JPS62220858A - Method for measuring total phosphorus - Google Patents

Abstract

PURPOSE:To eliminate the influence of an oxidative material and to exactly measure the concn. of total phosphorus by subjecting the phosphorus compd. in waste water to an oxidation decomposition treatment and reducing the oxidative material in the treated liquid. CONSTITUTION:The waste water is drawn into a reaction vessel 2, sulfuric acid 3 is added thereto and the waste water is heated; at the same time the ozone formed by treating the oxygen of a cylinder 6 by an ozone generator 7 is fed into the vessel from a diffuser 13. The ozone oxidizes and decomposes the phosphorus compd. to orthphosphoric acid and oxidizes chlorine ions to ClOx at the same instant. After the reaction is effected for the prescribed time, the heating is stopped and only the gaseous exygen is supplied. A sodium hydrogensulfide soln. 16 is thereafter added to the liquid to reduce the ClOx therein. The oxidation decomposition-treated liquid is then fed continuously to a mixing joint 19. An electrolyte 21 and the oxidation decomposition-treated liquid are mixed at a specified ratio and the reaction progresses further to form a molybdenum complex in the mixing joint 19. this complex is subjected to a constant potential electrolysis in an electrolytic cell 25 by which the reduc ing current proportional to the concn. of the phosphorus is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a method for automatically measuring the total phosphorus concentration in water such as wastewater and wastewater treatment water.

[Prior art and its problems]

First, a flowchart of a conventional method for measuring total phosphorus concentration is shown in FIG. In this method, phosphorus compounds contained in wastewater exist in various forms such as polyphosphoric acids, organic phosphorus compounds as animal and vegetable substances in addition to orthophosphate ions, so these are oxidized and decomposed as a pretreatment. It is measured after processing and conversion to orthophosphoric acid.

For this oxidative decomposition treatment, there is a method shown in the Technical Guidelines for the Official Phosphorus Measurement Method of the Environment Agency, in which treatment is carried out in a high-temperature heating container using an oxidizing agent such as potassium beroxonisulfate solution, and a patent application filed by the applicant in 1982. There is a method proposed in No. 263902, in which sample water is made acidic and ozone is bubbled through it while heating it to carry out oxidative decomposition.

Further, as a method for measuring orthophosphoric acid in wastewater subjected to oxidative decomposition treatment as described above, a method using constant potential electrolysis measurement of a phosphomolybdenum complex is known as a simple measurement method suitable for automation. This method is shown in Figure 6 as “
It is shown as "Measurement part". In this method, wastewater containing phosphoric acid and acidic molybdate solution are continuously mixed, and the resulting phosphomolybdenum complex is continuously subjected to constant potential electrolysis in an electrolytic cell, and the reduction current required for the electrolysis is contained in the wastewater. The phosphoric acid concentration can be rapidly measured by utilizing the fact that the phosphoric acid concentration is proportional to the orthophosphoric acid concentration.

The above is the conventional technique for measuring total phosphorus concentration.

However, it has been found that this prior art method presents major problems when chloride ions are present in the waste water.

That is, in the method shown in the above-mentioned technical guideline for the official phosphorus measurement method as well as in the method of Japanese Patent Application No. 59-26392, some of the chlorine ions are converted to ClO during the oxidative decomposition process.
It was confirmed through experiments that the value changes to x (x=l~3). This Cj! Since Ox undergoes electrical reduction in the subsequent constant potential electrolysis measurement, it was predicted that a reduction current would be generated that would cause errors in the measurement. The following experiment was conducted to confirm this phenomenon. In this experimental method, the phosphorus concentration is 0.5■/1 and the chloride ion concentration is 0■/j2.
．． Using a standard solution adjusted to 2°rrw/1 and 200nw/j2, constant potential electrolysis measurement is performed after pretreatment by the ozone oxidative decomposition method described in Japanese Patent Application No. 59-263902. The obtained results are shown as "conventional method" in FIG. From Figure 2, the initial chlorine ion concentration is 0■
/l, the reduction current value is proportional to the phosphorus concentration,
In this experiment, it can be seen that the reduction current value increases as the initial chloride ion concentration increases.

As described above, it has been revealed that the presence of chlorine ions in wastewater produces oxidizing substances, and these oxidizing substances cause errors in subsequent constant potential electrolysis measurements.

[Purpose of the invention]

The present invention eliminates the above-mentioned problems in the conventional methods for measuring total phosphorus concentration, and provides a method that enables more accurate measurement of total phosphorus concentration even for wastewater containing chloride ions. The purpose is to provide.

[Key points of the invention]

In the present invention, after oxidizing and decomposing phosphorus compounds in wastewater,
By reducing the oxidizing substances in the oxidative decomposition treatment solution,
This method removes the influence of oxidizing substances on the subsequent constant potential electrolysis measurement, thereby allowing accurate measurement of total phosphorus concentration.

