A method for calculating regional sewage overflow caused by rainfall

Abstract

A method for calculating the amount of regional sewage overflow caused by rainfall solves the problem of calculating the amount of regional sewage overflow caused by rainfall. The method calculates the amount of sewage overflow based on the sewage treatment capacity of the regional sewage treatment system, the pollutant concentration in the sewage and the accumulated rainfall. The method includes: parameter determination, reference value determination, judgment of the occurrence of sewage overflow events, overflow judgment, and bottom-line judgment. The actual amount of sewage overflow is calculated by calculating the amount of sewage overflow and the bottom-line amount of sewage. The present invention is based on the pollutant load and rainfall of the regional sewage treatment system as the main calculation basis to calculate the amount of sewage overflow caused by rainfall. The calculation method has few influencing factors, is simple to calculate, and the calculation results can be cross-validated. In particular, the statistics of the total amount of pollutants entering the natural environment caused by overflow are accurate. It can be used for ecological environmental pollution assessment, scientific and reasonable setting of sewage treatment systems and operation efficiency evaluation, and important data support for government supervision and law enforcement of pollution control.

Description

Technical Field

[0001] The present invention relates to the field of urban sewage treatment, and in particular to a method for calculating regional sewage overflow caused by rainfall, which is used for ecological environmental pollution assessment, sewage treatment system setting and operation efficiency evaluation, and important data support for government supervision and law enforcement on pollution control. Background Art

[0002] At present, most cities adopt a pipe network design that separates rainwater from sewage. Sewage pipes, culverts and reservoirs collect urban sewage (including some industrial and agricultural sewage and domestic sewage) and enter the sewage treatment system (sewage treatment plant). After the pollutant load in the sewage is collected and treated in the sewage treatment system, the water that meets the standards is recycled or enters natural water bodies such as rivers. When it rains, the rainwater pipes will directly discharge the collected rainwater into natural water bodies such as rivers.

[0003] In some special cases, due to sudden heavy rainfall, a large amount of rainwater poured into the sewage pipe network, resulting in rainwater and sewage mixing. A large amount of rainwater occupied the space of the sewage pipe, saturated the sewage pipe, and caused the rainwater to carry sewage overflow. Feedback to the sewage treatment system (sewage treatment plant) is an increase in the amount of water inflow, but due to the sharp drop in the concentration of influent pollutants, the collected pollutant load was significantly reduced. Obviously, a lot of sewage overflowed from the sewage pipe network with rainwater without being collected and treated by the sewage treatment system for pollutant load, and flowed into natural water bodies, causing pollution to the natural water environment of the city and affecting the water quality. For example, in May 2024, it was found in a city along the Yangtze River that more than 35 million tons of sewage from a sewage treatment plant in 2023 were directly discharged into the Yangtze River due to sewage overflow caused by rainfall. How to deal with the sewage overflow problem and accurately calculate the total amount of pollutants caused by sewage overflow into natural water bodies due to rainfall are currently building resilient and safe cities, strengthening watershed management, and rationally designing regional sewage treatment capacity and sewage pipe networks based on annual rainfall and rainfall distribution. Systemic problems that urgently need to be solved. Overflow monitoring and quantitative calculation have challenges such as high cost and difficulty in comprehensive coverage.

[0004] In the prior art, overflow estimation can be done by building a mechanism model and simulating and estimating through experimental data. However, model building technology is difficult, there are many influencing factors, high input data requirements, the estimation results cannot be verified, the credibility is low, and implementation is difficult.

[0005] For example, Chinese patent publication number CN 118111524 A published a "method for calculating the overflow of a rainwater and sewage system", which can quickly, conveniently and efficiently predict the overflow of the rainwater and sewage system on the corresponding date of the rainfall data based on the amount of rainwater mixed in. However, considering the uncertainty factors such as the sewage pipe network, box culvert and storage tank itself having a certain sewage storage capacity, the reliability of the overflow calculation result is low and the calculation result cannot be verified.

