JPH09141294A - Biological nitrogen removing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably and efficiently execute biological nitrification and denitrification without executing intermittent aeration in an aeration tank. SOLUTION: At the time of introducing a water containing an organic nitrogen or an ammonia nitrogen in an aeration tank 1 to biologically nitrificate and denitrificate under an aerobic condition, the DO(dissolved oxygen) concentration in the aeration tank 1 is controlled to >=1mg/l and the ORP(oxidation- reduction potential) is controlled to <=+100mV. As a result, the nitrification reaction is surely carried out since sufficient oxygen exceeding 1mg/l in DO is supplied to a raw water in the aeration tank 1. The denitrification reaction also proceeds to efficiently remove nitrogen since the ORP is kept lower regardlessly of high DO.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological nitrogen removal method, and more particularly to a biological nitrogen removal method for biologically nitrifying and denitrifying water containing organic nitrogen or ammonia nitrogen in an aeration tank. .

[0002]

2. Description of the Related Art Conventional biological nitrogen removal methods are based on nitrifying bacteria (N
Itrobacter), nitrite (Nitrosomonas) nitrifying process with autotrophic nitrifying bacteria, and denitrifying process with facultative anaerobic bacteria. It has been known.

A method in which a nitrification tank and a denitrification tank are arranged in series and the raw water is nitrified and then denitrified. A method of arranging a denitrification tank and a nitrification tank in series, providing a circulation system path from the nitrification tank to the denitrification tank, nitrifying the denitrification treatment liquid, and performing denitrification again. In the above method, a step denitrification method in which raw water is dispensed into a nitrification tank. A method in which anaerobic conditions (denitrification process) and aerobic conditions (nitrification process) are alternately set temporally by performing intermittent aeration in a single tank.

Further, as a method for simultaneously causing nitrification and denitrification in the aeration tank, there is a method described in JP-A-54-94756. This method uses a dissolved oxygen (DO) concentration of 1 mg / L or less and an oxidation-reduction potential (ORP) in the aeration tank.
By setting the voltage in the range of −100 to −400 mV, it is a method of performing anaerobic denitrification together with nitrification without performing intermittent aeration.

[0005]

Among the above-mentioned conventional biological nitrogen removal methods, in the methods of and, it is necessary to provide two tanks, a denitrification (anaerobic) tank and a nitrification (aerobic) tank, It is disadvantageous in terms of the number of installation tanks. In the method of
In order to promote the nitrification smoothly, it is necessary to remove BOD in the raw water in advance. The method (1) does not require such removal of BOD, but the method (2) has a drawback that a pump for circulation is further required. In addition, the method (1) has a drawback in that the water to be treated needs to be dispensed, which complicates the raw water introduction system.

According to the method of 1, the nitrification in only one tank,
Although it is possible to denitrify, it is difficult to appropriately control the aeration cycle, that is, the time for making the anaerobic condition in the tank and the time for the aerobic condition, and if this time allocation is inappropriate,
There is a drawback that it takes a long time to nitrify and denitrify and the treatment efficiency is lowered.

[0007] As disclosed in JP-A-54-94756, ORP is -100 to -4 at a DO concentration of 1 mg / L or less.
In the method of setting the range of 00 mV, nitrification and denitrification can be performed when treating wastewater having a high organic matter concentration and ammonia nitrogen concentration, for example, human waste, but when treating wastewater having a low concentration of these substances. However, although organic substances are decomposed, nitrification of ammonia is insufficient and nitrogen cannot be removed stably.

The present invention solves the above-mentioned conventional problems and provides a biological nitrogen removing method capable of performing stable and efficient biological nitrification and denitrification without performing intermittent aeration in an aeration tank. The purpose is to do.

[0009]

The biological nitrogen removing method of the present invention comprises introducing water (raw water) containing organic nitrogen or ammonia nitrogen into an aeration tank to biologically nitrify under aerobic conditions. In the denitrification method, dissolved oxygen (DO) in the aeration tank
It is characterized in that the concentration is kept higher than 1 mg / L and the redox potential (ORP) is adjusted to +100 mV or less.

Normally, in the aeration tank, DO is 1 mg /
Keep above L. In this case, the ORP becomes +150 mV or more. In particular, when nitrification / denitrification is performed in an aeration tank, the DO is set high in order to improve the nitrification efficiency.
In this case the ORP will be much higher, typically +
200 mV or more.

