Apparatus and method for detecting inflow of volatile liquid

Abstract

To provide a volatile liquid inflow detection device which has a low-power and simple configuration, has higher maintainability, installation property, and availability, and reduces an operation cost, and a volatile liquid inflow detection method.SOLUTION: A volatile liquid inflow detection device includes: a volatile gas sensor placed in an upper space of a sewer line so as to output a signal corresponding to a concentration of volatile gas in the air; a communication device; and a control device. The control device determines an inflow of a volatile liquid when the concentration of the volatile gas detected by the volatile gas sensor exceeds a predetermined value, and causes the communication device to transmit a notification signal to an outer side.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for easily detecting the inflow of volatile liquids into sewerage. [Background technology]

[0002] In recent years, with the background of increasing environmental awareness, importance is being attached to water level management and water quality improvement of rivers, oceans and sewage surrounding the living environment from the viewpoint of flood prevention, pollution prevention, environmental improvement, etc. In particular, if wastewater from factories etc. flows into sewage, it can have a significant impact on the quality of the sewage.

[0003] Among the various types of wastewater that flow into sewage, cyanide compounds used in processes such as heavy metals and plating are extremely toxic chemical substances that have a significant impact on sewage treatment plants and rivers, so strict wastewater treatment is regulated by law, and the Sewerage Act stipulates water quality acceptance standards for factories and businesses within sewage treatment areas. Local governments and other organizations also set discharge standards (exclusion standards, for example, cyanide ion concentration of 1 mg / L or less in Tokyo) for the concentration of cyanide ions (hereinafter cyanide ions) in sewage and rivers. If untreated wastewater containing cyanide ions flows into the sewer system, it will hinder the biological treatment functions of work inside the sewer system and treatment plants, and the quality of the effluent will deteriorate as a result.

[0004] In addition, in the event of fires or flooding at factories or gas stations due to traffic accidents, earthquakes, fires, etc., large amounts of fuel oils such as gasoline and diesel, industrial oils, organic solvents, etc. may flow into the sewerage system. The inflow of these liquids can also impede the sewage treatment function and deteriorate the quality of the discharged water. In particular, when highly volatile fuel oils or solvents flow into the sewerage system, there is a risk of fire or explosion in the sewer pipes or treatment plants, making it necessary to stop the operation of the sewage treatment equipment and remove the oils. For this reason, it is very important to detect the inflow of cyanide ions, oils, and solvents into the sewerage system.

[0005] For example, in the case of detecting the inflow of cyanide-containing wastewater, several methods have been devised as described below. As a first known technique, for example, (Non-Patent Document 1) "Development of a Cyanide Ion Analysis System in a Hydrogen Sulfide Mixture System: 69th Analytical Chemistry Symposium, C2022, 2008" is disclosed. FIG. 12 is an explanatory diagram of a first conventional cyanide ion detection method. Sewage 101 flows at the bottom of an underground sewer pipe 100, and a sampling pump 103 pumps up a small amount of sewage through a sampling tube 102-1 and sends it through a sampling tube 102-2 to an aeration type hydrogen sulfide removal device 104, a sampling tube 102-3, and a liquid phase ion electrode type cyanide ion detection device 105.

[0006] The liquid phase ion electrode type cyanide ion detector 105 is equipped with a cyanide ion electrode capable of detecting cyanide ions in solution with extremely high sensitivity. This is used to measure the cyanide ion concentration in the sewage. When the cyanide ion concentration exceeds a certain threshold, it is determined that cyanide-containing waste liquid has flowed in and an alarm is issued.

[0007] One problem with cyanide ion electrodes is that they are known to react strongly to hydrogen sulfide ions. Hydrogen sulfide is easily generated in sewage environments through biological reactions caused by microorganisms, and false detection of hydrogen sulfide ions generated by dissolution in sewage becomes a major problem. As a countermeasure to this, an aeration-type hydrogen sulfide removal device 104 is installed in the figure. This device prevents false detection of hydrogen sulfide ions by the cyanide ion electrode by blowing air into the sampled sewage to create an aeration effect, thereby vaporizing and removing the hydrogen sulfide ions.

[0008] Due to this configuration, the first known technology is a relatively large-sized device configuration that consumes a lot of power. For example, the sampling pump 103 and the aeration type hydrogen sulfide removal device 104 each have an internal motor, and therefore require several watts to several tens of watts of power to operate. This requires a large power supply from a high-power power supply device 106 such as an AC power source via a power cable 107. In addition, the liquid phase ion electrode type cyanide ion detection device 105 also requires various auxiliary devices for periodic electrode cleaning with a chemical solution for continuous automatic measurement, electrode polishing, etc., resulting in a large device scale and increased frequency and labor for maintenance and inspection, such as periodic refilling and cleaning of the chemical solution.

[0009] The second known technique (Non-Patent Document 2) "Development of a continuous measurement method for cyanide ions by a gas phase measurement method using a hydrogen cyanide sensor: Analytical Chemistry Vol. 39 pp. 693-698 (1990)" discloses a method for simplifying the configuration of Non-Patent Document 1 by combining a small pump, an air supply tube, and a hydrogen cyanide electrode that operates stably in the gas phase.

[0010] Fig. 13 is a block diagram of a second conventional cyanide ion detection device. The lower end of a purge pipe 110 is immersed in sewage 101, and a gas-phase cyanide ion electrode 111 is installed at the upper end of the purge pipe. Although not shown in the figure, an opening is provided at the upper end of the purge pipe for discharging gas in the purge pipe to the outside. Air (bubbles) 117 is sent from an air pump 114 through an air pipe 116 into the sewage 101 to aerate it, thereby vaporizing the cyanide ions dissolved in the sewage as hydrogen cyanide, and the amount of air sent required for this is said to be about 1 liter per minute.

[0011] The operating principle of the gas-phase cyanide ion electrode 111 is to measure the pH change caused by cyanide gas in the purge pipe dissolving into the internal liquid of the gas-phase cyanide ion electrode through a selectively permeable membrane as a potential difference generated across the glass ion electrode. The generated potential difference corresponds closely to the cyanide ion concentration in the sewage, so it is measured by a voltmeter 113 via an ion electrode cable 112, and after being converted into the cyanide ion concentration in the sewage, it is recorded on a recorder 118.

[0012] However, even with this method, false detection of sulfide ions by the cyanide ion electrode is an issue, and Non-Patent Document 2 discloses a method in which a granular lead column with an inner diameter of 15 mm and a length of 200 mm is placed to adsorb sulfide ions. The life of the adsorption column is about one week when the sulfide ion concentration is 0.01 mg / L.

