Method for distinguishing biological and chemical oxygen consumption pathways and application

Abstract

The invention relates to the technical field of environmental monitoring and analysis, and particularly discloses a method for distinguishing biological and chemical oxygen consumption pathways and application. According to the method, isotope information is deeply excavated from an oxygen consumption end by utilizing specific differences of oxygen isotopes in different oxygen consumption processes. According to a biological respiratory metabolism oxygen consumption process and an oxygen isotope fractionation rule related to reducing metal ions or compounds, residual oxygen concentration and isotope composition are changed according to a specific mode. A chemical probe is introduced as an auxiliary judgment, and a support is provided for further accurate judgment of oxygen consumption types by tracking dynamic changes due to the fact that degradation rates or products of probe molecules in biological and chemical oxygen consumption processes are different. Meanwhile, carbon isotope change monitoring is introduced, and deep key information behind the oxygen consumption process can be clearly known according to the isotope difference between the chemical oxidation organic carbon and the biological oxidation organic carbon. And the identification and distinguishing accuracy of the oxygen consumption source is improved according to the three dimensional indexes.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental monitoring and analysis, and particularly relates to a method and application for distinguishing biological and chemical oxygen consumption pathways. Background Art

[0002] Oxygen, as a fundamental substance for the survival of the vast majority of life on Earth and also a green economic oxidant, plays an irreplaceable role in the ecosystem and environmental remediation fields. Oxygen is the key terminal electron acceptor in the process of aerobic respiration of cells, driving the metabolic activities of almost all aerobic life forms from microorganisms to higher plants and animals; in the field of environmental remediation, either aeration means can be used to enhance the metabolic activities of aerobic microorganisms to achieve the biodegradation of pollutants, or exogenous chemical agents or in-situ actual environmental components can be used to activate oxygen to generate strongly oxidizing reactive oxygen species, thereby achieving the chemical degradation of pollutants. In these complex natural or artificial systems, the phenomenon of oxygen consumption is widespread and diverse. In natural ecosystems such as soil and lakes, the metabolic activities of microorganisms on organic matter continuously consume oxygen, and at the same time, the chemical redox reactions accompanied by the oxidation of minerals in the soil and the material exchange between water and the atmosphere are also important ways of oxygen consumption. Artificial systems such as biological treatment links in sewage treatment plants or in-situ remediation of sites rely on aerobic metabolism of microorganisms to degrade organic pollutants, and the complex chemical components coexisting in wastewater and polluted site media are also potential oxygen consumption items. These oxygen consumption processes are closely related to the structural stability and function of natural or artificial systems. Once the oxygen consumption is abnormal, such as the metabolic activities of biological oxygen consumption being impacted due to environmental stress, or the chemical oxygen consumption disrupting the original redox balance due to pollution intrusion, a series of problems such as ecological chain breakage and material cycle blockage may occur, thereby threatening the healthy operation of ecological / artificial systems.

[0003] At present, the monitoring and identification methods for oxygen consumption processes are relatively limited and have obvious shortcomings. Traditional methods mostly rely on the determination of biological oxygen demand (BOD) and chemical oxygen demand (COD) indicators. Although these indicators can reflect the oxygen consumption levels of the overall biological / chemical two paths to a certain extent, it is difficult to accurately identify the respective proportions and dynamic changes of biological and chemical oxygen consumption, which hinders the in-depth analysis of the mechanisms of material transformation and element cycling in the oxygen consumption process in the ecosystem. In addition, the two oxygen consumption paths potentially affect each other and may overlap in time and space. The direct summation of BOD and COD cannot effectively indicate the total oxygen consumption demand under in-situ conditions, which is not conducive to guiding the aeration oxygen supply in water treatment and site remediation, resulting in the oxygen supply in actual engineering often deviating from the actual demand, either causing energy waste or failing to meet the demand. These series of deficiencies make it lack accurate and effective data support both in understanding natural ecological processes and optimizing environmental governance strategies, and there is an urgent need for innovative solutions. Summary of the Invention

[0004] The object of the present invention is to provide a method and application for distinguishing biological and chemical oxygen consumption pathways in view of the deficiencies in the prior art. Through the synergistic effect of oxygen isotope monitoring technology, chemical probe technology and carbon isotope monitoring technology, the accuracy of oxygen consumption source identification and differentiation is improved in all directions from three dimensions. The present invention has the advantages of high accuracy, wide applicability, strong stability, etc., can provide data support for regulating oxygen consumption in multiple fields, help the efficient use of resources, and achieve a win-win situation of economic and environmental benefits.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The first aspect of the present invention is to provide a method for distinguishing biological and chemical oxygen consumption pathways, including the following steps:

[0007] S1. Sample collection;

[0008] Collect environmental samples of the oxygen consumption pathway to be analyzed, and store them sealed and away from light.

