Sampling analysis method suitable for composite water source circulating water system

Abstract

The invention relates to a sampling analysis method suitable for a composite water source circulating water system. According to the composite water source circulating water system, water from various different sources is mixed and recycled. The sampling analysis method comprises the step of setting sampling points at different positions of the circulating water system, wherein the positions cover a water source inlet, a mixing area, a key equipment inlet and outlet and the like. And the sampling accuracy and representativeness are ensured by adopting specific sampling tools and devices. The collected samples are subjected to multi-parameter analysis, including chemical oxygen demand (COD), biochemical oxygen demand (BOD), suspended solids (SS), hardness, pH value (pH) and other indexes of water quality. By establishing the data analysis model and comprehensively evaluating the quality condition of the circulating water, a scientific basis is provided for operation management, water quality regulation and control and equipment maintenance of the circulating water system, the operation efficiency of the composite water source circulating water system is effectively improved, the treatment cost is reduced, and the service life of equipment is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of circulating water systems, and particularly to a sampling and analysis method applicable to a composite water source circulating water system. Background Art

[0002] With the increasingly serious problem of water resource shortage, composite water source circulating water systems have been widely used in the fields of industry, agriculture, and urban water supply. A composite water source circulating water system is a system that mixes multiple water sources from different origins (such as surface water, groundwater, reclaimed water, etc.) and then recycles them. Although such a system can effectively save water resources, due to the different water quality characteristics of different water sources, complex changes in water quality may occur during the mixing and circulation process.

[0003] At present, there are some deficiencies in the water quality monitoring and analysis of composite water source circulating water systems. Traditional sampling methods often lack systematicness and cannot comprehensively reflect the water quality conditions in the entire circulating water system. For example, sampling at a single location may not be able to capture water quality differences caused by uneven water flow mixing or local reactions. Moreover, existing analysis methods may not accurately consider the influence of the interaction between different water source components on water quality indicators when dealing with composite water sources. In addition, there is a lack of effective data analysis means to comprehensively evaluate the water quality conditions, making it difficult to accurately regulate and manage the operation of the circulating water system.

[0004] Therefore, a sampling and analysis method specifically applicable to a composite water source circulating water system is needed, which can accurately and comprehensively obtain water quality information and conduct effective analysis to ensure the stable and efficient operation of the circulating water system. Summary of the Invention

[0005] 1. Setting of sampling points: Sampling points are set on the inlet pipes of each different type of water source (such as surface water inlet, groundwater inlet, reclaimed water inlet, etc.) entering the composite water source circulating water system. These sampling points should be located on the straight pipe sections of the pipes, at least 5 times the pipe diameter away from equipment that may affect the water flow state, such as pipe elbows and valves, to ensure that the collected water samples can represent the initial water quality of the corresponding water source. The number of sampling points is determined according to the actual types of water sources and the system scale. For a large-scale composite water source circulating water system, if there are multiple inlets of the same type of water source, sampling points should be evenly set at each inlet to comprehensively understand the water quality of different inlet water sources.

[0006] Set multiple sampling points in the area after different water sources are mixed. Since the mixing process may not be completely uniform, the sampling points should be distributed at different positions in the mixing area, including the center, edge of the mixing area, and at different distances from the mixing and stirring equipment (if any). According to the shape and size of the mixing area, the sampling points can be set in a grid-like distribution. For example, for a rectangular mixing area, sampling points can be set along the long side and short side at a certain interval (such as every 1 - 2 meters) to form a grid, ensuring that representative samples of the water quality after mixing can be accurately obtained.

[0007] Set sampling points at the inlets and outlets of key equipment related to water quality treatment (such as filters, cooling towers, heat exchangers, etc.) in the circulating water system. Sampling at the equipment inlet can understand the water quality condition before entering the equipment, so as to evaluate the water quality treatment effect of the equipment; sampling at the equipment outlet can determine whether the equipment is operating normally and whether the expected water quality treatment goal is achieved. The position of the sampling point should avoid being affected by abnormal internal flow fields of the equipment. For example, for equipment with complex internal structures, the sampling point should be set in the straight pipe section at the inlet and outlet of the equipment, at least 3 times the pipe diameter away from the connection of the equipment inlet and outlet.

