Method for predicting risk of disinfection by-products in reclaimed water of sewage plant

Abstract

The invention belongs to the technical field of new pollutant environmental risk evaluation, and discloses a method for predicting the risk of disinfection by-products in reclaimed water of a sewage plant, which comprises the following steps: defining a safety boundary value MOS of a fault event as an event in which a disinfection by-product discharge index exceeds a system design limit, setting the national standard permission as a maximum limit value Lm, and representing the numerical value by y; a variable F is calculated, a risk event, namely an event with F larger than 1, is defined as P, a numerical value obtained through calculation of the event P is represented by p, F accords with normal distribution, a value of a risk critical value Lc is obtained through calculation and is represented by l, and then the interval (l, y) is the MOS range of the disinfection by-product. Based on the probability density method, the early warning information of the discharge amount of the disinfection by-products is obtained, and the discharge water quality risk of the urban sewage treatment plant is discriminated and predicted. The method is high in prediction accuracy, and can reduce or eliminate risks caused by accumulation of disinfection by-products in the process treatment of the sewage plant, thereby protecting the environment and public health.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental risk assessment of new pollutants, and relates to a method for assessing and warning the risk of disinfection by-products in urban sewage treatment processes, and specifically relates to a method for predicting the risk of disinfection by-products in recycled water of a sewage treatment plant. Background Art

[0002] The main function of urban sewage treatment plants is to treat urban domestic sewage and industrial wastewater to reduce the discharge of pollutants and protect the water environment. After being treated by the sewage treatment plant, water that meets certain water quality standards is recycled water, which can be used for non-drinking purposes, such as urban landscape, agricultural irrigation, industrial water, etc. When recycled water that does not meet safety standards is reused in the ecological water environment, it will have a toxic effect on aquatic animals and plants, and further endanger human health through the food chain or water cycle. The safety of recycled water depends on its treatment process and the water quality standards that are finally achieved. Recycled water treatment usually includes multiple links such as pretreatment, biological treatment, solid-liquid separation, advanced treatment and disinfection to effectively remove harmful substances in sewage, such as pathogens, heavy metals and organic pollutants. However, some soluble organic matter is difficult to be completely biodegraded and will remain in the water. These substances will react with chlorine in the subsequent chlorination process to generate various disinfection by-products (Disinfection By-Products, DBPs). The generation of disinfection by-products can induce various types of diseases and endanger ecological safety and human health. Therefore, in order to ensure the safety and effective use of recycled water, controlling the content of DBPs in recycled water has become an important guarantee for water quality safety. Targeted management of disinfection by-products, online analysis and application of real-time data, development of scientific calculation methods, and multi-pronged implementation of scientific management and application of water resources are carried out.

[0003] Margin of Safety (MOS) usually refers to the maximum range allowed for a parameter in a specific system or process. Once this range is exceeded, dangerous problems may occur in the system. In the early stage, the MOS method was used to warn of risks such as eutrophication of water bodies, sludge bulking in biological treatment processes, and toxic substances in food, and its application in preventing water pollution problems in large river basins, production process stability problems, and food safety problems was explored. Based on probabilistic statistical analysis, the present invention calculates the safe boundary range of DBPs emissions during the disinfection of reclaimed water, which involves redefinition of risk management and water quality safety, ensuring that the reclaimed water meets the predetermined safety standards after disinfection, while taking into account possible uncertainties in the treatment process. By setting a safe boundary value, the discharge of disinfection by-products is managed without exceeding the preset risk level, thereby ensuring the safety and effective use of reclaimed water.

[0004] Since there is currently no risk prediction method for the content of disinfection by-products in sewage treatment plant drainage, the present invention fills this gap and can be used not only for early warning of the content of disinfection by-products, but also for early warning of the content of other harmful pollutants, providing technical support for ensuring that the drainage water quality of sewage treatment plants meets the standards and reducing and eliminating the risks caused by DBPs. Summary of the invention

[0005] The patent of this invention aims to take preventive measures before the problem occurs to reduce the formation of DBPs. It comprehensively considers historical data and on-site monitoring data, uses probability theory and statistical methods to set a safety boundary, finds the safe range value of disinfection by-product emission indicators, and ultimately achieves risk prevention and control of drainage water quality.

