Wetland substrate combination and evaluation method based on hydraulic performance

Abstract

The invention belongs to the field of constructed wetland water treatment, and particularly relates to a wetland substrate combination and evaluation method based on hydraulic performance, a combined substrate is used for establishing a wetland model, a tracer experiment method is used for testing the hydraulic performance of the substrate, and a retention time distribution curve is drawn; calculating the average hydraulic retention time, the effective volume ratio, the water flow dispersion degree, the standard flow dispersion and the hydraulic efficiency on the basis of the retention time distribution curve; and performing weighted calculation on the effective volume ratio, the water flow dispersion degree, the standard flow dispersion degree and the hydraulic efficiency according to weights to obtain a comprehensive performance index, and evaluating the advantages and disadvantages of the matrix according to the comprehensive performance index. The data of the method are easy to obtain, the result can be quickly output, and the feasibility is high.

Description

Technical Field

[0001] The invention belongs to the field of artificial wetland water treatment, and in particular relates to a wetland matrix combination and evaluation method based on hydraulic performance. Background Art

[0002] Constructed wetlands are an economical, efficient and environmentally friendly sewage treatment method based on the adsorption of pollutants by substrates, absorption by plants and degradation by microorganisms. As the largest component of constructed wetlands, the substrate not only plays a huge role in the decontamination process, but also serves as the hub of other components of constructed wetlands. It provides physical support and carriers for plants and microorganisms in constructed wetlands. Plant roots release oxygen into the substrate to form aerobic conditions, which helps microorganisms degrade pollutants. Therefore, the selection and arrangement of the substrate directly determines the efficiency of contaminated water purification in constructed wetlands. At present, there are many types of substrates. In current practical projects, a certain substrate is often used directly based on past experience and personal subjective judgment, resulting in poor treatment effects. Therefore, there is an urgent need for a universal law to guide the arrangement and combination of substrates and to make a rapid evaluation of such arranged and combined substrates.

[0003] At present, the methods for evaluating matrix combinations are mostly based on the purification efficiency of pollutants. The process is slow, and different operating conditions and pollutant concentrations lead to different purification efficiencies under the same matrix combination. In practical applications, it is easy for some matrixes to have good performance but some others to be particularly poor. How to comprehensively consider various performances and select the optimal matrix is ​​an urgent problem to be solved. Summary of the invention

[0004] In order to solve the problem that the evaluation method in the prior art is easily affected by the operating conditions and pollutant concentrations, and the existing evaluation method has poor economic efficiency, the present invention provides a wetland matrix combination and evaluation method based on hydraulic performance, and the application of the matrix combination screened by the method in artificial wetland water treatment. The specific scheme is as follows:

[0005] A method for evaluating a wetland matrix combination based on hydraulic performance, wherein a wetland model is established using the combined matrix, the hydraulic performance of the matrix is ​​tested using a tracer experimental method, and a residence time distribution curve is plotted; based on the residence time distribution curve, the average hydraulic residence time, effective volume ratio, water flow dispersion, standard flow dispersion, and hydraulic efficiency are calculated; the effective volume ratio, water flow dispersion, standard flow dispersion, and hydraulic efficiency are weighted and calculated to obtain a comprehensive performance index, and the matrix is ​​evaluated using the comprehensive performance index.

[0006] Furthermore, the closer the effective volume ratio is to 1, the better; the smaller the water flow dispersion and the standard flow dispersion are, the better; and the greater the hydraulic efficiency, the better.

[0007] Furthermore, the smaller the comprehensive performance index is, the better the matrix is.

[0008] Further, the following steps are included:

[0009] S1. Use the assembled matrix to establish a wetland model, use the tracer experimental method to test the hydraulic performance of the matrix, and draw a residence time distribution curve;

[0010] S2. Calculate the theoretical hydraulic retention time T of the wetland system based on the system size, filler porosity and water flow rate during different operations. n ;

[0011] S3. Read the time T when the concentration reaches the maximum during the tracer outflow process from the residence time distribution curve. p ; According to the detection time and concentration of the tracer, calculate the average hydraulic retention time T at the center of gravity of the residence time distribution curve m ; Calculate the water flow dispersion σ inside the wetland based on the tracer detection time and tracer concentration t 2 ;

[0012] S4, average hydraulic retention time T m Theoretical hydraulic retention time T n The effective volume ratio e is calculated based on the ratio of the theoretical hydraulic retention time T n The time T when the concentration reaches the maximum p Calculate the standard flow dispersion N; the time T when the concentration reaches the maximum p Theoretical hydraulic retention time T n The hydraulic efficiency λ is calculated by the ratio of

[0013] S5, according to the formula ABS(e-1)×0.2+σ t 2 ×10 -(LEN(σt2)-1) ×0.3+σ θ 2 ×0.2+1 / λ×0.3 to calculate the comprehensive performance index; compare the comprehensive performance indexes of different matrices, the smaller the value, the better the matrix performance.

