CN111537400B - Method for online determination of fractal dimension of particulate matter in water - Google Patents

Method for online determination of fractal dimension of particulate matter in water Download PDF

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CN111537400B
CN111537400B CN202010425930.7A CN202010425930A CN111537400B CN 111537400 B CN111537400 B CN 111537400B CN 202010425930 A CN202010425930 A CN 202010425930A CN 111537400 B CN111537400 B CN 111537400B
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particulate matter
fractal dimension
water
complex impedance
fractal
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CN111537400A (en
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王毅力
张达鑫
李俊仪
樊晓阳
高诗卉
李恩锐
韩志博
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Beijing Forestry University
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Abstract

The invention discloses a method for measuring fractal dimension of particulate matter in water on line, belongs to the technical field of detection of particulate matter in water, and aims to solve the problems of insufficient on-line analysis capability and the like of the conventional method. The invention utilizes an electrochemical impedance analyzer connected with a probe to perform online analysis on particles in water. When in test, the sample is not required to be specially processed, only the electrode probe is inserted into the particle suspension to be tested to carry out frequency scanning to determine the complex impedance modulus, and the obtained complex impedance modulus is corrected. And extracting the fractal dimension of the particulate matter according to the established scale-free model between the complex impedance modulus and the scanning frequency in the determined fractal interval. Compared with the prior art, the method has the advantages of wide applicable particle concentration range, no influence of the refractive index and the color of the particles to be detected and the dispersed phase, strong impurity pollution resistance, relatively simple equipment maintenance and capability of meeting the requirement of real-time analysis and control of the particles in water during industrial production operation.

