JPS6084199A - Method for controlling biological denitrification process - Google Patents

Abstract

PURPOSE:To always form a good denitrification state, by regulating the supply amount of org. carbon by correcting the objective redox potential value of an optimum denitrification state at reference pH so as to allow the same to correspond to an actually measured pH value. CONSTITUTION:In such a denitrification process that nitrate form nitrogen or nitrite form nitrogen in waste water is reduced to nitrogen gas in the presence of org. carbon, the redox potential and pH of a liquid mixture are detected. A preset objective redox potential value is corrected on the basis of this pH value. In the next step, the supply amount of the aforementioned org. carbon is regulated on the basis of this corrected objective value. By the above mentioned method, a good denitrification state is always formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a biological membrane nitrogen process, and particularly to an open-side method for supplying organic carbon suitable for forming a good deoxidized state.

[Background of the Invention] In closed water areas, water pollution due to eutrophication is significant and has become a major social problem. The organic compounds in wastewater are considered to be a cause of eutrophication, and their removal is being carried out.

Biological denitrification methods that utilize biological nitrogen σμ rings are common as a nitrogen removal method in sewage treatment plants. The disadvantage of the process configuration of this breakthrough method is that it has two microbial reaction tanks with different overnight storage conditions.

One is called a nitrification tank, and has the role of oxidizing NH3-N, which is converted from organic nitrogen through catabolic metabolism, into NO3N by nitrifying bacteria.

NU-L++ 202-1'JO3-+H20+ 2
H+ (1) The other tank is called a denitrification tank, and has the function of reducing No and -N generated in the nitrification tank to N2 gas by decomposing bacteria.

2NO3-+5 (H2)=Nz+4H20+20H-
(2) In formula (2), H2, which is necessary as a separator, is generally provided from organic carbon, which is highly compatible with methanol and the like. Therefore, a denitrification tank requires a certain amount of carbon.

In such an anastomological decolonization process, it is extremely important to properly manage these two microbial reaction mechanisms from the viewpoint of water quality and economy. In particular, in the denitrification tank, it is important to control the amount of dry carbon supplied. This is due to the fact that if the amount of carbon supplied is small, the desorption element is insufficient f) yJ < quality will deteriorate; Not only will it worsen, but it will also be uneconomical. Therefore, the appropriate supply of available carbon has become an operational issue.

In order to solve this problem, it is necessary to supply new organic carbon in accordance with the nitrate nitrogen concentration that represents the denitrification state and the ranked carbon magnification. However, since no measuring instruments have been developed to measure these denitrification tank management indicators online, no organic carbon control device using a direct detection method has been proposed. Therefore, at present, we have no choice but to rely on the needle injection method that constantly supplies organic carbon at a constant rate. Generally, the amount of nitrogen flowing into a sewage treatment area changes significantly from moment to moment, reflecting the life cycle of humans. If a fixed amount of organic carbon is injected in response to this nitrogen inflow, there will inevitably be a shortage of inorganic carbon collection, and water quality will inevitably deteriorate. According to the short-term method, the V4 gas produced in the denitrification reaction and the alkali agent required to neutralize the H+ produced during the nitrification reaction of formula (i) are used as indicators. A carbon-based Moe 1 method is being considered. However, it is difficult to accurately estimate the nitrate nitrogen concentration and organic carbon concentration in the denitrification tank from these indicators, so this cannot be considered a practical control method. As described above, the conventionally proposed methods are unable to control organic carbon appropriately in response to denitrification conditions.

[Purpose of the invention]

The purpose of the present invention is to be able to express the denitrification state with high accuracy;
An object of the present invention is to provide an organic carbon injection method and an apparatus for the same that are not restricted by process configurations.

[Summary of the invention]

The non-invention is to preset the target value of the redox potential that forms a good denitrification state in the basic $p month, measure the pH reference value as a whole, set the amount of redox potential corresponding to 11y as 2, and calculate this change. ``In particular, it is necessary to correct the target value of the 4th reduction target value and adjust the organic carbon supply lance based on the corrected redox potential l:I standard.

[Example of actual invention]

According to the present invention, the redox potential is effective as an index representing the entire state of denitrification, and the oxidation-reduction potential is
The present invention was accomplished by spontaneously discovering that there is a correlation with H. 9 below, the basic principles of the present invention based on the English and French 1 will be explained.

