JPS5815064B2 - Continuous measurement method for nitrate and nitrite ion concentrations in factory wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a novel method for simultaneously and continuously measuring nitrate ions and nitrite ions contained in industrial wastewater.

In recent years, denitrification treatments have been actively attempted.

There is no suitable analytical method or apparatus for continuous measurement of each of the above ions during the wastewater treatment process or at the point of discharge, and there is a strong need for the development of these.

In view of this, the present inventors have been carrying out research and development for some time, focusing on nitrate ions and nitrite ions in factory wastewater.

For measuring nitrate ions and nitrite ions in factory wastewater,
Until now, ultraviolet absorption method has rarely been used due to the large influence of coexisting components.

However, the present inventors have proposed a pretreatment method in which metal ions such as iron ions, which have a particularly significant influence, are precipitated and separated as hydroxides. ), has already invented a continuous measuring device for nitrate ions and nitrite ions based on the ultraviolet absorption method as shown in Japanese Patent Application No. 51-152828 (Japanese Patent Application Laid-Open No. 53-77585).

These inventions were very effective measuring devices for industrial wastewater containing sediments, metal ions, etc.; It was found that this method was not suitable for analyzing industrial wastewater.

In order to overcome these drawbacks, the present invention focuses on a method and apparatus for removing coexisting organic compound ions and coloring, and the detection and measurement method is based on the previously filed invention.

With the above objectives in mind, we are conducting research and development based on the basic principles of sediment removal, activated carbon treatment, and ultraviolet absorption. This has led to the provision of a simultaneous and continuous analysis method for nitrate ions.

In the present invention, nitrate ions (hereinafter referred to as NO3-) are removed after removing precipitates and turbidity contained in factory wastewater through filtration treatment, and removing coloring and organic components that interfere with ultraviolet absorption method through activated carbon treatment. The method is based on an ultraviolet absorption measurement method that measures each absorption by applying the fact that nitrite ion (hereinafter referred to as NO2-) has a maximum absorption wavelength in the ultraviolet region of 355 nm.

The present invention will be explained in detail with reference to explanatory diagrams of an embodiment of the present invention shown in FIGS. 1 to 3.

As shown in FIG. 1, the apparatus according to the present invention includes sediment separation sections 1 to 8 for removing fugitives contained in factory wastewater, activated carbon treatment sections 9 to 13 for removing colored wastewater and organic matter, and NO.
The main components are detection and measurement sections 14 to 18 that measure NO.3 and NO2 concentration using an ultraviolet absorption method.

Reference numeral 1 denotes a sample collection pipe, which is connected to a discharge point of industrial wastewater, etc., 2 a liquid pump, and 3 a pipe for supplying the collected wastewater sample to a continuous filtration device 4.

5 is the main part of the continuous filtration device, and is a filtration drum that filters out sediment and turbidity in the wastewater that may interfere with ultraviolet absorption measurement or clog the activated carbon column.

Reference numeral 8 denotes a suction pump, which sucks the clean sample solution filtered from the filter drum through the sample suction tube 7a and transfers it to the sample receiver 9.

The filtration application drum 5 is a sealed oblong cylinder with a large number of small holes drilled on the outer circumferential side and a filter cloth wrapped around the holes, and the sample is sucked downward onto the inner circumferential surface of the cylinder around which the filter cloth is wrapped. A suction port for a tube 7a is installed, and this sample suction tube 7a is brought out from the side of the cylinder and connected to a suction pump 8.

Factory wastewater containing sediment is supplied from the sample supply pipe 3 so as to fall onto the filter cloth surface around the outer periphery of the filtration drum 5.

By reducing the pressure inside the filtration drum with the suction pump 8, the precipitates in the supplied wastewater remain on the surface of the filter cloth, and the filtrate, which has become transparent after the precipitates are removed, is sucked through the sample suction tube 7a. It is sucked into the pump and sent to the receiver 9.

The filter cloth used was one in which a filter paper with a small pore size (such as Type 5 B) was layered on the inside and a filter cloth with a large pore size (such as felt) was layered on the outside, which was wrapped around the cylinder of the filtration drum 5.

Generally, industrial wastewater contains sediment and has some turbidity, but according to the above filtration method, the filtration process could be carried out continuously with a quick response without causing clogging or leakage.

In addition, even in the case of neutralized wastewater containing a large amount of iron ions, such as pickling wastewater, which is in a suspended state due to the precipitation of iron hydroxide, the sample supply pipe 3 drops onto the filter cloth surface. No sediment was deposited on the surface of the filter cloth that was hit by the wastewater, and the surface of the filter cloth always appeared clean, so that no clogging occurred and smooth continuous filtration could be carried out.

