Accounting Method for Fossil Source CO2 Emissions of a Closed Sewage Treatment System

Abstract

The present invention provides a method for accounting for fossil-source CO2 emissions in a closed sewage treatment system, including: dividing multiple stages of the sewage treatment process into a pretreatment stage, a biochemical treatment stage, and an advanced treatment stage; monitoring and accounting for greenhouse gas emissions at the total tail gas emission port according to the actual operating conditions of each stage to obtain the greenhouse gas emissions; collecting gas samples at the total tail gas emission port according to the actual operating conditions of each stage to measure the radiocarbon isotope and obtain the fossil carbon ratio of the samples; combining the previously obtained fossil carbon ratio and greenhouse gas emissions to calculate the emissions of fossil-source CO2 and its contribution to the direct greenhouse gas emission inventory. Based on the actual situation of the closed sewage treatment system, the present invention improves the system boundary for accounting for fossil-source CO2 emissions, establishes a comprehensive method for accounting for fossil-source CO2 emissions in the closed sewage treatment system, and enriches the content of the greenhouse gas emission inventory of the sewage treatment system.

Description

Technical Field

[0001] The present invention relates to the field of carbon emission accounting in the sewage treatment industry, and particularly relates to a method for accounting for fossil source CO2 emissions in a closed sewage treatment system. Background Art

[0002] The sewage treatment system is an important livelihood project for removing pollutants in water and reducing water pollution. However, a large amount of greenhouse gases such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are generated during the sewage treatment process. Therefore, it is a carbon emission source that cannot be ignored. The Sixth Assessment Report of the United Nations Intergovernmental Panel on Climate Change (IPCC) shows that the carbon emissions of the sewage treatment industry account for about 2% - 3% of the total social carbon emissions, and show an increasing trend year by year. Under the background of the "dual carbon" era, the "Implementation Plan for Coordinating Pollution Reduction and Carbon Reduction and Enhancing Efficiency" issued by the Ministry of Ecology and Environment in 2022 clearly states that it is necessary to carry out carbon emission measurement of urban sewage treatment and resource utilization, and promote the overall framework for coordinating pollution reduction and carbon reduction and enhancing efficiency in sewage treatment plants. Scientific research on the greenhouse gas emissions of sewage treatment systems has obtained a development opportunity.

[0003] Regarding the CO2 generated by the degradation of pollutants during the sewage treatment process, previous studies generally considered it as biogenic carbon emissions, that is, this part of CO2 comes from the contemporary atmosphere, continuously circulates in nature, and the total amount remains unchanged, and should not be included in the greenhouse gas emission inventory for management. However, recent studies have shown that with the entry of household detergents, medicines, and some industrial wastewater into urban sewage treatment plants, a considerable part of the CO2 emitted during the sewage treatment process is identified as fossil source emissions, that is, the raw materials of these substances come from fossil carbon such as oil and natural gas that were fixed and sealed in the earth's crust hundreds of millions of years ago. Ignoring the CO2 emissions generated by the metabolism of this part of fossil carbon will cause the lack of greenhouse gas emission inventory. Domestic and foreign scholars have measured that the content of fossil carbon in actual sewage is not low through radiocarbon determination methods and the application of the mass conservation method, and the fossil source CO2 accounts for 2 - 29% of the direct greenhouse gas emission inventory of sewage treatment plants. The IPCC 2019 report also points out that research methods related to fossil carbon emissions during the sewage treatment process should be improved.

[0004] As an important municipal infrastructure supporting urban development, sewage treatment plants are an important part of urban development, and their construction methods are also constantly advancing with the times. Most above-ground sewage treatment plants adopt a sealed design above the treatment facilities, effectively enclosing and centrally treating the odor-prone links, and greatly reducing the impact of odor dispersion on the surrounding environment. With the tension of urban space resources and the development of underground space technology, underground sewage treatment plants, with their characteristics such as concealment, environmental friendliness, climate adaptability, and high intelligence, have become an effective way to solve the contradiction between urban sewage treatment needs and land resources and improve the urban ecological environment. Whether it is an above-ground covered collection type or an underground closed sewage treatment plant, a modern exhaust gas management system has become a standard configuration. These systems not only effectively capture various exhaust gases, purify them centrally and then discharge them, significantly reducing the odor pollution to the atmospheric environment, but also provide convenient conditions for the accurate monitoring and scientific management of greenhouse gas emissions in the plant area.

