Closed sewage treatment system fossil source CO2 emission accounting method

Abstract

The invention provides a fossil source CO2 emission accounting method for a closed sewage treatment system, and the method comprises the steps: dividing a plurality of stages of a sewage treatment process into a pretreatment stage, a biochemical treatment stage and an advanced treatment stage; according to the actual working condition of each stage, greenhouse gas emission is monitored and checked at the tail gas total emission outlet, and the greenhouse gas emission amount is obtained; according to the actual working condition of each stage, a gas sample is collected at a tail gas total discharge outlet, radioactive carbon isotopes are measured, and the fossil carbon proportion of the sample is obtained; and calculating the emission amount of CO2 of the fossil source and the contribution of the CO2 to a direct greenhouse gas emission list by combining the fossil carbon proportion and the greenhouse gas emission amount which are obtained previously. Based on the actual situation of the closed sewage treatment system, the system boundary of the CO2 emission accounting of the fossil source is perfected, the comprehensive CO2 emission accounting method of the fossil source of the closed sewage treatment system is established, and the content of the greenhouse gas emission list of the sewage treatment system is enriched.

Description

Technical Field

[0001] The present invention relates to the field of carbon emission accounting in sewage treatment industry, and in particular to a method for calculating 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 from water and reducing water pollution. However, it produces a large amount of greenhouse gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) during the sewage treatment process, so it is a source of carbon emissions that cannot be ignored. The sixth assessment report of the Intergovernmental Panel on Climate Change (IPCC) of the United Nations shows that carbon emissions from the sewage treatment industry account for about 2% to 3% of the total carbon emissions of the whole society, and show an increasing trend year by year. In the context of the "dual carbon" era, the "Implementation Plan for Coordinated Efficiency Improvement of Pollution Reduction and Carbon Reduction" issued by the Ministry of Ecology and Environment in 2022 clearly pointed out that it is necessary to carry out carbon emission measurement and calculation of urban sewage treatment and resource utilization, and promote the overall framework of coordinated efficiency improvement of pollution reduction and carbon reduction in sewage treatment plants. Scientific research with greenhouse gas emissions from sewage treatment systems as the specific object has gained an opportunity for development.

[0003] Previous studies generally considered the CO2 produced by the degradation of pollutants in the sewage treatment process to be biogenic carbon emissions, that is, this part of CO2 comes from the contemporary atmosphere, circulates continuously in nature, and the total amount remains unchanged, and should not be included in the greenhouse gas emission inventory for management. However, in recent years, studies have shown that as detergents, medicines and some industrial wastewater used in residents' lives enter urban sewage treatment plants, a considerable part of the CO2 emitted in 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 this part of the CO2 emissions produced by the metabolism of fossil carbon will cause the lack of greenhouse gas emission inventory. Domestic and foreign scholars have measured the actual fossil carbon content in sewage through radiocarbon determination methods and applied the mass conservation method. The fossil source CO2 accounts for 2-29% of the direct greenhouse gas emission inventory of sewage treatment plants. The IPCC 2019 report also pointed out that the research methods related to fossil carbon emissions in sewage treatment processes 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 constantly advancing with the times. Most ground sewage treatment plants adopt a cover-sealed design above the treatment facilities, which effectively closes and centrally treats the links that are prone to odor, greatly reducing the impact of odor on the surrounding environment. With the tension of urban space resources and the development of underground space technology, underground sewage treatment plants have become an effective way to solve the contradiction between urban sewage treatment needs and land resources and improve the urban ecological environment with their concealment, environmental friendliness, climate adaptability, and high degree of intelligence. Whether it is a ground-covered collection type or an underground closed sewage treatment plant, a modern waste gas management system has become standard. These systems not only effectively capture various types of waste gas, centrally purify them before discharging them, significantly reducing 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 closed sewage treatment systems, incorporating fossil source CO2 into greenhouse gas emission accounting is necessary for formulating accurate guidelines and is of great significance for supplementing the definition of carbon emissions from sewage treatment in greenhouse gas emission inventories. Summary of the invention

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

[0007] An embodiment of the present invention provides a method for calculating fossil source CO2 emissions in a closed sewage treatment system, comprising:

