A method for determining ammonia nitrogen concentration in anaerobic digestion sludge

Abstract

The present invention relates to the field of environmental chemistry technology and discloses a method for determining the ammonia nitrogen concentration in anaerobic digestion sludge, comprising: (1) pre-treating the anaerobic digestion sludge: pre-treating the sample using an ultrasonic disruptor sonicator; (2) determining the ammonia nitrogen concentration: drawing a standard curve using an ammonia nitrogen standard working solution to obtain the intercept and slope of the standard curve; taking the sample pre-treated in (1), mixing it with a shielding agent and a color developing reagent, and testing the absorbance; and (3) calculating the ammonia nitrogen content in the anaerobic digestion sludge sample. The present invention uses an ultrasonic treatment method to pre-treat the diluted sludge sample, so that the ammonia nitrogen on the surface and interstitial space of the sludge particles is fully released, and then centrifugation is performed to remove interference from other impurities, and the ammonia nitrogen is determined using Nessler's reagent spectrophotometry. The method has more accurate determination results.

Description

Technical Field

[0001] The present invention relates to the field of environmental chemistry, and in particular to a method for measuring the concentration of ammonia nitrogen in anaerobic digestion sludge. Background Art

[0002] Anaerobic digestion of sludge is a common method for the stable degradation of organic pollutants, and can treat sludge with a high organic content. In this process, organic matter is anaerobically decomposed to produce a large amount of high-calorific value biogas as energy, turning the sludge into a resource. Therefore, it has been widely used in the harmless treatment and resource utilization of solid wastes such as agricultural waste, food waste and surplus sludge from sewage treatment plants. During the anaerobic digestion process, nitrogenous substances in the fermentation materials, such as protein, urea and nucleic acid, are eventually converted into ammonia nitrogen (including free ammonia NH3 and ammonium ions NH4 + Although ammonia nitrogen is an essential nutrient for anaerobic microorganisms in the anaerobic digestion process, and a certain concentration of ammonia nitrogen can provide a good buffering effect for the system, excessively high concentrations of ammonia nitrogen in the system often inhibit the normal life activities of microorganisms and are considered one of the most common causes of instability in anaerobic digestion systems. To ensure the stability of the anaerobic digestion process, the ammonia nitrogen content in the sludge must be regularly monitored.

[0003] Currently, there is no national standard for the determination of ammonia nitrogen in anaerobic digestion sludge. The industry often refers to standards or patents for the determination of ammonia nitrogen in water, sewage sludge, and soil. Therefore, distillation-neutralization titration or spectrophotometry are commonly used to determine ammonia nitrogen content. Titration is only applicable to sludge samples that have undergone high-temperature heating and distillation pretreatment. If the sludge sample contains substances that can be distilled under these conditions and react with acid during titration, such as volatile amines, the measurement result will be biased high. Although the Nessler reagent spectrophotometry method does not require distillation pretreatment, it can provide relatively accurate ammonia nitrogen measurements. However, when using the Nessler reagent spectrophotometry method, if conventional centrifugal filtration is used to pretreat anaerobic digestion sludge, the measured value may be underestimated due to factors such as incomplete release of ammonia nitrogen from interstitial spaces between sludge particles and ammonia nitrogen adsorption by sludge particles.

[0004] In summary, the existing technology is inaccurate when measuring the ammonia nitrogen content in anaerobic digestion sludge. Summary of the Invention

[0005] In response to the problems existing in the existing technology, the present invention uses an ultrasonic treatment method to pretreat the diluted sludge sample to fully release the ammonia nitrogen on the surface and gaps of the sludge particles, and then removes the interference of other impurities by centrifugation. The ammonia nitrogen is determined using Nessler's reagent spectrophotometry. The measurement results of this method are more accurate.

