JPH06182398A - Method for removing error data in monitoring equipment for digestion tank - Google Patents

Abstract

PURPOSE:To prevent deterioration of measuring precision which is caused by error data and to enhance monitoring precision of water quality by removing data containing an error of measurement in a time for acid-alkali titration in the case of calculating and processing the concentration of a measuring item to be monitored. CONSTITUTION:The pouring quantity of acid and alkali is decided by means of the command of a sequential controller 11. Combinations of data for the pouring quantity of chemicals and pH value are prepared at proper number and inputted to the storage device of the sequential controller 11 or a personal computer 12. When input is finished, arithmetic processing is performed by arithmetic output processing through multiple regression analysis to calculate the concentration of total organic acid, the concentration of total ammonia and the concentration of the whole inorganic carbon. Then, data containing an error of measurement are removed. Simulation of a titration curve is executed by the result of multiple regression analysis. Data are found out where a large error exists between an actual measurement and measured value. The data are removed in the following optimization processing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing error data in an apparatus adapted to monitor a state change in an anaerobic digestion tank for treating sludge.

[0002]

2. Description of the Related Art Generally, biological anaerobic sludge digestion is 2
It progresses in stages depending on the type of bacterial group. The first stage is called “acid production stage”, and sludge introduced into the digestion tank is decomposed into intermediate products such as organic acids by the action of hydrolyzing bacteria or acid producing bacteria. The second stage is called the "methane production stage", in which the intermediate products such as organic acids produced in the above acid production stage are decomposed into the final products such as methane gas, carbon dioxide and ammonia by the action of methanogens. It

Ammonia produced in the second step is
It has the function of neutralizing the organic acid produced in the first step and the pH buffering ability (ability to resist pH change) together with the bicarbonate generated by the dissolution of carbon dioxide, which is good for methanogens. It helps to create a weak alkaline environment inside the tank.

Since the growth rate of methanogenic bacteria is slower than that of acid-producing bacteria and they are more sensitive to environmental changes, it is generally said that the methanogenic stage determines the rate of digestion. Therefore, for good operation of the digestion tank, it is important to maintain a tank environment suitable for survival of methanogens.

From this point of view, in order to achieve and maintain good digestion of anaerobic sludge, it is extremely important to continuously monitor the state change in the digestion tank. If the condition becomes defective, it takes a long time to recover, so it is the most important task in operation management to promptly detect that the condition inside the tank is abnormal. Furthermore, when aiming for optimal operation control that also considers economic efficiency, the good operation range of the target digestion tank should be constantly monitored by continuous monitor monitoring, and the condition inside the tank should be kept within that good operation range. It is necessary to control while monitoring so as not to deviate.

The following four items are known as the operation management indexes of the digestion tank which have been known so far.

(1) pH control (2) Organic acid concentration control (3) Inorganic carbon concentration control (4) Methane gas production rate (gas production rate + gas composition) control Regarding the pH control in (1) above In other words, in the case of a digestion tank that is operating normally, the pH in the tank is maintained near neutral. However, when an abnormality occurs in the digestive tank, it first appears as a pH abnormality, that is, a phenomenon in which the pH deviates from around neutral. For example, when the activity of the methanogen in the second step is weakened, the organic acid produced in the first step of anaerobic digestion is accumulated without being decomposed, and a pH lowering (acidification) phenomenon occurs. If the ammonia production in the second stage is excessive compared to the acid production in the first stage,
Ascending phenomenon occurs.

Regarding the control of the organic acid concentration in (2) above, this organic acid is a substrate for methanogens, but when the organic acid concentration increases or the pH decreases, the organic acid is a weak acid. Therefore, non-ionized non-ionized organic acid increases. It is known that this non-ionized organic acid becomes a suppressive toxic substance for methanogens when the concentration exceeds a certain level, and the rancid phenomenon caused by the overload of organic substances on the digestive tank is caused by the non-ionized organic acid. It is said to be the result of the suppressive toxicity effect. The non-ionized organic acid concentration can be determined from the organic acid concentration as a function of pH.

Next, regarding the management of the inorganic carbon concentration in the above (3), since the sludge in the digestion tank has a high pH buffering ability, the abnormality in the digestion tank is prominently manifested as an abnormality in the pH. Is often in the advanced stage. However, the precursor of pH abnormality in the digestive tank can be grasped as a change in pH buffering ability. The alkalinity is an index showing the buffering ability of this pH. The alkalinity of anaerobic sludge is mainly due to soluble inorganic carbon. Soluble inorganic carbon buffers changes in the pH of the solution by changing the form of carbon dioxide, bicarbonate, and carbonic acid as the ionic charge in the solution changes. The molar ratio of these three forms of inorganic carbon can be obtained by theoretical calculation as a function of pH from the concentration of soluble inorganic carbon as the sum of the three forms.

Further, regarding the control of the methane gas production rate (4), abnormalities in the activity due to environmental changes of methanogens or inflow of inhibitory toxic substances (sulfides and heavy metals) appear as a decrease in the methane gas production rate. The generation rate of methane gas is obtained by multiplying the gas generation rate by the partial pressure (concentration) of methane gas in the gas. However, the partial pressure of methane gas can be calculated from the concentration of soluble inorganic carbonic acid in the above (3) without directly measuring the concentration of methane gas. That is, the methane gas partial pressure can be obtained by subtracting the carbon dioxide gas partial pressure from the one partial pressure because most of the digestive gas is composed of methane gas and carbon dioxide gas.

Further, the partial pressure of carbon dioxide gas in the digestion gas is
From Henry's law (vapor-liquid equilibrium), it is possible to obtain theoretical calculation from the soluble carbon dioxide concentration. The soluble carbon dioxide concentration is obtained by theoretical calculation from the soluble inorganic carbon concentration and pH in (3) above. Therefore, if the generated gas rate, the soluble inorganic carbon concentration and the pH are known, the methane gas generation rate can be estimated by calculation.

On the other hand, as a method for monitoring the condition in the anaerobic digestion tank, the present inventors have previously proposed Japanese Patent Application No. 3-34054.
No. 9 and Japanese Patent Application No. 4-4398 proposed a method for monitoring an anaerobic digester applying a titration method based on the acid-alkali equilibrium theory. Briefly speaking, the total organic acid concentration, total inorganic carbon concentration, and total ammonia concentration were selected as items to be monitored in the digestion tank, and the pH-titration data pair was analyzed by multiple regression analysis. After obtaining the water quality data of the item, the obtained water quality data is used as an initial value for the optimization treatment, and the optimization treatment is performed, and the water quality in the digestion tank is continuously monitored from the results of this optimization treatment. This is the monitoring method.

In addition to the above-mentioned items, non-ionized ammonia concentration is used as an index to be continuously monitored,
The total phosphorus concentration and the total sulfide concentration can be mentioned.

According to such a monitoring method, items such as total organic acid concentration, total inorganic carbon concentration, and total ammonia concentration, which are management indexes for continuously monitoring the water quality in the digestion tank, are simultaneously measured. In addition, it is possible to measure with high accuracy, and the initial value of the optimization process can be arbitrarily set within the constraint condition of each item by performing multiple regression analysis.

[0015]

The acid-alkali titration method, which is the measuring principle of the above-mentioned digestion tank monitoring method, is a pH curve obtained by titrating an acid or alkali in a sample solution according to the acid-alkali equilibrium theory. Since it is a method of analysis based on the above, if an error occurs in the measured value such as pH for some reason, the measured value of the item serving as the management index also has an error, and the accuracy of water quality monitoring is improved. There is a problem that it will decrease.

For example, when a certain amount of acid or alkali is injected from the dispenser based on a command signal from the control unit during titration, if there is an air reservoir in the hose through which the chemical passes, the set amount of The chemical may not be injected, which causes the above measurement error. As other causes, it is considered that the pH electrode itself is deteriorated or the pH electrode surface is contaminated when the digestion tank is monitored over a long period of time.

FIG. 3 shows an error curve in such an acid-alkali titration method. The circles in the figure show the measured values by the pH meter 8 and the solid lines show the calculated values. As the calculated value, for example, an analytical value optimized so that the sum of squares of the difference in pH value for each titer is minimized is used.

Due to the above-mentioned cause, the actual measured value may deviate greatly from the calculated value as shown by the black circle in FIG. 3, which lowers the measurement accuracy for obtaining the data to be monitored by the digestive tank, and measures against it. Therefore, it is required to consider the means for separately, which is a factor of decreasing the processing speed.

Therefore, it is an object of the present invention to provide a method for removing error data of a digestive tank monitoring device which can prevent a decrease in measurement accuracy due to error data during titration.

[0020]

In order to achieve the above object, the present invention has a filtrate tank in which digested sludge is stored, a digested sludge in the filtrate tank is sampled and introduced, and a pH meter is provided. It is equipped with an acid titration tank and an alkali titration tank that are provided, and a titration mechanism that dispenses an amount of reagent corresponding to the value obtained by the control unit to the acid titration tank and the alkali titration tank by a dispenser. An anaerobic digestion tank monitor that calculates each measurement item to be monitored based on the acid-alkali equilibrium theory from the sampling liquid pH value and reagent titer, and continuously monitors the digestion state of sludge Provided is a method for removing data including a measurement error at the time of acid-alkali titration when calculating the concentration of the measurement item to be monitored in the device.

Specifically, by performing a simulation of a titration curve using the reagent used for the titration,
Error data existing between the actually measured value and the calculated value is detected, and the error data is removed in the subsequent arithmetic processing. This error data is obtained from the difference between the actually measured value of pH by the pH meter and the calculated value that is optimized so that the sum of squares of the difference in pH value for each titration amount is minimized.

[0022]

The pH obtained by titrating an acid or alkali into a sample solution by using such error data removal method
When analyzing the curve based on the acid-alkali equilibrium theory,
Even if an error occurs in the measured value such as pH for some reason, the concentration of the measurement item is calculated after the error data is removed. There is no error in the value, and the effect of improving the water quality monitoring accuracy can be obtained.

[0023]

EXAMPLE A specific example of the error data removing method of the digestive tank monitoring apparatus according to the present invention will be described below. FIG. 2 is a schematic diagram for generally explaining the configuration of the apparatus of the present embodiment. In the figure, 1 is a sludge receiving tank for receiving digested sludge, 2 is a flocculating tank, 3 is a clarifying tank, and 4 is a filter. And this filter 4
The sample that has passed through is stored in the filtrate tank 5.

Reference numeral 6 is an acid titration tank, 7 is an alkali titration tank, and the acid titration tank 6 and the alkali titration tank 7 are provided with a pH meter 8 and thermometers 9, 9. 10a and 10b are dispensers for adding titration reagents to the acid titration tanks 6 and the alkali titration tanks 7, 11 is a sequence controller, and 12 is a personal computer.
And the personal computer 12 constitute a control unit 13.

The basic operation of such a device will be described below. First, digested sludge is sent from the digestion tank (not shown) to the sludge receiving tank 1, and the polymer coagulant 2a is added in the coagulation tank 2 in the next stage to aggregate the fine particle components. Next, after solid-liquid separation in the sedimentation tank 3, the supernatant of the sedimentation tank 3 is filtered by the filter 4 to obtain a filtrate having a target ss concentration or less, and the filtrate is stored in the filtrate tank 5. To be done.

Next, a certain amount of the filtrate is sampled,
The mixture was placed in the acid titration tank 6 and the alkali titration tank 7, and the titration reagents HCl and NaOH were added using the dispensers 10a and 10b to perform titration, and this titration amount and the pH meter 8 were measured. The pH value is input to the sequence controller 11 and the personal computer 12 that form the control unit 13, and the processing based on the acid-alkali equilibrium theory is performed, and the total organic acid concentration (A), the total ammonia concentration (N), and the total ammonia concentration (N) Inorganic carbon concentration (T) etc. are monitored. The data measured at this time is corrected by the liquid temperature value measured by the thermometers 9, 9.

In the above description, all the operating steps are fully automatically performed based on the program preinstalled in the sequence controller 11 or the personal computer 12 constituting the control unit 13, which is a feature of the present apparatus. There is. Specifically, pH-
All of the above-mentioned items to be continuously monitored can be measured from the titer data pair.

After the measurement is finished, the washing water is injected into each of the tanks by operating a fluid pump (not shown) to wash the inner wall surface, and after the washing, a standby state is prepared in preparation for the next measurement. .

Next, an outline of a control flow in the above-mentioned basic embodiment will be explained based on FIG. 1 (for details of the control, Japanese Patent Application No. 3-340549 and Japanese Patent Application No. 4-340549).
4398). That is, as described above, the injection amounts of acid and alkali are determined based on the command from the sequence controller 11, and as shown in step 100 of FIG. The created data is input to the storage device incorporated in the sequence controller 11 or the personal computer 12.

When the input of the above data is completed, in the next step 101, the calculation output process based on the multiple regression analysis
By solving the simultaneous equations of many formulas created by substituting each value into the charge balance formula based on the acid-alkali equilibrium theory, the total organic acid concentration (A) and the total ammonia concentration (N), which are measurement items, are solved in step 102. , Calculation processing for obtaining the total inorganic carbon concentration (T) is performed.

Next, at step 103, the measurement error data characteristic of this embodiment is removed. The removal of this measurement error data means that a simulation of the titration curve is executed based on the results of multiple regression analysis, data that has a large error between the actual measurement value and the calculated value is found, and the subsequent optimization processing is performed using that data. The main point of the present invention is to eliminate the data.

More specifically, assuming that the injection amount of acid and alkali at the time of titration is Mi, the measured liquid pH is TpHi, and the pH obtained by simulating the titration curve is SPHi, the measured pH value at each injection amount and the simulation p
The error ERi from H can be obtained as follows.

ERi = TpHi-SpHi ... (1) where i: 1 to n, n: number of actually measured data.

The equation (1) is normalized to obtain the variance σ. Further, the average value AVER of the error in the equation (1) is AVER = ERi / n ... (2) Data outside a certain range is deleted from the average value AVER or is set in advance such as 2σ.

In this way, the error ERi between the actually measured pH value and the simulated pH is obtained, and after removing this error data, the subsequent optimization processing is started.

Next, at step 104, an optimization process for enhancing the reliability of the result is carried out. In this optimization process,
Using the result of multiple regression analysis as an initial value, each concentration is randomly shaken to simulate a titration curve, and the calculation is performed until the error from the actual measurement data becomes the smallest. Then, in step 105, the calculation results of the obtained total organic acid concentration (A), total ammonia concentration (N), and total inorganic carbon concentration (T) are displayed on the CRT screen which is an output device of the personal computer 12, and the operation is performed. finish.

As described above, in the present embodiment, the pH curve obtained by titrating the sample solution with acid or alkali
When analyzing based on the alkali equilibrium theory, even if there is error data in the measured value, this error data is removed and the concentration of the measurement item that is the management index of the monitor is calculated. Can be increased.

[0038]

As described above in detail, the pH curve obtained by titrating an acid or an alkali in a sample solution by using the error data removing method of the digestion tank monitoring apparatus according to the present invention is used for acid-alkali equilibrium. Even if an error occurs in the measured value of pH, etc. for some reason during the analysis based on the theory, this error data is removed before the optimization process and the concentration of the measurement item are calculated. Therefore, there will be no error in the measured values of the items that serve as management indicators for the digestive tank, the accuracy of water quality monitoring will be improved, and no separate measures will be required for error prevention measures. The effect that the speed is improved is obtained.

[Brief description of drawings]

FIG. 1 is a chart showing a control flow of a digestive tank monitoring device to which the present invention is applied.

FIG. 2 is a schematic diagram showing the overall configuration of a digestive tank monitoring device to which the present invention is applied.

FIG. 3 is a graph showing an error between an actually measured value and a calculated value in a normal acid-alkali titration method.

[Explanation of symbols]

 1 ... Mud receiving tank 2 ... Flocculating tank 3 ... Sedimenting tank 4 ... Filter 5 ... Filtrate tank 6 ... Acid titration tank 7 ... Alkali titration tank 8 ... pH meter 9 ... Thermometer 10a, 10b ... Dispenser 11 ... Sequence controller 12 ... Personal computer 13 ... Control unit

Claims (4)

[Claims] 1. A filtrate tank in which digested sludge is stored, an acid titration tank and an alkali titration tank in which the digested sludge in the filtrate tank is sampled and introduced, and pH meters are respectively provided, and a controller. It comprises a titration mechanism that dispenses an amount of reagent corresponding to the obtained value into the above-mentioned acid titration tank and alkali titration tank by a dispenser. In the anaerobic digestion tank monitoring device that calculates each measurement item to be monitored based on the equilibrium theory and continuously monitors the digestion state of sludge, when calculating the concentration of the measurement item to be monitored In addition, a method for removing error data of a digestion tank monitoring device, characterized in that data including a measurement error at the time of acid-alkali titration is removed. 2. The error data existing between the actual measurement value and the calculated value is detected by executing the simulation of the titration curve by the reagent used for the titration, and the error data is removed in the subsequent arithmetic processing. The method for removing error data in a digestive tank monitoring device according to claim 1, wherein the method is adopted. 3. The error data is obtained from a difference between an actually measured value of pH by a pH meter and a calculated value optimized so that the sum of squares of the difference between pH values for each titration amount is minimized. The method for removing error data in a digestive tank monitoring device according to claim 1 or 2, wherein. 4. A sludge receiving tank for receiving digested sludge, a coagulating tank for coagulating the digested sludge by injecting a coagulant, and a precipitating tank for storing the supernatant of the coagulating tank before the filtrate tank. The method for removing error data of a digestion tank monitoring device according to claim 1, further comprising: a filter for filtering the supernatant of the precipitation tank.