[0008] For all sewage treatment units in the system, the sewage treatment process was investigated in advance, and the research boundary was determined as the entire sewage treatment process was divided into the pretreatment stage, the biochemical treatment stage and the deep treatment stage;

[0009] According to the actual working conditions of each stage, greenhouse gas emissions are monitored and calculated at the exhaust gas outlet;

[0010] According to the actual working conditions of each stage, gas samples are collected at the exhaust gas outlet to measure the radioactive carbon isotopes and obtain the fossil carbon ratio of the samples;

[0011] Calculate the CO2 emissions from fossil sources and their contribution to the direct greenhouse gas emissions inventory by combining the fossil carbon ratio and greenhouse gas emissions obtained previously;

[0012] The structures in the pretreatment stage generally include: a lifting pump room, a coarse and fine screen, and a grit chamber. The above sewage treatment reaction units are all in a closed state. Each reaction unit is equipped with an exhaust gas collection pipeline to collect the greenhouse gases generated in this link. The exhaust gas from multiple branch pipelines will be collected to the deodorization device and discharged into the atmosphere after treatment;

[0013] The structures in the biochemical treatment stage generally include: a biochemical reaction tank and a secondary sedimentation tank. 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 collected in a 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 for the time being.

[0014] The structures in the deep treatment stage generally include: filter tanks, disinfection tanks, and 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.

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

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

[0017]

[0018] Among them, E single gas,pri and E single gas,bio They are the emissions of a single greenhouse gas at the exhaust outlet during the pretreatment and biochemical treatment stages within a certain period of time (generally 24 hours a day), in kg; c pipeline,pri and c pipeline,bio Represents the mass concentration of CO2, CH4 or N2O at the exhaust outlet of the pretreatment and biochemical treatment stages, respectively, in g / m 3 ;c background It is the mass concentration of CO2, CH4 or N2O in the background atmosphere of the plant area, in g / m 3 ;v pri and v bio are the gas flow rates in the exhaust gas emission pipelines during the pretreatment and biochemical treatment stages, in 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, in m 2 ; t is the monitoring time span, which is generally 24 hours a day, 86400 seconds.

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

[0020]

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

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

[0023] For sewage treatment units equipped with gas collecting pipelines, 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. When formally collecting gas, the flow rate and pressure of the vacuum pump need to be controlled to reduce errors caused by human factors.

[0024] The radiocarbon content of CO2 in the gas sample is determined using accelerator mass spectrometry. The results of the test on the accelerator mass spectrometer are calculated by 14 C / 12 C value, and compared with modern carbon 14 C / 12 The modern carbon standard is defined as 95% of the natural oxalic acid produced in 1950. 14 C isotope abundance ratio ( 14 C / 12 C), and pre-stabilize its carbon isotope δ 13C is corrected to 19‰ and the results are expressed as the modern carbon fraction Fm:

[0025]

[0026] Where S, M and B represent sample, modern carbon standard and blank (excluding 14 C standard) 14 C / 12 C ratio. In order to avoid 14 C / 12 C is affected by isotope fractionation, and the Fm value is generally corrected to the assumed initial δ 13 The C value was kept at the same level of -25‰ to ensure that the radiocarbon isotope abundances in different samples were comparable.

[0027] Since the carbon isotope characteristics of the sample are composed of biogenic carbon signals and fossil carbon signals, 14 The complete decay of C (Fm f =0) leads to similar isotopic characteristics of biogenic carbon and atmospheric carbon (Fm bio =Fm atm ). Therefore, the modern carbon fraction of the background atmosphere at the time of sampling (Fm atm ), if Fm s Below Fm atm , the fossil carbon contribution (f) of the sample can be calculated using isotope mass balance. According to relevant research and international standard ASTM D6866-18, due to fossil carbon emissions from fossil fuel combustion, the amount of fossil carbon in the modern atmosphere is 14 The C level is being diluted. According to monitoring data in recent years, modern atmospheric 14 The C level is gradually decreasing at a rate of 0.005 / year. The actual measured value in 2019 (Fm atm =1) for calculation.