[0006] The present invention discloses a method for measuring the ammonia nitrogen concentration in anaerobic digestion sludge, comprising:

[0007] S1. Anaerobic digestion sludge pretreatment:

[0008] Anaerobic digestion sludge is placed in a container, water is added, the container is placed in an ice-water mixture, and an ultrasonic disruptor is immersed below the liquid level of the beaker for ultrasonication; the ultrasonicated sample liquid is centrifuged; the supernatant of the centrifuged sample liquid is centrifuged again, and the supernatant is collected again to obtain a pretreated sample; wherein the weight ratio of anaerobic digestion sludge to water is 1:50-60;

[0009] S2. Determination of ammonia nitrogen concentration:

[0010] (1) Draw a standard curve using the ammonia nitrogen standard working solution and obtain the intercept and slope of the standard curve;

[0011] (2) Take the sample pretreated in S1, mix it with the shielding agent and color developing reagent, and test the absorbance;

[0012] (3) Calculate the ammonia nitrogen content in anaerobic digestion sludge samples.

[0013] Preferably, the ultrasonic disruptor sound wave transmitter in S1 is immersed below 1 / 2 of the liquid surface height, the power is selected to be 540W, and the ultrasonication is performed for 10 minutes with 3 seconds of ultrasonication and 2 seconds of rest as one cycle to obtain the ultrasonicated sample liquid.

[0014] Preferably, the sample liquid after ultrasound is centrifuged at a rotation speed of 4000-9000 r / min for 30-40 min to obtain a centrifuged sample liquid.

[0015] Preferably, the supernatant of the centrifuged sample solution is centrifuged at a temperature of 1 to 4° C. and a rotation speed of 8000 to 9000 r / min for 30 to 40 minutes.

[0016] Preferably, the standard curve in S2 is drawn by adding 0.0, 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0 ml, and 15.0 ml of a 10 mg / L ammonia nitrogen standard working solution, measured in terms of N element concentration, to 9 50 ml colorimetric tubes, respectively, and adding water to the mark; adding 1.0 ml of potassium sodium tartrate solution and 1.0 ml of Nessler's reagent, mixing and coloring for 10 minutes; using water as a reference, measuring the absorbance with a 20 mm cuvette at a wavelength of 420 nm; the ammonia nitrogen standard solution content is used as the horizontal axis, and the corresponding absorbance after deducting the blank is used as the vertical axis.

[0017] Preferably, when determining the ammonia nitrogen concentration in S2, take the pretreated sample and measure the absorbance according to the same steps as the standard curve, that is: add the pretreated sample to the scale line in a 50mL colorimetric tube. If the concentration of the sample is high, take a small amount, add water to the scale line, and then add 1.0mL of shielding agent and 1.0ml of color developing reagent. Mix and react for 10 minutes. Use water as a reference and measure the absorbance with a 20mm cuvette at a wavelength of 420nm to test the absorbance; use water as a blank sample and test the absorbance according to the sample determination steps.

[0018] Preferably, the shielding agent is potassium sodium tartrate solution, and the preparation method of potassium sodium tartrate solution is as follows: weigh 50.0g potassium sodium tartrate and dissolve it in 100ml water, heat and boil to drive off ammonia, and then cool it down to 100ml.

[0019] Preferably, the calculation formula for the ammonia nitrogen content in the anaerobic digestion sludge sample in S2 is:

[0020]

[0021] c——mass fraction of ammonia nitrogen in the sludge sample, calculated as N element, mg / L;

[0022] A——absorbance value of the sample;

[0023] A0——absorbance of blank sample;

[0024] a——intercept of the standard curve;

[0025] b——the slope of the standard curve;

[0026] V1 - the volume of the sludge sample after dilution with water, ml, calculated using the formula V1 = 200 + V2;

[0027] V2——sludge sampling volume, ml, calculation formula V2=m / ρ;

[0028] m——sludge sampling mass, 4g;

[0029] ρ——sludge bulk density, g / mL.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The pretreatment steps of anaerobic digestion sludge samples are simple to operate, without adding additional reagents and without heating or distilling the original samples.

[0032] (2) Use Nessler's reagent for color development, which has a short development time and is fast.

[0033] (3) The result calculation process is simple.

[0034] (4) The lower limit of determination for this method is 5.0 mg / L, and the upper limit is 100.0 mg / L. These values ​​are based on the nitrogen concentration. Above this concentration, appropriate dilution is required. This method significantly reduces the dilution factor, minimizing the impact of significant sample dilution on the accuracy of the results, resulting in more accurate results. The detection limit, linearity, recovery, and precision of the present invention all reach levels difficult to achieve with similar detection methods. DETAILED DESCRIPTION

[0035] 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.

