JPH02259564A - Method and instrument for measuring bod - Google Patents

Abstract

PURPOSE:To eliminate the possibility of clogging even with a sample contg. insoluble materials and to allow exact measurement of BOD by inverting the flow direction of the liquid in a column when prescribed timing is attained. CONSTITUTION:The measuring instrument is constituted of the column 7 fixed with aerobic microorganisms, a liquid feed means consisting of liquid feed pumps P1, P2 and solenoid valves V1 to V6 which feed the liquid without contg. org. matter and sample liquid to be measured, oxygen concn. meters 9, 11 which detect the difference in the oxygen concn. of the liquid which does not contain the org. matter and the sample liquid past the column, as well as a rotary valve 5 which inverts the liquid flow direction to the column 7. The liquid which does not contain the org. matter and the sample liquid to be measured are separately passed to the column 7 fixed with the aerobic microorganisms and the flow direction of the liquid in the column 7 is inverted when the prescribed timing is attained. The BOD of the sample liquid is determined from the difference in the oxygen concn. of the respective liquids after the passage through the column 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to BOD measurement, and more particularly to a BOD measurement method and apparatus using a BOD sensor that combines immobilized microorganisms and an oxygen electrode.

[Prior Art] BOD refers to the amount of dissolved oxygen consumed by aerobic microorganisms in water, and is considered a basic indicator of water pollution caused by organic substances. The official test method for BOD is stipulated in the Japanese Industrial Standards (JISK-0102-1972), but this measurement method not only requires a long time of 5 days, but also requires complicated measurement operations. I need. Against this background, there is a strong desire to develop a BOD measurement method that can be measured easily and in a short time, and for some time, a method that combines immobilized aerobic microorganisms on a water-insoluble carrier and an oxygen electrode has been proposed. To the BOD sensor,
A liquid that does not contain organic matter, such as ion-exchanged water or a buffer solution, and a sample solution are fed separately, and at this time, the difference in the amount of oxygen decreased due to oxygen consumption by the immobilized microorganisms is quantified using an oxygen electrode.
Measurement methods for determining the BOD value of test liquids are being researched.

The form of the BOD sensor is as shown in Fig. 12.
An electrode contact type in which immobilized microorganisms 101 and oxygen electrode 102 are integrated, and a buffer solution after filling a cylindrical column with immobilized microorganisms 1O1 and passing through this column, as shown in FIG. There is also a column-type device in which the oxygen concentration of the sample liquid is detected using an oxygen electrode 102. 103 in the figure is a dissolved oxygen meter that calculates dissolved oxygen from the detection signal of the oxygen electrode 102.

[Problem to be solved by the invention] Incidentally, in the electrode contact type BOD sensor, diffusion of the sample liquid to the oxygen electrode 102 is a requirement, and therefore only substances dissolved in the sample liquid can be measured, and insoluble substances can be measured. The problem is that it is not detected.

On the other hand, if it is a type that allows the sample liquid to pass through, such as a column-type BOD sensor, it is possible to measure BOD even if the sample liquid contains insoluble substances, but this insoluble substance can pass through the column. When this happens, it accumulates in the column and causes clogging, resulting in the inability to feed the sample liquid at a constant flow rate, resulting in measurement errors or problems in which the liquid cannot be fed at all. Furthermore, when clogging occurs, it is necessary to remove the clogging and discharge it to the outside.

The present invention has been made to solve the above problems, and provides a column-type BOD sensor that enables accurate OD measurement even for sample liquids containing insoluble substances without the risk of clogging. The purpose is to provide a measurement method and device.

[Means for Solving the Problems] The BOD measurement method of the present invention involves passing a liquid containing no organic matter and a sample liquid to be measured separately through a column on which aerobic microorganisms are immobilized, and removing oxygen from the eight liquids after passing through the column. A BOD measuring method of determining the BOD of a sample liquid from the difference in concentration is characterized by reversing the flow direction of the liquid in the column at a predetermined timing. a liquid-containing column, a liquid-feeding means for sending a liquid containing no organic substances and a sample liquid to be measured to the column, and an oxygen concentration detection means for detecting a difference in oxygen concentration between the liquid containing no organic substances and the sample liquid after passing through the column. , and a liquid flow direction reversing means for reversing the liquid flow direction to the column.

[Function] According to the BOD measuring device to which the BOD measuring method of the present invention is applied, the liquid flow direction reversing means reverses the direction of flow into the column, for example, when switching between a liquid containing no organic matter and a sample liquid. This will prevent insoluble substances contained in the sample solution from accumulating on the column.
By backflowing a buffer solution or the like that does not contain organic matter into the column, accumulated insoluble substances are discharged.