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

[0029] Fm s =Fm bio ·x bio +Fm f ·f

[0030] x bio +f=1

[0031]

[0032] Among them, Fm s is the modern carbon fraction of the sample, Fm bio is the ratio of modern carbon to biogenic carbon, Fm fis the ratio of modern carbon to fossil carbon, Fm atm is the modern carbon fraction 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 fossil source CO2 emissions includes the following steps:

[0034] The CO2 emissions in the waste gas and the fossil carbon ratio of CO2 in the waste gas are combined to obtain the CO2 emissions from fossil sources in the waste gas. The specific calculation formula is as follows:

[0035]

[0036] in, It is the CO2 emission from fossil sources, in kg.

[0037] On this basis, the direct greenhouse gas emissions from sewage treatment are calculated to improve the contents of the emission inventory, including the CO2 equivalent emissions of CH4, the CO2 equivalent emissions of N2O and the CO2 emissions from fossil sources. The calculation formula is as follows:

[0038]

[0039] Among them, CHG direct is the direct greenhouse gas emissions from sewage treatment, in kg.

[0040] The contribution of fossil source CO2 emissions to the direct greenhouse gas emissions inventory is the proportion of fossil source CO2 emissions to the total direct greenhouse gas emissions, calculated as follows:

[0041]

[0042] in, CO2 is the contribution of fossil sources to direct greenhouse gas emissions, in %.

[0043] Compared with the prior art, the advantages and beneficial effects of the present invention are that the present invention can provide data support for the formulation and optimization of low-carbon pathways in the field of sewage treatment, and provide methodological guidance for quantifying fossil source CO2 emissions in closed sewage treatment systems.

[0044] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0045] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying 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 of the present invention. In the accompanying drawings:

[0047] Figure 1 is an overall flow chart of the method according to the present invention.

[0048] Figure 2 It is a specific process flow chart of a closed sewage treatment system according to an embodiment of the present invention.

[0049] Figure 3 is a data chart of greenhouse gas emissions according to an embodiment of the present invention.

[0050] Figure 4 4 is a graph showing the carbon isotope characteristics of the fossil samples according to an embodiment of the present invention.

[0051] Figure 5 This is a data chart of CO2 emissions from fossil sources according to an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The preferred embodiments of the present invention are described below in conjunction with the accompanying 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] Reference 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] The corresponding embodiment of the calculation method introduced in this method is to conduct a field test experiment on a sealed sewage treatment system with a cover on the ground in South China. The sewage treatment system mainly consists of three stages: pretreatment, biochemical treatment and deep treatment. Figure 2 As shown in the figure, the pretreatment part mainly includes the water inlet pump room, coarse screen, fine screen and cyclone sand settling tank; the biochemical treatment part consists of A 2 The system consists of an O-type oxidation ditch and a secondary sedimentation tank. The oxidation ditch can be divided into anaerobic zone, anoxic zone, aerobic zone, post-anoxic zone and post-aerobic zone; the deep treatment part includes a secondary lift pump room, a high-efficiency fiber filter, an ultraviolet disinfection pool and an artificial wetland; the sludge treatment part includes a sludge return pump room, a sludge storage tank and a dewatering machine room. In addition, the system is equipped with a first rain sedimentation tank to store and treat rainwater when the rainy season arrives. The system is equipped with a centralized waste gas collection system in the pretreatment part, the biochemical treatment part and the sludge treatment part. The collected waste gas is discharged into the atmosphere after being purified by biological treatment.

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

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

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

[0058] The method comprises the following steps:

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

[0060] According to the actual working conditions of each stage, greenhouse gas emissions are monitored and calculated at the exhaust gas outlet;

[0061] According to the actual working conditions of each stage, gas samples are collected at the exhaust gas outlet to measure the radioactive carbon isotopes and obtain the fossil carbon ratio of the samples;

[0062] Combining the fossil carbon ratio and greenhouse gas emissions obtained previously, the CO2 emissions from fossil sources and their contribution to the direct greenhouse gas emission inventory are calculated.