[0008] 2. Sampling tools and devices, using a specially designed multi-channel sampler. The sampler has multiple independent sampling channels, and each channel can be connected to a different sampling point. The material of the sampler should have good chemical stability and will not react chemically with the components in the water sample. For example, stainless steel or polytetrafluoroethylene materials can be used. The diameter of the sampling channel should be reasonably selected according to the expected water sample flow rate and sampling speed. Generally speaking, for areas with small flow rates but rapid water quality changes (such as near the water source inlet), sampling channels with a smaller diameter (such as 0.5 - 1 cm) can be used to improve the sampling resolution; while for the mixing area or equipment inlets and outlets with larger flow rates, the sampling channel diameter can be between 1 - 2 cm.

[0009] Equip a sampling pump to pump the water sample from the sampling point to the sampler. The flow rate of the sampling pump should be selected according to the number of sampling points, sampling volume, and sampling time requirements. When setting the sampling pump, it is necessary to consider avoiding cavitation phenomena to ensure the continuity and stability of sampling. To prevent the water sample from being contaminated or undergoing chemical reactions during transmission, use a sealed sampling pipe. The material of the sampling pipe can be the same as that of the sampler, and use joints with good sealing performance at the connections between the sampling pipe and the sampling point and the sampler, such as threaded sealing joints or rubber sealing joints.

[0010] 3. During the water sample collection process, before formal sampling, pre-rinse the sampling equipment and sampling tubes. The amount of pre-rinsing water should be no less than 3 times the sampling volume. For different types of sampling points, the pre-rinsing methods are slightly different. For the sampling points at the water source inlet, the pre-rinsing water can be directly discharged into the sewer; while for the sampling points at the mixing area and the inlets and outlets of key equipment, the pre-rinsing water should be returned to the circulating water system through a dedicated return pipeline to avoid wasting water resources.

[0011] After the pre-rinsing is completed, start the sampling pump and sample from each sampling point simultaneously. To ensure the synchronization of sampling, a timing control device is used. For example, set the sampling time to once every 15 minutes, and the duration of each sampling is 3 - 5 minutes. During the sampling process, ensure the flow rate of each sampling channel is stable, which can be achieved by installing a flow regulating valve on the sampling channel.

[0012] Determine the sampling volume for each sampling point according to the requirements of the analysis project. For conventional water quality analysis projects (such as COD, BOD, SS, etc.), the sampling volume for each sampling point is generally 500 - 1000 milliliters. If more detailed trace element analysis and other projects are required, the sampling volume may need to be appropriately increased. The collected water samples should be separately collected into pre-cleaned and labeled sample bottles, and the sample bottles should have good sealing performance and chemical stability.

[0013] 4. Water quality analysis items Chemical Oxygen Demand (COD) analysis: It is determined by the potassium dichromate method. In a strong acidic solution, a certain amount of potassium dichromate is used to oxidize the reducing substances in the water sample. The excess potassium dichromate uses ferroin as an indicator and is titrated back with ammonium ferrous sulfate solution. Calculate the COD value in the water sample according to the amount of ammonium ferrous sulfate used. This method can reflect the content of organic matter in the water sample and is one of the important indicators for evaluating the degree of water pollution. Biochemical Oxygen Demand (BOD) analysis: The dilution and inoculation method is used. After appropriately diluting the water sample, specific microbial strains are inoculated and cultured under specified temperature (generally 20°C) and time (5 days) conditions. Measure the difference in dissolved oxygen content in the water sample before and after cultivation, and then calculate the BOD value. The BOD value reflects the content of biodegradable organic matter in the water and is of great significance for evaluating the degree of organic matter pollution in the water body and the self-purification ability of the water body. Suspended Solids (SS) analysis: The gravimetric method is used. The water sample is filtered through a filter membrane with a pore size of 0.45 microns, and then the substances retained on the filter membrane are dried to a constant weight at 103 - 105°C. Calculate the SS content according to the mass difference before and after the filter membrane. The SS content reflects the amount of suspended particles in the water and has an important impact on the turbidity and filtration performance of the water.

