JPS5925635B2 - How to treat wastewater - Google Patents

Description

Detailed Description of the Invention The present invention involves adding and mixing hydrogen peroxide (H202) to wastewater to reduce nitrite in wastewater, which is a cause of increasing the COD value of industrial wastewater, and convert it into harmless nitrate. Regarding the complete processing method and its automation.

Generally, molten salt containing nitrite is widely used as a heating medium, and since the molten salt of nitrite adheres to the workpiece that has been heat-treated with the heating medium, this salt can be removed by washing with water. need to be removed.

Therefore, the waste water after washing contains nitrites and has a high COD value, which may cause pollution. The waste water is converted into H2O.
The method in step 2 is to oxidize it and turn it into harmless nitrate and discharge it.
This is already known from Japanese Patent Application Laid-Open No. 53-28952. However, this conventional method measures the oxidation-reduction potential (ORP) of wastewater, which changes due to continuous addition of H2O2, and detects the change in ORP at the end point of the treatment reaction under visual control using an ORP meter. At that time, all such work was done manually, such as stopping the injection of H2O2 by operating the pump. That is, the above H2O2
Figure 1 shows the change in 0RP due to continuous addition of water over time.As shown in the figure, 0R changes over time because it takes time for the H2O2 added to the entire wastewater in the tank to be uniformly stirred.
1, which represents P, rises while constantly vibrating up and down, and begins to fall at the falling point 2, which is the end point of the processing reaction, but it is difficult to accurately capture the potential at this falling point 2 by visual inspection. be. This is because the potential oscillates up and down even just before the falling point 2, so it may show the same potential as the falling point 2. Therefore, there is always a time lag in the visual judgment of the end point of the treatment reaction, and even with skilled workers and drillers, since H2O2 is continuously added, an excessive amount of H2O2 may be added, and there is a risk of secondary pollution occurring. Ta. Excessive injection of H2O2 also occurs when automatic control is performed by automatically measuring the potential instead of the operator. It is 0 due to continuous H2O2 input.
This is because the value of RP constantly oscillates up and down as shown in 1 in the figure, so it is equally difficult to accurately determine the point of descent 2, whether by visual observation or automatic measurement. This invention was made in view of the above points, and in a wastewater treatment method in which nitrites in wastewater are oxidized with H2O2, H2O2 is not continuously introduced into the wastewater, but is intermittently introduced into the wastewater. After each injection, measure 0RP at the time when the potential oscillation disappears and becomes stable, and stop adding H2O2 when the potential change between this stable potential and the stable potential after the previous injection is reversed (for example, from increasing to decreasing). By doing so, it has become possible to completely treat wastewater and operate it unmanned. In other words, this invention allows H2O2 to be added intermittently rather than continuously, in other words, H2O2 is added in small portions, and after each injection, H2O2 is stirred uniformly and stabilized when the 0RP vibration disappears. By measuring the potential, it is possible to obtain an accurate potential during the oxidation treatment, so automatic control of H2O2 injection is possible by automatically measuring the potential. In other words, since the accurate potential after each injection of H2O2 can be measured, it can be determined that the end point of the oxidation treatment reaction is the point at which the potential change is reversed compared to the potential after the previous injection. Therefore, this allows not only visual measurement but also automatic measurement of 0RP, and as a result, automatic control of H2O2 injection becomes possible.
In this invention, as for the amount of H2O2 added at one time, when the oxidation of nitrite is completely completed, an additional amount of excess H2O2 is added.
Even if H2O2 is added at the last time, the COD value due to the excess H2O2 contained in the total amount of treated wastewater will be lower than the target value, for example 1.
The amount of H2O2 added at one time may be such that the amount is 0 ppm or less.

For example, for 5 m3 of waste water, if 200 cc of 35% H2O2 is added at one time, the COD value will be approximately 1 even if an additional 200 cc is added when the oxidation reaction is completed.
It only becomes 0 ppm. Alternatively, if the concentration of nitrite in the wastewater does not change much, a relatively large amount of H2O2 may be added at the beginning of the intermittent injection, and a small amount of H2O2 may be added at the later stage. The end point of the oxidation treatment reaction according to this invention, that is, 0
The method for detecting when the change in RP is reversed is as follows.

Figure 2 shows the 0.0 0.00% when H2O2 is intermittently poured in small amounts into a fixed amount of wastewater containing nitrite using the method according to the present invention.
It is a chart showing changes in RP over time. According to the diagram, by intermittently pouring H2O2 into A, B, C, D, and E, 0RP initially vibrates up and down like 1 with each injection, but then vibrates sequentially like 3. stops and becomes stable, so the 0RP of stable A, b, c, d, e,
The measured value of will give the accurate 0RP after each injection of H2O2. Therefore, by always comparing the potential after the previous application and the potential after the current application, ie, a and b, b and C. c.
and D. By comparing the potentials at times d and e, it is possible to know the time when the change is reversed, that is, when e is measured, and this is the end point 2 of the oxidation treatment reaction. The time required for the potential oscillation to disappear after each addition of H2O2 depends on the amount of waste water containing nitrite, stirring conditions, etc., but the time required can be easily determined experimentally in advance, so the time required is 0R every time
What is necessary is to measure P. Of course, a detector can also be used to detect when the potential oscillations have disappeared. Next, an embodiment in which the detection of the end point of the oxidation treatment reaction and the injection of H2O2 are automatically controlled according to the present invention will be described in detail.

