Device and method for measuring N2O emission intensity of regional sewage collection system

Abstract

The invention provides a device and method for measuring the N2O discharge intensity of a regional sewage collection system.The device is composed of a drainage pipe, an injector, a submersible pump, a gas collection device, a manual flow valve and the like, during measurement, the submersible pump is placed in a sewage collection unit needing to be measured, one end of the drainage pipe is connected with the submersible pump, and the other end of the drainage pipe is connected with the manual flow valve; a gas collecting device modified by a reverse osmosis filter membrane is arranged in the middle of the water discharging pipe, is connected with an injector and is used for collecting N2O released from sewage, and the concentration of N2O in the collected gas is measured by using a gas chromatograph. According to the evaluation method, the N2O emission level of the sewage collection system with a complex topological structure in a region is deduced mainly according to the N2O emission intensity of the tail end of the sewage collection system in the region. According to the method, in-situ measurement of the dissolved N2O concentration in the sewage collection unit is utilized, the N2O emission intensity at the tail end of the regional sewage collection system is scientifically calculated, and the N2O emission level of the regional sewage collection system is accurately evaluated.

Description

Technical Field

[0001] The invention belongs to the field of ecological environment protection and relates to a method for measuring and calculating the N2O emission intensity of a regional sewage collection system, and specifically relates to a device for measuring the concentration of dissolved N2O in a sewage collection system and a method for calculating the N2O emission intensity in a sewage collection system with a complex topological structure. Technical Background

[0002] Nitrous oxide (N2O), also known as laughing gas, is a colorless, sweet-smelling gas that is an inevitable byproduct of biological denitrification. The sewage collection system is in a dark, closed anaerobic environment. Coupled with the continuous inflow of sewage as a carbon and nitrogen source, a huge anaerobic reactor is formed in the drainage collection system. This moist anaerobic environment is very suitable for the growth of nitrogen cycle bacteria, creating good conditions for the production of N2O. As an important greenhouse gas, N2O has a greenhouse potential of about 300 times that of CO2 and 21 times that of CH4. In addition, N2O can stay in the air for a long time, causing ozone holes in the stratosphere, acid rain and photochemical smog. Although N2O is not produced during nitrification and denitrification in the sewage collection system, N2O can be produced as a byproduct of nitrification and an intermediate product of denitrification.

[0003] At present, there is a lack of research on N2O emission intensity in the sewage collection and treatment industry. It mentions the use of the emission factor method to calculate the N2O emission intensity generated during the operation of the sewage treatment plant, but this method does not involve the sewage collection system. In the "Technical Guidelines for Carbon Accounting and Emission Reduction Pathways for Urban Water Systems" issued by the China Urban Water Supply and Drainage Association, the emission factor method used in the IPCC guidelines is imitated to calculate the N2O emission intensity in the sewage collection system. However, in the sewage collection system with a complex topology, the use of a unified emission factor to calculate the N2O emission intensity is questionable in terms of accuracy. According to existing research, N2O has a high solubility in water bodies. There is currently a lack of research on dissolved N2O monitoring devices in sewage collection systems, and it is difficult to accurately quantify the N2O emission level in sewage collection systems with complex topologies. Therefore, research on related devices and methods is urgently needed. Summary of the invention

[0004] 1. Problem to be solved

[0005] In view of the problems that the N2O emission level of regional sewage collection systems is difficult to accurately quantify, the emission pattern is unclear, and there is a lack of monitoring data to support its accuracy, the present invention provides a device and method for measuring the N2O emission intensity of regional sewage collection systems.

[0006] 2. Technical solution

[0007] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0008] A device for measuring the N2O emission intensity of a regional sewage collection system, the device is used to measure the dissolved N2O content in the sewage collection system, and indirectly characterizes the N2O emission intensity of the sewage collection system using the dissolved N2O content. The device consists of a drain pipe, a syringe, a submersible pump, a gas collecting device, a manual flow valve, etc. One end of the drain pipe is connected to the submersible pump, and the other end is connected to the manual flow valve. A gas collecting device modified by a reverse osmosis filter membrane is arranged in the middle of the drain pipe, and the gas collecting device is connected to the syringe.

[0009] As a further improvement of the present invention, the submersible pump adopts a portable sewage pump (DP) with a maximum flow rate of 15m 3 / h, with a maximum head of 13.3m. The submersible pump can lift the sewage in the sewage collection system to the ground, increase the water pressure, and inhibit the release of dissolved gases in the water. When the sewage flows through the middle part of the drain pipe, the gas collecting device under normal pressure can collect the dissolved gases released in the high water pressure.