[0005] In summary, considering the characteristics of the closed sewage treatment system, it is necessary to include fossil-source CO2 in the greenhouse gas emission accounting for formulating accurate guidelines, which is of great significance for supplementing the definition of carbon emissions from sewage treatment in the greenhouse gas emission inventory. Summary of the Invention

[0006] One of the purposes of the present invention is to provide a method for accounting fossil-source CO2 emissions in a closed sewage treatment system. Based on the actual situation of the sewage treatment system, the accounting boundary of carbon emissions is improved, and a comprehensive method for accounting fossil-source CO2 emissions in a closed sewage treatment system is established, making the accounting scope scientific and accurate, and providing content reference for supplementing the greenhouse gas emission inventory in the sewage treatment field.

[0007] A method for accounting fossil-source CO2 emissions in a closed sewage treatment system provided by an embodiment of the present invention includes:

[0008] For all sewage treatment units of the system, conduct preliminary research on the sewage treatment process of the sewage treatment system, determine that the research boundary is the entire sewage treatment process, which is divided into a pretreatment stage, a biochemical treatment stage, and a deep treatment stage;

[0009] According to the actual working conditions of each stage, monitor and account for greenhouse gas emissions at the total exhaust gas discharge port;

[0010] According to the actual working conditions of each stage, collect gas samples at the total exhaust gas discharge port, measure the radiocarbon isotope, and obtain the fossil carbon ratio of the samples;

[0011] Combining the previously obtained fossil carbon ratio and greenhouse gas emissions, calculate the emissions of fossil-source CO2 and its contribution to the direct greenhouse gas emission inventory;

[0012] The structures in the pretreatment stage generally include: lift pump house, coarse and fine grids, grit chamber. The above sewage treatment reaction units are all in a closed state, and each reaction unit is equipped with a tail gas collection pipeline to collect the greenhouse gases generated in this link. The tail gases of multiple branch pipelines will be aggregated to the deodorization device and discharged into the atmosphere uniformly after treatment;

[0013] The structures in the biochemical treatment stage generally include: biochemical reaction tank, secondary sedimentation tank. Among them, the biochemical reaction tank is in a closed state and is equipped with a tail gas collection pipeline to collect the greenhouse gases generated in this link. The tail gas will be aggregated to the deodorization device and discharged into the atmosphere uniformly after treatment. The secondary sedimentation tank is in an open state, so the greenhouse gas emissions in this link are not considered temporarily;

[0014] The structures in the advanced treatment stage generally include: filter tank, disinfection tank. The above sewage treatment units are generally in an open state, so the greenhouse gas emissions in this link are not considered temporarily.

[0015] The monitoring and accounting of the greenhouse gas emissions include the following steps:

[0016] Monitoring is carried out at the total discharge port of the exhaust gas centralized collection pipeline to obtain the mass concentrations of CO2, CH4 and N2O, as well as the flow velocity and cross-sectional area of the pipeline. At the same time, the mass concentrations of CO2, CH4 and N2O in the background atmosphere are measured, and the resolution of the test is in seconds. The daily emission formula of a single greenhouse gas is:

[0017]

[0018] Among them, E single gas,pri and E single gas,bio are the emissions of a single greenhouse gas at the exhaust gas discharge port in the pretreatment and biochemical treatment stages within a certain period of time (generally 24 hours a day), with the unit of kg; c pipeline,pri and c pipeline,bio represent the mass concentrations of CO2, CH4 or N2O at the exhaust gas discharge ports in the pretreatment and biochemical treatment stages respectively, with the unit of g / m 3 ; c background is the mass concentration of CO2, CH4 or N2O in the background atmosphere of the plant area, with the unit of g / m 3 ; v pri and v bio are the flow velocities of the gas in the exhaust gas discharge pipelines in the pretreatment and biochemical treatment stages respectively, with the unit of m / s; S pri and S bio are the cross-sectional areas of the exhaust gas discharge pipelines in the pretreatment and biochemical treatment stages respectively, with the unit of m 2 ; t is the monitoring time span, generally 24 hours a day, 86400 seconds.

[0019] The total greenhouse gas emissions of the closed sewage treatment system are the sum of the CO2 emissions, the CH4 emissions multiplied by the global warming potential data of CH4, and the N2O emissions multiplied by the global warming potential data of N2O. The emissions of CO2, CH4, and N2O are all the sum of the CO2, CH4, and N2O emissions in the pretreatment and biochemical treatment stages. The specific calculation formula is as follows:

[0020]

[0021] Among them, E plant is the total daily greenhouse gas emissions of the sewage treatment system, with the unit of kg; is the total daily CO2 emissions, with the unit of kg; is the total daily CO2 emissions in the pretreatment stage, is the total daily CO2 emissions in the biochemical treatment stage; is the total daily CH4 emissions, with the unit of kg; is the total daily CH4 emissions in the pretreatment stage, is the total daily CH4 emissions in the biochemical treatment stage; is the global warming potential data of CH4; is the total daily N2O emissions, with the unit of kg; is the total daily N2O emissions in the pretreatment stage, is the total daily N2O emissions in the biochemical treatment stage; is the global warming potential data of N2O.

