TWI665439B - A method for determining chemical oxygen demand of a water sample - Google Patents

Abstract

The invention provides a method for detecting COD in water, which includes providing a mixed solution containing water sample, an oxidizing agent and a strong acid, heating the mixed solution, and then injecting the mixed solution into a microchannel test strip, and centrifuging the microchannel test The sample was subjected to spectral analysis to obtain the COD in the water sample.

Description

Method for detecting chemical oxygen demand in water

The invention relates to a method for detecting water quality, in particular to a method for detecting chemical oxygen demand in water.

Wastewater caused by human activities often contains large amounts of organic matter. Organic matter in water can be decomposed into carbon dioxide and water by the biochemical action of microorganisms. During the decomposition process, dissolved oxygen in the water body is consumed. Once the water body is under anoxic conditions, these organics will decompose and decompose, which will worsen the water quality, produce a foul odor, and cause environmental problems.

Because there are many types of organic substances and their composition is complex, it is difficult to distinguish them one by one and measure them one by one. Therefore, in actual detection, Chemical Oxygen Demand (COD) is often used to indicate that water can be oxidized by chemical methods. The content of organic matter is used as an index for detecting the content of organic matter in water. The chemical oxygen demand is defined as the milligrams of oxygen consumed per liter of water sample. If the chemical oxygen demand is greater, it means that the content of organic matter in the water is higher, which means that the pollution of the water body is more serious.

In the current COD detection method, dichromic acid is used. Potassium is an oxidizing agent. It is heated under strong acid conditions to oxidize organic matter in water to carbon dioxide and water. The amount of potassium dichromate that is consumed is converted into the equivalent amount of oxygen, which is the chemical oxygen demand. The main steps include: mixing the water sample to be tested and potassium dichromate reagent, heating to boiling, setting up a reflux device and refluxing the mixed solution in the reflux device for 2 hours, and after the reflux, titrate the excess heavy chromium with ammonium ferrous sulfate. Potassium acid, thereby inferring the consumption of potassium dichromate, to obtain the chemical oxygen demand in water.

However, the current method has some disadvantages as follows. Since the current method needs to be carried out in the laboratory, it is not easy to test at the source of the pollution source, which causes inconvenience in local testing. In addition, the detection time of the current method is quite long, and each water sample must be reflowed for 2 hours. As a result, the test result cannot be obtained quickly in a short time, and the test personnel's time and energy are also consumed. In addition, the volume of samples and reagents for each test usually exceeds 60 ml, and the amount of reagents used is large. The generated waste liquid will also cause subsequent waste liquid treatment and recovery problems.

In view of this, in order to solve the aforementioned problems related to the portability of the instrument, the long detection time and the large amount of waste liquid, the present invention proposes a method for detecting chemical oxygen demand in water, thereby solving the problems faced by the prior art.

The invention provides a method for detecting COD in water, which includes the following steps: providing a water sample, an oxidation reagent, and a strong acid, mixing them to form a mixed solution, and then heating the mixed solution. The mixed solution is injected into a micro-channel test piece, and the flow-channel test piece is centrifuged to separate the mixed solution into a part to be detected and a light-blocking impurity. Next, for the separated micro-channel test piece, The part to be detected is subjected to spectral analysis to obtain the COD in the water sample.

In one embodiment, the oxidizing agent includes potassium dichromate.

In one embodiment, the strong acid includes sulfuric acid or nitric acid.

In one embodiment, the method further comprises adding a silver sulfate reagent to the mixed solution.

In one embodiment, the method further includes adding a mercury sulfate reagent to the mixed solution.

In one embodiment, the heating temperature is from about 120 ° C to about 180 ° C.

In one embodiment, the heating time is from about 8 minutes to about 15 minutes.

In one embodiment, the total volume of the mixed solution is from about 100 microliters to about 500 microliters.

In one embodiment, the method further includes taking a water sample using a robotic arm.

In one embodiment, the analysis time of the spectral analysis is 8 to 15 minutes.

In one embodiment, the detection wavelength range of the spectral analysis is about 340 nm to about 750 nm.

