A method for evaluating and controlling overflow pollution on rainy days

Abstract

The purpose of the present invention is to provide a method for evaluating and controlling overflow pollution on rainy days, comprising the following steps: determining an overflow port, evaluation factors and evaluation indicators for evaluating overflow pollution; collecting water quality data for evaluating overflow events at the overflow port; calculating evaluation indicators based on the collected water quality data; determining the amount of pollution load to be reduced based on the control target and formulating control measures based on the evaluation index calculation results; calculating the load contribution rate of each pollution source, determining the main pollution source, and implementing targeted control measures on the pollution source. The present invention implements effective control of overflow pollution by performing a graded evaluation on the overflow pollution emission characteristics, determining the amount of pollution load to be reduced based on the control target, and proposing targeted governance measures, which has the advantages of strong pertinence, strong applicability, and easy operation.

Description

Technical Field

[0001] The present invention belongs to the field of urban water environment management, and specifically relates to a method for evaluating and controlling overflow pollution during rainy days. Background Art

[0002] The urban drainage system is an engineering facility system for treating and removing urban sewage and rainwater. It can effectively avoid the hazards of sewage and rainstorm water accumulation and ensure the orderly progress of urban life and production. After years of continuous efforts, the structure of urban drainage pipe network in my country has been basically formed. According to the annual environmental bulletin, the sewage treatment rate in various places is basically above 90%, and the sewage collection and treatment rate is close to that of European and American countries. However, the water quality of urban water bodies is quite different. The high treatment rate hides the truth that sewage is directly discharged without treatment, resulting in serious pollution of urban rivers. With the advancement of black and odorous water body treatment, many urban water bodies have eliminated the black and odor on sunny days, but the black and odorous rivers on rainy days are accompanied. The black and odorous return of urban water bodies on rainy days has become a bottleneck for the treatment of black and odorous water bodies and the improvement of water environment quality. The overflow pollution of drainage outlets on rainy days has become the root cause of the "black water when it rains" in urban water bodies.

[0003] At present, the domestic drainage system is mainly divided into a separate system and a combined system. From the long-term practical experience and actual situation of urban drainage systems at home and abroad, the combined system and the separate system cannot completely avoid overflow pollution. Within the scope of environmental capacity, a certain degree of overflow is even reasonable. Rainy day overflow pollution control is a key measure to promote the treatment of black and odorous rivers, the construction of sponge cities, and the improvement of the quality and efficiency of sewage systems. However, there is currently a lack of treatment standards for combined system overflow pollution. Therefore, how to evaluate overflow pollution and how to formulate reasonable control measures are urgent issues that need to be solved in the current overflow pollution control. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for evaluating and controlling overflow pollution on rainy days. By performing a graded evaluation on the overflow pollution emission characteristics, the amount of pollution load that needs to be reduced is determined based on the control objectives, and targeted governance measures are proposed, thereby achieving effective control of overflow pollution.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for evaluating and controlling overflow pollution on rainy days comprises the following steps:

[0007] S1. Determine the overflow port, evaluation factors and evaluation indicators for overflow pollution assessment;

[0008] S2. Collecting water quality data of the overflow event of the evaluation overflow port;

[0009] S3. Calculate evaluation indicators based on the collected water quality data;

[0010] S4. According to the calculation results of the evaluation indicators, determine the amount of pollution load that needs to be reduced based on the control objectives and formulate control measures.

[0011] The evaluation factor in step S1 is total suspended solids TSS; the evaluation indicators include average concentration of pollutants and initial flushing effect.

[0012] The water quality data in step S2 includes overflow water volume and pollutant concentration.

[0013] In step S2, the data collection period is at least one flood season, and the collected rainfall types include at least two of light rain, moderate rain, heavy rain, and rainstorm. The collection method is manual or automatic monitoring and collection of instantaneous samples.

[0014] Step S2 is to take samples from the overflow port, with a sampling time interval of 10 minutes in the first hour, a sampling time interval of 15-30 minutes after 1 hour, and a sampling time interval of 30-60 minutes after 3 hours, and the sampling time length is not less than 80% of the total overflow time length.

[0015] The calculation method of the event mean concentration is:

[0016]

[0017] Where M is the pollutant load, g; V is the overflow, m 3 ; C t is the pollutant concentration of overflow sampling at time t, mg / L; Q t is the overflow volume in period t, m 3 ; j is the sampling times of a single overflow event; Δt is the sampling time interval, min.