[0013] In principle, the inflow of oils and solvents can be detected by visual inspection of the oil film or by an oil film sensor that optically detects the reflection of the oil film. However, problems include the inflow of liquids that do not form an oil surface being unable to be detected, the fact that sewage is highly contaminated with foreign matter and oil film sensors often fail to detect them, and the fact that a lot of cooking oil and fat from restaurants and other places always flows into sewage, making it difficult to distinguish between them. [Prior art documents] [Non-patent literature]

[0014] [Non-Patent Document 1] "Development of a cyanide ion analysis system in hydrogen sulfide mixtures: 69th Analytical Chemistry Symposium, C2022, 2008" [Non-Patent Document 2] "Development of a continuous measurement method for cyanide ion by a gas phase measurement method using a hydrogen cyanide sensor: Analytical Chemistry Vol.39 pp.693-698 (1990)" Summary of the Invention [Problem to be solved by the invention]

[0015] The first problem to be solved by the present invention is to provide a simple method for detecting the inflow of a volatile liquid that is easy to maintain, install, and use. Both of the above-mentioned two known examples use an ion electrode that detects cyanide with high accuracy. In general, ion electrodes require periodic cleaning and calibration using a chemical solution, which causes problems such as increased costs due to maintenance work and longer downtime of the detection device during maintenance. Since the liquid-phase ion electrode of the first known example is directly immersed in dirty sewage, deterioration of the electrode due to oxidation and sulfurization becomes noticeable, and constant or frequent polishing of the electrode, chemical cleaning, refilling of the chemical solution, and maintenance of pumps become necessary.

[0016] In the second known example, the lead column for hydrogen sulfide adsorption must also be replaced frequently, and the ion electrode must be calibrated periodically, and the moving parts of the pump must be maintained. Installation of the equipment also requires extensive installation work to stand the purge pipe upright while immersed in the sewage, and measurement becomes impossible when the water level reaches the top of the purge pipe (several tens of centimeters). There are also issues with detecting the inflow of fuel oil and solvents, such as the lack of a highly sensitive detection method with few false positives that can be used in a sewage environment.

[0017] The second problem that the present invention aims to solve is to provide a small, low-cost volatile liquid inflow detection device that operates with low power, has a high degree of freedom in the location of installation, and can be installed in a sewer pipe. The above-mentioned known technology requires pumps such as a sampling pump and an air pump, which results in a large device size and high power consumption. This causes problems such as the device being only installable in a location close to a commercial power source or a distribution board, and the cost and time required for laying a power cable and for a power contract. In particular, these pumps cannot be installed in a sewer pipe due to the risk of maintenance and submersion, and it is necessary to secure an installation location on the ground. There are also problems such as the sampling tube and air pipe from the sewage to the pump being long, which increases the effort and cost of piping. If the detection device can be installed in a sewer pipe, the installation cost can be reduced, but the inside of the sewer pipe is always highly humid, and there are risks such as submersion, generation of corrosive gas, and short circuit and corrosion of the power wiring.

[0018] An object of the present invention is to solve the above problems, and to provide a volatile liquid inflow detection device and a volatile liquid inflow detection method which consumes low power, has a simple configuration, is easy to maintain, install, and use, and has low operating costs. [Means for solving the problem]

[0019] A representative example of a volatile liquid inflow detection device of the present invention includes a volatile gas sensor that is disposed in the upper space of a sewer pipe and outputs a signal corresponding to the concentration of a volatile gas in the air, a communication device, and a control device. The control device determines that a volatile liquid has inflowed when the concentration of the volatile gas detected by the volatile gas sensor exceeds a predetermined value, and transmits a notification signal to the outside by the communication device. Effect of the Invention

[0020] According to the present invention, it is possible to provide a volatile liquid inflow detection device and a volatile liquid inflow detection method that consumes low power, has a simple configuration, is easy to maintain, install, and have high availability, and has low operating costs. [Brief description of the drawings]

[0021] [Figure 1] FIG. 2 is an explanatory diagram of a volatile liquid inflow detection method in a first embodiment of the present invention. [Diagram 2] FIG. 1 is a configuration diagram of a volatile liquid inflow detection device according to a first embodiment of the present invention. [Diagram 3] FIG. 11 is a configuration diagram of a volatile liquid inflow detection device according to a second embodiment of the present invention. [Figure 4] FIG. 2 is an explanatory diagram of a constant potential electrolysis type cyan gas sensor according to the present invention. [Diagram 5] 13 is an explanatory diagram of a volatile liquid inflow detection method according to a third embodiment of the present invention. FIG. [Figure 6] FIG. 11 is a configuration diagram of a volatile liquid inflow detection device according to a third embodiment of the present invention. [Figure 7A] FIG. 2 is an explanatory diagram showing the principle of detection of the inflow of a volatile liquid according to the present invention. [Figure 7B]FIG. 2 is an explanatory diagram showing the principle of detection of the inflow of a volatile liquid according to the present invention. [Figure 7C] FIG. 2 is an explanatory diagram showing the principle of detection of the inflow of a volatile liquid according to the present invention. [Figure 8] FIG. 2 is an explanatory diagram showing a method for estimating a cyan ion concentration in the present invention. [Figure 9] FIG. 13 is an explanatory diagram of a method for detecting an inflow of a volatile liquid in a fourth embodiment of the present invention. [Figure 10] FIG. 11 is a configuration diagram of a volatile liquid inflow detection device according to a fourth embodiment of the present invention. [Figure 11A] FIG. 13 is an explanatory diagram showing the influence of drift of a pH sensor in a fourth embodiment of the present invention. [Figure 11B] FIG. 13 is an explanatory diagram showing the influence of drift of a pH sensor in a fourth embodiment of the present invention. [Figure 12] FIG. 1 is an explanatory diagram of a first conventional volatile liquid inflow detection device. [Figure 13] FIG. 13 is a configuration diagram of a second conventional volatile liquid inflow detection device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] A technique for detecting the inflow of a volatile liquid is described below. An example of a volatile liquid inflow detection device described below includes a volatile gas sensor arranged in the upper space of a sewer pipe, a communication device, and a control device. When the volatile gas concentration detected by the volatile gas sensor exceeds a predetermined value, the control device transmits a notification signal to the outside by the communication device. Examples of such combinations of volatile liquid and volatile gas include "cyanide-containing waste liquid and cyanide gas" and "flammable fuel oil and a VOC sensor (volatile organic compound sensor) that is a flammable gas sensor."

[0023] When using gas sensors, the presence of interference gases (for example, hydrogen sulfide H2S and sulfur dioxide SO2 in the case of cyanogen gas) that have cross-sensitivity to volatile gas sensors (for example, cyanogen gas sensors and combustible gas sensors) can be an issue. This can be resolved by providing the volatile gas sensor with an interference gas permeation prevention film (an example of a mechanism for preventing false detection). Alternatively, it can be resolved by placing one or more interference gas sensors near the volatile gas sensor, using the volatile gas concentration signal and the interference gas concentration signal measured by both sensors as inputs, and removing the error components caused by one or more interference gases from the volatile gas concentration signal.