In the present invention, the DO of such an aeration tank is
Nitrogenation and denitrification are performed in the aeration tank by controlling ORP to be +100 mV or less by taking appropriate means in a state of being kept higher than mg / L.

In the present invention, since sufficient oxygen is supplied to the raw water in the aeration tank so that DO exceeds 1 mg / L,
The nitrification reaction is performed reliably.

Moreover, despite the high DO, the ORP
Is kept low, the denitrification reaction proceeds smoothly,
Efficient nitrogen removal is performed.

As described above, when DO> 1 mg / L, ORP ≦
By setting the voltage to +100 mV, the details of the reason for denitrification in the aeration tank are not clear, but nitric acid is hardly detected when the inside of the aeration tank is maintained under such conditions. on the other hand,
Since NO ₂ ⁻ or NH ₄ ⁺ may be detected, it is presumed that aerobic denitrification by trophic bacteria different from anaerobic bacteria occurs.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

1 to 3 are system diagrams showing a method according to an embodiment of the present invention.

In the present invention, conventionally, DO> 1 mg /
When L is set, ORP ≧ + 150 mV or O
In the aeration tank where RP ≧ + 200 mV, DO> 1 mg /
The L is controlled so that ORP ≦ + 100 mV. DO
Is less than 1 mg / L, oxygen is insufficient and nitrification cannot be performed stably. Further, if the ORP exceeds +100 mV, denitrification does not occur. If the DO is too high, the denitrification efficiency may decrease, and if the ORP is too low, the nitrification rate may decrease. Therefore, 1 mg / L <DO ≦ 5 mg /
L, ORP = −100 to −300 mV is preferable.

In this way, DO> 1 mg / L in the aeration tank
As a method for adjusting ORP ≦ + 100 mV in (1), for example, the following methods (1) to (4) can be adopted.

As shown in FIG. 1, when treating raw water in the aeration tank 1 and the precipitation tank 2, a reducing agent such as sodium sulfite and hydrazine is added to the aeration tank 1. In particular, hydrazine is difficult to decompose and is effective in reducing ORP. The amount of these reducing agents added may be such that the ORP value of the aeration tank falls within a predetermined range, and the addition location is at the aeration tank, the raw water introduction pipe to the aeration tank, or the settling tank at the subsequent step. When sludge is returned to the aeration tank from the above, etc., any of the sludge return piping and the like may be used.

As shown in FIG. 2, when the raw water is treated in the aeration tank 1 and the precipitation tank 2, a part or all of the sludge returned from the precipitation tank 2 is introduced into the anaerobic tank 3 and retained for a certain period of time. In this case, the higher the sludge concentration to be returned and the longer the retention time, the lower the ORP, and as a result, the O 2 in the aeration tank increases.
RP also decreases. Generally, the retention time of the returned sludge is set to the same level as or longer than the retention time of the raw water in the aeration tank, and it is preferably 6 to 24 hours, for example.

As shown in FIG. 3, when the raw water is treated in the aeration tank 1 and the precipitation tank 2, the anaerobic tank 3 is provided, and the raw water and the sludge returned from the precipitation tank 2 are mixed in the anaerobic tank 3 in advance. In this case, the higher the raw water BOD concentration and the longer the anaerobic tank residence time, the more the ORP decreases. In this case, the residence time of the anaerobic tank is about the same as or longer than the residence time of the raw water in the aeration tank, and is preferably 6 to 24 hours, for example.

The above methods may be used in combination of two or more.

In the present invention, the aerobic biological treatment in the aeration tank may be a floating method in which sludge is held in a floating state or a contact oxidation method in which sludge is held in a carrier. It is preferably a tank.

Such a method of the present invention is particularly applicable to wastewater having a low organic matter concentration and ammonia nitrogen concentration, such as BO.
D1000 mg / L or less and NH ₄ —N 100 mg / L or less, which is effective for treating the first settling water, food wastewater, and the like.

[0025]

The present invention will be described more specifically below with reference to examples and comparative examples.

First, a comparative example will be described for convenience of explanation.

Comparative Example 1 Biological nitrogen removal from raw water was carried out in the same manner as in FIG. 1 except that no reducing agent was added.

