Method for treating overflow pollution of urban drainage system

Abstract

The application discloses a kind of overflow pollution processing method of urban drainage system, it is applicable to the overflow pollution generated in the combined system interception overflow drainage outlet of urban drainage system, split-flow system interception overflow drainage outlet, by the integration of the data that can be collected such as per capita daily domestic water consumption, rainfall, raw sewage concentration, construct quantitative model, provide a kind of overflow pollution discharge theoretical concentration calculation method considering sewage collection rate, calculate the sewage quantity and rainwater quantity generated in unit time unit area in theory, and introduce the concept of actual sewage yield of pipe network, respectively according to the dischargeable concentration of rainwater and sewage Weighted average obtains the theoretical concentration of rainwater and sewage mixture, to determine the reasonable range of overflow pollution discharge concentration based on this, whether overflow pollution discharge can be quantified to reach standard, provide more reasonable basis for overflow pollution control of urban drainage system.

Description

Technical Field

[0001] This invention relates to a method for treating overflow pollution in urban drainage systems, belonging to the field of regional water environment pollution control technology. Background Technology

[0002] Overflow pollution is a common and unavoidable problem in urban water environments. While there is a consensus on overflow pollution caused by combined sewer systems, overflow pollution from separate sewer systems, caused by issues such as misconnection of pipes, pipe damage, and lack of separation between clean and wastewater, is often overlooked. Overflow pollution typically occurs during rainy days, and overflows only occur when the total amount of sewage and rainwater exceeds the storage capacity of the sewer network. Therefore, overflow pollution is characterized by the mixing of rainwater and sewage, and its discharge is intermittent.

[0003] Currently, there is a lack of scientific quantitative systems for assessing overflow pollution from combined and separate sewer systems. Using surface water environmental quality standards to quantify overflow pollution results in standards that are too high and fail to reflect the impact of sewage contamination. Using wastewater treatment plant discharge standards to quantify overflow pollution fails to reflect the significant proportion of rainwater involved in overflow pollution.

[0004] Existing quantitative standards lack a reasonable basis for controlling overflow pollution. Using existing quantitative standards not only makes it difficult to quantify whether the current overflow pollution situation of the drainage system is within a reasonable range, but also makes it difficult to provide the necessary quantitative data support for the implementation of overflow pollution treatment projects such as rainwater and sewage diversion renovation, pipeline dredging, and interception facilities. Therefore, it brings difficulties to the treatment of overflow pollution in urban drainage systems.

[0005] Due to the unavoidable mixing of rainwater and sewage in overflow pollution, the concentration of overflow pollution falls between that of surface water and sewage, but the theoretical range of values ​​still needs further research. To address these issues, existing methods quantify the most stringent standards under the condition of complete sewage collection and no incorrect connections. However, this quantification model is difficult to generalize to urban drainage systems where incorrect connections are common and complete sewage collection is challenging.

[0006] Therefore, how to combine the city's sewage collection rate and the actual situation of misconnected pipe networks to formulate overflow pollution treatment methods that conform to the current situation of drainage pipe networks, define the reasonable range of overflow pollution discharge, and provide a scientific basis for overflow pollution control are technical problems that urgently need to be solved by those skilled in the art. Summary of the Invention

[0007] Objective: To overcome the shortcomings of existing technologies, this invention provides a method for treating overflow pollution in urban drainage systems. The method calculates the volume of rainwater and sewage that constitute the overflow pollution, and uses a weighted average of directly dischargeable concentrations to obtain the mixed concentration of rainwater and sewage as the overflow discharge concentration limit. Based on comprehensive calculations using monitoring values ​​and available data, a quantitative model is constructed to determine whether the overflow pollution discharge meets the standards. Furthermore, overflow pollution control measures are proposed from the source-process-end perspective of the drainage system, quantifying the effect of engineering implementation on overflow pollution reduction and improvement, thus providing a more reasonable basis for the prevention and control of overflow pollution in urban drainage systems.

[0008] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0009] A method for treating overflow pollution from an urban drainage system includes the following steps:

[0010] The overflow pollution concentration limit C0 is calculated based on the overflow pollution concentration limit quantification model.

[0011] Obtain the overflow pollution concentration C at the overflow discharge point where the overflow pollution event occurred. f .

[0012] The overflow pollution concentration limit C0 and the overflow pollution concentration C f Compare, if C f If C ≤ C0, then the overflow pollution meets the standard; if C f If the overflow pollution level is greater than C0, the drainage system should be improved at the source, process, and end.