In summary, the present invention provides a method for detecting chemical oxygen demand in water. This method is easy to detect on-site, and can be used to pre-screen the polluted water body in accordance with environmental audit and monitoring requirements. In addition, the detection method of the present invention can complete the detection in a short period of time and quickly obtain the detection result, and can also save the time and energy of the detection personnel. Furthermore, the inspection of the present invention The test method has a small amount of reagents, and the total volume of the reagents is only about 100 microliters to about 500 microliters, thereby greatly reducing the problem of subsequent waste liquid treatment and recovery.

S1, S2, S3, S4 ‧‧‧ steps

200‧‧‧Micro channel test strip

210‧‧‧ Reagent plate body

211b‧‧‧First injection port

211c‧‧‧Second injection port

212‧‧‧Disc body

213a‧‧‧Quantity bath

213b‧‧‧‧Light blocking impurity disposal tank

214‧‧‧centrifugal runner

215‧‧‧The first capillary channel

216‧‧‧mixing tank

217‧‧‧Second capillary channel

218‧‧‧Distribution runner

218a‧‧‧Test slot

300‧‧‧Spectrum Analysis System

302‧‧‧light source

304‧‧‧Optical Module

306‧‧‧Mini Full Spectrum Analyzer

306a‧‧‧incidence slit

306b‧‧‧Reflective concave micro-grating

306c‧‧‧Linear Detector

400, 402, 404‧‧‧calibration lines

500, 600, 602‧‧‧ line segments

In order to make the above and other objects, features, advantages, and embodiments of the present invention more comprehensible, the description of the drawings is as follows: FIG. 1 illustrates the detection of COD in water according to an embodiment of the present invention Flow chart of the method; FIG. 2 is a top view of a microchannel test strip for centrifuging a mixed solution according to an embodiment of the present invention; and FIG. 3 is a utilization spectrum according to an embodiment of the present invention Schematic diagram of spectral analysis by the analysis system; Figure 4 shows the calibration curve of COD in water according to an embodiment of the present invention; Figure 5 shows the results of COD detection according to an embodiment of the present invention And FIG. 6 shows the chemical oxygen demand detection results according to an embodiment of the present invention and the chemical oxygen demand detection method NIEA W517.52B in water announced by the Environmental Protection Agency Environmental Inspection Agency (hereinafter referred to as the Environmental Inspection Agency). Correlation analysis of oxygen demand test results.

In order to make the description of the present invention more detailed and complete, the following presents an illustrative aspect of the present invention and specific embodiments. Description; but this is not the only form of implementing or using a particular embodiment of the invention. The embodiments disclosed below can be combined or replaced with each other under beneficial circumstances, and other embodiments can be added to an embodiment without further description or description. In the following description, many specific details will be described in detail to enable the reader to fully understand the following embodiments. However, embodiments of the invention may be practiced without these specific details.

The embodiments of the present invention are described in detail below, but the present invention is not limited to the scope of the examples.

The present invention provides a method for detecting chemical oxygen demand in water. The flow chart of this method is shown in FIG. 1. The content of each step in the first figure will be described in detail below.

Step S1 in FIG. 1 describes mixing a water sample, an oxidizing agent, and a strong acid to form a mixed solution. Among them, the oxidizing agent can decompose organic substances in the water sample by oxidation, and at the same time, the oxidizing agent itself is reduced.

In one embodiment, the oxidizing agent may be potassium dichromate (K ₂ Cr ₂ O ₇ ), potassium permanganate (KMnO ₄ ), potassium iodate (KIO ₃ ), cerium sulfate Ce (SO ₄ ) ₂ or the like. Similar to oxidation reagents. In one embodiment, the oxidizing agent is potassium dichromate. In one embodiment, the strong acid may be sulfuric acid, nitric acid, or a similar strong acid. In one embodiment, sulfuric acid is used as the strong acid.

When potassium dichromate oxidizes organics in water in an acidic environment, the hexavalent chromium of potassium dichromate will be reduced to trivalent chromium, and the organics will be decomposed, as shown in reaction formula 1: It can be observed from Reaction Formula 1 that if there are organics in the water sample, these organics will be oxidized and decomposed by potassium dichromate, and the hexavalent chromium of potassium dichromate will be reduced to trivalent chromium. If the organic matter in the water has been consumed by potassium dichromate, excess hexavalent chromium in potassium dichromate will remain in the water sample. Therefore, when the concentration and added volume of potassium dichromate are known, we can infer the consumption of potassium dichromate by detecting the content of hexavalent chromium remaining in water samples, so as to know the amount of potassium dichromate in water. Organic content, which is the chemical oxygen demand in water.

