JPS586284A - Method and device for measuring chlorine demand of water quality - Google Patents

Abstract

PURPOSE:To determine the fore chlorine demand corresponding to the characteristic of raw water by measuring the ammonium ion concn. of raw water and water temp., and determining the fore chlorine demand in a water purification plant by the use of these and the target value of the residual chlorine concn. near the inlet of a settling basin. CONSTITUTION:A device 40 is constituted of an ammonium ion cncn. mesuring part 41, a temp. indicating part 42, a target value setting part 43 for residual chlorine concn., an operator 44, and an indicating recorder 45. The raw water of a trough 5 is sampled with a sampling pump 16 or the like, and this is introduced into the part 41, by which the concn. of the ammonium ions in the raw water is measured. A temp. detector 46 is inserted into the trough 5 and the output thereof is inputted to the part 42, by which the temp. of the water is measured. The demand for the fore chlorine is determined by using these values and the target value of the residual chlorine concn. The fore chlorine corresponding to the momentarily changing characteristics of the raw water in the purification plant is quickly grasped.

Description

DETAILED DESCRIPTION OF THE INVENTION With urbanization and industrialization in recent years, the living environment has been deteriorating, and in particular, urban river water, lake water, and marsh water have become increasingly polluted. Purification of wastewater is progressing through the development and expansion of the Kume Sewerage System, while progress is being made in securing the quantity and quality of drinking water through the development and expansion of water purification plants.

The obligation to ensure the quality of drinking water at water treatment plants is as stipulated in the Water Supply Law, and the main items are shown in Table 1. The residual chlorine degree specified in Table 1 is for the purpose of completely sterilizing microorganisms, pathogenic bacteria, etc. in each water pipe and preventing their recurrence.

Maintenance and management of residual chlorine concentration is one of the most important routine tasks at a water treatment plant. This is accomplished by adding a certain amount of chlorine to raw water taken from a river or the like using a highly controlled chlorine injector.

The present invention relates to a method and apparatus for determining the amount of chlorine injection necessary for maintaining and managing the residual chlorine concentration in a water purification plant.

Figure 1 shows the flow of a typical water treatment plant. River water etc. flows into the intake well 3 through the gate and flow meter 2. Intake well 3
From there, the head is raised to the landing well 5 using the pump 4. Normally, the water up to landing well 5 is called raw water. The raw water in the receiving well 5 is transferred to a water conveyance pipe 6, a mixing tank 7, a sedimentation tank 8, and a filtration tank 9 depending on the head.
The water that passes through is sterilized and purified, stored in the nine-bag water treatment pond 10, and is supplied to a relay pumping station (not shown in the figure) using a pump 11 in accordance with the law 11, and is further supplied to end users.
Chlorine injection in iK is typically performed twice. The first
is carried out in the conduit 6 near the outlet of the landing well 5. This is called pre-chlorine. The purpose of prechlorination is the removal of metal ions such as iron and manganese, the removal of ammonia nitrogen, and sterilization. A second chlorine injection is performed in conduit 12 near the inlet of water treatment pond 10. This is called post-chlorine, and its purpose is to replenish the shortage of pre-chlorine, and to ensure that the residual chlorine concentration in the terminal water supply is maintained at 0.1 ppm or higher.

(All white below) The pre-chlorine injection amount is returned by inputting the output Q (m/H) of the flow meter 2 and the output M (g/H) of the chlorine injector 130 to the controller 14, and calculating the amount before formula (1). The purpose is to control the chlorine injection rate (pm) to a constant value, and to change the pre-chlorine injection rate according to changes in the properties of raw water, for example, the ammonia nitrogen content. Chlorine is stored in chlorine tank 15 and extracted.
It is guided to the chlorine injector 13 through a vaporizer (not shown).

(1) Hatamae Controlling the chlorine injection rate A to be constant is normal ratio control, and almost all water treatment plants have this function.

