JPS5999353A - Method and apparatus for measuring bod - Google Patents

Abstract

PURPOSE:To enable a continuously automatic measurement repeatedly at each of a set time by automatically measuring the required time for biochemical oxidation until the dissolved oxygen density begins to increase rapidly from the time of adding sample water to determine the BOD from a relationship between a BOD value prepared beforehand and the required time for the biochemical oxidation. CONSTITUTION:An activated sludge is automatically sampled into a measuring tank 1 while the sampling level is sensed with a level meter. An agitator 2, a dissolved oxygen density measuring devices 3 and 8, automatic pH adjustors 4 and 7, activated sludge densitometers 3 and 9 and an aerator 5 are attached as fixed in a constant temperature water tank 6 automatically adjusted to 20+ or -1 deg.C. Measured values of pH, DO and activated sludge density are transmitted to an arithmetic section 11. Upon the addition of a sample water, the aeration process is put into operation and a timer 10 starts. As the BOD source added is treated biologically, the dissolved oxygen density increases. When a set value is reached, the timer and the aeration process are stopped and the time is transmitted to an arithmetic circuit which calculates BOD for conversion by an arithmetic expression and the results are displayed digitally 15 and recorded with a recorder 16. Subsequently, a measuring device is cleased up with a cleaning device 14 to complete one process.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for rapidly measuring the biochemical oxygen demand (BOD) of industrial wastewater and other wastewater to be treated.

In wastewater treatment using the activated sludge method, BOD is an important management index, and its measurement is essential for proper and prompt treatment.

In the standard method for measuring BOD, 40-70% of the initial amount of dissolved oxygen is used, so it can be applied as is to water samples with a commensurately low BOD, but the BOD measurement range is To measure extremely narrow and high BOD water samples, it is necessary to dilute with water. Also, B
As countermeasures to widen the OD measurement range, the reaeration method, pressure detection method, and volume compensation method are known, but all of them require a long time of about 5 days to measure, and the measured value and The relationship with the total BOD after 5 days also fluctuated, making it impossible to perform proper and efficient sewage treatment. In addition, in order to measure BOD in a short period of time, a method was proposed in which the inflection point of the oxygen uptake rate was found on a recording paper using the Coulome l-I) equation, but even with this method, measurement results could not be obtained. It takes 0.2 to 2 days for this to occur, making it unsuitable for use as an output for automatic control. The measurement period of the 30D, which was a bottleneck for properly and quickly purifying industrial wastewater that is continuously discharged, and especially for doing so through automatic control, has been significantly shortened, making it quick and accurate. By finding a way to measure such 6
The goal was to develop a 111 constant system.

In line with such social demands, the present inventors have conducted intensive research on a method that can measure BOD extremely quickly, and as a result, we have discovered a desirable method for measuring BOD with high accuracy in a short time of about 10 to 30 minutes. and a device, leading to the present invention.

That is, in the present invention, a suspension of activated sludge that is well adapted to the organic substances (BOD components) in the test water to be measured is placed in a measurement container, and the dissolved oxygen concentration in the suspension is continuously measured while stirring at a constant speed. After confirming that the dissolved oxygen concentration due to endogenous respiration is almost at Oppm, a certain amount of sample water is added and aerated at one time, and the dissolved oxygen concentration is decreased from the time of addition of the sample water. B
As a method for measuring OD and a device suitable for the measurement,
BOI) measurement tank with aeration device and stirrer, pH
An automatic adjustment device, an automatic dissolved oxygen concentration measuring device connected in parallel with a terminal located in the measuring device, an automatic activated sludge concentration measuring device and a calculation section connected via a timer, a sample water addition device, and an activated sludge supply. Dissolved oxygen transfer efficiency, activated sludge endogenous respiration rate, and J■S measurement value conversion correction coefficient can be inserted in advance into the above-mentioned calculation section, and a recording section is connected to electronically transmit, display, and record the calculation results. Quick BO'
The present invention provides a D measuring device.

According to the device of the present invention and the BOD measurement method using the same, everything from collecting the sample water to displaying the measurement results is automated, the measurement error is within 20%, and the BOD measurement method is performed continuously and automatically at each set time. Measurements can be made repeatedly.

Based on the rapid BOD measurement results obtained by the present invention, the present invention is applied to similar wastewater treatment equipment, and by automatically controlling each part based on this output, purified treated water is constantly being produced, contributing to environmental conservation. It's something you get.

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

Figure 1 is a graph showing the correlation between BOD concentration and dissolved oxygen (DO) concentration and elapsed time when a certain amount of activated sludge is aerated and sample water is added.The solid line is the DO concentration (pp.
m ) and the dotted line shows the temporal change in BOD concentration. In addition, point A in the figure is when a certain amount of sample water has been converted into activated sludge, point B is when the dissolved oxygen concentration has substantially reached its minimum, and point 0 is when biological treatment of organic matter is completed during aeration treatment. At this point, no oxygen is consumed and the concentration of dissolved oxygen begins to increase rapidly, indicating the point at which the BOD concentration reaches a minimum and is maintained.

