Method for detecting fossil carbon components in sewage organic matters based on wet chemical oxidation and carbon-13 isotope detection

Abstract

The invention provides a method for detecting fossil carbon components in sewage organic matters based on wet chemical oxidation and carbon-13 isotope detection. The method comprises the following steps: 1, collecting a sewage sample, and adding phosphoric acid to adjust the pH value for pretreatment so as to inhibit microbial activity and remove soluble inorganic carbonate; step 2, taking enough persulfate solution as an oxidizing agent and transition metal salt solution as a catalyst, heating the sample in a water bath in a closed device with good air tightness to completely oxidize organic matters, and collecting generated CO2 gas; and 3, introducing the collected gas sample into a stable isotope ratio mass spectrometer, and determining the carbon-13 isotope abundance in the gas sample so as to calculate the proportion of fossil carbon in the sewage organic matters. The method can effectively determine the fossil carbon content in the sewage organic matters, is low in detection difficulty and cost, and is suitable for carbon emission reduction self-detection in the sewage treatment field.

Description

Technical Field

[0001] The present invention relates to environmental engineering and municipal engineering, and is particularly applicable to the field of sewage treatment. It focuses on a new detection method aiming to accurately evaluate the fossil carbon content in sewage organic matter. By combining wet chemical oxidation technology and carbon-13 isotope detection means, detection and calculation are realized to improve the accuracy and efficiency of carbon emission accounting for sewage treatment. Background Art

[0002] With the acceleration of the industrialization process, a large amount of greenhouse gases such as CO2 generated by the use of fossil fuels have led to global warming, directly or indirectly endangering human survival. To address the challenges, carbon emission reduction has become the primary goal; among them, industry carbon emission accounting is the primary step in formulating a carbon emission reduction plan. The organic matter in sewage can be traced back to two categories: biogenic carbon and fossil carbon. Among them, the CO2 emission from biogenic carbon does not exacerbate global warming and does not need to be accounted for. However, the CO2 generated from fossil carbon needs to be included in the content of carbon emission accounting. Therefore, detecting and determining the fossil carbon content in sewage organic matter can increase the accuracy of carbon accounting in sewage treatment plants and contribute to the realization of the carbon neutral goal.

[0003] Currently, the determination of the fossil carbon content in sewage mainly relies on the method combining combustion oxidation and carbon-14 measurement technology. This requires using the freeze-drying method to separate the organic matter in sewage and form solid particles, and putting them into a double-layer vacuum quartz tube. The inner layer uses copper oxide powder as the oxide, and silver powder to remove impurities, and burns the organic matter particles to generate pure CO2 gas. The outer layer uses iron powder and zinc powder as reducing agents to reduce CO2 back to graphite powder. Subsequently, the graphite powder is introduced into a radioactive isotope ratio mass spectrometer to measure the carbon-14 ratio and calculate the fossil carbon content.

[0004] However, the existing method has obvious deficiencies. First of all, the operation steps of this method are complex, involving multiple experimental links. Moreover, the proportion of carbon-14 in nature is extremely low, only one in a hundred thousand of the total amount of carbon elements, which requires extremely high precision for the measurement results, and the operators need to have high professional skills and experience. Furthermore, the equipment of the radioactive isotope ratio mass spectrometer is expensive and has a relatively narrow actual application range. Therefore, the number of laboratories with such equipment in the country is limited, resulting in high detection costs and long waiting periods. Finally, this method has certain safety risks. When burning the organic matter particles at high temperature, the quartz tube has the risk of bursting, and the radioactive isotope ratio mass spectrometer has a certain risk of radiation exposure, which may cause health harm to the operators. Summary of the Invention

[0005] The purpose of the present invention is to solve the above-mentioned defects in the prior art and provide a method for detecting the fossil carbon component in sewage organic matter based on wet chemical oxidation and carbon-13 isotope.

[0006] The specific technical solution of the present invention is as follows:

[0007] S1: Collect the raw sewage water sample and conduct pretreatment;

[0008] S2: Add the sample and reaction reagents;

[0009] S3: Install a reaction device with good airtightness and remove the CO2 gas in the device;

[0010] S4: Heat in a water bath, after completion, collect the gas generated by the reaction, and refrigerate the sample;

[0011] S5: Measure the carbon-13 isotope abundance in the gas sample;

[0012] S6: Calculate the proportion of fossil carbon in the sewage organic matter.

