JPS636455A - Analyzer for ammonia in water - Google Patents

Abstract

PURPOSE:To stably measure the concn. of ammonia nitrogen in water with high sensitivity by providing a gas-liquid contact part which incorporates the gas in a gaseous phase part into test water to equilibrate the concn. of NH3 in the test water and the gaseous phase and a standard soln. injecting mechanism. CONSTITUTION:The test water 1 is pumped P1 into a gas-liquid contact tank 2 and an alkali agent is added by an alkali injecting mechanism 6 into the test water 1 to convert the NH3-N in the test water to NH3. The test water is circulated from the bottom 2a of the tank 2 to the upper part 2b to incorporate the gas in the gaseous phase part 17 into the test water, by which the gas-liquid contact is effectively executed and the concn. of the NH3 between both the gaseous and liquid phases is equilibrated. The standard soln. such as NH4Cl is then added to the test water by the standard soln. injecting mechanism 11. The concn. of the NH3 in the gaseous phase before and after the addition of the standard soln. is measured by a gas permeation type ammonia electrode 7 and the concn. of the NH3 in the test water is determined from the output change of the electrode 7.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to an ammonia analyzer in water that measures 4 degrees of ammonia nitrogen (hereinafter abbreviated as NH, -N) in water online, and is particularly easy to maintain. In addition to enabling stable measurement over a long period of time,
-N? Ammonia analysis in water that can also be applied to Q degree measurement =
Regarding 2.

[Prior art and its problems]

In the biological denitrification process, it is necessary to measure the ammonia nitrogen (hereinafter abbreviated as NH'x-N) concentration in the treated water in order to monitor the process. On the other hand, in water treatment plants, the importance of NH and -N as indicators of contamination of raw water is known. Like this, NH3-N? The need for a device that can measure 7g degrees, especially a device that can automatically analyze it online over a long period of time, has been pointed out in various quarters.

In order to meet such demands, the present applicant proposed a gas purge type ammonia analyzer, and filed a patent application filed in 1983-2.
A patent application is pending as No. 81422. The basic principle of this WW is to make the sample water alkaline and bubble it with air to measure the NH3 content in the exhaust gas, and the standard addition method is applied to this.

FIG. 2 shows a configuration diagram of the analyzer according to the patent application.

In FIG. 2, a certain amount of test water 1 is sampled by a sampling pump P1 and injected into a gas-liquid contact tank 2. During this water test 1, air is injected through the diffuser 3 to perform aeration. P2 is an air pump for supplying air, 4 is a valve for adjusting the air flow rate, and 5 is a back pressure valve. After sampling, alkali injection mechanism 6
Sodium hydroxide is added to test water 1, and test water 1
to a pH of 11 or higher. NHzN in water exists as NH, and NH,'' and the relationship between them is N l(, +
It is expressed as H2O=NH, -+OH- (1). However, at pH>11 the reaction shifts almost completely to the left.

That is, NH and -N exist as dissolved NHff gas. When aeration as described above is performed in this state, NH3 in the water is released into the rising bubbles, and the exhaust gas contains NHj. NH3 in water now? m” degree χ1
, NH3'4 degrees in the exhaust gas is χ. Then, χG- becomes χL(2). Here it is a proportionality constant. The exhaust gas is passed through the electrode housing 8 in which the gas permeable NH and iJ electrodes are inserted.
It passes through the air and is released into the atmosphere. Therefore, the electrode 7 is χ. generates an output E corresponding to .

The relationship between χ0 and E is E = EO-Sl, 1χ0 F. Here, R is the gas constant, T is the absolute temperature, F is the Faraday constant, n is the number of charges of ions involved in the reaction within the electrode, and Eo is χ. = E at 1.

This equation is generally called the Nernst equation.

Substituting equation (2) into equation (3), E = E' o S l-n Z
LE′. -E, -SR, χL (4) are obtained. In other words, the relationship between χ and E is similar to equation (3),
It can be expressed by the Nernst equation. Therefore, when the test water 1 is made alkaline and aerated and the power output reaches a steady value, equation (4) holds true.

The electrode output is input to the arithmetic unit 10 via the converter 9, and the arithmetic unit 10 holds the electrode output at this point in time.

If this hold value is E, then E, = E'.

-SIRχL(5). Next, standard solution injection mechanism 1
1 is activated and a known concentration of N Ha Cf! A fixed amount of solution is injected. As a result, NHs in test water 1? The Hr degree increases and the electrode output also changes. NH3 concentration change is △χ1
, if the power output after the change is E2, then E, = E'. -81,l(χ,+△χL) (
6). Subtracting equation (5) from equation (6), ΔχL ΔE=Ez−E+=−sza(1+ −) (7)
ΔE and Δχ, which are χL, are known, and S can also be determined by measuring the temperature inside the electrode housing with the temperature sensor 12. Therefore, the estimated χ4 is measured using equation (7). When the measurement is completed, the pinch valve 13 is opened, the test water 1 is discharged, and the next measurement is started.

