Method and device for on-line determination of sludge concentration

Abstract

The invention discloses a method and a device for on-line determination of sludge concentration, and belongs to the technical field of environmental protection, analysis and measurement. The method comprises the following steps: measuring an impedance spectrogram of an unknown sludge sample by using an impedance measuring instrument, presetting a sludge concentration range based on a sludge water content range or an apparent form, firstly selecting a corresponding concentration calculation formula, then analyzing the impedance spectrogram to calculate an equivalent circuit parameter (Rt or R2) or a spectrogram fitting parameter P in the formula, and finally calculating the sludge concentration according to the equivalent circuit parameter (Rt or R2). The sludge concentration values are substituted into a concentration calculation formula to calculate corresponding sludge concentration values, if the concentration values fall into a preset concentration range, a result is output, if the concentration values are consistent, a result is output, and otherwise, the process is repeated until the reasonable concentration values are calculated. A device for realizing the method comprises an impedance measuring instrument, a conductivity electrode and a computer. The method overcomes the problems of a traditional drying method, an optical method and an ultrasonic method, can realize real-time rapid measurement of the sludge solid concentration, is especially suitable for a high-concentration sludge system, and has strong anti-interference capability.

Description

Technical Field This invention relates to the fields of environmental protection and analytical measurement technology, and in particular to a method and apparatus for online determination of sludge concentration. This method is suitable for the rapid online determination of sludge concentration. Background Technology

[0001] In the process of sludge treatment and disposal, timely acquisition of sludge concentration is crucial for sludge conditioning, dewatering, drying, and subsequent treatment. Currently, the standard method for determining sludge concentration is the drying and weighing method. Optical and ultrasonic methods are also widely used in sludge concentration determination. However, the drying and weighing method suffers from time-consuming measurement processes and cannot be performed online. In the application of optical measurement methods, CN120890901A discloses an activated sludge concentration detection method based on optical principles. This method involves diluting the sludge and acquiring images and absorbance data using an imaging device and a turbidity probe. Multiple dilution measurements are performed, and the original sludge concentration is inferred from the linear interval data. This method is not suitable for online measurement of high-concentration sludge, and multiple dilutions are not only time-consuming but also introduce significant errors, affecting the accuracy of sludge concentration measurement. Furthermore, the optical viewing window in this method is easily contaminated by sludge. In the application of ultrasonic methods, CN113008979A discloses a method for determining the concentration of suspensions using ultrasonic detection technology. This method uses a single-piece carrier element, arranging ultrasonic transducers and multiple reflecting surfaces, and determines the concentration value by measuring the propagation time of ultrasonic waves between different reflecting surfaces. However, the accuracy of this method is easily affected by air bubbles, temperature, flow rate, and particle distribution uniformity in the sludge, and the installation requirements are relatively high. In contrast, electrochemical impedance spectroscopy has advantages such as convenient installation, strong anti-interference ability, wide measurement range, and fast response, enabling rapid online determination of sludge concentration. Summary of the Invention

[0002] To address the aforementioned shortcomings of existing technologies, this invention aims to provide a method and apparatus for online determination of sludge concentration. The purpose is to solve the problems of time-consuming operation, susceptibility to interference, and short measurement range inherent in existing technologies. This method utilizes an impedance measuring instrument connected to a conductivity electrode to perform real-time frequency scanning of the sludge sample and acquire impedance spectra. Through analysis, multiple characteristic electrochemical parameters are obtained, and a mathematical model is established between sludge concentration and these electrochemical parameters. Different specific linear mathematical models are matched to different sludge properties. The sludge concentration is then fed back online. To achieve the above objective, the first aspect of this invention provides a method for online determination of sludge concentration, comprising the following steps: (1) Impedance measurement of sludge was performed to obtain its frequency scanning impedance spectrum; (2) For fluid sludge with a moisture content of over 85%, the area P is obtained by integrating the relaxation spectrum distribution function G(λ), and the sludge concentration (TSS, g / L) is calculated using formula (1): TSS=k1×P+b1(1) In the formula, k1 is the linear regression coefficient and b1 is the regression intercept, where the value of k1 ranges from -0.7 to -0.4 and the value of b1 ranges from 5.0 to 9.0. (3) For plastic sludge with a moisture content between 70% and 80%, the frequency scanning impedance spectrum is fitted using a Debye-like equivalent circuit to obtain the resistance element parameter R2. The sludge concentration (TSS, g / L) is then calculated using formula (2): TSS=k2×R2+b2(2) In the formula, k2 is the linear regression coefficient and b2 is the regression intercept; the value of k2 ranges from -0.8 to -0.4, and the value of b2 ranges from 2.0 to 6.0. The equivalent circuit is a circuit in which resistor R1 and capacitor C1 are connected in series and then in parallel with resistor R2. (4) For sludge with properties between fluidity and plasticity, its frequency sweep impedance spectrum is fitted using the Randles equivalent circuit to obtain... Resistor parameter R t The concentration of sludge (TSS, g / L) is calculated using formula (3): TSS=k3×R t +b3(3) In the formula, k3 is the linear regression coefficient and b3 is the regression intercept; the value of k3 ranges from -0.8 to -0.3, and the value of b3 ranges from 3.0 to 5.0.

