Diagnostic method for identifying and analyzing urban pipe network problem based on VOCs gas specificity

Abstract

The invention discloses a diagnosis method for identifying and analyzing urban pipe network problems based on VOCs gas specificity, and the method comprises the following steps: S1, analyzing a rainwater pipe topological relation of a to-be-detected region, and planning a pipeline monitoring inspection well and a monitoring point of the to-be-detected region; s2, performing gas production analysis on the VOCs of the inspection wells and the monitoring points to obtain map data of the VOCs in the monitoring points and the inspection wells; s3, performing similarity analysis on the TOF-MS atlas data to obtain the similarity between the monitoring point and each inspection well; and S4, quickly locking an abnormal area based on similarity data of each inspection well, and continuously encrypting VOCs detection and analysis of the inspection wells to accurately lock an abnormal external water or sewage convergence site. According to the method, the TOF-MS high-resolution detection technology is combined with the similarity analysis method to diagnose the urban pipe network problem, the rain and sewage mixing and misconnection condition can be quickly recognized, the diagnosis efficiency of the urban pipe network problem is effectively improved, and the diagnosis cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of urban pipe network problem troubleshooting, and in particular to a diagnostic method for urban pipe network problems based on VOCs gas-specific identification and analysis. Background Art

[0002] Comprehensive water environment management is a key component of my country's ongoing campaign to prevent and control pollution, and pipe network inspections are a top priority for comprehensive urban water environment management. The main objectives of urban pipe network inspections are: first, to identify misconnections, damaged pipes, and leaks in rainwater and sewage pipes; second, to pinpoint the sources of low-concentration wastewater within the pipe network, providing scientific guidance for improving wastewater collection rates and eliminating wastewater.

[0003] At present, the main technical means for troubleshooting pipeline network problems are traditional pipeline detection technologies such as QV detection and CCTV, as well as detection technologies such as pipeline water volume monitoring and characteristic pollutant concentration detection. Among them, the former detection technologies such as CCTV have harsh detection conditions in actual applications and require supporting preliminary work such as dredging and drainage; pipeline water quality and quantity monitoring technologies are affected by factors such as troubleshooting conditions and detection technology, and are difficult to use for complex pipe section analysis.

[0004] In order to overcome the shortcomings of the above-mentioned main screening technical means, various new screening technologies have been developed one after another. For example, patent application number CN202311470095.9 discloses a method, system and storage medium for tracing the source of mixed rainwater and sewage based on multi-source maps. By combining conventional water quality, electrochemical maps and spectra to compare target water samples and monitoring point water samples, tracing the source is achieved through the similarity of water sample characteristic data. The essence of this method is still to carry out water quality testing. The first step is to count the points that need to be tested based on the distribution of discharge outlets in the study area; the second step is to carry out water sample collection and analysis, including conventional water quality indicators, electrochemical maps and spectra, so as to collect characteristic spectra of all emission sources; the third step is to detect the pipe network detection wells, which also includes the steps of point layout, sampling and analysis, and test the conventional indicators, electrochemical maps and spectral data of water samples; the fourth step is to match the detection data of pipe network water samples and pollution source discharge outlets through similarity algorithms, so as to confirm the pollution source discharge outlet with the closest water quality to the pipe network.

[0005] Although the rainwater-sewage mixed connection tracing and identification method in this patent can troubleshoot the problem of rainwater-sewage mixed connection pipe network, it still has the following technical defects: First, in terms of implementation methods, this technology requires a large number of pollution source water sample tests and pipe network water sample tests, which requires a high investment of manpower and material resources, a long sample testing process, and low efficiency; second, it is difficult to ensure the comprehensiveness of the test data. The core step of this method is to match the map of the pipe network water sample with the map of the pollution source water sample. The key is to obtain sufficient pollution source data, but due to problems such as the discharge method, it is usually difficult to ensure comprehensiveness; third, the resolution of the test analysis is still low, and its test indicators are as follows: Conventional water quality includes COD, ammonia nitrogen, total phosphorus, suspended solids, total nitrogen and conductivity One or more items; the spectrum includes one or more items of fluorescence spectrum, ultraviolet-visible absorption spectrum and Raman spectrum; the electrochemical spectrum includes one or more items of cyclic voltammetry curve and electrochemical impedance spectrum. For sewage with rich information content, its resolution is still insufficient; fourthly, in terms of application scenarios, the main problem of urban pipelines at present is the intrusion of external water. Faced with external water that is not known where it comes from, this patent is difficult to provide technical support and lacks matching sources. This patent is more used for tracing the source of pollution in rainwater pipes, but it is still a point-to-point matching relationship, and it is difficult to grasp the flow route. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: to overcome the shortcomings of the existing technology and provide a drainage network problem diagnosis technology and method based on the detection and analysis of the specific composition of VOCs gas, so as to realize the rapid and accurate investigation of pipeline network problems and provide scientific guidance for subsequent pipeline network engineering management.