On the other hand, a method of tracking and controlling the chlorine injection rate according to the properties of raw water, which changes from time to time, involves sampling the raw water in the receiving well 5 at regular intervals and measuring the ammonia nitrogen concentration change d* (ppm). , a method of manually setting the pre-chlorine injection rate by multiplying this by a coefficient obtained empirically by the administrator, or a method of sampling the pumped water from the treatment plant near the entrance of the sedimentation tank 8 with a sampling pump 16 and measuring the residual chlorine concentration meter 17 Residual chlorine concentration a (ppm) using
Currently, a method is being considered in which the pre-chlorine injection rate is automatically set by measuring the amount of chlorine, inputting it into the control@14, and using a so-called feedback method such as proportional control.

However, the above-mentioned manual setting method has drawbacks such as increasing the bone dynamic load that causes individual differences depending on the experience of the worker, and causing a time delay in measurement. Residual chlorine meter 1
There are drawbacks such as not being able to obtain a stable residual chlorine concentration 1 because it is greatly influenced by the constant value of 7. For this reason, in many water treatment plants, based on the ammonia level - dl, which is normally measured once a day, and the residual chlorine concentration - t, which is continuously output by the residual chlorine meter 17, The pre-chlorine injection rate is determined.

Before describing practical examples of the present invention, the amount of chlorine required for raw water will be explained. Chlorine added to raw water is consumed by organic substances, reducing inorganic substances, etc. in the raw water. Of these, consumption by ammonia nitrogen and organic nitrogen is unique and large. An example of chlorine consumption by ammonia nitrogen is shown in FIG.

This is a result of injecting chlorine into a solution containing 0.4 ppm of ammonia nitrogen at one hour intervals and measuring the residual salt lA once. The dotted line in the figure is the total residual chlorine concentration, and the solid line is the free residual chlorine concentration. (Usually, it is often simply referred to as residual chlorine concentration, and in the text, it is also abbreviated as residual chlorine concentration below). D in the figure is referred to as a discontinuity point, and the chlorine injection rate required up to D is referred to as chlorine demand. Normally, the weight ratio of ammonia nitrogen to chlorine demand is 1:8 to 10 (1: Clean water test method, 1978 edition F-314,
Edited by Japan Water Works Association, hereinafter referred to as Document-1). If more chlorine is injected beyond the required amount of chlorine, an increase in residual chlorine will be seen which is approximately equal to the increase in the amount of chlorine injection.

Pre-chlorine injection at the water treatment plant is carried out by setting the target value of the residual chlorine concentration near the entrance of the sedimentation tank 8 in the range of 1 to 2 ppm9. ) is the formula (2)% formula% (2) Chlorine demand = (8~10) x ammonia nitrogen concentration according to literature-1
・・・・・・Equation (3) + 2), (3)
In order to verify this, the relationship between the ammonia nitrogen concentration d1 of the raw water and the actual value of the pre-chlorine injection rate A was investigated from one year's worth of data at a commercial water treatment plant, and this is shown in Figure 3. If formula (2)
If (3) holds throughout the year, A in the diagram
and dl should have good phase. However, the correlation between the two was extremely low. Therefore, equation (2)
In order to apply (3) to determining the pre-chlorine injection rate at water treatment plants, it is necessary to consider seasonal factors, weather factors, etc., and to establish a descriptive formula that can be used throughout the year.

The purpose of the present invention is to investigate the mechanism of reaction between raw water and chlorine, calculate the required amount of chlorine by formulating it, and provide a method and device for quickly and uniquely measuring the required amount of chlorine based on the formula. Our goal is to provide the following.

Figure 4 shows how to make a Jl solution with an ammonia nitrogen concentration of 1 ppm.
The reaction rate was investigated by adding 20 ppm of chlorine to this. The annual value of ammonia nitrogen concentration in raw water at many water treatment plants, which are heavily influenced by urbanization, is 0.1 to 1.5.
The water temperature was in the range of 2 to 30°C, and the experimental conditions were set to suit the actual situation. From this, 9 of the reaction between ammoniacal I1 element and pre-chlorine in raw water of a water treatment plant.
0- is estimated to be completed within 15 minutes throughout the year.