[0036] The experimental methods described in the examples of the present invention are conventional methods unless otherwise specified. The materials and reagents used are all commercially available unless otherwise specified.

[0037] The ultrasonic crusher sound wave transmitter used in the present invention is the FS-1800N ultrasonic processor produced by Shanghai Shengxi Ultrasonic Instrument Co., Ltd.

[0038] Example 1:

[0039] A method for determining the concentration of ammonia nitrogen in anaerobic digestion sludge comprises the following steps:

[0040] (1) Pretreatment of anaerobic digestion sludge samples:

[0041] Sludge samples were taken from three laboratory-scale anaerobic digestion reactors A, B, and C for livestock and poultry manure as samples for Example 1, Example 2, and Example 3, respectively. Three parallel tests were performed on each anaerobic digestion reactor for livestock and poultry manure.

[0042] Accurately weigh 4.0 g of anaerobic digestion sludge into a clean beaker and add 200 ml of pure water;

[0043] Place the beaker in the ice-water mixture, immerse the ultrasonic transmitter 15mm below the liquid level of the beaker, select the power of 540W, and sonicate for 10 minutes;

[0044] The sample solution after ultrasonication was centrifuged at 4000 r / min for 30 min; the supernatant was then taken and centrifuged at 9000 r / min for 30 min at 4°C;

[0045] (2) Drawing of standard curve:

[0046] Add 0.0, 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0, and 15.0 ml of 10 mg / L ammonia nitrogen standard working solution (calculated as N element) to nine 50 ml colorimetric tubes, respectively, and add water to the mark;

[0047] Add 1.0 ml of potassium sodium tartrate solution and 1.0 ml of Nessler's reagent, mix well and allow to develop color for 10 minutes;

[0048] With water as a reference, the absorbance was measured with a 20 mm cuvette at a wavelength of 420 nm;

[0049] Draw a standard curve with the ammonia nitrogen standard solution content as the horizontal axis and the corresponding absorbance after deducting the blank as the vertical axis;

[0050] (3) Sample determination:

[0051] Take 50 ml of the pretreated sample into a 50 ml colorimetric tube. If the concentration of the sample is high, take a small amount and add water to the scale line. Perform the test according to the same steps as drawing the standard curve. Test the experimental blank according to the sample determination steps.

[0052] Calculation formula:

[0053]

[0054] c——mass fraction of ammonia nitrogen in the sludge sample, calculated as N element, mg / L;

[0055] A——absorbance value of the sample;

[0056] A0——absorbance of blank sample;

[0057] a——intercept of the standard curve;

[0058] b——the slope of the standard curve;

[0059] V1 - the volume of the sludge sample after dilution with water, ml, calculated using the formula V1 = 200 + V2;

[0060] V2——sludge sampling volume, ml, calculation formula V2=m / ρ;

[0061] m——sludge sampling mass, g;

[0062] ρ——sludge bulk density, g / mL.

[0063] The obtained data are shown in Table 1.

[0064] Example 2

[0065] A method for determining the concentration of ammonia nitrogen in anaerobic digestion sludge comprises the following steps:

[0066] (1) Pretreatment of anaerobic digestion sludge samples:

[0067] Accurately weigh 4.0g of anaerobic digestion sludge into a clean beaker and add 240ml of pure water;

[0068] Place the beaker in the ice-water mixture, immerse the ultrasonic transmitter 15mm below the liquid level of the beaker, select the power of 540W, and sonicate for 10 minutes;

[0069] The sample solution after ultrasonication was centrifuged at 4000 r / min for 30 min; the supernatant was then taken and centrifuged at 9000 r / min for 30 min at 1°C;

[0070] The remaining operations are the same as in Example 1.

[0071] Example 3

[0072] A method for determining the concentration of ammonia nitrogen in anaerobic digestion sludge comprises the following steps:

[0073] (1) Pretreatment of anaerobic digestion sludge samples:

[0074] Accurately weigh 4.0g of anaerobic digestion sludge into a clean beaker and add 220ml of pure water;

[0075] Place the beaker in the ice-water mixture, immerse the ultrasonic transmitter 15mm below the liquid level of the beaker, select the power of 540W, and sonicate for 10 minutes;

[0076] The sample solution after ultrasonication was centrifuged at 4000 r / min for 30 min; the supernatant was then taken and centrifuged at 4000 r / min for 40 min at 1°C;

[0077] The remaining operations are the same as in Example 1.