[0009] S2. Oxygen isotope monitoring;

[0010] S21. Introduce the environmental sample of the oxygen consumption pathway to be analyzed into a glass bottle, purge with helium to ensure anoxic, inject pure oxygen, and then incubate with shaking at room temperature away from light. Continuously sample and test the oxygen concentration and oxygen isotope signal δ 18 O of the headspace oxygen at certain time intervals until the residual oxygen content is 20% - 80% of the initial value. At the same time, set up a high-temperature and high-pressure sterilization treatment group and a pre-oxidation treatment group to test a single oxygen consumption process;

[0011] S22. Based on the data of the change of oxygen content and isotope composition over time, calculate relevant parameters, draw a scatter plot and perform linear fitting to obtain the pseudo-first-order oxygen consumption kinetic constant k c and the oxygen consumption enrichment factor ε c , compare the enrichment factors of different treatment groups and the standard data values to determine the type of oxygen consumption;

[0012] S3. Chemical probe monitoring;

[0013] S31. According to the environmental sample of the oxygen consumption pathway to be analyzed collected in step S1, use the probe method to monitor the oxygen consumption pathway, and sample and analyze the probe concentration at the same time interval as the oxygen isotope monitoring in step S21;

[0014] S32. Draw a scatter plot of the change of probe concentration over time and perform linear fitting to obtain the pseudo-first-order oxygen consumption kinetic constant k p , compare the probe decay kinetics under the original environmental sample and sterilization treatment conditions to determine the dominant oxygen consumption pathway;

[0015] S4. Carbon isotope monitoring;

[0016] Under the oxygen consumption conditions of the environmental sample of the oxygen consumption pathway to be analyzed in step S21, the carbon isotope of the headspace carbon dioxide is tested at the same time interval over time;

[0017] S5. Discrimination of the oxygen consumption pathway;

[0018] By integrating the isotope fractionation characteristics in step S2, the probe kinetic characteristics in step S3, and the carbon isotope characteristics in step S4, a comprehensive discrimination criterion for biological / chemical oxygen consumption processes is established:

[0019] Characteristics of the chemical oxygen consumption-dominated stage, ε in isotope fractionation c <-10‰; in probe kinetics, the probe concentration shows a continuous exponential decay; in carbon isotope characteristics, the headspace δ 13 C-CO 2 Remains stable during the oxygen consumption reaction process;

[0020] Characteristics of the biological oxygen consumption-dominated stage, ε in isotope fractionation c >-10‰; in probe kinetics, the probe concentration shows a continuous exponential decay; in carbon isotope characteristics, the headspace δ 13 C-CO 2 Gradually decays to a negative value during the oxygen consumption reaction;

[0021] The steps S2, S3, and S4 can be executed in any order.

[0022] Furthermore, in step S1, the environmental sample of the oxygen consumption pathway to be analyzed is a sample collected in the environmental system to be studied according to the environmental monitoring standard method and represents the oxygen-consuming entity in this environmental area.

[0023] Furthermore, in step S21, the oxygen concentration and the oxygen isotope signal δ 18 O of the headspace oxygen in the glass bottle containing the environmental sample of the oxygen consumption pathway to be analyzed are sampled every half hour / or hour, expressed in per mil.

[0024] Furthermore, in step S21, an oxygen concentration and oxygen isotope analyzer is used to measure the oxygen concentration and the oxygen isotope signal of the headspace oxygen in the glass bottle.

[0025] Furthermore, in step S22, based on the changes in the oxygen content and its isotope composition obtained in the closed system over time, a scatter plot of ln(C t / C 0 ) versus time t is plotted and linearly fitted, where C t and C 0 respectively refer to the oxygen concentrations at times t and 0, and the slope obtained is the pseudo-first-order oxygen consumption kinetic constant k c .

[0026] Further, in step S22, according to the fact that the irreversible reaction in the closed system conforms to the Rayleigh fractionation model, a scatter plot of ln((δ 18 O t +1) / (δ 18 O 0 +1)) and ln(C t / C 0 ) is plotted, and linear fitting is performed, where δ 18 O t and δ 18 O 0 respectively refer to the oxygen isotope compositions at times t and 0, and the obtained slope is the oxygen consumption enrichment factor ε c .