The ammonia analyzer mentioned above detects NHs in water by measuring the NH3 concentration in exhaust gas. Since the sensor measures 1 degree, there is no contact between the sample water and the sensor, which prevents problems caused by contamination of the electrode membrane. Also, changes in water due to changes in electrode characteristics, changes in water quality, etc. are E'. However, depending on the standard solution addition method, E'. Measurement is possible without being affected by changes in

As described above, the above-mentioned NH3 analyzer according to the present applicant has excellent features, but on the other hand, it also has the following drawbacks.

First, as shown in equation (2), χ. is proportional to χL, but χ, is lower than the equilibrium concentration for χ. That is, the NH3 partial pressure in the exhaust gas is lower than that in water. This means that in measurements near the lower limit of quantification with the NH3 electrode,
Conventional measurement method in which an electrode is inserted directly into the liquid (NH in water,
(measures partial pressure).

The second drawback is the problem of foaming in the gas-liquid contact tank due to aeration. In particular, when measuring wastewater, bubbles are likely to occur, and the bubbles may accumulate on the liquid surface and even reach the inside of the electrode holder 8. Foaming wets and contaminates the gas-liquid contact f#2 and the inside of the piping. Since N Hx is easily absorbed in contaminated areas, χ with respect to the change in χL. The response is significantly delayed and eventually becomes unmeasurable.

[Purpose of the invention]

The present invention was made to solve the above-mentioned drawbacks of the conventional ammonia analyzer, and its purpose is to provide easy maintenance and stable measurement over a long period of time, as well as to make it possible to analyze low concentrations of NH3-N. An object of the present invention is to provide an on-line water ammonia analyzer that can be applied to the measurement of the concentration of .

[Key points of the invention]

In order to achieve the above-mentioned object, the present invention provides: - a bubble contact tank filled with a fixed amount of test water, and a gas in the gas phase in the tank by circulating the test water in the tank from the bottom to the top; a test water circulation system that involves the test water in the test water, a gas i3 type ammonia measuring electrode inserted into the tank so as to be in contact with the gas phase, and an alkali injection mechanism connected to the tank and injecting an alkaline agent into the test water. and a standard that is connected to the tank and injects a standard solution containing a known concentration of ammonia nitrogen into the sample water. After making the sample water alkaline by injecting an alkaline agent from the alkali injection mechanism, the output value is held when the electrode output reaches a certain value, and then from the standard solution injection mechanism. The present invention is characterized in that a fixed amount of the standard solution is injected into the test water to determine the amount of change in the electrode output from the hold value, and the ammonia nitrogen concentration in the test water is measured from this amount of change.

The above-mentioned present invention can be summarized as follows: - a gas-liquid contact part into which a fixed amount of test water is introduced, and having means for dispersing the gas in the gas phase into the test water;
A measuring electrode is used to measure the N H3 concentration in the sample water and the N in the gas phase.
A known amount of NH3-N is added to the test water while keeping the H3 concentration in an equilibrium relationship, and the NH:1 concentration in the test water is measured from the change in electrode output at that time.

The reason why the underwater ammonia analyzer according to the above-mentioned prior application employs the glance method is based on the idea that it takes a long time to bring NH into an equilibrium state between gas and liquid. In other words, in the glance method, if N Hy > la degree in the exhaust gas, is N H3 in water? Although the equilibrium of 4 degrees with respect to a degree is not achieved, the proportional relationship of equation (2) holds true. Since it is not an equilibrium relationship, it will vary depending on water quality, bubble diameter, etc., but the idea is that it is sufficient to be able to measure it in a manner that does not depend on fluctuations using the standard addition method.

On the other hand, as a result of repeated experiments and research, the present inventors found that
It has been found that vapor-liquid equilibrium is easily achieved in the case of NH. Furthermore, since NH is easily adsorbed in the control, it is necessary to increase the gas exchange rate between gas and liquid in order to speed up the response of changes in NH gas concentration in the gas phase to changes in NHs fi degree in the liquid. One thing became clear. The present invention is based on such knowledge, and will be explained in detail with reference to Examples below.

[Embodiments of the invention]

FIG. 1 is a block diagram of a specific example of an ammonia in water analyzer according to the present invention. In the figure, the same numbers as in FIG. 2 represent the same names. At the start of measurement, the water sampling pump P
1 is activated and test water 1 is injected into the gas-liquid contact tank 2 to fill it. If there is any water left in tank 2 from the previous test, some new sample water will be added to the overflow pipe 1.
4. The water is discharged through the water seal pot 15 and replaced with new test water. When the sampling of the test water 1 is completed, the alkali injection mechanism 6 connected to the tank 2 is activated to inject an alkaline agent into the test water I to make the pH of the test water I 11 or higher. As a result, N H3N in test water 1 becomes N H3.