[0018] The evaluation of the initial scour effect is based on the initial scour coefficient b value: when 0<b≤0.185, it is a strong initial scour effect; when 0.185<b≤0.862, it is a moderate initial scour effect; when 0.862<b≤1, it is a weak initial scour effect; when b>1, there is no initial scour effect.

[0019] The calculation method of the initial scour coefficient b is:

[0020] b = log F L,

[0021] Where L is the cumulative pollutant load, %; m(t) is the cumulative pollutant load from zero to time t, kg; M is the total pollutant load of the rainfall, kg; F is the cumulative overflow, %; v(t) is the cumulative overflow of pollutants from zero to time t, m 3; V is the total overflow of a rainfall event, m 3 .

[0022] The control measures include one or more of interception, regulation and storage, and terminal purification. For overflows with strong or moderate initial effects, regulation and storage measures are preferred; if the current regulation and storage facilities cannot meet the standards, interception is adopted; if none of them can be met, new or expanded regulation and storage facilities are constructed, or terminal purification is performed. For overflows with weak or no initial effects, a combination of regulation and storage and terminal purification is adopted.

[0023] The calculation method of the pollution load that needs to be reduced is:

[0024] W 可接收 =(W 总 -W 早天 )×0.8

[0025] M 可接收 =W 可接收 ×T 溢流

[0026] M 溢流 =M 径流 +M 污水 +M 流积物 =(M 径流 +M 污水 ) / 0.5

[0027] M 削减 =M 溢流 -M 可接收

[0028]

[0029] Where W 可接收 W is the pollution-absorbing capacity of the receiving water body on rainy days, g / s; 总 is the total pollution-carrying capacity of the receiving water body, g / s; W 旱天 is the actual pollution level of the receiving water body on dry days, g / s; M 可接收 is the acceptable pollution load of the receiving water body on rainy days, kg; T 溢流 is the time when the overflow event occurs, min; M 溢流 is the total regional overflow pollution load, kg; M 径流 is the total regional rainfall runoff load, kg; M 污水 is the total load of regional combined or mixed sewage, kg; M 沉积物 is the pipeline sediment load, kg; M 削减 is the total reduction of regional overflow pollution load, kg; M 排口削减 is the reduction of overflow pollution load, kg; M 排口 The pollution load discharged from the overflow port is kg.

[0030] Furthermore, the rainy day overflow pollution evaluation and control method also includes the step: S5. Calculate the load contribution rate of each pollution source, determine the main pollution source, and implement targeted control measures on the pollution source.

[0031] The pollution sources include one or more of surface runoff, combined or mixed sewage, and pipeline sediment.

[0032] The load contribution rate calculation method of the pollution source is:

[0033] M 流积物 =M 溢流 -(M 径流 +M 污水 )

[0034] M 污水 =V 污水 ×C 污水

[0035] M 径流 =V 径流 ×C 径流

[0036]

[0037] Where V 污水 is the total amount of combined or mixed sewage, m 3 ; C 污水 V is the concentration of combined or mixed sewage, mg / L; 径流 is the total rainfall runoff, m 3 ; C 径流 is the average concentration of rainfall runoff events, mg / L; C Ri is the average concentration of each runoff underlying surface within the overflow catchment area, mg / L; is the runoff coefficient of each underlying surface; S i is the catchment area of ​​each underlying surface, ha; i is the number of runoff underlying surfaces.

[0038] The beneficial effects of the present invention are as follows: TSS in rainy overflow pollution has a good correlation with other water quality indicators such as COD, TN, and TP. Through TSS concentration evaluation, the control and management of other pollutants can be effectively guided; the present invention is combined with the actual situation of most urban drainage systems, comprehensively considers various types of outlets, and can be applicable to rainy overflow pollution under different drainage systems; the proposed control measures are strictly based on the evaluation results of overflow pollution emission characteristics, and have the advantages of strong pertinence, strong applicability, easy operation, etc., and are suitable for popularization and use. DETAILED DESCRIPTION

[0039] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0040] Example 1

[0041] A method for evaluating and controlling overflow pollution on rainy days comprises the following steps:

[0042] S1. Select multiple overflow outlets of different types in an urban area of ​​a city for overflow pollution evaluation, using total suspended solids (TSS) as the target water quality evaluation factor. The evaluation indicators include average pollutant concentration and initial flushing effect.