In one embodiment, the method further comprises adding a silver sulfate reagent to the mixed solution. By adding silver sulfate reagent, it can catalyze the decomposition of some linear aliphatic organic compounds that are not easily oxidized in water, so that the organic compounds can be more effectively oxidized.

In one embodiment, the method further includes adding a mercury sulfate reagent to the mixed solution. By adding mercury sulfate reagent, the positive interference caused by the chloride ion being oxidized by potassium dichromate to generate chlorine can be eliminated as one of the processing methods to reduce the background interference, thereby increasing the accuracy of the inspection method.

In one embodiment, the total volume of the mixed solution is from about 100 microliters to about 500 microliters. Because the total volume of the mixed solution is about 100 microliters to about 500 microliters, the problem of subsequent waste liquid treatment and recovery can be greatly reduced.

In one embodiment, the method further includes taking a water sample using a robotic arm. In one embodiment, the method further includes using a robotic arm to take an oxidizing agent and a strong acid. In one embodiment, the method further includes using a robotic arm to take the silver sulfate reagent. In one embodiment, the method further includes using a robotic arm to take the mercury sulfate reagent.

Please refer to step S2 in FIG. 1 next. Step S2 describes heating the mixed solution. The purpose of heating the mixed solution is to promote Oxidation of potassium dichromate on organics in water. In one embodiment, the heating temperature is about 120 ° C to about 180 ° C, preferably about 135 ° C to about 170 ° C, and more preferably about 140 ° C to about 160 ° C. In one embodiment, the heating time is about 8 minutes to about 15 minutes, preferably about 9 minutes to about 12 minutes.

Next, please refer to step S3 in FIG. 1 and FIG. 2 at the same time. Step S3 in FIG. 1 describes that the mixed solution after heating is injected into the microchannel test strip, and the microchannel test strip is rotated by centrifugation. The centrifugation of the microchannel test strip can be achieved by using the microchannel test strip with a centrifuge. The purpose of centrifugation is to remove particles and bubbles that may cause interference, so as to separate the mixed solution into the part to be detected and the light blocking impurities, so that the part to be detected in the mixed solution is transparent, clear, and there is no solid precipitate or air bubbles. By removing the light-blocking impurities, the optical interference that light-blocking impurities may cause to subsequent spectral analysis can be removed as one of the processing methods to reduce background interference.

In one embodiment, the mixed solution heated in step S2 is injected into the microchannel test strip 200. Please refer to FIG. 2 for the structure of the microchannel test strip 200. The microchannel test strip 200 includes a reagent disk body 210, a first injection port 211b, a second injection port 211c, a disc body 212, a sample quantitative groove 213a, a light blocking impurity discarding groove 213b, a centrifugal flow channel 214, and a first capillary. The flow passage 215, the mixing groove 216, the second capillary flow passage 217, the distribution flow passage 218, and the detection groove 218a.

In one embodiment, after the heated mixed solution is injected into the first injection port 211b of the microchannel test strip 200, the mixed solution enters the sample quantitative tank 213a. The mixed solution can be separated into the part to be detected and the light blocking impurities by rotating the microfluidic channel test sheet 200 by centrifugation. When the microfluidic channel test piece 200 is centrifuged, the portion to be detected of the mixed solution flows through the first capillary flow channel 215. To the mixing tank 216, and is quantitatively distributed into the plurality of detection tanks 218a through the second capillary flow path 217 and the distribution flow path 218 for subsequent optical detection, and the light blocking impurities will be passed through the centrifugal flow path 214 Discarded in the light-blocking impurity disposal slot 213b. In another embodiment, the dilution liquid can be added into the mixing tank 216 through the second injection port 211c.

