JPS58104698A - Controlling method for biological denitrification - Google Patents

Abstract

PURPOSE:To stably make the quality of water excellent, by detecting amounts of nitrogen suboxide and CO2 formed in a reaerating tank from exhaust gas from the tank, and controlling the amount of organic carbon to be supplied on the basis of the detected values in response to residual nitrogen or the like in a denitrified liquid. CONSTITUTION:Exhaust gas 10 from a reaerating tank 2 is gathered by an exhaust gas collector 3, the concentrations of CO2 and Na2O are measured by a carbonic acid gas analyzer 14 and a nitrogen suboxide analyzer 15, respectively, and the resulting signals are inputted to an arithmetric circuit 21. In the arithmetic circuit 21, an amount of aerating gas measured by a flow meter 17 is inputted, amounts of formed Na2O and CO2 are calculated and outputted to a judging circuit 22. In the judging circuit 22, whether an amount of an organic carbon source to be supplied to a denitrifying step 1 is proper or not is judged on the basis of the amount of each of the formed gases and the concentration of sludge in the reaerating tank measured by a densitometer 16 for sludge.

Description

[Detailed Description of the Invention] The present invention relates to a biological denitrification method for biologically removing nitrogen compounds dissolved in wastewater, and particularly relates to a method for controlling organic carbon supply in a demineralization process. be.

Nitrogen compounds in wastewater are one of the causes of enrichment in lakes and inland seas, and so-called denitrification, which removes nitrogen compounds, is important. There are various methods for removing nitrification from wastewater, but the most commonly used is the biological nitrification/denitrification 11:a method in which wastewater is biologically dispersed as nitrogen gas (hereinafter referred to as N). The biological denitrification process consists of a nitrification process in which ammoniacal nitrogen is oxidized to nitrate or 11-nitrite nitrogen (hereinafter collectively referred to as NoxN), and a nitrification process in which ammoniacal nitrogen is oxidized to nitrate nitrogen (hereinafter collectively referred to as NoxN), and
It generally consists of a denitrification process in which nitrogen is reduced to gas under anaerobic conditions. In the denitrification step, a reducing agent is required for the desilination, and an organic carbon source such as methanol as a hydrogen donor is supplied. This organic carbon source supply is one of the important operations in the biological denitrification process.

That is, under-addition of the carbon source will not only result in a residual amount of N, but also cause the denitrification reaction to progress in the sinking system installed downstream of the process, causing sludge to float up and deteriorating the quality of the treated water. - Excessive addition of a carbon source completely reduces NOx Nt, but leaves the carbon source behind, and this residual carbon source increases the organic matter concentration in the treated water, deteriorating the quality of the treated water and making it unnecessary to use an expensive carbon source. It is uneconomical as it consumes a lot of energy. The supply of carbon source for this is NOx N to be reduced.
It must be done so that there is no excess or deficiency in the amount.

Conventional carbon source supply methods involve adding too much to avoid the inconvenience caused by adding too little, and then re-exposing the carbon source remaining in the denitrification process effluent to remove microorganisms. Another method is to measure the amount of nitrogen in wastewater using a phonetic analyzer and make the amount of carbon source supplied proportional to the measured value or the product of the measured value and the wastewater current. The reality is that water quality analyzers do not have sufficient reliability or maintainability, and they require pretreatment before testing water, making it impossible to establish a control method.

The present invention was devised to address the shortcomings of conventional organic carbon source supply control methods, and it
The purpose of this invention is to provide a highly reliable carbon source supply control method that appropriately supplies the carbon source necessary for complete reduction of the amount of carbon, improves the quality of treated water and stabilizes the process.