In the figure, for example, a certain amount of activated sludge suspension is put into a measuring device, and while aerating it at a constant aeration rate of, for example, 5 t/m, a certain amount of test water is added (point A), and the aeration process is performed. Continue. Before the sample water is added, the dissolved oxygen concentration is constant at a certain value within the range of 3 to 7 ppm due to the relationship between the supply of dissolved oxygen by aeration and the rate of consumption of dissolved oxygen by endogenous respiration of activated sludge. If it is outside this range, it is preferable to adjust the activated sludge concentration or aeration amount.

When the suspension is added, dissolved oxygen is consumed due to the biological treatment of 'I BOD, and the amount becomes mostly Oppm. -10,000 BO
The D concentration decreases at a constant rate from point A, and the added BOD
Approximately 3 hours after the biological treatment of
The concentration begins to increase rapidly. In such an operation, the BOD concentration from point A to point 0 decreases at a constant rate, and the amount of BOD added is proportional to the processing time from point A to point pc. Therefore, the time required for biochemical oxidation under certain conditions has a linear relationship with the BOD concentration of the sample water, and if this relationship is determined in advance, BOD can be easily measured from the required time. The present invention effectively utilizes this specific phenomenon, and can shorten the time by diluting the BOD concentration of the sample water.

However, in this method, for example, as shown in the graph of Figure 1, the dissolved oxygen concentration in the activated sludge suspension when the sample water is added is about 6.5 ppm, and at the end of the measurement it is about 0.5 ppm. In the case of a measuring tank capacity of 5 tons, approximately 3
A dissolved oxygen amount of 0 ■ is measured as a negative error. This error is extremely disadvantageous since it reduces measurement accuracy. However, this error can be solved by stopping aeration until the final test water is added, keeping the activated sludge in a state that only covers it, and bringing the dissolved oxygen concentration in the measurement tank to substantially Oppm through internal respiration. It was found that by making it a dot, it became smaller. In other words, when adding test water to activated sludge in this state and starting aeration at the same time, dissolved oxygen is kept at the minimum value from the starting point (point B), and the time from point B to point 0 is automatically set. By measuring, the difference in dissolved oxygen concentration between the start and end of the measurement can be reduced, and measurement errors can be minimized.

Still, FIG. 2 is a system diagram showing the configuration of an apparatus for carrying out the measurement method of the present invention, in which a stirrer 2 and various detection ends 3 and 4 are attached to the BOD measurement tank 1, and a A member having a large number of small holes for releasing air sent from the aeration device 5 is installed, and the measurement tank 1 is placed in a constant temperature tank 6. ])H automatic adjustment device 7 is connected to the detection end 4, and the other detection end 3 is connected in parallel to a dissolved oxygen concentration measuring device 8, an activated sludge concentration meter 9, and a timer 10. and 10 are further water-coupled to the calculation unit 11. The slag addition device 12, activated sludge collection device 13, and measurement tank cleaning device 14 are connected to a pipe having an open port inside the measurement device 1, and are used to supply activated sludge suspension, sample water, and washing water to the measurement device. It is designed so that the supply can take place through this tube.

The calculation unit 11 calculates oxygen transfer efficiency, activated sludge internal respiration rate,
The measurement tank capacity, the amount of water sampled, the correction coefficient for converting the actual measurement value to the JIS measurement value, etc. are artificially input in advance, and the calculation section performs calculations according to the following formula, and the obtained BOD is digitalized. It is displayed and recorded on the display device 15 and recorder 16.

The calculation formula is as follows.

((TXDyzu1xS-WxB))x-F-BOD(p
pm)T; Time from BOD addition to completion of treatment (seconds)
D; Oxygen transfer efficiency (tOz/see)SW
; Activated sludge amount Cj>B; Dissolved oxygen amount consumed by activated sludge 12 per second (R0
2/θθc/MLSS-2) Correction coefficient S for converting the 11 measured values to JIS measured values, amount of sampled water (Kq) Next, use the measuring device with this configuration to calculate the BOD of the sampled water.
This section provides an overview of how to measure .

Approximately 3,000 ppm suspension of activated sludge (5 tons) is automatically collected into a measuring tank 1 with a content of 5 tons (12), and the amount collected is detected by a meter at level/L. , dissolved oxygen concentration measuring device 3.8 (
DKK-7610 model), pH automatic regulator 4°7 (D
KK-6040 model), activated sludge concentration meter 3,9 (DKK-
3EtD-20), aeration device 5 (Seiko Sangyo).