On the other hand, excess waste water that has not been subjected to suction filtration is discharged to the outside from the sample residual liquid discharge pipe 6 together with the removed precipitate.

10a is sent from a continuous filtration device and is filtered and cleaned,
This is a constant flow pump for sending the wastewater sample received in the sample receiver 9 to the activated carbon column.

Reference numeral 10b denotes a constant flow pump for supplying a solution to mix a certain amount of salt solution with the above-mentioned wastewater sample.

12 is Y-shaped 3 for mixing the wastewater sample and the saline solution.
It is a bifurcation joint.

13 is a column filled with activated carbon.

Although the above-mentioned continuous filtration equipment removed the sediments and turbidity contained in the factory wastewater, the colored wastewater and coexisting organic compounds often exhibit ultraviolet absorption, and NO3- and NO2
In order to accurately measure the concentration of -, it is necessary to remove these as well.

It is known that activated carbon treatment can remove these coloring and coexisting organic compound ions, but NO3- and N
There was a problem that O2- was also adsorbed by the activated carbon.

According to the study results of the present inventors, the adsorption of NO3 and NO2- onto activated carbon is affected by the concentration of NO3- and NO2- and the pH of the solution.
It is affected by the amount of H, activated carbon, etc., but NO3-
It was found that when 10 g of coconut shell powder activated carbon was added to 100 ml of a solution containing about 10 ppm of NO3 and NO2=, about 40% of NO3 and NO2- were adsorbed by the activated carbon.

When the pH of the solution was 4 or less, the adsorption capture rate became even higher, and the same tendency was observed when the amount of activated carbon was increased.

Therefore, as a result of various studies on conditions in which coloring of the solution, organic compound ions, etc. were selectively removed and NO3 and NO2- were not adsorbed, it was found that more than a certain amount of Na+ and + in the wastewater sample was present.

It has become clear that this objective can be achieved by coexisting alkali metal ions such as Ca2+2Mg2+ or alkaline earth gold layer ions.

FIG. 2 shows an example of test results regarding the recovery rate of NO and NOi in activated carbon treatment when Na+ is added.

Figure 2 shows solution 1 containing 10 ppm of NO3- and NO2-.
O~0.8 as Na+ using NaCl in 00WLl
% was added, treated by adding 2 g of activated carbon, filtered under suction, and the amount of NO3- and NO2- in the obtained filtrate was determined to determine the recovery rate.

According to this result, when almost no Na+ is included, N
O, and NO" cannot be recovered by more than 60%, but 0.4%
In cases where the content exceeds 100%, it was possible to recover 100%.

In the experiment shown in Figure 2, instead of Na+: ni+, Mg2
+, also when Ca2+ or NH4+ is added, the second
Results similar to those shown in the figure were obtained, and chlorides containing these elements,
By adding and mixing a solution of inorganic salts such as sulfates to a wastewater sample, it has become possible to color the wastewater sample and adsorb and capture organic compound ions on activated carbon, thereby recovering 100% of NO3- and NO2-.

A salt solution as described above is stored in the salt solution tank 11, and a constant flow pump 10b is used from the salt solution tank 11 to feed the wastewater sample from the sample receiver 9 to the activated carbon column 13 by a constant flow pump 10a. The sucked salt solution is added and supplied at a constant flow rate through a three-way branch joint so as to have a predetermined concentration.

The activated carbon column used was a cylindrical tube with an inner diameter of 20 to 30 mm and a length of about 500 mm filled with about 50 to 100 meshes of coconut shell activated carbon.

Although FIG. 1 shows the case where a single column is used, it is practical to install a plurality of columns and switch over when the adsorption capacity decreases to regenerate the used column.

14, a wastewater sample from which sediment, turbidity, coloring, organic compound ions, etc. have been removed is passed to an ultraviolet absorber 16a using constant flow pumps 10a and 10b.

This is a sample transfer tube for sending the sample to the flow cells 15a and 15b of 16b.

18 is a sample discharge tube, 17a. 17b is a recorder.

As shown in Figure 5, NO3- and NO2- both exhibit absorption in the ultraviolet region, with wavelengths of 302 nm and 35 nm, respectively.
It has a maximum absorption wavelength of 5 nm.

The curve shown at 19 in FIG. 3 is the absorption spectrum of NO3-, and the curve shown at 20 is the absorption spectrum of NO2-.

Therefore, the out-of-trap absorption meters 16a and 16b need to have a structure that can measure absorption at wavelengths around 302 nm and 355 nm.

Although FIG. 1 shows a case in which two X-ray absorption meters 16a and 16b are provided, it is also possible to use one X-ray absorption meter with one light source and two types of measurement wavelengths.

