JPS5815027B2 - Method and device for detecting and controlling BOD value in wastewater based on wastewater turbidity - Google Patents

Description

[Detailed Description of the Invention] This invention was obtained by measuring BOD (biological oxygen demand) itself, which is used as an indicator of the amount of organic substances contained in wastewater and wastewater (hereinafter simply referred to as wastewater). BO due to wastewater turbidity instead of dealing with regulations based on measured values.
The present invention relates to a method and apparatus for detecting and controlling D approximately and within a short period of time.

The conventional method for measuring BOD itself is to oxidize organic matter in wastewater using microorganisms and measure the decrease in dissolved oxygen in wastewater that is consumed over 5 days at 20°C. .

According to this method, a long time of 120 hours (5 days) is required from the time the wastewater to be measured is collected until the results are known, and although it can be applied to stagnant wastewater, Water is discharged intermittently or continuously, such as water discharged from the product beverage industry, pharmaceutical industry1, livestock facilities, mass kitchen facilities, etc., and depending on operating conditions, BO may be released each time.
It has been difficult to apply this method to cases where the D concentration fluctuates.

Therefore, the C0D (chemical oxygen demand) method and the TOC (total organic carbon i method) are used as measurement methods in place of BOD.

In the COD method, organic matter in wastewater is oxidized with potassium permanganate or potassium dichromate, and the amount of consumed potassium permanganate or potassium dichromate is measured. A measurement time of at least 10 minutes is required.

On the other hand, in the case of the TOC measurement method currently in practical use,
After vaporizing the water in the wastewater in a heating furnace containing an oxidation catalyst, oxygen gas is introduced to convert organic matter into acid θ, and the carbon dioxide produced is quantified by gas chromatography to determine the total amount of organic carbon in the wastewater. This method requires at least 10 minutes and usually about 1 hour to measure.

In this way, it takes at least 10 minutes after water sampling to obtain a measurement result, and the BOD method requires as much as 120 hours, so BOD in wastewater that remains in large amounts in storage tanks and sedimentation ponds can be easily measured. It is applicable to measure the above factory,
This system detects changes in the concentration of wastewater that is discharged intermittently or continuously from facilities, etc. and flows through a water pit without fluctuations in concentration, and continuously records these detected values.
Furthermore, no feedback and control by regulating circuits was possible.

The C measured in this way took more than 10 minutes.
The OD value and TOC value also do not match the BOD value, as can be understood from the difference in the measurement target.

BO″D measures the amount of organic substances in wastewater that are subject to biological metabolism, whereas the COD method measures the amount of substances in wastewater that can be oxidized by an oxidizing agent, and the TOC method measures the amount of organic substances in wastewater that can be oxidized by an oxidizing agent. This is because the amount of carbon is measured.

In other words, BOD indicates the amount of reduced dissolved oxygen that is consumed when oxidizing using living organisms that exist in nature, so BOD is a measure of the amount of dissolved oxygen that is consumed during oxidation using living organisms that exist in the natural world. Substances that are most similar to purification effects and are difficult to biodegrade, such as plastic waste, are excluded from the measured values, so they are the most reliable as basic values when actually designing biological treatment facilities. I can put it there.

On the other hand, COD and TOC measurements involve strong oxidizing agents and heating operations, which introduce elements that cannot be expected to decompose or purify in the natural world.

Therefore, BOD is mainly used as an indicator for regulating water pollution, and to deal with this, BOD is used as a source of wastewater.
This makes it necessary to perform measurements and controls based on OD.

In order to convert measurement results to correspond to BOD values using either the COD method or the TOC method, the composition of the wastewater, which is specified by various variable factors such as raw materials and final processing agent products, which differ depending on the factory or facility, is required. It is essential to understand.

Furthermore, no matter which method is used to measure BOD, COD, or TOC, the automatic measuring device required for labor saving is extremely expensive.

Except in special cases, water becomes turbid due to organic matter dissolved in the water.

The inventor of the present invention focused on this point and as a result of investigating and researching many wastewaters, the BOD
It was found that there is a correlation between turbidity and turbidity.

Figure 1 is an example of this, where the output voltage of a turbidity meter is plotted on the vertical axis, and the BOD value is plotted on the horizontal axis, indicating the turbidity of wastewater from a dairy factory in a certain city, both plotted on a logarithmic scale graph. Figures 2 and 3, where the curves shown in the results were obtained, are wastewater from a cheese manufacturing factory, city milk, and butter manufacturing factory, respectively, and Figures 4 and 5 are for A and B, which are treated with phosphoric acid film. Figure 6 is a graph obtained from similar measurements of wastewater from the metal surface treatment factories of both companies, and wastewater from a simple septic tank at the company's research institute. I can see what is being shown.