[0027] Further, in step S31, the probe is an organic molecule, and the type of the organic molecule has one or more of the following characteristics:

[0028] a. It can be metabolized and utilized by the microbial oxygen consumption process and can also be degraded by the chemical oxygen consumption process;

[0029] b. Small molecule carboxylic acids or sugars absorbed by microbial metabolism but difficult to be chemically oxidized;

[0030] c. Organic molecules (such as chlorinated hydrocarbons such as trichloroethylene) that are difficult to be used as microbial metabolic carbon sources but can be chemically oxidized.

[0031] Further, in step S32, based on the change of the probe concentration obtained in the closed system with time, a scatter plot of ln(C pt / C p0 ) and time t is plotted, and linear fitting is performed, where C pt and C p0 respectively refer to the concentrations of the probe at times t and 0, and the obtained slope is the pseudo-first-order oxygen consumption kinetic constant k p .

[0032] Further, the organic molecule includes any one or more of phenol, acetic acid, glucose, and trichloroethylene.

[0033] The second aspect of the present invention is to provide the application of the above method for distinguishing biological and chemical oxygen consumption pathways in the field of environmental remediation.

[0034] Compared with the prior art, the beneficial effects brought by the technical solution provided by the present invention are:

[0035] (1) The method for distinguishing biological and chemical oxygen consumption pathways provided by the present invention can improve the time precision of distinguishing biological and chemical oxygen consumption compared with the traditional method that only relies on rough indicators such as COD and BOD. Through the collaborative monitoring of multiple substances (oxygen-consuming end-member, pattern probe compound, oxidized end-member organic carbon substrate) and multi-dimensional indicators (substance concentration and its corresponding isotope composition), it can accurately capture the oxygen consumption changes in both ecological systems and the oxygen consumption differences in the technological processes of artificial systems, providing reliable and accurate data support for subsequent regulation measures.

[0036] (2) The method proposed by the present invention has a wide range of applications and is not limited to a single type of environmental medium. Whether it is aquatic ecosystems such as fresh water and seawater, terrestrial ecosystems such as forests and farmlands, or artificial regulation systems such as site remediation and sewage treatment, or even heterogeneous media containing multiple components, as long as oxygen consumption analysis is involved, it can be applied, greatly expanding the application boundary of oxygen consumption monitoring technology.

[0037] (3) The method provided by the present invention has good stability. For example, high-precision stable isotope mass spectrometers, stable probe molecules, and standard sampling procedures ensure the reliability and coherence of data during long-term sequence monitoring, effectively avoiding misjudgment caused by monitoring batch errors, and providing stable technical support for long-term ecological research, process optimization and upgrading, etc.

[0038] (4) The present invention helps to achieve efficient utilization of resources. After clarifying the biological and chemical oxygen consumption pathways and their proportions, each field can allocate resources targeted, avoiding resource waste caused by blind investment in the traditional way. For example, precise aeration and oxygen supply in sewage treatment plants and site remediation fields, precise fertilization and ventilation in agriculture and fishery, etc., to achieve a win-win situation of economic and environmental benefits. Description of the Drawings

[0039] Figure 1 It is a schematic flow chart of a method for distinguishing biological and chemical oxygen consumption pathways provided by the present invention;

[0040] Figure 2 It is a working flow chart for the complete identification and distinction of biological and chemical oxygen consumption pathways using the specific solid-phase environmental medium - sediment / soil of the present invention;

[0041] Figure 3 It is a graph showing the differences in oxygen consumption kinetics and the changes in enrichment factors of chemical / biological oxygen consumption pathways of aquifer sediments in the original / sterilized / pre-oxidized states in the embodiments of the present invention;

[0042] Figure 4 It is a graph showing the attenuation of phenol oxidation concentration and its kinetics of aquifer sediments using probe phenol under original / sterilized conditions in the examples of the present invention;

[0043] Figure 5 This is the graph showing the change of δ 2 C of CO 13 in the headspace during the oxidation process of the aquifer sediment in its original / sterilized state in the examples of the present invention over time. Detailed implementation manners

[0044] To make the objectives, technical solutions and advantages of the present invention clearer, the following further describes in detail the specific implementation manners of the present invention with reference to specific embodiments and the accompanying drawings. For the embodiments where specific test methods, instrument equipment or conditions are not specified, they shall all be carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0045] Refer to Figure 1 , which is a schematic diagram of the principle of a method for distinguishing biological and chemical oxygen consumption pathways provided by the present invention, and specifically includes the following steps:

[0046] (1) Sampling and preservation of samples: The environmental samples are collected according to the environmental monitoring standard method (HJ 495-2009) in the environmental system to be studied, and represent the oxygen-consuming main body in this environmental area.