[0007] The technical solution adopted by the present invention to solve the technical problem is: a diagnostic method based on VOCs gas-specific identification and analysis of urban pipe network problems, comprising the following steps: S1. Sort out the basic situation of the pipe network in the area to be tested, analyze the topological relationship of the rainwater pipes in the area to be tested, determine the key nodes of the rainwater pipes in the area to be tested, and plan the pipeline monitoring inspection wells and monitoring points in the area to be tested; S2. Perform gas sampling and analysis on VOCs in each inspection well and monitoring point, detect the VOCs composition of each inspection well and monitoring point, form a VOCs spectrum in the monitoring point and each inspection well, and obtain the spectrum data of VOCs in the monitoring point and each inspection well; S3. Perform similarity analysis on the TOF-MS spectrum data of VOCs in the monitoring point and the TOF-MS spectrum data of VOCs in each inspection well to obtain the similarity between the monitoring point and each inspection well, and quickly obtain the correlation between the monitoring point and each inspection well. This similarity is called the similarity of each inspection well. For example, the similarity between the monitoring point and inspection well A is called the similarity of inspection well A, and the similarity between the monitoring point and inspection well B is called the similarity of inspection well B. S4. Quickly locate abnormal areas based on the similarity data of each inspection well, and accurately locate abnormal external water or sewage inflow sites by continuously encrypting VOCs detection and analysis of inspection wells.

[0008] Furthermore, step S2 also includes performing dimensionality reduction and clustering on the TOF-MS spectral data of VOCs at the monitoring points and in each manhole using principal component analysis (PCA) to generate a PCA plot to quickly determine the connectivity between the monitoring points and each manhole. Using principal component analysis, a three-dimensional spatial distribution of VOCs in different manholes can be obtained. The PCA plot indicates that manholes with more concentrated distributions and clusters have a higher similarity in VOC composition and belong to the same cluster, indicating that the water sources within these pipes are homologous and that they belong to connected pipes. This can be used to preliminarily determine which pipes are connected.

[0009] Furthermore, the specific operating steps of step S2 are: after collecting VOCs gas from each inspection well and monitoring point with a collection tube, the VOCs gas is detected and analyzed based on the PTR-TOF-MS high-resolution detection technology to form a TOF-MS spectrum of VOCs in the monitoring point and each inspection well, and obtain TOF-MS spectrum data of VOCs in the monitoring point and each inspection well.

[0010] Furthermore, the conditions for VOCs gas detection and analysis using PTR-TOF-MS are: mass scanning range 1-500 amu, instrument vacuum degree less than or equal to 10 -4 Pa, drift tube pressure 50-500Pa.

[0011] Preferably, the instrument vacuum degree is 10 -4 Pa.

[0012] Furthermore, the monitoring point is a network management node of the area to be measured or a water outlet point of the area.

[0013] Furthermore, the TOF-MS spectrum data includes ion mass-to-charge ratio and ion signal intensity.