[0013] The calculation formula for the overflow pollution concentration limit quantification model is as follows:

[0014]

[0015] In the formula, Q s Q represents the amount of wastewater generated. r C represents the amount of rainwater generated. s C represents the dischargeable concentration of wastewater. r This refers to the concentration of rainwater that can be directly discharged.

[0016] Furthermore, Q s The calculation formula is as follows:

[0017] Q s =P÷A×S

[0018] Where P is the number of people served at the end point, A is the service area of ​​the wastewater treatment plant at the end point, and S is the per capita wastewater generation at the source.

[0019] Furthermore, Q rThe calculation formula is as follows:

[0020] Q r =α×R

[0021] Where α is the comprehensive runoff coefficient at the process location, and R is the average annual rainfall at the process location.

[0022] Furthermore, C s The calculation formula is as follows:

[0023] C s =C1×γ+C2×(1-γ)

[0024] Wherein, C1 is the standard for pollutants discharged from wastewater treatment at the end point, γ is the wastewater collection rate at the source, and C2 is the concentration of raw wastewater at the source.

[0025] Furthermore, C r The calculation formula is as follows:

[0026] C r =EMC COD

[0027] Among them, EMC COD The EMC concentration of COD in the stormwater runoff at the process point is given.

[0028] Furthermore, the formula for calculating S is as follows:

[0029] S = D × 6

[0030] Where D is the average daily domestic water consumption per person, and δ is the pollution reduction coefficient.

[0031] Furthermore, EMC COD The calculation formula is as follows:

[0032]

[0033] Where t represents the duration of the rainfall event, and C t Q represents the COD concentration in rainwater runoff. t Let be the stormwater runoff. j represents the j-th sample in the stormwater runoff, and n represents the total number of samples.

[0034] Furthermore, C2 is derived from Table 1-1, "Generation Coefficient of Urban Domestic Water Pollutants," in the "Handbook of Emission Source Statistical Survey and Pollution Discharge Accounting Methods and Coefficients."

[0035] Furthermore, R is generated from the 30-year average annual rainfall data of the China Surface Accumulated Daily Value Data Set of the National Meteorological Center.

[0036] Furthermore, the overflow pollution concentration C of the overflow event. f The calculation formula is as follows:

[0037]

[0038] In the formula, t is the time elapsed for the overflow event, and c t q represents the COD concentration in the overflow pollution emissions. t Let i represent the overflow flow rate, i represent the i-th sample in the discharge of an overflow event, and n represent the total number of samples.

[0039] Beneficial Effects: This invention provides a method for treating overflow pollution in urban drainage systems, aiming to address the shortcomings of existing technologies, such as the lack of consideration for actual collection rates in pipe networks and insufficient research on overflow pollution concentration limits, leading to difficulties in quantifying overflow pollution emissions and a lack of control basis. The method is applicable to evaluating overflow pollution generated by combined sewer interception overflow outlets and separate sewer interception overflow outlets in urban drainage systems. It constructs a quantitative model by integrating collectable data such as per capita daily domestic water consumption, rainfall, and raw sewage concentration, providing a method for calculating the theoretical concentration of overflow pollution emissions considering sewage collection rates. This method calculates the theoretical amount of sewage and rainwater generated per unit time and per unit area, and introduces the concept of actual sewage collection rate in the pipe network. A weighted average is performed based on the dischargeable concentrations of rainwater and sewage to obtain the theoretical concentration of the mixed rainwater and sewage. This serves as the basis for determining a reasonable range for overflow pollution emission concentrations, which can be used to quantify whether overflow pollution emissions meet standards, providing a more reasonable basis for controlling overflow pollution in urban drainage systems. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating the analytical method of the present invention. Detailed Implementation

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0042] The present invention will be further described below with reference to specific embodiments.

[0043] A method for treating overflow pollution from an urban drainage system includes the following steps:

[0044] Step 1: Obtain relevant data. Taking the wastewater collection area of ​​each town's wastewater treatment plant as a unit, data collection and on-site surveys and monitoring are conducted separately for source, process, and end-of-pipe treatment, and the relevant data are integrated to obtain the following:

[0045] 1.1 Relevant data at the source include: per capita sewage generation S, sewage collection rate γ, and raw sewage concentration C2 (in terms of COD (chemical oxygen demand)).

[0046] 1.2. Relevant data for the process include: average annual rainfall R, comprehensive runoff coefficient α, and EMC concentration of COD in stormwater runoff. COD ;

[0047] 1.3 The relevant data at the end point include: the service area A of the wastewater treatment plant, the number of people served P, and the wastewater discharge pollutant standard C1 (in terms of COD).