[0010] As a further improvement of the present invention, the gas collecting device is a T-shaped three-way pipe, which is composed of a connected horizontal pipe and a vertical pipe, wherein the horizontal pipe is installed in the drainage pipe, and the vertical pipe is vertically placed in the middle of the horizontal pipe, one end of which is connected to the horizontal pipe, and the other end is provided with a reverse osmosis filter membrane. The reverse osmosis filter membrane is used to make a gas collecting device, and the reverse osmosis filter membrane is used to connect the connection between the sewage in the drainage pipe and the gas collecting device. Under the water pressure conditions provided by the portable sewage pump (DP), it can be ensured that the sewage will not flow through the reverse osmosis filter membrane, and the dissolved gas in the sewage will flow out of the reverse osmosis filter membrane. The head of the syringe is inserted into the reverse osmosis filter membrane, and the syringe is used to balance the pressure in the gas collecting device and collect gas for external detection.

[0011] As a further improvement of the present invention, the manual flow valve is used to adjust the sewage flow, and the one-way regulating valve controls the increase of sewage flow and water pressure.

[0012] The method for using the device for measuring the concentration of dissolved N2O in a sewage collection system and the method for calculating the N2O emission intensity of a regional sewage collection system include the following steps:

[0013] S1: During measurement, the submersible pump is placed in the sewage collection system. One end of the drain pipe is connected to the submersible pump and the other end is connected to a manual flow valve. A gas collecting device modified from a reverse osmosis filter membrane is set in the middle of the drain pipe. The gas collecting device is connected to a syringe to collect N2O released from the sewage. The N2O concentration in the collected gas is measured using a gas chromatograph.

[0014] S2: According to Henry's law, calculate the saturated solubility of N2O in the sewage in the sewage collection system. It is known that the volume fraction of N2O in the atmosphere above the sewage in the sewage collection system is C, the vapor pressure of water at 25°C is P, and the Henry constant of N2O is K (25°C). Calculate the solubility of N2O in water. The saturated partial pressure of N2O in water is P N2O =(1.013-P)×C, the saturated solubility of N2O in sewage is N=K×P N2O .

[0015] S3: Use a submersible pump to lift sewage from the sewage collection system to the ground, place a bucket on the ground, lift the sewage volume V within the collection time t, and use a gas chromatograph to measure the N2O concentration G in the gas collected by the syringe. The volume of the syringe cavity is U, and the total N2O amount is calculated to be M=G×U. From this, the dissolved N2O concentration can be calculated to be T=M / V.

[0016] S4: Compare the saturated solubility N of N2O in sewage calculated by Henry's law theory with the measured dissolved N2O concentration T. If T<N, the measured dissolved N2O concentration is used to represent the N2O emission intensity CES in the regional sewage collection system; if T=N, the concentration is monitored upstream according to the pipe network topology until the point where T=N is found. The pipeline distance from the starting end to the end of the entire sewage collection system is L, and the pipeline distance from the point with the same concentration to the end is L1.

[0017] S5: When the saturated solubility N of N2O in sewage calculated by Henry's law theory is equal to the measured dissolved N2O concentration T, the calculation formula for N2O emission intensity in the regional sewage collection system is as follows:

[0018]

[0019] 3. Beneficial effects

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention can collect and measure dissolved N2O in a regional sewage collection system, and can be used for in-situ monitoring of N2O gas emission intensity in the sewage collection system;

[0022] (2) The present invention fully considers the calculation method of N2O emission level in regional sewage collection systems under different conditions, greatly improving the accuracy of N2O emission intensity calculation;

[0023] (3) The present invention can evaluate the N2O emission level in the regional sewage collection system and scientifically guide the construction of a low-carbon sewage collection system;

[0024] (4) The present invention has a simple structure, reasonable design, and is easy to manufacture. The N2O emission intensity calculation method is reliable and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the use of the device in the present invention;

[0026] Figure 2 This is a structural diagram of the connection between the submersible pump and the drainage pipe of the present invention;

[0027] Figure 3 This is a structural diagram of the connection between the syringe and the gas collecting device of the present invention;

[0028] Figure 4 This is the point distribution diagram of dissolved N2O in the sewage collection system of the measurement area of ​​the present invention, where "○" represents the device of the present invention.