[0024] Furthermore, by designing the volatile gas sensor to be replaceable via a connector and mounting the volatile gas sensor, interference gas false detection prevention mechanism, and communication device in a waterproof housing, it is possible to install the device in sewer pipes where there is a possibility of it being submerged, and it is also possible to easily replace the volatile gas sensor during regular inspections or when it deteriorates or breaks down.

[0025] Moreover, by providing one or more liquid-phase sensors placed under the water surface in the sewer pipe and estimating the concentration of the volatile liquid in the sewage from the output signal of the liquid-phase sensor, it becomes possible to estimate the concentration of the volatile liquid in the sewage more accurately. For example, in the case of detecting the inflow of cyanide-containing waste liquid, a throw-in type pH sensor in which an electrolyte is sealed can be used as such a liquid-phase sensor. Furthermore, by connecting the throw-in type pH sensor using a waterproof connector, it becomes possible to easily replace it when it deteriorates, breaks down, or undergoes regular inspection.

[0026] In addition, by calculating periodic fluctuations according to time and long-term drift components of the pH sensor from the pH value signal by dynamic averaging, and correcting and outputting the pH value signal using these dynamic average values, it becomes possible to improve the accuracy of estimating the cyanide ion concentration.Furthermore, by providing an electrical conductivity sensor, which is one of the liquid phase sensors and outputs a signal corresponding to the electrical conductivity of the sewage, and by using the electrical conductivity signal to correct the change in pH value caused by water flowing into the sewer pipe, it becomes possible to further improve the accuracy of estimating the cyanide ion concentration.

[0027] By equipping the device with a transmitter that transmits report signals, estimated volatile liquid concentration values, and measurement values ​​from each sensor installed in the device to the outside via optical, electrical, or wireless signals, this information can be output to the outside in real time and used for a variety of purposes, such as notifying facility managers or surrounding municipalities, recording or disclosing sensing information, and stopping or switching sewage treatment equipment.

[0028] In particular, a realistic form of the volatile liquid inflow detection device of this specification can be realized by a configuration that includes a replaceable battery, a wireless transmitter, and an antenna, and operates using power stored in the battery to intermittently perform sensing operations and external transmission operations.

[0029] It can also be realized by having an optical transmitter, an optical receiving circuit, and an optical fiber cable, and operating using the power obtained by photoelectric conversion in the optical receiving circuit of the power supply light transmitted from outside via the optical fiber cable, and having a configuration in which an optical signal output from the optical transmitter is transmitted to the outside via the optical fiber cable, and intermittently performing sensing operations and transmitting optical signals to the outside.

[0030] The volatile liquid inflow detection technology of the present specification can easily detect the inflow of volatile liquid into a sewer pipe with low power consumption. The configuration of the volatile liquid inflow detection device of the present specification does not require pumps or motors as in the known examples, so that the operating power can be significantly reduced and long-term operation is possible by utilizing various types of power with limited power, such as batteries, solar cells, environmental power generation, and optical power supply.

[0031] In addition, by detecting the inflow of a corresponding volatile liquid using a volatile gas sensor such as a cyan gas sensor or a combustible gas sensor with high detection selectivity, it is possible to reduce false detections and increase reliability. Furthermore, it is also possible to estimate the concentration of a volatile liquid in sewage by using a liquid phase sensor such as a pH sensor in combination. Furthermore, by making each sensor easily replaceable and making the part installed in the sewer pipe waterproof, it is possible to greatly improve maintainability, ease of installation, and availability. Several embodiments of the present invention will be described below with reference to the drawings. EXAMPLES

[0032] 1 is an explanatory diagram of a volatile liquid inflow detection method according to a first embodiment of the present invention, and this configuration is an example of detecting the inflow of cyanide waste liquid by using cyanide gas in a volatile gas sensor. A volatile liquid inflow detection device 200 of this embodiment is disposed in an upper space inside a sewer pipe 100. The volatile liquid inflow detection device 200 includes a cyanide gas sensor 201 and a sensing node 211 which is a control device. A feature of this embodiment is that the cyanide gas sensor 201 is used to detect cyanide gas 220 which is generated in the process of sewage 101 flowing down the sewer pipe.

[0033] The plating solution used in plating processes contains a high concentration of cyanide ions, and it is known that the cyanide ions in such solutions volatilize almost completely at a nearly neutral pH of 6.7, being released into the air as cyanide gas, and that volatility is nearly zero at a strongly alkaline pH of 11 or higher. For this reason, untreated plating solutions with a high cyanide concentration are adjusted to a strongly alkaline state to prevent the volatilization of the cyanide ions.

[0034] Since sewage is generally weakly alkaline (pH 8-9), if untreated plating liquid is discharged into the sewer as cyanide-containing waste liquid, it is thought that cyanide gas will be released little by little as it flows down the sewer pipe. Since the specific gravity of cyanide gas compared to air is 0.95, if the sewer pipe is sealed, it will accumulate in the upper part. Therefore, by placing a cyanide gas sensor at the top of the sewer pipe, it is possible to efficiently detect cyanide gas that has naturally evaporated.

[0035] 2 is a configuration diagram of a volatile liquid inflow detection device 200 in a first embodiment of the present invention. A cyanide gas concentration signal (current) 202 that is approximately proportional to the cyanide gas concentration accumulated in a sewer pipe is output from a constant potential electrolysis type cyanide gas sensor 201. A gas sensor drive circuit 203 converts this current into a cyanide gas concentration signal (voltage) 204 using an internal electric circuit such as a transimpedance amplifier, and outputs it.

[0036] A voltage comparison circuit 206 compares the cyan gas concentration signal (voltage) 204 with a threshold voltage generated by a threshold voltage generator 205, and if the cyan gas concentration signal (voltage) exceeds this value, activates a notification signal generation circuit 207. The notification signal generation circuit 207 issues a notification signal 208 to a notification signal transmission cable 209 leading to the outside, and notifies an external device or administrator of the detection of inflow of cyan waste liquid. The gas sensor drive circuit 203, the voltage comparison circuit 206, and the notification signal generation circuit 207 are included in the control device.