[0022] The gas sample collection and fossil carbon detection method includes the following steps:

[0023] For the sewage treatment unit equipped with a gas collection pipeline, gas is collected at the opening of the gas collection pipeline. Before sampling, the gas sampling tube needs to be washed with the gas in the gas collection pipeline in advance. When officially collecting gas, the flow rate and pressure of the vacuum pump need to be controlled to reduce the error caused by human factors.

[0024] The accelerator mass spectrometry method is used to determine the radiocarbon content of CO2 in the gas sample. The test result of the radiocarbon isotope on the accelerator mass spectrometer is obtained by calculating the 14 C / 12 C value of the sample and comparing it with the 14 C / 12 C ratio in modern carbon. The standard sample of modern carbon is defined as the 95% 14 C isotope abundance ratio ( 14 C / 12 C) in natural oxalic acid produced in 1950, and its stable carbon isotope δ 13The δ14C is corrected to 19‰, and the result is expressed as the modern carbon fraction Fm:

[0025]

[0026] where S, M, and B represent the 14C / 12C ratios in the sample, modern carbon standard, and blank (a standard sample without 14C), respectively. To avoid the influence of isotope fractionation on 14C / 12C in the actual environment, the Fm value is generally corrected to the same level assuming an initial δ14C value of -25‰ for the sample, ensuring the comparability of the radiocarbon isotope abundances in different samples. 14 in the 14 14C / 12 12C ratio. 14 14C / 12 12C in the actual environment is affected by isotope fractionation. The Fm value is generally corrected to the same level assuming an initial δ14C value of -25‰ for the sample to ensure the comparability of the radiocarbon isotope abundances in different samples. 13 To ensure the comparability of the radiocarbon isotope abundances in different samples.

[0027] Since the carbon isotope signature of the sample consists of a biogenic carbon signal and a fossil carbon signal, and the complete decay of 14C in fossil carbon (Fm = 0) results in a biogenic carbon isotope signature similar to that of the atmosphere (Fm = Fm0). Therefore, given the modern carbon fraction of the background atmosphere (Fm0) at the time of sampling, if Fm is lower than Fm0, the fossil carbon contribution (f) of the sample can be calculated using isotope mass balance. According to relevant research and the international standard ASTM D6866-18, the 14C level in the modern atmosphere is continuously diluted due to fossil carbon emissions from the combustion of fossil fuels. Based on recent monitoring data, the 14C level in the modern atmosphere is decreasing at a rate of 0.005 / year. The measured value in 2019 (Fm0 = 1) is used for the calculation. 14 complete decay of 14C in fossil carbon (Fm f = 0) results in a biogenic carbon isotope signature similar to that of the atmosphere (Fm bio = Fm atm 0). Therefore, given the modern carbon fraction of the background atmosphere (Fm atm 0) at the time of sampling, if Fm s is lower than Fm atm 0, the fossil carbon contribution (f) of the sample can be calculated using isotope mass balance. According to relevant research and the international standard ASTM D6866-18, the 14C level in the modern atmosphere is continuously diluted due to fossil carbon emissions from the combustion of fossil fuels. Based on recent monitoring data, the 14C level in the modern atmosphere is decreasing at a rate of 0.005 / year. The measured value in 2019 (Fm 14 0 = 1) is used for the calculation. 14 14C level in the modern atmosphere is decreasing at a rate of 0.005 / year. The measured value in 2019 (Fm atm 0 = 1) is used for the calculation.

[0028] The isotope mass balance and the formula for calculating the fossil carbon contribution of the sample are as follows:

[0029] Fm s = Fm bio ·x bio + Fm f ·f

[0030] x bio + f = 1

[0031]

[0032] where Fm s is the modern carbon fraction of the sample, Fm bio is the modern carbon fraction of the biogenic carbon, and Fm fis the modern carbon ratio of fossil carbon, Fm atm is the modern carbon ratio of the contemporary atmosphere, x bio is the percentage of biogenic carbon in the sample, and f is the percentage of fossil carbon in the sample, that is, the fossil carbon ratio of the sample.