[0047] Determine the environmental area to be studied, select representative sampling points according to the research purpose and preliminary investigation, and collect samples respectively using a professional water sampler (liquid phase), a soil drill (solid phase) or a combination of both (mixed), ensuring that the sampling process is pollution-free and does not damage the sample structure. After collection, immediately seal and wrap the samples and store them in the dark. If they cannot be transported immediately on-site, use an incubator or a mixture of ice and water to store them at 0-4°C, and transport them to the laboratory as soon as possible and put them in a 4°C refrigerator. Ensure that the samples are kept at low temperature, in the dark and sealed throughout the process.

[0048] (2) Pretreatment and experimental operation of samples: According to the experimental requirements, quickly transfer an appropriate amount of the preserved original sample to a glass bottle pre-wrapped with aluminum foil paper, add anaerobic water according to the concentration requirement and seal it. Three parallel samples are set for each original sample. The sealed samples should be in a solution (liquid phase) or suspension (solid phase) system and have a certain amount of headspace. On the basis of the original environmental samples, take some for high-temperature and high-pressure sterilization treatment, and take some for pre-oxidation treatment (to completely chemically oxidize the samples), and then culture them respectively in the above-mentioned manner. The sterilization treatment group simulates a single chemical oxygen consumption process, and the pre-oxidation treatment group simulates a single biological oxygen consumption process. By comparing the experimental results of different treatment groups, distinguish the chemical and biological oxygen consumption processes and their effects on oxygen isotope fractionation. Connect the pre-treated sealed bottles to a helium purge device. The purge flow rate and purge time should be set based on ensuring an anaerobic background atmosphere to ensure that the original air in the bottle is completely replaced, creating an anaerobic environment for subsequent injection of pure oxygen. Inject a certain amount of pure oxygen into the bottle with a syringe and place it in a light-proof constant-temperature shaking incubator for shaking culture. The theoretical oxygen injection amount is injected at 120% - 180% of the theoretical oxygen demand of the sample, and other culture conditions are set according to actual needs.

[0049] (3) Monitoring of oxygen concentration and oxygen isotope signal: Continuously monitor the change in the oxygen content in the glass bottle until the residual oxygen content reaches 20% - 80% of the initial oxygen content. According to the experimental requirements and the oxygen consumption characteristics of the samples, determine the sampling time interval, and calculate the ratio of the residual oxygen content to the initial oxygen content in real time based on the oxygen concentration measurement data, which is used as the basis for judging whether to continue monitoring. At each sampling time point, use a calibrated syringe with good airtightness to slowly draw an appropriate amount of gas from the headspace of the glass bottle, and quickly inject the drawn gas into the oxygen concentration and oxygen isotope analysis instruments (such as gas chromatograph and stable isotope ratio mass spectrometer), and sequentially measure the oxygen concentration and oxygen isotope signal (δ 18 O, expressed in per mille) of the headspace oxygen in the glass bottle according to the instrument operation procedures (GB / T 37847-2019).

[0050] (4) Data analysis and comparison: For the original samples, high-temperature and high-pressure sterilization treatment group samples, and pre-oxidation treatment group samples, respectively analyze the data of the change in oxygen content and its isotope composition measured in a closed system over time. First, calculate ln(ln(C t / C 0 )) at each time point t and draw a scatter plot with time t. After linear fitting, obtain the pseudo-first-order oxygen consumption kinetic constant k c ; then use the δ 18 O measured at different times and the δ 0 O corresponding to the initial C i 18 O to calculate ln(δ 18 O + 1) / (δ i18 O + 1), and also with ln(C t / C 0 ) as the abscissa and ln(δ 18 O + 1) / (δ i 18 O + 1) as the ordinate to plot a graph and perform linear fitting to obtain the oxygen consumption enrichment factor ε c . Compare the ε values of each treatment group c and combine with the standard data values of biological / chemical oxygen consumption to judge the oxygen consumption type. If there is a mixed oxygen consumption situation, use the isotope end-member mixing model, with the ε c of the sterilization group and the pre-oxidation group as the end-members and the ε c of the original sample as the mixing value to quantify the contribution ratios of biological oxygen consumption and chemical oxygen consumption in the original sample, and record the analysis results to provide data support for the research.