[0013] Further, specifically in step S1:

[0014] (1) Collect 100 ml of the influent water of the sewage treatment plant every 2 hours, and the sampling is not less than 3 times; (2) After mixing all the collected samples evenly, collect the mixed sample; (3) Add an appropriate amount of phosphoric acid to the sample, shake evenly for 10 minutes, and maintain the pH value below 2 to remove inorganic carbonates and inhibit microbial activities; (4) Store the sample in a hard glass bottle, refrigerate it in the dark at 0 to 4 °C, and the storage period does not exceed 7 days.

[0015] Further, specifically in step S2:

[0016] Add the sewage sample, a persulfate solution 10 times in excess as an oxidant, and an appropriate amount of transition metal salt solution as a catalyst to the round-bottom flask in sequence.

[0017] Further, specifically in step S3:

[0018] Use a round-bottom flask, a spherical condenser and a piston air suction joint, and apply vacuum grease at 2 / 3 of the ground glass joint to install a reaction device with good airtightness, or use a sealed glass tube with a rubber stopper and draw the device into a vacuum state, or purge the inside of the device with an inert gas without CO2 for 10 minutes to remove the CO2 in the device.

[0019] Further, specifically in step S4:

[0020] Heat the device in a water bath to 100 °C and maintain for 1 hour. After the heating is completed and the device cools naturally, collect the gas naturally escaping from the device and store it at 4 °C for refrigeration.

[0021] Further, specifically in step S5:

[0022] A gas sample is introduced into a stable isotope ratio mass spectrometer to measure the abundance of carbon-13 isotope therein.

[0023] Further, specifically in step S6:

[0024] The ratio of fossil carbon to biogenic carbon in the sewage sample is calculated according to the following formula: Where: R FC is the proportion of fossil carbon in the sewage, %; δ sam is the measurement result of the abundance of carbon-13 isotope in the sample, ‰; δ ff is the abundance of carbon-13 isotope in fossil fuels, usually taken as -28‰; δ hw is the abundance of carbon-13 isotope in human excreta, usually taken as -20‰; R BC is the proportion of biogenic carbon in the sewage.

[0025] The present invention has the following advantages over the prior art:

[0026] 1. The present invention uses the wet chemical oxidation method to replace the burning method. This method has an operation process and required devices similar to the water sample detection method routinely carried out in sewage treatment plants, with strong compatibility and is easy for operators to master.

[0027] 2. The present invention uses the detection of carbon-13 isotope to replace the detection of carbon-14 isotope. Carbon-13 isotope has a higher natural abundance, which is more conducive to accurate detection. At the same time, the detection of carbon-13 isotope only requires a gas sample, which can simplify the operation process. At the same time, the detection of carbon-13 isotope has a wider application, enabling more stable isotope ratio mass spectrometers to be available, which can reduce the detection cost and waiting period.

[0028] 3. The operation process in the present invention is safer, significantly reducing the risk of high-temperature operation and avoiding the risk of radioactive substance exposure, improving the overall operation safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below in conjunction with the drawings and embodiments.

[0030] Figure 1 is the overall process schematic diagram of the present invention.

[0031] Figure 2 is the device used in the present invention in a vacuum state.

[0032] Figure 3 is the device used in the present invention during gas purging.

[0033] Figure 4 is the glass tube device with a piston used in the present invention.

[0034] In the figure: 1. round-bottom flask, 2. spherical condenser, 3. glass three-way joint, 4. first piston air extraction joint, 5. second piston air extraction joint, 6. two-neck flask, 7. third piston air extraction joint, 8. glass tube, 9. Teflon film, 10. butyl rubber stopper, 11. perforated plastic lid. Detailed implementation method

[0035] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0036] Embodiment 1:

[0037] In this embodiment, an artificial sewage prepared by mixing a completely bio-derived glucose standard sample with a known carbon-13 isotope content and a phthalic acid standard sample completely derived from fossil fuels in different proportions is taken as an example.

[0038] As Figure 1 shown, this embodiment is a method for detecting fossil components in sewage organic matter based on wet chemical oxidation and carbon-13 isotope detection, including the following steps:

[0039] S1. Add 85% phosphoric acid solution to the sample, adjust the pH to less than 2.0 and shake evenly, and maintain for 10 minutes. Then store the sample in a hard glass bottle and refrigerate it in the dark at 0 to 4°C.

[0040] S2. Add 50 ml of the sample, 110 ml of a 4% potassium persulfate solution, and 5 ml of a 1% silver nitrate solution to the round-bottom flask in sequence.

[0041] S3. The experimental device is as Figure 2 shown, including a round-bottom flask 1, a spherical condenser 2, a glass three-way joint 3, a first piston air extraction joint 4, and a second piston air extraction joint 5. After applying vacuum grease at 2 / 3 of the ground glass joints of each component, install them in sequence: insert the lower end of the spherical condenser 2 into the round-bottom flask 1. Connect the inlet and outlet of the cooling water above the spherical condenser 2 to the water source for cooling water to enter, and the lower part is the outlet for cooling wastewater to flow out. Install the glass three-way joint 3 at the upper end of the spherical condenser 2, install the first piston air extraction joint 4 on the right side of the glass three-way joint 3, and then connect it to the air bag through a hose. Install the second piston air extraction joint 5 at the top of the glass three-way joint 3 and connect it to the vacuum pump through a hose. Open the first piston air extraction joint 4 and the second piston air extraction joint 5, turn on the vacuum pump and suck until the vacuum degree in the device reaches 0.1 MPa and maintain for 5 minutes. Then close the second piston air extraction joint 5 and the vacuum pump.

[0042] S4. Heat the round-bottom flask in a water bath to 100 °C for 1 hour. After the heating is completed, wait for the device to cool naturally, and then close the second piston air extraction joint 5 and the air bag switch. After removing the air bag, place it in a refrigerator at 4 °C and store it in the dark for 24 hours.

[0043] S5. Introduce the gas sample into a stable isotope mass spectrometer to measure the abundance of carbon-13 isotope in the sample.

[0044] S6. Calculate the proportion of fossil carbon in the sewage according to the following formula: Where: R FC is the proportion of fossil carbon in the sewage, %; δ sam is the measurement result of the abundance of carbon-13 isotope in the sample, ‰; δ ff is the abundance of carbon-13 isotope in fossil fuels, usually taken as -28‰; δ hw is the abundance of carbon-13 isotope in human excreta, usually taken as -20‰; R BC is the proportion of biogenic carbon in the sewage. Calculate the proportion of fossil carbon in the sample and compare it with the theoretical value of the standard sample, with a deviation less than 3%.

[0045] Example 2:

[0046] Except for the following different steps, the remaining steps are the same as those in Example 1:

[0047] S3. The experimental device includes a spherical condenser 2, a glass three-way joint 3, a first piston air extraction joint 4, a second piston air extraction joint 5, a double-neck flask 6, and a third piston air extraction joint 7. Add the sample and the reagent into the double-neck flask 6. After applying vacuum silicone grease at 2 / 3 of the ground glass joints of each component, install them in sequence: Install the third piston air extraction joint 7 into the side interface of the double-neck flask 6, and connect an external hose to a 99% high-purity argon gas cylinder without carbon dioxide gas. Install the lower end of the spherical condenser 2 into the top interface of the double-neck flask 6. Connect the inlet and outlet of the cooling water above the spherical condenser 2 to the water source for cooling water to enter, and the lower part is the outlet for cooling wastewater to flow out. Install the glass three-way joint 3 at the upper end of the spherical condenser 2, install the first piston air extraction joint 4 on the right side of the glass three-way joint 3, and then connect it to the air bag through a hose. Install the second piston air extraction joint 5 at the top of the glass three-way joint 3. Open the second piston air extraction joint 5 and the third piston air extraction joint 7, and close the second piston air extraction joint 5. Open and adjust the outlet pressure of the gas cylinder to 0.2 MPa and blow for 10 minutes. After the blowing is completed, close the gas cylinder, the second piston air extraction joint 5 and the third piston air extraction joint 7 in sequence, and open the first piston air extraction joint 4.

[0048] Example 3:

[0049] Except for the following different steps, the remaining steps are the same as those in Example 1:

[0050] S2. Add 5 mL of the pretreated sample, 11 mL of a 4% potassium persulfate solution, and 0.5 mL of a 1% silver nitrate solution into the glass tube 8 in sequence.

[0051] S3. The experimental device includes a glass tube 8, a Teflon film 9, a butyl rubber stopper 10, and a plastic lid 11 with holes. Cover the glass tube opening with a 0.1-mm-thick Teflon film 9. Insert the butyl rubber stopper 10. Tighten the plastic lid 11 with holes. Subsequently, use a hollow long needle connected to a vacuum pump to penetrate the middle hole of the plastic lid 11 with holes, pierce through the butyl rubber stopper 10 and the Teflon film 9, and insert it into the glass bottle. Open the vacuum pump and suck until the vacuum degree in the bottle reaches 0.1 MPa and maintain it for 5 minutes. Then pull out the long needle and close the vacuum pump.

[0052] S4. Heat the glass bottle in a water bath to 100 °C for 1 hour. After the heating is completed and it cools naturally, use a syringe with good airtightness to insert into the glass bottle and collect the gas that naturally escapes. After pulling out the syringe, quickly transfer the gas to an airbag.

Claims

1. A method for detecting fossil carbon components in sewage organic matter based on wet chemical oxidation and carbon-13 isotope detection, the steps are as follows: S1: Collect raw sewage samples and pre-treat them; S2: Add samples and reaction reagents; S3: Install a reaction device with good airtightness and completely remove the carbon dioxide (CO2) gas in the device; S4: heating in a water bath, collecting the CO2 gas generated by the reaction after completion, and refrigerating the sample; S5: Determine the carbon-13 isotope abundance in the gas sample; S6: Calculate the proportion of fossil carbon in the organic matter in the sewage.

2. The method for detecting fossil carbon components in sewage organic matter based on wet chemical oxidation and carbon-13 isotope detection according to claim 1, wherein the characteristics are as described in step S1, and the specific process is as follows: (1) Collect 100 ml of influent water from the sewage treatment plant every 2 hours, and collect samples for no less than 3 times; (2) Mix all the collected samples evenly and collect the mixed sample; (3) Add an appropriate amount of phosphoric acid to the sample, shake it evenly for 10 minutes, and maintain the pH value below 2; (4) Store the sample in a hard glass bottle and refrigerate it at 0 to 4°C away from light.

3. The method for detecting fossil carbon components in sewage organic matter based on wet chemical oxidation and carbon-13 isotope detection as claimed in claim 2, wherein the characteristics are as described in step S2, and the specific process is as follows: Add sewage sample, sufficient persulfate solution as oxidant, and appropriate amount of transition metal salt solution as catalyst into a round-bottom flask in sequence.

4. The method for detecting fossil carbon components in sewage organic matter based on wet chemical oxidation and carbon-13 isotope detection as claimed in claim 3, wherein the characteristics are as described in step S3, and the specific process is as follows: Use a round-bottom flask, a spherical condenser and a piston exhaust joint, and apply vacuum silicone grease to 2 / 3 of the frosted mouth to install it into an airtight reaction device, or use a sealed glass tube with a rubber stopper, and evacuate the inside of the device to a vacuum state, or purge the inside of the device with an inert gas that does not contain CO2 to remove CO2 from the device.

5. The method for detecting fossil carbon components in sewage organic matter based on wet chemical oxidation and carbon-13 isotope detection according to claim 4, wherein the characteristics are as described in step S4, and the specific process is as follows: Heat the device to 100°C in a water bath. After the heating is completed and the device is cooled naturally, collect the gas naturally escaping from the device and store it in a refrigerator at 4°C.

6. The method for detecting fossil carbon components in sewage organic matter based on wet chemical oxidation and carbon-13 isotope detection according to claim 5, wherein the characteristics are as described in step S5, and the specific process is as follows: The gas sample is introduced into a stable isotope ratio mass spectrometer to measure the carbon-13 isotope abundance in the gas sample.

7. The method for detecting fossil components in organic matter in sewage based on wet chemical oxidation and carbon-13 isotope detection according to claim 6, wherein the characteristics are as described in step S6, and the specific process is as follows: The ratio of fossil carbon to biogenic carbon in sewage samples is calculated as follows:

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