[0006] For example, Chinese patent publication number CN 110334468 A announced "a method for quantifying rainwater inflow and overflow in urban drainage pipe networks". This method also uses a pipe network model to quantify overflow. The disadvantages of this technical solution are: difficulty in data acquisition, high difficulty in modeling, long calculation cycle, many factors affecting the results, and the reliability of the quantitative results cannot be verified. Summary of the invention

[0007] In view of the shortcomings of current sewage overflow calculations, such as difficulty in constructing a mechanism model, low reliability of overflow calculation results, and inability to verify calculation results, the present invention provides a method for calculating regional sewage overflow caused by rainfall.

[0008] The technical solution of the present invention to achieve its technical purpose is: a method for calculating the amount of regional sewage overflow caused by rainfall, which is based on the sewage treatment capacity of the regional sewage treatment system, the concentration of pollutants in the sewage and the accumulated rainfall, and calculates the amount of sewage overflow caused by the sewage overflow event caused by this rainfall, characterized in that: the calculation method includes the following steps:

[0009] Step 1. Parameter determination

[0010] (1) Rainfall threshold: Determine the maximum rainfall threshold that the sewage treatment system can withstand based on the sewage collection and treatment capacity of the sewage treatment system;

[0011] (2) Time definition of sewage overflow event: from the day when the accumulated rainfall is greater than the threshold for two consecutive days to the day before the accumulated rainfall is zero for two consecutive days, this is the time definition of this sewage overflow event;

[0012] (3) Determine the baseline value of pollution load collection and the baseline value of pollutant concentration in sewage;

[0013] Determination principle: Based on the load constant principle, in the absence of rainfall interference, and in the absence of obvious changes in personnel or industrial production activities within a certain period of time, the pollution load collection volume is set as a constant amount, load collection volume = sewage collection volume x pollutant concentration;

[0014] Base value of collected load: Take the pollutant load collected values ​​on consecutive rainless days, remove the highest and lowest values ​​with drastic changes, and take the average as the base value of collected load;

[0015] Baseline pollutant concentration value: Take the pollutant concentration values ​​of consecutive rainless days, remove the highest and lowest values ​​with large changes in values, and take the average as the base pollutant concentration value;

[0016] Step 2. Determine the occurrence of sewage overflow caused by rainfall

[0017] If the accumulated rainfall for two days is greater than the rainfall threshold, and the load collection volume is less than the load collection volume benchmark value, it is determined that there is sewage overflow;

[0018] Step 3. Determine whether the sewage treatment system has sewage backup during rainfall

[0019] The excess sewage storage capacity of the sewage treatment system pipe network, box culverts and reservoirs is defined as the sewage backup;

[0020] If the accumulated rainfall for two days is greater than the rainfall threshold, and the load collection volume is greater than the load collection volume benchmark value, it is judged that there is sewage backup;

[0021] Step 4. Calculation of sewage overflow volume caused by rainfall during the sewage overflow event time

[0022] When the conditions of step 2 are met, it is determined that there is a sewage overflow time period;

[0023] The overflow calculation formula is:

[0024] Overflow volume = ∑ (base value of load collection volume - base value of load collection volume) / base concentration of pollutants

[0025] Step 5. Calculation of sewage backup volume caused by rainfall during sewage overflow event time

[0026] When the conditions of step 3 are met, it is determined that there is sewage backup time period;

[0027] The calculation formula for the sewage bottom volume is:

[0028] Sewage backup volume = ∑ (load collection volume - load collection volume benchmark value) / pollutant benchmark concentration value

[0029] Step 6. Calculation of actual sewage overflow volume during the sewage overflow event time

[0030] The calculation formula for the actual sewage overflow is:

[0031] Actual sewage overflow volume = sewage overflow volume - sewage backup volume.

[0032] The beneficial effects of the present invention are as follows: the method is based on the sewage treatment capacity of the sewage treatment system when there is no rainfall in the area, the pollutant concentration in the sewage and the accumulated rainfall this time, as the main calculation basis, to calculate the sewage overflow caused by rainfall, and the calculation method has few influencing factors, the calculation is simple, and the accuracy of the calculation results can be cross-verified. The sewage overflow is calculated by citing different pollutant loads in the sewage, and the overflow calculation results have high reliability, the calculation results can be cross-verified, the credibility of the calculated data is high, or the mean of the calculated data can be obtained. In particular, the statistics of the total amount of pollutants directly entering the natural environment due to overflow are accurate and reliable. The present invention can be widely used in ecological environmental pollution assessment, sewage treatment system setting and operation efficiency evaluation, and important data support for government supervision and law enforcement of pollution control.