[0033] The calculation of the fossil-source CO2 emissions includes the following steps:

[0034] Combining the emissions of CO2 in the waste gas and the fossil carbon ratio of CO2 in the waste gas to obtain the emissions of fossil-source CO2 in the waste gas. The specific calculation formula is as follows:

[0035]

[0036] Among them, is the emissions of fossil-source CO2, with the unit of kg.

[0037] On this basis, calculate the direct greenhouse gas emissions of sewage treatment to improve the content of the emission inventory, including the CO2 equivalent emissions of CH4, the CO2 equivalent emissions of N2O, and the emissions of fossil-source CO2. The calculation formula is as follows:

[0038]

[0039] Among them, CHG direct is the direct greenhouse gas emissions of sewage treatment, with the unit of kg.

[0040] The contribution of fossil-source CO2 emissions to the direct greenhouse gas emission inventory is the proportion of the emissions of fossil-source CO2 in the total direct greenhouse gas emissions. The calculation formula is as follows:

[0041]

[0042] Among them, is the contribution of fossil-source CO2 to the direct greenhouse gas emissions, with the unit of %.

[0043] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: The present invention can provide data support for formulating and optimizing the low-carbon path in the field of sewage treatment, and provide method guidance for quantifying the fossil-source CO2 emissions of closed sewage treatment systems.

[0044] Other features and advantages of the present invention will be described in the subsequent specification, and some of them will become obvious from the specification, or be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures specifically pointed out in the written specification, claims, and drawings.

[0045] The technical solutions of the present invention will be further described in detail below through the drawings and embodiments. Description of the Drawings

[0046] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. In the drawings:

[0047] Figure 1 is the overall flowchart of the method according to the present invention.

[0048] Figure 2 is the specific process flowchart of the closed sewage treatment system in the embodiment according to the present invention.

[0049] Figure 3 is the greenhouse gas emission data chart in the embodiment according to the present invention.

[0050] Figure 4 is the sample fossil carbon isotope characteristic data chart in the embodiment according to the present invention.

[0051] Figure 5 is the fossil source CO2 emission situation data chart in the embodiment according to the present invention. Detailed Embodiments

[0052] The following describes the preferred embodiments of the present invention with reference to the drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0053] Referring to Figures 1 to 5 , in some embodiments, the present invention discloses a method for accounting for fossil source CO2 emissions in a closed sewage treatment system.

[0054] For the embodiments corresponding to the measurement methods introduced by this method, field detection experiments were carried out on a covered and sealed sewage treatment system in South China. The sewage treatment system mainly consists of three sections: pretreatment, biochemical treatment, and advanced treatment. Referring to Figure 2 as shown, the pretreatment section mainly includes an influent pump house, a coarse grille, a fine grille, and a vortex grit chamber; the biochemical treatment section consists of an A 2 / O oxidation ditch and a secondary sedimentation tank. The oxidation ditch can be divided into an anaerobic zone, an anoxic zone, an aerobic zone, a post-anoxic zone, and a post-aerobic zone; the advanced treatment section includes a secondary lift pump house, a high-efficiency fiber filter, an ultraviolet disinfection tank, and a constructed wetland; the sludge treatment section includes a sludge return pump house, a sludge storage tank, and a dewatering room. In addition, the system is equipped with a first flush sedimentation tank for storing and treating rainwater when the rainy season arrives. The system is equipped with an exhaust gas centralized collection system in the pretreatment section, the biochemical treatment section, and the sludge treatment section. The collected exhaust gas is purified by biological treatment and then discharged into the atmosphere.

[0055] Continue to refer toFigure 2 , except for the secondary sedimentation tank, high-efficiency fiber filter, and ultraviolet disinfection tank located at the rear end, all process treatment sections of the sewage treatment system are in a closed state.

[0056] Figure 2 The reaction tanks corresponding to the pretreatment part and biochemical treatment part are within the scope of the calculation method of the present invention. Each reaction tank is provided with a small number of small-area openable covers for daily maintenance and routine detection of water samples. Since sewage treatment plants usually transport the generated sludge to a third party for disposal, the system boundary excludes the greenhouse gas emissions during the sludge treatment and disposal process of the sewage treatment plant.

[0057] The greenhouse gas emission accounting method for a closed sewage treatment system of the present invention, according to Figure 2 the actual situation of the water treatment plant in the embodiment, conducts monitoring of greenhouse gas emissions, collection of samples, and accounting of fossil source CO2 emissions. The specific implementation refers to the method described in the present invention.