Figure 5 shows chemical oxygen demand (JIS K-0102) 1
A 0 ppm humic acid solution was prepared, a certain amount of chlorine was added to the solution, and the changes in residual chlorine over time were investigated. In many water treatment plants, there are slight differences depending on changes in the amount of water intake, but the time it takes from pre-chlorine injection to the outlet of mixing basin 7 is 30 minutes and 11 degrees. From FIG. 5, the consumed concentration of chlorine during the elapsed time of 30 minutes is shown in Table 2.

Table 2 From Table 2, the amount of chlorine consumed by the amino acid in 30 minutes is shown by the schematic formula (4). Also, the reaction of formula (4) is about 11 times smaller than the reaction of Figure 4! Degree and difference.

Chlorine consumption II 1 degree = chlorine addition concentration 1 eX water temperature X 0026
(4) From the above experiments, in the pre-chlorine consumption reaction at a water treatment plant, the reaction with ammonia nitrogen in the raw water is completed first, and the reaction between the remaining chlorine and organic matter such as humic acid occurs. It is determined that the process will progress.

The simplest way to express this is equation (5).

Input xC1dl +c, -a-T+a+01 ””
(5) Define the symbols again here.

A: Pre-chlorine injection rate (pp pm > a: Residual salt in sedimentation tank 8 artificial water 11. (pprn) C
1* C1+ C@: Constant d,: 'Ammonia nitrogen S degree in raw water (pprfl)
T: Temperature of raw water <”o> Figure 6 shows the verification results of equation (a) 5). This uses data from the 9゛ base water treatment plant described in Figure 3 for one year. The new chlorine consumption B is This is defined by equation (6) and the correlation between B and dl was investigated.

B=mu-C1aT-a == f6) □C
I is an undefined constant. Verification result Ct=4X10de
When g-1, the correlation coefficient between B and dl is r B O, 99.

The regression line is equation (7). From equation (7), C, , C, can be said to be 9.5-0.1, respectively.This result proves the effectiveness of equation 5), and the required pre-chlorine injection rate (referred to as the required amount of chlorine) It was found that zb can be predicted with high accuracy by formula (8) using the ammonia nitrogen concentration 1 fdt in the raw water throughout the year, the water temperature T of the raw water, and the target value a of residual chlorine in the water at the inlet of the settling tank 80. .

B=9.5 dt O,1(r-0,99)
・”” (7) A=9.5 dB +0.04-51
$ -T+a* 0.1 = - (8) The inventor further created a diagram similar to Figure 6 based on one year's worth of data from multiple other water treatment plants, and as shown in Table 3. In both cases, the correlation coefficient r between B and dl was 0.95 or higher, indicating a high correlation.

Consequently, it has been found that equation (5) can be generally applied to water purification plants with high accuracy.

Table 3 (hereinafter all white) The chlorine demand of river water and lake water (point D in the above-mentioned Figure 3) is used for the 0111 constant.

An example of a conventional device will be explained using FIG. 7.

Sample water to be measured is intermittently supplied to a needle metering tank 21 using a solenoid valve 20, and guided to a reaction tank 23 using a pump 22. On the other hand, the agglomerated trichum aqueous solution is stored in a reagent tank 24 and supplied in excess to a chlorine generating tank 26 using a pump 25.

The chlorine generation tank 26 contains a sodium chloride aqueous solution 27. Sodium chloride water-liquid outlet 28, diaphragm 29, cathode 30, anode 31. It is composed of a chlorine gas outlet 32, a hydrogen gas outlet 33, etc., and is well known for its ring formation.

Anodic reaction 1 C4-+ -CAB +1 -... (9) Cathode reaction Na +H10+j -+Na''+OH-+ -L H
l...@-Hydrogen gas (Hs) generated at the cathode is exhausted from the hydrogen gas outlet 33 using an appropriate exhaust means,
Only the chlorine gas (Cj, ) generated at the anode is guided to the reaction tank 23 using a conduit (.