[0003] (5) Based on the sludge moisture content range or apparent morphology, preset the sludge concentration range, and select the appropriate formula mentioned above to preliminarily determine the sludge concentration; (6) Compare the initially determined sludge concentration with the preset concentration range. If the measured concentration is within the preset concentration range, output the result; if it falls outside the preset concentration range, continue to use the other two formulas in formulas (1), (2), and (3) to calculate until the initially determined sludge concentration falls within the preset concentration range, then output the valid result.

[0004] Furthermore, P is obtained by integrating the relaxation spectrum distribution function G(λ), and the solution formula (4) for the relaxation spectrum distribution function G(λ) is as follows: (4) In the formula: For input frequency, Let be the relaxation spectrum distribution function to be determined. For characteristic frequencies, Z ∞ represents the phase shift at the high-frequency limit; Furthermore, P is the area of ​​integration of the relaxation spectrum distribution function G(λ) within the characteristic relaxation time interval [λ1, λ2], which is obtained through formula (5): (5) In the formula: λ1 and λ2 are the characteristic relaxation times. Furthermore, λ1 and λ2 are obtained by solving for the upper and lower limits of the frequency scan, respectively, and their general solution formulas are as follows: (6) In the formula: This is the input frequency.

[0005] Furthermore, the R t The complex impedance formula (7) for the Randle equivalent circuit is obtained by fitting the formula: (7) In the formula, R is the input frequency. c R is the bulk resistivity of the sludge system. t For charge transfer resistance, C p This represents the amplitude of the double-layer capacitance. It is a dimensionless diffusion index. This is the Worburg coefficient.

[0006] Furthermore, R2 is obtained by fitting the complex impedance formula (8) of the Debye-like equivalent circuit: (8) In the formula, R1 is the input frequency, R2 is the solid phase resistor, and C1 is the liquid phase resistor.

[0007] Furthermore, during impedance measurement, the instrument applies a sinusoidal AC voltage ranging from 10 to 500 mV, and a frequency scan range of 100 Hz to 50 MHz.

[0008] Furthermore, the method is applicable to measuring one or more of activated sludge, digested sludge, water supply sludge, dredged sludge, or pipeline sludge. The corresponding solids concentration range is 0.01 ~ 450 g / L.

[0009] Furthermore, the linear regression coefficients k1 range from -0.7 to -0.4, k2 ranges from -0.8 to -0.4, and k3 ranges from -0.8 to -0.3; the regression intercepts b1 range from 5.0 to 9.0, b2 ranges from 2.0 to 6.0, and b3 ranges from 3.0 to 5.0.

[0010] Furthermore, the method compares the initially determined sludge concentration with the preset concentration range to determine whether the selected model is correct. If the measured concentration falls within the preset concentration range, then the concentration is the final effective concentration. If it falls outside the preset concentration range, the applicable formula is re-determined based on the appearance morphology, and the concentration of the sludge sample is calculated using the three calculation formulas corresponding to steps (2), (3), and (4). The measured results that fall within the preset concentration range are selected and used as the final effective concentration.

[0011] Furthermore, the Randles equivalent circuit consists of two sets of circuits connected in series, one of which is the bulk resistance R of the sludge system. c The other circuit consists of charge transfer resistor R t With double-layer capacitance C p They are connected in parallel.

[0012] Furthermore, the Debye-like equivalent circuit consists of two circuits connected in parallel. One circuit is composed of a solid-phase resistor R1 and a polarization capacitor C1 connected in series, while the other circuit is composed of a liquid-phase resistor R2.

