JPS5814997A - Control method for biological denitrification process - Google Patents

Abstract

PURPOSE:To properly supply a carbon source to a denitrifying step without any surplus or shortage, by calculating a C amount necessary for the complete reduction of a nitrified N amount obtained from N2O and CO2 concentration in exhaust gas from a waste water-nitrifying step, sludge thickness and a flow rate, and controlling operation on the basis of the calculated C amount. CONSTITUTION:Inflow water 4 and returned sludge 10 are introduced into a nitrifying step 1, and aerated and agitated by air 8 from an aerator 11, so that NH3-N in the water 4 is oxidized into nitric or nitrous N(NOX-N) by nitrifying bacteria. Organic substance in the water 4, acting as a reducing agent, is converted into CO2. Exhaust gas 9 collected by a collector 3 is introduced into N2O and CO2 analyzers 13, 14, to output each concentration C(N2O), C(CO2) to an operation circuit 18. Sludge concentration Sm and an amount Qo of a nitrified liquid from meters 15, 16 are inputted into the circuit 18. In the circuit 18, the total NOX-N amount TN in the water 4 is computed by the formulaI (V is reaction capacity). A necessary amount Qc of a carbon source 7 to be supplied to a denitrifying step 2 is calculated from the formula II (k is the concentration of the carbon source) by the circuit 18. A carbon source-supply means 12 is controlled by a controlling circuit 19.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nitrification/denitrification process for biologically removing nitrogen compounds dissolved in wastewater, and particularly to a method for controlling organic carbon supply in the denitrification process.

Nitrogen compounds in wastewater are one of the causes of eutrophication in lakes and inland seas, so it is important to remove all nitrogen compounds, so-called denitrification. There are various methods for denitrifying wastewater, but the biological nitrification and denitrification method, which biologically disperses nitrogen gas (hereinafter referred to as N2), is most commonly used. The biological membrane nitrogen process consists of a centripetalization process in which ammonia nitrogen is oxidized to nitrate or nitrite nitrogen (hereinafter collectively referred to as NOx N) under aerobic conditions, and NOx Nk to N2 gas under anaerobic conditions. It generally consists of a denitrification process that reduces nitrogen to In the denitrification process, the reducing agent for denitrification becomes multi-fibered, and an organic carbon source such as methanol which is a hydrogen donor is supplied. This organic carbon source supply is one of the important operations in the biological denitrification process. That is, if too little carbon source is added, the amount of NOx and N will remain, and the denitrification reaction will proceed in the sedimentation tank installed downstream of the process, resulting in sludge floating and deteriorating the quality of treated water. On the other hand, excessive addition of a carbon source completely reduces the amount of NOx and N, but leaves a residual carbon source.This residual carbon source increases the organic matter concentration in the treated water, deteriorating the quality of the treated water and requiring the use of an expensive carbon source. It is unreasonable consumption and uneconomical. For this purpose, the carbon source must be supplied in such a way that the amount of NOx and N to be reduced is not excessive.

Conventional carbon source supply methods have adopted a contradictory method of over-adding771- to avoid the inconveniences caused by under-adding, and removing microorganisms from the carbon source remaining in the denitrification process effluent in a re-aeration tank. . Another method is to measure the amount of nitrogen in wastewater using a nitrogen analyzer, and then increase the amount of carbon source supplied in proportion to the measured value or the product of the measured value and the flow rate of the wastewater. However, water quality analyzers lack sufficient reliability and maintainability.
Also, 1.

The reality is that it is difficult to establish a control method due to drawbacks such as the need for pre-treatment of the sample water.

The purpose of the present invention was devised to address the shortcomings of conventional organic carbon source supply control methods.
The object of the present invention is to provide a highly reliable carbon source supply control method that appropriately supplies all the carbon sources necessary for complete reduction of the amount of x 7 N, improves the quality of treated water and stabilizes the process.