[0029] List of reference numerals:

[0030] Submersible pump 1, drain pipe 2, syringe 3, manual flow valve 4, gas collecting device 5, reverse osmosis filter membrane 6. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The present invention provides a device for measuring the concentration of dissolved N2O in a sewage collection system. Figure 1-4 As shown, the device includes a submersible pump 1, a drain pipe 2, a syringe 3, a manual flow valve 4 and a gas collecting device 5. The gas collecting device is a T-shaped three-way pipe, which is composed of a connected horizontal pipe and a vertical pipe, wherein the horizontal pipe is installed in the drain pipe, and the vertical pipe is vertically placed in the middle of the horizontal pipe, one end of which is connected to the horizontal pipe, and the other end is provided with a reverse osmosis filter membrane 6.

[0033] When testing the concentration of dissolved N2O in the sewage collection system, place the submersible pump in the sewage collection system, connect the submersible pump with one end of the drain pipe, connect the manual flow valve with the other end, connect the gas collection device in the middle of the drain pipe, and balance the partial pressure with a syringe on the gas collection device. After the above device is assembled, after turning on the submersible pump, the sewage transmitted in the sewage collection system can be lifted to the ground through the submersible pump and the drain pipe, and the water pressure can be increased by the submersible pump. When the pressure of the sewage increases, the dissolved gas passes through the reverse osmosis membrane to reach the gas collection device for collection, and the collected gas is used to measure the N2O concentration by gas chromatograph. Use a submersible pump to lift the sewage from the sewage collection system to the ground, place a bucket on the ground to collect the sewage volume V within the collection time t, and measure the N2O concentration G in the gas collected by the syringe by gas chromatograph. The volume of the syringe cavity is U, and the volume fraction of N2O in the atmosphere above the sewage in the sewage collection system is C. The saturated solubility of N2O in sewage calculated by Henry's law theory is N, and the measured dissolved N2O concentration is T calculated by the above parameters.

[0034] There are two cases for calculating the N2O emission intensity of the regional sewage collection system. The principle of selecting the measurement location is to first select the sewage treatment plant inlet end. If the dissolved N2O content at the sewage treatment plant inlet end is less than the saturated solubility of N2O in sewage, the N2O emission intensity of the regional sewage collection system is calculated according to the first method; if the dissolved N2O content at the sewage treatment plant inlet end is greater than the saturated solubility of N2O in sewage, the dissolved N2O content is tested at a certain distance along the main pipe of the municipal pipeline network (determined according to the total length of the municipal pipeline) until the dissolved N2O content is equal to the saturated solubility of N2O, and the distance from the point where the two are equal to the end is obtained. At this time, the N2O emission intensity of the regional sewage collection system is calculated according to the second method. The specific calculation method is as follows:

[0035] ① If T<N, the measured dissolved N2O concentration T is used to represent the N2O emission intensity CES in the regional sewage collection system.

[0036]

[0037] ② If T = N, it is necessary to conduct upstream concentration monitoring according to the topological structure of the pipe network until the point where T = N is found, and then calculate the N2O emission intensity CES in the regional sewage collection system according to the following formula. The distance from the starting end to the end of the entire sewage collection system is L, and the distance from the point where T = N to the end of the pipeline is L1.

[0038]

[0039] Using the above device and calculation method, the N2O emission level of the sewage collection system with a length of 10km and 30km was evaluated respectively. The specific steps are as follows:

[0040] S1: The dissolved N2O in the sewage was collected by using a dissolved N2O concentration device in the sewage collection system, and then the N2O concentrations in the sewage collection system at 10km and 30km were measured by gas chromatograph to be 1.2% and 5.5% respectively.

[0041] S2: The instrument measured the N2O volume fraction in the atmosphere above the sewage in the sewage collection system to be 0.1 ppb, and the vapor pressure of water at 25°C to be 0.03167×10 5 Pa, N2O Henry constant is 2.5×10 -2 mol / (L·Pa)(25℃), the calculation results of N2O saturated solubility are as follows.

[0042] N = (1.013-0.03167) × 10 5 ×1×10 -10 ×2.5×10 -2 =2.453×10 -7 mol / L=1.079×10 -2 mg / L

[0043] S3: Submersible pumps were used to lift sewage from the sewage collection system to the ground. Buckets were placed on the ground to collect sewage. The volume of sewage was 100 L within 1 h. The volume of the syringe cavity was 10 ml. The total amount of N2O in the sewage collection system with a total length of 10 km and 30 km was 0.236 mg and 1.082 mg, respectively. The concentration of dissolved N2O was 2.360×10 -3 mg / L and 1.082×10 -2 mg / L.