[0058] The method includes the following steps:

[0059] Conduct a preliminary investigation on the sewage treatment system, determine the research boundary as all sewage treatment units of the entire sewage treatment system, and divide the sewage treatment process into a pretreatment stage, a biochemical treatment stage, and a deep treatment stage;

[0060] According to the actual working conditions of each stage, monitor and account for greenhouse gas emissions at the total tail gas discharge port;

[0061] According to the actual working conditions of each stage, collect gas samples at the total tail gas discharge port, measure the radiocarbon isotope, and obtain the fossil carbon ratio of the sample;

[0062] Combine the previously obtained fossil carbon ratio and greenhouse gas emissions to calculate the emissions of fossil source CO2 and its contribution to the direct greenhouse gas emission inventory.

[0063] The structures in the pretreatment stage generally include: a lift pump house, coarse and fine grids, and a grit chamber. All the above sewage treatment units are in a closed state and are equipped with tail gas collection pipelines to collect the greenhouse gases generated in this link. The tail gases of multiple branch pipelines will be aggregated to a deodorization device and then uniformly discharged into the atmosphere after treatment;

[0064] The structures in the biochemical treatment stage generally include: a biochemical reaction tank and a secondary sedimentation tank. Among them, the biochemical reaction tank is in a closed state and is equipped with a tail gas collection pipeline to collect the greenhouse gases generated in this link. The tail gases will be aggregated to a deodorization device and then uniformly discharged into the atmosphere after treatment. The secondary sedimentation tank is in an open state, so the greenhouse gas emissions in this link are not considered temporarily;

[0065] The structures in the advanced treatment stage generally include: filter tanks and disinfection tanks. The above sewage treatment units are generally in an open state, so the greenhouse gas emissions in this link are not considered for the time being.

[0066] The monitoring and accounting of the greenhouse gas emissions include the following steps:

[0067] Monitoring is carried out at the total emission outlet of the exhaust gas centralized collection pipeline to obtain the mass concentrations of CO2, CH4, and N2O, as well as the flow velocity and cross-sectional area of the pipeline. At the same time, the mass concentrations of CO2, CH4, and N2O in the background atmosphere are measured, and the resolution of the test is in seconds. The daily emission calculation formula for a single greenhouse gas is:

[0068]

[0069] where E single gas,pri and E single gas,bio are the emissions of a single greenhouse gas at the exhaust gas emission outlet in the pretreatment and biochemical treatment stages within a certain period of time (usually 24 hours a day), with the unit of kg; c pipeline,pri and c pipeline,bio represent the mass concentrations of CO2, CH4, or N2O at the exhaust gas emission outlets in the pretreatment and biochemical treatment stages, with the unit of g / m 3 ; c background is the mass concentration of CO2, CH4, or N2O in the background atmosphere of the plant area, with the unit of g / m 3 ; v pri and v bio are the flow velocities of the gas in the exhaust gas emission pipelines in the pretreatment and biochemical treatment stages, with the unit of m / s; S pri and S bio are the cross-sectional areas of the exhaust gas emission pipelines in the pretreatment and biochemical treatment stages, with the unit of m 2 ; t is the monitoring time span, usually 24 hours a day, 86,400 seconds.

[0070] The total greenhouse gas emissions of the closed sewage treatment system are the emissions of CO2 plus the emissions of CH4 multiplied by the global warming potential data of CH4, plus the emissions of N2O multiplied by the global warming potential data of N2O. Among them, the emissions of CO2, CH4, and N2O are all the sum of the emissions of CO2, CH4, and N2O in the pretreatment and biochemical treatment stages. The specific calculation formula is:

[0071]

[0072] where E plant is the total daily greenhouse gas emissions of the sewage treatment system, with the unit of kg; is the total daily emissions of CO2, with the unit of kg; is the total daily CO2 emissions during the pretreatment stage, is the total daily CO2 emissions during the biochemical treatment stage; is the total daily CH4 emissions, with the unit of kg; is the total daily CH4 emissions during the pretreatment stage, is the total daily CH4 emissions during the biochemical treatment stage; is the global warming potential data of CH4; is the total daily N2O emissions, with the unit of kg; is the total daily N2O emissions during the pretreatment stage, is the total daily N2O emissions during the biochemical treatment stage; is the global warming potential data of N2O.

[0073] The gas sample collection and fossil carbon detection method includes the following steps:

[0074] For the sewage treatment unit equipped with a gas collecting pipeline, gas is collected at the opening of the gas collecting pipeline. Before sampling, the gas sampling tube needs to be cleaned with the gas in the gas collecting pipeline in advance. When officially collecting gas, the flow rate and pressure of the vacuum pump need to be controlled to reduce the errors caused by human factors.