[0051] (5) Carbon isotope monitoring: Refer to the oxygen consumption experiments of the original environmental samples in steps (1) and (2). At the established same time intervals, use a syringe to separately extract appropriate amounts of aqueous solution samples and headspace gas samples. If necessary, perform pretreatment on the aqueous solution samples, and inject the samples into the corresponding carbon isotope analysis instrument for testing. Plot a curve with time as the abscissa and δ 13 C-CO 2 as the ordinate, and observe and analyze the dynamic change trends of the concentration and carbon isotope composition of carbon dioxide in the headspace during the oxygen consumption process of the original environmental samples. Combine with oxygen concentration, oxygen isotope, and other relevant experimental data (such as the physical and chemical properties of the samples, microbial activity, etc.) to comprehensively analyze the internal relationship between the carbon isotope change and the oxygen consumption process. Explore the degradation and transformation process of dissolved organic carbon, the sources of carbon dioxide generation, and their roles and significance in the carbon cycle process in the underground aquifer medium, providing more basis for in-depth understanding of the material cycle mechanism in the underground aquifer ecosystem.

[0052] (6) Auxiliary comparison of chemical probes: Except for adding specific chemical probes to the suspension in step (1) during sample treatment, the remaining steps are the same as those in (1) and (2). For the original environmental samples and sterilized samples, calculate ln(C pt / C p0 ) according to the probe concentration at different times in the closed system and plot a scatter diagram with time t. After linear fitting, obtain the pseudo-first-order oxygen consumption kinetic constant k p . Compare the k p of the two. If they are similar, the original environmental sample is in the stage dominated by chemical oxygen consumption; if the difference is large, it is in the stage dominated by biological oxygen consumption.

[0053] It should be noted that one or more of the three types of organic probes are selected according to the characteristics of the environmental components to be monitored. (a) It can be metabolized and utilized by the microbial oxygen consumption process and can also be degraded by the chemical oxygen consumption process, but there are attenuation kinetic differences in the two paths, such as phenol; (b) small molecule carboxylic acids or sugars (such as acetic acid, glucose) that are easily metabolized and absorbed by microorganisms but are difficult to chemically oxidize; (c) organic molecules (such as chlorinated hydrocarbons such as trichloroethylene) that are difficult to be used as microbial metabolic carbon sources but can be chemically oxidized. Generally, probes of type (a) are preferably used. If the oxidation kinetics of the probes of type (a) are all too fast to distinguish, probes of type (b) or (c) are added to identify the dominant oxygen consumption process. The selected probes are added to the same original environmental sample system and sterilization treatment system as in (1) with a syringe at a precise concentration, and the same oxygen injection operation is maintained to start the oxygen consumption monitoring. Samples are taken at the same time intervals as in (1) to analyze the probe concentration in the experimental system.

[0054] The following takes specific examples to elaborate in detail on a method and application for distinguishing biological and chemical oxygen consumption pathways provided by the present invention.

[0055] Example 1

[0056] This example provides the identification and distinction of the biological and chemical oxygen consumption processes of typical sediments (collected at 30.461636°N, 114.665929°E, Zui Li Lake, Ezhou City, Hubei Province) in the aquifer porous medium. The schematic flow diagram of this method is as Figure 2 shown, and the specific steps are as follows:

[0057] Step S1, sediment sample collection and preservation: At a sampling point near a natural lake shore, the groundwater level is 0.5 m. Sediment samples are collected at a depth of 1.5 m at the sampling point using sampling equipment. The collected clay sediment samples are immediately wrapped tightly with plastic wrap and covered with tin foil to avoid light, and then further placed in a vacuum bag and evacuated and sealed to isolate contact with air, ensuring that the samples remain in their in-situ state and are transported to the laboratory.

[0058] Step S2, prepare several 310 ml anaerobic bottles. In the anaerobic glove box, accurately weigh a certain amount of sediment samples respectively, add a certain volume of ultrapure water to make the suspension concentration reach 200 g / L, and the liquid volume is 125 mL, leaving enough headspace for injecting oxygen and sampling. The anaerobic suspension is dispersed in a shaker at a speed of 220 rpm for 12 h to form a uniform sediment suspension. The sterilization treatment group sterilizes the sediment suspension by high temperature and high pressure to eliminate the microbial oxygen consumption process; the pre-oxidation group completely oxidizes the reducing chemical components in the sediment through aeration; the original group is not treated at all.