The shape of the curve does not necessarily have to be gentle, and there is no difference in processing even a complicated curve as long as it can be processed by a computer.

However, in order for such a characteristic curve to be applicable, the emission source process must be of a single type, and as shown in Figures 1 and 2, for example, a factory producing a single variety of milk or cheese, or a As in the case of the metal processing plants using phosphoric acid coating on steel by companies A and B in Figures 4 and 5, the raw materials and treatment processes used hardly change, so the BOD and turbidity of the discharged wastewater are correlated in the graph. It can be controlled by

In the case of the city milk and butter manufacturing factory shown in FIG. 3, the ratio of production of city milk and butter within the same plant is constant X depending on the equipment, so it can be treated as a single type process.

In the case of a zero-company research institute in Figure 6, as long as there is no change in the personnel structure, it can be treated in the same way as a single-product production factory.

When wastewater from multiple types of processes is discharged within the same workplace, it becomes difficult to determine the correlation between turbidity and BOD after they have combined, as in the present invention. Before wastewater from disparate processes join together,
It is necessary to measure and control each process.

It goes without saying that the method of the present invention cannot be applied even if wastewater from a single process is discharged into a public sewer or the like.

From the above results, for wastewater from a single process,
It was confirmed that by measuring the turbidity, it was possible to correlate it with the actual BOD value.

Methods for physically measuring turbidity include a transmitted light method, a scattered light method, and a method that measures the ratio of transmitted light and scattered light.

With transmitted light type turbidity meters, if suspended solids produced by microorganisms present or generated in wastewater adhere to the surface of the sample container, they will block the transmission of light and cause errors in measured values.
It must be removed by cleaning, etc., and maintenance requires human labor, and automatic measurement is not possible.

It is not suitable for use in control, etc.

Therefore, in the present invention, a scattered light type turbidity meter that is not affected by dirt on the sample window is used as the detection end, and the part corresponding to the sample container or cell window is eliminated, and only the light source part and light receiving part of the turbidity meter are measured. It has a structure that allows it to float on the target wastewater surface.

FIG. 7 shows the turbidity detection end used in the present invention, and the whole is indicated by the number 1.

In the figure, 2 is a light source, and the light emitted from this S passes through a lens 3 and an aperture 4, and is scattered on the water surface and underwater 5.

This scattered light is detected by a light receiving section 6 using a 5pD (solar cell), Cd3 (cadmium sulfide) or pin photodiode, and is logarithmically amplified by an amplifier circuit shown in FIG. It is sent to a signal conversion device or other device, where it is converted to BOD based on the above-mentioned correlation between turbidity and BOD, and used as a control system of a wastewater treatment device.

7 in FIG. 7 is a float for floating and holding the detection section on the water surface.

FIG. 9 is a block diagram showing an embodiment in which a biological wastewater treatment device is automatically controlled based on the BOD value measured by the scattered light turbidity meter shown in FIG.

8 in the figure is a wastewater bit that flows into the wastewater treatment equipment, and the wastewater that flows into this bit is measured by a turbidity meter 9 and the BOD is determined.
Detect.

When the self-regulation value of the effluent from the process is set at 20ppQ], when the BOD value of the effluent is below 201]11E, the effluent is led to the storage tank 10, and when the BOD value is 20ppQ or higher, the effluent is guided to the storage tank 10. operates the pump or valve 12.13 to direct the reservoir 11 to the biological treatment device.

The wastewater introduced into the storage tank 10 is discharged after its pH is adjusted by the pH adjustment device 14.

After the pH of the wastewater led to the storage tank 11 is adjusted by a pH controller 15, the BOD is measured by a turbidity meter 16, and the wastewater is introduced into a biological wastewater treatment device 18 by a flow rate adjustment pump or valve 17. This allows the BOD load on the wastewater treatment device to be maintained in a favorable state.