Description

Method for online determination of fractal dimension of particulate matter in water
Technical Field
The invention relates to the technical field of detection of particulate matters in water, in particular to a method for online determination of fractal dimension of particulate matters in water.
Background
The fractal dimension is a measure of the degree of irregularity of the particulate matter, and the size of the fractal dimension can reflect the degree of occupation of corresponding space by the particulate matter, and represents the compactness of the particulate matter. Therefore, the method plays an important role in characterizing the properties of the particles and controlling the industrial process related to the particles.
At present, methods for measuring the fractal dimension of particulate matters in water mainly comprise a microscopic image method, a rheological method, a free settling method and a light scattering method. However, these methods have drawbacks and are difficult to meet the requirements for real-time analysis and control in industrial processes. The microscopic image method mainly extracts the area, perimeter and radius of a single particle through an optical microscope or an electron microscope, so as to calculate the fractal dimension of the particle. However, the method reflects the fractal characteristics of a single particle, and a large number of samples in a particle group are needed to ensure the accuracy of the result during testing. The rheology method requires the preparation of suspension samples of different concentrations and the preparation before testing is time consuming. The free-fall rule requires the determination of the rate of settling of particles under specific conditions (free-fall). Therefore, the fractal characteristics of the particulate matters are difficult to be rapidly reflected on line by the methods. The light scattering method is the most applied test method at present, and different scattering intensities are obtained by changing different scattering wave vectors in the test process. And calculating the fractal dimension of the particulate matter according to a scale-free model between the scattering intensity and the wave vector. The method has the characteristics of high analysis speed and online performance. However, the light scattering method is applicable to a narrow concentration window of particles in water, is not suitable for a thick system, is easily interfered by factors such as the refractive index of the particles and the color of a disperse phase, and has poor pollution resistance of a light chamber in the practical application process. The presence of these problems limits the scope of application of the process in industrial processes.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a method for measuring the fractal dimension of particulate matters in water on line, which aims to bypass the defects of the prior method, utilize electrical equipment connected with a probe to measure the electrical characteristics of the particulate matters in water during frequency scanning on line, obtain the structural information of the particulate matters according to the established model and extract the fractal dimension of the particulate matters.
The invention can be realized by the following technical approaches:
the method comprises the steps of testing a particle suspension by using a commercial electrochemical impedance meter connected with a conductive electrode, wherein a sample is not required to be specially processed during testing, only inserting an electrode probe into a particle suspension to be tested to perform frequency scanning to determine complex impedance modulus, correcting the obtained complex impedance modulus, and extracting the fractal dimension of the particle in a determined fractal interval according to an established scale-free model between the corrected complex impedance modulus and scanning frequency.
Furthermore, the concentration range of the particle suspension sample is 1mg/L-100g/L, the temperature is kept constant during measurement, the sine voltage range applied by the electrochemical impedance meter is 1-1000mV, and the scanning frequency range is 0.1Hz-10MHz.
Further, the corrected complex impedance modulus is equal to the corresponding complex impedance modulus at each scanning frequency minus the complex impedance modulus at the highest frequency.
Further, the set up scale-free model between the corrected complex impedance modulus and the scanning frequency is as follows:
Figure BDA0002498722320000021
wherein, | Z c I is the corrected complex impedance modulus, f is the scanning frequency, D f Is the fractal dimension of the particles in water.
The method for extracting the fractal dimension of the particulate matter comprises the following steps: with | Z c The logarithm value of | is Y axis, the logarithm value of scanning frequency f is X axis to make graph, in the defined fractal interval the linear regression analysis is used to fit the graph, and the obtained slope is substituted into | Z c And (4) obtaining the fractal dimension of the particles by a scale-free model between the I and the f.
And the fractal interval is a frequency interval in which the logarithmic value of the corrected complex impedance modulus linearly decreases along with the increase of the logarithmic value of the frequency.
The invention has the beneficial effects that:
compared with the existing method, the method has the advantages that the applicable particle concentration range is wide, the influence of the refractive index and the color of the particles to be detected and a dispersion phase is avoided, the impurity pollution resistance is strong due to the absence of an optical path system, the equipment maintenance is relatively simple, and the requirement of real-time analysis and control of the particles in the water during industrial production operation can be met.
Drawings
FIG. 1 is a schematic diagram of fractal dimension measurement of a suspension of particles in water.
In the figure: 1-thermostat, 2-conductive electrode, 3-particle suspension, 4-commercial electrochemical impedance meter, 5-electrochemical impedance meter and connecting wire between electrodes.
Fig. 2 is a schematic diagram illustrating determination of a fractal interval according to the present invention.
Detailed Description
The present invention will be described in detail with reference to the drawings and examples, which are only exemplary and should not be construed as limiting the scope of the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention, and that such changes and substitutions are intended to be within the scope of the invention.
Acquisition of the corrected complex impedance modulus: a commercial electrochemical impedance analyzer with a frequency scanning function is firstly connected with a conductivity electrode as a tool for online testing. The impedance meter is preferably a daily IM3570, the performance parameters of which are described in Table 1. The electrically conductive electrode is preferably a Tetracon 325 electrode, the main performance parameters of which are described in Table 2.
TABLE 1 Main Performance parameters Table of impedance Analyzer
Figure BDA0002498722320000022
TABLE 2 conductivity electrode Primary Performance parameters
Figure BDA0002498722320000023
Figure BDA0002498722320000031
As shown in fig. 1, the conductive electrode is used as a probe to be inserted into the suspension of the particles to be measured for frequency scanning, and the insertion depth of the probe is ensured to ensure that the sample is submerged in the contact wafer of the electrode. The concentration of the suspension is 1mg/L-100g/L. During scanning, the impedance instrument applies 1-1000mV sine voltage, the scanning frequency is 0.1Hz-10MHz, the complex impedance modulus under different frequencies is recorded, and the number of acquisition points is 201. To reduce the effect of the difference in conductivity of the suspension, the obtained complex impedance modulus at each scanning frequency needs to be corrected by subtracting the complex impedance modulus at the highest frequency.
Determining a fractal interval: and respectively carrying out logarithmic transformation on the corrected complex impedance modulus and the corrected frequency and plotting, wherein as shown in fig. 2, when the logarithmic value of the corrected complex impedance modulus linearly decreases along with the increase of the logarithmic value of the frequency, the corresponding frequency interval is the determined fractal interval.
Establishing a scale-free model: it is assumed that each particle in the water is made up of several primary particles. When the frequency changes within a certain frequency range of the alternating electric field, the number of primary particles involved in the electron movement region also changes. If the scanning frequency of the ac electric field is defined as a scale, the number of primary particles in the electron movement region has self-similarity in a certain scale regardless of the scale size. Thus, it is possible to obtain
Figure BDA0002498722320000032
Wherein, | Z c I is the corrected complex impedance modulus, f is the scanning frequency, D f Is the fractal dimension of the particle.
And (3) solving an equation to extract a fractal dimension:
taking logarithm of two sides of the model
Figure BDA0002498722320000033
Wherein C is a constant.
Within a determined fractal interval, in lg | Z c Plot | as the Y axis and lgf as the X axis, and fit using linear regression analysis to obtain the slope k.
According to the above-mentioned established model, there are
Figure BDA0002498722320000034
The fractal dimension D of the particles can be obtained by solving the equation f
The steps of determining the fractal interval, solving an equation, extracting the fractal dimension and the like can be realized through programming, so that the fractal dimension of the particulate matter in the water can be fed back on line through the designed program steps by only inserting a test probe into the suspension to be tested to obtain the complex impedance modulus during frequency scanning and correcting.
The invention is further illustrated by the following examples:
the first embodiment is as follows:
taking activated sludge (marked as sludge 1) as particles to be measured from a membrane bioreactor of which the daily treated water amount is 10 ten thousand tons in a certain regeneration water plant (marked as regeneration water plant 1) in Beijing. The sludge concentration is 17.9g/L. Other assay procedures were as described in the detailed description. Lg | Z in the obtained fractal interval c The values of | and lgf are shown in Table 3. The fractal dimension of the obtained sludge 1 was 2.534.
Example two:
excess activated sludge (marked as sludge 2) is taken as particles to be detected from an anaerobic/anoxic/aerobic biological reaction process with daily treatment water amount of 20 ten thousand tons in a certain regeneration water plant (marked as regeneration water plant 2) in Beijing. The sludge concentration is 18.1g/L. Other assay procedures were as described in the detailed description. Lg | Z in the obtained fractal interval c The values of | and lgf are shown in Table 3. The fractal dimension of the obtained sludge 2 was 2.362.
Example three:
taking residual activated sludge (marked as sludge 3) as particles to be detected from an anaerobic/aerobic biological reaction process in which the daily treated water amount of a certain reclaimed water plant (marked as reclaimed water plant 3) in Beijing is 100 ten thousand tons. The sludge concentration is 18g/L. Other assay procedures were as described in the detailed description. Lg | Z in the obtained fractal interval c The values of | and lgf are shown in Table 3. The fractal dimension of the obtained sludge 3 was 2.552.
Example four:
the residual activity is obtained from the oxidation ditch biological reaction process of which the daily treated water amount is 20 ten thousand tons in a certain reclaimed water plant (marked as reclaimed water plant 4) in BeijingSludge (marked as sludge 4) is used as the particulate matter to be detected. The sludge concentration is 18.5g/L. Other assay procedures were as described in the detailed description. Lg | Z in the obtained fractal interval c The values of | and lgf are shown in Table 3. The fractal dimension of the obtained sludge 4 was 2.5.
Example five:
preparing a suspension of polyacrylamide cross-linked ferric hydroxide gel (FHG-PAM) particles as the particles to be measured. The concentration of the particles was 3.25g/L. Other assay procedures were as described in the detailed description. Lg | Z in the obtained fractal interval c The values of | and lgf are shown in Table 3. The fractal dimension of the obtained FHG-PAM was 2.564.
Example six:
a suspension of Cationic Hydrogel (CH) particles was prepared as the particulate material to be tested. The concentration of the particles was 0.2g/L. Other assay procedures were as described in the detailed description. Lg | Z in the obtained fractal interval c The values of | and lgf are shown in Table 3. The fractal dimension of the obtained CH was 2.132.
Lg | Z in the fractal interval obtained by testing in the example of Table 3 c I and lgf
Figure BDA0002498722320000041
Figure BDA0002498722320000051

