JPS6093952A - Continuous measurement of bod - Google Patents

Abstract

PURPOSE:To suppress the change in the BOD component in a standard solution and the generation of slime in a pipeline, in a BOD measuring method using a diaphragm type oxygen electrode and a microorganism electrode comprising a microorganism membrane, by adjusting the pH of the org. substance-containing standard solution to a predetermined value. CONSTITUTION:A measuring cell 5 is attached to the lower parts of a diaphragm type oxygen electrode 3 and a microorganism electrode 2 comprising a microorganism membrane. A buffer solution B, a specimen S, standard solutions C1-C3, a washing solution N and air are supplied to the measuring cell 5 according to a process preset by a control circuit 8 such as a microcomputer and the BOD value of the specimen S is calculated on the basis of the output current of the microorganism electrode 2. Each of the standard solution is an aqueous solution of a glucose-glutamic acid mixture and the pH thereof is adjusted to about 2-3. By using these standard solutions, the change in the BOD component in each standard solution is eliminated even in long-time continuous measurement and the generation of slime in the standard solution within a pipeline is suppressed and BOD can be measured continuously.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous BOD measurement method. More specifically, the present invention relates to a method of measuring EOD continuously over a long period of time using a microbial electrode formed by combining a diaphragm-type oxygen electrode and a microbial membrane.

Conventionally, various methods for measuring BOD using microbial electrodes have been proposed. As one of these, a neutral buffer solution is flowed into a flow cell equipped with a microbial electrode to maintain neutral conditions, and air is blown into the flow cell to maintain a substantially air-saturated condition. A method is carried out in which the amount of dissolved oxygen decreased in the 7μ corresponding to the BOD component in the liquid to be measured, that is, the amount of dissolved oxygen consumed by the metabolism of microorganisms, is detected and measured as the output of the diaphragm oxygen electrode. It is. Such measurements are performed based on the output when an organic matter-containing standard solution with a known BOD is supplied instead of the above-mentioned liquid to be measured.In other words, the output, BOD, and calibration are calculated every predetermined number of measurements. This is done by calibrating the m tube.

Conventionally, as the organic matter-containing standard solution, J.
A neutral glucose-g-tamic acid mixed standard solution, which is used as a standard solution for KOlog-210BOD measurement, is used.

However, using such conventional organic matter-containing standard solutions, BO
There were various problems when conducting continuous measurement tube D. One of the problems is that the BOD of an organic matter-containing standard solution, which is stored in a predetermined amount for long-term continuous measurement, gradually decreases over time, giving a large error to the measured value. Although the cause of this is not clear, it is thought that the BOD component in the standard solution is gradually decomposed and consumed. Therefore, it was necessary to replace each stored standard solution with a new standard solution within a short period of time. On the other hand, such a standard solution is guided into the flow cell through a pipe at a predetermined period, but during long-term continuous measurements, microorganisms in this pipe take in the standard solution as a substrate and proliferate, resulting in a large amount of microorganisms. There is also the problem that slime is generated, gradually blocking the piping system and reducing the flow rate, leading to complete blockage, or that the BOD component of the test liquid is consumed by the slime.

This invention was made in order to solve these conventional problems, and it does not cause measurement errors due to changes in the standard solution even during long-term continuous measurements, and it also eliminates slime in the standard solution pipe. It is an object of this invention to provide a method that can continuously measure BOD while suppressing its occurrence.

As a result of various studies, the inventors of this invention found that the pH of the organic matter-containing standard solution, which was conventionally used as a neutral solution, was increased from about 2 to
By adjusting the standard solution to 3, it is possible to perform measurements without causing a decrease in the BOD of the standard solution itself due to long-term use, and by using such a standard solution, slime problems in the pipes are also reduced. This invention was achieved by discovering the fact that ξ is possible.

Thus, according to the present invention, a liquid to be measured is supplied through a pipe in the presence of a neutral buffer and under S gas treatment into a measurement flow cell equipped with a diaphragm-type oxygen electrode and a microbial electrode consisting of a microbial membrane. Detect the output of the microbial electrode 3- by using the microbial electrode 3-, and compare this output with the reference output when supplying a standard solution containing organic matter with a known BOD, which is measured every predetermined number of measurements, to continuously determine the BOD of the liquid to be measured. pHFJ2 is used as the organic matter-containing standard solution for measurement.
A continuous BOD measurement method is provided, which is characterized in that it uses an aqueous organic matter solution that has been conditioned to ail.

