JPH087183B2 - Batch continuous automatic ammonia measurement method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for analyzing ammonia in water for online measurement of ammoniacal nitrogen (NH ₃ —N) concentration in water, which is particularly easy to maintain and long-term. The present invention relates to a batch continuous automatic ammonia measuring method which enables stable measurement over a period of time and can be applied to measurement of low concentration of ammonia nitrogen.

(Prior Art) In a biological denitrification process, it is necessary to measure the concentration of NH ₃ —N in the treated water in order to monitor the process. On the other hand, the importance of NH ₃ —N is known as an index of pollution of raw water in water purification plants. As described above, the need for an apparatus capable of measuring the NH ₃ —N concentration, particularly on-line for a long time and automatically analyzed, has been pointed out in various fields.

In order to meet such requirements, the applicant of the present invention has proposed a method for analyzing ammonia in water (Japanese Patent Laid-Open No. 63-16).
(See Japanese Patent No. 5751).

FIG. 3 shows a schematic configuration diagram of the analysis method according to the above-mentioned application. In the figure, the solid line represents the flow of substances and the broken line represents the flow of signals. The sample water is pumped up by the water sampling pump P ₁ and introduced into the water sampling tank 13 installed outside the analyzer rocker. Into the rocker is introduced a small amount of sample water, pinch valves V1, enters the measuring cell 4 via the tube pump P _3. In this process, NH ₄ Cl standard solution and alkaline agent (NaOH)
Is mixed into the sample water. This NaOH is injected from the alkali tank 14 into the sample water flow path on the discharge side of the tube pump P ₃ by the metering pump P ₄ . The injection flow rate is determined so that the pH of the liquid to be measured becomes 11 or more, and this relationship is expressed by the equation (1).

NH ₄ ⁺ + OH ^- NH ₃ + H ₂ O (1) This equation (1) moves to the left almost completely at pH> 11. That is, NH ₂ —N exists as dissolved NH ₃ gas.

In this way, the liquid to be measured formed by mixing the sample water and the alkaline agent is continuously introduced into the measurement cell 4. on the other hand,
In the standard solution mixing mechanism A, the standard solution passes from the standard solution tank 15 through the pinchben V ₂ and enters the suction passage of the tube pump P ₃ . The liquid to be measured is introduced into the measuring cell 4, stirred at a slow speed, and flows out.

Inside the measurement cell 4, a gas phase portion (not shown) is formed between the liquid surface of the liquid retention portion and the measurement surface of the alkali gas electrode 3, and when the liquid to be measured is circulated in the measurement cell 4, The NH ₃ -N concentration X _{G in the} gas phase maintains an equilibrium state with the NH ₃ -N concentration X _L in the measured liquid.

 That is, the expression (2) is established.

X _G = X _L / H (2) where H is the Henry's constant.

Therefore, the output E of the ammonia gas electrode 3 is E = E _{O ′} −SlogX _L E _{0 ′} = E ₀ + SlogH (3) where S is the Nernst coefficient, and this output signal E is input to the calculator 1 The ammoniacal nitrogen concentration in the measurement liquid can be calculated. In addition, the computing unit 1 has a pinch valve V ₁
The standard liquid addition rate r is adjusted by generating an on / off signal for alternately opening V ₂ and adjusting the on / off ratio.

For example, the addition rate r is cyclically changed (cycle Tm = 1 hour) in two steps (r1 and r2, r1 <r2). Here, r1 is determined so that the NH ₃ —N concentration of the measured liquid becomes equal to or higher than the measurement limit of the ammonia gas electrode 3. The electrode output E also changes periodically with a change in the addition rate r, and this is used for measurement. The change in the electrode output E may include not only the change in the addition ratio r but also the change in the environmental conditions (particularly the temperature). .

Therefore, in order to solve this problem, while changing the addition rate r in a constant cycle, the moving average of the electrode output E over a time corresponding to an integral multiple of the addition rate changing cycle and half the moving average time are equivalent. The concentration of ammonia nitrogen in the liquid to be measured is obtained by using the past electrode output value for the period of time.

(Problems to be Solved by the Invention) However, since such an alkali analyzer is a continuous flow type, an alkaline agent is constantly injected, and the amount of chemicals increases, so that it reacts with the alkaline agent. , Scale may accumulate in the pipe and block it, the accuracy of the equipment cannot follow the accuracy of addition of standard solution, lack of stability, the amount of drained liquid increases, it takes too long to stabilize, There were important issues to be solved, such as the slow response due to taking the moving average, and the inability to cope with rapid changes in concentration.