Next, please refer to step S4 in FIG. 1 and FIG. 3 at the same time. In step S4 of FIG. 1, it is recorded that the portion to be detected of the mixed solution separated in the microchannel test strip is subjected to spectral analysis to detect the absorbance of hexavalent chromium. Since the absorption wavelengths of hexavalent chromium and trivalent chromium are different, the chemical requirements in water can be obtained by detecting the absorbance of hexavalent chromium at a specific wavelength and comparing it with the absorbance calibration curve of chemical oxygen demand. Oxygen concentration.

In one embodiment, after obtaining the desired portion of the mixed solution, the spectral analysis system 300 is used to perform spectral analysis on the desired portion of the mixed solution. FIG. 3 is a schematic diagram of performing spectral analysis on the part to be detected of the mixed solution using the spectral analysis system 300 in an embodiment. In one embodiment, the spectrum analysis system 300 includes a light source 302, an optical module 304, and a miniature full spectrum analyzer 306. The miniature full spectrum analyzer 306 includes an entrance slit 306a, a reflective concave miniature grating 306b, and a linear detector 306c, as shown in FIG. It should be understood by those having ordinary knowledge in the technical field that the above-mentioned spectrum analysis system is merely an example, and the spectrum analysis system to which the present invention is applicable is not limited thereto.

In one embodiment, the detection wavelength range of the spectral analysis system 300 is about 340 nm to about 750 nm. The detection target of the spectral analysis system 300 is hexavalent chromium. This hexavalent chromium is derived from excess potassium dichromate organically in oxidized water. Residual hexavalent chromium. In one embodiment, the light source 302 emits light in a wavelength range of about 340 nm to about 750 nm, and observes the absorbance values of hexavalent chromium at a wavelength of about 340 nm and a wavelength of about 450 nm. The oxygen absorbance calibration lines are compared to obtain the COD concentration of the portion to be detected in the mixed solution.

In one embodiment, when the absorbance of the portion to be detected in the mixed solution is detected by the spectral analysis system 300, the light emitted by the light source 302 first enters the optical module 304, which is used to adjust the light intensity. To increase the light intensity near 400 nm. The light emitted by the light source 302 enters the optical module 304 to adjust the light intensity, and then enters the plurality of detection grooves 218a of the micro-channel test strip 200, and enters the mixed solution detection portion in the detection groove 218a. Serving. The light emitted from the portion to be detected of the mixed solution in the detection groove 218a will be received by the entrance slit 306a, and then spread by the reflective concave micro-grating 306b spatial dispersion, and then be detected by the linear detector 306c and generated An absorbance value. By comparing the obtained absorbance value with the COD absorbance calibration curve, the COD concentration of the detected water sample can be known.

In one embodiment, the time for performing the absorbance detection with the mini-full spectrum analyzer 306 is about 8 minutes to about 15 minutes, preferably about 9 minutes to about 12 minutes.

In one embodiment, the detection method of the present invention also includes controlling a mechanical arm by a computer to suck water samples and reagents into the tip of a micro-test tube, or injecting a mixed solution into a micro-channel test strip. The use of a robotic arm can quickly complete the sampling and addition of water samples and reagents to shorten the completion of the inspection Measure the time required. In addition, the use of the robotic arm can also ensure the accuracy of the sampling volume under the requirement of microvolume, to avoid absorbing too much or too little water samples and reagents, resulting in inspection errors and excessive waste liquid. In one embodiment, the detection method of the present invention also includes controlling a robotic arm to perform continuous automatic sampling by a computer to establish continuous COD detection data in a time zone. In one embodiment, the detection method of the present invention also includes transmitting the detected COD data results in the cloud and remote monitoring.

Hereinafter, the method for testing COD in water of the present invention will be explained more clearly with two examples. The following examples are merely examples and are not intended to limit the present invention. Those with ordinary knowledge in the technical field to which the present invention pertains should flexibly select an appropriate reagent volume ratio and detection conditions according to actual needs.