[0014] Furthermore, the specific operation of quickly locking the abnormal area based on the similarity data of each inspection well in step S4) is as follows: analyzing the similarity of each inspection well, when the similarity of the inspection well is greater than or equal to 90%, it means that the pipeline between the inspection well and the monitoring point is the same water, and there is no external water or sewage inflow; When the similarity of the inspection well is less than 90%, it indicates that there may be external water or sewage flowing into the pipeline between the inspection well and the monitoring point. To further narrow the scope of the anomaly, on the pipeline network connecting the inspection well and the monitoring point, select the surrounding inspection wells with a similarity greater than or equal to 90% located around the inspection well, and calculate the absolute value d1 of the difference in similarity between the inspection well and its surrounding inspection wells; When there are surrounding inspection wells with d1 < 30%, there is no external water or sewage flowing into the pipes between the inspection well and the surrounding inspection wells with d1 < 30%. When there are surrounding inspection wells with d1 ≥ 30%, there may be external water or sewage flowing into the pipes between the inspection well and the surrounding inspection wells. The abnormal range can be quickly narrowed down, and the inspection well can be named as the preliminary locked inspection well, and the surrounding inspection well can be named as the auxiliary locked inspection well.

[0015] Furthermore, the specific operation of continuously encrypting the VOCs detection and analysis of the inspection wells in step S4) to accurately locate the external water or sewage inflow site is as follows: in order to further determine whether there is external water or sewage inflow between the preliminary locked inspection well and the auxiliary locked inspection well, the rainwater pipe topology relationship between the preliminary locked inspection well and the auxiliary locked inspection well is further subdivided, and the inspection well located between the two is named as the inspection well to be checked, and the inspection well to be checked is tested for VOCs, and the TOF-MS spectrum data of the VOCs in the inspection well to be checked is used to perform similarity analysis one by one with the TOF-MS spectrum data of the VOCs in the monitoring point, and the absolute value d2 of the difference in similarity between the preliminary locked inspection well and the inspection well to be checked, and the absolute value d3 of the difference in similarity between the auxiliary locked inspection well and the inspection well to be checked are calculated; When there is no inspection well to be checked with d2≥30%, there is no external water or sewage inflow between the preliminary locked inspection well and the auxiliary locked inspection well; when there is an inspection well to be checked with d2≥30% and d3<30%, there is external water or sewage inflow between the inspection well to be checked and the preliminary locked inspection well, thereby locking the abnormal external water or sewage inflow site.

[0016] The beneficial effects of the drainage network problem diagnosis technology and method based on VOCs gas specific composition detection and analysis of the present invention are as follows: The present invention uses a method of detecting VOCs (volatile gases) and combining it with similarity analysis to diagnose urban pipe network problems. During the sampling process, the sampling tube can be directly inserted through the air vent of the inspection well to carry out analysis and detection. The detection sampling and analysis process does not require opening the inspection well. The detection time is only 5 seconds. All information about VOCs (volatile gases) in the pipeline can be obtained, and the spectrum data used for principal component analysis and similarity analysis can be obtained. The detection and analysis efficiency is fast, and the manpower and material resources required for continuous detection are low. It can effectively improve the diagnosis efficiency of urban pipe network problems and reduce diagnosis costs. In addition, the sampling process is applicable to various complex pipeline detection conditions, ensuring the comprehensiveness of analysis and evaluation data. (2) The method of the present invention can quickly grasp the connectivity relationship between different inspection wells through high-resolution rapid monitoring of VOCs in the inspection wells, combined with similarity analysis or similarity analysis and principal component analysis. It can not only match the detection of rainwater and sewage pipes and quickly identify the mixing and misconnection of rainwater and sewage, but also conduct inspection and analysis of each inspection well. By analyzing the differences in VOCs results, it can quickly lock the points where the concentration changes are abnormal, thereby grasping the points of external water intrusion. At the same time, based on the refined analysis of VOCs gas differences, it can provide data support for pipe network geophysical exploration and form a rapid matching system for inspection well "fingerprints". By identifying the odor of any inspection well, the connectivity relationship of each inspection well can be quickly matched. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 — is a pipe network topology analysis diagram of the area to be measured in Example 1; Figure 2 - is the TOF-MS spectrum of point AF in Example 1; Figure 3 — is the similarity analysis result diagram of points AF in Example 1; Figure 4 — is a diagram showing the similarity analysis of points AH in Example 1 and the locking results of the mixed and misconnected problem points. DETAILED DESCRIPTION