[0013] A second aspect of the present invention provides an apparatus for online determination of sludge concentration, characterized in that the apparatus comprises: (1) Impedance measuring instruments, including impedance spectrometers or electrochemical workstations, whose core function is to automatically acquire impedance spectrum data based on preset parameters (such as 50mV measurement voltage and 1kHz ~ 10MHz scanning frequency). (2) Conductivity electrode, connected to impedance measuring instrument, as a sensor, can be easily installed on the reserved interface of sludge pipe or container, and its sensing part is immersed in sludge. (3) Computer: Connected to the impedance measuring instrument, it controls the operation of the impedance measuring instrument and the collection of impedance spectrum data, function simulation, formula calculation, and obtains the concentration results of sludge samples.

[0014] The beneficial effects of this invention are as follows: This invention enables online real-time measurement of sludge concentration, with the measurement process taking only a few minutes, completely overcoming the severe lag of traditional drying methods; it effectively avoids the problem of easy contamination of the viewing window in optical methods; it has a wide measurement range and rapid response characteristics, supporting online real-time monitoring of high-concentration sludge without dilution; and it avoids the problem of air bubble interference in ultrasonic methods, making installation convenient. Therefore, this invention provides a solution for online monitoring of sludge concentration and has broad application prospects. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Appendix Figure 1 Flowchart of the method of the present invention Appendix Figure 2 The relationship between parameter P and sludge concentration in this invention. Appendix Figure 3 Parameter R of the present invention t Relationship with sludge concentration Appendix Figure 4 The relationship between parameter R2 and sludge concentration in this invention. Appendix Figure 5 Debye equivalent circuit diagram Appendix Figure 6 Randles equivalent circuit diagram Detailed Implementation Exemplary embodiments of the present invention are described in detail below. This detailed description should not be considered a limitation of the present invention, but rather a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. The following embodiments are only some embodiments of the present invention. Any simple modifications and improvements based on the technical concept of the present invention, without departing from the core technical solution of the present invention, should fall within the protection scope of the present invention. Furthermore, for numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art described herein. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of the present invention. The terms "comprising," "including," "having," "containing," etc., as used herein, are open-ended terms, meaning they include but are not limited to.

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0018] The impedance measuring instrument should be an impedance analyzer with scanning measurement function, preferably the MFIA type impedance analyzer from Zurich Instruments, Switzerland.

[0019] Table 1. Main performance parameters of the impedance analyzer

[0020] The conductivity electrode connected to the impedance analyzer is preferably a Tetracon 325 electrode, and its main performance parameters are shown in Table 2.

[0021] Table 2 Main performance parameters of conductivity electrodes

[0022] The present invention will be further illustrated by the following embodiments: Example 1: 1. Sample preparation Test subject: Sludge from a sedimentation tank at a water supply plant in North China. Three test samples with different moisture contents were collected on-site.

[0023] 2. Measurement parameters and process Drying method: Three samples were taken and laboratory tests were conducted strictly according to the standard method (drying at 105°C to constant weight). The results were used as the concentration benchmark. The sludge concentration of the samples was calculated using formula (9).

[0024] TSS=(W2-W1) / V(9) In the formula: W1 is the mass of the crucible (g), W2 is the total mass of the crucible and the dried sludge (g), and V is the volume of the sludge (ml).

[0025] The method of this invention involves observing and judging the properties of three types of sludge samples collected on-site, determining the corresponding parameters and calculation formulas for parameter measurement, immersing the probe of the device of this invention sequentially into sludge samples of three different concentrations, starting the measurement program, completing frequency scanning, extracting characteristic parameters (Rt, R2, P), and inputting them into the corresponding calculation formulas to output the concentration measurement value in real time. Simultaneously, parallel sampling is performed for each sample, and a baseline concentration is determined using the drying method.

[0026] For sample A, it was determined to be fluid sludge based on its apparent characteristics. Accordingly, suitable characteristic parameters and corresponding calculation formulas were selected. After the characteristic parameters were detected and the concentration was calculated, the measurement results were compared with the preset concentration range. The measured value fell within the preset range, thus achieving accurate measurement in one go.

[0027] For samples B and C, their apparent properties were observed and determined to be sludge and plastic sludge, respectively, which are between fluid and plastic. The measurement steps for sample A were repeated, and the results all fell within the preset range, achieving accurate measurement in one go.

[0028] Impedance sweep sinusoidal voltage: 50mV Frequency scanning range: 1000Hz ~ 10MHz 3. Results Analysis and Comparison The online measured values ​​of the method of the present invention were compared with the reference values ​​of the drying method, and the results are shown in the table below: Table 3. Comparison of online measured values ​​and drying method baseline values ​​of sludge from different sources in water supply.

[0029] Example 2: 1. Sample and Equipment Configuration Test subjects: Activated sludge collected from three municipal wastewater treatment plants in North China. Three samples with different moisture contents (corresponding sample numbers A1~A3, B1~B3, and C1~C3) were prepared for each source of sludge through in-situ sampling.