[0033] The present invention will be described in more detail below with reference to the embodiments. DETAILED DESCRIPTION

[0034] A method for calculating the amount of regional sewage overflow caused by rainfall, the method calculating the amount of sewage overflow caused by the current rainfall event based on the sewage treatment capacity of the regional sewage treatment system, the concentration of pollutants in the sewage and the accumulated rainfall, the method comprising the following steps:

[0035] Step 1. Parameter determination

[0036] (1) Rainfall threshold: Determine the maximum rainfall threshold that the sewage treatment system can withstand based on the sewage collection and treatment capacity of the sewage treatment system.

[0037] (2) Time definition of sewage overflow event: from the day when the accumulated rainfall is greater than the threshold for two consecutive days to the day before the accumulated rainfall is zero for two consecutive days, which is the definition time of this sewage overflow event.

[0038] (3) Determine the baseline value of pollution load collection and the baseline value of pollutant concentration in sewage;

[0039] Determination principle: Based on the principle of constant load, in the absence of rainfall interference and in the absence of obvious changes in human or industrial production activities in the area within a certain period of time, the pollution load collection amount is assumed to be constant, and the load collection amount = sewage volume x pollutant concentration.

[0040] Baseline value of collected load: Take the pollutant load collected on consecutive rainless days, remove the highest and lowest values ​​with drastic changes, and take the average as the base line value of collected load.

[0041] The load collection volume benchmark value can also be taken as the pollutant load collection volume value of the most recent consecutive rainless day before the rainfall overflow occurs as the calculation base.

[0042] Baseline pollutant concentration value: take the pollutant concentration values ​​of consecutive rainless days, remove the highest and lowest values ​​with drastic changes, and take the average as the base line pollutant concentration value.

[0043] Similarly, the pollutant baseline concentration value can also be taken as the pollutant concentration value of the most recent consecutive rainless day before the rainfall overflow occurs as the calculation base.

[0044] Step 2. Determine the occurrence of sewage overflow caused by rainfall

[0045] If the accumulated rainfall for two days is greater than the rainfall threshold and the load collection volume is less than the load collection volume benchmark value, it is judged that sewage overflow occurs.

[0046] Step 3. Determine whether the sewage treatment system has sewage backup during rainfall

[0047] The excess sewage storage capacity of the sewage treatment system pipe network, box culverts and reservoirs is defined as the sewage backup;

[0048] Considering that the pipelines, box culverts and regulating reservoirs of the sewage treatment system themselves have a certain sewage storage capacity, the sewage treated due to less rainfall on the previous day may not necessarily overflow. It is also possible that the sewage system will have to treat it on the second day, that is, there is a possibility of a safety net.

[0049] If the accumulated rainfall for two days is greater than the rainfall threshold, and the load collection volume is greater than the load collection volume benchmark value, it is judged that there is sewage backup;

[0050] Step 4. Calculation of sewage overflow volume caused by rainfall during the sewage overflow event time

[0051] When the conditions of step 2 are met, it is determined that there is a sewage overflow time period;

[0052] The overflow calculation formula is:

[0053] Overflow volume = ∑ (base value of load collection volume - base value of load collection volume) / base concentration of pollutants

[0054] Step 5. Calculation of sewage backup volume caused by rainfall during sewage overflow event time

[0055] When the conditions of step 3 are met, it is determined that there is sewage backup time period;

[0056] The calculation formula for the sewage bottom volume is:

[0057] Sewage backup volume = ∑ (load collection volume - load collection volume benchmark value) / pollutant benchmark concentration value

[0058] Step 6. Calculation of actual sewage overflow volume during the sewage overflow event time

[0059] The calculation formula for the actual sewage overflow volume is: actual sewage overflow volume = sewage overflow volume - sewage backup volume.

[0060] In the embodiment of the present invention, the method is based on multiple regions and multiple sewage treatment systems, and the multiple sewage treatment systems have sewage coordination scheduling, and the sewage overflow volume is calculated;

[0061] The sewage treatment volume and pollutant concentration data of multiple sewage treatment systems are weighted and integrated and calculated uniformly.