[0018] The present invention provides a diagnostic method for urban pipe network problems based on VOCs gas-specific identification and analysis, comprising the following steps: S1. Sort out the basic situation of the pipe network in the area to be tested, analyze the topological relationship of the rainwater pipes in the area to be tested, determine the key nodes of the rainwater pipes in the area to be tested, and plan pipeline monitoring inspection wells and monitoring points in the area to be tested; the monitoring points are the network management nodes or water outlet locations of the area to be tested; the inspection wells to be monitored are selected from the inspection wells at the key nodes of the rainwater pipes; S2. Based on the PTR-TOF-MS high-resolution detection technology, a collection tube is used to collect gas for VOCs analysis at each inspection well and monitoring point. The collected gas is sampled into a proton transfer reaction time-of-flight mass spectrometer for VOCs detection, forming a TOF-MS spectrum of VOCs at the monitoring point and each inspection well, and obtaining TOF-MS spectrum data of VOCs at the monitoring point and each inspection well; The conditions for VOCs gas detection and analysis using PTR-TOF-MS are: mass scanning range 1-500 amu, instrument vacuum degree less than or equal to 10 -4 Pa, drift tube pressure 50-500Pa; Following step S2, the process also includes performing dimensionality reduction and clustering on the TOF-MS spectral data of VOCs at the monitoring points and in each manhole using principal component analysis (PCA) to generate a PCA plot to quickly determine the connectivity between the monitoring points and each manhole. Using principal component analysis, a three-dimensional spatial distribution of VOCs in different manholes can be obtained. The PCA plot reveals that manholes with more concentrated distributions and clusters have a higher similarity in VOC composition and belong to the same cluster, indicating that the water sources within these pipes are homogenous and that they belong to connected pipes. This can be used to preliminarily determine which pipes are connected.

[0019] S3. Performing similarity analysis on the TOF-MS spectrum data of VOCs at the monitoring point and the TOF-MS spectrum data of VOCs in each inspection well to obtain the similarity between the monitoring point and each inspection well, and quickly obtain the correlation between the monitoring point and each inspection well, which is called the similarity of each inspection well; the TOF-MS spectrum data includes ion mass-to-charge ratio and ion signal intensity; S4. Based on the similarity data of each inspection well, the abnormal area is quickly identified, and the abnormal external water or sewage inflow location is accurately identified by continuously encrypting the VOCs detection and analysis of the inspection well. The specific operation steps are as follows: The specific operation of quickly locking the abnormal area based on the similarity data of each inspection well in step S4) is as follows: analyzing the similarity of each inspection well, when the similarity of the inspection well is greater than or equal to 90%, the pipeline between the inspection well and the monitoring point is the same water, and there is no external water or sewage inflow; When the similarity of the inspection well is less than 90%, there may be external water or sewage flowing into the pipeline between the inspection well and the monitoring point. To further narrow the scope of the anomaly, on the pipeline network connecting the inspection well and the monitoring point, select the surrounding inspection wells with a similarity greater than or equal to 90% located around the inspection well and calculate the absolute value d1 of the difference in similarity between the inspection well and its surrounding inspection wells; When there is a surrounding inspection well with d1 < 30%, there is no external water or sewage flowing into the pipeline between the inspection well and the surrounding inspection wells with d1 < 30%; When there are peripheral inspection wells with d1 ≥ 30%, there may be external water or sewage flowing into the inspection well and the pipelines between the inspection well and the surrounding inspection wells. The abnormal scope can be quickly narrowed down, and the inspection well can be named as the preliminary locking inspection well, and the surrounding inspection wells can be named as the auxiliary locking inspection well.

[0020] The specific operation of continuously encrypting the VOCs detection and analysis of the inspection wells in step S4) to accurately locate the external water or sewage inflow site is as follows: in order to further determine whether there is external water or sewage inflow between the preliminary locked inspection well and the auxiliary locked inspection well, the rainwater pipe topology relationship between the preliminary locked inspection well and the auxiliary locked inspection well is further subdivided, and the inspection well located between the two is named as the inspection well to be checked, and VOCs detection is performed on the inspection well to be checked. The TOF-MS spectrum data of VOCs in the inspection well to be checked are used to perform similarity analysis one by one with the TOF-MS spectrum data of VOCs in the monitoring point, and the absolute value d2 of the difference in similarity between the preliminary locked inspection well and the inspection well to be checked, and the absolute value d3 of the difference in similarity between the auxiliary locked inspection well and the inspection well to be checked are calculated; When there is no inspection well with d2≥30% to be checked, there is no external water or sewage flowing between the preliminary locked inspection well and the auxiliary locked inspection well; When there is an inspection well to be checked with d2≥30% and d3<30%, there is external water or sewage flowing in between the inspection well to be checked and the preliminary locked inspection well, thereby locking the abnormal external water or sewage inflow site.