In view of the above points, the present invention effectively solves the problems of the prior art, the response time is shortened, the amount of chemicals used is reduced, the maintenance is easy, and a batch capable of stable measurement for a long time is provided. It is an object to provide a continuous automatic ammonia measuring method.

(Means for Solving the Problems) In order to achieve such an object, according to the present invention, a fixed amount of sample water is injected into a measurement cell housed in a constant temperature bath,
The sample water was injected with a standard additive solution of known concentration of ammonia nitrogen for the first time, and further with an alkaline agent to adjust the pH.
The stable output of the ammonia gas electrode installed in the measuring cell after being stirred at 11 or more and accommodated in the thermostatic chamber and the ammonia gas electrode after the second standard addition liquid was injected and stirred It is characterized in that the stable outputs are respectively held and arithmetic processing is performed to measure the concentration of ammonia nitrogen in the sample water.

(Operation) By the way, by such a technical means, in the ammonia measuring method of the present invention, while the conventional sample water is continuously circulated and the standard addition liquid and the alkaline agent are mixed in the sample water, In this method, the first standard addition liquid of known concentration of ammonia nitrogen was injected into a certain amount of sample water, and then an alkaline agent was injected to adjust the pH to 11 or more, and the stable output of the ammonia gas electrode and the first By measuring the concentration of ammonia nitrogen in the sample water, which holds the stable output of the ammonia gas electrode after injecting and stirring the standard addition liquid for the second time and performs arithmetic processing,
Since the measurement time for each measurement is determined, the response time is shortened, the amount of chemicals used is reduced, maintenance is easy,
Stable measurement is possible over a long period of time.

(Example) Next, the Example of this invention is described in detail based on drawing.

FIG. 1 shows a schematic configuration diagram of an embodiment of the present invention. In the figure, parts having the same functions as in FIG. 3 are denoted by the same reference numerals. The batch continuous automatic ammonia measuring device 100 mainly comprises an ammonia gas electrode 3, a measuring cell 4, a water sampling tank 13, an alkali tank 14, and a standard additive liquid tank 15.
And an arithmetic unit 20. The ammonia electrode 3 and the measurement cell 4 are housed in a constant temperature bath 21 indicated by a chain line in order to remove the influence of temperature.

The sample water is introduced into the measuring cell 4 from the water sampling tank 13 by the water sampling pump 7. At this time, the inside of the measuring cell 4 is cleaned by opening the pinch valves 10 and 11. By closing the pinch valve 10 and opening the pinch valve 11, the sample water in the measuring cell 4 overflows and is quantified. The standard addition liquid pump 9 is operated from the standard addition liquid tank 15 to perform the first injection of the standard addition liquid into the measurement cell 4. Further, the alkaline pump 8 is operated from the alkaline tank 14 to inject the alkaline agent into the measuring cell 4 to adjust the pH to 11 or more. In this state, the stirrer 5 and the stirrer 6 provided in the measurement cell 4 stir the liquid to be measured and keep it until the output of the ammonia electrode 3 becomes stable, and when the output becomes stable, the output is passed through the converter 2. The sample hold element (FIG. 2) 22 of the arithmetic unit 20 is made to hold.

Next, the standard addition liquid is injected for the second time, and the liquid to be measured is similarly stirred by the stirrer 5 and the stirrer 6 and kept until the output of the ammonia electrode 3 becomes stable. The sample hold element 23 is held. The arithmetic unit 20 performs arithmetic processing based on the electrode outputs of the first and second times to obtain a measured value.

The arithmetic processing by the arithmetic unit 20 is basically the same as that of the conventional arithmetic unit 1 shown in FIG. However, since the ammonia measuring apparatus 100 is of batch processing type, it is not necessary to use the moving average of the cycle for the change in the addition amount of the standard addition liquid, and the configuration is simplified.

Ammonia concentration (X _L ) in the measured liquid shown in equation (2)
And the ammonia gas concentration (X _G ) in the gas phase in the measuring cell 4
With respect to the vapor phase equilibrium relationship with, the Henry constant H is kept constant within one batch of processing by placing the measuring cell 4 and the ammonia gas electrode 3 in the constant temperature bath 21.

The electrode output E ₁ when the standard solution addition rate r = r ₁ is given by the following equation (4)
Is established.

E ₁ = E ₀ −SlogX _G1 (4) When this output E ₁ becomes stable, the next standard solution addition rate r
The following equation (5) holds for the electrode output E ₂ when = r2 (r1 <r2).