[0014] Furthermore, according to the formula Calculate the theoretical hydraulic retention time T n , where: V is the volume covered by the matrix in the wetland system; Q is the volume flow of water passing through the wetland system; ξ is the porosity of the filler.

[0015] Furthermore, according to the formula Calculate the average hydraulic retention time T m ; According to the formula Calculate the water dispersion σ within the wetland t 2 ; Where: t is the time when the tracer concentration is detected; c(t) is the tracer concentration; Δt is the time interval between two adjacent measurements.

[0016] Furthermore, the time t for detecting the tracer concentration is calculated from the instant when the tracer is added.

[0017] Furthermore, according to the formula Calculate the standard flow dispersion σ θ 2 .

[0018] A matrix combination screened by the above evaluation method consists of no less than two layers of matrix, and the uppermost matrix has the lowest permeability and the lowermost matrix has the highest permeability; the permeability coefficients of the uppermost and lowermost matrices differ by 1 to 8 orders of magnitude.

[0019] An application of the matrix combination screened by the above-mentioned evaluation method in artificial wetland water treatment.

[0020] By adopting the above scheme, the method of the present invention has the following advantages:

[0021] 1. The evaluation method of the present invention is based on the evaluation from the perspective of hydraulic performance, is not affected by other factors such as operating conditions and pollutant concentrations, and does not require repeated measurement of pollutant concentrations, thus avoiding the loss of equipment and reagents. The data is easy to obtain, the results can be output quickly, and the feasibility is strong.

[0022] 2. The evaluation method of the present invention involves multiple factors and can comprehensively evaluate multiple performance indicators to conduct a comprehensive evaluation of the matrix combination, coordinate the differences in the evaluation methods of each performance, and select the most practical and optimal combination.

[0023] 3. The evaluation method of the present invention has accurate results and reasonable weight settings. It can integrate the average hydraulic retention time, effective volume ratio, water flow dispersion, standard flow dispersion and hydraulic efficiency indicators, and objectively and scientifically evaluate the quality of the matrix through a comprehensive performance index.

[0024] 4. The matrix combination screened by the evaluation method of the present invention can make the flow field and pollutant migration more uniform, and the hydraulic performance of the wetland is also better. It can alleviate the internal short-circuit phenomenon of the wetland, increase the effective area of ​​the wetland, and improve the wetland performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the residence time distribution curve of Examples 1 to 3.

[0026] Figure 2 It is the residence time distribution curve of Examples 4 to 6.

[0027] Figure 3 It is the residence time distribution curve of Examples 7 to 10.

[0028] Figure 4 It is the residence time distribution curve of the comparison ratio. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Evaluation Example:

[0031] S1. Use the assembled matrix to establish a wetland model, use NaCl as a tracer, and when the wetland model is in a saturated state, keep the inlet and outlet water flow unchanged, quickly pulse 100mL of 1g / L NaCl solution into the wetland model through the water inlet, and start testing the outlet water conductivity at a frequency of 5 to 10 minutes per time until the conductivity returns to the background value before the test, and draw the residence time distribution curve;

[0032] S2. According to the size of the system, the porosity of the packing and the water flow rate during different operations, the formula Calculate the theoretical hydraulic retention time T of the wetland system n , where: V is the volume covered by the matrix in the wetland system; Q is the volume flow of water through the wetland system; ξ is the porosity of the filler;

[0033] S3. Read the time T when the concentration reaches the maximum during the tracer outflow process from the residence time distribution curve. p ; According to the detection time and concentration of the tracer, according to the formula Calculate the average hydraulic retention time T at the centroid of the retention time distribution curve m ; According to the detection time and concentration of the tracer, according to the formula Calculate the water dispersion σ within the wetland t 2 ; Where: t is the time when the tracer concentration is detected (starting from the instantaneous addition of the tracer); c(t) is the tracer concentration; Δt is the time interval between two adjacent measurements;