[0014] The complexometric titration method is adopted. Using Eriochrome Black T as the indicator, in an ammonia-ammonium chloride buffer solution with pH = 10, the total amount of calcium and magnesium ions in the water sample is titrated with a standard solution of disodium ethylenediaminetetraacetate (EDTA), and then the water hardness is calculated. Hardness is an indicator to measure the content of calcium, magnesium and other ions in water, and has an important impact on the scaling and corrosion problems in the circulating water system. pH analysis: The glass electrode method is adopted. The glass electrode and the reference electrode are inserted into the water sample, and by measuring the potential difference between the electrodes, the pH value of the water sample is determined according to the pre-calibrated curve. The pH value reflects the acidity and alkalinity of the water sample, and is of great significance for aspects such as the growth of microorganisms and corrosion control in the circulating water system. Nutrient analysis: It includes the determination of nutrient elements such as nitrogen and phosphorus. For the determination of nitrogen, the ammonia nitrogen content can be determined by the Nessler's reagent spectrophotometric method, and the nitrate nitrogen content can be determined by the ultraviolet spectrophotometric method; for the determination of phosphorus, the total phosphorus content can be determined by the ammonium molybdate spectrophotometric method. The content of these nutrients will affect the growth and reproduction of microorganisms in the circulating water system.

[0015] 5. Data Analysis and Evaluation Collect the water quality analysis data collected at each sampling point and at each time. Establish a dedicated database, which should include information such as the location information of the sampling point, the sampling time, the analysis items, and the corresponding water quality index values. Classify and organize the collected data for subsequent analysis and processing.

[0016] Adopt multivariate statistical analysis methods to establish a data analysis model. For example, the principal component analysis (PCA) method can be used to perform dimensionality reduction on numerous water quality indicators and extract the main influencing factors. At the same time, combined with the cluster analysis method, classify the water quality data at different sampling points and different times, and identify the laws of regions and time periods with similar water quality. Establish a comprehensive water quality evaluation index model. Assign different weights to each water quality indicator according to its importance to the operation of the circulating water system, and calculate the comprehensive water quality evaluation index by weighted summation. For example, for the pH value and hardness indicators that are more critical for corrosion control in the circulating water system, relatively higher weights can be assigned, while for some trace element indicators that have less impact on equipment operation, lower weights can be assigned.

[0017] According to the established data analysis model, the water quality status of the composite water source circulating water system is evaluated. The real-time water quality data is input into the model to determine whether the water quality is within the normal range. If the water quality indicators exceed the normal range, the possible causes are found through model analysis, such as sudden changes in the water quality of a certain water source, operating failures of certain equipment, etc. The historical water quality data and the established prediction model are used to predict the future water quality status. For example, time series analysis methods can be adopted to predict the changes in water quality indicators in the future according to the water quality change trend in the past period, providing a basis for the advance regulation of the circulating water system.

[0018] Example 1: The composite water source circulating water system in this example is mainly composed of three water sources: surface water, groundwater, and reclaimed water. This system is applied to a large industrial plant area to provide cooling water for the production equipment in the plant area. The scale of the circulating water system is large, including multiple water source inlets, a large mixing tank, a series of water quality treatment equipment (such as filters, cooling towers, etc.), and a water supply network connected to each production equipment.

[0019] For the surface water inlet, a sampling point is set at a position 10 times the pipe diameter (the pipe diameter is 0.5 m, that is, 5 m) from the elbow in the inlet pipe. The sampling instrument uses a stainless steel multi-channel sampler with a sampling channel diameter of 1 cm. For the groundwater inlet, a sampling point is set at a similar position in the inlet pipe. A sampling point is also set at the reclaimed water inlet, and the sampling point position and sampling instrument are the same as those of the surface water inlet.

[0020] For the mixing area, the mixing tank is rectangular, 10 m long and 8 m wide. A sampling point is set at the center of the mixing tank, and a total of 9 sampling points are set at the grid intersection points 1 m away from the pool wall (along the long side and short side respectively), forming a 10×10 grid distribution (excluding the center point). The sampling point uses a sampler made of polytetrafluoroethylene with a sampling channel diameter of 1.5 cm. The sampling pump flow rate is selected as 10 L / min according to the water volume of the mixing tank and the sampling requirements, and the sampling pipe is connected with a threaded seal joint with good sealing performance.

[0021] Sampling points are set at the inlet and outlet of the filter respectively. The inlet sampling point is located in the straight pipe section at the filter inlet, 3 times the pipe diameter (the filter inlet pipe diameter is 0.3 m, that is, 0.9 m) from the connection, and the sampling channel diameter is 1 cm. The outlet sampling point is located 3 times the pipe diameter from the connection in the outlet straight pipe section. The inlet and outlet of the cooling tower are also set with sampling points in a similar manner, and the materials of the sampling points and sampling instruments are the same as those at the inlet and outlet of the filter. The sampling pump flow rate is selected as 5 L / min according to the water volume of the equipment and pipeline, and the sampling pipe is connected with a rubber seal joint.