In the reaction tank 23, the above-mentioned amount of sample water was collected! Ill
(!st) When chlorine gas reacts with ammonia nitrogen, organic substances, and reducing inorganic substances contained in chlorine gas, if chlorine gas is supplied in excess of the amount of chlorine required, residual chlorine will remain in the reaction liquid. occurs. This is detected by residual chlorine detection @ 34, and the amount of chlorine required for the paper sample water is calculated from the formula (b) K from the amount of chlorine gas supplied until the residual chlorine exceeds a predetermined value (usually 0.1 pμmm).

n1TomiD=-XIO” (ppm) ・・・・・・
・(6)1 The calculation of formula (b) is executed by the controller 35, and the instruction enhancer 3
6.

The amount of chlorine gas required for the reaction is indirectly determined using the integrating current needle 37 or the like based on the formula @. Here, t is the current (ampere) and t is the time (seconds) required for the reaction.

ms -35,5XI-t/96500
"""Q'1 column After the measurement, the drain valve 3B is opened and the inside of the reaction tank 23 is drained.

FIG. 8 shows an example of the results of measuring the chlorine demand of raw water at a certain water treatment plant using a conventional device. The dotted line in the figure is the indicated value of the conventional device, and XI is the result of manual analysis performed at the same time.

In the conventional example described above, (1) the trace elements contained in the sodium chloride aqueous solution in the reagent tank 24
and the surface of the anode 31 (hereinafter abbreviated as electrode 30.31 stone) is coated and deteriorated; (2) a gradient in the chain degree of sodium chloride occurs near the electrode 30.31; and (3) the diaphragm 29 closes. The above-mentioned 20s has problems such as loss of functionality.
Based on K < Theoretical value of CI3 generation amount - and actually generated C
! There is a difference of several tens of degrees between proverbs in a short period of time. Therefore, it has been extremely difficult to maintain and manage conventional devices based on the measurement principle of equation (2). Also, it usually takes 30 minutes from collecting the sample water to displaying the chlorine demand measurement on the instruction manual @36! This causes a degree of time delay. In the flow of the water treatment plant shown in Figure 1, the residence time of raw water in the water conduit 6 and the mixing pond γ is normally 20 to 30 minutes. The above-mentioned time delay is a fatal flaw when trying to use it as An example of the configuration of the device is shown in FIG. The device 40 includes an ammonium ion concentration measuring section 41, a temperature indicating section 42, a residual chlorine concentration target value setting section 43, an arithmetic unit 44, an indicator performance needle 45, and the like. Raw water from the landing well 5 is sampled using a spring pump 16 or the like, and introduced into the ammonium ion concentration measuring section 41 to measure the ammonium ion concentration in the raw water. The measured value of ammonium ion (W) (hereinafter abbreviated as d) is converted into ammonia nitrogen #l direct d1 using equation (b). A theoretical value of 0.778 is used for C4.

d, -(:a d...(2)d
s = 0.778 d (b) A temperature detector 46 is inserted into the front landing well 5, and its output is input to the temperature indicator 42 to measure the water temperature. Target value of residual chlorine a
As mentioned above, . is usually in the range of 1 to 2 ppm. By substituting these into equation (5), the required amount of chlorine can be continuously calculated using equation (to) using d, T, and heat.

Mu tmc@ C4d+c1 Ill@ ・T+m
@+c, ・m5OJ! Here constant c, ,
Although c', , c, , and C4 vary slightly depending on the water treatment plant, they are approximate from the wL3 table and formula (b).

c, s, s, C1+0.04 + C14”0
°O, Cm +0.78 So, if C1 and C4 are Cm, then Cm +7.4.

