JP2007064741A - Bod measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a BOD measuring method capable of securing a sufficient dilution ratio, and capable of measuring accurately a BOD without being affected by an inhibitor. <P>SOLUTION: In this BOD measuring method of diluting a raw water of a BOD measuring object with dilution water to measure the BOD based on a dissolved oxygen consumption of the diluted water mixture after a prescribed time, the dilution is regulated to be brought into the dilution ratio capable of eliminating an influence of an inhibitor concentration of generating biological inhibition, and to make a BOD concentration of the dilution water bring a recommended measured value of the BOD in the water mixture. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a BOD measurement method for measuring BOD (biological oxygen demand) in waste water.

  Various methods for measuring BOD in wastewater have been proposed (see, for example, Patent Document 1). The present invention relates to a method for accurately measuring BOD by a method defined in JIS without being affected by an inhibitor.

  The method for measuring BOD is generally carried out in accordance with JIS K0102-21 (old K0400-21). In this case, the BOD is calculated by the difference between the numerical value (mg / L) before and after the test of the dissolved oxygen concentration of the waste water as the specimen. In other words, when organic matter is present in the waste water, dissolved oxygen in the waste water is consumed in the decomposition. The test is conducted at 20 ° C. for 5 days. Usually, the saturated dissolved oxygen concentration is 8.84 mg / L in pure water at 20 ° C. and 1 atm. For this reason, the wastewater with a high organic substance concentration cannot be measured as it is, but dilution is performed, and the BOD of the wastewater is obtained from the measured value after dilution and the dilution factor. In JIS, the dilution ratio is determined as follows.

_{C 1/3 <(C 1} -C 2) <2 × C 1/3
Where C ₁ : concentration of dissolved oxygen before incubation of the diluted sample (mg / L)
C ₂ : concentration of dissolved oxygen (mg / L) after 5 days of diluted sample
In the above formula, since (C ₁ -C ₂ ) corresponds to BOD, the measured BOD is required to be between 3 and 6 mg / L from the relationship with the saturated dissolved oxygen concentration described above. Usually, the original waste water (raw water) is diluted with a target of 4.4 mg / L which is an intermediate value. For example, when the BOD of raw water is 6,000 mg / L, the dilution is about 1360 times (6000 ÷ 1360 = 4.41).

  Thus, when the BOD concentration of raw water is high, a large dilution ratio can be taken. The fact that the dilution factor can be increased can eliminate the influence of the inhibitor even if the wastewater contains an inhibitor that causes biological inhibition.

  However, if the BOD of the wastewater is not so high, even if an inhibitor is present, a sufficiently large dilution factor can be taken for dilution to obtain the target measurement value: 4.4 mg / L. Disappear. For example, when the BOD is estimated to be about 40 mg / L, the dilution factor is 9 times. Thus, when the dilution factor is about 9 times, the inhibitor concentration may not be sufficiently small, and biological inhibition may appear.

  Under the above conditions, the measured value of BOD should be originally 4.4 mg / L from the following formula, but actually becomes a value smaller than 4.4 mg / L due to biological inhibition.

40 mg / L ÷ 9 = 4.4 mg / L
For this reason, the measured BOD concentration rebated is smaller than the original value of 40 mg / L. That is, a phenomenon in which the BOD varies depending on the dilution rate occurs, and the true BOD cannot be recognized.
JP 2002-333440 A

  As described above, when the dilution factor necessary for the BOD measurement is smaller than the dilution factor necessary until it is not affected by the inhibitor, the influence of the inhibitor occurs, and it is difficult to accurately measure the BOD.

  In other words, with the recommended dilution factor required for BOD measurement, the influence of the inhibitor may not be negligible, and in this case, the correct BOD cannot be measured. Moreover, if it dilutes to the magnification which does not show the influence of an inhibitor, it will become smaller than the measurement BOD density | concentration recommended by JIS. Thus, when an extremely small BOD concentration is obtained, an error when rebating becomes large.

  An object of the present invention is to provide a BOD measurement method capable of taking a sufficient dilution ratio and accurately measuring BOD without being affected by an inhibitor.

  The BOD measurement method of the present invention is a BOD measurement method in which raw water to be measured for BOD is diluted with dilution water, and BOD is measured from the dissolved oxygen consumption after a predetermined time of the diluted mixed water. The dilution ratio is such that the influence of the inhibitor concentration causing the biological inhibition is eliminated, and the BOD concentration of the dilution water is adjusted so that the BOD of the mixed water becomes the recommended measurement value.

  In the present invention, the recommended measurement value is an appropriate value between 3 and 6 mg / L.

  In the present invention, diluted water whose BOD concentration is adjusted with an artificial substrate or the like is used.

  Furthermore, in the present invention, the inhibitor is any one of various heavy metals, chelating agents, disinfectants such as sodium hypochlorite, surfactants, tannin, lignin or nitrate ions, nitrite ions, hydrogen sulfide and the like.

  According to the present invention, by adjusting the BOD concentration of the dilution water with respect to the raw water, it can be diluted with a sufficient dilution factor that does not affect the inhibitor concentration, and can be measured with the recommended measurement value. Can be measured.

  Hereinafter, an embodiment of a BOD measurement method according to the present invention will be described in detail.

  The BOD measuring method of the present invention is a BOD measuring method in which raw water to be measured for BOD is diluted with diluted water, and BOD is measured from the dissolved oxygen consumption after a predetermined time of the diluted mixed water. In this case, the dilution is performed at a dilution ratio that eliminates the influence of the inhibitor concentration that causes biological inhibition, and the BOD concentration of the diluted water is adjusted so that the BOD of the mixed water becomes a recommended measurement value.

  For example, wastewater in which an inhibitor is mixed (inhibited substances include various heavy metals, chelating agents, disinfectants such as sodium hypochlorite, surfactants, tannin, lignin, etc.) or inhibitors When the wastewater generated in the treatment process (nitrate ions, nitrite ions, hydrogen sulfide, etc. are generated by biological treatment) is purified by biological treatment, the BOD of the treated water is accurately determined (with no difference in value depending on the dilution factor) ) Need to measure. The present invention is a method used in such a case, and BOD can be accurately measured without being affected by an inhibitor in waste water.

  Here, the dilution water in the conventional method is obtained by adding various salt solutions to distilled water or water of equivalent purity, and is free from organic substances, oxidizing or reducing substances, and metal contamination. However, in this diluted water, as described above, true BOD may not be measured in the presence of an inhibitor.

  Therefore, a sample whose BOD concentration is known in advance is prepared with an artificial substrate (added with sucrose and nutrient salts) and distilled water. The BOD concentration in this document is, for example, BOD 4.4 mg / L, which is the measurement target of the conventional method. Further, this sample is aerated to obtain diluted water having a DO (dissolved oxygen concentration) of 8 mg / L or more.

  In the example of the raw water, where the BOD is estimated to be about 40 mg / L, it is assumed that 50-fold dilution is necessary to eliminate the influence of the inhibitor. When measured by the conventional method, the following equation is obtained.

40 mg / L ÷ 50 = 0.8 mg / L
In this case, the measured value: 0.8 mg / L does not fall within the range of the recommended measured value: 3-6 mg / L described above, and is difficult to measure.

  In addition, if a 5-fold dilution is performed by the conventional method, the following equation is obtained.

40 mg / L ÷ 5 = 8.0 mg / L
In this case, the measured value: 8.0 mg / L is not in the range of the recommended measured value: 3 to 6 mg / L described above, and is a case where measurement is not possible. However, in actuality, it can be measured within the recommended value due to the influence of the inhibitor, and there is a possibility of erroneous measurement.

  On the other hand, in the method of the present invention, in the example of raw water where BOD is estimated to be about 40 mg / L, using dilution water adjusted to BOD of 4.4 mg / L, the influence of the inhibitor is reduced by 50 times. It shall be diluted. In this case, the BOD measurement value of the mixed water diluted under the above conditions is as follows.

(40 × 1 + 4.4 × 49) ÷ 50 = 5.1 mg / L
The measurement value in this case: 5.1 mg / L falls within the range of the recommended measurement value described above: 3 to 6 mg / L, and accurate measurement is possible. That is, an accurate BOD measurement that is not affected by the inhibitor can be performed.

  Thus, even if the dilution is sufficiently performed until the influence of the inhibitor is eliminated, the BOD value falls within the recommended measurement value, and a reliable numerical value is obtained.

  If the BOD concentration of the water to be measured is predicted to be 100 mg / L or higher, increase the dilution factor or set the BOD concentration of the diluted water to the recommended minimum value of 3 mg / L.

  Table 1 below shows BOD (mg / L) values when 50-fold dilution is performed. The dilution water, mixed water, and measured water in Table 1 are defined as follows.

  Dilution water: The BOD concentration is known in advance.

  Mixed water: After diluting and mixing, the BOD concentration is actually measured.

Water to be measured: Water whose raw BOD concentration is desired (raw water).

  Thus, even if BOD of to-be-processed water (raw water) is 9.4-153.0, the influence of an inhibitor does not come out by adjusting BOD of dilution water to 4.4-3.0. By diluting at a dilution factor of 50 times, the measured value of the mixed water becomes a value of 4.5 to 6.0 which is within the range of recommended measured value: 3.0 to 6.0. From this, it is possible to accurately measure the BOD of the water to be treated without being affected by the inhibitor.

Claims (4)

A method for measuring BOD, in which raw water for BOD measurement is diluted with dilution water, and BOD is measured from dissolved oxygen consumption after a predetermined time of the diluted mixed water,
The dilution is performed at a dilution ratio that eliminates the influence of the inhibitor concentration causing bioinhibition, and the BOD concentration of the diluted water is adjusted so that the BOD of the mixed water becomes a recommended measurement value. Method.   The BOD measurement method according to claim 1, wherein the recommended measurement value is an appropriate value between 3 and 6 mg / L.   The method for measuring BOD according to claim 1 or 2, wherein dilution water whose BOD concentration is adjusted with an artificial substrate or the like is used.   The inhibitor is any of heavy metals, chelating agents, disinfectants such as sodium hypochlorite, surfactants, tannin, lignin or nitrate ions, nitrite ions, hydrogen sulfide, etc. 2. The BOD measuring method according to 1.