[0062] In an embodiment of the present invention, in the pollutant load, two or more groups of pollutant data with stable contents can be selected as overflow measurement data respectively, and the overflow measurement data obtained are used to cross-validate the credibility of the measurement data or obtain the mean of the measurement data.

[0063] For example, in the embodiment of the present invention, ammonia nitrogen and total phosphorus are used as pollutant loads to calculate the sewage overflow volume of area A in 2023. The actual sewage overflow volumes are 44.59 million tons and 37.66 million tons, respectively. By comparing the actual sewage overflow volumes of 44.59 million tons and 37.66 million tons calculated by using ammonia nitrogen and total phosphorus as pollutant loads, the calculation results are stable and reliable. The mean of the calculated data can also be used as the calculation result.

Claims

1. A method for calculating the amount of regional sewage overflow caused by rainfall, which is based on the sewage treatment capacity of the regional sewage treatment system, the concentration of pollutants in the sewage and the accumulated rainfall, and calculates the amount of sewage overflow caused by the current rainfall, and is characterized by: The calculation method includes the following steps: Step 1. Parameter determination (1) Rainfall threshold: Determine the maximum rainfall threshold that the sewage treatment system can withstand based on the sewage collection and treatment capacity of the sewage treatment system; (2) Time definition of sewage overflow event: from the day when the accumulated rainfall is greater than the threshold for two consecutive days to the day before the accumulated rainfall is zero for two consecutive days, this is the time definition of this sewage overflow event; (3) Determine the baseline value of pollution load collection and the baseline value of pollutant concentration in sewage; Determination principle: Based on the principle of constant load, in the absence of rainfall interference, and in the absence of obvious changes in personnel or industrial production activities in a certain period of time, the pollution load collection amount is set to be constant, load collection amount = sewage treatment amount x pollutant concentration; Base value of collected load: Take the pollutant load collected values ​​on consecutive rainless days, remove the highest and lowest values ​​with drastic changes, and take the average as the base value of collected load; Baseline pollutant concentration value: Take the pollutant concentration values ​​of consecutive rainless days, remove the highest and lowest values ​​with large changes in values, and take the average as the base pollutant concentration value; Step 2. Determine the occurrence of sewage overflow caused by rainfall If the accumulated rainfall over two days is greater than the rainfall threshold, and the load collection volume is less than the load collection volume benchmark value, it is determined that there is sewage overflow; Step 3. Determine whether the sewage treatment system has sewage backup during rainfall The excess sewage storage capacity of the sewage treatment system pipe network, box culverts and reservoirs is defined as the sewage backup; If the accumulated rainfall for two days is greater than the rainfall threshold, and the load collection volume is greater than the load collection volume benchmark value, it is judged that there is sewage backup; Step 4. Calculation of sewage overflow volume caused by rainfall during the sewage overflow event time When the conditions of step 2 are met, it is determined that there is a sewage overflow time period; The overflow calculation formula is: Overflow volume = ∑ (base value of load collection volume - base value of load collection volume) / base concentration of pollutants Step 5. Calculation of sewage backup volume caused by rainfall during sewage overflow event time When the conditions of step 3 are met, it is determined that there is sewage backup time period; The calculation formula for the sewage bottom volume is: Sewage backup volume = ∑ (load collection volume - load collection volume benchmark value) / pollutant benchmark concentration value Step 6. Calculation of actual sewage overflow volume during the sewage overflow event time The calculation formula for the actual sewage overflow volume is: actual sewage overflow volume = sewage overflow volume - sewage backup volume.

2. The method for calculating the amount of regional sewage overflow caused by rainfall according to claim 1 is characterized by: This method is based on multiple regions and multiple sewage treatment systems. At the same time, there is sewage coordination scheduling in multiple sewage treatment systems to calculate the sewage overflow volume; The sewage treatment volume and pollutant concentration data of multiple sewage treatment systems are weighted and integrated and calculated uniformly.

3. A method for calculating regional sewage overflow caused by rainfall according to claim 1 or 2, characterized in that: In the pollutant load, two or more groups of pollutant data with stable content can be selected as overflow volume calculation data respectively, and the overflow volume calculation data obtained are used to cross-validate the credibility of the calculation data or obtain the mean of the calculation data.