Evaluation method for water quality safety of recycled production wastewater of water supply plant
Through an evaluation method based on the principle of fuzzy relationship matrix and maximum membership, the problem of lack of safety assessment of wastewater reuse in water supply plants is solved, and effective judgment and risk reduction of the safety of reused water quality are achieved.
Patent Information
- Application Number
- CN202411835870.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-13
- Publication Date
- 2025-05-13
AI Technical Summary
There is a lack of specific assessment methods for the safety of water quality reuse of wastewater in water supply plants in the prior art, which may lead to a decrease in the quality of water quality of the factory and an increase in the risk of water supply safety.
A method for evaluating the safety of water quality of production wastewater reuse in water supply plants is proposed. By collecting raw water into the plant and the production wastewater samples to be evaluated, the safety evaluation indicators for reuse of production wastewater are selected for testing, and an evaluation factor set is formed. Then, the membership of each evaluation factor corresponding to different evaluation levels is calculated using the trapezoid membership function, forming a fuzzy relationship matrix. Based on the average quotient rate in the factory water in the past year and the square average of the maximum quotient rate, the weight matrix of each evaluation factor is determined, and finally, the comprehensive evaluation is carried out through the principle of maximum membership to judge the safety of reuse of production wastewater.
Through this evaluation method, the water quality safety of production wastewater reuse to water purification process can be effectively judged, the water supply safety risks caused by reuse can be reduced, and the water supply plants can be guided to carry out production wastewater reuse more safely and efficiently.
Smart Images
Figure CN119990851A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of water treatment, in particular to a method for evaluating the water quality safety of recycled wastewater produced by a water supply plant. Background Art
[0002] The production wastewater of a water supply plant mainly refers to the wastewater generated during the production process of the water supply plant to ensure normal operation, mainly including the wastewater generated by the coagulation sedimentation (or clarification) tank, the backwash wastewater and primary filtration water of the sand (or carbon) filter tank, the membrane washing wastewater or concentrated water, the separation water of the sludge dewatering facility, and other process units. In addition, there is a small amount of water generated by the maintenance of facilities and equipment such as the cleaning (or disinfection) water of the water purification structure, the circulating cooling water, and the water quality monitoring discharge water. If the production wastewater of the water supply plant is discharged directly without treatment, it may not only cause environmental pollution problems, but also waste precious water resources, and thus restrict the green transformation and low-carbon development of the water industry to a certain extent, which is contrary to the "water conservation first" water management policy currently advocated by my country.
[0003] By rationally reusing the wastewater produced by water supply plants to the water purification process for re-treatment, the use of chemical agents such as coagulants can be effectively reduced, the water loss rate can be reduced, and the water-saving and low-carbon level of water supply plants can be improved. In view of the increasing importance of urban water conservation, the reuse of wastewater produced by water supply plants has become an important part of the implementation of the "water conservation first" and "low-carbon consumption reduction" policies by water companies in various places, and has received increasing attention from both inside and outside the industry. Faced with the huge demand for the reuse of wastewater produced by water supply plants, there is currently a lack of specific reuse safety assessment methods in water management practices. Unreasonable reuse may lead to a decline in the water quality of the water leaving the plant, increase the risk of water supply safety, and pose a threat to the stability of the water supply system. Therefore, it is urgent to establish a set of assessment methods for the water quality safety of the reuse of wastewater produced by water supply plants, so as to provide scientific and standardized guidance for water supply plants to achieve safe and efficient reuse of wastewater. Summary of the invention
[0004] The present invention provides a method for evaluating the water quality safety of recycled wastewater from a water supply plant, so as to solve the technical problem in the prior art that there is a lack of a specific reuse safety assessment method for recycled wastewater from a water supply plant, thereby preventing an increase in the safety risk of discharged water due to unreasonable reuse.