[0037] In this embodiment and this specification, the volatile liquid inflow detection device 200 is used mainly to detect the inflow of cyanide waste liquid, but it can also be used to detect other volatile liquids without any problems. For example, by replacing the cyanide gas sensor with the above-mentioned VOC sensor, it can be used to detect fuel oil or organic solvents that have flowed into sewage. EXAMPLES

[0038] 3 is a configuration diagram of a volatile liquid inflow detection device in a second embodiment of the present invention. The volatile liquid inflow detection device of this embodiment includes two components, a sensing node 211 as a main body and a gas sensor unit 210, and is configured to wirelessly transmit a notification signal of the detection of a volatile liquid to be detected to an external device. The gas sensor unit 210 of this embodiment is disposed separately from the sensing node 211. Since the embodiments of this specification achieve the intended functions by combining a plurality of components, it is possible to separately dispose some of the components as necessary, such as for replacing components or batteries due to failure, deterioration, or life expectancy.

[0039] In this embodiment, the gas sensor unit 210 and the sensing node 211 are housed in waterproof housings 221-1 and 221-2, respectively, and are connected to each other via a waterproof cable 222. This allows the entire volatile liquid inflow detection device to have a watertight structure that can withstand submersion in water, making it possible to install the device in a sewer pipe.

[0040] Furthermore, one end of the waterproof cable 222 and the waterproof housing 221-2 are connected using a waterproof connector 223, and the structure allows the entire gas sensor unit 210 to be easily replaced when the cyan gas sensor 201 reaches the end of its sensor life or deteriorates. The lifespan of many gas sensors, such as a constant electric field type gas sensor, is about one to several years, and by making the gas sensor easily replaceable as in this example, the lifespan of the device can be extended and maintenance and operation costs can be reduced.

[0041] In the gas sensor unit 210 of this embodiment, a constant potential electrolysis type cyan gas sensor 201 and a gas sensor driving circuit 203 are disposed, and a cyan gas concentration signal (voltage) 204 is transmitted to a sensing node 211. When detecting a volatile liquid such as a flammable liquid, the constant potential electrolysis type cyan gas sensor 201 may be replaced with a VOC gas sensor.

[0042] This signal is AD converted by an AD converter 212 and input as a cyan gas concentration signal (digital) 213 to a CPU (Central Processing Unit) 214. The CPU 214 issues a notification signal 217 when the input cyan gas concentration signal (digital) 213 exceeds a threshold value previously stored in an internal memory.

[0043] This signal is sent to a wireless transmitter 218 and then to a host monitoring device or the like located at a remote location via a wireless antenna 219. In this way, the processes of this embodiment, such as threshold determination and notification generation, can be written as a software program and realized by the operation of a CPU.

[0044] In this example, a battery 215 is disposed inside the sensing node 211, which provides the operating power of the sensing node 211 and also supplies power 216 to the gas sensor unit 210. The embodiments of this specification do not have moving parts such as a sampling pump, an air supply pump, an electrode polishing device, a chemical pump, etc. that require a large amount of power, such as a motor or a solenoid, and therefore can operate for a long time even with a battery that has a limited amount of power supply. Although not shown in this example, the battery 215 can also be mounted in an independent waterproof case like the gas sensor unit 210 and attached via a waterproof connector, making it possible to facilitate periodic replacement work and reduce maintenance and operation costs.

[0045] 4 is an explanatory diagram of a constant-potential electrolysis type cyanide gas sensor in an embodiment of this specification. The constant-potential electrolysis type cyanide gas sensor 201 is a small gas sensor with extremely high gas selectivity, and has a selective gas permeable membrane and an electrolyte disposed therein. Outside air is introduced into the gas sensor through a gas inlet 230, and only the gas to be detected permeates the gas permeable membrane and reaches the electrolyte.

[0046] Three electrodes - a reference electrode (R), a working electrode (W), and a counter electrode (C) - are inserted into the electrolyte section from the outside. An electrolytic reaction of the target gas is generated while the potential of the working electrode relative to the reference electrode is kept constant, and the concentration of the target gas is detected from the magnitude of the detection current flowing to the working electrode.

[0047] The constant potential electrolysis type cyanide gas sensor is particularly suitable for realizing this embodiment because it can selectively detect the cyanide gas accumulated in the sewer pipe, which is the detection target of the present invention, with a high sensitivity of about 0.1 ppm and operates with low power. However, it is also possible to apply a volatile gas sensor based on another detection principle as long as it is capable of selectively detecting the volatile gas to be detected with high sensitivity.

[0048] It is known that the above-mentioned constant-potential electrolysis type cyanide gas sensor has a large cross-sensitivity to hydrogen sulfide gas, which has a similar molecular structure. Hydrogen sulfide gas is frequently generated in sewer pipes and acts as an interference gas. Therefore, in the constant-potential electrolysis type cyanide gas sensor 201 of this example, a hydrogen sulfide permeation prevention film 231 that selectively removes hydrogen sulfide is attached to the gas introduction hole 230 as a mechanism for preventing false detection. This makes it relatively easy to prevent the influence of hydrogen sulfide. Cyanide gas sensors may also show cross-sensitivity to sulfur dioxide gas, etc., and it is possible to provide multiple gas permeation prevention films as necessary, depending on the possibility and frequency of generation at the installation location of this device. EXAMPLES

[0049] 5 is an explanatory diagram of a volatile liquid inflow detection method in a third embodiment of the present invention. This device includes a sensing node 211, a gas sensor unit 210, and a throw-in type pH sensor 232 placed in the sewage for the purpose of detecting the inflow of cyanide-containing waste liquid. An external connection cable 235 is connected to the sensing node 211 for communication with the outside and for power supply.

[0050] Since cyanide gas does not exist in the air and is not produced by biochemical reactions in sewer pipes, the use of a cyanide gas sensor makes it possible to detect the inflow of cyanide-containing wastewater into sewage with a high degree of reliability. However, the concentration of cyanide gas that accumulates in sewer pipes is affected by various parameters, such as the distance from the inflow point of cyanide-containing wastewater, the diameter and water level of the sewer pipes, the pH value of the sewage, the junction and branching structure of the sewer pipes, the wind speed inside the pipes, and the presence or absence of an inflow point of outside air.

[0051] For this reason, it is highly likely that the cyanide gas concentration detected by the cyanide gas sensor does not necessarily correspond to the cyanide ion concentration in the sewage. Therefore, in addition to the cyanide gas sensor described above, this configuration is equipped with a throw-in pH sensor 232 that measures the pH value of the sewage, and the cyanide ion concentration is indirectly estimated from the pH value of the sewage measured by this sensor. When using to estimate the concentration of other specific volatile liquids, a liquid-phase sensor that outputs an appropriate indicator, not necessarily a pH value, may be used.

[0052] 6 is a configuration diagram of a volatile liquid inflow detection device according to a third embodiment of the present invention. As described above, the volatile liquid to be detected is a cyanide-containing waste liquid. The aforementioned throw-in type pH sensor 232 is connected to the sensing node 211 via a pH sensor cable 233.

[0053] The pH signal (voltage) 234 output from the throw-in pH sensor 232 is a weak voltage signal corresponding to the pH value of the sewage. The pH signal (voltage) 234 is amplified by a high impedance voltage amplifier circuit 243 arranged in the sensing node 211, and is converted into a digital value by an AD converter inside the CPU 214.

[0054] A typical glass electrode type pH sensor can be used as the throw-in pH sensor 232, but when installed in sewage, the entire sensor may be submerged due to a rise in the water level. For this reason, it is more suitable to use a throw-in sensor that has a fixed amount of electrolyte sealed inside the electrode to make the entire sensor waterproof.

[0055] The throw-in pH sensor 232 is attached to the waterproof housing 221-2 of the sensing node 211 using a waterproof connector 223-2, and can be replaced as necessary. The glass electrode type pH sensor is a part with a finite life span, in which the electrolyte inside is gradually consumed over time, and it may be subject to various deteriorations and failures, such as a decrease in sensitivity due to contamination by sewage and cracking of the electrode due to impact. For this reason, it is desirable to clean or replace it as needed. By configuring the connection via a waterproof connector as described above, it is possible to easily replace and maintain the sensor unit while maintaining the watertightness and airtightness of the entire device.

[0056] In addition, the connection cable 235 of this embodiment is assumed to be a composite cable containing multiple electric wires (core wires), and in Fig. 6, two of these are used as a communication signal line 247 and a power transmission line 252. A communication signal 244 output from the CPU 214 is converted by a transmitter 245 into a serial code for communication or the like, and is transmitted via the communication signal line 247 to another device (e.g., a higher-level device) or an administrator connected to the other end of the connection cable 235. The content of the communication signal can include various information, such as the above-mentioned report signal, measurement results of cyanide gas concentration and pH value, and an estimated signal of an estimated concentration of cyanide ions in sewage.

[0057] On the other hand, the power transmission line 252 supplies the power required for the operation of the sensing node 211 and the gas sensor unit 210. In this example, the connection cable 235, which is a two-core electric cable, is used for communication and power, but other cores such as signal lines and grounds may be added as necessary. Also, the connection cable 235 may be branched to connect multiple sensing nodes.

[0058] In addition to the above-mentioned constant potential electrolysis type cyanide gas sensor 201 and its gas sensor drive circuit 203-1, a constant potential electrolysis type hydrogen sulfide gas sensor 240 and its gas sensor drive circuit 203-2 are also arranged in the gas sensor section 210 in the figure as another gas sensor. The hydrogen sulfide gas concentration signal (current) 241 output from the constant potential electrolysis type hydrogen sulfide gas sensor 240 is converted into a hydrogen sulfide gas concentration signal (voltage) 242 by the gas sensor drive circuit 203-2 and input to the CPU 214 together with the cyanide gas concentration signal (voltage) 204. These signals are each converted into digital signals by an A / D converter inside the CPU 214. The hydrogen sulfide gas sensor 240 is an example of an interference gas sensor, and is arranged near the cyanide gas sensor 201 at approximately the same position.

[0059] The hydrogen sulfide gas concentration in the sewer pipe measured in this way is used to convert the cyanide gas concentration measured in a similar manner into the correct cyanide gas concentration by subtracting the effect of hydrogen sulfide gas from the cyanide gas concentration. The effect of hydrogen sulfide gas on the output signal of a constant potential electrolysis type cyanide gas sensor is called cross-sensitivity, and the cross-sensitivity α is a fixed constant that can be either positive or negative. For this reason, it is possible to know the correct cyanide gas concentration by subtracting the effect of hydrogen sulfide (α * hydrogen sulfide concentration) from the gas concentration obtained from the cyanide gas sensor.

[0060] Such a correction calculation of the cyanide gas concentration may be performed by the CPU 214, or may be performed by providing a dedicated correction circuit or correction CPU inside the gas sensor unit 210, or may be performed by an external device connected via a connection cable 235.

[0061] In addition, it is known that the sensitivity and cross sensitivity of each sensor vary from sensor to sensor, and also change little by little due to deterioration caused by long-term use. For this reason, it is effective to use an adaptive correction calculation for the above correction calculation, which adaptively adjusts the sensitivity α of the interference gas sensor so that the correction value of the cyanide gas sensor approaches zero (approximately zero) during normal times when the detection target gas (e.g. cyanide gas) is not generated.

[0062] For this type of processing, adaptive digital filters widely used in communications and AI learning processing can be used. The number of types of interference gas sensors does not necessarily have to be one, and can be increased appropriately according to the types of interference gases that may occur in the sewer pipe. In general, the target gas and interference gas are not always generated. Therefore, in order to keep the value of α appropriate, the effect of interference gas can be almost completely eliminated by optimizing the correction value α through learning only when the output values ​​of both gas sensors are non-zero, making it possible to extract only the output signal corresponding to the target gas.

[0063] This example shows a configuration in which the entire gas sensor unit 210 can be removed and replaced using the waterproof connector 223-1. Alternatively, for example, the constant potential electrolysis type cyanide gas sensor 201 and the constant potential electrolysis type hydrogen sulfide gas sensor 240 may be mounted using connectors, and the waterproof casing 221-1 may be opened and only the internal gas sensor replaced as necessary. When the gas sensor is attached to the inside of the waterproof casing 221-1, a gas inlet may be provided in a part of the waterproof casing 221-1, and a waterproof patch such as Gore-Tex (registered trademark) may be attached to the gas inlet, thereby achieving both waterproofness and gas permeability. EXAMPLES

[0064] 7A to 7C are explanatory diagrams showing the principle of estimating the concentration of cyanide-containing wastewater in the examples of this specification, and show the relationship between the cyanide ion concentration in sewage measured in the experiment (horizontal axis), the generated cyanide gas concentration, the pH value of the sewage, and the electrical conductivity of the sewage. The horizontal axis of the graph is the cyanide ion concentration in the sewage, and the cyanide ion concentration was changed by adding small amounts of diluted cyanide-containing untreated plating solution (prepared to have a pH value of about 11 and a cyanide concentration of 100 mg / L) to the sewage collected in a beaker. The experiment was conducted in a closed system to prevent the generated gas from escaping. To confirm reproducibility, the experiment was conducted twice, and the experimental results are plotted in each graph with two solid lines (● for the first time, ▲ for the second time).

[0065] The vertical axis of Figure 7A is the concentration of cyanogen gas generated, and it can be seen that cyanogen gas is actually generated by diluting the cyanogen-containing wastewater with sewage. The standard for cyanogen discharge into sewage is approximately 1 mg / L, and the HCN gas concentration at this time was approximately 1 ppm. This value is well above the minimum sensitivity of a typical commercially available cyanogen gas sensor, which is 0.1 to 0.3 ppm, and can be fully detected by the configuration of the examples of this specification.