According to the present invention, phosphorus compounds in water such as wastewater are oxidatively decomposed into phosphoric acid, the oxidatively decomposed solution and molybdate oxide solution are mixed, and the resulting phosphomolybdenum complex is introduced into an electrolytic cell. , a method of performing constant potential electrolysis and measuring the total phosphorus concentration in water from the reduction current value, characterized in that the constant potential electrolysis measurement is performed after reducing oxidizing substances in the oxidative decomposition treatment solution. A method for measuring total phosphorus concentration is provided.

The oxidative decomposition treatment of wastewater in the method of the present invention includes, for example,
This can be conveniently carried out by the method disclosed in Japanese Patent Application No. 59-263902. This method consists of making the sample water acidic to a pH of 3 or lower and bubbling ozone through it while heating it to a concentration of 80° C. or higher. In this oxidative decomposition treatment, phosphorus compounds are oxidized to orthophosphoric acid by ozone, and at the same time, chlorine ions contained in water are also oxidized to Cl0x. The method of the present invention is based on this C7! It reduces oxidizing substances such as Ox and eliminates the influence of the oxidizing substances on subsequent potentiostatic electrolysis measurements. Reduction can be performed using a reducing agent such as sodium bisulfite or electrical reduction.

The solution subjected to the reduction treatment is then mixed with an acidic molybdic acid solution to form a phosphorous molybdenum complex, which is subjected to constant potential electrolysis measurement using a known method to determine the total phosphorus concentration in water.

[Embodiments of the invention]

FIG. 1 is a schematic diagram of an apparatus used to carry out a specific example of the method for measuring total phosphorus concentration according to the present invention. Dotted line A
The part is a part that performs a process of oxidizing a phosphorus compound to orthophosphoric acid by ozone oxidation. The dotted line B is the core part of the present invention, and is the part that reduces the oxidizing substance in the oxidative decomposition treatment liquid. The dotted line C is the part where the phosphoric acid concentration is measured.

First, the measurement method will be explained with reference to FIG. First, wastewater is collected into a reaction tank 2 by a sampling pump 1 via a stop pulp 9, and an aqueous acid solution such as sulfuric acid 3 is added via a pump 4 and a stop valve 10 to adjust the pH to 3, and then the reaction takes place. The tank 2 is heated to 80 DEG C. or higher by a heater 5, and the ozone generated by treating oxygen in an oxygen cylinder 6 with an ozone generator 7 is sent into the reaction tank 2 from a dihydrogen 13. This ozone oxidizes and decomposes phosphorus compounds contained in the acidic wastewater into orthophosphoric acid, and simultaneously oxidizes chlorine ions contained in the wastewater into Cl0x. Next, after reacting for a certain period of time, the heating is stopped, the ozone generator 7 is turned off, and only oxygen gas is vented to degas the dissolved ozone in the waste water. The degassed gas is sent to the wandering ozone decomposer 8. Thereafter, sodium bisulfite solution 16 is added via pump 15 and stop pulp 11 to reduce Cl0x in the solution. This reaction is C120x + x Na HS Oa
-CIV, -+xNaH3O4.

Thereafter, the stop valve 12 is opened, and the oxidized decomposition treatment liquid is introduced into the receiver 14, and from the receiver 14, the metering pump 18 passes the filter tube 17 and continuously into the mixing joint 19.
send to At mixing joint 19, metering pump 2
Since the liquid feeding amount of 0 is larger than the liquid feeding amount of metering pump 18,
The electrolytic solution 21 and the oxidative decomposition treatment solution are mixed at a constant ratio,
The reaction further proceeds in the mixing tube 22 to form a phosphomolybdenum complex. Note that the electrolytic solution 21 used at this time is a mixed reagent consisting of sulfuric acid, sodium molybdate, and ethanol. This molybdenum complex is then applied on the carbon electrode in the electrolytic cell 25 at a voltage of 250-300 mV vs Ag
- Subjects to potentiostatic electrolysis of AgCIl, producing a reduction current proportional to phosphorus concentration. The phosphorus concentration is measured by measuring this reduction current using the potentiostand 26 and the recorder 27. Note that water 23 and phosphoric acid standard solution 24 connected to the measurement system via three-way valves 28 and 29 are used for calibration of measurement.

Next, the total phosphorus concentration in water was measured using the measurement method according to the above configuration. The samples used were adjusted to have a phosphoric acid concentration of 0.5 ■/l and a chloride ion concentration of O ■/l, 20 ■/β, and 200 ■/l, which were used when examining the conventional method described above. This is a standard solution. The obtained results are shown in FIG. 2 as "the present invention". In addition, as for the reduction treatment conditions, 2 ml of a 5 w/v % solution of hydrogen sulfite (IJ) was added to 100 ml of the oxidative decomposition treatment solution. From Figure 2,
In the conventional method, the reduction current due to constant potential electrolysis increased significantly as the initial chloride ion concentration increased, but in the method of the present invention, the reduction current is not affected by the initial chloride ion concentration, and the reduction of the phosphomolybdenum complex It can be seen that only the current value associated with is shown.

Furthermore, in the present invention, even if the reducing agent is added in excess of the oxidizing substance in the oxidative decomposition treatment solution and the reducing agent remains in the solution, this does not adversely affect the subsequent constant potential electrolysis measurement. I understand. This fact was confirmed by the following experiment.

In this experiment, 0.5 μ/l of phosphorus and 100 ml of 5 w/v% sodium hydrogen sulfite solution were added to OmC.
2ml.

It consists of performing potentiostatic electrolysis using standard solutions adjusted to be present in amounts of 4 ml and 6 ml.

The results obtained are shown in FIG. Even if the amount of sodium hydrogen sulfite increases, the reduction current value is the same as when only phosphorus is used. Therefore, it can be seen that even if sodium hydrogen sulfite remains in the oxidation-decomposed solution, it does not affect the measurement.

Next, Table 1 shows the results of measuring the phosphorus concentration in actual sewage treated water using the method of the present invention. For comparison, measurement results for the same sample water are also shown in accordance with the Environmental Agency's Official Phosphorus Measurement Method Technical Guidelines. Both have good losses.

Table 1 As described above, according to the present invention, it has become possible to measure the total phosphorus concentration using the potentiostatic electrolytic measurement method, which is suitable for automation, even in actual sewage treatment where the chloride ion concentration is high.

In this example, oxidative substances in the oxidative decomposition treatment liquid are reduced by electrical reduction instead of using a reducing agent, and then the phosphorus concentration is measured by constant potential electrolysis. Here is an example of how to do this. The configuration of the apparatus used in this method is shown in FIG.

In this measurement method including electrical reduction, after performing oxidation treatment in the same manner as in Example 1, the stop valve 12 is opened to guide the oxidized decomposition treated liquid to the receiver 14, and from the receiver 12 to the metering pump 1.
8 leads to the electrolytic cell 30 via the filter cylinder 17. Here, after performing the electrolytic reduction treatment, the liquid is sent to the mixing joint 19, and measurements are performed in the same manner as in Example 1.

In addition, each member and device having each reference number in FIG. 5 is the same as that shown in FIG. 1, and has the same function.

Here, the structure of the electrolytic cell 30 described above is shown in FIG. Carbon fibers 33 or carbon spheres are packed as working electrodes in the diaphragm inner cylinder 32 of the electrolytic cell 30, and the oxidative decomposition treatment liquid passes through the diaphragm inner cylinder 32.

Here, the oxidizing substance in the treatment liquid can be reduced by applying a potential for reducing the oxidizing substance to the working electrode.

Next, the effect on the measurement of chloride ions was investigated using the present example described above. In the conventional method without reduction treatment, which was used for comparison, a reduction current of 180 μA was recorded as a measured value when saline water with a CIt-ion concentration of 100 μ/L was used as the test water. In the example, the current was 5 μA, and almost no reduction current flowed.

Therefore, according to this example, the total phosphorus concentration in water can be measured while sufficiently excluding the influence of chlorine ions.

〔Effect of the invention〕

According to the present invention, the oxidizing substances present in the liquid are reduced after the oxidative decomposition treatment of phosphorus compounds to phosphoric acid. It became possible to measure total phosphorus concentration.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus used to carry out an example of the method for measuring total phosphorus concentration in water of the present invention. FIG. 2 is a graph showing comparative measurement results between the conventional method and the method of the present invention in the presence of chloride ions. FIG. 3 is a graph showing the influence of sodium bisulfite added as a reducing agent on the measurement. FIG. 4 is a schematic diagram of an apparatus used to carry out another embodiment of the method of the present invention. FIG. 5 is a schematic diagram of an electrolytic cell used to reduce oxidizing substances. FIG. 6 is a flow diagram of a method for measuring total phosphorus concentration according to the prior art. 1... Sample collection pump, 2... Reaction tank, '3...
Sulfuric acid for pH adjustment, 5... Heater, 7... Ozone generator, 14... Receiver, 16... Sodium bisulfite solution, 18°20... Metering pump, 19... Mixing station 21... Electrolyte, 22... Mixing tube, 23... Water, 24... Phosphoric acid standard solution, 25...
・Electrolytic cell, 26.31... Potentiostat, 2
7... Recorder, 30... Electrolytic cell, A... Oxidation processing section, B... Reduction processing section, C... Measuring section Liiwa concentration up to the initial stage (4)

Claims (1)

[Claims] 1) A method of oxidatively decomposing phosphorus compounds in water such as wastewater to phosphoric acid, mixing the oxidatively decomposing solution with an acidic molybdic acid solution, and introducing the resulting phosphomolybdenum complex into an electrolytic cell. A method of performing constant potential electrolysis and measuring the total phosphorus concentration in water from the reduction current value, which is characterized by reducing oxidizing substances in the oxidative decomposition solution and then performing constant potential electrolysis measurement. How to measure phosphorus concentration. 2) A method for measuring the total phosphorus concentration in water according to claim 1, wherein the reduction is carried out using a reducing agent. 3) A method for measuring the total phosphorus concentration in water according to claim 1, wherein the reduction is performed by electrical reduction.