Another example of the configuration of this device is shown in Fig. 1''0. 5°K raw water is sampled from a regulating tank using a sampling pump 16 etc. not shown in the figure, and a temperature sensor 51 is inserted into the regulating tank 50 to measure the water temperature T. On the other hand, the raw water in the adjustment hinoki 5o is introduced into the reaction @53 using a bong! When the raw water is maintained at 11 or higher in the reaction tank 53, a Niso reaction occurs and the generated ammonia (NHl) is measured using a commercially available diaphragm electrode 56, etc. When ammonium ion - [d is measured, T and d are input to the calculator 57 and 1. is set, the required amount of chlorine t is continuously determined from K using the above-mentioned formula.

+ - NH, +OH → NH, +H, O...1 Also, dirt on the wetted piping and dirt on the diaphragm of the diaphragm electrode 56 can be removed by running pressurized clean water or using an aqueous solution of several - nitric acid. By adding a cleaning function, this can be prevented and stable performance can be maintained for a long period of time.

FIG. 11 shows an example of measurement at a certain water purification plant mentioned above using the chlorine requirement measuring device described in FIG. 10.

Here, we set a to 1.5 ppm Ic, sampled raw water at each time separately to verify the measured values, and calculated the amount of chlorine injection required to bring the residual chlorine concentration to 1.5 ppm according to Reference-1. This is indicated with an x mark. Both results showed good agreement, demonstrating the effectiveness of this device.

In both the embodiments described in FIGS. 9 and 10, the required amount A of chlorine is determined continuously, but the present invention is not limited thereto. For example, as shown in Figure 12, 1
It is possible to embody equation (5) as a simple device. This device includes a water temperature input section 60, an ammonia nitrogen concentration (or ammonium ion concentration) input section 61, and a residual chlorine concentration target value input section 62. It is composed of a calculation section 63, an instruction section 64, and the like. This involves measuring the temperature T of the raw water using a suitable means, while keeping the ammonia nitrogen concentration d1 (or ammonium ion concentration d) of the raw water constant, and adjusting T, dl (or d) and residual salt Il [target value 1 to the water temperature input section 6o, ammonia nitrogen concentration (or ammonium ion concentration long time section 61, and residual chlorine concentration target value input section 62), and the calculation section 63 calculates the formula (5).
It executes calculations based on K and displays the required amount of chlorine on the indicator 64.

To collect T and ds (or d), a telemeter or the like is used to transmit data from a remote location, and the measuring person directly reads the instructions from the on-site instrument. Many methods are possible, such as taking sample water home and analyzing it. Further, for K inputting T, dl (or d), and a. into the respective input sections 60, 61.degree. 62, an ordinary method such as a resistance division method or a voltage division method is used.

The modification described above is not only compact and portable, but also allows multiple water treatment plants to be used by inputting the water temperature T and ammonia ion concentration d1 (or ammonium io/II degrees d) from each water treatment plant. It is possible to control the pre-chlorine injection rate.

In the present invention, T is the temperature of raw water, but in a water purification plant, the difference in water temperature between the water intake well 3 and the water purification pond 5 is at most 5°C, and usually 2 to 3°C. In equation (5), this level of temperature difference does not have any effect on practical use. Therefore, measurement of the water temperature T is not limited to the water intake well 3 and the water receiving well 5, and may be carried out in any well, pond, or water conduit in the treatment process of a water purification plant without causing any practical problems.

Further, the residual chlorine concentration target value near the entrance of the settling tank 8 may be used as the residual chlorine degree target value. The definition of this vicinity means anywhere from the inlet of the mixing pond 70 to downstream for 10 to 20 minutes in terms of residence time. The reason for this is that, as mentioned earlier, the reaction between chlorine and ammonia nitrogen is fast, taking about 15 minutes, whereas the reaction between bulk elements and organic matter is relatively slow, and the residual chlorine concentration is usually analyzed from the collection of sample water. The reality is that it takes 10 to 20 minutes, including the time to carry it. Therefore, the residence time from the entrance of the mixing pond 70 is 1
This is because no matter where the residual chlorine concentration is measured downstream for 0 to 20 minutes, almost the same results will be obtained.

