JPS60227885A - Treatment of hydrazine-containing waste water - Google Patents

Abstract

PURPOSE:To treat waste water without having remaining hypochlorite with less chemical consumption by mixing the treated water with preliminary waste water having the concn. of hydrazine below effluent standard and treating the same with the hypochlorite. CONSTITUTION:The concn. of the hydrazine in the inlet of a reaction vessel 1 is measured and the waste water is stored in a storage tank 12 if the measured value is below the effluent standard. The waste water is introduced into the vessel 1 and the hypochlorite is added approximately at the equiv. of the hydrazine to the waste water to oxidize and decompose the hydrazine if the measured value is above the effluent standard. The treated water is mixed with the preliminary waste water in order to decompose the remaining hypochlorite under the treatment. The treatment without having the remaining hypochlorite is thus executed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a treatment device for wastewater containing hydrazine, and particularly to a treatment method for decomposing hydrazine using hypochlorite.

At thermal power plants and nuclear power plants, when the operation of Plan 1~ is stopped for periodic inspection etc., the water is filled with pure water containing hydrazine to prevent corrosion of equipment and piping. When the plant is started up, this water is discharged, but since hydrazine is detected as COD, it must be treated. Therefore, a conventional method has been to add sodium hypochlorite to such hydrazine-containing wastewater to oxidize and decompose the hydrazine in the wastewater. In this method, an excess of sodium hypochlorite is added to hydrazine, and the concentration of sodium hypochlorite in the treated water is measured using a residual chlorine meter.
The amount of sodium hypochlorite added was controlled to be within the range of m. However, with this method, sodium hypochlorite remains in the treated water, which causes new water pollution. This is because hypochlorite is highly toxic, so even if it remains in trace amounts, there is concern that it will not harm aquatic life. Therefore, it is desired to develop a treatment method that does not leave hypochlorite residue. However, there are limits to the accuracy and detection limits of the hypochlorite concentration measuring instruments, and the problem of residual hypochlorite could not be resolved.

The object of the present invention is to solve the above-mentioned drawbacks of the prior art, to provide hydrazine that can decompose hydrazine without leaving hypochlorite in treated water, and that can be applied to wastewater where the hydrazine concentration fluctuates widely. An object of the present invention is to provide a method for treating wastewater containing wastewater.

The present invention focuses on the fact that although hydrazine is a COD source, as long as it is below a predetermined concentration, the discharged light will not directly harm aquatic organisms, and the concentration of hypochlorite is measured. This was achieved by measuring the hydrazine concentration and treating only wastewater containing hydrazine above a predetermined concentration with hypochlorite.

That is, the method for treating hydrazine-containing wastewater according to the present invention is as follows:
The hydrazine concentration at the inlet of the reaction tank is measured, and if the measured value is below the discharge standard, the wastewater is stored in a storage tank, and if the measured value is above the discharge standard, it is introduced into the reaction tank and then The method is characterized in that chlorite is added in approximately the reaction equivalent amount to hydrazine to oxidize and decompose the hydrazine, and treated water from the reaction tank and wastewater from the storage tank are mixed in an appropriate ratio.

In the method of the present invention, the hydrazine concentration of wastewater is first measured, and if the measured value is above the release/M standard, the wastewater is introduced into a reaction tank and hypochlorite is added in approximately the reaction equivalent amount. . However, the hydrazine concentration in the treated water was 10pp.
m or less, hypochlorite remains as shown in FIG. Therefore, in the method of the present invention, the discharge standard of hydrazine concentration is set, for example, 1100 pp (40 pp as COD).
m) Separate and store the following wastewater and mix it with the hypochlorous acid treated water to reduce the hydrazine concentration to 10pp.
Hypochlorite was prevented from remaining in the treated water by adjusting m to -J=.

The amount of hypochlorite injected into the reaction tank may be controlled based on any of (1) the hydrazine concentration at the reaction tank inlet, (2) the hydrazine concentration at the reaction tank outlet, and (3) the hydrazine concentration in the mixed water.

In the case of (1), the concentration of 1' radine in the treated water or mixed water is not reflected, so if the standards for hydrazine discharge are not strict or the standards for hydrazine discharge are relaxed, the amount of hypochlorite injected may be changed. It is possible to cope with it with a small amount.

FIG. 2 shows a processing flow sheet that employs the control method based on (2). In this device, the monitoring tank 1 includes:
An inlet pipe 2, a discharge pipe 3, a bypass pipe 4, and a hydrazine concentration meter 5 are connected to the hydrazine-containing wastewater. Discharge pipe 3
is equipped with a HALPRO and connected to a reaction tank 7, and the reaction tank 7 is connected to a mixing tank 10 via a conduit 9 in which a hydrazine concentration meter 8 is installed. A valve 11 is installed in the bypass pipe 4.
is connected to the storage tank 12, and the storage tank 12 is connected to the pump 1.
3 and is connected to the mixing tank 10 by a conduit 14. Further, a hydrazine concentration meter 15 is installed in the mixing tank 10. A hypochlorite supply pipe 17 having a valve 16 is connected to the reaction tank 7 .

In addition, the hydrazine concentration meter 5 is connected to a controller 18 that opens and closes the HALPRO and the valve 11.
is connected to a controller 19 that adjusts the opening degree of the valve 16,
Further, the hydrazine concentration meter 8 and the hydrazine concentration meter 15 are connected to a controller 20 that starts or stops the pump 13.