[0048] Step 2: Construct a quantitative model for overflow pollution concentration limits, where C0 is the overflow pollution concentration limit. The calculation formula is as follows:

[0049]

[0050] Among them, Q s The formula for calculating the amount of wastewater generated is as follows:

[0051] Q s =P÷A×S (2)

[0052] Wastewater generation represents the product of the number of people per unit area within the service area of ​​the wastewater treatment plant and the per capita wastewater generation.

[0053] Q r The formula for calculating rainwater production is as follows:

[0054] Q r =α×R (3)

[0055] C s The dischargeable concentration of wastewater is calculated using the following formula:

[0056] c s =C1×γ+C2×(1-γ) (4)

[0057] The dischargeable concentration of wastewater means that the dischargeable concentration of wastewater collected by the pipe network is within the limit of the pollutant discharge standard of the urban wastewater treatment plant. Wastewater not collected by the pipe network is discharged directly.

[0058] C r The concentration of rainwater that can be directly discharged is calculated using the following formula:

[0059] C r =EMC COD (5)

[0060] Based on formulas (2)-(5), the overflow pollution concentration limit quantification model C0 can be optimized as follows:

[0061]

[0062] Step 3: Overflow pollution quantification. Based on the overflow pollution concentration limit quantification model, calculate the overflow pollution concentration limit C0. For the drainage outlet that generates overflow pollution, obtain the overflow pollution concentration C of the overflow event. f (Calculated as COD), the overflow pollution concentration limit C0 and the overflow pollution concentration C f Compare, if C f If C ≤ C0, then the overflow pollution meets the standard; if C f If the overflow pollution level is greater than C0, the drainage system should be improved from the source, process, and end.

[0063] Furthermore, the formula for calculating the per capita wastewater generation S in step 1 above is as follows:

[0064] S=D×δ (7)

[0065] In the formula, D represents the per capita daily domestic water consumption, which can be referenced from the per capita daily domestic water consumption index (L) of the national urban municipal public facilities level category in the "China Urban Construction Statistical Yearbook". δ is the pollution reduction coefficient, which takes a value of 0.8 to 0.9. It can be referenced from the pollution reduction coefficient in Appendix 1 "Handbook of Pollution Reduction Methods and Coefficients for Domestic Sources" of the "Statistical Survey of Emission Sources". It refers to the ratio of urban comprehensive domestic sewage volume to urban comprehensive domestic water consumption. When the per capita daily domestic water consumption is ≤150 liters / person·day, the pollution reduction coefficient is 0.8; when the per capita daily domestic water consumption is ≥250 liters / person·day, it is 0.9; when the per capita daily domestic water consumption is between 150 liters / person·day and 250 liters / person·day, it is determined by interpolation.

[0066] Table 1. Surface types and their runoff coefficient values

[0067]

[0068] Furthermore, the formula for calculating the comprehensive runoff coefficient α in step 1 above is as follows:

[0069] α=∑ i L i ·r i / ∑ i L i (8)

[0070] In the formula, L i Let r be the area occupied by the i-th type of land. i Let be the runoff coefficient of the i-th type of land.

[0071] Furthermore, the EMC concentration of COD in the rainwater runoff in step 1 above... COD The calculation formula is as follows:

[0072]

[0073] In the formula, t represents the duration of the rainfall event, and C... t Q represents the COD concentration in rainwater runoff. t This represents the stormwater runoff. j represents the j-th sample in the stormwater runoff, and n represents the total number of samples. EMC COD It can be obtained through actual measurements or literature.

[0074] Furthermore, the concentration of raw wastewater C2 (calculated as COD) in step 1 above can be referenced from the generation coefficient index in Table 1-1 "Generation Coefficient of Urban Domestic Water Pollutants" of the "Manual of Methods and Coefficients for Calculation of Pollutant Generation and Discharge from Emission Sources".

[0075] Furthermore, the annual average rainfall R in step 1 above can be referenced from the 30-year average annual rainfall data of the China Surface Accumulated Daily Value Dataset (Surface Climate Standard Value Annual Value Dataset) from the National Meteorological Center.

[0076] Furthermore, the wastewater treatment discharge pollutant standard C1 (calculated as COD) in step 1 above can be referenced from the local urban wastewater treatment plant pollutant discharge standard.