The treatment status of the denitrification tank is as follows:
It can be expressed as: (generic term for N and NO2N) and residual organic matter including organic carbon supplied to the tiller: Figure 1 shows
These are the results of varying the amount of inflowing water, the concentration of nitrogen inflowing, and the amount of carbon injection to vary the relationship between the denitrification state and the redox potential at the stage when a steady state is reached. The experiment was conducted at a pH of 7.
．． Set OK! After the ammonium chloride source was nitrified, it was introduced into a desorption tank, and methanol was used as an organic carbon source. From this figure, it can be seen that if the residual organic carbon increases, that is, methanol is excessive, the redox potential decreases, and No.
As N increases, that is, methanol becomes insufficient, the redox potential tends to increase, and it can be seen that there is a clear correlation between the two. In addition, to achieve complete denitrification,
The condition is the presence of a minimum amount of stale carbon. From these results, it can be seen that methanol is not excessive and No and -N are low and a good denitrification state is formed, which is 7. This range exists between approximately 10 QmV and -200 mV. The result of FIG. 1 shows that the tt reduction potential can be applied as a control indicator for methanol, which is a reducing agent.

On the other hand, the redox potential is expected to be affected not only by NOx N and organic carbon but also by many devices. As a result of experimental studies on various factors, it was found that the influence of pH cannot be ignored, as shown in FIG. In Figure 2, the amount of change in oxidation-reduction potential is p)-(==7.0
The value at the time was used as the standard, and it was expressed as the amount of deviation from the standard value. From this figure, the redox potential is linearly correlated with pH,
The correlation coefficient was approximately -60111 J'/PH.

The above results can be explained theoretically. The denitrification reaction mediated by microorganisms can be divided into two stages. NG 1st stage is 7
In the grading reaction of bale carbon, the following formula is obtained when methanol is used as the organic carbon.

0.5 CH2O+0 0.5 CH2O+H”10 e
'1+ ``'''''''(a) 0.5 CH2O+0
．． 5H20=0.5 CO2+2H"+28',
2・・・・・・・・・(4) If we find the redox potential M of these reactions, we get the following formula, where K
1. 2 is the equilibrium constant, F is the Fallate constant, R is the gas constant, and T is the absolute temperature. The second stage is the reduction of NO and -N, and since the majority of NO and -N are NOsN,
This reaction formula is 0.2NOi +1.2H"+ e"
'0.1 N2 +0.6 H20; Kg (6)
The oxidation-reduction potential Eo of this reaction is expressed by the following formula.

・・・・・・・・・・・・(7) From equation (5) and equation (7), the redox potential of denitrification reaction E 1
1, where n is the reaction coefficient. From (8), it can be seen that the redox potential in the denitrification reaction depends on the ratio of NO3N and methanol, and still decreases as the pH increases regardless of the denitrification state. This relationship theoretically supports FIGS. 161 and 2. Figure 3 summarizes the above results. In other words, this indicates that the oxidation-reduction potential when a good denitrification state is formed changes in correlation with pH.

By the way, it is known that the flow rate and water quality of wastewater vary greatly even during a day. Figure 4 shows an example of this. This change in the concentration of inflowing elements is expressed by Takeshi (1) and the formula (
In 2), the factors influencing H+ and OH- production are changed by changing the pI-I of the nitrification tank and the ventrifying tank. Therefore, the fourth
The inflow water conditions are similar to those shown in the figure, and the pH of the nitrification tank is set to 7.
Disaster of supplying methanol to the denitrification tank, which is adjusted to 0 and capable of complete denitrification! tried me. As a result, it was found that the pH of the dechambering tank fluctuated, which was expected to be affected by denitrification and changes in the grains.

To maintain good denitrification conditions in such a denitrification tank,
From equation (8), a method can be considered in which the PH is adjusted to a constant value, and then the organic carbon supply ψ is controlled by 1 so as to maintain the redox potential at a constant value.

A conventional method for solving this problem is to adjust the pH to a constant value and then set the amount of organic carbon supplied so as to maintain the redox potential at a constant value.

By the way, it is known that as the supply of NH3-N and organic carbon in wastewater changes over time, the concentration of generated NO3-N also changes accordingly.

This means that 0H-1f7t, which is a by-product during denitrification, is dissolved and the Pt1 value changes accordingly. Therefore, in order to maintain a constant pH in such a denitrification tank, it is necessary to inject an alkaline agent or an acid depending on the state of the denitrification reaction. This is a complex control method in which two manipulated variables are adjusted with one index), and is not practical. In the nitrification tank z1, as shown in equation (1), in order to prevent 1) H from decreasing due to H+ production, an alkaline agent is usually injected under pressure to perform 1]H control. In addition to this, it is not a good idea to adjust the pH in the denitrification tank as it would increase the operating cost. Furthermore, the OH- produced during the denitrification reaction is used as an agent for the 11+ Nakamoto 1] produced during the nitrification reaction. The production amount is suppressed, and the amount of alkaline agent in the nitrification tank increases, leading to a rise in % MA conversion cost.