[0034] S4, average hydraulic retention time T m Theoretical hydraulic retention time T n The effective volume ratio e is calculated based on the ratio of the theoretical hydraulic retention time T nThe time T when the concentration reaches the maximum p , according to the formula Calculate the standard flow dispersion σ θ 2 ; The time T when the concentration reaches the maximum p Theoretical hydraulic retention time T n The hydraulic efficiency λ is calculated by the ratio of

[0035] S5, according to the formula ABS(e-1)×0.2+σ t 2 ×10 -(LEN(σt2)-1) ×0.3+σ θ 2 ×0.2+1 / λ×0.3 to calculate the comprehensive performance index; compare the comprehensive performance indexes of different matrix combinations, the smaller the value, the better the matrix performance.

[0036] The matrix combinations of the embodiments and comparative examples, and the use of Figures 1 to 4 The average hydraulic retention time T measured by the residence time distribution curve m , Theoretical hydraulic retention time T n , effective volume ratio e, water flow dispersion σ t 2 , standard flow dispersion σ θ 2 And hydraulic efficiency λ are shown in the following table:

[0037]

[0038]

[0039] The comprehensive performance index of each embodiment and comparative example was calculated using the evaluation example, and the results are as follows:

[0040]

[0041]

[0042] Combining the hydraulic properties and the comprehensive performance index, it can be seen that the greater the difference in permeability of the upper, middle and lower layers of the wetland matrix, the better the overall performance of the matrix. Average hydraulic retention time T of Example 3 of the combination of loess, coarse sand and gravel m The theoretical hydraulic retention time is 16414s. n is 17307s, and the effective volume ratio e is 0.949, slightly less than 1, which is closest to 1 compared with the other 9 embodiments and comparative examples, indicating that compared with other examples, only a small amount of dead zone phenomenon occurs inside the wetland of embodiment 3; the water flow dispersion degree σ t 2 7.45×107 s 2 , the standard flow dispersion is 0.249, which are relatively small, indicating that the water flow inside the wetland is more uniform and stable, the water flow dispersion is small, which is conducive to the degradation of pollutants; the hydraulic efficiency λ is 0.713, indicating that there are few dead zones inside the wetland and the wetland performance is good. The comprehensive performance index of Example 3 is 0.71. The permeability of each layer of the upper, middle and lower layers of Example 3 is very different, and the hydraulic characteristics are all good, which is consistent with the comprehensive performance index, indicating that the evaluation method of the present invention has high accuracy.

[0043] It can be found from the table that the hydraulic performance of the wetland system of each embodiment with a combination of multiple substrates and a large difference in permeability coefficient between the top and bottom layers of the substrate is significantly better than that of a single substrate and a substrate with a small difference in permeability coefficient. The standard flow discreteness of each comparative example is around 0.5, which is relatively high, and the effective volume ratio is also far from 1, which indicates that the dead zone phenomenon inside these comparative wetlands is relatively serious. At the same time, the flow inside the wetland is relatively uneven, and the speed and direction of the water flow may fluctuate greatly, thereby affecting the overall treatment efficiency of the wetland. The comprehensive performance index of the comparative examples is greater than 2, which is consistent with the results of the parameter analysis.

[0044] As the permeability of the lower layer substrate increases, the effective volume ratio of the wetland decreases. For example, when the lower layer of the medium sand in Comparative Example 1 is replaced by the gravel in Example 3, the effective volume ratio e of the wetland increases from 0.609 to 0.853, 6.99×10 8 s 2 Reduced to 1.75×10 8 s 2 , the standard flow dispersion decreased from 0.508 to 0.372, which shows that the short-circuiting phenomenon inside the wetland has been alleviated, the dispersion of water flow inside the wetland system has become smaller, the effective area of ​​the wetland has become larger, the wetland performance has been enhanced, and the comprehensive performance index has also been reduced from more than 3.28 to 1.19.

[0045] The greater the difference in permeability between the top layer and the bottom layer, the stronger the wetland properties. For example, if the medium sand, coarse sand, and gravel in Example 10 are replaced with loess, coarse sand, and gravel, the effective volume ratio of the wetland will increase; the water flow dispersion and standard flow dispersion will decrease, and the number of continuous reaction mixers will increase; these indicate that when the middle and lower layer substrates remain unchanged, the reduction in the permeability of the upper layer substrate will lead to a reduction in the dead zone inside the wetland, an increase in the effective volume, and a more uniform partial fluid in the wetland.

[0046] The standard flow dispersion of Example 6 is higher than that of Comparative Example 3, and the other parameters are better than those of Comparative Example 3, and the comprehensive performance index of 1.36 is also significantly lower than 2.17 of Comparative Example 3. This shows that even if individual performance improves, the changes in other performance deterioration can be captured by the evaluation method of the present invention, avoiding excessive errors or even distortions caused by single factor evaluation. The matrix combination screened by the method of the present invention is highly practical.

[0047] For those skilled in the art, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all of these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. A method for evaluating a wetland matrix combination based on hydraulic performance, characterized in that: A wetland model was established using the assembled matrix, and the hydraulic performance of the matrix was tested using the tracer experimental method, and the residence time distribution curve was drawn. Based on the residence time distribution curve, the average hydraulic residence time, effective volume ratio, water flow dispersion, standard flow dispersion and hydraulic efficiency were calculated. The effective volume ratio, water flow dispersion, standard flow dispersion and hydraulic efficiency were weighted and calculated to obtain a comprehensive performance index, which was used to evaluate the quality of the matrix.

2. The method for evaluating a wetland matrix combination based on hydraulic performance according to claim 1, characterized in that: The closer the effective volume ratio is to 1, the better; the smaller the water flow dispersion and the standard flow dispersion are, the better; the greater the hydraulic efficiency, the better.

3. The method for evaluating a wetland matrix combination based on hydraulic performance according to claim 1, characterized in that: The smaller the comprehensive performance index is, the better the matrix is.

4. The method for evaluating a wetland matrix combination based on hydraulic performance according to claim 1, characterized in that: The following steps are involved: S1. Use the assembled matrix to establish a wetland model, use the tracer experimental method to test the hydraulic performance of the matrix, and draw a residence time distribution curve; S2. Calculate the theoretical hydraulic retention time T of the wetland system based on the system size, filler porosity and water flow rate during different operations. n ; S3. Read the time T when the concentration reaches the maximum during the tracer outflow process from the residence time distribution curve. p ; According to the detection time and concentration of the tracer, calculate the average hydraulic retention time T at the center of gravity of the residence time distribution curve m ; Calculate the water flow dispersion σ inside the wetland based on the tracer detection time and tracer concentration t 2 ; S4, average hydraulic retention time T m Theoretical hydraulic retention time T n The effective volume ratio e is calculated based on the ratio of the theoretical hydraulic retention time T n The time T when the concentration reaches the maximum p Calculate the standard flow dispersion σ θ 2 ; The time T when the concentration reaches the maximum p Theoretical hydraulic retention time T n The hydraulic efficiency λ is calculated by the ratio of S5, according to the formula ABS(e-1)×0.2+σ t 2 ×10 -(LEN(σt2)- 1) ×0.3+σ θ 2 ×0.2+1 / λ×0.3 to calculate the comprehensive performance index; compare the comprehensive performance indexes of different matrices, the smaller the value, the better the matrix performance.

5. The method for evaluating a wetland matrix combination based on hydraulic performance according to claim 4, characterized in that: By formula Calculate the theoretical hydraulic retention time T n , where: V is the volume covered by the matrix in the wetland system; Q is the volume flow of water passing through the wetland system; ξ is the porosity of the filler.

6. The method for evaluating a wetland matrix combination based on hydraulic performance according to claim 4, characterized in that: By formula Calculate the average hydraulic retention time T m ; According to the formula Calculate the water dispersion σ within the wetland t 2 ; Where: t is the time when the tracer concentration is detected; c(t) is the tracer concentration; Δt is the time interval between two adjacent measurements.

7. The method for evaluating a wetland matrix combination based on hydraulic performance according to claim 6, characterized in that: The time t for detecting the tracer concentration is calculated from the instant when the tracer is added.

8. The method for evaluating a wetland matrix combination based on hydraulic performance according to claim 4, characterized in that: By formula Calculate the standard flow dispersion σ θ 2 .

9. A matrix combination obtained by screening by the evaluation method according to claim 1, characterized in that: It is composed of at least two layers of matrix, with the uppermost layer having the lowest permeability and the lowermost layer having the highest permeability; the permeability coefficients of the uppermost and lowermost layers differ by 1 to 8 orders of magnitude.

10. Use of the evaluation method according to claim 1 in artificial wetland water treatment.

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