[0044] S4: Total length 10 km, dissolved N2O concentration is 2.360×10 -3 mg / L, lower than the saturated solubility of N2O 1.079×10 -2 mg / L, so the N2O emission intensity in the sewage collection system with a total length of 10 km is 2.360×10 -3 mg / L. The total length of 30 km is 1.082×10 -2 mg / L, approximately equal to the saturated solubility of N2O 1.079×10 -2 mg / L. The distance from the point with the same concentration to the end is 10km, and the calculation results of N2O emission intensity are as follows.

[0045] CES = 1.082 × 10 -2 ×(1+1 / 3)=1.443×10 -2 mg / L.

Claims

1. A device for determining the N2O emission intensity of a regional sewage collection system, characterized in that: The device is used to measure the dissolved N2O content in a sewage collection system, and uses the dissolved N2O content to indirectly characterize the N2O emission intensity of the sewage collection system; the device comprises a drain pipe, a syringe, a submersible pump, a gas collecting device and a manual flow valve, one end of the drain pipe is connected to the submersible pump, and the other end is connected to the manual flow valve, a gas collecting device modified by a reverse osmosis filter membrane is arranged in the middle of the drain pipe, and the gas collecting device is connected to the syringe.

2. A device for determining the N2O emission intensity of a regional sewage collection system according to claim 1, characterized in that: The submersible pump is a portable sewage pump with a maximum flow rate of 15m 3 / h, with a maximum head of 13.3m. The sewage in the sewage collection system is lifted to the ground through a submersible pump, and the water pressure is increased to suppress the release of dissolved gases in the water. When the sewage flows through the middle part of the drain pipe, the gas collecting device under normal pressure conditions collects the dissolved gases released in the high water pressure.

3. The device for determining the N2O emission intensity of a regional sewage collection system according to claim 1, characterized in that: The gas collecting device is a T-shaped three-way pipe, which is composed of a connected horizontal pipe and a vertical pipe, wherein the horizontal pipe is installed in the drain pipe, and the vertical pipe is vertically placed in the middle of the horizontal pipe, one end of which is connected to the horizontal pipe, and the other end is provided with a reverse osmosis filter membrane. Under the water pressure conditions provided by the submersible pump, it can be ensured that the sewage will not flow through the reverse osmosis filter membrane, while the dissolved gas in the sewage will flow out of the reverse osmosis filter membrane. The head of the syringe is inserted in the reverse osmosis filter membrane to balance the pressure in the gas collecting device and collect gas for external detection.

4. The device for determining the N2O emission intensity of a regional sewage collection system according to claim 1, characterized in that: The manual flow valve is used to adjust the sewage flow, and the one-way regulating valve controls the sewage flow and water pressure.

5. A method for determining the N2O emission intensity of a regional sewage collection system, characterized in that: The method adopts the device according to any one of claims 1 to 4, and specifically comprises the following steps: S1: During the measurement, a submersible pump is placed in the sewage collection system, one end of the drain pipe is connected to the submersible pump, and the other end is connected to a manual flow valve. A gas collecting device modified from a reverse osmosis filter membrane is set in the middle of the drain pipe. The gas collecting device is connected to a syringe to collect N2O released from the sewage. The N2O concentration in the collected gas is measured using a gas chromatograph; S2: According to Henry's law, calculate the saturated solubility of N2O in the sewage in the sewage collection system; the volume fraction of N2O in the atmosphere above the sewage in the sewage collection system is known to be C, the vapor pressure of water at 25°C is P, and the Henry constant of N2O is K. Calculate the solubility of N2O in water; the saturated partial pressure of N2O in water is P N2O =(1.013-P)×C, the saturated solubility of N2O in sewage is N=K×P N2O ; S3: Use a submersible pump to lift sewage from the sewage collection system to the ground, place a bucket on the ground, lift the sewage volume V within the collection time t, measure the N2O concentration G in the gas collected by the syringe by gas chromatograph, the volume of the syringe cavity is U, and calculate the total amount of N2O to be M=G×U, and thus calculate the dissolved N2O concentration to be T=M / V; S4: Compare the saturated solubility N of N2O in sewage calculated by Henry's law theory with the measured dissolved N2O concentration T. If T<N, the measured dissolved N2O concentration is used to represent the N2O emission intensity CES in the regional sewage collection system; if T=N, upstream concentration monitoring is performed according to the pipe network topology until the point where T=N is found; the pipeline distance from the starting end to the end of the entire sewage collection system is L, and the pipeline distance from the point with the same concentration to the end is L1; S5: When the saturated solubility N of N2O in sewage calculated by Henry's law theory is equal to the measured dissolved N2O concentration T, the calculation formula for N2O emission intensity in the regional sewage collection system is as follows:

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