[0063] The structures in the pretreatment stage generally include: a lifting pump room, a coarse and fine screen, and a grit chamber. The above sewage treatment units are all in a closed state and equipped with tail gas collection pipelines to collect greenhouse gases generated in this link. The tail gas from multiple branch pipelines will be collected in a deodorization device and 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. 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 collected in a 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 for the time being.

[0065] The structures in the deep treatment stage generally include: filter tanks, disinfection tanks, and 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 greenhouse gas emissions includes the following steps:

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

[0068]

[0069] Among them, E single gas,pri and E single gas,bio They are the emissions of a single greenhouse gas at the exhaust outlet during the pretreatment and biochemical treatment stages within a certain period of time (generally 24 hours a day), in kg; c pipeline,pri and c pipeline,bio Represents the mass concentration of CO2, CH4 or N2O at the exhaust outlet of the pretreatment and biochemical treatment stages, respectively, in g / m 3 ;c background It is the mass concentration of CO2, CH4 or N2O in the background atmosphere of the plant area, in g / m 3 ;v pri and v bio are the gas flow rates in the exhaust gas emission pipelines during the pretreatment and biochemical treatment stages, in 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, in m 2 ; t is the monitoring time span, which is generally 24 hours a day, 86400 seconds.

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

[0071]

[0072] Among them, E plant is the total daily greenhouse gas emissions from the sewage treatment system, in kg; is the total daily emission of CO2, in kg; is the total daily CO2 emission in the pretreatment stage, is the total daily emission of CO2 in the biochemical treatment stage; is the total daily emission of CH4, in kg; is the total daily emission of CH4 in the pretreatment stage, is the total daily emission of CH4 in the biochemical treatment stage; is the global warming potential data for CH4; is the total daily emission of N2O, in kg; is the total daily emission of N2O in the pretreatment stage, is the total daily emission of N2O in the biochemical treatment stage; This is the global warming potential data for N2O.

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

[0074] For sewage treatment units equipped with gas collecting pipelines, 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. When formally collecting gas, the flow rate and pressure of the vacuum pump need to be controlled to reduce errors caused by human factors.

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

[0076]

[0077] Where S, M and B represent sample, modern carbon standard and blank (excluding 14 C standard) 14 C / 12 C ratio. In order to avoid 14 C / 12 C is affected by isotope fractionation, and the Fm value is generally corrected to the assumed initial δ 13 The C value was kept at the same level of -25‰ to ensure that the radiocarbon isotope abundances in different samples were comparable.

[0078] Since the carbon isotope characteristics of the sample are composed of biogenic carbon signals and fossil carbon signals, 14 The complete decay of C (Fm f =0) leads to similar isotopic characteristics of biogenic carbon and atmospheric carbon (Fm bio =Fm atm ). Therefore, the modern carbon fraction of the background atmosphere at the time of sampling (Fm atm ), if Fm s Below Fm atm , the fossil carbon contribution (f) of the sample can be calculated using isotope mass balance. According to relevant research and international standard ASTM D6866-18, due to fossil carbon emissions from fossil fuel combustion, the amount of fossil carbon in the modern atmosphere is 14 The C level is being diluted. According to monitoring data in recent years, modern atmospheric 14 The C level is gradually decreasing at a rate of 0.005 / year. The actual measured value in 2019 (Fm atm =1) for calculation.

[0079] The isotope mass balance and the fossil carbon contribution of the sample are calculated 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 fraction of the sample, Fm bio is the ratio of modern carbon to biogenic carbon, Fm f is the ratio of modern carbon to fossil carbon, Fm atm is the modern carbon fraction 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 fossil source CO2 emissions includes the following steps:

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

[0086]

[0087] in, It is the CO2 emission from fossil sources, in kg.

[0088] On this basis, the direct greenhouse gas emissions from sewage treatment are calculated to improve the contents of the emission inventory, including the CO2 equivalent emissions of CH4, the CO2 equivalent emissions of N2O and the CO2 emissions from fossil sources. The calculation formula is as follows:

[0089]

[0090] Among them, GHG direct is the direct greenhouse gas emissions from sewage treatment, in kg.

[0091] The contribution of fossil source CO2 emissions to the direct greenhouse gas emissions inventory is the proportion of fossil source CO2 emissions to the total direct greenhouse gas emissions, calculated as follows:

[0092]

[0093] in, CO2 is the contribution of fossil sources to direct greenhouse gas emissions, in %.