[0005] In order to achieve the above object, the present invention proposes a method for evaluating the water quality safety of recycled wastewater from a water supply plant, comprising the following steps:
[0006] Collect samples of incoming raw water and production wastewater to be evaluated, select production wastewater reuse safety evaluation indicators for testing, and screen the production wastewater samples for n indicators whose measured maximum values are higher than the basic item Class I standard limit or supplementary item and specific item standard limit in GB 3838 "Surface Water Environmental Quality Standard" 1 ,u2 ,……,u i ……,u n , forming an evaluation factor set U = {u 1 ,u 2 ,……,u i ……,u n};
[0007] For a specific indicator u i A three-level evaluation standard is established, and the membership of each evaluation factor corresponding to different evaluation levels is calculated using the trapezoidal membership function to form a fuzzy relationship matrix R;
[0008] For a specific indicator u i Calculate the average standard rate and the square average of the maximum standard rate in the factory water in the past year Q i , similarly, for any other specific index u j Calculate the average standard rate and the square average of the maximum standard rate in the water discharged from the factory in the past year Q j , and obtain the relative importance judgment matrix D of each evaluation factor:
[0009]
[0010] Among them, d ij Q i With Q j The ratio of
[0011] Find the eigenvector corresponding to the maximum eigenvalue of D, and normalize the eigenvector to obtain the weight matrix B of each evaluation factor = [b 1 ,b 2 ,……,b i ……,b n ];
[0012] Matrix dot product B·R=[f 1 ,f 2 ,f 3 ], the maximum membership principle is adopted to determine the evaluation level corresponding to the maximum membership value in B·R, which is the comprehensive evaluation level of industrial wastewater corresponding to the three-level evaluation standard.
[0013] In a preferred embodiment, the safety evaluation indicators for the reuse of production wastewater include permanganate index, ammonia nitrogen, iron, manganese, copper, zinc, selenium, arsenic, mercury, cadmium, chromium (hexavalent), lead, molybdenum, beryllium, boron, antimony, nickel, barium, thallium, chloroform, acrylamide, and fecal coliform.
[0014] In a preferred embodiment, in the three-level evaluation standard, the first-level evaluation level indicates that the water quality risk before being directly reused to the front-end treatment facility of the water supply plant is low. Before it can be reused to the appropriate treatment facility of the water supply plant, the corresponding first-level limit value should not be higher than half of the maximum value of the raw water measured, half of the standard limit value of Class II of the basic project of GB3838, or the standard limit value of the supplementary project or specific project of the water quality index before being reused directly to the front-end treatment facility of the water supply plant. The second-level evaluation level indicates that the water quality risk before being directly reused to the front-end treatment facility of the water supply plant is relatively low. The water cannot be reused to the front-end treatment facilities of the water supply plant before it is reused. Its corresponding second-level limit should not be higher than the maximum value actually measured for raw water, the standard limit of Class III of the basic items of GB3838, or the standard limit of supplementary items or specific items; the third-level evaluation grade means that the water quality risk is higher before it is directly reused to the front-end treatment facilities of the water supply plant without treatment. The water cannot be reused to the front-end treatment facilities of the water supply plant without treatment. Its corresponding third-level limit should not be higher than twice the maximum value actually measured for raw water, the standard limit of Class IV of the basic items of GB3838, or the standard limit of supplementary items or specific items.
[0015] In a preferred embodiment, a trapezoidal membership function is used to calculate the membership of each indicator in the evaluation factor set U corresponding to the first-level, second-level, and third-level evaluation levels. The fuzzy relationship matrix R of the evaluation factor set U is as follows:
[0016]
[0017] Among them, r 1 (x i ), r 2 (x i ), r 3 (x i ) are the specific indicators u in the evaluation factor set U i The maximum value of x i When , it corresponds to the first, second and third level evaluation levels.
[0018] In a preferred embodiment, the specific indicator u i The maximum value of x i When , the trapezoidal membership function used is as follows:
[0019]
[0020] Among them, a, b, c are specific indicators u i The first-level limit, second-level limit and third-level limit of the three-level evaluation standard.
[0021] In a preferred embodiment, the specific indicator u i The average proportion of standard water in the factory in the past year W iand the maximum occupancy rate M i They are:
[0022]
[0023] M i =max[max(x i / L i ),0.01]
[0024] Among them, x i , L i are specific indicators u i The measured maximum value and the factory water standard limit, N is the specific index u i The number of tests in the factory water in the past year; i is fecal coliform group, x i , L i are the maximum value of Escherichia coli measured and the standard limit of factory water, respectively; N is the number of times Escherichia coli was detected in factory water in the past year.