The present invention is based on the fact that under aerobic conditions, N, 0 gas is generated in response to the amount of N0x-N in wastewater, and CO, gas is generated in response to the amount of organic matter, and the N,0 gas in the reaeration tank exhaust gas is generated. ,
The amount of O generated and the amount of CO1 generated are detected, and when the amount of N and 0 generated is above a predetermined amount, the organic carbon to the denitrification process is increased based on the amount generated, and when the amount of CO1 generated is above the specified amount is C
The special mission is to reduce the amount of carbon based on the amount of O8 generated and to prevent the amount of NOx-N and carbon from remaining in the denitrification liquid of the denitrification process.

First, the basic principle of the present invention will be explained.

The present inventors found that when wastewater containing nitrogen compounds and organic compounds is brought into aerobic conditions by intervening microorganisms, nitrous oxide (hereinafter abbreviated as N, 0) gas However, it was experimentally discovered that carbonic acid (hereinafter abbreviated as CO3) gas is generated in response to organic compounds. Generally N,
Although zero gas is generated under anaerobic conditions, it has been confirmed that it is also generated in detectable amounts under aerobic conditions. N, O, and CO gas concentrations in aeration exhaust gas can be measured online using an infrared spectrophotometer or the like. Figure 1 shows the relationship between the amount of N, 0 generated R1o and the amount of nitrogen TN. Figure 2 Fico shows the relationship between the generated amount Reed and the organic matter load, and the relationships of equations (1) and (2) hold true. Here, S is the sludge concentration field, * “I e
bl * bl is Rlwl o = J ” TN+ b
l ” Swa song/song (i) Reol = ”1
・L + b@ ・8w* ”” (2) Each is a constant. On the other hand, the amount of N and 0 generated in exhaust gas and the amount of CO
The amount of 2 generation is expressed by equation (3), (47).

Here 'Flyg o = kt ' C-t o @Qg
...”””” (3) Rco = kg ・C
co, ・Qg …・l−… (4) kl * k
l is a constant, C1o is N and O gas concentration, Cco *
The riCO* gas concentration, Q, is the exhaust gas flow rate or aeration flow rate. (3), (By substituting the respective generation amounts obtained in Equations 43 into Equations (1) and (2J), it is possible to estimate the amount of nitrogen in wastewater TN and the organic matter load. If elemental components exist, N and O gases are generated, and the amount of nitrogen is determined by the amount of N and 0 gases generated in the exhaust gas.Also, if organic substances are present, CO1 gas is generated, and the organic substances The amount is determined from the amount of CO3 generated in the exhaust gas.

The present invention applies this basic relationship to the supply of organic carbon sources in the denitrification process of biological withdrawal voting. FIG. 3 explains one embodiment of the present invention, which is directed to a syrocess configuration in which a re-aeration tank 2 is placed downstream of the demineralization step 1.

In Fig. 3, 4 is an inflow containing an amount of NOx -N, 6 is an organic carbon source that serves as a reducing agent for NOx N, 5 is a mixed liquid of Takiiri and carbon sources, 7 is a dewriting liquid, and 8 is a Fi processing liquid. , 9 is an aeration gas in which air is generally used, 11 is a carbon source supply device, and 12 is an air supply device.