Claims (5)

1. A method for online measuring fractal dimension of particulate matter in water comprises the steps of testing a particulate matter suspension by using a commercial electrochemical impedance meter connected with a conductive electrode, and is characterized in that a sample is not required to be specially processed during testing, only an electrode probe is inserted into the particulate matter suspension to be measured to carry out frequency scanning to measure complex impedance modulus, the obtained complex impedance modulus is corrected, the fractal dimension of the particulate matter is extracted in a determined fractal interval according to an established scale-free model between the corrected complex impedance modulus and scanning frequency, and the established scale-free model between the corrected complex impedance modulus and the scanning frequency is as follows:
Figure FDA0004029172210000011
wherein, | Z c I is the corrected complex impedance modulus, f is the scanning frequency, D f Is the fractal dimension of the particles in water.
2. The method for online determination of fractal dimension of particulate matter in water as claimed in claim 1, wherein the concentration of particulate matter suspension sample is in the range of 1mg/L to 100g/L, the temperature is kept constant during determination, the sinusoidal voltage applied by electrochemical impedance meter is in the range of 1 to 1000mV, and the scanning frequency is in the range of 0.1Hz to 10MHz.
3. A method for on-line determination of fractal dimension of particles in water as claimed in claim 1 wherein said corrected complex impedance modulus is equal to the corresponding complex impedance modulus at each scanning frequency minus the complex impedance modulus at the highest frequency.
4. The method for on-line measuring the fractal dimension of particulate matter in water as claimed in claim 1, wherein the method for extracting the fractal dimension of particulate matter comprises the following steps: at | Z c The logarithm value of | is Y axis, the logarithm value of scanning frequency f is X axis to make graph, in the defined fractal interval the linear regression analysis is used to fit the graph, the obtained slope is substituted into | Z c And (4) obtaining the fractal dimension of the particulate matter by a scale-free model between the I and the f.
5. The method for on-line determination of fractal dimension of particulate matter in water as claimed in claim 1, wherein said fractal interval is a frequency interval in which the logarithmic value of the corrected complex impedance modulus decreases linearly with increasing logarithmic value of frequency.
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