[0066] The vertical axis in Fig. 7B represents the change in pH value. Since the cyanide-containing waste liquid is highly alkaline, as the cyanide ion concentration increases, the pH value of the sewage rises. Also, it can be seen that the reproducibility of the two experimental results is high and the approximate cyanide ion concentration can be estimated from the pH value. When calculating the theoretical pH value at a cyanide ion concentration of 5 mg / L at the right end of the graph, the diluted untreated cyanide-containing plating solution is further diluted 20-fold. Therefore, the theoretical pH value is approximately 11 - log10(20) = 9.7, but actually it is 9.0 or lower. This is presumably because of the buffering effect of the sewage, that is, the increase in pH value is hindered by various biological substances and impurities contained in the sewage. Therefore, in estimating the cyanide ion concentration in the sewage of the examples in this specification, it can be seen that it is desirable to estimate considering the buffering effect using the experimental results as shown in Fig. 7B rather than using the theoretical formula.

[0067] As an estimation formula for the cyanide ion concentration X (mg / L) when the pH value of the sewage is P, using the simplest dilution theoretical formula with the initial pH value of the sewage set to 7.0 (Equation 1) X = 10^(P - 7) * C can be approximated in the form of. The constant C is C = 0.01 (when there is no buffering effect), and C = 0.05 (approximating the case with the buffering effect in Fig. 7B).

[0068] The dotted line with white circles drawn in Fig. 7B represents the characteristics of the cyanide ion concentration estimation formula in the case of C = 0.05 (with buffering effect), and it can be seen that it generally matches the experimental results in the region where the cyanide ion concentration exceeds 1 mg / L. On the other hand, there is a large error between the estimated value and the experimental results in the region of the cyanide ion concentration of 1 mg / L on the left side of the graph, which is because the influence of the initial pH value of the sewage (the pH value at a cyanide concentration of 0, pH = 8.2 in this experiment) is ignored. As an estimation formula considering the initial pH value P0 of the sewage, for example (Equation 2) X = 10^(P - 7) * C - 10^(P0 - 7) * C (when P > P0) X = 0 (when P < P0) can be used.

[0069] The dotted line with white triangles in Figure 7B is the case where C = 0.05 in (Equation 2), and it can be seen that this line almost perfectly matches the experimental results. Note that the above equation for estimating the cyanide ion concentration is only one example, and it can also be realized by using approximations with various other functions (for example, area division using linear approximation).

[0070] 8 is an explanatory diagram (graphs 401 to 403) showing a method for estimating cyanide ion concentration in an embodiment of this specification, and graph 402 shows an example of fluctuation in the pH value of sewage. Although the pH value of sewage is weakly alkaline at around pH8, the value is not constant and fluctuates to a certain extent due to the inflow of rainwater or other waste liquids, measurement errors, etc. For this reason, it is difficult to detect the inflow of cyanide-containing waste liquid using the pH value alone, and in the present invention, the reliability is greatly improved by using cyanide gas detection, which has high substance selectivity, as an essential condition for detecting the inflow of cyanide-containing waste liquid.

[0071] In estimating the cyanide ion concentration in sewage, masking with a cyanide gas detection signal is also effective in improving the reliability of the measurement results. That is, as shown in graph 401, the period during which the cyanide gas concentration exceeds a predetermined threshold (0.5 ppm in this example) is determined to be the inflow of cyanide-containing waste liquid, and the estimated value of the cyanide ion concentration is valid only while the cyanide-containing waste liquid is inflowing, as shown in graph 403, and is set to zero when cyanide gas is not detected. In reporting the inflow of cyanide-containing waste liquid generated by this device, the condition of the cyanide ion concentration can also be taken into account, and in that case, the reliability of the present invention can be further improved by setting the conditions that cyanide gas is detected and the estimated value of the cyanide ion concentration is equal to or higher than a certain value.

[0072] In addition, the initial pH value P0 of the sewage in (Equation 2) is the hypothetical pH value of the sewage when there is no inflow of cyanide-containing wastewater, but this value is not constant and strictly speaking changes from moment to moment due to the inflow of rainwater, etc. Therefore, if the inflow of cyanide-containing wastewater is short and no significant pH fluctuation occurs during that time due to other factors, the value of P0 can be, for example, the sewage pH value (7.8 in this example) a certain time before the inflow of cyanide-containing wastewater is detected, as shown in graph 402. This can improve the estimation accuracy of the cyanide ion concentration in (Equation 2).

[0073] On the other hand, in cases where the inflow of cyanide-containing wastewater continues for a long period of time and a large amount of rainfall or the like inflows during that time, diluting the concentration in the sewage and causing a large pH fluctuation, causing a change in p0 (in formula 2), the estimation error of the cyanide ion concentration increases. Figure 9 is an explanatory diagram of a method for detecting cyanide-containing wastewater in a fourth embodiment of the present invention, which is configured by additionally mounting a throw-in type electrical conductivity sensor 260 to the configuration of the third embodiment, and adding a function to estimate the change in sewage flow rate due to the inflow of rainwater from the electrical conductivity of the sewage measured by this sensor, and to correct the initial sewage pH value p0 used in the above (formula 2).

[0074] In this configuration, the sensing node 211 is connected to an optical power supply device 271 arranged outside the sewer pipe via an optical fiber cable 270, and transmits and receives power and communications by light. In this configuration, the optical power supply device 271 may also be a part of the volatile liquid inflow detection device. The optical power supply device 271 can share at least some of the functions, such as generating a notification signal of volatile liquid inflow when the detected gas concentration exceeds a predetermined value, estimating the concentration of volatile liquid in the sewer, and notifying the outside via a network 272 of the notification signal of volatile liquid inflow and various measurement values ​​including the above-mentioned concentration estimate value, as necessary.

[0075] 9 shows a configuration in which the sensing node 211 is disposed inside the sewer pipe. However, if there is sufficient sensor cable length, a flexible device arrangement is possible, such as disposing the sensing node 211 outside the sewer pipe and installing only the gas sensor unit 210, the throw-in type pH sensor 232, and the throw-in type electrical conductivity sensor 260 inside the sewer pipe.

[0076] 10 is a configuration diagram of a volatile liquid inflow detection device according to a fourth embodiment of the present invention. In this configuration, a gas sensor unit 210, a throw-in type pH sensor 232, and a throw-in type electrical conductivity sensor 260 are connected to a waterproof housing 221-2 of a sensing node 211 via waterproof connectors 223-1, 223-2, and 223-3, respectively.

[0077] In this example, a single optical fiber core 273 is disposed inside the optical fiber cable 270 connected to the waterproof housing 221-2. A high-intensity power supply light 278 is transmitted to this optical fiber core 273 from a remotely disposed optical power supply device 271. Inside the sensing node 211, an optical splitter 274 is used to separate the wavelength components of the power supply light with low loss and input them to an optical power receiving circuit 276.

