A wetland substrate combination and assessment method based on hydraulic performance

Abstract

The present application belongs to the field of artificial wetland water treatment, and particularly relates to a wetland substrate combination and evaluation method based on hydraulic performance, a wetland model is established using the combined substrate, the hydraulic performance of the substrate is tested using a tracer experiment method, and a residence time distribution curve is drawn; based on the residence time distribution curve, the average hydraulic residence time, the effective volume ratio, the water flow dispersion degree, the standard flow dispersion degree and the hydraulic efficiency are calculated; the effective volume ratio, the water flow dispersion degree, the standard flow dispersion degree and the hydraulic efficiency are weighted and calculated according to the weight, and a comprehensive performance index is obtained, and the substrate is evaluated according to the comprehensive performance index. The data of the method of the present application is easy to obtain, the result can be quickly output, and the method is feasible.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of constructed wetland water treatment, and particularly relates to a wetland substrate combination and evaluation method based on hydraulic performance. BACKGROUND

[0002] Constructed wetland is an economical, efficient and environmentally friendly wastewater treatment method, which is based on the adsorption of substrates, the absorption of plants and the degradation of microorganisms. As the largest component of the constructed wetland, the substrate not only plays a huge role in the decontamination process, but also is the hub of other components of the constructed wetland. It provides physical support and carrier for plants and microorganisms in the constructed wetland, and the plant root system releases oxygen to the substrate to form an aerobic condition, which helps microorganisms to degrade pollutants. Therefore, the selection and arrangement of the substrate directly determines the efficiency of the constructed wetland in purifying pollution. At present, there are various types of substrates, and in current practical projects, a certain substrate is often directly used through past experience and personal subjective judgment, resulting in poor treatment effect. Therefore, a universal rule is urgently needed to guide the arrangement and combination of the substrate, and a rapid evaluation of the arranged and combined substrate is needed.

[0003] At present, the method for evaluating the substrate combination is mostly based on the purification efficiency of pollutants, which is slow, and different operating conditions and pollutant concentrations result in different purification efficiencies under the same substrate combination. In practical application, the individual performance of the substrate may be good, but the individual performance may be particularly poor. Therefore, how to select the optimal substrate by comprehensively considering various performances is a problem to be solved. SUMMARY

[0004] In order to solve the problems in the prior art that the evaluation method is easily affected by operating conditions and pollutant concentrations, and the existing evaluation method is poor in economy, the present application provides a wetland substrate combination and evaluation method based on hydraulic performance, and an application of the substrate combination selected by the method in constructed wetland water treatment, and the specific scheme is as follows:

[0005] The evaluation method of the wetland substrate combination based on hydraulic performance uses the combined substrate to establish a wetland model, uses a tracer test method to test the hydraulic performance of the substrate, and draws a residence time distribution curve. On the basis of the residence time distribution curve, the average hydraulic residence time, the effective volume ratio, the water flow dispersion degree, the standard flow dispersion degree and the hydraulic efficiency are calculated. After the effective volume ratio, the water flow dispersion degree, the standard flow dispersion degree and the hydraulic efficiency are weighted and calculated according to the weight, the comprehensive performance index is obtained, and the substrate is evaluated according to the comprehensive performance index.

[0006] Further, the closer the effective volume ratio is to 1, the better; the smaller the water flow dispersion degree and the standard flow dispersion degree, 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 the 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 influent flow rate during different operation processes. 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 dispersion degree σ within the wetland based on the tracer detection time and tracer concentration t 2 ;

[0012] S4, average hydraulic retention time T m and 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 and 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; when comparing 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 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 flow dispersion degree sigma of the wetland t 2 ; Wherein: t is the time of tracer concentration detection; c(t) is the tracer concentration; Delta t is the time interval of adjacent two measurements.

[0016] Further, the time t of tracer concentration detection is calculated from the moment of tracer addition.

[0017] Further, the standard flow dispersion degree sigma is calculated according to the formula Calculate the water flow dispersion degree sigma of the wetland θ 2 .

[0018] A matrix combination screened by the above-mentioned evaluation method, which is composed of no less than two layers of matrices, and the permeability of the uppermost layer of the matrix is the lowest, and the permeability of the lowermost layer of the matrix is the highest; the permeability coefficients of the uppermost layer and the lowermost layer of the matrix differ by 1-8 orders of magnitude.

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

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

[0021] 1. The evaluation method is based on the angle of hydraulic performance, is not affected by other factors such as operating conditions and pollutant concentrations, does not need to repeatedly measure the pollutant concentration, avoids the loss of equipment and reagents, the data is easy to obtain, the result can be quickly output, and the feasibility is strong.

[0022] 2. The evaluation method involves multiple factors, can comprehensively evaluate multiple performance indicators, and can comprehensively evaluate the matrix combination, coordinate the unevenness of the evaluation method of the advantages and disadvantages, and select the most practical optimal combination.

[0023] 3. The evaluation method has accurate results and reasonable weight setting, can integrate the average hydraulic retention time, the effective volume ratio, the water flow dispersion degree, the standard flow dispersion degree and the hydraulic efficiency index, and objectively and scientifically evaluates the advantages and disadvantages of the matrix through the comprehensive performance index.

[0024] 4. The matrix combination screened by the evaluation method can make the flow field and pollutant migration more uniform, the hydraulic performance of the wetland is better, the internal short circuit phenomenon of the wetland can be relieved, the effective area of the wetland is increased, and the performance of the wetland is improved. BRIEF DESCRIPTION OF DRAWINGS

[0025] Fig. 1 is the retention time distribution curve of examples 1-3.

[0026] Fig. 2 is the retention time distribution curve of examples 4-6.

[0027] Fig. 3 7 to 10 are the residence time distribution curves of Examples 7 to 10.

[0028] Fig. 4 is the residence time distribution curve of the comparative ratio. DETAILED DESCRIPTION

[0029] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts 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. When the wetland model is saturated, maintain the inlet and outlet water flow rates unchanged. Rapidly pulse 100 mL of 1 g / L NaCl solution into the wetland model through the water inlet. Begin to test the outlet water conductivity at a frequency of 5 to 10 minutes until the conductivity returns to the pre-test background value. Plot the residence time distribution curve.

[0032] S2. According to the size of the system, the porosity of the filler 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 center of gravity 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 measured (calculated from the moment the tracer is added); c(t) is the tracer concentration; Δt is the time interval between two adjacent measurements;

[0034] S4, average hydraulic retention time T m and theoretical hydraulic retention time T n The effective volume ratio e is calculated based on the ratio of the theoretical hydraulic retention time T nT is the time taken for the concentration to reach a maximum p , the standard flow dispersion σ is calculated according to the formula θ 2 ; the hydraulic efficiency λ is calculated as the ratio of T p , the time taken for the concentration to reach a maximum, to T n , the theoretical hydraulic retention time;

[0035] The comprehensive performance index is calculated 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; the comprehensive performance index of different substrate combinations is compared, and the smaller the value, the better the performance of the substrate.

[0036] The substrate combinations of the examples and comparative examples, and the average hydraulic retention time T m , the theoretical hydraulic retention time T n , the effective volume ratio e, the flow dispersion σ t 2 , the standard flow dispersion σ θ 2 and the hydraulic efficiency λ measured using the retention time distribution curve of the substrate according to the formula Figs. 1-4 are shown in the following table:

[0037]

[0038]

[0039] The comprehensive performance index of each example and comparative example is evaluated according to the formula, and the results are as follows:

[0040]

[0041]

[0042] It can be seen from the hydraulic characteristics and the comprehensive performance index that the greater the difference in permeability of the upper, middle and lower substrates of the wetland, the better the performance of the substrate as a whole. The average hydraulic retention time T m of example 3, which is a combination of loess, coarse sand and gravel, is 16414s, the theoretical hydraulic retention time T n is 17307s, and the effective volume ratio e is 0.949, which is slightly less than 1 and is closest to 1 among the other 9 examples and comparative examples, indicating that there is only a small amount of dead zone in the wetland of example 3 compared to the other examples; the flow dispersion σ t 2 is 7.45×107 s 2 The standard flow dispersion is 0.249, which is relatively small, indicating that the water flow in the wetland is more uniform and stable, the water flow dispersion degree is small, and the degradation of pollutants is facilitated; the hydraulic efficiency λ is 0.713, indicating that the dead zone in the wetland is small, and the performance of the wetland is good. The comprehensive performance index of Example 3 is 0.71, the permeability of each layer of the upper layer, the middle layer and the lower layer of Example 3 is large, and each hydraulic characteristic is good, which is suitable for the comprehensive performance index, indicating that the evaluation method of the present application has high accuracy.

[0043] It can be found from the table that the hydraulic performance of the wetland system of each example with a large difference in the permeability coefficient between the top layer and the bottom layer of the multi-layer substrate combination is obviously better than that of the single substrate and the substrate with a small difference in the permeability coefficient. The standard flow dispersion of each comparative example is about 0.5, which is relatively high, and the effective volume ratio is also far from 1, which indicates that the dead zone phenomenon in the wetland is serious, and the flow in 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 example is greater than 2, which is suitable for the results of parameter analysis.

[0044] With the increasing permeability of the lower layer substrate, the effective volume ratio of the wetland becomes smaller. For example, if the middle sand of the lower layer of Comparative Example 1 is replaced by the gravel of Example 3, the effective volume ratio e of the wetland increases from 0.609 to 0.853, and the 6.99x10 8 s 2 decreases to 1.75x10 8 s 2 , and the standard flow dispersion decreases from 0.508 to 0.372, which indicates that the short circuit phenomenon in the wetland is alleviated, the water flow dispersion degree in the wetland system becomes smaller, the effective area of the wetland becomes larger, and the performance of the wetland is enhanced, and the comprehensive performance index decreases 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 performance of the wetland. For example, if the middle sand, coarse sand and gravel in Example 10 are replaced by loess, coarse sand and gravel. The effective volume ratio of the wetland will increase; the water flow dispersion, the standard flow dispersion will decrease, and the number of continuous reaction mixers will increase; which indicates that under the condition that the middle and lower layer substrates are unchanged, the decrease of the permeability of the upper layer substrate will lead to the decrease of the dead zone in the wetland, the increase of the effective volume and the more uniform distribution of the fluid in the wetland.

[0046] The standard flow dispersion of Example 6 is higher than that of Comparative Example 3, and the rest of the parameters are better than those of Comparative Example 3, and the comprehensive performance index 1.36 is also obviously lower than 2.17 of Comparative Example 3. It is illustrated that even if the individual performance is changed to be better, but the rest of the performance is changed to be worse, the change can be captured by the evaluation method of the application, and the error or distortion caused by the single factor evaluation is avoided. The matrix combination screened by the method of the application has strong practicability.

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

Claims

1. A method for evaluating wetland substrate combinations based on hydraulic performance, characterized in that: The wetland model was established using the assembled matrix, and the hydraulic performance of the matrix was tested using the tracer experimental method. The residence time distribution curve was drawn. Based on the residence time distribution curve, the average hydraulic residence time T was calculated. m , effective volume ratio e, water flow dispersion σ t 2 , standard flow dispersion σ θ 2 and hydraulic efficiency λ; effective volume ratio e, water flow dispersion σ t 2 , standard flow dispersion σ θ 2 and hydraulic efficiency λ, 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; when comparing the comprehensive performance indexes of different matrices, the smaller the value, the better the matrix performance.

2. The method for evaluating wetland substrate combinations 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; and the greater the hydraulic efficiency, the better.

3. The method for evaluating wetland substrate combinations based on hydraulic performance according to claim 1, wherein: 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 the residence time distribution curve; S2. Calculate the theoretical hydraulic retention time (T) of the wetland system based on the system size, filler porosity and influent flow rate during different operation processes. 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 dispersion degree σ within the wetland based on the tracer detection time and tracer concentration t 2 ; S4, average hydraulic retention time T m and theoretical hydraulic retention time T n The effective volume ratio e is calculated based on the ratio of the water flow dispersion σ within the wetland. t 2 and the average hydraulic retention time T m Calculate the standard flow dispersion σ θ 2 ; The time T when the concentration reaches the maximum p and theoretical hydraulic retention time T n The hydraulic efficiency λ is calculated by the ratio of S5. Calculate and compare comprehensive performance indices.

4. The method for evaluating a wetland matrix combination based on hydraulic performance according to claim 3, wherein: 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 through the wetland system; ξ is the porosity of the filler.

5. The method for evaluating wetland substrate combinations based on hydraulic performance according to claim 3, wherein: 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.

6. The method for evaluating wetland substrate combinations based on hydraulic performance according to claim 5, characterized in that: The time t for detecting the tracer concentration is calculated from the instant when the tracer is added.

7. The method for evaluating wetland substrate combinations based on hydraulic performance according to claim 3, wherein: According to the formula Calculate the standard flow dispersion σ θ 2 .

8. A matrix combination obtained by screening according to the evaluation method of 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.

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

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