[0021] The following is a clear and complete description of the technical solutions of the present invention by way of embodiments in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0022] Example 1

[0023] In a certain area, there is a phenomenon of mixed and misconnected rainwater pipes. Sewage has been flowing at the outlet of the rainwater pipes in this area for a long time. It is necessary to trace the source of the mixed and misconnected rainwater pipes. This embodiment uses a diagnostic method based on VOCs gas-specific identification and analysis of urban pipe network problems to identify and locate the abnormal sewage inflow point. Specifically, the following steps are included: S1. Sort out the basic situation of the pipe network in the area to be tested, and analyze the topological relationship of the rainwater pipes in the area to be tested (such as Figure 1 As shown in the figure), determine the key nodes of the rainwater pipes in the area to be tested, plan the pipeline monitoring inspection wells and monitoring points in the area to be tested; from the pipe network topology relationship analysis diagram of the area to be tested ( Figure 1 ) It can be seen that the outlet point A of the area to be measured is used as the monitoring point, and the inspection wells used for monitoring are points B, C, D, E, and F; S2. Based on the PTR-TOF-MS high-resolution detection technology, the VOCs in sites A, B, C, D, E, and F were sampled and analyzed using a gas sampling tube. The collected gas was injected into a proton transfer reaction time-of-flight mass spectrometer for VOCs detection, forming TOF-MS spectra of VOCs in the monitoring point (site A) and each inspection well (site B, C, D, E, and F). The results are as follows: Figure 2 As shown; obtaining TOF-MS spectrum data of point A, point B, point C, point D, point E, and point F, wherein the TOF-MS spectrum data includes ion mass-to-charge ratio and ion signal intensity; The conditions for VOCs gas detection and analysis using PTR-TOF-MS are: mass scanning range of 300 amu, instrument vacuum of 10 -4 Pa, the mass spectrometry background spectrum is mainly water peak, the water vapor injection volume is 1-50 mL / min, and the drift tube pressure is 250 Pa; S3. Perform similarity analysis on the TOF-MS spectrum data of VOCs in the monitoring point and the TOF-MS spectrum data of VOCs in each inspection well using the dot product method to obtain the similarity between point A and each inspection well (point B, point C, point D, point E, point F) (e.g. Figure 3 As shown in the figure), the correlation between the monitoring point and each inspection well is quickly obtained. The similarity between point A and point B becomes the similarity of point B, and the similarity between point A and point C becomes the similarity of point C, and so on to point F. S4. Based on the similarity data of each inspection well, the abnormal area is quickly identified, and the abnormal external water or sewage inflow location is accurately identified by continuously encrypting the VOCs detection and analysis of the inspection well. The specific operation steps are as follows: Quickly locate abnormal areas based on the similarity data of each inspection well: Depend on Figure 3 It can be seen that compared with point A, the similarity of point B is 99%, the similarity of point C is 99%, the similarity of point D is 10%, the similarity of point E is 10%, and the similarity of point F is 30%. Among them, the similarity of the inspection wells at points B and C is greater than 90%, indicating that the pipes at points B, C and A contain the same water, and there is no external water or sewage inflow. The similarities of points D, E, and F are all less than 90%, indicating that sewage may be entering the pipelines between points D, E, F, and point A. To further narrow the scope of the anomaly, it is necessary to further identify the inspection wells around points D, E, and F to preliminarily determine the sewage inflow location. For point D, in the pipe