Reference numeral A denotes a test water circulation system, which circulates the test water 1 in the tank 2 from the bottom 2a to the top 2b of the tank 2, and involves the gas in the gas phase 17 in the tank 2 into the test water 1. That is, the sample water I is drawn out from the bottom 2a of the gas-liquid contact tank 2 via the pipe 18, and is circulated again by the circulation pump P3 so as to flow into the tank 2 from the top 2b of the tank 2. At this time, as the upper part 2a of the test water 1 falls, the gas in the gas phase portion 17 in the tank 2 is drawn into the test water 1, and gas-liquid contact is effectively performed. With this method, the bubbles floating on the water surface of test water 1 are caught up in the water and disappear, so there is no need to worry about bubbles accumulating on the water surface, unlike in the conventional method.

The gas-permeable ammonia electrode 7 is inserted into the gas phase section 17 inside the tank 2 from the upper part 2b of the tank 2, and its output signal is inputted to the arithmetic unit 1o via the signal converter 9. After a certain period of time elapses after the start of the measurement, the NH concentration χ in water and the NH concentration χ in the gas phase reach equilibrium. That is, χ6=(1/H) χL(8). Here H is Henry's constant. therefore,
The standard addition method described above can be applied. That is, when the electrode output becomes stable, the value is held, and then the standard solution injection mechanism 11 connected to the tank 2 is activated. A solution containing ammoniacal nitrogen, such as N84Cj!
Inject constant N of standard solution. As a result, the power output changes, and χ is calculated based on the amount of change in the output from the hold value. These series of operations are performed by the computing unit 10.

Further, control of water sampling, operation of the chemical injection mechanism, calculation timing, etc. is performed by the soak controller 16.

〔Effect of the invention〕

As described above, in the ammonia in water analyzer according to the present invention, the gas-liquid contact is performed so that the gas in the gas phase in the gas-liquid contact tank is involved in water, so troubles due to foaming do not occur. Furthermore, since the inner wall of the tank is kept clean, there is less delay in response due to NH3 adsorption. Furthermore, in this method, the high rate of gas exchange between gas and liquid also helps to improve response speed.

In the conventional vapor deposition method, it was not possible to increase the amount of air injected at to suppress the generation of bubbles.

Therefore, the amount of NH3 released from the liquid is small, and the adsorption E
It was easy to receive l. That is, NH in water.

After the NH in the released gas changes with the change in concentration,
In order for the NHz concentration in the electrode part to quickly settle to a constant value, NH must be removed between the gas phase part and the inner wall of the tank.

must reach adsorption equilibrium quickly. To achieve this, it is necessary to increase the rate of NH3 exchange between gas and liquid.
Conventional methods cannot do that. In contrast, with the present invention, since there is no need to worry about foaming, it is possible to increase the amount of sample water circulated, increase the amount of gas entrained (equivalent to the amount of air injected in the conventional method), and increase the gas exchange rate. .

Next, the present invention utilizes the relationship of equation (8), which is similar to equation (2). However, since χ6 in (8) is the equilibrium concentration with respect to χL, (1/H)>.

That is, for the same sample water, in the case of the present invention, the NHi? The degree of W is higher than that of conventional products. Therefore, according to the present invention, it is possible to measure a higher concentration. Also,
Since (8) is a vapor-liquid equilibrium relationship, H is a function of temperature and does not vary due to various factors as in (8), which is also an advantage in obtaining stable measurements. .

[Brief explanation of drawings]

FIG. 1 shows a configuration diagram of a specific example of the device according to the present invention, and FIG. 2 shows a configuration diagram of a conventional device. 1. Water test, 2. Gas-liquid contact tank, 2a. Bottom, 2b.
・Upper part, 6. Alkali injection mechanism, 7. Gas-permeable ammonia electrode, 11. Standard solution injection mechanism, 17. Gas phase section, A. Water test circulation system.

Claims (1)

[Claims] a gas-liquid contact tank filled with a certain amount of test water; a test water circulation system that circulates the test water in the tank from the bottom of the tank to the top to involve gas in the gas phase in the tank; a gas-permeable ammonia measuring electrode inserted into the tank so as to be in contact with the tank; an alkali injection mechanism connected to the tank to inject an alkaline agent into the test water; and an alkali injection mechanism connected to the tank to inject a known concentration into the test water a standard solution injection mechanism for injecting a standard solution containing ammonia nitrogen of and then inject a certain amount of the standard solution from the standard solution injection mechanism into the sample water to determine the amount of change in the electrode output from the hold value, and measure the ammonia nitrogen concentration in the sample water from this amount of change. An underwater ammonia analyzer characterized by: