JP3312413B2 - Biological denitrification treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for biological denitrification, and more particularly to an improved method for membrane separation of biologically treated water obtained by biologically denitrifying human wastewater.

[0002]

2. Description of the Related Art Conventionally, there is a biological denitrification treatment as a treatment method for human wastewater, and a method of alternately performing a nitration step and a denitrification step in a single biological treatment tank is adopted as one of the treatment methods. Have been. In this case, a membrane separation method is often used for the solid-liquid separation treatment after the biological denitrification treatment, and the nitrogen removal ratio of the obtained membrane permeated water to the raw water is about 90 to 95%.

In such a treatment, a nitrogen removal rate of 98
In order to perform an advanced treatment of up to 99%, it is necessary to perform a further advanced denitrification treatment (hereinafter, this denitrification treatment is referred to as “finishing denitrification treatment”) to further remove nitrogen.

In this case, the residual nitrogen is removed under an anaerobic condition using an organic substance such as methanol or a component obtained by self-digestion of sludge as a BOD source. Conventionally, the oxidation-reduction potential (ORP) in this finishing denitrification treatment system is -1.
It is known that 00 to -200 mV is appropriate.

[0005]

In the above-mentioned conventional finish denitrification treatment, not only nitric acid or nitrite nitrogen NO _x -N but also ammonia nitrogen NH ₄ -N There is also. Nevertheless, the conventional finish denitrification treatment conditions, that is, the system is made anaerobic and OR
When P is maintained at −100 to −200 mV, NO _x −
Although N can be removed, there is a problem that NH ₄ -N cannot be removed.

[0006] In addition, since unsatisfactory treatment cannot be performed in this finishing denitrification treatment, the remaining undecomposed substances increase the viscosity of the effluent, so that in the subsequent membrane separation step,
There was also a problem that the flux of the film was significantly reduced.

The present invention solves the above-mentioned conventional problems and provides a method for membrane separation of biologically treated water obtained by biologically denitrifying sewage wastewater, wherein nitrogen is highly removed by finishing denitrification. It is an object of the present invention to provide a biological denitrification method for obtaining high-quality treated water and preventing a decrease in flux in membrane separation treatment.

[0008]

According to the biological denitrification method of the present invention, the human wastewater is subjected to biological denitrification, the resulting biologically treated water is aerated in an aeration tank, and then subjected to membrane separation treatment. A biological denitrification treatment method, wherein the oxidation-reduction potential in the aeration tank is controlled at 0 to -20 mV.

[0009]

By maintaining the ORP of the aeration tank through which biologically treated water is subjected to membrane separation at 0 to -20 mV, N
H ₄ —N is nitrated to be denitrified, and can be efficiently treated together with NO _x —N.

[0010] Further, since the undecomposed substance is digested under the ORP condition, an increase in viscosity due to the undecomposed substance is prevented, so that the flux in the membrane separation step can be kept high.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an example of an apparatus suitable for carrying out the biological denitrification treatment method of the present invention.

In FIG. 1, 1 is a biological treatment tank, 2 is a relay tank, 3 is a UF raw water tank, and 4 is a UF membrane (ultrafiltration membrane) separator. The biological treatment tank 1 is provided with an aeration tube 13 including a circulation pump 11 and an air ejector 12. Further, an aeration device 14 and an ORP meter 15 are provided in the UF raw water tank 3, and the aeration by the aeration device 14 is controlled according to the measurement value of the ORP meter 15. 1
Reference numerals 6 to 21 denote pipes, 22 and 23 denote pumps, and 24 denotes a valve.

That is, in this embodiment, the UF raw water tank 3
Is used as a finishing denitrification tank, and this UF raw water tank 3
Is aerated under ORP control.

In the method shown in FIG. 1, raw water (human waste) is first introduced into the biological treatment tank 1 through a pipe 16 and subjected to biological nitrification and denitrification in a batch system according to a conventional method.

The biologically treated water in the biological treatment tank 1 is supplied to a pipe 1
7. Introduced to the UF membrane separation device 4 via the relay tank 2, the pipe 18, the UF raw water tank 3, and the pipe 19, and at this time, the ORP in the tank in the UF raw water tank 3 becomes 0 to -20 mV. Is aerated.

By processing under this ORP condition,
Along with the denitrification of NO _X -N remaining in the biological treatment water, NH
The nitrification and denitrification of _4- N proceed efficiently, and the nitrogen concentration is significantly reduced. Undegraded substances are also digested.