[Example] Column type BO to which the present invention is applied in Figs. 1 and 2
An example of a D measuring device is shown.

1 is a sample liquid to be measured, and 2 is a standard sample liquid whose BOD value is known. 3 is a buffer solution. These 8
Liquids 1 to 3 are kept saturated with dissolved oxygen by blowing air from an air pump.

Vl-V4 and ■5 to ■6 are electromagnetic valves (hereinafter simply referred to as valves), and PI and P2 are liquid pumps. By opening and closing these valves v1 to v6 as appropriate to drive the liquid pumps Pi and P2, the six liquids 1 to 3 are
is selectively delivered.

5 is a rotary valve, and in Fig. 1, pipe Q1
and Q2, QB and Q4, QB and QB, and Ql and QB are each connected by a rotary valve 5. In FIG. QB, Q4 and QB,
QB and Ql, and QB and Ql are now connected, respectively.

The outlet of pump P1 is connected to piping Ql, and the outlet of pump P2 is connected to piping Q6.

6 is a sample loop for retaining a certain amount of sample liquid 1 or standard sample liquid 2, and is provided between piping Q7 and Q2. 7 is a cylindrical column in which microorganisms are immobilized, and is provided between piping Q3 and QB. 8 is
A flow cell is installed in the drain pipe from the pipe Q8, and 9 is an oxygen concentration meter for detecting the dissolved oxygen concentration of the six liquids flowing through the pipe Q8. lO is
This is a flow cell installed in the drain pipe from the pipe Q4, and 11 is an oxygen concentration meter that detects the dissolved oxygen concentration of the six liquids in the flow cell IO.

There are two methods for measuring BOD using the apparatus shown in FIGS. 1 and 2. The first method is a continuous method in which a buffer solution and a sample solution are alternately and continuously fed to the column 7 for a fixed period of time.

In this continuous method, the sample loop 6 merely serves as a pipe. The second method is a volumetric method in which a fixed volume of sample liquid is held in the sample loop 6 and is flushed with a buffer solution at fixed time intervals to be sent to the column 7. Volumetric methods are generally suitable for measuring high BOD samples.

First, the operation when the apparatus shown in FIGS. 1 and 2 is used as a continuous method will be explained.

The rotary valve 5 is set to the rotational position shown in FIG. 1, valves Vl, V2 and v5 are opened, and valves V 3 , V
4 and v6 are closed, and the pumps P 1 and 'P2 are operated (open valves are blacked out in the figure). As a result, the sample liquid l is fed by the pump PI, and the sample liquid l is
From there, it passes through the rotary valve 5, flows into the pipe Q2 (hereinafter written as Ql → Q2), passes through the sample loop 6,
It flows from Q7 to Q8 and is discharged as drain after passing through the flow cell 8.

On the other hand, buffer solution 3 is driven by pump P2, passes through QB-QB via valve v5, flows into column 7 from the right end in the figure, passes through Q3→Q4, passes through flow cell 10, and is discharged as drain. .

The operation of passing the buffer solution 3 through the column 7 in this manner is called loading. This loading state is performed for about 5 minutes, during which time,
The dissolved oxygen concentration Do, s of the sample solution 1 is determined by the oxygen concentration meter 9.
is detected, and the dissolved oxygen concentration Do, b after the buffer solution 3 passes through the column is detected by the oxygen concentration meter 11.

After this loading operation is completed, the rotary valve 5 is rotated clockwise to the position shown in FIG. 2, and the valve V2. Open V3 and ■6, and open valves Vl, V4 and V.
Close 5. As a result, the sample liquid 1 is pumped by the pump P2 to the valve V2. Via V3, pass through Q6→Q7→sample loop 6→Q2→Q3, then enter column 7 from the left end, then pass through Q5→Q4, and flow into the flow cell lO
After passing through, it is discharged. On the other hand, the buffer solution 3 is pump P
1, it passes through the valve V6, Ql-QB, and the flow cell 8, and then is discharged. The operation of passing the sample liquid 1 through the column 7 in this manner is called injection.

This injection was carried out for about 5 minutes, during which time the oxygen concentration meter 9 detected the dissolved oxygen concentration DO,b of the buffer solution 3, and the oxygen concentration meter 11 detected the dissolved oxygen concentration of the sample solution 1 after passing through the column. The concentration Do,s is detected.