[0078] Table 1 Ammonia nitrogen content in anaerobic digestion sludge measured by the method of the present invention

[0079]

[0080] As shown in Table 1, four reproducibility experiments were conducted for each example, and the relative standard deviations were very small, indicating that the scheme has good reproducibility.

[0081] Experiment 1: Comparison of ammonia nitrogen determination results between samples with and without ultrasonic pretreatment

[0082] (1) Anaerobic digestion sludge sample collection:

[0083] Two sludge samples were taken from each of the three laboratory-scale anaerobic digestion reactors for livestock and poultry manure, R1, R2, and R3. Accurately weigh 20 g of sludge and place it in a 50 mL centrifuge tube. These were sample 1-1 and sample 1-2 from R1, sample 2-1 and sample 2-2 from R2, and sample 3-1 and sample 3-2 from R3.

[0084] The sludge samples were grouped as follows: control group 1, including sample 1-1, sample 2-1, and sample 3-1; experimental group 1, including sample 1-2, sample 2-2, and sample 3-2; note that the two samples in R1, R2, and R3 are parallel samples, but the ammonia nitrogen test methods are different.

[0085] Determine the sludge bulk density ρ of each reactor.

[0086] Note: All anaerobic digestion reactors are continuous stirred tank reactors, which are operated in a semi-continuous manner with material loading and unloading once a day, and the sludge temperature is maintained at 37±0.5℃ by circulating hot water.

[0087] (2) Sample pretreatment:

[0088] Accurately weigh 4.0g of each of the above samples into a clean 500mL beaker and add 200ml of pure water;

[0089] Test Group 1 samples: Place a beaker in an ice-water mixture, immerse the ultrasonic transmitter 15 mm below the liquid surface of the beaker, select 540 W power (30% of the rated power of 1800 W), and sonicate for 10 minutes;

[0090] Control group 1 sample: Place the beaker in the ice-water mixture and let it stand for 10 minutes;

[0091] After mixing the sample solution in the beaker in the above step, centrifuge at 4000 r / min for 30 min; then take the supernatant and centrifuge at 9000 r / min at 4°C for 30 min.

[0092] (3) Drawing of standard curve:

[0093] Add 0.0, 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0, and 15.0 ml of a 10 mg / L ammonia nitrogen standard working solution (based on N element concentration) to nine 50 ml colorimetric tubes, respectively, and add water to the mark.

[0094] Add 1.0 ml of potassium sodium tartrate solution and 1.0 ml of Nessler's reagent, mix well and allow to develop color for 10 minutes;

[0095] With water as a reference, the absorbance was measured at a wavelength of 420 nm using a 20 mm cuvette;

[0096] Draw a standard curve with the ammonia nitrogen standard solution content as the horizontal axis and the corresponding absorbance after deducting the blank as the vertical axis;

[0097] (4) Sample determination:

[0098] Take 2.0 mL of the pretreated sample and transfer it to a 50 mL colorimetric tube. Since the sample concentration is relatively high, take a smaller amount and add water to the scale line. Perform the test according to the same steps as for drawing the standard curve. Test the experimental blank according to the sample determination steps.

[0099] Calculation formula:

[0100]

[0101] c——mass fraction of ammonia nitrogen in the sludge sample, calculated as N element, mg / L;

[0102] A——absorbance value of the sample;

[0103] A0——absorbance of blank sample;

[0104] a——intercept of the standard curve;

[0105] b——the slope of the standard curve;

[0106] V1 - the volume of the sludge sample after dilution with water, ml, calculated using the formula V1 = 200 + V2;

[0107] V2——sludge sampling volume, ml, calculation formula V2=m / ρ;

[0108] m——sludge sampling mass, g;

[0109] ρ——sludge bulk density, g / mL.

[0110] The obtained data are shown in Table 2.