[0078] The optical receiving circuit 276 converts the power supply light 278 into electricity using a photoelectric conversion element such as a photodiode, and stores this in an internal storage element such as a battery to obtain operating power for the sensing node 211 and the gas sensor unit 210. In addition, the communication signal 244 transmitted from the CPU 214 is converted into upstream transmission light 277 by the optical transmitter 275. The upstream transmission light 277 is an optical signal with a different wavelength from the power supply light 278, and the optical splitter 274 wavelength-multiplexes this signal into the optical fiber core 273 and transmits it to the optical power supply device 271 located remotely.

[0079] In the above configuration, it is possible to realize long-distance wiring (several tens of meters to several kilometers) connecting the sensing node 211 installed inside the sewer pipe and the optical power supply device 271 outside the sewer pipe using only optical fiber. Optical fiber is far more explosion-proof and corrosion-resistant than electric cables, reducing the risk of short circuits and explosions and improving the safety and reliability of the system. In addition, compared to the configuration using a battery shown in Figure 3, there are also advantages in that battery maintenance and replacement work is unnecessary and there is more power available, allowing for an increased frequency of measurement and communication and an increased number of sensors to be installed.

[0080] The throw-in type electrical conductivity sensor 260 can be an electrical resistance type that directly measures electrical conductivity from the resistance value of two electrodes exposed in the sewage, or an electromagnetic induction type that measures induced electromotive force by placing two coils closely together in the sewage. In this example, the electrical conductivity signal (voltage) 262 obtained from the sensor is input to a voltage amplifier circuit 263 inside the sensor node 211 via an electrical conductivity sensor cable 261, where the voltage is amplified, and then converted into a digital signal by an AD converter inside the CPU 214.

[0081] Electrical conductivity is a parameter that indicates how easily electricity passes through a liquid, and it is known that the electrical conductivity of sewage can be used as a guide to the sewage flow rate. Generally, sewage contains many ions, so it is easy for electricity to pass through it, and its electrical conductivity is a large value of around several hundred to 1,000 uS / m. In contrast, fresh water that flows in during rainfall does not conduct electricity well, so its electrical conductivity is a small value of less than 100 uS / m. When sewage is diluted with rainwater when it flows in, its electrical conductivity E decreases inversely proportional to the dilution rate, so if the electrical conductivity of sewage in a steady state with no rainwater inflow is E0, the change in sewage flow rate (dilution rate) can be roughly approximated as (E / E0).

[0082] On the other hand, the pH of the inflowing rainwater is almost neutral (~7). If the pH value of the sewage water under normal conditions is P0, the pH value of the sewage water diluted by the inflow of rainwater, P0', changes as a logarithmic function of the dilution rate, so (Equation 3) p0′=log10(10^(p0-7)*(E0 / E))+7 It can be estimated by the following approximation:

[0083] By replacing P0 in (Equation 2) with P0' calculated using (Equation 3), it is possible to determine the change in the initial sewage pH value P0 due to the inflow of rainwater, thereby improving the accuracy of estimating the cyanide ion concentration. Note that (Equation 3) is an approximation derived by setting the electrical conductivity of the inflowing rainwater to zero, and it is possible to replace it with an approximation with a higher accuracy or a simpler form as necessary.

[0084] Although the vertical axis of FIG. 7C represents electrical conductivity, it can be seen that the above calculation of the change in sewage flow rate can be performed regardless of the cyanide ion concentration, since electrical conductivity is not affected by the cyanide ion concentration.

[0085] 11A and 11B are explanatory diagrams showing the influence of pH sensor drift in the fourth embodiment. FIG. 11A is a schematic diagram of the change in pH value when pH sensor drift occurs. It is known that even if the pH value of the sewage is constant (8.0 in this figure), the pH sensor may experience drift, in which the output voltage gradually shifts due to deterioration of the glass electrode, etc. The drift component is a gradual deviation from the steady pH value, so if the steady pH value is obtained in advance by an averaging operation, the drift component can be calculated by dynamic averaging.

[0086] By removing the drift component determined in this manner from the measured pH value, the correct pH value with the drift component removed can be obtained, as shown in Figure 11B, and the estimation accuracy of the cyanide ion concentration in (Equation 1) and (Equation 2) can be improved.

[0087] Furthermore, if the measured pH value has known fluctuations, such as periodic fluctuations according to the time of day, this fluctuation can be used as the steady state for each time, i.e., P0 in (Equation 3), to correct the estimated cyanide ion concentration and improve the estimation accuracy. For example, if there is a periodic fluctuation according to the time of day, it can be calculated by classifying the obtained pH value by the time of day and performing a dynamic averaging operation between the data for the same time over several days to several weeks.

[0088] The above-mentioned sewage flow rate correction and pH sensor drift correction may be performed by the CPU 214 in the sensing node 211, or may be performed inside the optical power supply device 271 (host device), or in a device connected via a network. In addition, at least a part of the functions (control functions) of the volatile liquid inflow detection device described in the above embodiments may be implemented in a host device that communicates via a network with a device installed in a sewer pipe including a gas sensor. The volatile liquid inflow detection device is configured to include functions included in the host device.

[0089] For example, the host device may obtain a detection value from the gas sensor, and when the volatile gas concentration exceeds a predetermined value, may determine that a volatile liquid has flowed in and report it to the outside. The host device may also remove error components caused by interference gases, and may adaptively adjust cross sensitivity and signal timing so that the output value of the volatile gas concentration signal approaches zero over time.

[0090] The present invention is not limited to the above-described embodiments, and includes various modified examples and equivalent configurations within the spirit of the appended claims. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all of the configurations described. In addition, a part of the configuration of one embodiment may be replaced with a configuration of another embodiment. In addition, a configuration of another embodiment may be added to a configuration of one embodiment. In addition, a part of the configuration of each embodiment may be added, deleted, or replaced with another configuration.

[0091] In addition, each of the aforementioned configurations, functions, processing units, processing means, etc. may be realized in hardware, for example by designing some or all of them as an integrated circuit, or may be realized in software by a processor interpreting and executing a program that realizes each function.

[0092] Information such as programs, tables, files, etc. that realize each function can be stored in a storage device such as a memory, a hard disk, or an SSD (Solid State Drive), or in a recording medium such as an IC (Integrated Circuit) card, an SD card, or a DVD (Digital Versatile Disc).