After this injection operation is completed, the above-mentioned loading operation resumes, and the loading operation and the injection operation are repeated every 5 minutes.

Now, the above detected concentrations, DO+S, DO!
b, D In O1bDots, D O, b-D
O, b indicates the difference in dissolved oxygen concentration △DOb between before and after the buffer solution 3 passes through column 7, and this difference in dissolved oxygen concentration △DOb is caused by the internal concentration of immobilized microorganisms in column 7. It is associated with the consumption of living breath.

On the other hand, DO+5-Dots indicates the difference in dissolved oxygen concentration △DOs before and after the sample liquid 1 passes through column 7. This includes the oxygen consumption during oxidation and the oxygen consumption associated with endogenous respiration described above. Therefore, △DO=△Dos-△DOb = (DO+s Down) (DOlb DOtb
)...(1) The ΔDo obtained from this is the net decrease in oxygen consumed due to the assimilation of organic matter.

In addition, if the oxygen reduction amount △DO0 for the standard sample liquid 2 whose BOD concentration is known instead of the sample liquid 1 is determined by the same operation as described above, the BOD of this standard sample liquid 2 can be calculated.
Using the relationship between the OD concentration and the oxygen decrease amount ΔDo0, the BOD concentration for the sample liquid 1 in which the oxygen decrease amount is ΔDo can be determined.

By the way, in the above apparatus, if the sample liquid 1 is injected into the column 7 and the sample liquid 1 contains insoluble substances, the inert substances will accumulate inside the column 7 and cause clogging. However, during loading after 5 minutes, the buffer solution 3 flows back into the column 7, so the insoluble substances accumulated in the column 7 are discharged as drain.

FIG. 9 is a graph showing the pressure increase on the inlet side of column 7 due to column clogging. The Δ mark indicates the operation in which a sample solution containing the same inert substance is injected in one direction into column 7 for 5 minutes, and the buffer solution flows back into column 7 for the next 5 minutes. It shows the pressure increase value when repeated.

As can be seen in this graph, when a sample solution containing an inert substance is continuously injected in one direction, clogging occurs and the inlet feed pressure of column 7 increases, but the direction of inflow into column 7 is reversed. When this was done, there was almost no pressure increase, and therefore, the accumulated insoluble material was expelled by backflow injection of buffer solution.

Fig. 1θ shows the dissolved oxygen concentration DO of the sample detected by the above-mentioned device, and the base value X is kept almost constant. On the other hand, for comparison, the dissolved oxygen concentration DO when the direction of inflow into the column 7 is not reversed is shown in FIG. 11, and in this figure, the base value X° gradually decreases. This is thought to be due to the accumulation of insoluble substances within the column. When the base value decreases in this way, the detection range of the dissolved oxygen concentration DO becomes narrower, and the measurement accuracy also decreases.

Figures 3 and 4 are the BO of the continuous method in Figures 1 and 2.
A schematic diagram of a D measuring device configured with only ordinary valves is shown.

Figure 3 shows the loading state, with valves V12 and V
l 3. V15. V l B and V 19 are open, and the buffer solution 3 flows into the column 7 from the upper end in the figure.

FIG. 4 shows the state at the time of injection, with valve V11.
V12. V16. V17. V2O is in an open state, and the sample liquid 1 flows back through the column 7 from the bottom end.

Next, a measurement method using the volumetric method using the BOD measurement apparatus shown in FIGS. 1 and 2 will be explained with reference to FIGS. 5 and 6.

FIG. 5 shows the loading state. rotary valve 5
is in the same rotational position as shown in Figure 1, and the valve ■
The opening/closing states of 1 to 6 are also the same as in FIG. The operation in this loaded state is also the same as that described in connection with FIG.
The buffer solution 3 flows into the column 7 from the right end, passes through the flow cell IO, and is measured by the oxygen concentration meter 11 to measure the oxygen concentration DO of the buffer solution 3 after passing through the column.
s is detected.

After this loading state continues for about 10 minutes, for example, the injection state shown in FIG. 6 is entered. In FIG. 6, the rotary valve 5 is in the same rotational position as in FIG. 2, and valves 1 to V6 are the same as in FIG. 5 without any change. In this injection state, the sample liquid l is pumped by the pump 1 through the valve V2. It flows through rotary valve 5 to Ql-QB via Vl, passes through flow cell 8, and is discharged as drain 4, without passing through sample loop 6.