E ₂ = E ₀ −SlogX _G2 (5) The following equation (6) holds for the difference ΔE between the electrode outputs E ₁ and E ₂ .

Here, XL1 = HXG1 (7) X _L2 = HX _G2 (8) Further, the formulas (9) and (10) hold for the ammonia concentration of the measurement liquid when r = r1 and r2. .

X _L1 = (1-r1) X ₀ + r1X _S … (9) X _L2 = (1-Δr-r1) X ₀ + (Δr + r1) ・ X _S … (10) where X ₀ : ammonia concentration in the sample water X _S : Ammonia concentration of standard solution Δr = r2-r1 Next, in order to transform _{XL 1} using the equations (6) to (10), the equations (9) to (11) are changed to Then, X ₀ = (X _L1 −r1X _S ) / (1−r1) (11) Substituting into equation (10), we obtain equation (12).

Here, if the ratio of XL1 and XL2 is R, then equation (13) holds.

Equation (13) is transformed into equation (14).

By substituting the equation (14) into the equation (11), the ammonia concentration X ₀ in the sample water can be obtained from the known Δr, r1, R, X _S by the equation (15).

That is, Next, FIG. 2 is a block diagram of the arithmetic unit shown in FIG. In the figure, the arithmetic unit 20 is mainly composed of sample and hold elements 22, 23, a divider 24 and a four-law arithmetic unit 25. Electrode outputs E ₁ and E ₂ shown in equations (4) and (5)
Are held in the sample and hold elements 22 and 23, respectively. From the held output, the divider 24 calculates the ratio R of the concentrations X _L1 and X _L2 shown in the equation (13). The four-law arithmetic unit 25 performs the arithmetic processing shown in the equation (15) to obtain a known Δr,
Calculate the ammonia concentration X ₀ in the sample water from r1, R, X _S.

Thus, the alkali gas electrode 3 and the measuring cell 4
Is housed in a constant temperature bath 21 to reduce environmental fluctuations, adopts a batch processing method, and the response time is determined by each measurement time, the amount of chemicals used can be reduced, and stable injection of standard additive solution is possible. It is possible. Further, by incorporating a washing step with the sample water in the measurement cell 4 for each measurement, it is possible to significantly reduce the adhesion of scale in the pipe.

(Effects of the Invention) As described above, according to the present invention, a fixed amount of sample water is injected into the measurement cell housed in the constant temperature bath, and the first concentration of ammonia nitrogen is added to the sample water. Stable output of the ammonia gas electrode housed in the thermostat and installed in the measuring cell after the known standard additive solution was injected and the alkaline agent was further injected to pH 11 or above and stirred, and the second standard By maintaining the stable output of the annimonia gas electrode after the added liquid is injected and agitated to perform the arithmetic processing to measure the concentration of ammonia nitrogen in the sample water, the problems of the prior art are effectively obtained. Solved by adopting the batch processing method, the response time is determined by the measurement time for each time, so the time is shortened, and the amount of chemicals used is reduced, so stable standard solution addition is possible and maintenance is possible. Easy, as well as a possible long term stable measurement over an effect such as may be applied to low concentration measurement of ammonia nitrogen.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, and FIG.
FIG. 3 is a block diagram of the arithmetic unit shown in the figure, and FIG. 3 is a schematic configuration diagram of a conventional ammonia analysis method. 3 ... Ammonia gas electrode 4 ... Measuring cell 7 ... Water sampling pump 8 ... Alkaline pump 9 ... Standard addition liquid pump 13 ... Water sampling tank 14 ... Alkaline tank 15 ... Standard addition liquid tank 20 ... Calculator 22, 23 ... Sample hold element 24 … Divider 25… 4 arithmetic unit 100… Batch continuous automatic ammonia measuring device

Claims (1)

[Claims] 1. A fixed amount of sample water is injected into a measurement cell housed in a constant temperature bath, a standard additive solution of known concentration of ammoniacal nitrogen for the first time is injected into the sample water, and an alkaline agent is further injected. The stable output of the ammonia gas electrode installed in the measuring cell after being adjusted to pH 11 or more and stirred and stored in the constant temperature bath, and the ammonia gas after the second standard addition liquid is injected and stirred A batch continuous automatic ammonia measuring method, characterized in that a stable output of each electrode is held and arithmetic processing is performed to measure the concentration of ammonia nitrogen in the sample water.