[0030] 2. Measurement parameters and process The sludge concentrations measured in this embodiment were calibrated and compared with the results obtained by the drying and weighing method (standard method) given in Example 1. Using the prediction method and device of this invention, online measurements were conducted according to the following procedure: First, the sample type was preliminarily determined by observing its appearance, and suitable characteristic parameters and corresponding calculation formulas were selected; then, the detection probe was directly inserted into the sludge sample, the online measurement program was started, frequency scanning impedance measurement was completed, the spectrum was fitted, and the corresponding characteristic parameters (Rt, R2, P) were extracted, substituted into the matching formula, and the concentration measurement value was output in real time. Parallel sampling was performed for each sample to ensure data reliability.

[0031] The specific determination and measurement process for samples from each wastewater treatment plant in this embodiment is as follows: Plant A: After initial appearance property assessment, parameter adaptation, and measurement calculation, samples A1 and A2 showed results within the preset concentration range, achieving an accurate prediction of sludge concentration in one measurement. Sample A3, initially assessed as sludge between flowability and plasticity, showed results outside the preset range after selecting corresponding parameters and formulas for measurement calculation. After changing parameters and formulas for a second measurement calculation, the results fell within the preset range, and the second measurement output an accurate concentration value.

[0032] Plant B: After the initial determination, parameter adaptation, and measurement calculation of samples B1 and B3, the results met the preset range requirements, achieving an accurate prediction of sludge concentration in one measurement. Sample B3 was initially determined to be fluid sludge. After selecting the corresponding parameters and formulas for measurement, the results deviated from the preset range. After changing the parameters and formulas for a second measurement, the results fell within the preset range, and the second measurement output an accurate concentration value.

[0033] Plant C: After the initial determination and measurement calculation of samples C1 and C3, the results fell within the preset range, achieving an accurate prediction of sludge concentration. Sample C2 was initially determined to be plastic sludge, and the measurement result did not fall within the preset range. After changing the parameters and formulas, the measurement result still did not meet the standard. Finally, after calculating all three characteristic parameters, the correct concentration value was output.

[0034] Impedance sweep sinusoidal voltage: 50mV Frequency scanning range: 5000Hz ~ 8MHz 3. Results Analysis and Comparison Table 4. Comparison of online measured values ​​and drying method baseline values ​​of activated sludge concentrations from different sources.

[0035] Example 3: 1. Sample and Equipment Configuration Subjects of measurement: Pipe sediments with different moisture contents were taken from the drainage pipe network of a city in North China and numbered as samples A, B and C.

[0036] 2. Measurement parameters and process The sludge concentrations measured in this embodiment were calibrated and compared with the results of the drying and weighing method (national standard method) given in Example 1.

[0037] The online measurement using the method and apparatus of this invention follows this process: First, the type of each sample is determined by observing its appearance, and suitable characteristic parameters and corresponding calculation formulas are selected. Then, the detection probe of the apparatus is directly inserted into the corresponding sample, the online measurement program is started, frequency scanning impedance measurement is completed, impedance spectrum is fitted and characteristic parameters (Rt, R2, P) are extracted, and the concentration is calculated by substituting them into the matching calculation formula. The measured value is output in real time. The measurement results are compared with the preset concentration range. Each sample is accurately determined and the results meet the standards on the first attempt, without the need for secondary verification or repeated checks.

[0038] Impedance scanning sinusoidal voltage: 200mV Frequency scanning range: 1000Hz ~ 10MHz Table 5. Comparison of online measured values ​​and drying method benchmark values ​​for pipe sludge of different concentrations.

Claims

1. A method for online determination of sludge concentration, characterized in that, The procedure is carried out using a device that includes an impedance measuring instrument, conductivity electrodes, and a computer, and includes the following steps: (1) Impedance measurement of sludge was performed to obtain its frequency scanning impedance spectrum; (2) For fluid sludge with a moisture content of over 85%, the area P is obtained by integrating the relaxation spectrum distribution function G(λ), and the sludge concentration (TSS, g / L) is calculated using formula (1): TSS=k1×P+b1(1) In the formula: k1 is the linear regression coefficient, b1 is the regression intercept, where the value of k1 ranges from -0.7 to -0.4, and the value of b1 ranges from 5.0 to 9.0; (3) For plastic sludge with a moisture content between 70% and 80%, the frequency scanning impedance spectrum is fitted using a Debye-like equivalent circuit to obtain the resistance element parameter R2. The sludge concentration (TSS, g / L) is then calculated using formula (2): TSS=k2×R2+b2(2) In the formula: k2 is the linear regression coefficient, and b2 is the regression intercept; the value of k2 ranges from -0.8 to -0.4, and the value of b2 ranges from 2.0 to 6.