network connecting the inspection well and the monitoring point, its surrounding inspection wells are points C and E. The similarity between point E and point D is the same, indicating that there is no external water or sewage flowing into the pipes connected to them; while the similarity of point C is 99%>90%, and the absolute difference in the similarity between point D and point C is calculated to be d1=98%>30%, indicating that there may be sewage flowing into the pipes between point D and point C, which affects the composition and concentration of VOCs and requires further intensified monitoring; point D is the preliminary locked inspection well, and point C is the auxiliary locked inspection well; For point F, its surrounding inspection well is point C, and the similarity of point C is 99%>90%. The absolute difference in similarity between point F and point C is d1=69%>30%, indicating that sewage may flow into the pipeline between point F and point C, affecting the composition and concentration of VOCs, and further intensified monitoring is needed; point F is the preliminary locked inspection well, and point C is the auxiliary locked inspection well; For point E, in the pipe network connecting the inspection well and the monitoring point, the surrounding inspection well is point D, and the similarity between the two is the same, indicating that there is no sewage flowing into the pipes connected to the two. Therefore, based on the similarity data of each inspection well, it was preliminarily found that the pipelines where sewage may flow in are between points F and C, and between points D and C; The specific operations for continuously increasing VOCs detection and analysis in inspection wells to accurately locate the inflow points of external water or sewage are as follows: In order to further determine whether there is external water or sewage between the preliminary locked inspection wells (points F and D) and the auxiliary locked inspection well (point C), the rainwater pipe topological relationship between points F and C, and points D and C was further subdivided, and the inspection wells located between the two (points G and H, respectively) were named inspection wells to be checked. VOCs detection was carried out on points G and H, and the TOF-MS spectrum data of VOCs in points G and H were used to perform similarity analysis with the TOF-MS spectrum data of VOCs in point A one by one. The results are as follows Figure 4 As shown by Figure 4 It can be seen that the similarity of point G is 30%, and the similarity of point H is 96%; The absolute value of the difference in similarity between point F and point G, d2, is 0, and the absolute value of the difference in similarity between point F and other inspection wells to be checked from point F to point C, d2, is less than 30%. There are no inspection wells to be checked between point F and point C with d2 ≥ 30%, indicating that there is no sewage inflow point between point F and point C. The absolute value of the difference in similarity between point D and point H is d2 = 86% > 30%. There is a manhole to be checked (point H) with d2 > 30% between points D and C, and the absolute value of the difference in similarity between points C and H is d3 3% < 30%, indicating that sewage is entering the pipeline between the manhole to be checked (point H) and the preliminary locked manhole (point D), thus locking the sewage inlet location. Therefore, by adopting the method of this embodiment, it can be found that the sewage inflow point is between point H and point D, and after on-site investigation, it is found that there is indeed a phenomenon of rainwater mixing and misconnection on the pipe between point D and point H, and there is a sewage inflow point, indicating that the present invention accurately finds the sewage inflow point in a relatively short time by adopting the VOCs detection analysis and similarity analysis methods, effectively solving the problem of tracing the source of the mixed and misconnected rainwater pipes in the area.