[0111] Table 2 Ammonia nitrogen concentrations measured with and without ultrasonic pretreatment

[0112]

[0113]

[0114] After calculation, the ammonia nitrogen concentrations measured in the test group 1 were 9.12%, 9.54% and 9.57% higher than those of the corresponding samples in the control group 1, respectively, indicating that the ultrasonic pretreatment in the method of the present invention can promote the release of ammonia nitrogen in the gaps of anaerobic digestion sludge, and the measured ammonia nitrogen data are closer to the actual values.

[0115] Experiment 2: Recovery test of the spiked method of the present invention

[0116] (1) Anaerobic digestion sludge sample collection:

[0117] Two sludge samples were taken from each of the three laboratory-scale anaerobic digestion reactors R1, R2, and R3. Accurately weigh 20 g of sludge in a 50 mL centrifuge tube. These were sample 1-3 and sample 1-4 from R1, sample 2-3 and sample 2-4 from R2, and sample 3-3 and sample 3-4 from R3.

[0118] The sludge samples were grouped as follows: control group 2, including samples 1-3, 2-3, and 3-3; experimental group 2, including samples 1-4, 2-4, and 3-4; note that the two samples in R1, R2, and R3 are parallel samples, but the ammonia nitrogen test methods are different.

[0119] Note: All anaerobic digestion reactors are continuous stirred tank reactors, which are operated in a semi-continuous manner with material loading and unloading once a day, and the sludge temperature is maintained at 37±0.5℃ by circulating hot water.

[0120] (2) Sample spike:

[0121] Test Group 2: Each sample was added with 4.0 mL of ammonia nitrogen standard stock solution with a nitrogen concentration of 1 mg / mL, and then mechanically shaken to mix thoroughly;

[0122] Control group 2: 4.0 mL of pure water was added to each sample, followed by mechanical shaking to mix thoroughly.

[0123] Determine the bulk density ρ of the sample after spiked.

[0124] (3) Sample pretreatment:

[0125] Accurately weigh 4.0g of each of the above samples into a clean beaker, add 200ml of pure water, and stir thoroughly;

[0126] Place each beaker in the ice-water mixture, immerse the ultrasonic transmitter into the liquid surface of the beaker, select the power of 540W, and sonicate for 10 minutes;

[0127] After mixing the sample solution in the beaker in the above step, centrifuge at 4000 r / min for 30 min; then take the supernatant and centrifuge at 9000 r / min at 4°C for 30 min.

[0128] (4) Drawing of standard curve:

[0129] Add 0.0, 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0, and 15.0 ml of a 10 mg / L ammonia nitrogen standard working solution (based on N element concentration) to nine 50 ml colorimetric tubes, respectively, and add water to the mark.

[0130] Add 1.0 ml of potassium sodium tartrate solution and 1.0 ml of Nessler's reagent, mix well and allow to develop color for 10 minutes;

[0131] With water as a reference, the absorbance was measured at a wavelength of 420 nm using a 20 mm cuvette;

[0132] Draw a standard curve with the ammonia nitrogen standard solution content as the horizontal axis and the corresponding absorbance after deducting the blank as the vertical axis;

[0133] (5) Sample determination:

[0134] Take 2.0mL of the pretreated sample and transfer it to a 50mL colorimetric tube. If the concentration of the sample is too high, take a smaller amount and add water to the scale line. Perform the test according to the same steps as for drawing the standard curve. The experimental blank should be tested according to the sample determination steps.

[0135] Calculation formula:

[0136]

[0137] c——mass fraction of ammonia nitrogen in the sludge sample, calculated as N element, mg / L;

[0138] A——absorbance value of the sample;

[0139] A0——absorbance of blank sample;

[0140] a——intercept of the standard curve;

[0141] b——the slope of the standard curve;

[0142] V1 - the volume of the sludge sample after dilution with water, ml, calculated using the formula V1 = 200 + V2;

[0143] V2——sludge sampling volume, ml, calculation formula V2=m / ρ;

[0144] m——sludge sampling mass, g;

[0145] ρ——sludge bulk density, g / mL.

[0146] The obtained data are shown in Table 3.

[0147] Table 3 Calculation of spiked recovery of the method of the present invention

[0148]

[0149]

[0150] Note: “-” means no result.