[0094] In the above-mentioned embodiment, the greenhouse gas emissions of the sewage treatment system were measured by an online greenhouse gas monitoring analyzer. Figure 3 The greenhouse gas emission range of CO2, CH4 and N2O in the table covers the pretreatment and biochemical treatment parts. The CO2 emission of this system is 504.35±86.84kg CO2 / d, and the CH4 emission is 972.98±106.17kg CO 2-eq / d, N2O emission 410.32±141.24kg CO 2-eq / d.

[0095] In the measurement of the above embodiment, the collected gas samples were subjected to isotope analysis. Figure 4 The modern carbon ratio (Fm s )、C14 age( 14 C age, BP) and fossil carbon contribution (f). The contribution of fossil carbon in CO2 in 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] On this basis, the CO2 emissions from fossil sources were calculated to enrich the contents of the greenhouse gas emission inventory, see Figure 5The accounting of fossil CO2 emissions. The CO2 emissions from fossil sources are 31.35±5.64kg; the direct greenhouse gas emissions (including fossil CO2, CH4 and N2O) are 1414.65±253.04kg; the contribution of fossil CO2 emissions to direct greenhouse gas emissions is 2.21%.

[0097] In summary, the present invention effectively overcomes the more significant drawbacks of the existing technical system and measurement ideas, and has high scientific research experiment and industrial application value.

[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 their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for calculating CO2 emissions from fossil sources in a closed sewage treatment system, characterized in that: The following steps are involved: Conduct preliminary research on the sewage treatment system and determine the research boundary as all sewage treatment units in the entire sewage treatment system. Divide the multiple stages of the sewage treatment process into: pretreatment stage, biochemical treatment stage and deep treatment stage; According to the actual working conditions of each stage, greenhouse gas emissions are monitored and calculated at the total exhaust gas emission outlet to obtain greenhouse gas emissions; According to the actual working conditions of each stage, gas samples are collected at the exhaust gas outlet to measure the radioactive carbon isotopes and obtain the fossil carbon ratio of the samples; Combined with the previously obtained fossil carbon ratio and greenhouse gas emissions, the fossil source CO2 emissions and their contribution to the direct greenhouse gas emission inventory are calculated. The structures in the pretreatment stage generally include: a lifting pump room, a coarse and fine screen, and a grit chamber. The above sewage treatment units are all in a closed state and equipped with tail gas collection pipelines to collect greenhouse gases generated in this link. The tail gas from multiple branch pipelines will be collected in a deodorization device and discharged into the atmosphere after treatment; The structures in the biochemical treatment stage generally include: a biochemical reaction tank and a secondary sedimentation tank. 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 collected in a 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 for the time being. The structures in the deep treatment stage generally include: filter tanks, disinfection tanks, and 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.

2. According to claim 1, a closed sewage treatment system fossil source CO2 emission accounting method is characterized in that: The monitoring and accounting of greenhouse gas emissions includes the following steps: 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 rate and cross-sectional area of ​​the pipeline. The mass concentrations of CO2, CH4 and N2O in the background atmosphere are also measured. The test resolution is seconds. The daily emission of a single greenhouse gas is calculated as follows: Among them, E single gas，pri and E single gas，bio are the emissions of a single greenhouse gas at the exhaust outlet during the pretreatment and biochemical treatment stages within a certain period of time, in kg; c pipeline，pri and c pipeline，bio分 Respectively represents the mass concentration of CO2, CH4 or N2O at the exhaust outlet of the pretreatment and biochemical treatment stages, in g / m 3 ;c background It is the mass concentration of CO2, CH4 or N2O in the background atmosphere of the plant area, in g / m 3 ;v pri and v bio are the gas flow rates in the exhaust gas emission pipelines during the pretreatment and biochemical treatment stages, in 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, in m 2 ; t is the monitoring time span, which is 24 hours a day, 86400 seconds; The total greenhouse gas emissions of a closed sewage treatment system are the emissions of CO2 plus the emissions of CH4 multiplied by the global warming potential of CH4, plus the emissions of N2O multiplied by the global warming potential of N2O, where the emissions of CO2, CH4 and N2O are 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 plan t is the total daily greenhouse gas emissions from the sewage treatment system, in kg; is the total daily emission of CO2, in kg; is the total daily CO2 emission in the pretreatment stage, is the total daily emission of CO2 in the biochemical treatment stage; is the total daily emission of CH4, in kg; is the total daily emission of CH4 in the pretreatment stage, is the total daily emission of CH4 in the biochemical treatment stage; is the global warming potential data for CH4; is the total daily emission of N2O, in kg; is the total daily emission of N2O in the pretreatment stage, is the total daily emission of N2O in the biochemical treatment stage; This is the global warming potential data for N2O.