Therefore, methods for controlling organic carbon supply that do not require new chemicals and are independent of process configuration are important in sewage treatment plants. An embodiment ff of the present invention is shown in FIG. In Figure 5, in denitrification tank l, No, -N and denitrification tank l
The inflowing water 6 containing the dog is guided and the stirring device 4 maintains the flow excited state.

On the other hand, organic carbon 8, which is a source agent, is injected from the storage tank 2 through the supply device 3 into the denitrification tank 1. The effluent water 7 that has completed the denitrification reaction becomes a mixed liquid in which No and -N are removed and is led to the next step. In such a denitrification tank 1, an oxidation-reduction potential meter 11 and a pH meter 12 are installed to detect the oxidation-reduction potential and pH sound, respectively. Among these, the oxidation-reduction potential target value e corresponding to p is input to the pH detection value upper calculation circuit 14.
7 is set. This setting method begins with PHH quasi-value 1
) Redox potential reference value e that forms a good denitrification state at o. is set in advance, and a relational expression between the pH deviation and the reduction potential change Δe is given. In equation (9), Δe=f 1p−po ) (9) If p>po, Δe becomes negative, and if p×po, Δe takes a positive value. Using the calculated Δe, the redox potential target value e'' is set according to the following equation.

e"=eo+Δe (10) Therefore, if e"beam>I)o, then e. The quotient value and 4v, p<p. If the value is low, the value of the oxidation-reduction potential that forms a good denitrification state is always set. The oxidation-reduction potential target value e 4 output from the arithmetic circuit 14 is input to the comparison circuit 15 . The comparison circuit 15 compares the actually measured f-curing reduction potential detection value e and the target value e'', and outputs the deviation ε ε=e −e'' to the adjustment circuit 16. The adjustment circuit 16 operates the supply device 3 according to the deviation ε to adjust the amount of organic carbon supplied.

The organic carbon supply amount decreases if the deviation ε is negative, that is, the target value e'' is lower than the detected value e, and increases if the deviation is negative.

In this way, by performing the setting operation of the oxidation-reduction potential target value based on the PHH output value, a good denitrification state is always established.

〔Effect of the invention〕

According to the present invention, the denitrification state can be expressed with high precision, and organic carbon injection control that is not restricted by the process configuration becomes possible.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the oxidation-reduction potential and the denitrification state in the denitrification tank. Characteristic diagram showing the relationship between the oxidation-reduction potential and pH that forms the nitrogen state, No. 4
The figure shows the daily fluctuation pattern of inflow water flow rate and nitrogen,
FIG. 5 is a block diagram of one embodiment of the present invention. l...Denitrification tank, 3...Organic carbon supply device, 6...
Denitrification tank inflow water, 11...oxidation-reduction potential meter, 12...
pH meter, 14... Arithmetic circuit, 15... Comparison circuit, 1
6...Adjustment circuit. 2. ζ7 1st ward d Kuchii and ■Kimachi = Densa (7L”F) 20th pHc-)

Claims (1)

[Claims] 1. In the denitrification method of the biological membrane nitrogen process, the denitrification process is based on: 1. Reducing nitrate or nitrite nitrogen in wastewater to nitrogen gas in the presence of organic carbon. P in the mixture at
The method is characterized in that the oxidation-reduction potential of H1 is determined, a preset oxidation-reduction potential target value is corrected based on the PH value, and the supply amount of the fmJm carbon shown on the right is adjusted by this corrected oxidation-reduction potential target value. Methods for controlling biological membrane nitrogen processes. 2. Determine the pH group 4 value for the target value of the oxidation-reduction potential, calculate the amount of change in the oxidation-reduction potential from the deviation between this pH standard value and the PI value, and calculate the amount of change in the oxidation-reduction potential at this severe reduction potential change - city 2. A method for controlling a biological decarboxylation process according to claim 1, wherein the potential target value is corrected. 3. A permissible pH range for the pH standard 1 shift is set, and the redox potential target value is corrected when the pH value deviates from the permissible range. The method for controlling a biological membrane nitrogen process according to item 1.