The aeration tank capacity is 2 L and the sedimentation tank capacity is 2.5 L.
Water was passed at a flow rate of L / day.

Raw water quality BOD: 160 mg / L SS: 45 mg / LT-N: 39 mg / L NH ₄ -N: 28 mg / L NO _x -N: ND In addition, the sewage activated sludge is MLSS 3500 m in the aeration tank.
The operation was started by adding so as to be g / L, and NaOH was automatically added as needed so that the pH did not become 7 or less.

When the treated water after 1 week of water flow was analyzed,
BOD 5 mg / L or less, NH ₄ —N 0.7 mg /
_{L, NO 3 -N 29mg / L} , NO 2 -N 0.1m
g / L.

The DO in the aeration tank at this time is 2.1 mg /
L and ORP were +200 mV.

In the measurement of BOD, BOD was measured by adding allylthiourea as a nitrification inhibitor in an amount of 2 mg / L.

Example 1 In Comparative Example 1, 0.5 mg / L of hydrazine was added with the amount of aeration in the aeration tank unchanged. As a result, DO in the aeration tank was lowered to 2.2 mg / L and ORP was lowered to -10 to +20 mV.

The treated water thus obtained initially contained 6% NH ₄ --N.
Approximately mg / L was detected, but it decreased after 2 days and decreased to 2 mg
/ L or less. At the same time, NO ₃ -N also decreases,
It became 0.1-0.4 mg / L. NO ₂ -N is 0.9
-3.7 mg / L was detected. BOD was 5 mg / L or less.

Example 2 In Example 1, when the aeration amount was increased and the DO in the aeration tank was set to 5 mg / L or more, the ORP was also increased to +85.
It became +97 mV.

The treated water thus obtained is NH ₄ --N: 2.9-
3.4 mg / L, NO ₃ -N: 1.1 to 1.6 mg /
L, NO ₂ -N: was 2.9~3.4mg / L. B
The OD was 5 mg / L or less.

Example 3 Biological nitrogen removal similar to the raw water treated in Comparative Example 1 was performed according to the method shown in FIG.

An anaerobic tank having a capacity of 1 L was used, and the sludge return rate (ratio of the returned sludge flow rate to the raw water amount) in the settling tank was 25%. The other conditions were the same as in Comparative Example 1.

As a result, the DO in the aeration tank was 1.2 mg / L.
And ORP also fell to +88 to +95 mV.

The obtained treated water is NH ₄ --N: 0.8-
2.5 mg / L, NO ₃ -N: 0 to 1.2 mg / L, N
O ₂ -N: 0.7-2.5 mg / L and BOD 5 mg / L
L or less.

Comparative Example 2 In Comparative Example 1, by reducing the aeration amount, the DO in the aeration tank was set to 0.3 to 0.5 mg / L, which is 1 mg / L or less, and the ORP was set to -100 to -150 mV. Other than that, the treated water obtained was NH ₄ −.
_{N: 23~32mg / L, NO 3} -N: 0.1~0.8
_{mg / L, NO 2 -N:} 0.4~3.1mg / L, BO
D: It was 5-12 mg / L.

The above results are summarized in Table 1.

[0043]

[Table 1]

From Table 1, it is clear that according to the method of the present invention, nitrogen can be efficiently removed by performing nitrification and denitrification in the aeration tank.

[0045]

As described in detail above, according to the method for removing biological nitrogen of the present invention, nitrogen is stably and reliably biologically nitrified and denitrified without intermittent aeration in the aeration tank. It can be removed efficiently.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a method of an embodiment of the biological nitrogen removal method of the present invention.

FIG. 2 is a system diagram showing another embodiment method of the biological nitrogen removal method of the present invention.

FIG. 3 is a system diagram showing another example method of the biological nitrogen removal method of the present invention.

[Explanation of symbols]

 1 Aeration tank 2 Precipitation tank 3 Anaerobic tank

Claims (1)

[Claims] 1. Water containing organic nitrogen or ammonia nitrogen is introduced into an aeration tank to biologically nitrify under aerobic conditions,
In the denitrification method, the dissolved oxygen concentration in the aeration tank is set to 1 m.
Maintained higher than g / L and redox potential +100
A method for removing biological nitrogen, which comprises adjusting the concentration to be mV or less.