Spectral detection method for available plant phosphorus in residual sludge hydrothermal carbon

Abstract

The invention discloses a spectrum detection method for plant available available phosphorus in residual sludge hydrothermal carbon, and belongs to the field of detection method development. The method comprises the following steps: fully performing hydrothermal reaction on municipal sludge, and treating the obtained sludge hydrothermal carbonization system to obtain sludge hydrothermal carbon; mixing the sludge hydrothermal carbon with a citric acid solution, oscillating and filtering to obtain an available phosphorus extracting solution; treating the available phosphorus extracting solution by using a molybdate developing method and an ultraviolet spectrophotometer to obtain the available phosphorus concentration; performing XRD (X-Ray Diffraction) characterization on the sludge hydrothermal carbon to obtain map data; analyzing map data by adopting MDI Jade software, and calculating to obtain the crystallinity of the sludge hydrothermal carbon sample; correlation analysis is established on the available phosphorus concentration and the sludge hydrothermal carbon crystallinity, and a quantitative relation model is established. The invention provides a lossless and convenient spectrum detection method for determining available available phosphorus of the sludge hydrothermal carbon plant, and establishes a quantitative relation model of the available available phosphorus content and crystallinity of the sludge hydrothermal carbon plant.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of detection method development, and particularly relates to a method for detecting plant available effective phosphorus in sewage sludge hydrochar. BACKGROUND

[0002] Sewage sludge contains abundant phosphorus, which can be fixed in sewage sludge hydrochar through hydrochar technology. When sewage sludge hydrochar is used for land use, the content of plant available effective phosphorus is considered as one of the important indicators for evaluating the land use potential of sewage sludge hydrochar. According to the Hedley sequential extraction method, phosphorus forms are divided into three types: directly available effective phosphorus (soil solution phosphorus, weakly adsorbed phosphorus), moderately available phosphorus (iron, aluminum oxide / hydroxide combined phosphorus), and difficult to use phosphorus (calcium combined state phosphorus, Ca-P). When plants face the lack of key nutrients (phosphorus, iron) or environmental toxic factors, plants secrete organic acids such as citric acid and oxalic acid in the rhizosphere, and weakly crystalline Ca-P can be used by plants. Therefore, 2% citric acid (CA) is used as an extractant (EU directive 2003 / 2003 method 3.1.3) to evaluate the content of plant available effective phosphorus (CA-P) in sewage sludge hydrochar. Although this method can accurately evaluate the content of CA-P, the experimental steps of this method include 2% CA extraction, molybdate coloration, and spectrophotometer determination, which is relatively complicated. SUMMARY

[0003] The purpose of the present application is to overcome the defects in the prior art and provide a method for detecting plant available effective phosphorus in sewage sludge hydrochar, which aims to quickly and non-destructively determine the content of CA-P in sewage sludge hydrochar. The present application proposes a non-destructive detection method based on X-ray diffraction spectroscopy (XRD), which determines the crystallinity of sewage sludge hydrochar by XRD, and establishes a quantitative relationship model between the content of CA-P in sewage sludge hydrochar and the crystallinity.

[0004] The specific technical solutions adopted by the present application are as follows: The present application provides a method for detecting plant available effective phosphorus in sewage sludge hydrochar, which is as follows: S1: Municipal sludge is subjected to sufficient hydrothermal reaction to obtain a sludge hydrochar system; S2: The sludge hydrochar system is subjected to centrifugation, freeze-drying, grinding, and sieving in sequence to obtain sludge hydrochar; S3: The sludge hydrochar is mixed with a citric acid solution, shaken, and filtered to obtain an effective phosphorus extract; S4: The effective phosphorus extract is subjected to molybdate coloration and ultraviolet spectrophotometry to obtain the concentration of effective phosphorus; S5: The sludge hydrochar is characterized by XRD to obtain pattern data; S6: The pattern data is analyzed by MDI Jade software to calculate the crystallinity of the sludge hydrochar sample; S7: The effective phosphorus concentration and the crystallinity of the sludge hydrochar are correlated to establish a quantitative relationship model.