When performing treatment using this device, hydrazine-containing water is introduced into the monitoring tank 1 from the introduction pipe 2, and the value measured here by the hydrazine concentration meter 5 is the discharge standard for the hydrazine concentration.
For example, when it is below 1100 ppm (COD 40 ppm), the controller 18 closes the HALPRO, opens the valve 11, and temporarily stores it in the storage tank 12 through the bypass pipe 4. Further, when the hydrazine concentration is equal to or higher than the discharge standard, the valve 11 is closed, the HALPRO is opened, and the hydrazine-containing wastewater is introduced into the reaction tank 7 through the discharge pipe 3.

Here, the hydrazine in the wastewater comes into contact with the hypochlorite fed through the supply pipe 17 and is decomposed into nitrogen and water.

This treated water is introduced into a mixing tank 10 through a pipe 9.

At that time, the hydrazine concentration of the treated water is measured with the hydrazine concentration meter 8 installed in the pipe line 9, and the opening degree of the valve 1G is adjusted by the controller 19 according to this output signal, so that the hydrazine concentration is determined according to the discharge standard, e.g. The hydrazine concentration is controlled within a range of 1100 ppm or less and no hypochlorite remains, and the hydrazine concentration is 1Q ppm or more.

Furthermore, if the hydrazine concentration in the raw water changes rapidly, and the measured value of the hydrazine concentration meter 8 becomes lOppm or less, the controller 20 starts the pump 13 to remove the hydrazine stored in the storage tank 12. Mixing tank 10 containing wastewater
The hydrazine concentration is controlled such that the hydrazine concentration measured by the hydrazine concentration meter 15 is 10 ppm or more.

The apparatus shown in FIG. 2 employs the control method based on (2) above, and in this case, control in the reaction tank is most reliable. However, when the hydrazine concentration of the preliminary wastewater in the storage tank is unknown, a means for determining the mixing ratio is required, and since the mixing ratio is determined regardless of the amount of water stored, there are difficulties in adjusting it.

The device shown in FIG. 3 employs the control method based on the above (3), and can perform control according to the amount of water stored in the storage tank 12. In this device, the controller 21 controls the opening degree of the valve 16 and/or the pump 13 (or ) is adjusted. A liquid level gauge 22 is installed in the storage tank 12,
It is connected to the controller 21. When the amount of water stored in the storage tank 12 is small, the amount of hypochlorite injected into the reaction tank is slightly reduced, and the mixing ratio of reserve water is also lowered. On the other hand, when there is a large amount of water stored, the amount of hypochlorite injected may be slightly increased and the mixing ratio of reserve water may be increased.

With such control, if the hydrazine concentration in the mixed water tends to increase, mainly due to the hydrazine concentration in the reserve water, the injection amount of hypochlorite is increased, and hydrazine tends to decrease. It is further preferred to provide a control circuit to reduce the amount of hypochlorite injection, if any.

According to the present invention, since hypochlorite and hydrazine are reacted in approximately equivalent amounts in the reaction tank, both hypochlorite and hydrazine can be suppressed to low levels. and,
In order to decompose residual hypochlorite in the treated water due to fluctuations in hydrazine concentration and time lag in control, the treated water is mixed with preliminary wastewater whose hydrazine concentration is below the discharge standard, and the hypochlorite in the mixed water is mixed with hydrazine. reaction to ensure that no hypochlorite remains in the effluent. In addition, the amount of hypochlorite consumed can be reduced compared to conventional reaction equivalent and total amount treatments.

Next, the present invention will be explained in detail based on the drawings, but the present invention is not limited thereto.

Example Raw water with a hydrazine concentration varying between 200 and 500 ppm was treated with sodium hypochlorite as the hypochlorite using the equipment shown in Figure 2. As a result, the hydrazine concentration at the outlet of the mixing tank was It was 15 to 90 ppm, and no sodium hypochlorite remained.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between the hydrazine concentration and the sodium hypochlorite concentration in treated water, Fig. 2 is a flow sheet showing an embodiment of an apparatus for implementing the method of the present invention, and Fig. 3 is a diagram showing the relationship between the concentration of hydrazine and the concentration of sodium hypochlorite in treated water. 1 is a flow sheet illustrating another embodiment of the apparatus for implementation. 5.8.15... Hydrazine concentration meter, 7... Reaction tank, 10... Mixing tank, 12... Storage tank, 18, 19
, 20.21...Controller, 22...Liquid level gauge Patent applicant/Hitachi Plan)/Kensetsu Co., Ltd.

Claims (1)

[Claims] 4) In a method for treating hydrazine-containing wastewater in which hydrazine-containing wastewater is brought into contact with hypochlorite to decompose hydrazine, the hydrazine concentration at the inlet of the reaction tank is measured, and if this measured value is below the discharge standard, The wastewater is stored in a storage tank, and if the measured value is at the discharge standard level -, it is introduced into the reaction tank and hypochlorite is added in an approximately reaction equivalent amount to hydrazine to oxidize the hydrazine. A method for treating hydrazine-containing wastewater, which comprises decomposing the water and mixing the treated water from a reaction tank and the wastewater from a storage tank in an appropriate amount.