[0025] In a preferred embodiment, the maximum membership principle is adopted as follows: when f 1 >max(f 2 ,f 3 ) the comprehensive evaluation level of production wastewater is level one, when f 2 >max(f 1 ,f 3 ) or f 2 =f 1 >f 3 The comprehensive evaluation level of production wastewater is Level 2 when the wastewater is produced, and it is Level 3 in other cases.
[0026] The present invention provides an evaluation method for the water quality safety of recycled production wastewater from a water supply plant. The method determines the relative importance weight of each indicator in the fuzzy evaluation through the percentage of each evaluation factor in the water discharged from the plant in the past year, and conducts a multi-indicator comprehensive evaluation on the reuse safety of the production wastewater based on the fuzzy set theory. Through the fuzzy evaluation based on the maximum membership principle, the water quality safety of specific production wastewater reused in the water purification process for re-treatment is intuitively judged, which is of great significance for reducing the water supply safety risk caused by the reuse of production wastewater and guiding the water supply plant to carry out the reuse of production wastewater more safely and efficiently. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0028] Figure 1 A flow chart of the steps of a method for evaluating the water quality safety of recycled wastewater from a water supply plant disclosed in the present invention;
[0029] Figure 2 It is the function graph of the trapezoidal membership function used in the present invention. DETAILED DESCRIPTION
[0030] In order to make the above and other features and advantages of the present invention more clear, the present invention is further described below in conjunction with the accompanying drawings. It should be understood that the specific embodiments given herein are for the purpose of explaining to those skilled in the art and are only exemplary and not restrictive.
[0031] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.
[0032] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.
[0033] like Figure 1 As shown, according to an embodiment of the present invention, a method for evaluating the water quality safety of recycled wastewater from a water supply plant is provided, comprising the following steps:
[0034] S11, collect samples of incoming raw water and production wastewater to be evaluated, select production wastewater reuse safety evaluation indicators for testing, and screen the production wastewater samples for n indicators u whose maximum values actually measured are higher than the basic item Class I standard limit or the supplementary item and specific item standard limit in GB 3838 "Surface Water Environmental Quality Standard" 1 ,u 2 ,……,u i ……,u n , forming an evaluation factor set U = {u 1 ,u 2 ,……,u i ……,u n}.
[0035] Among them, the safety evaluation indicators for industrial wastewater reuse include permanganate index, ammonia nitrogen, iron, manganese, copper, zinc, selenium, arsenic, mercury, cadmium, chromium (hexavalent), lead, molybdenum, beryllium, boron, antimony, nickel, barium, thallium, chloroform, acrylamide, and fecal coliform.
[0036] S12, for a specific indicator u i A three-level evaluation standard is established, and the trapezoidal membership function is used to calculate the membership of each evaluation factor corresponding to different evaluation levels to form the fuzzy relationship matrix R.
[0037] In a preferred embodiment, in the three-level evaluation standard, the first-level evaluation level indicates that the water quality risk before being directly reused to the front-end treatment facility of the water supply plant is low. Before it can be reused to the appropriate treatment facility of the water supply plant, the corresponding first-level limit value should not be higher than half of the maximum value of the raw water measured, half of the standard limit value of Class II of the basic project of GB3838, or the standard limit value of the supplementary project or specific project of the water quality index before being reused directly to the front-end treatment facility of the water supply plant. The second-level evaluation level indicates that the water quality risk before being directly reused to the front-end treatment facility of the water supply plant is relatively low. The water cannot be reused to the front-end treatment facilities of the water supply plant before it is reused. Its corresponding second-level limit should not be higher than the maximum value actually measured for raw water, the standard limit of Class III of the basic items of GB3838, or the standard limit of supplementary items or specific items; the third-level evaluation grade means that the water quality risk is higher before it is directly reused to the front-end treatment facilities of the water supply plant without treatment. The water cannot be reused to the front-end treatment facilities of the water supply plant without treatment. Its corresponding third-level limit should not be higher than twice the maximum value actually measured for raw water, the standard limit of Class IV of the basic items of GB3838, or the standard limit of supplementary items or specific items.