0. The equivalent circuit is a circuit in which resistor R1 and capacitor C1 are connected in series and then in parallel with resistor R2. (4) For sludge with properties between fluidity and plasticity, its frequency sweep impedance spectrum is fitted using the Randles equivalent circuit to obtain... Resistor parameter R t The concentration of sludge (TSS, g / L) is calculated using formula (3): TSS=k3×R t +b3(3) In the formula: k3 is the linear regression coefficient, b3 is the regression intercept; the value of k3 ranges from -0.8 to -0.3, and the value of b3 ranges from 3.0 to 5.0; (5) Based on the sludge moisture content range or apparent morphology, preset the sludge concentration range, and select the appropriate formula mentioned above to preliminarily determine the sludge concentration; (6) Compare the initially determined sludge concentration with the preset concentration range. If the measured concentration is within the preset concentration range, output the result; if it falls outside the preset concentration range, continue to use the other two formulas in formulas (1), (2), and (3) to calculate until the initially determined sludge concentration falls within the preset concentration range, then output the valid result.

2. The method for online determination of sludge concentration according to claim 1, characterized in that, The P is obtained by integrating the relaxation spectrum distribution function G(λ), and the solution formula (4) for the relaxation spectrum distribution function G(λ) is as follows: （4） In the formula: For input frequency, Let be the relaxation spectrum distribution function to be determined. For characteristic frequencies, Z ∞ represents the phase shift at the high-frequency limit; P is the area of ​​integration of the relaxation spectrum distribution function G(λ) in the characteristic relaxation time interval [λ1, λ2], which is obtained by formula (5): （5） In the formula, λ1 and λ2 are the characteristic relaxation times, which are obtained by solving the upper and lower limits of the frequency scan, respectively. The general solution formula (6) is as follows: （6） In the formula: This is the input frequency.

3. The method for online determination of sludge concentration according to claim 1, characterized in that, R2 is obtained by fitting the complex impedance formula (7) of the Debye equivalent circuit; （7） In the formula: R1 is the input frequency, R2 is the solid phase resistor, and C1 is the liquid phase resistor.

4. The method for online determination of sludge concentration according to claim 1, characterized in that, R t The complex impedance formula (8) of the Randle equivalent circuit is obtained by fitting the formula. （8） In the formula: R is the input frequency. c R is the bulk resistivity of the sludge system. t For charge transfer resistance, C p This represents the amplitude of the double-layer capacitance. It is a dimensionless diffusion index. This is the Worburg coefficient.

5. The method for online determination of sludge concentration according to claim 1, characterized in that, The frequency scanning range of the impedance spectrum is 100Hz ~ 50MHz.

6. The method for online determination of sludge concentration according to claim 1, characterized in that, The method is applicable to measuring one or more of activated sludge, digested sludge, water supply sludge, dredged sediment or pipeline sediment, with a corresponding solid concentration range of 0.01 g / L to 450 g / L.

7. The method for online determination of sludge concentration according to claim 1, characterized in that, The linear regression coefficients have the following values: k1 ranges from -0.7 to -0.4, b1 ranges from 5.0 to 9.0, k2 ranges from -0.8 to -0.4, b2 ranges from 2.0 to 6.0, k3 ranges from -0.8 to -0.3, and b3 ranges from 3.0 to 5.

0.

8. The method for online determination of sludge concentration according to claim 1, characterized in that, The method compares the initially determined sludge concentration with the preset concentration range to determine whether the selected model is correct. If the measured concentration falls within the preset concentration range, the concentration is the final effective concentration. If it falls outside the preset concentration range, the applicable formula is re-determined based on the appearance morphology. The three calculation formulas corresponding to steps (2), (3), and (4) are used to calculate the concentration of the sludge sample. The measured results that fall within the preset concentration range are selected and used as the final effective concentration.

9. The method for online determination of sludge concentration according to claim 1, characterized in that, The device includes: (1) Impedance measuring instruments, including impedance spectrometers or electrochemical workstations; (2) Conductivity electrode, connected to impedance measuring instrument, installed on sludge pipe or container, and inserted into sludge; (3) A computer is connected to an impedance measuring instrument to control the operation of the impedance measuring instrument and the collection, processing, function simulation, and formula calculation of impedance spectrum data to obtain the concentration results of sludge samples.

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