[0059] Step S3: Use helium to purge the anaerobic bottle to ensure a pure background atmosphere, and then precisely inject 25 mL of O into the anaerobic bottle through a syringe. 2 , and then place it in a constant temperature shaker at 220 rpm for reaction in the dark. During the reaction, at predetermined time intervals of 1 h (for the first 5 h), 3 h (from 5 to 15 h), and 5 h (from 15 to 24 h), use a microsyringe to extract 50 μL of gas from the anaerobic bottle and manually inject it into a gas chromatograph (GC) coupled with a gas stable isotope ratio mass spectrometer (IRMS) to measure the residual oxygen concentration and its δ 18 O. Repeat sampling to synchronously test the δ 2 of 13 C.

[0060] Step S4: Plot a scatter diagram of ln(C t / C 0 )(where C t and C 0 refer to the oxygen concentrations at times t and 0 respectively) against time t, and perform a linear fit to obtain the pseudo-first-order oxygen consumption kinetic constant k c . Further, based on the Rayleigh fractionation model, plot ln((δ 18 O t +1) / (δ 18 O 0 +1))(where δ 18 O t and δ 18 O 0 refer to the oxygen isotope compositions at times t and 0 respectively) against ln(C t / C 0 ) and perform a linear fit. The slope obtained is the oxygen consumption enrichment factor ε c .

[0061] Step S5: Use a phenol probe to assist in determining the oxygen consumption pathway. Take another sediment and form a suspension through the same treatment steps as in S1 and S2, but add 20 μM of phenol before oxygen injection. Take 1 mL of sediment suspension samples at the same time intervals as in Step S1, and filter them using a 0.22 μm nylon filter membrane. Mix 500 μL of the filtrate with 500 μL of methanol, and then test the phenol concentration of the sample by high-performance liquid chromatography to obtain the decay of the probe phenol concentration over time, and plot a scatter diagram of ln(C pt / C p0 )(where C pt and C p0 refer to the concentrations of the probe phenol at times t and 0 respectively) against time t, and perform a linear fit. The slope obtained is the pseudo-first-order oxygen consumption kinetic constant k p .

[0062] Reference Figure 3Graph showing the variation of oxygen concentration and oxygen isotope fractionation with time during the chemical and biological consumption of oxygen in the oxidation process of clay sediments. In the figure, (a) shows the variation of headspace oxygen concentration, (b) shows the determination of the pseudo-first-order oxygen consumption kinetic constant, (c) shows the enrichment factor ε of oxygen consumption by the sediment over time, and (d) shows the enrichment factor ε for separately testing the chemical and biological oxygen consumption stages of the clay sediment c determination, and (d) shows the enrichment factor ε for separately testing the chemical and biological oxygen consumption stages of the clay sediment c . Before 15 h, the oxygen isotope enrichment factor ε c = -6.46‰; after 15 h of the reaction, the oxygen isotope enrichment factor ε c = -18.14‰. The reduced clay sediment after sterilization treatment did not show a segmented phenomenon, and the oxygen isotope fractionation enrichment factor ε c = -7.77‰, which is close to the enrichment factor (ε c = -6.46‰) of the original sediment during the first 15 h of oxidation and is significantly smaller than the enrichment factor (ε c = -18.14‰) of the original sediment after 15 h of oxidation. This indicates that the oxygen in the sediment is consumed chemically within the first 15 h. After 15 h, a large number of microorganisms are activated, and the oxygen isotope fractionation effect of biological oxygen consumption is more significant, while the enrichment factor of oxygen consumption by the chemical pathway is closer to 0. From the pseudo-first-order oxygen consumption kinetic constant k t fitted from the linear fitting of ln(C 0 / C c )-t at each time point, it can be seen that the sterilized and original clay sediments show similar kinetic characteristics during the chemical oxygen consumption stage from 0 to 5 h. However, after the biological pathway is activated from 15 to 25 h, there are clear kinetic differences between the original sediment and the sterilized sediment. The oxygen consumption kinetic constant k c = 0.0091 h -1 , and its oxygen consumption rate is much smaller than that of the sterilized group (k c = 0.0591 h -1 ).