The organic aqueous solution used in this invention is a swollen product and/or
Alternatively, an aqueous solution of an amino acid is suitable, and specific examples thereof include glucose, fructose, sucrose, 2-ctose, soluble starch, glycine, glutamic acid, histidine, and the like. A representative example of these is a mixed aqueous solution of Glucosug I tamic acid. However, organic compounds other than these, such as fatty acids and ayco-μ compounds, may also be used depending on the case. These concentrations are appropriately determined depending on the supply amount, microbial activity, etc.

In this invention, the pH of the organic substance aqueous solution is about 2 to 3.
is adjusted to The pH is usually easily adjusted by dissolving the organic substance in water and adding a small amount of a mineral acid such as hydrochloric acid, sulfuric acid, or nitric acid. Note that if the pH is less than about 2 (for example, pH 2), the acidity is too strong, and when introduced into the flow cell, the system becomes acidic even in the presence of a commonly used neutral buffer solution, and normal microorganisms cannot survive. There is a risk that the activity of the neutral buffer may be inhibited, and therefore it may be inappropriate to increase the amount of salt in the neutral buffer. Also, pE (exceeding about 3 (e.g. I)H4) and BOD
No effect can be expected to prevent or suppress deterioration or slime generation.

It is usually preferred to adjust the pH to about 3.

As the microbial electrode used in this invention, JP-A No. 54-4
A so-called microbial electrode used in publications such as T16998 and JP-A-56-108951 can be used.

Further, as the neutral buffer, a phosphate buffer with a pH of 1 is suitable (J), and one with a concentration of about 0.0 IM is suitable.

Note that it is more preferable to supply a cleaning liquid with a pH of about 3 to the measurement pipe for each measurement in order to prevent slime generation.

Hereinafter, the method of the present invention will be explained in more detail with reference to the accompanying drawings.

(1) shown in FIG. 1 is a BOD continuous measuring device, which is an embodiment of the measuring device that implements the method of the present invention.

(2) is a microbial electrode, which has a known configuration consisting of a combination of a diaphragm type oxygen electrode (3) and a microbial membrane (4).

A measurement cell/L/(5) is attached to the lower part of the microorganism electrode (2), and the liquid flowing into the measurement cell (5) from the liquid inlet (5a) and flowing out to the liquid outlet (5b) collects microorganisms. Membrane (4)
It is now possible to come into contact with The liquid is microorganism A11 (4)
K Make sure that the 1st liquid inlet (δa) and P are in effective contact with the liquid outlet (
5b) It is installed at a different position on the lower floor.

These microorganism electrodes (2) and measurement cell/L/(5) are
It is maintained at a predetermined temperature (for example, 30° C.) in a constant temperature water bath (6). ('1) is a carp-shaped flow path, and the length is determined so that the liquid reaches approximately a predetermined temperature while passing through the channel.

(8) is a control circuit such as a microcomputer, which controls the H street solution (B) and sample solution (S) according to preset procedures.
, standard solutions (C1) to CC5), cleaning solution (N) and air to the measuring cell (5), pumps (9) (10)
, air pump (12) and switching pulp (13). Also, based on the output current of the microbial electrode (2), B
Calculate the OD value.

Standard solutions CC1) to (Ca) are a mixed aqueous solution of glucose μ-sug p-tamic acid adjusted to pf (3) with hydrochloric acid and stored, and each has a BOD of 25 Da/1.5o1.
ag/, g and 1ooq//? 0 indicates a standard solution adjusted to pH 3. Note that the cleaning solution (N) was adjusted to pH 3 by adding hydrochloric acid to tap water.

Next, to explain the operation, first, phosphate buffer (0.01M
, pH 7) is supplied to the measuring cell A/(5) by the roller pump (9) to maintain neutral conditions in the cell, and the washing liquid (N) is supplied to the measuring cell A/(5) by the roller pump (9).
) and the measuring cell (5) via the roller pump (9)
supplied to In addition, air is constantly supplied from the air pump (12), so that the inside of the cell/l/(5) is exposed to air. The flow rate of the buffer solution (E) is, for example, 1.0
d/min, the flow rate of the cleaning solution (N) is, for example, lnwl1 min,
The air flow rate is, for example, 1000114/min.

When measuring a sample, the switching valve (13) is switched,
Instead of the cleaning liquid (N), a sample liquid (S) such as factory wastewater is supplied via a collection pump (No) and a filter (18). The supply of buffer solution (B) etc. are the same as before.

The output current of the mold electrode (2) is the BOD of the sample solution (S).
shows a decrease value proportional to .

As mentioned above, the sample liquid CF3) is supplied to the measurement cell (5) for about 5 minutes every 30 minutes, and the cleaning liquid (N) is supplied at other times.

At a predetermined calibration set time Kfk, the switching pulp (13) is switched to use the standard solution (Ct) instead of the cleaning solution (N).

