge 8 precipitated and separated in the second settling tank E is transferred to an aeration tank F, and the solubilized sludge is reduced by aerobic biological treatment, and phosphorus is eluted. The rest is circulating sludge 7
Is returned to the ozone oxidation tank D. The first settling tank B
The separated water 3 separated and settled in step 3 and a part of the separated water 10 separated and settled in the third settling tank G merge into a granular filter medium filling tank C.
Is transferred to The granular filter medium filling tank C is filled with a granular filter medium to which denitrifying bacteria have adhered.
Since the separated water 10 separated and settled from the sludge solubilized in the above contains soluble BOD, the nitrate nitrogen contained in the separated water 3 when passing through the granular filter medium packed bed is methanol or the like. The nitrate nitrogen is biologically denitrified at high speed in the granular filter medium filling tank C without using any chemicals, and at the same time, the SS contained in the separation water 3 and the separation water 10 is also filtered. As a result, The highly treated water 13 in which nitrogen and SS are at a level of 1 to 2 mg / liter is obtained. As described above, there is almost no generation of excess sludge due to sewage treatment other than the above-mentioned coagulated sludge. It is possible to obtain highly treated water in which nitrogen and SS are at a level of 1 to 2 mg / liter without using a chemical such as methanol. That is a feature of the present invention.

[0010] The particle size of the filter medium in the granular filter medium filling tank is 2-3 m.
m, the thickness of the filling layer is suitably about 2 m, and the water flow rate of the filling tank is preferably 100 to 200 m / day. As the type of the filled filter medium, in addition to a settling filter medium such as anthracite and ceramic, a floating filter medium such as styrene foam, polypropylene, and polyethylene can be used. According to the experiment of the present inventor, BO from sludge by ozone oxidation
D elution amount is 40-60 g BOD per 1 kg of activated sludge.
Met. The addition flow rate of the sludge solubilized solution by ozone to the biologically treated water is 3 kBOD / kg of nitrate nitrogen.
The flow rate may be set to about g.

Further, the present invention has a remarkable effect of reducing the amount of excess sludge generated. That is, the excess sludge is solubilized by ozone to enhance biodegradability, converted into activated sludge substrate (microbial food) again, and then aerated (separate from the biological nitrification and denitrification tank of the wastewater). It is important to use a tank.) In this way, the excess sludge that had to be disposed of outside the system can be biologically decomposed into carbon dioxide gas and water in the aeration tank, and the amount of generated sludge can be reduced to zero. In addition, by providing an anaerobic tank in front of the denitrification tank as the biological treatment step of the wastewater of the present invention, it is possible to incorporate a biological phosphorus removal step by an anaerobic or aerobic method.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Based on the process of FIG.
Biological nitrification denitrification tank A, ozone oxidation tank D, aeration tank F,
An example in which the purification treatment of the organic wastewater using the granular filter medium filling tank C and the first to third settling tanks is described below.
However, the following embodiment is an example of the present invention and does not limit the present invention.

Example 1 Table 1 shows the quality of raw water (sewage) used in the treatment.

[0014]

[Table 1]

A three-month verification test was conducted on the raw water under the following treatment conditions. The type of the biological nitrification denitrification tank is a nitrification liquid circulation type. The flow rate of raw water is 48 liters /
When the biological treatment was carried out under the conditions of 2 hours in the denitrification section and 4 hours in the nitrification section, the water quality of the slurry discharged from the biological nitrification and denitrification tank is as shown in Table 2.

[0016]

[Table 2]

Hereinafter, the ozone oxidation step, aeration step, and phosphorus removal step (treatment conditions with an inorganic coagulant, etc., shown in FIG. 1 are as follows. Ozone oxidation step: From biological nitrification denitrification tank to ozone oxidation tank The amount of excess sludge withdrawn is: excess sludge withdrawal: 4 g SS / day The amount of ozone supplied to the ozone oxidation tank is: ozone supply: 1.8 g / day The solubilized sludge is solidified in the second sedimentation tank. The separated sludge is transferred to an aeration tank, and the amount of separated sludge transferred: 3.5 g / day • Aeration step The amount of MLSS in the aeration tank is 5500 mg / L. Time is 48 hours Phosphorus removal step An inorganic coagulant is added to the water separated from the second sedimentation tank to remove phosphorus, slaked lime is used as the inorganic coagulant, and the injection rate is 400 mg / liter. It is.

Denitrification and SS filtration process The separated water from the first sedimentation tank and the separated water from the third sedimentation tank are combined and sent to the granular filter medium filling tank. The amount of water separated from the first sedimentation tank: 48 liters / day The amount of water separated from the third sedimentation tank: 1 liter / day The granular filter medium filling tank is filled with anthracite having a particle diameter of 3 mm to which denitrifying bacteria are attached as a granular filter medium. Here, the separated water is denitrified and simultaneously subjected to SS filtration. The conditions of the granular filter medium filling tank are as follows. Height of the filling tank: 2 m Filtration speed: 200 m / day The quality of the highly treated water flowing out from the granular filter medium filling tank is as shown in Table 3.

[0019]

[Table 3]

The amount of organic raw sludge discharged outside the system is zero. Also, a small amount of coagulated sludge is discharged out of the system.

[0021]

According to the present invention, the following excellent effects are obtained when biological treatment is performed on sewage by applying the biological nitrification denitrification method. Surplus sludge can be reduced to almost zero. Since a chemical such as methanol does not have to be used in the denitrification step in the biological nitrification denitrification method, the cost is greatly reduced. Highly treated water can be obtained at low cost. By adding an inorganic coagulant, phosphorus can be recovered as a useful substance.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a biological treatment flow of a biological nitrification denitrification method of the present invention in which an ozone oxidation tank and a granular filter medium filling tank are provided.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw water 2 Outflow slurry 3 Separation water (1st settling tank) 4 Return sludge 5 Excess sludge 6 Ozone oxidation sludge 7 Circulating sludge 8 Separated sludge 9 Separated water (2nd settling tank) 10 Separated water (3rd settling tank) 11 Circulation Sludge 12 Coagulant 13 Highly treated water A Biological nitrification denitrification tank B First sedimentation tank C Granular filter material filling tank D Ozone oxidation tank E Aeration tank F Second sedimentation tank G Third sedimentation tank

Claims (1)

[Claims] 1. A method of treating organic wastewater such as sewage by a biological nitrification and denitrification method, wherein a part of the activated sludge of the biological nitrification and denitrification treatment is extracted and oxidized with ozone by an ozone oxidizing unit. Solid-liquid separation, an inorganic coagulant is added to the separated water to perform coagulation separation, and the separated water from the coagulation separation is added to the separated water from the biological nitrification denitrification treatment, and denitrifying bacteria are attached. The biological treatment step of supplying the granular filter medium packed bed and performing denitrification and SS filtration to obtain highly treated water, and solid-liquid separation of the ozone oxidized sludge coming out of the ozone oxidizing section,
A method for advanced purification of organic wastewater, comprising a step of reducing excess sludge by aerating separated sludge obtained by the solid-liquid separation treatment and then circulating the sludge to an ozone oxidizing section.