[0075] The accelerator mass spectrometry is used to determine the radiocarbon content of CO2 in the gas sample. The test results of radiocarbon isotopes on the accelerator mass spectrometer are obtained by calculating the 14 C / 12 C value in the sample and comparing it with the 14 C / 12 C ratio in modern carbon. The standard sample of modern carbon is defined as 95% of the 14 C isotope abundance ratio ( 14 C / 12 C) in natural oxalic acid produced in 1950, and its stable carbon isotope δ 13 C is pre-corrected to 19‰. The result is expressed as the modern carbon ratio Fm:

[0076]

[0077] where S, M, and B represent the 14 C / 14 C / 12 C ratios in the sample, modern carbon standard sample, and blank (standard sample without 14 C), respectively. To avoid the influence of 14 C / 12 C in the actual environment being affected by isotope fractionation, the Fm value is generally uniformly corrected to the same level assuming the initial δ 13 C value of the sample is -25‰. To ensure the comparability of the radiocarbon isotope abundances in different samples.

[0078] Since the carbon isotope characteristics of the sample consist of a biogenic carbon signal and a fossil carbon signal, and the complete decay of 14 C in fossil carbon (Fm f = 0) results in the biogenic carbon having a similar carbon isotope characteristic to that in the atmosphere (Fm bio = Fm atm ). Therefore, given the modern carbon ratio (Fm atm ) of the background atmosphere during sampling, if Fm s is lower than Fm atm , the fossil carbon contribution (f) of the sample can be calculated using isotope mass balance. According to relevant research and the international standard ASTM D6866-18, due to fossil carbon emissions from fossil fuel combustion, the 14 C level in the modern atmosphere is continuously diluted. Based on monitoring data in recent years, the 14 C level in the modern atmosphere is gradually decreasing at a rate of 0.005 / year. The measured value in 2019 (Fm atm = 1) is selected for calculation.

[0079] The isotope mass balance and the calculation formula for the fossil carbon contribution of the sample are as follows:

[0080] Fm s = Fm bio ·x bio + Fm f ·f

[0081] x bio + f = 1

[0082]

[0083] Among them, Fm s is the modern carbon ratio of the sample, Fm bio is the modern carbon ratio of biogenic carbon, Fm f is the modern carbon ratio of fossil carbon, Fm atm is the modern carbon ratio of the contemporary atmosphere, x bio is the percentage of biogenic carbon in the sample, and f is the percentage of fossil carbon in the sample, that is, the fossil carbon ratio of the sample.

[0084] The calculation of the fossil source CO2 emissions includes the following steps:

[0085] Combining the emissions of CO2 in the waste gas and the fossil carbon ratio of CO2 in the waste gas to obtain the emissions of fossil source CO2 in the waste gas. The specific calculation formula is as follows:

[0086]

[0087] Among them, It is the emission of fossil - sourced CO2, with the unit of kg.

[0088] Based on this, the direct greenhouse gas emissions of sewage treatment are calculated to improve the content of the emission inventory, including the CO2 - equivalent emissions of CH4, the CO2 - equivalent emissions of N2O, and the emissions of fossil - sourced CO2. The calculation formulas are as follows:

[0089]

[0090] Among them, GHG direct is the direct greenhouse gas emissions of sewage treatment, with the unit of kg.

[0091] The contribution of fossil - sourced CO2 emissions to the direct greenhouse gas emission inventory is the ratio of the emissions of fossil - sourced CO2 to the total direct greenhouse gas emissions. The calculation formula is as follows:

[0092]

[0093] Among them, is the contribution of fossil - sourced CO2 to the direct greenhouse gas emissions, with the unit of %.

[0094] In the measurement of the above - mentioned embodiment, the greenhouse gas emissions of the sewage treatment system were determined by a greenhouse gas on - line monitoring analyzer, referring to Figure 3 the greenhouse gas emission range chart of CO2, CH4, and N2O. The greenhouse gas emissions in the table cover the pretreatment and biochemical treatment parts. The CO2 emissions of this system are 504.35 ± 86.84 kg CO2 / d, the CH4 emissions are 972.98 ± 106.17 kg CO 2-eq / d, and the N2O emissions are 410.32 ± 141.24 kg CO 2-eq / d.