[0093] In addition, the control lines and information lines shown are those considered necessary for the explanation, and do not necessarily show all the control lines and information lines necessary for implementation. In reality, it can be considered that almost all components are connected to each other. [Industrial Applicability]

[0094] The present invention relates to a method for easily detecting the inflow of volatile liquids into sewage, and is applicable to monitoring sewage quality and sewage treatment facilities. Information from this device can be used to switch sewage treatment processes and automate operations. [Explanation of symbols]

[0095] 100: sewer pipe, 101: sewage, 102: sampling tube, 103: Sampling pump, 104: Aeration type hydrogen sulfide removal device, 105: Liquid phase ion electrode type cyanide ion detector; 106: power supply unit, 107: power cable, 110: purge pipe, 111: gas phase cyanide ion electrode, 112: Ion electrode cable, 113: voltmeter, 114: air pump, 115: intake pipe, 116: air supply pipe, 117: air (bubbles), 118: recorder, 200: A volatile liquid inflow detection device of the present invention, 201: A constant potential electrolysis type cyan gas sensor, 202: Cyanogen gas concentration signal (current), 203: Gas sensor drive circuit, 204: Cyanogen gas concentration signal (voltage), 205: Threshold voltage generator, 206: voltage comparison circuit, 207: notification signal generation circuit, 208: notification signal, 209: Notification signal transmission cable, 210: gas sensor unit, 211: sensing node, 212: AD converter, 213: Cyan gas concentration signal (digital), 214: CPU, 215: battery, 216: power, 217: notification signal, 218: radio transmitter, 219: radio antenna, 220: cyanide gas, 221: waterproof housing, 222: waterproof cable, 223: waterproof connector, 230: gas inlet hole, 231: hydrogen sulfide permeation prevention film, 232: Throw-in pH sensor, 233: pH sensor cable, 234: pH signal (voltage), 235: external connection cable, 240: constant potential electrolysis type hydrogen sulfide gas sensor, 241: hydrogen sulfide gas concentration signal (current), 242: hydrogen sulfide gas concentration signal (voltage), 243: high impedance voltage amplifier circuit, 244: communication signal, 245: transmitter, 246: transmission signal, 247: communication signal line, 250: power receiving circuit, 251: power, 252: power transmission line, 260: Throw-in type electrical conductivity sensor, 261: Electrical conductivity sensor cable, 262: Electrical conductivity signal (voltage), 263: Voltage amplifier circuit, 270: optical fiber cable, 271: optical power supply device, 272: network 273: optical fiber core, 274: optical splitter, 275: optical transmitter, 276: optical receiving circuit, 277: upstream communication light, 278: power supply light,

Claims

1. a volatile gas sensor that is disposed in an upper space of the sewer pipe and outputs a signal corresponding to the concentration of a volatile gas in the air; A communication device; A control device; and one or more throw-in type pH sensors having an electrolyte sealed therein, the throw-in type pH sensors being disposed under the water surface in the sewer pipe. The control device determines that a volatile liquid has flowed in when the concentration of the volatile gas detected by the volatile gas sensor exceeds a predetermined value, and transmits a notification signal to the outside by the communication device. the volatile liquid is a cyanide-containing liquid; the volatile gas sensor is a cyanogen gas sensor; The control device is a volatile liquid inflow detection device that calculates an estimated value of cyanide ion concentration from the sewage pH value signal obtained from the throw-in type pH sensor.

2. A volatile liquid inflow detection device as described in claim 1, A volatile liquid inflow detection device comprising a volatile gas sensor provided with a mechanism for preventing erroneous detection with respect to one or more interfering gases having cross-sensitivity to the volatile gas sensor.

3. A volatile liquid inflow detection device as described in claim 1, one or more interference gas sensors arranged near the volatile gas sensor and outputting a signal corresponding to a concentration of the interference gas in the air, the interference gas sensors being cross-sensitive to one or more interference gases having cross-sensitivity to the volatile gas sensor; The control device is a volatile liquid inflow detection device characterized in that it receives as input a concentration signal of the volatile gas and a concentration signal of the one or more interference gases, and removes error components caused by the one or more interference gases from the concentration signal of the volatile gas.

4. A volatile liquid inflow detection device as described in claim 3, The control device is a volatile liquid inflow detection device characterized in that when the volatile gas concentration signal and the one or more interference gas concentration signals are non-zero, the control device adaptively adjusts at least one of the cross sensitivity and signal timing so that the output value of the volatile gas concentration signal approaches zero over time.

5. A volatile liquid inflow detection device as described in claim 1, The volatile gas sensor has a structure that allows it to be replaced via a connector, A volatile liquid inflow detection device, characterized in that the volatile gas sensor and the communication device are mounted in a waterproof housing.

6. A volatile liquid inflow detection device as described in claim 1, The control device receives the pH value signal as an input, calculates a dynamic average value of at least one of the periodic fluctuations according to time and the long-term drift component of the throw-in type pH sensor from the pH value signal, and corrects and outputs the pH value signal using the dynamic average value.

7. A volatile liquid inflow detection device as described in claim 1, A conductivity sensor is provided for outputting a signal corresponding to the electrical conductivity of the sewage. The control device is characterized in that it uses a signal corresponding to the electrical conductivity to correct a change in pH value caused by water flowing into the sewer pipe.

8. A volatile liquid inflow detection device as described in claim 1, The control device includes: A volatile liquid inflow detection device characterized in that the notification signal or the detection value of the volatile gas sensor is transmitted to the outside by the communication device as an optical signal, an electrical signal or a wireless signal.

9. A volatile liquid inflow detection device as claimed in claim 8, The device includes a replaceable battery, a radio transmitter, and an antenna; The volatile liquid inflow detection device is characterized in that it operates using the power stored in the battery and is periodically started up to perform sensing operations and external transmission operations.

10. A volatile liquid inflow detection device as claimed in claim 8, The optical transmitter, the optical receiving circuit, and the optical fiber cable are provided. The optical power receiving circuit converts the power supply light transmitted from the outside through the optical fiber cable into an electric power obtained by the photoelectric conversion. Transmitting the optical signal output from the optical transmitter to an outside via the optical fiber cable; A volatile liquid inflow detection device that is periodically activated to perform sensing operations and transmit optical signals to the outside.

11. A method for detecting the inflow of a volatile liquid into a sewer, comprising: A signal corresponding to the concentration of a volatile gas in the air is obtained from a volatile gas sensor disposed in an upper space of the sewer pipe, When the concentration of the volatile gas detected by the volatile gas sensor exceeds a predetermined value, it is determined that the volatile liquid has flowed in and a notification signal is transmitted to the outside. the volatile liquid is a cyanide-containing liquid; the volatile gas sensor is a cyanogen gas sensor; The method further includes calculating an estimate of cyanide ion concentration from a sewage pH signal obtained from one or more immersion type pH sensors having an electrolyte sealed therein and disposed below the water surface in the sewer pipe.

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