In such a process i, part or all of the exhaust gas lO from the reaeration tank 2 is collected by the exhaust gas collector 3,
CO with a carbon dioxide gas analyzer 14 and a stratified tube element analyzer 15,
The concentration Ccol and the Neo concentration Cw@o are fixed, and their signals are input to the arithmetic circuit 21. The aeration gas amount Q1 measured by the flow meter 17 is input to the calculation circuit 21, and (
3) and (4), the amount of N and O generation RhQ and Cot
The generated amount Rco 1 is calculated and output to the determination circuit 22. The determination circuit 22 determines whether or not the amount of organic carbon source supplied in the threat element process 1 is appropriate based on the respective generated amounts and the sludge concentration S1 in the reaeration tank measured by the sludge concentration meter 16. That is, in the denitrification step 1, if the amount of carbon source supplied is too large relative to the N0x-Nt in the inflow 4, the excess carbon source remains in the denitrification solution 7, and the CO and gas corresponding to the excess are removed in the re-aeration tank 2. occurs. Also, conversely, NOx N
If the carbon source is too small relative to the amount, Now-N will remain,
N and O gases corresponding to the amount of residual Now-N are generated from the reaeration tank 2. From this, if there is a lack of organic carbon power supply, the amount of N,0 generated RN @ o will be charged, and the residual N0x - N amount ΔTN can be found from equation (1), and if there is an excess of carbon sources, the amount of generated CO, The amount 1% co@ is paid, and the amount of residual organic matter jL is determined from equation (2), and the selected output residual No.
The t-N amount ΔTNTo or the residual organic matter amount IL is output from the determination circuit 22 to the calculation circuit 23. Furthermore, the right-hand sides of equations (1) and (2)! 2″tli is N by the microorganism itself,
9 represents the amount of O generated and the amount of CO1 generated, residual NOx
- The amount of N and the amount of residual organic matter are calculated based on the amount generated excluding the influence of the amount of these microorganisms. The arithmetic circuit 23 calculates the amount of change jQc in the amount of carbon source based on the input signals ΔTN and ΔL using the formula (8), <5), and the control circuit 24
Output to. Here, k.

k is a calculation coefficient, which is the coal source concentration, reaction molar ratio, conversion ΔQ,
= to, ・ΔTN ・・・・・・・・・・・・ (5
)ΔQ,=−,・,IfL・・・・・・・・・・
...(Considering the 6J rate, etc.) The control circuit 24 includes a flowmeter 1.
8, the current carbon source Q, is input, and is added to the carbon source change amount ΔQ from the n1 calculation circuit 23 to create a new manipulated variable Q,''
The carbon source supply device 11 is adjusted accordingly. The carbon source operation amount Q g '' is increased by equation (5) when the organic carbon source is insufficient, and reduced by equation (6) when it is in excess.
, by performing carbon source supply operation based on the amount of change in nine carbon sources calculated from the amount of 0 emissions and the amount of CO8 emissions,
The carbon source necessary for the denitrification reaction is maintained appropriately.

Although the shape of the denitrification process in the present invention is not limited, a complete mixed type denitrification process is preferable for improving control accuracy and reliability.

According to the present invention, it is possible to implement operational management that maintains the amount of residual nitrogen and the amount of residual carbon sources in the denitrification solution at zero, thereby improving the quality of treated water and saving carbon sources.

In addition, the amount of insufficient or excess carbon source can be accurately predicted by highly accurate and reliable gas measurement, and a highly reliable carbon source supply control method can be realized.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram of the amount of NOx-N and the amount of N and O generated under aerobic conditions, Figure 2 is a characteristic diagram of the amount of organic matter load and amount of CO generated, and Figure 3 is an example of the present invention. FIG.

Claims (1)

[Claims] 1. A denitrification process in which nitrate nitrogen or nitrite nitrogen in inflow wastewater is reduced in the presence of organic carbon and removed as nitrogen gas, and a denitrification liquid flowing out from the nuclear denitrification process. In a biological denitrification process that has a re-aeration tank in which residual organic carbon is oxidized and fractionated by air aeration, the amount of nitrous oxide and carbon dioxide generated in the extra-nuclear aeration tank is transferred to the re-aeration tank. The amount of residual nitrogen or residual organic carbon in the denitrifying solution is determined based on the amount of nitrous oxide or the amount of carbon dioxide. A method for controlling biological denitrification, characterized in that the amount of organic material supplied to a nitrogen process is controlled. 2.4I In the method of claim 11i, if the amount of nitrous oxide and the amount of carbon dioxide are within a predetermined range, the amount of carbon supplied by the denitrification technique is maintained at the previously operated amount, and the amount of nitrous oxide is The amount of organic carbon to be fed to the denitrification process is adjusted so as to prioritize and increase the required amount of organic carbon calculated from the amount of nitrous oxide when the amount of nitrous oxide exceeds the predetermined range. (voting) control method.