[0095] In the measurement of the above - mentioned embodiment, isotope analysis was carried out on the collected gas samples, referring to Figure 4 the modern carbon ratio (Fm s ) of each sample, the carbon - 14 age ( 14 C age, BP), and the fossil carbon contribution (f). The contribution of fossil carbon in CO2 during the pretreatment stage is 0.0691 ± 0.0025, and the contribution of fossil carbon in CO2 in the biochemical pool is 0.0396 ± 0.0021.

[0096] Based on this, the emissions of fossil - sourced CO2 were calculated to enrich the content of the greenhouse gas emission inventory. See Figure 5Accounting of fossil - sourced CO2 emissions. The emissions of fossil - sourced CO2 are 31.35 ± 5.64 kg; the direct greenhouse gas emissions (including fossil - sourced CO2, CH4 and N2O) are 1414.65 ± 253.04 kg; the contribution of fossil - sourced CO2 emissions to direct greenhouse gas emissions is 2.21%.

[0097] In summary, the present invention effectively overcomes the relatively significant drawbacks in the existing technical system and measurement ideas, and has high scientific research, experimental and industrial application values.

[0098] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and its equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A method for calculating fossil source CO2 emissions of a closed sewage treatment system, characterized in that, Including the following steps: Conduct a preliminary investigation on the sewage treatment system, determine the research boundary as all sewage treatment units of the entire sewage treatment system, and divide the multiple stages of the sewage treatment process into: pretreatment stage, biochemical treatment stage, and advanced treatment stage; According to the actual working conditions of each stage, monitor and calculate the greenhouse gas emissions at the total exhaust gas outlet to obtain the greenhouse gas emissions; According to the actual working conditions of each stage, collect gas samples at the total exhaust gas outlet and measure the radioactive carbon isotope to obtain the fossil carbon ratio of the samples; Combined with the previously obtained fossil carbon ratio and greenhouse gas emissions, calculate the emissions of fossil source CO2 and its contribution to the direct greenhouse gas emission inventory; The structures in the pretreatment stage generally include: lift pump house, coarse and fine grids, grit chamber. The above sewage treatment units are all in a closed state and are equipped with tail gas collection pipelines to collect the greenhouse gases generated in this link. The tail gases of multiple branch pipelines will be aggregated to the deodorization device and discharged into the atmosphere after treatment; The structures in the biochemical treatment stage generally include: biochemical reaction tank, secondary sedimentation tank. Among them, the biochemical reaction tank is in a closed state and is equipped with a tail gas collection pipeline to collect the greenhouse gases generated in this link. The tail gas will be aggregated to the deodorization device and discharged into the atmosphere after treatment. The secondary sedimentation tank is in an open state, so the greenhouse gas emissions in this link are not considered temporarily; The structures in the advanced treatment stage generally include: filter tank, disinfection tank. The above sewage treatment units are generally in an open state, so the greenhouse gas emissions in this link are not considered temporarily; The gas sample collection and fossil carbon detection method includes the following steps: For the sewage treatment unit equipped with a gas collection pipeline, collect gas at the opening of the gas collection pipeline. Before sampling, it is necessary to wash the gas sampling tube with the gas in the gas collection pipeline in advance. When officially collecting gas, it is necessary to control the flow rate and pressure of the vacuum pump; Determining the radiocarbon content of CO2 in a gas sample using accelerator mass spectrometry; the test results of radiocarbon isotopes on an accelerator mass spectrometer are obtained by calculating the 14 C / 12 C value in the sample and comparing it with the 14 C / 12 C ratio in modern carbon; the standard of modern carbon is defined as the 95% 14 C isotope abundance ratio 14 C / 12 C in natural oxalic acid produced in 1950, and its stable carbon isotope δ 13 C is pre-corrected to 19‰, and the result is expressed as the modern carbon ratio Fm: where S, M, and B represent the sample, modern carbon standard, and blank, respectively, i.e., the 14 C in the 14 C / 12 C ratio; to avoid the influence of 14 C / 12 C by isotope fractionation, the Fm value is generally corrected to the same level assuming an initial δ 13 C value of -25‰ for the sample; to ensure the comparability of the abundances of radiocarbon isotopes in different samples; Since the carbon isotope characteristics of the sample consist of a biogenic carbon signal and a fossil carbon signal, and the complete decay of 14 C in fossil carbon, i.e., Fm f = 0, results in the biogenic carbon having a carbon isotope characteristic similar to that in the atmosphere, i.e., Fm bio = Fm atm ; Given the modern carbon ratio Fm atm of the background atmosphere during sampling, if Fm s is lower than Fm atm , the fossil carbon contribution f of the sample is calculated using isotope mass balance; According to relevant research and the international standard ASTM D6866-18, due to fossil carbon emissions from fossil fuel combustion, the 14 C level in the modern atmosphere is continuously diluted; Based on the monitoring data in recent years, the 14 C level in the modern atmosphere is gradually decreasing at a rate of 0.005 / year. The measured value in 2019, i.e., Fm atm = 1, is selected for calculation; The calculation formula for isotope mass balance and the fossil carbon contribution of the sample is: Fm s = Fm bio · x bio + Fm f · f x bio +f = 1 Among them, Fm s is the modern carbon ratio of the sample, Fm bio is the modern carbon ratio of biogenic carbon, Fm f is the modern carbon ratio of fossil carbon, Fm atm is the modern carbon ratio of the contemporary atmosphere, x bio is the percentage of biogenic carbon in the sample, and f is the percentage of fossil carbon in the sample, that is, the fossil carbon ratio of the sample.

2. The method for calculating the fossil source CO2 emissions of a closed sewage treatment system according to claim 1, wherein, The monitoring and calculation of the greenhouse gas emissions include the following steps: Carry out monitoring at the total exhaust gas outlet of the waste gas centralized collection pipeline to obtain the mass concentrations of CO2, CH4, and N2O, as well as the flow rate and cross-sectional area of the pipeline. At the same time, measure the mass concentrations of CO2, CH4, and N2O in the background atmosphere. The resolution of the test is in seconds. The daily emission calculation formula for a single greenhouse gas is: Among them, E single gas,pri and E single gas,bio are respectively the emissions of a single greenhouse gas at the exhaust gas outlet during the pretreatment and biochemical treatment stages within a certain period of time, with the unit of kg; c pipeline,pri and c pipeline,bio respectively represent the mass concentrations of CO2, CH4 or N2O at the exhaust gas outlet during the pretreatment and biochemical treatment stages, with the unit of g / m 3 ; c background is the mass concentration of CO2, CH4 or N2O in the background atmosphere of the plant area, with the unit of g / m 3 ; v pri and v bio are respectively the gas flow velocities in the exhaust gas pipelines during the pretreatment and biochemical treatment stages, with the unit of m / s; S pri and S bio are respectively the cross-sectional areas of the exhaust gas pipelines during the pretreatment and biochemical treatment stages, with the unit of m 2 ; t is the monitoring time span, taking 24 hours a day, 86,400 seconds; The total greenhouse gas emissions of the closed sewage treatment system is the emissions of CO2 plus the emissions of CH4 multiplied by the global warming potential data of CH4, plus the emissions of N2O multiplied by the global warming potential data of N2O. Among them, the emissions of CO2, CH4, and N2O are all the sum of the emissions of CO2, CH4, and N2O in the pretreatment and biochemical treatment stages. The specific calculation formula is: Among them, E plant is the total daily greenhouse gas emissions of the sewage treatment system, with the unit of kg; is the total daily CO2 emissions, with the unit of kg; is the total daily CO2 emissions in the pretreatment stage, is the total daily CO2 emissions in the biochemical treatment stage; is the total daily CH4 emissions, with the unit of kg; is the total daily CH4 emissions in the pretreatment stage, is the total daily CH4 emissions in the biochemical treatment stage; is the global warming potential data of CH4; is the total daily N2O emissions, with the unit of kg; is the total daily N2O emissions in the pretreatment stage, is the total daily N2O emissions in the biochemical treatment stage; is the global warming potential data of N2O.

3. A method for calculating fossil source CO2 emissions of a closed sewage treatment system according to claim 2, characterized in that, The calculation of the emissions of fossil source CO2 includes the following steps: Combine the emissions of CO2 in the waste gas and the fossil carbon ratio of CO2 in the waste gas to obtain the emissions of fossil source CO2 in the waste gas. The specific calculation formula is as follows: Among them, is the emission of fossil-source CO2, in kg; is the proportion of fossil carbon in CO2 in the waste gas; On this basis, calculate the direct greenhouse gas emissions of sewage treatment to improve the content of the emission inventory, including the CO2 equivalent emissions of CH4, the CO2 equivalent emissions of N2O, and the emissions of fossil-source CO2; the calculation formulas are as follows: Among them, GHG direct is the direct greenhouse gas emissions from sewage treatment, in kg; The contribution of fossil-source CO2 emissions to the direct greenhouse gas emission inventory is the proportion of the emissions of fossil-source CO2 in the total direct greenhouse gas emissions, and the calculation formula is as follows: Among them, is the contribution of fossil-derived CO2 to direct greenhouse gas emissions, in %.

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