[0006] The technical solution of the present invention is as follows:

[0007] A method for predicting the risk of disinfection byproducts in the reclaimed water of a sewage treatment plant is provided. The safety margin range MOS is defined as the difference between the load associated with the maximum limit value Lm and the load associated with the risk critical value Lc of the national standard permitted emission index of the disinfection byproducts, and is calculated according to formula (1). A fault event is defined as an event in which the disinfection byproduct emission index exceeds the system design limit.

[0008] MOS=Lm-Lc (1)

[0009] The variable F is defined as the ratio of the actual amount of disinfection byproducts discharged z to the maximum limit value Lm (the value of Lm is represented by y), which can be calculated according to formula (2), and the obtained value is represented by f. Then F < 1 represents a successful event, that is, the disinfection byproducts discharge meets the standard; F > 1 represents a risk event, that is, the disinfection byproducts discharge does not meet the standard.

[0010] F=z / y=f (2)

[0011] Define the risk event, i.e., the event with F>1, as P, and calculate it according to formula (3):

[0012]

[0013] Where p(f) is the probability density function of F, and F conforms to the normal distribution. The calculated value of event P is expressed as p. The risk critical value Lc can be considered as the difference between the maximum limit value Lm permitted by the national standard and the risk value. Therefore, when the disinfection byproduct emission index is normally distributed, it can be calculated by formula (4):

[0014] MOS=Lm-(Lm-H risk *S)=H risk *S (4)

[0015] Where: S is the standard deviation of multiple numbers f calculated by formula (2), and the result is represented by s;

[0016] H risk : The standard normal distribution number for any specified acceptable risk level is obtained by looking up the result p in the table, and the result is denoted as h.

[0017] According to formula (4), the MOS value is expressed as m, as shown in formula (5):

[0018] MOS=H risk *S=h*s=m (5)

[0019] The value of Lc is obtained according to formula (1), represented by l, which is formula (6).

[0020] Lc=ym=l (6)

[0021] The interval (l, y) is the MOS range of disinfection by-products.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention uses the safety boundary value method to warn the discharge of disinfection byproducts, thereby achieving a certain risk prediction for the water quality of urban sewage treatment plants. The early warning results are highly accurate, which reduces the risks brought by the accumulation of disinfection byproducts in the process of sewage treatment plants to a certain extent, thereby protecting the environment and public health. The application of the MOS method provides a reasonable range for the safe discharge of disinfection byproducts in the effluent of sewage treatment plants, improves the quality of drinking water, and can also provide a scientific basis for the formulation of relevant regulatory policies and standards, and promote the construction of laws and regulations for the safe management of recycled water. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The normal distribution diagram of chloroform in water was obtained by three sampling measurements. DETAILED DESCRIPTION

[0025] The present invention is described in detail below by specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0026] In addition to being applied to "predicting the risk of disinfection by-products in recycled water from sewage treatment plants", the invention of this application can be expanded to other fields. It only needs to monitor the emission data of a certain harmful substance in the sewage treatment plant, and then use this algorithm to calculate its safety boundary value, give a certain risk range, and issue an early warning.

[0027] The main disinfection by-products include trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitrile (HANs), formaldehyde, acetaldehyde, chloropicrin, 2,4,6-trichlorophenol, etc.

[0028] Chloroform is the most representative substance in disinfection byproducts, so this application uses this as an example to set the safety boundary value. If the data of other disinfection byproducts in sewage treatment plants are known, this invention can also be used to set their safety boundary values.

[0029] Example 1

[0030] During the chlorination process of drinking water, chlorine reacts with natural organic matter in the water to generate more than 600 DBPs with toxic and "three-hazard" effects, among which trihalomethanes have the highest content, accounting for 20.1% of DBPs; haloacetic acid is second, accounting for about 12.8%. The most common and representative of trihalomethanes is chloroform (CHCl3), and various studies have shown that the critical value of the amount of disinfection by-products affecting water quality is uncertain. Since chloroform is representative, chloroform is taken as an example.