On the other hand, buffer solution 3 flows from valve V5 through Q6 → Q7 → sample loop 6 → Q2 → Q3, flows into column 7 from the left end, then passes through Q5 → Q4, and enters flow cell 10 by pump P2. , the oxygen concentration after passing through column 7 is detected. In the route just described, the buffer solution 3 comes to pass through the sample loop 6, so the sample solution 1 that remained in the sample loop 6 in the loading state is injected into the buffer solution 3 in this injection state. You will be swept away by this. When the sample liquid 1 passes through the column 7, the organic matter contained in the sample liquid 1 is assimilated by the immobilized microorganisms and oxygen is consumed, so the sample liquid 1 in which this oxygen has been consumed passes through the flow cell 10. At this time, the oxygen concentration detected by the oxygen concentration meter 11 temporarily decreases. Assuming that the oxygen concentration at which the oxygen concentration has become lowest is DO4, the amount of oxygen decrease ΔDo in the sample liquid 1 can be determined by the following equation.

ΔDO=DOa−Do.

FIGS. 7 and 8 are configuration diagrams in which the volumetric measuring device shown in FIGS. 5 and 6 is implemented using an ordinary valve. In the loaded state shown in Fig. 7, valves V12, VlB, and V15
．． VlB and V19 are open, and the buffer solution 3 flows into the column 7 from the top end. On the other hand, in the injection state shown in FIG. 8, the buffer solution 3 pushes out the sample solution 1 in the sample loop 6. and enter column 7 from the bottom end.

[Effects of the Invention] As explained above, since the direction of liquid flow in the column is reversed, even if insoluble substances accumulate in the column due to liquid feeding in one direction, the direction of liquid flow can be reversed. By inverting, the accumulated insoluble substances are discharged, preventing clogging, and therefore, sample liquid etc. can be supplied at a constant flow rate, allowing highly accurate BOD measurement. Incidentally, if the liquid flow direction in the column is reversed when switching between the buffer solution and the sample liquid, the effort of reversing the liquid flow direction can be saved.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are configuration diagrams showing one embodiment of a BOD measuring device to which the BOD measuring method of the present invention is applied.
The figure shows the loading state in the continuous method, and the second
The figure shows the injection state in the continuous method, Figures 3 and 4 are block diagrams of the apparatus shown in Figures 1 and 2, respectively, implemented with a normal valve, and Figures 5 and 6 are , is a configuration diagram showing another embodiment of the BOD measuring device to which the BOD measuring method of the present invention is applied, FIG. 5 is a diagram showing the loading state in the volumetric method, and FIG. 6 is a diagram showing the loading state in the volumetric method. Figures 7 and 8 are diagrams illustrating the state, respectively, are configuration diagrams of the apparatuses shown in Figures 5 and 6 using a normal valve, and Figure 9 is a diagram showing the apparatus shown in Figures 1 and 2. Figure 1O shows the dissolved oxygen concentration detected by the apparatus shown in Figures 1 and 2. Figure 2 shows the dissolved oxygen concentration detected by a conventional BOD measurement device, and Figure 12 shows the BOD of the electrode contact type.
FIG. 13 is a schematic diagram of a column-type BOD sensor. 1...Sample solution, 3...Buffer solution, 5...Rotary valve, 6...Sample loop, 7...Column, 8 ■0...Flow cell, 9.11
...Oxygen concentration meter, V l ~V 6. V 11 to V 20 = - valve.

Claims (4)

[Claims] (1) A BOD measurement method in which a liquid containing no organic matter and a sample liquid to be measured are passed separately through a column fixed with aerobic microorganisms, and the BOD of the sample liquid is determined from the difference in oxygen concentration of each liquid after passing through the column. , A BOD measurement method characterized by reversing the flow direction of the liquid in the column at a predetermined timing. (2) The BOD measurement method according to claim (1), wherein the direction of liquid flow in the column is reversed when switching between feeding the organic substance-free liquid and the sample liquid to the column. (3) A column on which aerobic microorganisms are immobilized, a liquid feeding means for sending a liquid containing no organic matter and a sample liquid to be measured to the column, and a difference in oxygen concentration between the liquid containing no organic matter and the sample liquid after passing through the column. What is claimed is: 1. A BOD measuring device comprising: an oxygen concentration detecting means for detecting oxygen concentration; and a liquid flow direction reversing means for reversing the direction of liquid flow to the column. (4) The BOD measuring device according to claim 3, wherein the liquid flow direction reversing means operates in response to switching between feeding a liquid containing no organic matter and a sample liquid to the column by the liquid feeding means.