[0038] In a preferred embodiment, a trapezoidal membership function is used to calculate the membership of each indicator in the evaluation factor set U corresponding to the first-level, second-level, and third-level evaluation levels. The fuzzy relationship matrix R of the evaluation factor set U is as follows:
[0039]
[0040] Among them, r 1 (x i ), r 2 (x i ), r 3 (x i ) are the specific indicators u in the evaluation factor set U i The maximum value of x i When , it corresponds to the first, second and third level evaluation levels.
[0041] Specific indicators i The maximum value of x i When , the trapezoidal membership function used is as follows:
[0042]
[0043]
[0044] Among them, a, b, c are specific indicators u i The first-level limit, second-level limit and third-level limit of the three-level evaluation standard.
[0045] S13, for a specific indicator u i Calculate the average standard rate and the square average of the maximum standard rate in the water discharged from the factory in the past year Q i , similarly, for any other specific index u j Calculate the average standard rate and the square average of the maximum standard rate in the water discharged from the factory in the past year Q j , and obtain the relative importance judgment matrix D of each evaluation factor:
[0046]
[0047] Among them, d ij Q i With Q j The ratio of
[0048] Among them, the specific indicator u i The average proportion of standard water in the factory in the past year W i and the maximum occupancy rate M i They are:
[0049]
[0050] M i =max[max(x i / L i ),0.01]
[0051] In the above formula, x i , Li are specific indicators u i The measured maximum value and the factory water standard limit, N is the specific index u i The number of tests in the factory water in the past year; i is fecal coliform group, x i , L i are the maximum value of Escherichia coli measured and the standard limit of factory water, respectively; N is the number of times Escherichia coli was detected in factory water in the past year.
[0052] S14, find the eigenvector corresponding to the maximum eigenvalue of D, and normalize the eigenvector to obtain the weight matrix B of each evaluation factor = [b 1 ,b 2 ,……,b i ……,b n ];
[0053] S15, matrix dot product B·R=[f 1 ,f 2 ,f 3 ], the maximum membership principle is adopted to determine the evaluation level corresponding to the maximum membership value in B·R, which is the comprehensive evaluation level of industrial wastewater corresponding to the three-level evaluation standard.
[0054] In this embodiment, the maximum membership principle adopted is that when f 1 >max(f 2 ,f 3 ) the comprehensive evaluation level of production wastewater is level one, when f 2 >max(f 1 ,f 3 ) or f 2 =f 1 >f 3 The comprehensive evaluation level of production wastewater is Level 2 when the wastewater is produced, and it is Level 3 in other cases.
[0055] In order to further illustrate the technical solution of the present application, a specific example is provided below.
[0056] In the following embodiments, taking a water supply plant in East China as an example, the daily designed water supply scale can reach 100,000 tons. The embodiment of the present invention is implemented in one of the production lines with a daily designed water supply scale of 50,000 tons and adopting the "pre-ozone → coagulation and sedimentation → sand filtration → post-ozone → carbon filtration → ultrafiltration → disinfection" water purification process.
[0057] In this embodiment, from January to June 2023, the permanganate index, ammonia nitrogen, iron, manganese, copper, zinc, selenium, arsenic, mercury, cadmium, chromium (hexavalent), lead, molybdenum, beryllium, boron, antimony, nickel, barium, thallium, chloroform, acrylamide, and fecal coliform group of the raw water, carbon filter backwash wastewater, and ultrafiltration physical flushing wastewater samples of the water supply plant are collected once a month. For the carbon filter backwash wastewater samples, the indicators whose maximum measured maximum values may exceed the standard limits of Class I of the basic items of GB 3838 or the standard limits of the supplementary items and specific items are permanganate index (maximum 2.0 mg / L), ammonia nitrogen (maximum 0.45 mg / L), and mercury (maximum 0.00013 mg / L), and the evaluation factor set U T ={permanganate index, ammonia nitrogen, mercury}; for ultrafiltration physical flushing wastewater samples, the maximum measured maximum values that may exceed the standard limits of Class I of basic items in GB 3838 or the standard limits of supplementary items and specific items are ammonia nitrogen (maximum 0.25 mg / L), mercury (maximum 0.00007 mg / L), and fecal coliform bacteria (maximum 3000 / L). The evaluation factor set U UF ={ammonia nitrogen, mercury, fecal coliform}.