The present invention is capable of calculating the total amount of nitrified nitrogen from N2o gas and CO2 gas generated by oxidation and denitrification in the process of bringing nitrogen compounds and organic compounds into contact with microorganisms under aerobic conditions, as well as sludge concentration and inflow water volume. Based on this, and using the fact that a similar phenomenon occurs in the nitrification process, we can calculate the amount of N20t, C02Ill in the exhaust gas in the nitrification process.
The overall feature is to determine the amount of carbon necessary to completely reduce the amount of nitrified nitrogen calculated from the sludge concentration and flow rate, and to supply this necessary amount of carbon to the denitrification process.

The invention is based on nitrous oxide (nitrous oxide) in exhaust gas under aerobic conditions.
The generated amount RN20 (hereinafter referred to as N20) is proportional to the product of the NOx N concentration t in the waste water and the organic matter concentration f as shown in Figure 1, and the organic matter load l is as shown in Figure 2 in the exhaust gas. Carbon gas (hereinafter referred to as C02) generation amount Rc
This is based on the experimental discovery that it can be expressed by o2. From Figure 1, the amount of N20 generated is RNO-'.・f、tゎ・・・・・・・・・(1)
The flow rate Q is given by the following equation, and the N20 concentration CN
It is also determined by 20.

RN2o="'n ・CN?O"Qt/Sm ・U...
・・・・・・・・・・・・(2) Here, S□ is the sludge concentration, and U is 'filk in the reaction volume 1.
``U'' is a calculation coefficient. From equations (1) and (2), N0x
-One N concentration is ta=-・CN2o-Qr/f-sm -cr...
・・・・・・・・・・・・(3) (k, = k I,
”/ni'I,) On the other hand, the organic load t is the amount of CO2 generated R
The second term on the right side of this equation is the amount of CO2 generated by self-respiration of microorganisms, and k'c, A>> b
Therefore, it can be almost ignored. k'C is a calculation coefficient.

The organic matter load t is L= f-Qo/S, ・V ・・・・・・・・・・・
・ (5) Q here. is the wastewater flow rate. Cabinet, CO2
Generation amount Rco 2 RCo5-//ceCco2・Qg/S0-■...
・・・・・・・・・ (6) If we rearrange equations (4), (5), and (6) with respect to f, we get f = kc −CCO2”Q, g /Qo
(kC=k”C/+1・・・・・・・・・・・・
('I) Here, CCO2 is the CO2 concentration in the exhaust gas. (3)
By substituting the formula (7) into the equation, the NQx N concentration 1ゎ in the wastewater can be found, and the total NOx N amount in the wastewater TNT N
” 'a.Q.

・・・・・・・・・・・・ (8) Is the non-invention the amount of NOx -N measured by a general-purpose measuring device? An embodiment of the present invention will be described with reference to FIG. 3, which is based on the fact that it can be detected. FIG. 3 shows an example of a general biological membrane nitrogen process in which a nitrification step 1 and a denitrification step 2 are a series. Inflow water 4 and return sludge 10 flow into the nitrification process 1, where they are aerated and agitated by air 8 from an aeration device 11, and ammonia nitrogen in the inflow water 4 is oxidized to NOx N by the action of nitrifying bacteria. The inflow water 4 contains organic substances, and this organic substance acts as a reducing agent to cause denitrification and scatter N20 gas.

Further, the organic substances in the inflow water 4 are oxidized and decomposed and converted into CO2 gas. From this, the exhaust gas after aeration contains N20 gas and CO2 gas generated during the nitrification process. Therefore, by monitoring the exhaust gas, sludge concentration, and nitrification liquid amount in the nitrification step 1, the amount of NOx N can be known in advance. In the denitrification process 2, N0x-N of the nitrification liquid 5 is supplied to the carbon source 7 from the carbon source supply device 12.
The denitrifying liquid 6 from which nitrogen has been removed is discharged. In such a process, in the embodiment, a nitrification process lVC exhaust gas collector 3 is installed, and the collected exhaust gas 9 is passed through a nitrous oxide analyzer 13 and a carbon dioxide gas analyzer 14.
The measured N20 concentration CN20 and CO2 concentration Cc
The o2 signal is output to the full calculation circuit 18.゛Arithmetic circuit 18
, the sludge concentration S0 from the sludge concentration meter 15 installed in the nitrification process 1 and the nitrified liquid amount Q from the flow meter 16. is input and (
8) The total NOx N amount TN of the nitrifying liquid 5 is calculated based on the formula.