Wastewater after biological treatment is measured by turbidity meter 19.
is measured, and if it is less than 20pIXn, it is discharged, and 201]p
In the case of H1 or higher, the discharge is stopped and biological treatment is continued. In the figure, 20 is a signal conversion device 6

[Brief explanation of drawings]

Figures 1 to 6 show a city milk manufacturing factory, a cheese manufacturing factory, a city milk manufacturing factory, a butter manufacturing factory, and a phosphoric acid film treatment for steel (
The output voltage V (!1-BOD value of the turbidity meter of the wastewater from the metal surface treatment factories of Company A and 8 companies that carry out Parkerizing) and the treated raw wastewater from the simple septic tank of Company 0's laboratory is This is a graph showing the correlation between the two using a logarithmic scale graph, FIG. 7 is an explanatory diagram showing the structure of the scattered light type turbidity meter used in the example of the present invention, and FIG. Amplifying circuit for amplifying the output from the turbidity meter, FIG. 9 is a block diagram showing a control loop of a treatment facility for detecting and controlling BOD of industrial wastewater according to the present invention. The components corresponding to each number are shown below. 1 is the turbidity detection end, 2 is the light source, 3 is the lens, 4 is the aperture, 5
is the part above the water surface and just below the water surface, 6 is the light receiving part, 7 is the float,
8 is a wastewater pit, 9 is a turbidity meter for measuring discharged water, 10 and 11 are storage tanks, 12 and 13 are pumps or valves, 14
15 is a pH adjustment device, 16 is a turbidity meter provided in the storage tank 11, 17 is a flow rate adjustment pump or valve, 1
8 is a biological wastewater treatment device, 19 is a turbidity meter provided at the final control end, and 20 is a signal conversion device.

Claims (1)

[Claims] 1. BO due to turbidity of wastewater discharged from a single process.
The method for detecting and controlling the D value includes (a) determining in advance the correlation between the turbidity of wastewater discharged from the single process and the BOD value; A step of detecting the turbidity with a turbidity meter and converting it into a BOD value of the wastewater based on the above correlation; c. Treating the wastewater according to the BOD value of the wastewater so that it falls within the permissible limit of discharge regulations and then discharging it. A method for detecting and controlling a BOD value based on the turbidity of wastewater characterized by stages. 2. A method for detecting and controlling a BOD value based on the turbidity of wastewater according to claim 1, wherein a scattered light turbidity meter is used as the turbidity meter. 3 BO due to turbidity of wastewater discharged from a single process
A device that detects and controls the D value includes (a) a wastewater pit into which wastewater from a single process flows, a mouth, a turbidity meter installed in the wastewater pit, and (c) amplification of the output signal from the turbiditymeter. an amplifier circuit; 2. converting the amplified output signal to a predetermined turbidity and BO;
An arithmetic circuit that converts the D value into a BOD value from the correlation; e. If the converted BOD value is within the permissible limit of wastewater regulations, the wastewater is discharged, and if it exceeds the permissible limit of the wastewater regulations, the wastewater is discharged. A device comprising: a flow path switching device that allows wastewater to flow into the treatment device; 4. The device according to claim 3, wherein the turbidity meter is placed on a float floating in the wastewater pit. 15. In the device according to claim 4,
The turbidity meter is a device configured to be a scattered light type turbidity meter. 6. In the device according to claim 3, the flow path switching device includes a first pump or a first valve that discharges wastewater from the wastewater pit, and a first valve that causes the wastewater to flow into the wastewater treatment device. A device comprising a second pump or a second valve. 7. In the device according to claim 3, the flow path switching device allows the wastewater to flow into the wastewater treatment device when the BOD value of the wastewater exceeds the permissible limit of the wastewater 1 regulation, A device configured to discharge wastewater if the BOD value of the wastewater is below the permissible limit of wastewater regulations. 8 Depending on the turbidity of wastewater discharged from a single processB
A device that detects and controls OD values includes: (a) a storage tank into which wastewater from a single process flows; a wastewater treatment device connected to the storage tank; and (c) wastewater treated by the wastewater treatment device. (2) A turbidity meter installed in the storage tank; (E) An amplification circuit that amplifies the output signal from the turbidity meter; and B.O.
(a) an arithmetic circuit that converts the D value into a BOD value from the correlation; A device comprising: 9. The device according to claim 8, wherein the turbidity meter is placed on a float floating in the storage tank. 10. The apparatus according to claim 9, wherein the turbidity meter is a scattered light type turbidity meter. 11. The apparatus according to claim 8, wherein the flow rate adjustment device is a pump or a valve capable of adjusting the flow rate. 12. The apparatus of claim 8, wherein the wastewater is configured such that the BOD value of the wastewater is controlled within acceptable limits for the design of the wastewater treatment system. 13. The device according to claim 8, wherein the discharge device is provided with a turbidity meter, and the BOD value of the discharged water is detected by the turbidity meter.