[0058] Establish a three-level evaluation standard. Based on the test results of raw water samples entering the factory from January to June 2023, the limit values of each level of the three-level evaluation standards for permanganate index, ammonia nitrogen, mercury, and fecal coliform group are shown in Table 1.
[0059] Table 1 Limits of evaluation factors at various levels of evaluation standards
[0060]
[0061] For a specific indicator, a, b, c, and x are the first-level limit, second-level limit, and third-level limit of the three-level evaluation standard and the measured maximum value of the indicator, respectively. The trapezoidal membership function shown below is used (the function graph is shown in Figure 2 As shown), calculate the membership r corresponding to the first, second and third level evaluation levels 1 (x), r 2 (x), r 3 (x), and obtain the evaluation factor set U T and U UF The fuzzy relationship matrix R T , R UF They are as follows:
[0062]
[0063] According to the test results of the water discharged from the water supply plant from January to December 2022, the average percentage, maximum percentage and square average of each indicator in the water discharged from the water supply plant in the past year are shown in Table 2.
[0064] Table 2 Average percentage, maximum percentage and square average of each indicator
[0065] Permanganate Index Ammonia nitrogen mercury Fecal coliform bacteria Average bid rate 0.41 0.52 0.18 0.01 Maximum Occupancy Rate 0.48 0.62 0.40 0.01 Square mean 0.45 0.57 0.31 0.01
[0066] Evaluation factor set U T and U UF The relative importance judgment matrix D of each evaluation factor T , D UF They are as follows:
[0067]
[0068] Evaluation factor set U T and U UF The weight matrix B of each evaluation factor T , B UF They are as follows:
[0069] B T =[0.338 0.429 0.233]
[0070] B UF =[0.641 0.347 0.012]
[0071] Matrix dot product B T ·R T =[0 0.571 0.429], the maximum membership principle was used to determine that the comprehensive evaluation level of carbon filter backwash wastewater corresponding to the three-level evaluation standard was level 2, and the water quality risk before it was directly reused to the front-end treatment facilities of the water supply plant was low, and it could not be reused after the front-end treatment facilities of the water supply plant before being treated.
[0072] Matrix dot product B UF ·B UF =[0.073 0.927 0], the maximum membership principle was used to determine that the ultrafiltration physical flushing wastewater corresponded to the second level of the comprehensive evaluation standard of the third-level evaluation standard. The water quality risk before it is directly reused to the front-end treatment facilities of the water supply plant is low, and it cannot be reused after the front-end treatment facilities of the water supply plant before being treated.
[0073] According to the evaluation results of the water quality safety of the two types of production wastewater reused from the water supply plant, the carbon filter backwash wastewater and ultrafiltration physical flushing wastewater were directly reused before the front-end treatment facilities of the water supply plant, and the water quality of the water outgoing water of the water supply plant was tracked and monitored. All water quality indicators in the outgoing water from July 2023 to June 2024 met the standard limits of outgoing water, with a compliance rate of 100%, and the average percentage of each water quality indicator was basically the same as before the reuse. After the water quality safety evaluation of the reused production wastewater of the water supply plant, the reuse of the two types of production wastewater did not cause the water quality of the outgoing water to deteriorate and the risk of water supply safety to increase.
[0074] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.