3. The method for calculating fossil source CO2 emissions from a closed sewage treatment system according to claim 1, characterized in that: The gas sample collection and fossil carbon detection method comprises the following steps: For sewage treatment units equipped with gas collection pipelines, gas is collected at the opening of the gas collection pipeline. Before sampling, the gas sampling tube needs to be cleaned with the gas in the gas collection pipeline. When formally collecting gas, the flow rate and pressure of the vacuum pump need to be controlled; The radiocarbon content of CO2 in a gas sample is determined using accelerator mass spectrometry; the results of the test on the accelerator mass spectrometer are calculated by 14 C / 12 C value, and compared with modern carbon 14 C / 12 The modern carbon standard is defined as 95% of the natural oxalic acid produced in 1950. 14 C isotope abundance ratio ( 14 C / 12 C), and pre-stabilize its carbon isotope δ 13 C is corrected to 19‰ and the results are expressed as the modern carbon fraction Fm: Where S, M and B represent sample, modern carbon standard and blank (i.e., no carbon content) respectively. 14 C in the standard sample 14 C / 12 C ratio in order to avoid 14 C / 12 C is affected by isotope fractionation, and the Fm value is generally corrected to the assumed initial δ 13 The C value is at the same level of -25‰; to ensure that the radiocarbon isotope abundance in different samples is comparable; Since the carbon isotope characteristics of the sample are composed of biogenic carbon signals and fossil carbon signals, 14 The complete decay of C is Fm f = 0, resulting in similar isotopic characteristics of biogenic carbon and atmospheric carbon, namely Fm bio =Fm atm ; The fraction of modern carbon in the background atmosphere at the time of sampling is known (Fm atm ), if Fm s Below Fm atm , the fossil carbon contribution (f) of the sample is calculated using isotope mass balance; according to relevant research and international standard ASTM D6866-18, due to fossil carbon emissions produced by fossil fuel combustion, the modern atmosphere 14 C levels are constantly being diluted; according to monitoring data in recent years, modern atmospheric 14 The C level is gradually decreasing at a rate of 0.005 / year. The actual measured value in 2019, Fm atm =1 for calculation; The isotope mass balance and the fossil carbon contribution of the sample are calculated as follows: Fm s =Fm bio ·x bio +Fm f ·f x bio +f=1 Among them, Fm s is the modern carbon fraction of the sample, Fm bio is the ratio of modern carbon to biogenic carbon, Fm f is the ratio of modern carbon to fossil carbon, Fm atm is the modern carbon fraction 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.

4. The method for calculating fossil source CO2 emissions from a closed sewage treatment system according to claim 1, characterized in that: The calculation of fossil source CO2 emissions includes the following steps: The CO2 emissions in the waste gas and the fossil carbon ratio of CO2 in the waste gas are combined to obtain the CO2 emissions from fossil sources in the waste gas; the specific calculation formula is as follows: in, is the CO2 emission from fossil sources, in kg; On this basis, the direct greenhouse gas emissions from sewage treatment are calculated to improve the contents of the emission inventory, including the CO2 equivalent emissions of CH4, the CO2 equivalent emissions of N2O and the CO2 emissions from fossil sources; the calculation formula is 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 emissions inventory is the proportion of fossil source CO2 emissions to the total direct greenhouse gas emissions, calculated as follows: in, CO2 is the contribution of fossil sources to direct greenhouse gas emissions, in %.

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