[0005] Preferably, in S1, the moisture content of the municipal sludge is 85%, the temperature of the hydrothermal reaction is 180-220℃, and the reaction time is 1-24h.

[0006] Preferably, in the hydrothermal reaction process, the pH is adjusted to 2.13-12.38 by using concentrated sulfuric acid with a mass fraction of 98% and potassium hydroxide with a purity of 99%.

[0007] Preferably, in S2, the centrifugal rate is 12000r / min, the running time is 5min, and the ground sample is sieved through a 100 mesh sieve.

[0008] Preferably, in S3, the mass fraction of the citric acid solution is 2%, the volume is 20mL, the mass of the sludge hydrochar is 0.2g, the oscillation time is 30min, the rotation speed is 30-32r / min, the oscillation temperature is 30℃, and the effective phosphorus extract is obtained by filtering through a 0.22μm filter membrane.

[0009] Preferably, in S4, 0.05mL of the effective phosphorus extract is removed, 0.2mL of molybdate solution is added, mixed for 30 seconds, then 0.1mL of ascorbic acid solution with a mass fraction of 10% is added, and finally the volume is made up to 5mL; after 10 minutes of reaction, the absorbance is measured at a wavelength of 710nm using a UV spectrophotometer to obtain the effective phosphorus concentration.

[0010] Preferably, in S6, according to the pH value used in the hydrothermal reaction process, when calculating the crystallinity, the sludge hydrochar samples are classified into group 1 representing strongly acidic sludge hydrochar with initial pH≤4 and group 2 representing non-strongly acidic sludge hydrochar with initial pH>4, and the crystallinity of the sludge hydrochar samples is calculated; according to the calculation results, the strongest crystallinity sample is selected from each group, and the information including different peak positions and half-peak widths is obtained using MDI Jade software, and the crystalline peaks with a half-peak width less than 3 are set as fixed peak positions; on this basis, the remaining samples are added to each group and fitted to obtain the crystallinity of different sludge hydrochars.

[0011] Preferably, in S6, the XRD peak of silicon dioxide is deducted when calculating the crystallinity.

[0012] As preferred, the group 1 contains the peak positions with a half-peak width less than 3: 35.917, 23.018, 29.359, 39.379, 43.104, 47.039, 48.455, 47.485, 60.529, 57.332, 64.598, 20.695 degrees.

[0013] As preferred, the group 2 contains the peak positions with a half-peak width less than 3: 16.454, 22.908, 25.455, 31.341, 38.627, 48.680, 52.254, 55.694, 36.217, 40.804, 41.316, 43.359, 74.1 degrees.

[0014] As preferred, in the S7, when the quantitative relationship model is established, in the origin software, the data of the group 1 and the group 2 are combined, the sludge hydrochar crystallinity is taken as the horizontal coordinate, the sludge hydrochar effective phosphorus content is taken as the vertical coordinate, and the linear fitting is performed to obtain the quantitative relationship model of the two.

[0015] Compared with the prior art, the present application has the following beneficial effects: A non-destructive and convenient spectral detection method is provided for the determination of the plant available effective phosphorus of sludge hydrochar, and a quantitative relationship model of the plant available effective phosphorus content and the crystallinity of sludge hydrochar is established. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 It is the effective phosphorus data graph of different sludge hydrochar; Figure 2 It is the XRD spectrum data of different sludge hydrochar; Figure 3 It is the fitting peak obtained by the MDI Jade software analysis of the group 1; Figure 4 It is the fitting peak obtained by the MDI Jade software analysis of the group 2; Figure 5 It is the crystallinity data graph of different sludge hydrochar; Figure 6 It is the quantitative relationship model constructed by the plant available effective phosphorus and the crystallinity of sludge hydrochar. DETAILED DESCRIPTION

[0017] In order to make the above objectives, characteristics and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below with reference to the drawings. In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the spirit of the present application, so the present application is not limited to the specific embodiments disclosed below. The technical features in each embodiment of the present application can be combined accordingly without conflict.