MD-ao) and fixed in a constant temperature water bath 6 (Coolnics, 0TR-3 type) automatically adjusted to 20°C ± 1°C. The measured values of PH, Do, and activated sludge concentration are electronically transmitted to the calculation unit 11. At the same time as the test water addition 12 from 10 to 12, the aeration process begins, and the timer 10 (Omron, Digital, 115A-4D) is activated. Added BOD
When the source is biologically treated, the dissolved oxygen concentration increases. When the set value (Fig. 1, point 0) is reached, the timer and aeration process are stopped, and this time (seconds) is electronically transmitted to the calculation circuit, and according to the above calculation formula, ! 7BOD has been converted and digital display 15
and recorded in a total of 16 notes. Subsequently, the measuring tank is cleaned by the cleaning device 14, and one process is completed.

Next, the present invention will be explained in more detail with reference to an example using the apparatus of the present invention configured as described above.

Example 1 As various setting conditions, the temperature for BOD measurement was conducted in a constant temperature water tank at 20° C. according to the JIS-0102 factory wastewater test method. In addition, the capacity of the measurement tank is 5L, and when the activated sludge concentration is below 2000 ppm, it is difficult to maintain the dissolved oxygen concentration in the measurement tank at Oppm, and when it is above 5000p1)m, it is blank due to endogenous respiration. Since the value becomes high, it was set at about 3000 ppm. pH is 7
．． Automatically neutralized to a range of 0 to 7.5.

The internal respiration rate was measured by a conventional method using a sealed container with a content of 2 L. The experimental results are 10~20my02/H
r.activated sludge was in the range of 17. To measure oxygen transfer efficiency, a certain amount of sodium bisulfite was added to pH 7-7,5.
, water temperature 20'C, measurement tank answer t5t, ventilation rate O, SZ/
The efficiency was 0.09 to 0.11 my
02/sec range.

The activated sludge used was returned sludge from a municipal sewage treatment plant, separated into each tank, and acetic acid and methanol were used as BoD substrates.

1% solutions of phenol, glucose, and glutamic acid were each added to separate aquariums, and the dissolved oxygen concentration was continuously measured. After the dissolved oxygen concentration increased with the completion of biological treatment of BOD, additional water was added and the water was acclimatized for about 1 month. It is something.

The following table summarizes the BOD measurement results for 1% aqueous solutions of each organic compound and the equivalent compound of glutamic acid and glucose.

This table shows the BOD of organic compounds measured by the method of the present invention in comparison with conventional methods published in literature. For acetic acid and methanol, which are easily biodegradable, measurement values close to those obtained using conventional methods were obtained, but for glutamic acid and other substances, lower measurement values were obtained. However, it will be understood that these compounds also have poor reproducibility, and by making corrections, measured values close to the true BOD can be obtained in a short time.

[Brief explanation of drawings]

Figure 1 shows the correlation between BOD concentration, dissolved oxygen concentration, and treatment time, and A in the figure is the test water addition point;
B is the point at which the test water was added at the time of measurement, and C is the point at which BOD biological treatment is completed. FIG. 2 is a system diagram showing the configuration of the rapid BOD measuring device. The symbols in the diagram are 1-Measurement tank, 2-Agitator, 3.4-Various detection ends, 5-Aeration device, 6-Thermostatic water tank, 7-Automatic pH adjustment device, 8-Dissolved oxygen concentration measuring device, 9-Activity These are a sludge concentration meter, 10-timer, 11-computation unit, 12-sample water addition device, 13-activated sludge sampling device, 14-measuring tank cleaning device, 15-digital display device, and 16-recorder.

Claims (1)

[Scope of Claims] 1. A suspension of activated sludge that is well adapted to the organic substances in the sample water to be measured is placed in a measurement container, and the dissolved oxygen concentration in the suspension is continuously measured while stirring at a constant speed. After confirming that the dissolved oxygen concentration due to internal respiration is almost at Oppm, a certain amount of sample water is added to the sample water and aerated under certain conditions, and from the time the sample water is added, the dissolved oxygen concentration sharply decreases. Rapid BOD measurement characterized by automatically measuring the time required for biochemical oxidation until it begins to increase, and determining the BOD concentration from the relationship between the smoothed BODit and the time required for biochemical oxidation. Method. 2 BOD measuring tank equipped with an aeration device and a stirrer, p
H automatic adjustment device, automatic dissolved oxygen concentration measuring device connected in parallel with terminals located in the measuring device, automatic activated sludge concentration measuring device and calculation unit connected via a timer, test water addition device, activated sludge It consists of a supply device, dissolved oxygen transfer efficiency, activated sludge internal respiration rate, and JIS measurement value conversion correction coefficient are inserted in advance into the calculation section, and a recording section is connected to electronically transmit and display and record the calculation results. Quick BOD
measuring device.