[0151] As shown above, the spiked recovery of the method of the present invention is 97.05% to 103.82%, which is close to 100%, indicating that the method of the present invention has a high accuracy for determining the ammonia nitrogen concentration in anaerobic digestion sludge.

[0152] The formula for calculating the spike recovery rate is: spike recovery rate R = (spike sample measurement value - sample measurement value) / spike amount × 100%

[0153] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0154] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for determining the concentration of ammonia nitrogen in anaerobic digestion sludge, characterized in that: include: S1. Anaerobic digestion sludge pretreatment: Place anaerobic digestion sludge in a container, add water, and place it in an ice-water mixture. Immerse the ultrasonic transmitter of the ultrasonic disruptor below 1 / 2 of the liquid level in the beaker, select 540 W power, and sonicate for 10 to 15 minutes with 3 seconds on and 2 seconds off as one cycle to obtain the sonicated sample liquid. The ultrasonic sample solution is centrifuged at a speed of 4000-9000 r / min for 30-40 minutes to obtain a centrifuged sample solution; the supernatant of the centrifuged sample solution is then centrifuged at a temperature of 1-4°C and a speed of 8000-9000 r / min for 30-40 minutes, and the supernatant is collected again to obtain a pretreated sample; wherein the weight ratio of anaerobic digestion sludge to water is 1:50-60; S2. Determination of ammonia nitrogen concentration: (1) Draw a standard curve using the ammonia nitrogen standard working solution and obtain the intercept and slope of the standard curve; (2) Take the sample pretreated in S1, mix it with the shielding agent and color developing reagent, and test the absorbance; (3) Calculate the ammonia nitrogen content in anaerobic digestion sludge samples.

2. The method for determining the ammonia nitrogen concentration in anaerobic digestion sludge according to claim 1, wherein: The standard curve in S2 was drawn by adding 0.0, 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0, and 15.0 ml of a 10 mg / L ammonia nitrogen standard working solution (based on N element concentration) to nine 50 ml colorimetric tubes, respectively, and adding water to the mark; then adding 1.0 ml of potassium sodium tartrate solution and 1.0 ml of Nessler's reagent, mixing, and developing the color for 10 minutes; using water as a reference, the absorbance was measured at a wavelength of 420 nm using a 20 mm cuvette; the ammonia nitrogen standard solution content was used as the horizontal axis, and the corresponding absorbance after deducting the blank was used as the vertical axis.

3. The method for determining the ammonia nitrogen concentration in anaerobic digestion sludge according to claim 2, wherein: When determining the ammonia nitrogen concentration in S2, take the pretreated sample and measure the absorbance according to the same steps as the standard curve, that is: add the pretreated sample to the scale line in a 50 mL colorimetric tube, add water to the scale line, then add 1.0 mL of shielding agent and 1.0 ml of colorimetric reagent, mix and react for 10 minutes, use water as a reference, and measure the absorbance at a wavelength of 420 nm with a 20 mm cuvette to test the absorbance; use water as a blank sample and test the absorbance according to the sample determination steps.

4. The method for determining the ammonia nitrogen concentration in anaerobic digestion sludge according to claim 3, wherein: The shielding agent is potassium sodium tartrate solution, and the preparation method of potassium sodium tartrate solution is as follows: weigh 50.0 g of potassium sodium tartrate and dissolve it in 100 ml of water, remove ammonia, and then fully cool and dilute to 100 ml.

5. The method for determining the ammonia nitrogen concentration in anaerobic digestion sludge according to claim 3, wherein: The color developing reagent is Nessler's reagent.

6. The method for determining the ammonia nitrogen concentration in anaerobic digestion sludge according to claim 3, wherein: The calculation formula for the ammonia nitrogen content in the anaerobic digestion sludge sample in S2 is: c ——The mass fraction of ammonia nitrogen in the sludge sample, calculated as elemental N, mg / L; A ——absorbance value of the sample; A 0 ——Absorbance of blank sample; a ——intercept of the standard curve; b —the slope of the standard curve; V 1——The volume of the sludge sample after dilution with water, ml, calculated by the formula V 1 =200+ V 2 ; V 2——Sludge sampling volume, ml, calculation formula V 2 = m / 𝜌 ; m ——Sludge sampling mass, 4 g; 𝜌——sludge bulk density, g / mL.

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