[0031] The international standard emission limit of chloroform is 0.06mg / L, which is the maximum value Lm of chloroform in the normal drainage of the plant. The sewage treatment effect of the plant is relatively stable. The average chloroform content measured by annual sampling is 0.0594mg / L, and the standard deviation S is 0.0245.

[0032] Table 1 Monitoring results of chloroform in 1789 municipal water supplies in Guangyuan City from 2019 to 2022

[0033]

[0034] (Note: )

[0035] Because F>1 is a fault event, the maximum F value in the five samples is taken as the upper limit, so the interval of F is set to (1,4).

[0036]

[0037] From this, we can get H by looking up the standard normal quantile table. risk =0.5438,

[0038] So MOS=H risk *S=0.5438×0.0245=0.0133.

[0039] According to formula (1), the critical value of chloroform can be obtained as Lc=Lm-MOS=0.06-0.0133=0.0467mg / L. It can be deduced that the safety margin range of chloroform is 0.0467~0.06mg / L, that is, Figure 1 The area between the two red dotted lines and the blue area are the risk areas.

[0040] According to the above calculation of chloroform emission indicators for sewage treatment plants, if the content of disinfection by-products is lower than 0.0467 mg / L, it indicates that the sewage treatment system is stable and the quality of recycled water discharge meets the requirements; if the content of disinfection by-products is in the MOS area of ​​0.0467-0.06 mg / L, it indicates the need for close attention and analysis of process conditions to prevent the occurrence of uncertain risks; if the content of disinfection by-products is higher than 0.06 mg / L, it indicates the occurrence of risks, that is, the recycled water treatment is unqualified.

[0041] The data document in Example 1 comes from the analysis of arsenic and chloroform content and health risk assessment in Guangyuan municipal water supply from 2019 to 2022.

[0042] The above-described embodiments are only preferred embodiments of the present invention, but not all feasible embodiments of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A method for predicting the risk of disinfection by-products in recycled water from a sewage treatment plant, characterized in that: The fault event safety boundary range MOS is defined as the event that the disinfection byproduct emission index exceeds the system design limit, and its national standard permission is set to the maximum limit value Lm, and the value is expressed by y; Calculate the variable F, define the risk event, i.e., the event with F>1, as P, and define the calculated value of event P as p. F conforms to the normal distribution, and the risk critical value Lc of disinfection by-products is calculated. The value is expressed by l, and the interval (l, y) is the MOS range of disinfection by-products.

2. The method for predicting the risk of disinfection byproducts in recycled water from a sewage treatment plant according to claim 1, characterized in that: MOS is calculated according to formula (1): MOS=Lm-Lc (1).

3. The method for predicting the risk of disinfection byproducts in recycled water from a sewage treatment plant according to claim 1, characterized in that: The variable F is calculated according to formula (2): F=z / y=f (2).

4. The method for predicting the risk of disinfection byproducts in recycled water from a sewage treatment plant according to claim 1, wherein P Calculate according to formula (3): Where p(f) is the probability density function of F, F is assumed to be normally distributed, and the calculated value of event P is expressed by p.

5. The method for predicting the risk of disinfection byproducts in recycled water of a sewage treatment plant according to claim 1, characterized in that: When the disinfection byproduct emission index is normally distributed, it is calculated by formula (4): MOS=Lm-(Lm-H risk *S)=H risk *S (4) Where: S is the standard deviation of multiple numbers f calculated by formula (2), and the result is represented by s; H risk : The standard normal distribution number for any specified acceptable risk level can be obtained by looking up the result p in the table and expressing it in h; According to formula (4), the value of MOS is expressed as m, as shown in formula (5): MOS=H risk *S=h*s=m(5)。 6. The method for predicting the risk of disinfection byproducts in recycled water from a sewage treatment plant according to claim 1, characterized in that: Lc is calculated according to formula (1).

7. The method for predicting the risk of disinfection byproducts in recycled water from a sewage treatment plant according to claim 1, characterized in that: l is calculated according to formula (6): Lc=ym=l (6).

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