(Ox) and (Os) are respectively supplied to the measurement set and measured for each. Each standard solution (C1
), (Os).

Since the BOD value of (C3) is known, the output value of the microbial electrode (2) for these is set to '1&', and the control circuit (8)
calibrates the standard curve. This calibration is performed every predetermined number of measurements, for example several times a day.

8- Based on the above calibration, the BOD of each sample solution will be measured continuously. And the standard solutions (Ct) to (C3) have pH
3, each BOD does not decrease even during long-term continuous measurements, making it possible to perform accurate measurements. In addition, the generation of slime is particularly suppressed in the standard solution supply pipeline, which is advantageous during long-term measurements.

Example 1 Conventional method 2 consisting of a mixed aqueous solution of glucose-sug μ-tamic acid
Prepare a neutral aqueous solution of the seed concentration and leave it indoors for 1 m.
Changes in BOD during this time were measured according to the JIS method. The results were as shown in Table 1.

Table 1 (Comparative Example) As can be seen, the BOD decreased after being left for one week, and it was found that the solution was unsuitable as a standard solution to be stored for continuous BOD measurement.

On the other hand, BOD preparation concentration 150 w/43 (BO
D-measured value 121. '? ) and added hydrochloric acid to adjust the pH to 3. Similar measurements were performed on a mixed aqueous solution of gucose-sug μ tannic acid, and the results showed that the BO
The D value was 1211, which was virtually unchanged, and it was found to be suitable as a standard solution for continuous BOD measurements.

Example 2 Results of continuous measurement of BOD using the device shown in Figure 1.
Slime was first observed to grow inside the standard solution supply tube after one week, but it was found that the growth thereafter was slow and there was no problem with continuous measurement for about 14 days.

Continuous measurements were performed in the same way except for using a pH 1 standard solution for the slippage, and slime was formed after 3 days, making measurements difficult after 1 week.

Example 3 In order to more quantitatively demonstrate the effect of Example 2, a siphon dripping system as shown in FIG. 2 was set up to measure the "degree of crushing".

Here, (21) is a vinyl tube with an inner diameter of 1 inch used for continuous measurement, and the length between A and B is 2 m, and % (2
0) is tap water, and (23) is a graduated cylinder. Here, the "stiffness" X was calculated using the formula: Dropped amount before continuous measurement (wl/mj-n) x 100.

The results are shown in Table 2.

Table 2 - It can be seen that the method of the present invention is advantageous in that it suppresses slime damage.

Example 4 EOD of initial sedimentation effluent of a certain sewage treatment plant using the device shown in Figure 1.
was measured. Here, the neutral buffer is 0. OIM.

A phosphate M balanced solution of 1 l-pH was used, and the flow rate by the pump (9) was 1.66 d/min for both the standard solution side and the buffer solution side.

The BOD value obtained by this measurement and the BOD value determined by the JIS method had a good correlation coefficient of 0.88 at 26 measurement points. This shows that even if the pH of the standard solution is lowered to about 2 to 3, there will be no adverse effect on the microbial electrode itself.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram illustrating a measuring device suitable for carrying out the BOD continuous measurement method of the present invention, and FIG. 2 is a schematic diagram illustrating an instrument for measuring "Tsumashi degree" in Example 3. . (1)...BOD continuous measuring device, (2)...microbial electrode, (3)...diaphragm oxygen electrode, (4)...microbial layer, (5)...measurement p, (
5a)...Liquid inlet, (5b)...Liquid outlet, (9)
... Roller pump, (10) ... Collection pump, (
12)...Air pump, (13)...Switching pulp,
12- (B)... Neutral buffer solution, (S)... Sample solution, (N)
...Cleaning liquid, (Ct) (Cz) (Cm) ...
41 Early liquid.

Claims (3)

[Claims] (1) Into a measurement cell 70 equipped with a microbial electrode consisting of a diaphragm-type oxygen electrode and a microbial membrane, in the presence of a neutral buffer solution and under aeration treatment, a liquid to be measured is supplied through a pipe to the microbial electrode. The BOD of the liquid to be measured is continuously measured by detecting the output of the sample and comparing this output with the standard output when supplying a standard solution containing organic matter whose BOD is known and which is measured over a predetermined number of measurements. KARANASHI: A continuous BOD measurement method in which the organic matter aqueous solution adjusted to pH approximately 2 to 3 is used as the organic matter-containing standard solution. (2) The measuring method according to claim 1, wherein the organic substance aqueous solution is a rehydrated product and/or an amino acid aqueous solution. (3) The measuring method according to claim 1 or 2, wherein the organic substance aqueous solution is a glucose-glutamic acid mixed aqueous solution.