The effluent from the UF raw water tank 3 is
The water treated by the membrane separator 4 is discharged from the pipe 21 as treated water to the outside of the system. On the other hand, the concentrated water is returned from the pipe 20 to the UF raw water tank 3.

In the present invention, the aeration tank such as the UF raw water tank is aerated so that the ORP is 0 to -20 mV. If this ORP is lower than −20 mV, NH ₄ −
Nitrification and denitrification of N do not proceed smoothly. Conversely, when the ORP exceeds 0 mV, the NO _x -N denitrification efficiency decreases. Therefore, ORP is -20 to 0 mV, preferably -15 to-
It is desirable to control so as to be 5 mV, especially −10 mV.

The illustrated embodiment shows one embodiment of the present invention, and the present invention does not depart from the gist of the present invention.
The present invention is not limited to the illustrated ones.

For example, an MF (microfiltration) membrane separator can be used as the membrane separator in addition to the UF membrane separator.

The control of the aeration includes the control of the aeration time,
It can also be performed by controlling the amount of aeration per unit time.

Hereinafter, the present invention will be described in more detail with reference to specific examples and comparative examples.

Example 1 Using the apparatus shown in FIG. 1, human waste having the following properties was treated according to the method of the present invention. Human excrement property BOD: 9500 mg / l NH ₄ -N: 1700 mg / l First, night soil was treated in a single batch biological treatment tank 1. NH ₄ -N: 10 mg / l, NO _X -N: 15 m
g / l of treated water was obtained. This treated water (UF raw water tank inflow water) is transferred to the relay tank 2 and the UF raw water tank (MLSS = 2600
(0 mg / l) 3 and introduced into a UF membrane separator 4 for treatment. At that time, the ORP of the UF raw water tank 3 is -20 to 0 m
V, the aeration amount was inverter-controlled so that the average was -10 mV. The OR of the UF raw water tank in this treatment system
The relationship between P and the N concentration of the permeated water was as shown in FIG.

Table 1 shows the quality of the obtained permeated water. Further, the chemical cleaning cycle of the membrane of the UF membrane separation apparatus was as shown in Table 1, and the time-dependent change of the flux was as shown in FIG.

Comparative Example 1 Average ORP of UF raw water tank without aeration of UF raw water tank
Was carried out in the same manner as in Example 1 except that was treated at -150 mV.

Table 1 shows the quality of the obtained permeated water. Further, the chemical cleaning cycle of the membrane of the UF membrane separation apparatus was as shown in Table 1, and the time-dependent change of the flux was as shown in FIG.

[0028]

[Table 1]

According to Table 1 and FIG. 2, according to the method of the present invention for controlling the ORP of the UF raw water tank to -20 to 0 mV, NH
It is clear that can be processed together efficiently ₄ -N and NO _X -N.

Further, from FIG. 3, the average ORP of the UF raw water tank is shown.
Is controlled to -10 mV, it is clear that the flux can be prevented from lowering, and the cleaning frequency can be significantly reduced as compared with the case where the average ORP is set to -150 mV.

[0031]

As described above in detail, according to the biological denitrification treatment method of the present invention, a method of subjecting human wastewater to biological denitrification treatment followed by membrane separation treatment, wherein nitrogen is highly removed. As a result, high quality treated water can be obtained stably and efficiently. A reduction in the flux of the membrane of the membrane separation device can be prevented, the frequency of cleaning the membrane can be reduced, and the efficiency of membrane treatment can be increased. And the like, which is extremely advantageous industrially.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an example of an apparatus suitable for carrying out a biological denitrification treatment method of the present invention.

FIG. 2 is a graph showing the relationship between the ORP of a UF raw water tank and the N concentration of membrane permeated water in Example 1.

FIG. 3 is a graph showing a change over time of a flux of a membrane separation device in Example 1 and Comparative Example 1.

[Explanation of symbols]

 Reference Signs List 1 biological treatment tank 2 relay tank 3 UF raw water tank (aeration tank) 4 UF membrane separation device

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-58-34093 (JP, A) JP-A-2-36000 (JP, A) JP-A-3-77699 (JP, A) JP-A-5-305 220494 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 3/34

Claims (1)

(57) [Claims] 1. A biological denitrification treatment method in which human wastewater is subjected to biological denitrification treatment, the resulting biological treatment water is aerated in an aeration tank, and then subjected to membrane separation treatment. A biological denitrification treatment method characterized by controlling the oxidation-reduction potential of the compound to 0 to -20 mV.