[0043] S2. Collect water quality data of the overflow event at the overflow outlet for evaluation, the collected water quality data include overflow water volume and pollutant concentration, the data collection period is one flood season, the collected rainfall types include light rain, moderate rain, heavy rain and rainstorm, and the collection method is manual monitoring and collection of instantaneous samples; sampling starts from the overflow of the overflow outlet, the sampling time interval within the first 1 hour is 10 minutes, the sampling time interval after 1 hour is 15-30 minutes, and the sampling time interval after 3 hours is 30-60 minutes, and the duration of each collection is not less than 80% of the total overflow duration.

[0044] S3. Calculate the evaluation index based on the collected water quality data; the calculation method of the average concentration of pollutants (Event Mean Concentration) is:

[0045]

[0046] Where M is the pollutant load, g; V is the overflow, m 3 ; C t is the pollutant concentration of overflow sampling at time t, mg / L; Q t is the overflow volume in period t, m 3 ; j is the sampling times of a single overflow event; Δt is the sampling time interval, min.

[0047] The calculation method of the initial scour coefficient b is:

[0048] b = log F L,

[0049] Where L is the cumulative pollutant load, %; m(t) is the cumulative pollutant load from zero to time t, kg; M is the total pollutant load of the rainfall, kg; F is the cumulative overflow, %; v(t) is the cumulative overflow of pollutants from zero to time t, m 3; V is the total overflow of a rainfall event, m 3 .

[0050] The maximum emission limit of the target water quality evaluation factor TSS is set at 50 mg / L as specified in the "Sponge City Construction Evaluation Standard" (GB / T 51345-2018). Overflow events with an average concentration below 50 mg / L can be discharged directly, and overflows with an average concentration above 50 mg / L will be evaluated for initial flushing effects.

[0051] Based on the measured data of a city's separate rainwater and sewage overflow outlet, the average TSS concentration of overflow events under different rainfall conditions is shown in Table 1.

[0052] Table 1 Average concentration of TSS in overflow events under different rainfall conditions

[0053] Rainfall events 1 2 3 4 5 6 Average TSS concentration (mg / L) 164.2 133.3 211.7 129.5 117.1 119.4

[0054] The evaluation of the initial scour effect is based on the initial scour coefficient b value: when 0<b≤0.185, it is a strong initial scour effect; when 0.185<b≤0.862, it is a moderate initial scour effect; when 0.862<b≤1, it is a weak initial scour effect; when b>1, there is no initial scour effect.

[0055] S4. According to the calculation results of the evaluation indicators, determine the amount of pollution load that needs to be reduced based on the control objectives and formulate control measures.

[0056] The control measures include one or more of interception, regulation and storage, and terminal purification. For overflows with strong or moderate initial effects, regulation and storage measures are preferred; if the current regulation and storage facilities cannot meet the standards, interception is adopted; if none of them can be met, new or expanded regulation and storage facilities are constructed, or terminal purification is performed. For overflows with weak or no initial effects, a combination of regulation and storage and terminal purification is adopted.

[0057] The calculation method of the pollution load that needs to be reduced is:

[0058] W 可接收 =(W 总 -W 早天 )×0.8

[0059] M 可接收 =W 可接收 ×T 溢流

[0060] M 溢流 =M 径流 +M 污水 +M 沉积物 =(M 径流 +M 污水 ) / 0.5

[0061] M 削减 =M 溢流 -M 可接收

[0062]

[0063] Where W 可接收 W is the pollution-absorbing capacity of the receiving water body on rainy days, g / s; 总 is the total pollution-carrying capacity of the receiving water body, g / s; W 旱天 is the actual pollution level of the receiving water body on dry days, g / s; M 可接收 is the acceptable pollution load of the receiving water body on rainy days, kg; T 溢流 is the time when the overflow event occurs, min; M 溢流 is the total regional overflow pollution load, kg; M 径流 is the total regional rainfall runoff load, kg; M 污水 is the total load of regional combined or mixed sewage, kg; M 沉积物 is the pipeline sediment load, kg; M 削减 is the total reduction of regional overflow pollution load, kg; M 排口削减 is the reduction of overflow pollution load, kg; M 排口 The pollution load discharged from the overflow port is kg.