[0063] Reference Figure 4It is a graph showing the attenuation change of phenol for verifying chemical and biological oxygen consumption during sediment oxidation using a probe. In the 0 - 5h period, the phenol concentrations in both the sediment sterilization treatment group and the original group decreased significantly, indicating that chemical oxygen consumption occurred during this time. During the 5 - 15h period, the phenol concentration remained stable, indicating that the chemical oxygen-consuming substances in the sediment were almost completely consumed at this time, and biological oxygen consumption was slowly starting. After 15h, the phenol concentration in the sediment sterilization treatment group remained almost unchanged, while the original sediment group showed a significant decreasing trend and approached 0 at 24h. At this time, microorganisms used phenol as a carbon source for aerobic metabolism, and the sediment oxygen consumption process was mainly biological. The overall experimental phenomenon was that phenol first decreased significantly, then remained stable for a period of time, and then showed a large consumption trend. Through the phenol probe method and the oxygen isotope fractionation process, it was assisted to identify that sediment oxidation consumed oxygen mainly through chemical pathways in the 0 - 5h period, microbial activities gradually started in the 5 - 15h period, and a large number of organisms participated in the oxidation reaction after 15h. The demarcation point between chemical consumption and biological consumption was determined at 15h after the start of oxidation.

[0064] Reference Figure 5 It is a curve graph for long-term change monitoring of the δ 13 C-CO in the headspace during chemical and biological oxygen consumption in two types of subsurface sediments. It was observed that during the chemical oxygen consumption period, the carbon isotope value of carbon dioxide was positively biased and remained basically stable within this stage. This was because CO 2 produced by the inorganic carbon balance was the main source during the chemical oxygen consumption stage. After the start of biological metabolic oxygen consumption, during the metabolic process, microorganisms preferentially used lighter carbon for respiration during metabolic respiration, resulting in relative depletion of 2 C in the produced carbon dioxide, thus causing the carbon isotope composition to shift towards negative values. This change trend was in sharp contrast to the chemical oxygen consumption stage, further confirming that the carbon isotope of headspace carbon dioxide had different change characteristics under different oxygen consumption mechanisms, providing an important basis for accurately distinguishing chemical and biological oxygen consumption processes in subsurface aquifer media. 2 13 18 c

[0065] In summary, the oxygen isotope fractionation technique (δ 18 O) can be used as an effective diagnostic tool for sediment oxygen consumption mechanisms, and the change characteristics of its fractionation coefficient (ε c ) are significantly correlated with the redox path. Specifically, when approaching 0 (ε c < -10‰), the content of reducing substances in the sediment is relatively high, and the chemical oxygen consumption process dominates; while when it is significantly negatively biased (ε c>-10‰), the microbial activity is relatively high and the biological oxygen consumption process dominates. The probe phenol with different chemical and biological oxygen consumption degradation rates was selected to verify the probe degradation kinetics. Its microbial degradation rate is one order of magnitude faster than the chemical degradation rate. The pseudo-first-order kinetic constant k p ≈0.06 h -1 for chemical oxygen consumption degradation of phenol, while the pseudo-first-order kinetic constant k p ≈0.24 h -1 for microbial oxygen consumption degradation. Further combining with the trend of carbon dioxide changing with time during the oxidation process, when the carbon isotope of carbon dioxide remains stable and relatively enriched in heavy isotopes, it indicates that the oxygen consumption process is a chemical oxygen consumption process, while in the stage where carbon dioxide gradually becomes depleted, it is the microbial oxygen consumption stage. By coupling the isotope fractionation effect with the kinetic parameters of the probe reaction, this technical system has the advantages of high precision, wide applicability, and strong stability. It can be widely applied to the research of oxygen consumption and oxygen supply in the fields of ecological environment, pollution remediation, wastewater treatment engineering, etc., providing key data support for revealing the material transformation mechanism and element cycling path during the oxygen consumption process in the ecosystem, providing a scientific basis for optimizing the utilization of oxygen resources and improving the efficiency of environmental governance, and realizing the coordinated optimization of economic and ecological benefits.

[0066] In the case of no conflict, the above embodiments and the features in the embodiments in this article may be combined with each other.