[0022] Before the official sampling starts at 8:00 am every day, all sampling instruments and sampling pipes are pre-rinsed. For the sampling points at the water source inlet, the pre-rinsing water volume is 3 liters (3 times the sampling volume of 1 liter), and it is directly discharged into the sewer. For the sampling points in the mixing area and at the inlets and outlets of key equipment, the pre-rinsing water flows back to the circulating water system through the return pipeline. The pre-rinsing time is 10 minutes to ensure that the inside of the sampling instruments and sampling pipes is clean and free of residual impurities.

[0023] Start the timing control device and set the sampling time to once every 2 hours, with each sampling duration being 4 minutes. During the sampling process, through the flow regulating valves installed on each sampling channel, ensure the flow rate of each sampling channel is stable. For example, for a sampling channel of the surface water inlet sampler, the flow rate is stable at 0.5 liters per minute to ensure that 2 liters of water samples are collected within 4 minutes.

[0024] According to the requirements of the analysis items, for the analysis of conventional water quality indicators (such as COD, BOD, SS, etc.), the sampling volume at each sampling point is 800 milliliters. The collected water samples are respectively collected into pre-cleaned and labeled 500-milliliter stoppered glass bottles (for the analysis of conventional indicators) and polyethylene plastic bottles (for the analysis of special indicators, such as nutrient analysis). For special water quality indicators (such as the analysis of nutrients like nitrogen and phosphorus), according to the specific analysis method, appropriately increase the sampling volume. For example, for the determination of total phosphorus content, the sampling volume is 1 liter.

[0025] Chemical Oxygen Demand (COD) Analysis: The determination is carried out according to the operating steps of the potassium dichromate method. Exactly 20 mL of the water sample is pipetted into a digestion tube, and an appropriate amount of potassium dichromate standard solution and sulfuric acid - silver sulfate solution are added, and then heated under reflux for 2 hours. After cooling, ferroin indicator is added, and the solution is titrated with ammonium ferrous sulfate standard solution until the solution changes from yellow to blue - green and then to reddish - brown as the end - point. The COD value is calculated based on the amount of ammonium ferrous sulfate used. For example, after determination, the COD value of a surface water inlet water sample is 50 mg / L. Biochemical Oxygen Demand (BOD) Analysis: First, the water sample is appropriately diluted to ensure that the dissolved oxygen in the water sample can meet the measurement requirements before and after incubation. After inoculating with specific microbial strains, the water sample is incubated in a constant - temperature incubator at 20 °C for 5 days. The dissolved oxygen content in the water sample is measured before and after incubation. For example, in a batch of water samples, the dissolved oxygen content before incubation is 8 mg / L, and after incubation is 5 mg / L. The initial volume of the water sample is 100 mL, and the dilution factor is 2 times. Then, the BOD value is calculated to be 6 mg / L according to the formula. Suspended Solids (SS) Analysis: The water sample is filtered through a 0.45 - micron filter membrane, and the substances retained on the filter membrane are dried to a constant weight at 105 °C. For example, after filtering a water sample from a mixed area through the filter membrane, the initial mass of the filter membrane is 1.5 g, and the mass after drying is 1.6 g. Then the SS content is 100 mg / L ((1.6 - 1.5) / 0.1×1000, assuming the volume of the filtered water sample is 100 mL).

[0026] Hardness Analysis: In an ammonia - ammonium chloride buffer solution with pH = 10, adding eriochrome black T indicator, and titrating the total amount of calcium and magnesium ions in the water sample with disodium ethylenediaminetetraacetate (EDTA) standard solution. For example, for a groundwater inlet water sample, 20 mL of EDTA standard solution is consumed after titration. Based on the concentration of the EDTA standard solution (0.01 mol / L) and the volume of the water sample (50 mL), the hardness of the water is calculated to be 200 mg / L (calculated as calcium carbonate). pH (Acidity and Alkalinity) Analysis: Insert the glass electrode and reference electrode into the water sample, measure the potential difference between the electrodes through a pH meter, and obtain the pH value of the water sample after pre - calibration. For example, the pH value of a water sample at the outlet of a cooling tower is 7.2.

[0027] Determination of ammonia nitrogen content (Nessler's reagent spectrophotometry): Take a certain amount of water sample, add Nessler's reagent, and a colored complex is formed by the reaction. Measure the absorbance at a specific wavelength, and calculate the ammonia nitrogen content according to the standard curve. For example, the ammonia nitrogen content of a reclaimed water inlet water sample was measured to be 10 mg / L. Determination of nitrate nitrogen content (ultraviolet spectrophotometry): Utilize the characteristic absorption of nitrate nitrogen in the ultraviolet region, and calculate its content by measuring the absorbance. The nitrate nitrogen content of a water sample in a mixing area was 5 mg / L. Determination of total phosphorus content (ammonium molybdate spectrophotometry): Add reagents such as ammonium molybdate to the water sample to convert phosphorus into molybdophosphorus complex, measure the absorbance at a specific wavelength, and calculate the total phosphorus content. For example, the total phosphorus content of a water sample at the inlet of a filter was 0.5 mg / L.

[0028] Enter the water quality analysis data collected at each sampling point and at each time into a specially established database. The database contains the location information of each sampling point (such as the name of the water source inlet, the coordinates of the mixing area, the name of the equipment and its inlet and outlet, etc.), the sampling time (accurate to minutes), the analysis items (such as COD, BOD, etc.), and the corresponding water quality index values and other information. Classify and organize the data, for example, classify and store them according to the water source type, equipment type, etc., for subsequent analysis and processing.

[0029] Principal Component Analysis (PCA): Conduct principal component analysis on numerous water quality indicators. For example, select 8 water quality indicators such as COD, BOD, SS, hardness, pH, ammonia nitrogen, nitrate nitrogen, and total phosphorus. By analyzing a large amount of historical data (such as data from the past year), extract the main influencing factors. Through calculation, it is found that the three indicators of COD, BOD, and ammonia nitrogen have relatively high loadings on the first principal component, and these three indicators mainly reflect the organic pollution situation in the water sample; while hardness and pH have relatively high loadings on the second principal component, mainly reflecting the water quality characteristics that affect equipment corrosion and scaling. Cluster Analysis: Use the cluster analysis method to classify water quality data at different sampling points and different times. For example, cluster the water sample data at the inlet and outlet of the same equipment. It is found that the water samples at the inlet and outlet of the same equipment have similarities in some water quality indicators, such as relatively small changes in indicators such as hardness and pH; while there are obvious cluster differences in the organic matter content (COD, BOD) between the water samples after mixing different water sources and the water samples at the inlet of a single water source. Water Quality Comprehensive Evaluation Index Model: Assign different weights to each water quality indicator according to its importance to the operation of the circulating water system. For example, for the pH value and hardness indicators that are crucial for corrosion control in the circulating water system, assign a weight of 0.3 respectively; for the organic matter indicator (represented by COD) that has a greater impact on microbial growth, assign a weight of 0.25; for the nutrient indicators (ammonia nitrogen, nitrate nitrogen, total phosphorus), assign weights of 0.05 respectively. Calculate the water quality comprehensive evaluation index by the method of weighted summation. For example, the water quality data at a certain sampling point at a certain moment is: COD $$I = 0.3\times\frac{180 - 100}{200}+0.3\times\frac{7.0 - 6.5}{8.5 - 5.5}+0.25\times\frac{60 - 50}{100}+0.05\times\frac{8 - 5}{20}+0.05\times\frac{4 - 2}{10}+0.05\times\frac{0.4 - 0.2}{0.5}= 0.13$$ (here, it is assumed that the standard ranges and calculation methods of each indicator are only examples). Judge the water quality status according to the size of the water quality comprehensive evaluation index. For example, if the index is less than 0.2, it indicates good water quality; 0.2 - 0.5 indicates average water quality; and greater than 0.5 indicates poor water quality.

[0030] According to the established data analysis model, the water quality status of the composite water source circulating water system is evaluated. The real-time water quality data is input into the model. After the real-time data of the water sample in a certain mixing area at a certain moment is input, the comprehensive water quality evaluation index is calculated to be 0.3, and it is judged that the water quality is in a general state. Through model analysis, it is found that due to the recent change in the mixing ratio in this area, the organic matter content has increased slightly. Using the historical water quality data and the established prediction model, the time series analysis method is adopted. According to the water quality change trend in the past week, the change of water quality indicators in this area in the next three days is predicted. For example, it is predicted that the COD value will increase at a rate of 2 mg / L per day, and corresponding control measures are taken in advance, such as adjusting the water source mixing ratio or increasing the operation intensity of water quality treatment equipment.