[0024] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A diagnostic method for urban pipe network problems based on VOCs gas-specific identification and analysis, characterized in that: The following steps are involved: S1. Sort out the basic situation of the pipe network in the area to be tested, analyze the topological relationship of the rainwater pipes in the area to be tested, determine the key nodes of the rainwater pipes in the area to be tested, and plan the pipeline monitoring inspection wells and monitoring points in the area to be tested; S2. Perform gas sampling and analysis on VOCs in each inspection well and monitoring point, detect the VOCs composition of each inspection well and monitoring point, form a VOCs spectrum in the monitoring point and each inspection well, and obtain the spectrum data of VOCs in the monitoring point and each inspection well; S3. Perform similarity analysis on the TOF-MS spectrum data of VOCs at the monitoring point and in each inspection well to obtain the similarity between the monitoring point and each inspection well, which is called the similarity of each inspection well, and quickly obtain the correlation between the monitoring point and each inspection well; S4. Quickly locate abnormal areas based on the similarity data of each inspection well, and accurately locate abnormal external water or sewage inflow sites by continuously encrypting VOCs detection and analysis of inspection wells.

2. A diagnostic method for urban pipe network problems based on VOCs gas-specific identification and analysis as claimed in claim 1, characterized in that: After step S2, the method also includes using principal component analysis to perform dimensionality reduction clustering processing on the TOF-MS spectrum data of VOCs in the monitoring points and each inspection well, and drawing a PCA graph to quickly obtain the connectivity between the monitoring points and each inspection well.

3. A diagnostic method for urban pipe network problems based on VOCs gas-specific identification and analysis as claimed in claim 1, characterized in that: The specific operation steps of step S2 are: after collecting VOCs gas from each inspection well and monitoring point with a collection tube, the VOCs gas is detected and analyzed based on the PTR-TOF-MS high-resolution detection technology to form a TOF-MS spectrum of VOCs in the monitoring point and each inspection well, and obtain TOF-MS spectrum data of VOCs in the monitoring point and each inspection well.

4. A diagnostic method for urban pipe network problems based on VOCs gas-specific identification and analysis as claimed in claim 3, characterized in that: The conditions for VOCs gas detection and analysis using PTR-TOF-MS are: mass scanning range 1-500 amu, instrument vacuum degree less than or equal to 10 -4 Pa, drift tube pressure 50-500Pa.

5. A diagnostic method for urban pipe network problems based on VOCs gas-specific identification and analysis as claimed in claim 1, characterized in that: The monitoring point is a network management node of the area to be measured or a water outlet point of the area.

6. A diagnostic method for urban pipe network problems based on VOCs gas-specific identification and analysis as claimed in claim 2, characterized in that: The TOF-MS spectrum data includes ion mass-to-charge ratio and ion signal intensity.

7. A diagnostic method for urban pipe network problems based on VOCs gas-specific identification and analysis as claimed in claim 1, characterized in that: The specific operation of quickly locking the abnormal area based on the similarity data of each inspection well in step S4) is as follows: analyze the similarity of each inspection well. When the similarity of the inspection well is greater than or equal to 90%, the pipeline between the inspection well and the monitoring point is the same water, and there is no external water or sewage flowing in; when the similarity of the inspection well is less than 90%, the pipeline between the inspection well and the monitoring point may have external water or sewage flowing in. At the same time, in the pipeline network connecting the inspection well and the monitoring point, select the pipelines located around the inspection well with a similarity greater than or equal to 90%. The surrounding inspection wells are selected and the absolute value d1 of the similarity difference between the inspection well and its surrounding inspection wells is calculated. When there are surrounding inspection wells with d1 < 30%, there is no external water or sewage flowing into the pipeline between the inspection well and the surrounding inspection wells with d1 < 30%. When there are surrounding inspection wells with d1 ≥ 30%, there may be external water or sewage flowing into the pipeline between the inspection well and the surrounding inspection wells. The abnormal range can be quickly narrowed down, and the inspection well is named as the preliminary locked inspection well, and the surrounding inspection wells are named as the auxiliary locked inspection well.

8. A diagnostic method for urban pipe network problems based on VOCs gas-specific identification and analysis as claimed in claim 7, characterized in that: The specific operation of continuously encrypting the VOCs detection and analysis of the inspection wells in step S4) to accurately locate the external water or sewage inflow site is as follows: in order to further determine whether there is external water or sewage inflow between the preliminary locked inspection well and the auxiliary locked inspection well, the rainwater pipe topology relationship between the preliminary locked inspection well and the auxiliary locked inspection well is further subdivided, and the inspection well located between the two is named as the inspection well to be checked, and the VOCs detection is performed on the inspection well to be checked, and the TOF-MS spectrum data of the VOCs in the inspection well to be checked is compared one by one with the TOF-MS spectrum data of the VOCs in the monitoring point. The S spectrum data is analyzed for similarity, and the absolute value d2 of the similarity difference between the preliminary locked inspection well and the inspection well to be checked, as well as the absolute value d3 of the similarity difference between the auxiliary locked inspection well and the inspection well to be checked are calculated. When there is no inspection well to be checked with d2 ≥ 30%, there is no external water or sewage inflow between the preliminary locked inspection well and the auxiliary locked inspection well; when there is an inspection well to be checked with d2 ≥ 30% and d3 < 30%, there is external water or sewage inflow between the inspection well to be checked and the preliminary locked inspection well, thereby locking the abnormal external water or sewage inflow site.

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