Alternatively, a spectrophotometer that can accurately set measurement wavelengths of 302 nm and 355 nm or an ultraviolet absorption meter that uses an interference filter that can set measurement wavelengths of around 302 nm and 355 nm may also be used.

However, as shown in Figure 3, the absorption spectrum of N03 is interfered with by the absorption spectrum of NO2, causing a positive error, so the measured value of NO3- concentration must be corrected by the measured value of NO2- concentration. .

The correction is made by checking in advance the proportion of correct error due to the NO2 concentration at the NO3 measurement wavelength, and subtracting the amount of absorption affected by this.

The measurement wavelengths of NO3- and NO2- were set to 302 nm and 3
If the wavelength is set to 55 nm, the measured value of NO3- will receive a positive error equivalent to about 30% of the measured value of NO2-, which was present, so there will be a difference of 0.3% from the measured value of NO3- to the measured value of NO2-.
Correct by subtracting the value multiplied by the nearby value.

This correction may be calculated and corrected based on the measured values, but
Automatic correction can be easily performed by incorporating an electric circuit.

In addition, the absorption amount of NO2- at the thickest absorption wavelength of NO3 is as shown by the arrow in Figure 3.
Since the absorption amount is the same as that of NO3 at 302 nm, the absorption at a wavelength of 384 nm is measured separately.
Correction can also be easily performed by two-wavelength photometry, which subtracts this value from the absorption amount of -.

The flow cells 15a and 15b are made of quartz and have as small an internal volume as possible to facilitate replacement of the sample solution.

An example of a calibration curve for measuring NO3- and NO2- concentrations when using a flow cell with an optical path length of 40 nm is shown in FIG.

As explained in detail above, the present invention is such that the industrial wastewater collected by the sample collection tube 1 is subjected to a continuous filtration device 4 in which sediments and turbidity are removed, an activated carbon column 13 in which coloring and organic compound ions are removed, and ultraviolet rays are removed. Absorption meter 16a,
NO3- and NO2- concentrations are simultaneously and continuously measured at 16b.

In addition, z n2 +, pb2 that may coexist
+, Cr3 +.

Metal ions of Cu'', Ni'', Co2''@ or F
y C1p SO4" tThere is no interference from ions such as NH4+ and Ca2+.

The coexistence of hexavalent crumb and iron ions gives a positive error, but if the former is reduced to trivalent chromium by adding a reducing agent and the latter is converted to iron hydroxide by adding an alkaline solution during the wastewater sample collection stage, this effect can be avoided. can be excluded.

The analytical accuracy is also very good because the measurement method is extremely simple, and the response is also excellent.

In addition, the device of the present invention has excellent durability and is free from breakdowns and troubles due to its simple principle and structure, making it a useful and practical new device as a device for simultaneously and continuously measuring nitrate ions and nitrite ions.

The present invention greatly contributes to the field of environmental analysis of factory wastewater, etc., which has become particularly important in recent years, as well as to fields such as wastewater treatment processes, monitoring of wastewater, and analysis of process pipes in production plants.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the apparatus according to the present invention, Figure 2 is an explanatory diagram of the effect of salt addition in activated carbon treatment, Figure 3 is an ultraviolet absorption spectrum diagram of nitrate ions and nitrite ions, and Figure 4 is an illustration of the present invention. It is a figure showing a calibration curve by an apparatus. 1...Sample collection tube, 2...Liquid pump, 3...Sample supply tube, 4...Continuous filtration device, 5...・Filtration drum, 6... Sample residual liquid discharge tube, 7a, 7b... Sample suction tube, 8
...Suction pump, 9...Sample receiver, 1
0a, 10b... Constant flow pump, 11...
... Salt solution tank, 12 ... Three-way branch joint, 13 ... Activated carbon column, 14 ...
- Sample transfer tube, 15a. 15b... Distribution cell, 16a, 16b...
... Ultraviolet absorption meter, 17a, 17b ... Recorder, 18 ... Sample discharge tube, 19 ... Nitrate ion absorption spectrum, 2υ ... Nitrous acid Ion absorption spectrum.

Claims (1)

[Claims] 1. Filter the analysis sample solution such as factory wastewater, add and mix a salt solution containing alkali metal or alkaline earth metal ions to the filtrate, and then send the solution that has passed through the activated carbon layer into the flow cell of the ultraviolet absorption meter. , measuring the amount of absorption at each wavelength around 302 nm and around 355 nm,
The nitrite ion concentration was determined from the absorption amount near 355 nm by 3
Nitric acid in factory wastewater characterized by simultaneously and continuously determining the nitrate ion concentration based on the absorption amount obtained by subtracting the absorption amount near 355 nm multiplied by about 0.3 from the absorption amount near 02 nm. Continuous measurement method for ion and nitrite ion concentrations.