Claims

1. A sampling and analysis method applicable to a composite water source circulating water system, characterized in that, It includes the following steps: Sampling points are set at the inlets of different water sources in the composite water source circulating water system. The positions of the sampling points are located in the straight pipe sections of the inlet pipelines, at least 5 times the pipe diameter away from devices such as pipe elbows and valves that affect the water flow state; multiple sampling points are set in the mixing area after the different water sources are mixed. The sampling points are distributed at different positions in the mixing area, including the central position and at different distances from the mixing and stirring equipment, and the sampling points are distributed in a grid pattern; sampling points are set at the inlets and outlets of key equipment in the composite water source circulating water system. The sampling points are located in the straight pipe sections of the equipment inlets and outlets, at least 3 times the pipe diameter away from the connection points.

2. The sampling and analysis method applicable to the composite water source circulating water system according to claim 1, characterized in that The different water sources include surface water, groundwater, and reclaimed water.

3. The sampling and analysis method applicable to the composite water source circulating water system according to claim 1, characterized in that, When collecting water samples at the sampling points, a multi-channel sampler is used. The material of the multi-channel sampler is stainless steel or polytetrafluoroethylene. According to the sampling and analysis method applicable to the composite water source circulating water system described in claim 1, before collecting water samples, the sampling instruments and sampling pipes are pre-rinsed. The amount of pre-rinsing water is not less than 3 times the sampling volume. And for sampling points at different positions, the discharge or reflux methods of the pre-rinsing water are different. The pre-rinsing water at the water source inlet is directly discharged, and the pre-rinsing water at the mixing area and the inlets and outlets of key equipment is refluxed back to the circulating water system through the reflux pipeline. According to the sampling and analysis method applicable to the composite water source circulating water system described in claim 1, the sampling time during the water sample collection process is once every 1 - 2 hours, and the duration of each sampling is 3 - 5 minutes.

4. The sampling and analysis method applicable to the composite water source circulating water system according to claim 1, characterized in that, During the water sample collection process, the sampling volume at each sampling point is 500 - 1000 milliliters. For the analysis of special water quality indicators, the sampling volume is appropriately increased according to the specific analysis method.

5. The sampling and analysis method applicable to the composite water source circulating water system according to claim 1, wherein, The water quality analysis items include the analysis of conventional water quality indicators and special water quality indicators. The analysis of conventional water quality indicators includes the analysis of chemical oxygen demand (COD), biochemical oxygen demand (BOD), and suspended solids (SS). The analysis of special water quality indicators includes the analysis of hardness, pH value, nutrients (nitrogen, phosphorus, etc.).

6. The sampling and analysis method applicable to the composite water source circulating water system according to claim 7, wherein, The chemical oxygen demand (COD) is analyzed by the potassium dichromate method, the biochemical oxygen demand (BOD) is analyzed by the dilution and inoculation method, the suspended solids (SS) are analyzed by the gravimetric method, the hardness is analyzed by the complexometric titration method, the pH value is analyzed by the glass electrode method, the nitrogen in the nutrients is analyzed by the Nessler reagent spectrophotometry or ultraviolet spectrophotometry, and the phosphorus is analyzed by the ammonium molybdate spectrophotometry.

7. The sampling and analysis method applicable to the composite water source circulating water system according to claim 1, characterized in that The data analysis includes establishing a data analysis model. The data analysis model includes a principal component analysis (PCA) model, a cluster analysis model, and a water quality comprehensive evaluation index model. The principal component analysis model is used to perform dimensionality reduction processing on numerous water quality indicators and extract the main influencing factors. The cluster analysis model is used to classify the water quality data at different sampling points and different times. The water quality comprehensive evaluation index model is used to assign weights according to the importance of each water quality indicator and calculate the comprehensive evaluation index.

8. The sampling and analysis method applicable to the composite water source circulating water system according to claim 9, wherein In the comprehensive water quality evaluation index model, higher weights are assigned to the indicators affecting the corrosion control of the circulating water system, moderate weights are assigned to the indicators reflecting organic pollution, and lower weights are assigned to the nutrient indicators.

9. The sampling and analysis method applicable to the composite water source circulating water system according to claim 1, characterized in that According to the data analysis results, the water quality status is evaluated. When the comprehensive water quality evaluation index is less than 0.2, the water quality is judged to be good; when it is between 0.2 and 0.5, the water quality is judged to be average; when it is greater than 0.5, the water quality is judged to be poor.

10. The sampling and analysis method applicable to the composite water source circulating water system according to claim 1, characterized in that, According to the historical water quality data and the established prediction model, the future water quality status is predicted, and the time series analysis method is used for the prediction model.