[0018] The present application provides a method for detecting the effective phosphorus spectrum of plant available in residual sludge hydrothermal carbon, which specifically comprises the following steps: S1: Municipal sludge is fully subjected to hydrothermal reaction to obtain a sludge hydrothermal carbonization system.

[0019] As a preferred embodiment of the present application, the water content of the municipal sludge in this step can be 85%, the temperature of the hydrothermal reaction can be 180-220℃, and the reaction time can be 1-24h.

[0020] As a preferred embodiment of the present application, in the hydrothermal reaction process of this step, the pH is adjusted to 2.13-12.38 by using concentrated sulfuric acid with a mass fraction of 98% and potassium hydroxide with a purity of 99%.

[0021] S2: The above sludge hydrothermal carbonization system is sequentially subjected to centrifugation, freeze-drying, grinding and sieving treatment to obtain sludge hydrothermal carbon.

[0022] As a preferred embodiment of the present application, in this step, the centrifugation rate is 12000r / min, the running time is 5min, and the ground sludge is sieved through a 100-mesh sieve.

[0023] As a preferred embodiment of the present application, in this step, the mass fraction of the citric acid solution is 2%, the volume is 20mL, the mass of the sludge hydrothermal carbon is 0.2g, the oscillation time is 30min, the rotation speed is 30-32r / min, the oscillation temperature is 30℃, and the effective phosphorus extract is obtained by filtering through a 0.22μm filter membrane.

[0024] S4: The above effective phosphorus extract is subjected to molybdate coloration and ultraviolet spectrophotometry to obtain the effective phosphorus concentration.

[0025] In a preferred embodiment of the present invention, in this step, 0.05 mL of the effective phosphorus extract is transferred and 0.2 mL of 40 g / L molybdate solution is added. After mixing for 30 seconds, 0.1 mL of 10% ascorbic acid solution is added, and the volume is finally adjusted to 5 mL. After reacting for 10 minutes, the absorbance is measured at a wavelength of 710 nm using a UV spectrophotometer to obtain the effective phosphorus concentration.

[0026] S5: The above-mentioned sludge hydrothermal carbon was characterized by XRD to obtain spectral data.

[0027] S6: The crystallinity of the sludge hydrothermal carbon sample was calculated by analyzing the above spectral data using MDI Jade software.

[0028] In a preferred embodiment of the present invention, in this step, based on the pH value used in the hydrothermal reaction process, the crystallinity is calculated by dividing the samples into two groups: Group 1, representing strongly acidic sludge hydrothermal carbon with an initial pH ≤ 4, and Group 2, representing non-strongly acidic sludge hydrothermal carbon with an initial pH > 4. The crystallinity of the sludge hydrothermal carbon samples is calculated separately for each group. Based on the calculation results, the sample with the strongest crystallinity is selected from each group, and information including different peak positions and half-maximum widths (WHMs) is obtained using MDI Jade software. Crystalline peaks with WHMs less than 3 are fixed at their peak positions. Based on this, other samples are added to each group and fitted to obtain different crystallinities of the sludge hydrothermal carbon.

[0029] Specifically, the operation in the MDI Jade software is as follows: Select the sample with the strongest crystallinity in each group. In the MDI Jade software, select the linear background line, click "BE" in the editing toolbar, and click on various points on the background line to make the background line tangent to the sample line, but do not perform background removal. Left-click on the "BE" in the editing toolbar. To manually label peaks, click the "" button in the editing toolbar; once labeling is complete, right-click the "" button in the editing toolbar. To perform a fitting process, click the "Refine" button in the Profile Fitting interface. Then, click "Report" in the Profile Fitting interface to obtain information such as peak positions and FWMH. Click each peak individually to clarify the FWMH information. Peaks with an FWMH less than 3 are crystalline; check the "2-Theta" checkbox under "Variables to Refine" to fix the peak position. Peaks with an FWMH greater than 3 are amorphous and should not be checked. Add other samples and perform fitting processes by clicking "Refine" in the Profile Fitting interface. Finally, click "Fit All Overlays" in the Profile Fitting interface to complete the fitting of other samples and obtain different hydrothermal carbon crystallinities in sludge.