[0077] Furthermore, the overflow pollution concentration C emitted during the overflow event in step 3 above... f The calculation formula (based on COD) is as follows:

[0078]

[0079] In the formula, t is the time elapsed for the overflow event, and c t q represents the COD concentration in the overflow pollution emissions. t Let i represent the overflow flow rate, i represent the i-th sample in the discharge of an overflow event, and n represent the total number of samples.

[0080] Example 1:

[0081] This invention provides a method for treating overflow pollution in urban drainage systems, as shown in the attached figure. Figure 1 The diagram shown is a flowchart of the method of the present invention. In this embodiment, data is collected within the water intake area D of a sewage treatment plant C in City B, Province A. By integrating collectable data such as per capita daily domestic water consumption, rainfall, and raw sewage concentration, a quantitative model for overflow pollution discharge concentration limits is constructed and calculated. Based on this, a reasonable range for overflow pollution discharge concentration is determined to quantify whether overflow pollution discharge meets the standards. The method includes the following steps:

[0082] Step 1: Taking the catchment area D of urban wastewater treatment plant C as the unit, data is obtained from the source, process, and end point, as follows:

[0083] Sources: per capita wastewater generation S, wastewater collection rate γ, and raw wastewater concentration C2 (in COD).

[0084] Process: Annual average rainfall R, comprehensive runoff coefficient α EMC concentration of COD in rainwater runoff.

[0085] End point: Service area of ​​wastewater treatment plant A, number of people served P, and wastewater discharge pollutant standard C1 (in COD).

[0086] Calculate the per capita wastewater generation S:

[0087] S=D×δ=296.5L / d×0.9=266.85L / d

[0088] In the formula, D is the per capita daily domestic water consumption. According to the 2020 China Urban Construction Statistical Yearbook, the per capita daily domestic water consumption in City B is 296.5 L / d. δ is the pollution reduction coefficient, which is 0.8 to 0.9. According to the "Emission Source Statistical Survey Pollution Discharge Accounting Method", when the per capita daily domestic water consumption is ≥250 liters / person·day, it is taken as 0.9.

[0089] The sewage collection rate γ is taken as 88% based on the statistical data of the centralized collection rate of urban domestic sewage from relevant departments in Province A. The raw sewage concentration C2 (calculated as COD) is taken as 340 mg / L based on the "Statistical Survey of Emission Sources and Emission Accounting Method".

[0090] According to the China Surface Accumulated Daily Value Data Set (Surface Climate Standard Value Annual Value Data Set) from the National Meteorological Center, the average annual rainfall R in City B from 1990 to 2020 was 1133 mm.

[0091] Within the water collection area D, buildings comprise 40%, roads 35%, and green spaces 25%. Based on the ground types and their runoff coefficient values ​​in Table 1, the formula for calculating the comprehensive runoff coefficient α is as follows:

[0092] α=∑ i L i ·r i = 40% × 0.9 + 35% × 0.8 + 25% × 0.2 = 0.71

[0093] In the formula, L i Let r be the area occupied by the i-th type of land. i Let be the runoff coefficient for the i-th type of land, where i=1 is buildings, i=2 is roads, and i=3 is green space.

[0094] The EMC concentration of COD in rainwater runoff within the water collection area D is taken as 100 mg / L according to the reference.

[0095] Wastewater treatment plant C serves an area A of 175 km². 2 The number of people served, P, is 1.48 million.

[0096] The standard for pollutant discharge from wastewater treatment plant C1 (calculated as COD) is 50 mg / L, based on the discharge standard for urban wastewater treatment plants in Province A.

[0097] Step 2: Calculate the overflow pollution concentration limit C0:

[0098]

[0099] Step 3: Quantify overflow pollution and calculate the overflow pollution concentration C of the overflow event. f (in COD terms):

[0100]

[0101] In the formula, C f Based on the monitoring values, t = 60 min is determined to be the duration of the overflow event, c t qt represents the COD concentration (mg / L) of the overflow pollution discharge, and qt represents the overflow volume (m³). 3 For the first 30 minutes, the overflow flow and water quality are monitored every 5 minutes, and after 30 minutes, the overflow flow and water quality are monitored every 10 minutes.

[0102] Therefore, the overflow pollution concentration C in this overflow event f Compared with the overflow pollution concentration limit C0, the emission is within the range of the quantitative indicator C0 limit and is considered to meet the standard.