According to the present invention as described above, a device is provided that can respond to the ever-changing properties of raw water at a water treatment plant and can quickly and uniquely grasp chlorine throughout the year, allowing for proper pre-chlorine injection and stabilization of water quality. Contribute to

[Brief explanation of the drawing]

Figure 1 is a flow diagram showing the water purification system of a general water treatment plant, Figure 2 is a characteristic diagram showing the consumption of chlorine by ammonia nitrogen, and Figure 3 is the ammonia nitrogen concentration and pre-chlorine injection rate at a certain water treatment plant. Fig. 4 is a characteristic diagram showing an example of the reaction between ammonia nitrogen and chlorine, Fig. 5 is a characteristic diagram showing an example of the reaction between humic acid and chlorine, and Fig. 6 is a diagram showing the relationship between the ammonia nitrogen concentration and the actual value of chlorine consumption according to the present invention, Figure 7 is an explanatory diagram showing an example of a conventional device for measuring chlorine demand, and Figure 8 is a diagram showing the relationship between the ammonia nitrogen concentration and the actual value of chlorine consumption measured by the present invention FIG. 3 is a characteristic diagram showing an example of measurement of the required amount. FIG. 9 is a block diagram showing a configuration example of the chlorine requirement measuring device according to the present invention, FIG. 10 is an explanatory diagram showing an embodiment of the chlorine requirement measuring device according to the present invention, and FIG. A characteristic diagram showing an example of measuring the required amount of chlorine using the measuring device, and FIG. 12 is a block diagram showing a modification of the required amount of chlorine measuring device of the present invention. 1...Gate? ...Flow rate needle 3
...Intake well 5゛°...Water landing well 70
00.1. Mixing basin 8...Sedimentation basin 9...
... Filtered oil 10 ... Water purification pond 13 ...
...Chlorine injector 14...Controller 15...
Chlorine tank 16...Sampling pump 17...Residual chlorine concentration meter 21...Measuring tank 22
, 25...Pump 23...Reaction tank 2
4... Reagent tank 26... Chlorine generator 2
7...NaC1 solution population 28...NaC1 solution outlet 29...Separation 1I30...Cathode 31...Anode 32...Chlorine gas outlet 33...Hydrogen gas Outlet 34...Residual chlorine detector 3s...Controller 36...Indication brass device 37...Accumulating current needle 40...Chlorine required amount measuring device 41...7y Monium ion concentration measuring section 42... Temperature indicating section 43... Residual chlorine szb target value setting section 44... Computing unit 45... Indication recorder 46...
Warm honey detector 50... Adjustment tank 51... Temperature detection 19 52.5! S...Pump 53...
... Reaction tank 54 ... Reagent tank 56 ...
Diaphragm type electrode 57... Calculator 6o... Water temperature input section 61... Ammonia nitrogen concentration (or ammonium ion concentration vt> input section 62... Residual chlorine concentration target value input section 63 ...Calculation part 64...Instruction part (7317) Substitute person Benzoshi Nori Chika Kensuke (and 1 other person) Figure 2? Figure 3 Figure 4 Figure 5 Memorization question Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Time Figure 12

Claims (2)

[Claims] (1) When injecting pre-chlorine at a water treatment plant, the ammonium ion concentration and water temperature of the raw water are measured, and the required amount of pre-chlorine is determined using these and the target value of the residual chlorine concentration near the entrance of the settling tank. How to measure the chlorine requirement of water. (2) At the water treatment plant, input the temperature detector for raw water or treatment process water, the ammonium ion concentration measuring unit connected to the raw water via piping, the target value setting unit for residual chlorine concentration near the entrance of the settling tank, and their output signals. A device that measures the required amount of chlorine for water quality, consisting of a calculator, etc., that measures the required amount of pre-chlorine using target values for water temperature, ammonium ion concentration, and residual chlorine concentration.