[0030] As a preferred embodiment of the present application, in the step of calculating the crystallinity, the XRD peak of silicon dioxide needs to be deducted.

[0031] As a preferred embodiment of the present application, the group 1 needs to contain the peak positions with a half-peak width less than 3: 35.917, 23.018, 29.359, 39.379, 43.104, 47.039, 48.455, 47.485, 60.529, 57.332, 64.598, and 20.695 degrees.

[0032] As a preferred embodiment of the present application, the group 2 needs to contain the peak positions with a half-peak width less than 3: 16.454, 22.908, 25.455, 31.341, 38.627, 48.680, 52.254, 55.694, 36.217, 40.804, 41.316, 43.359, and 74.1 degrees.

[0033] S7: Correlate the effective phosphorus concentration and the sludge hydrochar crystallinity to establish a quantitative relationship model.

[0034] The method and effects of the present application will be specifically described below through examples.

[0035] Example The present example provides a method for detecting the plant available effective phosphorus spectrum in residual sludge hydrochar, which is specifically as follows: S1: Put the municipal sludge into a hydrothermal reactor, control the reaction temperature, residence time, and initial pH, adjust the pH by using concentrated sulfuric acid and potassium hydroxide, and obtain a sludge hydrochar system.

[0036] The water content of the municipal sludge is 85%, the hydrothermal reaction temperature is 180-220℃, the residence time is 1-24h, and the initial pH is 2.13-12.38. The mass fraction of the concentrated sulfuric acid is 98%, and the purity of the potassium hydroxide is 99%.

[0037] S2: The obtained sludge hydrochar system is sequentially subjected to centrifugation (12000r / min for 5min), freeze-drying, grinding, and sieving (100 mesh) to obtain sludge hydrochar.

[0038] S3: Mix 0.2g of the obtained sludge hydrochar with a citric acid solution (mass fraction of 2%, volume of 20mL), oscillate at a speed of 30-32r / min and a temperature of 30℃ for 30min, and filter the effective phosphorus extract solution by using a 0.22μm filter membrane.

[0039] S4: Transfer 0.05 mL of the obtained effective phosphorus extract to a centrifuge tube. Using the molybdate colorimetric method, add 0.2 mL of molybdate solution to the centrifuge tube, mix for 30 seconds, then add 0.1 mL of 10% ascorbic acid solution, and finally bring the volume to 5 mL. After reacting for 10 minutes, measure the absorbance at 710 nm using a UV spectrophotometer to obtain the effective phosphorus concentration.

[0040] like Figure 1 The figure shows the available phosphorus data obtained by the molybdate colorimetric method. As can be seen from the figure, with the initial pH increasing from 2.13 to 12.38, the available phosphorus concentration in the hydrothermal carbon of the sludge increased from 1 mg / g to 21 mg / g, indicating a positive correlation between increasing the initial pH of the hydrothermal reaction and the available phosphorus concentration in the hydrothermal carbon of the sludge. Furthermore, increasing the hydrothermal treatment time does not affect the available phosphorus content of the hydrothermal carbon of the sludge.

[0041] S5: The hydrothermal carbon of the sludge obtained in S2 was characterized by XRD to obtain spectral data.

[0042] like Figure 2 The figure shows the XRD patterns of different hydrothermal chars from sludge under different initial pH conditions. It can be seen from the figure that the XRD peaks of the hydrothermal char obtained under strong acid conditions (initial pH 2.13) are significantly different from those of other hydrothermal chars from sludge. Therefore, the crystallinity needs to be calculated separately for hydrothermal chars obtained under strong acid conditions and those not obtained under strong acid conditions. Furthermore, a significant SiO2 peak can be seen in all hydrothermal chars, but SiO2 crystallinity is not correlated with phosphorus; therefore, the SiO2 peak is subtracted when calculating the crystallinity of the hydrothermal char.