Example 1 is to establish a calibration curve by using the chemical oxygen demand test method of the present invention. In Example 1, the calibration curve between the COD concentration and the absorbance was established based on a series of water samples with known COD concentration. In one embodiment, a known concentration of potassium hydrogen phthalate (Kotassium hydrogen phthalate, KHP) is used as a standard of organic matter in a water sample, and its absorbance is measured to establish a calibration curve of the KHP standard. In one embodiment, a water sample of a printed circuit board manufacturing wastewater with a known chemical oxygen demand concentration is selected to measure its absorbance to establish a calibration line for the printed circuit board manufacturing wastewater. In one embodiment, a water sample of sewer sewage with a known chemical oxygen demand concentration is used to determine its absorbance to establish a sewer sewage calibration line. This is based on the consideration that wastewater from different discharge sources may contain organic matter with different structures and different chain lengths. In order to avoid the difference in wastewater matrix from affecting the test results, Therefore, separate calibration lines are established for different emission sources. In addition, in order to meet the aforementioned requirements for pre-screening polluted water bodies, it is assumed that wastewater from the same discharge source has a similar wastewater matrix, and calibration curves can be further adjusted based on the characteristics of wastewater from different discharge plants.

Please refer to FIG. 4, which shows the chemical oxygen demand measurement line 400 of the KHP standard product established in Example 1, the chemical oxygen demand measurement line 402 of the printed circuit board manufacturing wastewater and The chemical oxygen demand measurement line 404 of the sewage is in the horizontal axis is the chemical oxygen demand concentration of the water sample in mg / L; the vertical axis is the absorbance of the water sample (no unit).

Perform a linear regression analysis on the calibration curve 400, the calibration curve 402, and the calibration curve 404. The linear regression formula of the calibration curve 400 is y = -0.0015x + 1.9288, and the R-squared value is 0.9705. The linear regression formula is y = -0.0022x + 1.5609, and the R-squared value is 0.9425; the linear regression formula of the calibration line 404 is y = -0.0024x + 0.8659, and the R-squared value is 0.8394. It can be observed that each of the calibration line 400, calibration line 402, and calibration line 404 has a good linear relationship. It can be seen that the method for detecting COD of the present invention can be well applied to the actual detection of COD in water.

Next, Example 2 will be used to illustrate the reagent volume ratio, operation steps, detection conditions and obtained chemistry when using the method for detecting COD in water in an on-site chemical oxygen demand test in a wastewater treatment plant. Oxygen demand concentration results. In addition, the chemical oxygen demand detection method NIEA W517.52B announced in the environmental inspection institute simultaneously performs chemical oxygen demand detection, and the chemical oxygen demand concentration obtained by the detection method of the present invention Results of correlation analysis.

In Example 2, the volume of sewage water sample used was 60 μL, the volume of potassium dichromate / mercury sulfate reagent was 115 μL, and the volume of silver sulfate / sulfuric acid reagent was 155 μL. The concentration of potassium dichromate was 20 mM, the concentration of sulfuric acid was 35 mM, the concentration of silver sulfate was 3.2 mM, and the concentration of mercury sulfate was 35.17 mM.

In Example 2, a computer-controlled robotic arm was used to draw sewage water samples, potassium dichromate / mercury sulfate reagent and silver sulfate / sulfuric acid reagent into the tips of micro-tubes, and the water samples and reagents were added to a glass tube. To form a mixed solution.

Next, the mixed solution in the glass tube was heated for a heating time of 10 minutes and a heating temperature of 150 ° C. Next, a computer-controlled mechanical arm was used to suck the heated mixed solution into the tip of a micro-tube, and then injected into the micro-channel test piece 200. The microfluidic channel test strip 200 is rotated by centrifugation to separate the mixed solution into a part to be detected and light blocking impurities.

The microchannel test strip 200 is placed in a spectrum analysis system 300 to perform a spectrum analysis on a portion to be detected of the mixed solution. In the spectral analysis, the wavelength of the light emitted by the light source 302 ranges from 340 nm to 750 nm, and the spectral analysis time is 10 minutes.

The COD detection result obtained by the detection method of the present invention is provided in FIG. 5, where the horizontal axis is the on-site water sample collection time, and the vertical axis is the COD concentration obtained by the detection method of the present invention. The line segment 500 shows the COD concentration obtained by the detection method of the present invention in a time period.