[0064] According to the relevant provisions of the "Sponge City Construction Evaluation Standard" (GB / T 51345-2018), the annual average reduction in the total amount of TSS of overflow pollutants in the combined system should not be less than 50%. Taking into account the area occupied by the storage pond, economic costs, etc., the optimal operation standard of the storage facility is to intercept 25% of the overflow water volume of the overflow event and intercept 50% of the pollutant load. For drainage areas with a large catchment area, it is advisable to set up a storage pond during the process. The pollution capacity of the receiving water body is calculated based on the natural properties of the water body and the influx of various types of pollution sources. Taking into account the non-point source pollution directly entering the river from the slope on rainy days or the pollution load brought in by the rainwater background, the pollution load discharged into the receiving water body through various overflow outlets, culverts, etc. should be lower than 80% of the actual pollution capacity of the river on rainy days.

[0065] Overflow pollution is characterized by randomness, complexity, and continuity, and has high requirements for the processing time and process of the terminal purification process. Biological processes are not suitable, and physical processes such as rapid filtration, sedimentation, and cyclone separation are suitable. Overflow outlets with low pollution concentrations can be discharged into artificial wetland systems. The effluent quality of the terminal purification process should be based on the standard of Class 1A discharge of sewage treatment plants. When setting up terminal purification devices, the principle of proximity should be adopted, and the treated tail water should be discharged into surrounding rivers as replenishment water.

[0066] S5. Calculate the load contribution rate of each pollution source, identify the main pollution sources, and implement targeted control measures on the pollution sources.

[0067] The pollution sources include one or more of surface runoff, combined or mixed sewage, and pipeline sediment.

[0068] The load contribution rate calculation method of the pollution source is:

[0069] M 沉积物 =M 溢流 -(M 径流 +M 污水 )

[0070] M 污水 =V 污水 ×C 污水

[0071] M 径流 =V 径流 ×C 径流

[0072]

[0073] Where V 污水 is the total amount of combined or mixed sewage, m 3 ; C 污水 V is the concentration of combined or mixed sewage, mg / L; 径流 is the total rainfall runoff, m 3 ; C 径流 is the average concentration of rainfall runoff events, mg / L; C Ri is the average concentration of each runoff underlying surface within the overflow catchment area, mg / L; is the runoff coefficient for each underlying surface; S i is the catchment area of ​​each underlying surface, ha; i is the number of runoff underlying surfaces.

[0074] For surface runoff monitoring, multiple underlying surfaces such as roads, green spaces, and roofs in the drainage area are selected to carry out simultaneous monitoring of water quantity and quality, so as to grasp the pollution characteristics of runoff on different underlying surfaces; for drainage areas with combined or mixed sewage, dry day monitoring is carried out to grasp the daily variation of sewage volume and concentration; because it is difficult to sample pipeline sediments on rainy days, the contribution of pipeline sediment pollution load is obtained based on the difference between the total overflow pollution load and the runoff and sewage load. Table 3 shows the contribution rate of three pollution sources of multiple overflow outlets in a typical rainfall event in a certain city.

[0075] Table 3 Analysis of overflow source in a city

[0076] Sources of pollution Surface runoff Mixed sewage Pipeline sediment Overflow port 1 12.6％ 21.1％ 66.3％ Overflow port 2 9.5％ 52.3％ 38.2％ Overflow port 3 41.9％ 0％ 58.1％

[0077] For the above-mentioned overflow port 1, pipeline sediments are the main source of pollution output, and it is advisable to give priority to using pipeline process control technology for dredging and repair, such as winch dredging, high-pressure water jets, etc.; for overflow port 2, overflow pollution mainly comes from the inside of the pipeline, and it is advisable to give priority to repairing and rectifying the wrong mixing points, increasing the interception multiples, and carrying out dredging and repair; for overflow port 3, it is advisable to carry out sponge city construction in the corresponding drainage area, add low-impact development facilities, and combine gray and green, such as biological retention ponds, green roofs, permeable pavements, etc. At the same time, dredging and repair should be carried out regularly inside the pipeline, and subsequent maintenance management should be strengthened.