[0043] S6: The obtained spectral data were analyzed using MDI Jade software to calculate the crystallinity of the sludge hydrothermal carbon sample. This step is detailed below: Based on the pH value used in the hydrothermal reaction process of step S1, the crystallinity was calculated by dividing the sludge hydrothermal carbon into two groups: Group 1, representing strongly acidic sludge hydrothermal carbon with an initial pH ≤ 4, and Group 2, representing non-strongly acidic sludge hydrothermal carbon with an initial pH > 4. The crystallinity of the sludge hydrothermal carbon was calculated separately for each group. For Group 1 and Group 2, the sample with the highest crystallinity was selected. In the MDI Jade software, a linear background line was selected, and "BE" was clicked in the editing toolbar. Points on the background line were clicked to make the background line tangent to the sample line, but no background removal was performed. The left-click button in the editing toolbar... To manually label peaks, click the "" button in the editing toolbar; once labeling is complete, right-click the "" button in the editing toolbar. button, click "Refine" in the Profile Fitting interface to perform fitting processing; click "Report" in the Profile Fitting interface to obtain information of different peak positions and FWMH, and click each peak to determine the FWMH information, and the FWMH less than 3 belongs to a crystalline peak, check the "2-Theta" checkbox in the "Variables to Refine" to realize fixed peak setting; the FWMH greater than 3 belongs to an amorphous peak, and no checkbox is checked; on this basis, add other samples, click "Refine" in the Profile Fitting interface to perform fitting processing; finally, click "Fit All Overlays" in the Profile Fitting interface to complete fitting of other samples, and obtain crystallinity of different sludge hydrochar.

[0044] As shown in Figure 3 and Figure 4 , respectively, are fitting peaks obtained by MDI Jade software analysis of group 1 and group 2. As can be seen from the figure, the SiO2 peak is not included in the crystallinity calculation range, and the fitting results of other peaks are good.

[0045] As shown in Figure 5 , it is a sludge hydrochar crystallinity data graph. As can be seen from the figure, as the initial pH increases from 2.13 to 12.38, the sludge hydrochar crystallinity decreases from 50% to about 10%, indicating that increasing the initial pH of hydrothermal reaction is negatively correlated with the sludge hydrochar crystallinity. In addition, increasing the hydrothermal treatment time can improve the sludge hydrochar crystallinity to a certain extent.

[0046] S7: Establish a correlation analysis between the obtained effective phosphorus concentration and sludge hydrochar crystallinity, and establish a quantitative relationship model. The specific steps are as follows: Through origin software, a quantitative linear relationship model of sludge hydrochar effective phosphorus content and sludge hydrochar crystallinity is established with sludge hydrochar crystallinity as the abscissa and sludge hydrochar effective phosphorus content as the ordinate.

[0047] As shown in Figure 6 , it is a quantitative relationship model of sludge hydrochar plant available effective phosphorus and crystallinity. As can be seen from the figure, there is a linear negative correlation between the sludge hydrochar effective phosphorus content and the sludge hydrochar crystallinity, and the correlation coefficient R 2 =0.910, indicating that the correlation is good, and the sludge hydrochar crystallinity can reflect the sludge hydrochar effective phosphorus content.

[0048] The above-described embodiments are only the preferred ones of the present application, and are not intended to limit the present application. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application. Therefore, any technical solutions obtained by equivalent replacement or equivalent transformation shall fall within the protection scope of the present application.

Claims

1. A method for the spectral detection of plant-available phosphorus in hydrothermal biochar of waste sludge, characterized in that, Specifically as follows: S1: The municipal sludge is fully subjected to hydrothermal reaction to obtain a sludge hydrothermal carbonization system; S2: The sludge hydrothermal carbonization system is subjected to centrifugation, freeze drying, grinding and sieving in sequence to obtain sludge hydrothermal carbon; S3: Mix the sludge hydrothermal carbon with citric acid solution, shake and filter to obtain an effective phosphorus extract; S4: The effective phosphorus extract is subjected to molybdate colorimetric method and ultraviolet spectrophotometer to obtain the effective phosphorus concentration; S5: The hydrothermal carbon of the sludge is characterized by XRD to obtain spectral data; S6: The crystallinity of the sludge hydrothermal carbon sample was calculated by analyzing the spectral data using MDI Jade software. S7: Establish a correlation analysis between the effective phosphorus concentration and the hydrothermal carbon crystallinity of the sludge, and establish a quantitative relationship model.