FIG. 3 is a block diagram of a voltage comparator P equipped with the necessary devices for the above control. To explain with reference to the diagram below, the 0RP measured by the 0RP meter 4 becomes the input voltage of the voltage comparator, is amplified by the amplifier 5, and is amplified by the measurement timing device 6.
When a measurement start command is received from , it is converted into a digital signal amount by an analog/digital converter (A/DCONV) 7. In this way, the digital signal of 0RP at each measurement time is calculated by the comparison calculator (UP/DOWN COUNTER) 8, which compares the previous measurement value and the current measurement value (a and B, .b and C in Fig. 2,
．． c and D,. The measured values of d and e1 are compared and calculated, and the comparison calculation value is sent to a comparator (COMPARATE) 9.
This is further compared with the voltage value preset in the digital setting device 10. When the comparison calculation value in the comparison calculator 8 is greater than the previous measurement value > the current measurement value (measurement values of d and e), that is, the change in both measurement values is reversed from increase to decrease, and this amount of change (difference) is digital. When the voltage is higher than the voltage value preset in the setting device 10, the relay (RY) 11 is activated and the subsequent injection of H2O2 is stopped. If this difference is smaller than the set voltage value of digital setting device 10, relay 1
1 does not operate and intermittent H2O2 injection continues. The digital setting device 10 is provided to prevent automatic control from malfunctioning due to instrument measurement errors. If the potential change (difference) between the previous measurement value and the current measurement value is within the range of instrument measurement error (e.g. due to electrical noise, impurity adhesion to the 0RP electrode set in the drainage water, etc.) If there is only a change in potential, it may be erroneously determined that the change in potential is decreasing or reversing even though it is increasing, and the relay may malfunction if the setting voltage of the digital setting device does not work. Therefore, a digital setting device is provided so that the relay is activated only when the difference between the two measured values output from the comparator 9 is greater than the set voltage of the digital setting device. Through the method according to the present invention as described above, the processing amount is 5 m3.
Add 35% H2O2 into the wastewater at a time of 200ml,
Throwing time: 16sec/time, Throwing interval: approx. 110sec, 0
The RP measurement time was 5 sec/time, and the set voltage of the digital setting device was set to 0.05 mV, and the COD after processing was 10 ppm or less.

When the same wastewater as above was treated using the conventional method of continuously adding H2O2, the COD was 40 to 100 ppm. Clearly, the processing method according to the invention has advantages over conventional methods. In the automatic control example described above, the 0RP value was converted into a digital signal and controlled using the digital quantity because the control was relatively easy and the accuracy was good. Needless to say, it can be used as an analog quantity.

As detailed above, the method for treating wastewater according to the present invention is as follows:
It is close to complete processing, there are no individual differences in processing accuracy, and unmanned operation is possible through automation, making it effective in industrial environments.

[Brief explanation of the drawing]

Figure 1 is a chart showing changes in oxidation-reduction potential (0RP) due to continuous injection of hydrogen peroxide (H2O2).
The figure shows 0R due to intermittent injection of H2O2 according to the present invention.
3 is a diagram showing changes in P, and FIG. 3 is a block diagram of a voltage comparator P equipped with various control devices according to the present invention. 1: Redox potential (0RP), 2: Treatment reaction end point, 3:
Redox potential at stable time (0RP), 4: Redox potential measuring instrument (0RP meter), 5: Amplifier (AMP), 6: Measurement timing device, 7 Real analog/digital converter (A/
DCONV), 8: Comparison calculator (UP/DOWNCOU
NTER), 9: Comparator (COMPARATE), 10
: Digital setting device, 11: Relay (RY).

Claims (1)

[Scope of Claims] 1. In a wastewater treatment method in which hydrogen peroxide is added to and mixed with wastewater containing nitrite to oxidize the nitrite, the amount of water required to completely oxidize the nitrite contained in a certain amount of wastewater is Inject hydrogen peroxide in an amount sufficiently smaller than the amount of hydrogen peroxide into the wastewater intermittently, measure the potential when the oxidation-reduction potential no longer oscillates after each addition, and calculate the potential between this potential and the potential after the previous addition. A wastewater treatment method characterized by stopping the addition of hydrogen peroxide when the change is reversed. 2. The wastewater treatment method according to claim 1, wherein the addition of hydrogen peroxide is stopped when the amount of potential change when the potential change is reversed is larger than a predetermined amount. 3. The redox potential is measured with a redox potential meter, this measured voltage is amplified with an amplifier, and after each injection of hydrogen peroxide, when a measurement start command signal is issued from a measurement timing device, the amplified measurement voltage is The voltage is converted into a digital quantity using an analog/digital converter, this digital quantity is stored in a comparison calculator, and the comparison calculator calculates the amount of change between this digital quantity and the digital quantity of the measured voltage since the previous input. ,
Continue to add hydrogen peroxide intermittently until this amount of change is reversed,
2. A method for treating wastewater according to claim 1, characterized in that the addition of hydrogen peroxide is stopped after the point of reversal. 4 Compare the amount of change during the above reverse rotation with a predetermined amount preset on the digital setting device using a comparator, and when the amount of change is greater than the predetermined amount, activate the relay and stop adding hydrogen peroxide. A method for treating wastewater according to claim 3, characterized in that: