JPH05169100A - Method for monitoring anaerobic digestion tank - Google Patents

Abstract

PURPOSE:To measure an item becoming a controlling index with high precision without using many measuring instruments by analyzing the data pairs of pH- titer and performing optimization treatment while keeping the obtained water quality data as initial value and continuously monitoring the water quality in a digestion tank from the result thereof. CONSTITUTION:The data pairs of pH-titer obtained by a titration method based on an acid-alkali equilibrium theory are analyzed by a multiple regression analysis method 102. The obtained water quality data are used as initial value and optimization processing 104 is performed. The water quality in a digestion tank is continuously monitored from the result. Thereby five items of the concentration of the whole organic acid, the concentration of total inorganic carbon, the concentration of the whole ammonia, the concentration of total phosphorus and the concentration of total sulfide which are items becoming a controlling index are simultaneously measured at high precision. Accordingly the need for securing analytic instruments necessary for respective analyses is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the change of state in an anaerobic digestion tank for treating sludge, total organic acid concentration, total inorganic carbon concentration,
The present invention relates to a monitoring method for continuously monitoring the five items of total ammonia concentration, total phosphorus concentration, and total sulfide concentration.

[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 intermediate products such as organic acids produced in the 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 generated in the first step and the pH buffering ability (ability to resist pH change) together with the bicarbonate generated by dissolution of carbon dioxide, which is good for methanogens. It helps to create a weak alkaline environment inside the tank.

[0004] Since the growth rate of methanogens is slower than that of acid-producing bacteria and they are sensitive to environmental changes, it is generally said that it is the methanogenic stage that 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. In case of failure, it takes a long time to recover, so it is the most important task in operation management to 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 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.

[0006] The following four items are known as the operation management index of the digestion tank which has been known so far.

(1) Management of pH (2) Management of organic acid concentration (3) Management of alkalinity (4) Management of methane gas generation rate (gas generation rate + gas composition) The pH management of the above (1) will be described. Generally, in the case of a digestion tank that is operating well, 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. Also, 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 of the above (2), 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 at a certain concentration or higher, 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 control of alkalinity (3), since the sludge in the digestion tank has a high pH buffering ability, the abnormality in the digestion tank is prominent as a pH abnormality.
In many cases, it is in the final stage where troubles have progressed considerably. 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 changes as the ionic charge in solution changes,
It buffers changes in solution pH by changing the form of carbon dioxide, bicarbonate, and carbonic acid. The molar ratio of these three-form 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 of (3) and pH. 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.

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. That is, the ammonia production in the second stage of anaerobic digestion is indispensable for maintaining near neutral pH in the tank when this is appropriate, but when ammonia production is excessive,
This causes an increase in pH in the tank, creating an environment unfavorable for methane production. Higher p
It has been reported that H and excessive accumulation of ammonia result in an increase in the concentration of free non-ionized ammonia, and when this free ammonia is high, it has a suppressive toxic effect on methanogens. The free ammonia concentration can be calculated from the ammonia concentration and pH.

Further, the digested sludge contains phosphoric acid and hydrogen sulfide in an amount of several mg / l to several hundred mg / l, and in order to accurately grasp the state change in the digestion tank, the total phosphorus concentration and It is also necessary to monitor the item of total sulfide concentration.

Other monitoring items include nutrient salt balance (C / N ratio, trace amount of essential heavy metal) and control of tank temperature. However, the nutrient salt balance does not need to be monitored frequently and continuously unless the composition of the input sludge changes suddenly, and the temperature inside the tank is an item that has been sufficiently monitored and controlled.

Further, in recent studies on digestion of anaerobic sludge, the role as an index of propionic acid among hydrogen gas and organic acids has been emphasized. However, hydrogen gas and propionic acid are non-measurable substances in the digestive tank monitor this time, and they will be left for future study.

(Regarding the above technique, for example, as a reference, Colin, F., "Development of
an automatic equipment f
or the study of acid-base eq
uibria for the control of auaero
"Bic Digestion," and a French patent,
F. See Colin, 0056117, etc. )

[0017]

Although it has been described above that the items which are preferably monitored continuously in the anaerobic digestion tank are mentioned, it is very difficult to actually monitor all of the above items.

For example, the following are used as existing equipment for measuring the above continuous monitoring items. pH: pH electrode Organic acid: Liquid chromatograph Inorganic carbonate: Alkali by IC meter or titration Degree measurement Methane gas ···· Gas chromatograph Gas production rate ··· Gas flow meter Ammonia ··· Ammonia electrode Conventionally, all analytical equipment required for each such analysis is secured. In addition, many instruments require pretreatment, and special instruments for samples are required, so that few instruments can be continuously measured. Furthermore, there is the complexity of having to create a calibration curve for each device during measurement, and the greater the number of measuring devices, the greater the number of workers who must perform maintenance and inspection.

Therefore, the present invention solves the problems that occur when performing such conventional digestion tank monitoring, without using many measuring devices, and as a management index item, the total organic acid concentration, An object of the present invention is to provide a method for monitoring an anaerobic digestion tank, which can select five items including total inorganic carbon concentration, total ammonia concentration, total phosphorus concentration, and total sulfide concentration with high accuracy. It is what

[0020]

In order to achieve the above object, the present invention provides a digestion tank monitoring apparatus to which a titration method based on the acid-alkali equilibrium theory is applied. 5 of acid concentration, total inorganic carbon concentration, total ammonia concentration, total phosphorus concentration, total sulfide concentration
After selecting any item or a combination of any items from the items and analyzing the pH-titration data pair by multiple regression analysis as a monitoring method to obtain water quality data for each of the above items, the water quality obtained Provided is a method for monitoring an anaerobic digestion tank, which performs optimization processing by using data as an initial value for optimization processing and continuously monitors the water quality in the digestion tank based on the result of this optimization processing.

As an optimization processing method, a simplex method is used in which an evaluation function is calculated using each item to be monitored as a parameter and a parameter search for reducing an evaluation error is performed.

Further, the initial value of the optimization process can be arbitrarily set within the range of the upper and lower limit set values of the constraint condition of the item to be monitored, and an evaluation function weighted to a specific pH range can be used. It is also possible to use it to carry out the calculation of the evaluation function.

[0023]

[Operation] According to the anaerobic digester monitoring method,
The pH-titration data pair obtained by the titration method based on the acid-alkali equilibrium theory is analyzed by multiple regression analysis,
By using the obtained water quality data as the initial values for the optimization treatment, the total organic acid concentration, total inorganic carbon concentration, which are items that serve as management indicators for continuous monitoring of the water quality in the digestion tank, Total ammonia concentration, total phosphorus concentration,
Five items of total sulfide concentration can be measured simultaneously and with high accuracy. The simplex method is adopted as a method of this optimization processing, and the initial value of the optimization processing can be arbitrarily set within the constraint conditions of each item, in addition to the above multiple regression analysis result.

Further, by performing the calculation of the evaluation function by using the evaluation function weighted to the specific pH range,
It is possible to improve the measurement accuracy of the management index.

[0025]

EXAMPLES An example of a method for monitoring an anaerobic digester according to the present invention will be described in detail below.

The present invention aims to provide a continuous monitoring method for an anaerobic digester based on the acid-alkali equilibrium theory. The greatest feature is that one monitor device has the following five items: (1) total organic acid concentration (non-ionized organic acid concentration), (2) total inorganic carbon concentration (alkalinity + gas composition), (3) ) Total ammonia concentration (free ammonia concentration),
(4) Total phosphorus concentration (phosphoric acid) and (5) Total sulfide concentration (hydrogen sulfide) are measured continuously. Specifically, as a digestion tank monitor, all of the above-mentioned items to be continuously monitored can be measured from the pH-titration data pair.

First, the acid-alkali equilibrium theory, which is the basic principle of the present invention, will be described. That is, the present example is characterized in that the concentration of 17 or less substances is determined from the acid-alkali titration curve for sludge in the digestion tank. ^{[H +], [OH -} ], [CH 3 COO -], [CH 3 COOH], [H 2 CO 3],
^{_{[HCO 3 -], [CO}} 3 2-], pCO 2, [NH 4 +], [NH 4 OH], [PO 4
_{^{3-], [HPO 4 2-]}} , [H 2 PO 4 -] [H 3 PO 4], [S 2-], [H
S ^-], [organic acids H ₂ S] digestion tank are acetic, propionic acid, butyric acid, etc., these are organic acids 1.76 × 10 ^-5, 1.34 × 10
^It has relatively similar ionization constants of ^-5 and 1.54 × 10 ^-5 . Therefore, when these organic acids are collectively considered as acetic acid in a batch form, it can be assumed that the ionization constant is 1.5 × 10 ⁻⁵ .

Then, the following chemical equilibrium relational expression holds between the above-mentioned substance concentrations.

[0029]

[Equation 1]

[0030]

[Equation 2]

[0031]

[Equation 3]

[0032]

[Equation 4]

[0033]

[Equation 5]

[0034]

[Equation 6]

The equations (1) to (6) excluding the above equation (3) are:
The formula can be modified as follows according to the total organic acid concentration (A), total ammonia concentration (N), total inorganic carbon concentration (T) and hydrogen ion concentration.

[0036]

[Equation 7]

[0037]

[Equation 8]

[0038]

[Equation 9]

[0039]

[Equation 10]

[0040]

[Equation 11]

Further, in the acid-alkali equilibrium, the charge balance equation holds. This is the law that the sum of charges of positive ions is equal to the sum of charges of negative ions. If this is expressed by a formula, formula (12) is obtained.

[0042]

[Equation 12]

[Z] is the total net cation concentration. In the actual sample, the above organic acids, ammonia,
A few mg of phosphoric acid and hydrogen sulfide in addition to ions such as inorganic carbon
/ L to several hundreds mg / l. However, since metals such as iron, zinc, copper, lead, and cadmium react with dissolved sulfides to form insoluble metal sulfides, the sulfides are partly involved in the balance equation.

[0044] Therefore _{^{[H +], [NH 4}} +], [HCO 3 -], [CO 3
^{_{2-], [CH 3 COO -}} ], [OH -] plus the sum of the charges of all ions other than the ion - constant (sum of cationic charge negative sum of ionic charge) as the cation concentration of net [Z] Can be treated.

[NH ₄ ⁺ ], [HC
^{_{O 3 -], [CO 3}} 2-], [CH 3 COO -], [OH -] concentration is above the total organic acid concentration as also shown (A), the total ammonia concentration (N), total inorganic It can be expressed by the formula (13) by the carbon concentration (T) and the hydrogen ion concentration.

[0046]

[Equation 13]

Since the hydrogen ion concentration can be easily measured with a pH meter, the unknowns in the charge balance equation are total organic acid concentration (A), total ammonia concentration (N), and total inorganic carbon concentration (T). The four items are the net cation concentration (Z). Here, four equations are required to obtain four unknowns from the relationship between the unknowns of the simultaneous equations and the number of equations.

One is obtained by measuring the pH of an untitrated sample. The other three can be obtained by titrating with acid or alkali to achieve three different pH values. However, in this case, the net cation concentration (Z) is corrected by titration of acid or alkali.

For example, when an acid (HCl) is injected at X1 mol / L and the pH becomes pH 1,

[0050]

[Equation 14]

It becomes Therefore, four simultaneous equations are established if only the pH of the sample that has not been titrated and the titration amount when three different pH values are achieved by titration are known, and by solving these simultaneous equations, four unknowns The organic acid concentration (A), total ammonia concentration (N), total inorganic carbon concentration (T) and net cation concentration (Z) can be determined. However, in practice, the pH value and the titration amount naturally include the measurement error of the instrument, so it is necessary to statistically determine four unknowns from four or more data (all titration point data) by multiple regression analysis. ..

Then, by obtaining the above four unknowns, it is possible to calculate other ion concentrations by using the equations (7) to (11). In particular, it is derived based on the acid-alkali equilibrium theory (chemical equilibrium equation, charge balance equation) (Equation 1
4) From hydrogen ion concentration (pH) and total inorganic carbon concentration (T), total ammonia concentration (N), total organic acid concentration (A)
Can ask for the relationship.

Therefore, first, a fixed amount of acid or alkali is automatically injected into the sample, each pH titration amount (X mol) is recorded and stored, and the value is applied to the above (Equation 14) to obtain four unknown values T. , N, A and Z. The multiple regression analysis method is adopted as the calculation method of these four unknowns.

That is, the above (formula 14) can be transformed into the following multiple regression formula (formula 15). y = Z + b1 · N + b2 · T + b3 · A (15) where y = X1− [H ⁺ ] + Ke / [H ⁺ ] (16) b1 = 1 / (1 + Kn / [H ⁺ ]) ... (17) b2 = -1 / (1+ [H ⁺ ] / K1 + K2 / [H ⁺ ])-2 / (1+ [H ⁺ ] / K2 + [H ⁺ ] ² / K1 /K2)...(18) b3 = -1 / (1+ [H ⁺ ] / Ka) .... (19) On the other hand, sample The phosphoric acid contained therein is dissociated into the following three stages.

[0055] ^{_{H 3 PO 4 ← → H +}} + H 2 PO 4 - · ························· (20) H 2 PO 4 - ← → H ⁺ ＋ HPO ₄ ^2-・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (21) HPO ₄ ^2- ← → H ⁺ + PO ₄ ^3-・(22) Further, hydrogen sulfide contained in the sample dissociates into the following two stages.

[0056] ^{_{H 2 S ← → H + +}} HS - · · · · · · · · · ························· (23) HS ^- ← → H ⁺ + S ² ----------------- (24) Chemical equilibrium equation Using, the total phosphorus concentration (P) and the total sulfide concentration (S) can be obtained as follows.

[0057] total phosphorus concentration _{(P) = [H 3 PO} 4] + [H 2 PO 4 -] + [HPO 4 2-] + [PO 4 3-] ············ ··· (25) K3 = ([ H +] [H 2 PO 4 -]) / [H 3 PO 4] K4 = ([H +] [HPO 4 2-]) / [H 2 PO 4 2- ^{] K5 = ([H +]} [PO 4 3-]) / [HPO 4 2-] [H 2 PO 4 -] = P / ([H +] / K3 + K4 / [H +] +1) [HPO 4 2 ^{-] = P / ([H} +] 2 / K3 / K4 + [H +] / K4 + 1) [PO 4 3-] = P / ([H +] 3 / K3 / K4 / K5 + [H +] 2 / K4 / ^{K5 + [H +] / K5} ) total sulphide concentration ^{(S) = [HS -]} + [H 2 S] + [S 2-] ··········· (26) K6 = ( ^{[H +] [HS -]} ) / [H 2 S] K7 = ([H +] [S 2-]) / [HS -] [HS ^- ] = S / (K7 [H ⁺ ] + [H ⁺ ] / K6 + 1) [ ^S2- ] = S / ([H ⁺ ] ² / K6 / K7 + [H ⁺ ] / K7 + 1) Above (25) ( Considering the total phosphorus concentration (P) and the total sulfide concentration (S) in the equation (26), the equation (15) is as follows.

Y = Z + b1 * N + b2 * T + b3 * A + b4 * P + b5 * S (27) Here, y = X1- [H ⁺ ] + Ke / [H ⁺ ] ... (28) b1 = 1 / (1 + Kn / [H ⁺ ]) ........ (29) b2 = -1 / (1+ [H ⁺ ] / K1 + K2 / [H ⁺ ])-2 / (1+ [H ⁺ ] / K2 + [H ⁺ ] ² / K1 / K2) .. (30) b3 = -1 / (1+ [H ⁺ ] / Ka) ... (31) b4 = -1 / (1+ [H ⁺ ] / K3 + K4 / [H ⁺ ])-2 / (1+ [H ⁺ ] / K4 + [H ⁺ ] ² / K3 / K4) -3 / ([H ⁺ ] / K5 + [H ⁺ ]] ^{2 / K4 / K5 + [H} +] 3 / K3 / K4 / K ) ····················· (32) b5 = -1 / (1+ [H +] / K6 + K7 / [H +]) -2 / (1+ [ H ⁺ ] / K7 + [H ⁺ ] ² / K6 / K7) ... (33) y, b1, b2, b3 from titer X1 and pH at all observation points (titration points) obtained by acid-alkali titration , B
By calculating 4, b5 and using the multiple regression analysis method, it is possible to calculate the values of T, N, A, Z, P, and S that are statistically most suitable for all the titration data.

In this example, four or more (pH-titration)
The method of statistically determining the unknowns from the data pair of was adopted by the multiple regression analysis method.

In order for the multiple regression analysis method to work effectively with respect to its application target, the error (ε) included in the multiple regression equation has four assumptions: (1) unbiased and (2) equal variance. , (3)
No correlation, (4) Normality must be satisfied. When these (1) to (4) are aggregated, "the error follows the normal distribution of mean 0 and variance (σ ² ) independently of each other".

However, in reality, these preconditions are usually not satisfied, and if the variance of the error (ε) is not uniform, the accuracy of estimation by the ordinary least square method cannot be guaranteed. ..

Therefore, there is an error analysis method as a method for examining whether or not the above error satisfies the precondition. An example of applying this error analysis method to the present embodiment will be shown below. FIG. 5 is a pH-titration curve when the filtrate obtained by centrifuging the digester sludge and filtering the supernatant is used as a measurement sample and alkali NaOH or acid HCl is titrated. (◯) in FIG. 5 shows the actual measurement value, and the solid line shows the curve calculated using the acid-alkali equilibrium theory.

Therefore, by obtaining the magnitude of the difference (residual difference) between the measured value and the calculated value and the appearance frequency, the distribution chart shown in the histogram of FIG. 6 can be obtained. It can be seen from FIG. 6 that the residual is not a normal distribution, and the distribution may have two peaks depending on the sample, so that sufficient accuracy cannot be obtained only by applying the multiple regression analysis method.

Therefore, this embodiment adopts a method of determining the unknowns Z, T, N, A, P, S based on the flowchart shown in FIG. That is, first in step 101,
The measured data such as pH-titration relationship and water temperature is read, and then, in step 102, the multiple regression analysis method is applied based on the above (Equation 27) to apply a plurality of water quality items Z, T,
Calculate N, A, P, S. However, since the multiple regression analysis result is used as the initial value of the optimization process, it is only necessary to obtain the approximate value, and in the multiple regression analysis, if the number of variables is increased more than necessary, the overall accuracy will decrease. There is also
Since the concentration of total phosphorus and sulfide is low compared to other items (total organic acid, total inorganic carbon, total ammonia concentration), multiple regression analysis may be performed with only four items, Z, T, N, and A. it can. In this case, the multiple regression equation may use the equation (15). When total phosphorus and sulfides are included, the formula (27)
To use.

Next, initial values Z ₀ , T ₀ , N ₀ , A ₀ , P ₀ , for optimizing the water quality data of Z, T, N, A, P, S, etc. read in step 103, The setting of S ₀ is performed, and the optimization process is performed in step 104. Items to be optimized are, for example, T, N, A, Z, T, N,
A, Z, T, N, A, P, Z, T, N, A, S,
Combinations of Z, T, N, A, S, P and the like are conceivable, but the initial value of the optimization process needs to be changed depending on which item is selected. For example, when the above Z, T, N, and A are desired to be optimized, four items of the results of the multiple regression analysis (four items are set in accordance with the optimization process) are set to the initial values (Z ₀ ,
T ₀ , N ₀ , A ₀ ).

Generally, multiple regression analysis is used as the initial value for the optimization process, but any value within the range of the upper and lower limit set values of each of Z, T, N, A, P and S items is used as the initial value. It is also possible to

Although various methods have been proposed as a method of optimization processing, the simplex method is used in this embodiment. This simplex method is one of non-linear programming method-direct search method. Specifically, if the number of parameters to be optimized is NPA%, first, NPA% + 1.
The error is evaluated directly by combining the individual parameters. In case of digestive tank monitor, the above parameters are maximum Z, T,
There are 6 of N, A, P and S. Next, using this result,
In step 105, the evaluation function is calculated and a new parameter is searched for so that the evaluation error becomes smaller. After that, the new combination is replaced with the combination showing the maximum error evaluation, and the convergence check is performed in step 106.

By repeating the above steps 104, 105 and 106, the NPA% + 1 parameter combination is converged while moving to the optimum point, and the difference in the evaluation error between the NPA% + 1 parameter combinations becomes sufficiently small. It is considered that the convergence has reached the optimum point, and the optimization process ends.

In this embodiment, the initial value of the optimization process is arbitrarily set within the range of the unknown number constraint condition of each item of T, N, A, P and S to be monitored.

Below, an artificial sample containing T, N, A, P, S was prepared to prepare a pH-titration data pair based on this titration method, and a multiple regression analysis and optimized calculation values and artificial values were prepared. The results of comparison with the sample preparation concentration are shown in FIGS. Figure 2
Shows the result when only the multiple regression analysis is performed, and FIG. 3 shows the result when the multiple regression analysis and the optimization process are combined. The broken lines in FIGS. 2 and 3 show the ideal relationship (theoretical calculation value) between the titration method and the artificial sample preparation concentration. As is clear from FIG. 3, by combining the multiple regression analysis with the optimization process, it is understood that the measurement accuracy is significantly improved compared to the case of FIG. 2 in which only the multiple regression analysis is performed.

In the five graphs shown in FIG. 4, the total organic acid concentrations (A) are 10 mg / l and 100 mg / l in order from the top.
1, 200 mg / l, 400 mg / l, 500 mg / l
The relationship between pH and titration amount in the case of is shown. According to FIG. 4, it can be seen that there is a difference in the range of pH change with respect to the difference in the total organic acid concentration (A) depending on the pH range. In this example, the difference in the total organic acid concentration (A) is from pH 4 to pH 6 and pH 7-
It can be seen that it appears particularly well in the pH 9 range. Therefore, in order to improve the calculation accuracy of the total organic acid concentration, it is necessary to pay attention so that the actual measurement value and the calculated value of the pH-titration amount in the above pH range match.

In the present embodiment, by using an evaluation function in which a specific pH range is weighted in advance, the weighting coefficient is made larger than the other pH ranges when the characteristic pH range is calculated. The means for carrying out the calculation of the evaluation function using N, A, P and S items as parameters was adopted. Thereby, the measurement accuracy of the total organic acid concentration can be further improved.

Further, in the multiple regression analysis, Z, which is an unknown number,
Since the concentration range of T, N, A, P, S cannot be specified, a physically meaningless negative value may be output as a calculated value, but in addition to multiple regression analysis, optimization processing is also possible. By carrying out, it becomes possible to add constraints such as upper and lower limit values to each unknown, and there is an effect that the stability of the calculation result is enhanced.

[0074]

As described in detail above, according to the method for monitoring an anaerobic digester according to the present invention, the total organic acid concentration, total inorganic carbon concentration, and total ammonia are the items to be monitored in the digester. Concentration, total phosphorus concentration, and total sulfide concentration are selected from the five items, or any combination of items is selected, and the multiple regression analysis method is applied to the pH-titration data pair obtained by the titration method based on the acid-alkali equilibrium theory. By using it as an initial value for analysis and optimization treatment by the method described above, it is possible to highly accurately measure the above-mentioned plurality of items serving as a management index for continuously monitoring the water quality in the digestion tank. Therefore, it is not necessary to secure the analytical instruments necessary for each analysis as in the conventional method, so that a worker who maintains and inspects these instruments is unnecessary, and the operational complexity of each instrument is eliminated. Is obtained.

Further, by using an evaluation function weighted to a specific pH range, the evaluation function is calculated,
It is possible to further improve the measurement accuracy of the management index.

[Brief description of drawings]

FIG. 1 is a chart showing an example of a method for monitoring an anaerobic digestion tank according to the present invention.

FIG. 2 is a graph comparing the results when only multiple regression analysis based on the present invention is performed with theoretical calculated values.

FIG. 3 is a graph comparing the results of the combination of the multiple regression analysis and the optimization processing according to the present invention with the theoretical calculation values.

FIG. 4 is a graph showing a comparison between measured values and calculated values of pH-titration amount by total organic acid concentration.

FIG. 5: pH when a measurement sample is titrated with alkali or acid
-A graph showing a comparison between the measured value of the titration curve (o) and the calculated value using the acid-alkali equilibrium theory (solid line).

FIG. 6 is a histogram showing the appearance frequency of the residual between the measured value and the calculated value in FIG.

Claims (4)

[Claims] 1. A digestion tank monitoring apparatus applying a titration method based on the acid-alkali equilibrium theory, wherein items to be monitored in the digestion tank are total organic acid concentration, total inorganic carbon concentration, total ammonia concentration, and total phosphorus concentration. Select any item or a combination of any items from the five items of total sulfide concentration, and monitor the pH as
-A pair of titration data is analyzed by multiple regression analysis to obtain water quality data for each of the above items, and then the obtained water quality data is used as an initial value for the optimization treatment, and then the optimization treatment is performed. A method for monitoring an anaerobic digestion tank, which comprises continuously monitoring the water quality in the digestion tank based on the result of this optimization treatment. 2. As an optimization processing method, an evaluation function is calculated using each item to be monitored as a parameter,
The method for monitoring an anaerobic digester according to claim 1, wherein a simplex method for searching for a parameter for minimizing an evaluation error is used. 3. The method for monitoring an anaerobic digester according to claim 1, wherein the initial value of the optimization process is arbitrarily set within a range of upper and lower limit set values of constraints of items to be monitored. .. 4. The method for monitoring an anaerobic digestion tank according to claim 1, wherein the evaluation function is calculated using an evaluation function weighted in a specific pH range.