2. The method for spectroscopic detection of plant-available phosphorus in hydrothermal biochar of residual sludge according to claim 1, characterized in that, In S1, the municipal sludge has a moisture content of 85%, the hydrothermal reaction temperature is 180-220℃, and the reaction time is 1-24h.

3. The method for spectroscopic detection of plant-available phosphorus in hydrothermal biochar of residual sludge according to claim 2, characterized in that, During the hydrothermal reaction, the pH is adjusted to 2.13-12.38 using concentrated sulfuric acid with a mass fraction of 98% and potassium hydroxide with a purity of 99%.

4. The method for spectroscopic detection of plant-available phosphorus in hydrothermal biochar of residual sludge according to claim 1, characterized in that, In S2, the centrifugation rate is 12000 r / min, the running time is 5 min, and the ground material is passed through a 100-mesh sieve.

5. The method for spectroscopic detection of plant-available phosphorus in hydrothermal biochar of residual sludge according to claim 1, characterized in that, In step S3, the citric acid solution has a mass fraction of 2% and a volume of 20 mL; the sludge hydrothermal carbon has a mass of 0.2 g; the shaking time is 30 min, the rotation speed is 30-32 r / min, the shaking temperature is 30℃, and the effective phosphorus extract is obtained by filtration through a 0.22 μm filter membrane.

6. The method for spectroscopic detection of plant-available phosphorus in hydrothermal biochar of waste sludge according to claim 1, characterized in that, In step S4, 0.05 mL of the effective phosphorus extract is transferred to 0.2 mL of 40 g / L molybdate solution, mixed for 30 seconds, and then 0.1 mL of 10% ascorbic acid solution is added. Finally, the volume is adjusted to 5 mL. After reacting for 10 minutes, the absorbance is measured at a wavelength of 710 nm using a UV spectrophotometer to obtain the effective phosphorus concentration.

7. The method for spectroscopic detection of plant-available phosphorus in hydrothermal biochar of residual sludge according to claim 1, characterized in that, In step S6, based on the pH value used in the hydrothermal reaction process, when calculating crystallinity, the samples are divided into two groups: Group 1, representing strongly acidic sludge hydrothermal carbon with an initial pH ≤ 4, and Group 2, representing non-strongly acidic sludge hydrothermal carbon with an initial pH > 4. The crystallinity of the sludge hydrothermal carbon samples is calculated separately. Based on the calculation results, the sample with the strongest crystallinity is selected from each group, and information including different peak positions and half-peak widths is obtained using MDI Jade software. The crystalline peaks with a half-peak width less than 3 are fixed at their peak positions. On this basis, the remaining samples are added to each group and fitted to obtain different crystallinities of sludge hydrothermal carbon.

8. The method for spectroscopic detection of plant-available phosphorus in hydrothermal biochar of residual sludge according to claim 7, characterized in that, In step S6, the XRD peaks of silicon dioxide are subtracted when calculating crystallinity.

9. The method for spectroscopic detection of plant-available phosphorus in hydrothermal biochar of residual sludge according to claim 7, characterized in that, Group 1 includes the following peaks with a half-maximum width (FWHM) less than 3: 35.917, 23.018, 29.359, 39.379, 43.104, 47.039, 48.455, 47.485, 60.529, 57.332, 64.598, and 20.695 degrees; Group 2 includes the following peaks with a FWHM less than 3: 16.454, 22.908, 25.455, 31.341, 38.627, 48.680, 52.254, 55.694, 36.217, 40.804, 41.316, 43.359, and 74.1 degrees.

10. The method for spectroscopic detection of plant-available phosphorus in hydrothermal biochar of residual sludge according to claim 7, characterized in that, In S7, in the Origin software, after merging the data from Group 1 and Group 2, a quantitative relationship model was established between the two by using the crystallinity of sludge hydrothermal carbon as the abscissa and the effective phosphorus content of sludge hydrothermal carbon as the ordinate through linear fitting.

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