Claims
1. A method for evaluating the water quality safety of recycled wastewater from a water supply plant, characterized in that: The steps include: S11, collect samples of incoming raw water and production wastewater to be evaluated, select production wastewater reuse safety evaluation indicators for testing, and screen the production wastewater samples for n indicators u1, u2, ..., u1, whose maximum values are higher than the standard limits of basic items Class I or supplementary items and specific items in GB 3838. i ……,u n , forming an evaluation factor set U = {u1,u2,……,u i ……,u n }; S12, for a specific indicator u i A three-level evaluation standard is established, and the membership of each evaluation factor corresponding to different evaluation levels is calculated using the trapezoidal membership function to form a fuzzy relationship matrix R; S13, for a specific indicator u i Calculate the average standard rate and the square average of the maximum standard rate in the water discharged from the factory in the past year Q i , similarly, for any other specific index u j Calculate the average standard rate and the square average of the maximum standard rate in the water discharged from the factory in the past year Q j , and obtain the relative importance judgment matrix D of each evaluation factor: Among them, d ij Q i With Q j The ratio of S14, find the eigenvector corresponding to the maximum eigenvalue of D, and normalize the eigenvector to obtain the weight matrix B of each evaluation factor = [b1, b2, ..., b i ……,b n ]; S15, matrix dot product B·R=[f1,f2,f3], the maximum membership principle is adopted to determine the comprehensive evaluation level of the production wastewater corresponding to the three-level evaluation standard.
2. The evaluation method according to claim 1, characterized in that: The safety evaluation indicators for industrial wastewater reuse include permanganate index, ammonia nitrogen, iron, manganese, copper, zinc, selenium, arsenic, mercury, cadmium, hexavalent chromium, lead, molybdenum, beryllium, boron, antimony, nickel, barium, thallium, chloroform, acrylamide, and fecal coliform.
3. The evaluation method according to claim 1, characterized in that: Among the three-level evaluation standards, the first-level evaluation level indicates that the water quality risk before being directly reused to the front-end treatment facilities of the water supply plant is low. On the premise of ensuring that the various water quality indicators of the outgoing water are not lower than the reuse point, it can be reused to the appropriate treatment facilities of the water supply plant. The corresponding first-level limit should not be higher than half of the maximum value of the raw water measured, half of the standard limit of Class II of the basic items of GB3838 or the standard limit of the supplementary items and specific items; the second-level evaluation level indicates that the water quality risk before being directly reused to the front-end treatment facilities of the water supply plant is low, and it cannot be reused before being treated. After being used in the front-end treatment facilities of the water supply plant, its corresponding secondary limit should not be higher than the maximum value actually measured for raw water, the standard limit of Class III of the basic items of GB3838, or the standard limit of supplementary items or specific items; the third-level evaluation level means that the water quality risk before being directly reused in the front-end treatment facilities of the water supply plant is higher, and it cannot be reused in the front-end treatment facilities of the water supply plant without treatment. Before being reused in the front-end treatment facilities of the water supply plant, its corresponding third-level limit should not be higher than twice the maximum value actually measured for raw water, the standard limit of Class IV of the basic items of GB3838, or the standard limit of supplementary items or specific items.
4. The evaluation method according to claim 1, characterized in that: The trapezoidal membership function is used to calculate the membership of each indicator in the evaluation factor set U corresponding to the first-level, second-level, and third-level evaluation levels. The fuzzy relationship matrix R of the evaluation factor set U is as follows: Among them, r1(x i )、r2(x i )、r3(x i ) are the specific indicators u in the evaluation factor set U i The maximum value of x i When , it corresponds to the first, second and third level evaluation levels.
5. The evaluation method according to claim 4, characterized in that: Specific indicators i The maximum value of x i When , the trapezoidal membership function used is as follows: Among them, a, b, c are specific indicators u i The first-level limit, second-level limit and third-level limit of the three-level evaluation standard.
6. The evaluation method according to claim 1, characterized in that: Specific indicators i The average proportion of standard water in the factory in the past year W i and the maximum occupancy rate M i They are: M i =max[max(x i / L i ),0.01] Among them, x i , L i are specific indicators u i The measured maximum value and the factory water standard limit, N is the specific index u i Number of tests in factory water in the past year.
7. The evaluation method according to claim 1, characterized in that: The maximum membership principle adopted is that when f1>max(f2,f3), the comprehensive evaluation level of production wastewater is level one; when f2>max(f1,f3) or f2=f1>f3, the comprehensive evaluation level of production wastewater is level two; in other cases, the comprehensive evaluation level of production wastewater is level three.