In order to understand the detection results and compliance of the detection method of the present invention Correlation between the chemical oxygen demand test results of the water chemical oxygen demand detection method announced by the Environmental Inspection Agency NIEA W517.52B. Next, the correlation results of the detection results of the above two methods are analyzed. The correlation analysis result is shown in FIG. 6, wherein the horizontal axis represents the chemical oxygen demand detection result of the method announced by the Environmental Inspection Agency NIEA W517.52B, and the vertical axis represents the chemical oxygen demand detection result of the detection method of the present invention. The line segment 600 represents a linear regression straight line of the detection result of the detection method of the present invention; and the line segment 602 represents a comparison baseline of the chemical oxygen demand detection results of the method announced by the National Institute of Environmental Inspection, NIEA W517.52B.

As shown in Figure 6, in the actual detection of the sewage treatment plant in Example 2, the detection method of the present invention and the chemical oxygen demand test results obtained by the environmental inspection institute ’s published method NIEA W517.52B have a fairly good correlation. The correlation coefficient (r ² ) can reach 0.926. In addition, from the analysis results, it is found that the measured value of the detection method of the present invention has a high background value at a low concentration portion, and the measured value can be corrected by subtracting the background value. Since it only takes about 20 minutes for the field test to obtain a measurement value with a high correlation with the conventional method for 2 hours of reflow, the feasibility of the detection method of the present invention for field test can be confirmed.

In addition, the detection method of the present invention and the method announced by the Environmental Inspection Agency, NIEA W517.52B, are compared with the test results of another simple chemical oxygen demand reagent. This simple COD reagent uses the colorimetric card method commonly used in current on-site COD detection. The colorimetric card is used to evaluate the color of the mixed solution after the reaction between water sample and potassium dichromate. The COD was measured semi-quantitatively. The comparison results are shown in Table 1: It can be observed from Table 1 that the detection method of the present invention and the method of environmental inspection institute NIEA W517.52B are quite close to the detection results of another simple chemical oxygen demand reagent, so it can also be confirmed that the detection method of the present invention is applied to the field Feasibility of testing.

In summary of the above two embodiments, in Embodiment 1, the method for detecting COD of the present invention provides a printed circuit board manufacturing line or a sewage line calibration line, and each calibration line shows a good linear relationship. . In Example 2, the on-site detection of chemical oxygen demand for a sewage treatment plant was conducted. The total detection time was 20 minutes, the total volume of the reagent used was 330 μL, the amount of reagent used was relatively low, and the time was relatively short in 20 minutes. Complete the test. In addition, the test result of Example 2 also showed a good correlation with the test result of the method announced by the Environmental Inspection Institute, confirming the feasibility of the test method of the present invention applied to field testing.

Although the present invention has been disclosed in the above embodiments, other embodiments are also possible. Therefore, the scope of the requested items is not limited to the description contained in the embodiments herein.

Anyone skilled in the art will understand that without departing from the invention Within the spirit and scope, various modifications and retouching can be made. Therefore, the scope of protection of the present invention shall be determined by the scope of the attached patent application.

Claims (9)

A method for detecting COD in water includes the following steps: providing a mixed solution of a water sample, an oxidation reagent, and a strong acid, wherein the total volume of the mixed solution is 100 microliters to 500 microliters; heating the mixed solution; After heating the mixed solution, the mixed solution is then injected into a microchannel test piece, and the microchannel test piece is centrifuged to separate the mixed solution into a part to be detected and light blocking impurities; and the microchannel test The part to be detected separated in the film is subjected to spectral analysis, wherein a detection wavelength range in the spectral analysis is 340 nm to 750 nm. The method of claim 1, wherein the oxidation reagent comprises potassium dichromate. The method of claim 1, wherein the strong acid comprises sulfuric acid or nitric acid. The method according to item 1 of the patent application scope, further comprising adding a silver sulfate reagent to the mixed solution. The method according to item 1 of the patent application scope, further comprising adding a mercury sulfate reagent to the mixed solution. The method according to item 1 of the patent application range, wherein the heating temperature is 120 ° C to 180 ° C. The method of claim 1, wherein the heating time is from 8 minutes to 15 minutes. The method according to item 1 of the patent application scope further comprises using a robotic arm to take the water sample and the oxidation reagent. The method according to item 1 of the patent application range, wherein the analysis time of the spectral analysis is 8 minutes to 15 minutes.