[0103] If the overflow pollution concentration C of the overflow event f If the discharge does not meet standards, such as when the overflow pollution concentration at a discharge outlet within the catchment area of ​​another wastewater treatment plant E is 95.2 mg / L, then improvements can be made to the drainage system from the source, process, and end to achieve the goal of overflow pollution control. The specific derivation of the overflow pollution control effect is as follows:

[0104] In actual overflow pollution control, overflow pollution is controlled from the source, process, and end. Improving the centralized collection rate of domestic sewage at the source can increase it from 88% to 93%. Monitoring of overflow pollution concentrations (C') under similar rainfall events at the same discharge outlet is also relevant. f (in COD terms) is:

[0105] C' f =93.69mg / L≥C0=92.31mg / L

[0106] Compared to the overflow discharge concentration of 95.2 mg / L before the sewage collection rate control, it has decreased by 5.8%, which shows a certain effect on overflow pollution control. However, the overflow pollution concentration still does not meet the standard, and further measures need to be taken to control it.

[0107] By controlling runoff during the process, sponge city engineering was implemented to reduce the road surface area to 30% and increase the green space area to 30%. Monitoring of overflow pollution concentrations (C) at similar rainfall events at the same outlets was conducted. f (in COD terms) is:

[0108] C” f =90.32mg / L≤C0=92.31mg / L

[0109] Compared to the overflow discharge concentration of 95.2 mg / L before the implementation of the sponge city project, it decreased by 5.1%, and the overflow pollution concentration was able to meet the standards, indicating that the sponge city project can effectively reduce overflow pollution.

[0110] The overflow pollution volume is controlled by an integrated facility at the end of the drainage system. The overflow pollution concentration C is monitored under similar rainfall events at the same outlet. f "(in COD) is:

[0111] C f ”'=90.11mg / L≤C0=92.31mg / L

[0112] Compared to the overflow discharge concentration of 95.2 mg / L before the implementation of the sponge city project, it was reduced by 5.4%, and the overflow pollution concentration was able to meet the standards, indicating that integrated facilities can also effectively reduce overflow pollution.

[0113] The above embodiments demonstrate that the overflow pollution quantification method of the present invention can scientifically assess the reduction of overflow pollution emission concentration after the implementation of actual engineering measures.

[0114] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for treating overflow pollution from an urban drainage system, characterized in that: Includes the following steps: The overflow pollution concentration limit is calculated based on the overflow pollution concentration limit quantification model. ; Obtain the overflow pollution concentration C at the overflow discharge point where the overflow pollution event occurred. f ; Limits on overflow pollution concentrations With overflow pollution concentration C f Compare, if If the overflow pollution meets the standards; if If the overflow pollution does not meet the standards, improvements can be made to the drainage system at the source, process, and end. The calculation formula for the overflow pollution concentration limit quantification model is as follows: ； In the formula, Wastewater generation Rainfall generation The discharge concentration of wastewater. The concentration of rainwater that can be directly discharged; The calculation formula is as follows: ； Wherein, C1 is the standard for pollutants discharged from wastewater treatment at the end point, γ is the wastewater collection rate at the source, and C2 is the concentration of raw wastewater at the source; The calculation formula is as follows: ； Among them, EMC COD EMC concentration of COD in stormwater runoff at the process point; EMC COD The calculation formula is as follows: ； Where t represents the duration of the rainfall event, and C t Q represents the COD concentration in rainwater runoff. t denoted as stormwater runoff; j represents the j-th sample in the stormwater runoff, and n represents the total number of samples.

2. The method for treating overflow pollution in an urban drainage system according to claim 1, characterized in that: The calculation formula is as follows: ； Where P is the number of people served at the end point, A is the service area of ​​the wastewater treatment plant at the end point, and S is the per capita wastewater generation at the source.

3. The method for treating overflow pollution in an urban drainage system according to claim 1, characterized in that: The calculation formula is as follows: ； Where α is the comprehensive runoff coefficient at the process location, and R is the average annual rainfall at the process location.

4. The method for treating overflow pollution in an urban drainage system according to claim 2, characterized in that: The formula for calculating S is as follows: ； Where D represents the average daily domestic water consumption per person. This is the pollution reduction factor.

5. A method for treating overflow pollution in an urban drainage system according to claim 3, characterized in that: R is generated from the 30-year average annual rainfall data set of the China Surface Accumulated Daily Values ​​dataset from the National Meteorological Center.

6. The method for treating overflow pollution in an urban drainage system according to claim 1, characterized in that: The overflow pollution concentration C of the overflow event. f The calculation formula is as follows: ； In the formula, t is the time elapsed for the overflow event, and c t q represents the COD concentration in the overflow pollution emissions. t Let i represent the overflow flow rate, i represent the i-th sample in the discharge of an overflow event, and n represent the total number of samples.

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