The amount of carbon source supplied to the denitrification step 2 may be the amount Qc'x required to reduce the amount of NOxN TN in the inflowing nitrification liquid. This required amount of carbon source Qc is N Ox N
It is obtained from JL T N using the following formula. Here, k is the carbon source concentration Qc- to -TN (9) Here, k is the proportionality coefficient that takes into account the carbon source concentration and the reaction coefficient between the carbon source and NOx N. Out. The arithmetic circuit 18 calculates the required amount of carbon source Qc based on the equation (9) incorporated into Kirin.
k is calculated and output to the control circuit 19.

The control circuit 19 adjusts the carbon source supply device 12 so that the amount of carbon source supplied to the denitrification step 2 is maintained at the required amount Qck of carbon source. By using such a control method, the carbon source supply corresponding to the amount of NOx N in the nitrifying solution is constantly operated, and the entire denitrifying solution without residual NOx N and carbon sources can be provided.

In the embodiment, the flowmeter 16 is intended for the nitrification liquid 5, but if the nitrification process is an overflow type, the measurement delay can be eliminated by installing the weir type flowmeter in the entire nitrification process. In addition to organic carbon sources such as methanol and dulcose, the carbon source may also be sewage containing organic pollutants, digestion gas containing methane, and the like. Furthermore, the dead time of the control system can be completely shortened by locating the exhaust gas collection and sludge concentration measurement in the nitrification process at the rear part where nitrification and biological oxidation are stabilized, although the position is not limited to %.

According to the present invention, since carbon is supplied in proportion to the amount of nitrified nitrogen, carbon sources can be saved, and high-quality treated water without residual carbon sources and nitrogen can be provided. Furthermore, since the amount of nitrified nitrogen can be detected using established measuring instruments, a highly reliable carbon source supply control system can be realized. Hotly,
Since the amount of nitrified nitrogen can be predicted before the denitrification process, feedforward control becomes possible.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram of the amount of N20 generated versus the product of NOx N concentration and organic matter concentration in wastewater, and Figure 2 is a characteristic diagram of organic matter load and C
A characteristic diagram of the amount of O2 generated, FIG. 3 is a system diagram showing an embodiment of the present invention. 1... Nitrification process, 2... Denitrification process - 3... Exhaust gas collector, 4... Inflow water, 5... Nitrification liquid, 6...
・Denitrification liquid, 7... Carbon source, 9... Exhaust gas, 11...
・Aeration device, 12... Carbon source supply device, 13... Nitrous oxide analyzer, 14... Carbon dioxide gas analyzer, 15...
・Sludge concentration meter, 16...Flow meter, 18...Arithmetic circuit, 19...Control circuit, 8...Air, ¥-l Hard; Chi2 Hard! (ηichi gourd/ri, ss/i)! 3rd eye

Claims (1)

[Claims] 1. Nitrogen compounds and organic pollutants in influent wastewater are oxidized under aerobic conditions, and nitrate nitrogen or nitrite nitrogen is reduced in the presence of total organic carbon in the nitrification solution flowing out from the nitrification process. In a biological membrane nitrogen process that includes a denitrification process in which nitrogenous gas is removed, the nitrous oxide and carbon dioxide concentrations of the gas emitted from the nitrification process are measured, and the sludge concentration from the nitrification process is measured. and the flow rate of the nitrifying solution, and calculating the nitrified nitrogen t'r in the nitrifying solution from the nitrous oxide concentration, carbon dioxide concentration, sludge concentration, and nitrifying solution flow rate. Calculate the amount of organic carbon required, and determine the amount of organic carbon to be supplied to the denitrification process based on the amount of organic carbon. A method for controlling biological membrane nitrogen processes characterized by 'regulation'.