[0078] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by technicians in this technical field within the technical scope disclosed in the present invention should be covered within the protection scope of the present invention. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for evaluating and controlling overflow pollution on rainy days, characterized in that: The steps include: S1. Determine the overflow port, evaluation factors and evaluation indicators for overflow pollution assessment; S2. Collecting water quality data for evaluating overflow events at the overflow port; the water quality data includes overflow water volume and pollutant concentration; S3. Calculate the evaluation index based on the collected water quality data; The evaluation indicators include average concentration of pollutants and initial flushing effect; The calculation method of the average concentration of the pollutants is: ; In the formula, M is the pollutant load, g; V is the overflow volume, m³; C t for t Pollutant concentration at overflow sampling at the moment, mg / L; Q t for t Overflow volume during the period, m³; j The sampling times for a single overflow event; Δ t is the sampling time interval, min; The initial flushing coefficient b The calculation method is: ; In the formula, L is the cumulative load of pollutants, %; m(t) Zero to t Accumulated pollutant load at the moment, kg; M is the total amount of pollutant load of rainfall, kg; F is the cumulative overflow, %; v (t) Zero to t Accumulated pollutant overflow at the moment, m 3 ; V is the total overflow of a rainfall event, m 3 ; The evaluation factor is total suspended solids TSS; the maximum discharge limit of the target water quality evaluation factor TSS is set at 50 mg / L, and the overflow port event average concentration below 50 mg / L can be directly discharged, and the overflow port above 50 mg / L is subject to initial flushing effect assessment; The initial flushing effect is evaluated based on the initial flushing coefficient b Value: When 0< b ≤0.185, it is a strong initial scouring effect; when 0.185< b ≤0.862, it is a medium initial scouring effect; when 0.862< b When ≤1, it is a weak initial scouring effect; when b When >1, there is no initial flushing effect; S4. According to the calculation results of the evaluation indicators, determine the amount of pollution load that needs to be reduced based on the control objectives and formulate control measures; The control measures include one or more of interception, storage and terminal purification. For overflow outlets with strong or moderate initial effects, storage measures are adopted; if the current storage and regulation facilities cannot meet the standards, interception is adopted; if all the requirements cannot be met, new storage and regulation facilities are built or expanded, or terminal purification is carried out; for overflow outlets with weak or no initial effect, a combination of storage and regulation and terminal purification is adopted.

2. The rainy day overflow pollution evaluation and control method according to claim 1 is characterized in that: In step S2, the data collection period is at least one flood season, and the collected rainfall types include at least two of light rain, moderate rain, heavy rain, and rainstorm. The collection method is manual or automatic monitoring and collection of instantaneous samples.

3. The rainy day overflow pollution assessment and control method according to claim 1 or 2, characterized in that: Step S2 is to sample from the overflow port, with a sampling time interval of 10 min within the first hour, a sampling time interval of 15-30 min after 1 hour, and a sampling time interval of 30-60 min after 3 hours, and the sampling time length shall not be less than 80% of the total overflow time length.

4. The rainy day overflow pollution evaluation and control method according to claim 1 is characterized in that: The calculation method of the pollution load that needs to be reduced is: ; ; ; ; ; In the formula, W 可接收 is the pollution-absorbing capacity of the receiving water body on rainy days, g / s; W 总 is the total pollution assimilating capacity of the receiving water body, g / s; W 旱天 is the actual pollution level of the receiving water body on dry days, g / s; M 可接收 is the acceptable pollution load of the receiving water body on rainy days, kg; T 溢流 is the time when the overflow event occurs, min; M 溢流 is the total regional overflow pollution load, kg; M 径流 is the total regional rainfall runoff load, kg; M 污水 is the total load of regional combined or mixed sewage, kg; M 沉积物 is the pipeline sediment load, kg; M 削减 is the total reduction of regional overflow pollution load, kg; M 排口削减 is the reduction of pollution load at the overflow port, kg; M 排口 The pollution load discharged from the overflow port is kg.

5. The rainy day overflow pollution assessment and control method according to claim 1, characterized in that: It also includes the steps: S5. Calculate the load contribution rate of each pollution source, determine the main pollution sources, and implement targeted control measures on the pollution sources; The pollution sources include one or more of surface runoff, combined or mixed sewage, and pipeline sediments; the load contribution rate calculation method of the pollution source is: ; ; ; ; In the formula, V 污水 is the total amount of combined or mixed sewage, m 3 ; C 污水 It is the concentration of combined or mixed sewage, mg / L; V 径流 is the total rainfall runoff, m 3 ; C 径流 is the average concentration of rainfall runoff events, mg / L; C Ri is the average concentration of each runoff underlying surface within the overflow catchment area, mg / L; φ i is the runoff coefficient for each underlying surface; S i is the catchment area of ​​each underlying surface, ha; i is the number of underlying surfaces for runoff.

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