[0067] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for distinguishing biological from chemical oxygen consumption pathways, characterized in that The following steps are involved: S1. Sample collection; Collect environmental samples for the oxygen consumption pathway to be analyzed and store them in a sealed and light-proof place; S2, oxygen isotope monitoring; S21. Introduce the environmental sample of the oxygen consumption pathway to be analyzed into the sample bottle, purge it with helium to ensure that it is oxygen-free, inject pure oxygen, and incubate it in the dark at room temperature with shaking. Continuously sample the oxygen concentration and oxygen isotope signal δ of the headspace oxygen at a certain time interval. 18 O, and continued until the residual oxygen content was 20% to 80% of the initial value. At the same time, a high temperature and high pressure sterilization treatment group and a pre-oxidation treatment group were set up to test a single oxygen consumption process; S22. Based on the data of oxygen content and isotope composition changing with time, calculate the relevant parameters and draw a scatter plot for linear fitting to obtain the pseudo-first-order oxygen consumption kinetic constant k c and oxygen accumulation factor ε c , compare the enrichment factors and standard data values ​​of different treatment groups to determine the type of oxygen consumption; S3, chemical probe monitoring; S31, based on the environmental sample of oxygen consumption pathway to be analyzed collected in step S1, the oxygen consumption pathway is monitored by the probe method, and the probe concentration is sampled and analyzed at the same time interval as the oxygen isotope monitoring in step S21; S32. Draw a scatter plot of the probe concentration versus time and perform linear fitting to obtain the pseudo-first-order oxygen consumption kinetic constant k p , compare the probe decay kinetics under original environmental samples and sterilization conditions to determine the dominant oxygen consumption pathway; S4, carbon isotope monitoring; In step S21, under the oxygen consumption condition of the environmental sample for the oxygen consumption pathway to be analyzed, the carbon isotope of the headspace carbon dioxide is tested over time at the same time interval; S5. Identification of oxygen consumption pathways; By integrating the isotope fractionation characteristics of step S2, the kinetic characteristics of the probe S3, and the carbon isotope characteristics of S4, a comprehensive discrimination standard for biological / chemical oxygen consumption processes is established: Characteristics of the chemical oxygen consumption-dominated phase, ε in isotope fractionation c <-10‰; the probe concentration in the probe kinetics showed a continuous exponential decay; the headspace δ 13 C-CO2 remains stable during the oxygen consumption reaction; Characteristics of the dominant phase of biological oxygen consumption, ε in isotope fractionation c >-10‰; the probe concentration in the probe kinetics shows a continuous exponential decay; the carbon isotope characteristic headspace δ 13 C-CO2 gradually decays to a negative value during the oxygen consumption reaction; The steps S2, S3 and S4 may be performed in any order.

2. The method according to claim 1, characterized in that In step S1, the environmental samples for the oxygen consumption pathway to be analyzed are corresponding samples collected from the environmental system to be studied according to the standard method of environmental monitoring, and represent the main oxygen consumption in the environmental area.

3. The method according to claim 2, characterized in that In step S21, the oxygen concentration of the headspace oxygen in the sample bottle containing the environmental sample of the oxygen consumption pathway to be analyzed is measured every half hour / or hour. 18 O, expressed in thousandths.

4. The method according to claim 3, characterized in that In step S21, an oxygen concentration and oxygen isotope analysis instrument is used to measure the oxygen concentration and oxygen isotope signal of the headspace oxygen in the sample bottle.

5. The method according to claim 3, characterized in that In step S22, based on the change of oxygen content and its isotopic composition obtained in the closed system over time, ln(C t / C0) and time t, and make a linear fit, where C t and C0 refer to the oxygen concentration at time t and time 0, respectively. The slope obtained is the pseudo-first-order oxygen consumption kinetic constant k c .

6. The method according to claim 4, characterized in that In step S22, according to the Rayleigh fractionation model of the one-way irreversible reaction in a closed system, ln((δ 18 O t +1) / (δ 18 O0+1)) and ln(C t / C0) and make a linear fit, where δ 18 O t and δ 18 O0 refers to the oxygen isotope composition at time t and time 0, respectively, and the slope obtained is the oxygen enrichment factor ε c .

7. The method according to claim 1, characterized in that In step S31, the probe is an organic molecule, and the type of the organic molecule has any one or more of the following characteristics: a. It can be metabolized and utilized by microbial oxygen consumption process, and can also be degraded by chemical oxygen consumption process; b. Small molecular carboxylic acids or sugars that are absorbed by microbial metabolism but are difficult to chemically oxidize; c. Organic molecules that are difficult to metabolize as carbon sources for microorganisms but can be chemically oxidized.

8. The method according to claim 7, characterized in that In step S32, based on the change of probe concentration obtained in the closed system over time, ln(C pt / C p0 ) and time t, and make a linear fit, where C pt and C p0 refers to the concentration of the probe at time t and time 0, respectively. The slope obtained is the pseudo-first-order oxygen consumption kinetic constant k p .

9. The method according to claim 8, characterized in that The organic molecules include any one or more of phenol, acetic acid, glucose and trichloroethylene.

10. Use of the method according to any one of claims 1 to 9 in the field of environmental remediation.

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