CN112794298A

CN112794298A - Method for recovering phosphorus from phosphorus-containing sludge

Info

Publication number: CN112794298A
Application number: CN202011589297.1A
Authority: CN
Inventors: 王飞; 吕文潇; 韩晓敏; 周北海; 陈辉伦; 袁蓉芳
Original assignee: University of Science and Technology Beijing USTB
Current assignee: University of Science and Technology Beijing USTB
Priority date: 2020-12-29
Filing date: 2020-12-29
Publication date: 2021-05-14

Abstract

The invention discloses a method for recovering phosphorus from phosphorus-containing sludge, belonging to the technical field of sludge treatment, and the method comprises the steps of mixing phosphorus-containing sludge with water, hydrolyzing to obtain a mixed hydrolysate, then adding anaerobic granular sludge, performing anaerobic digestion, and recovering phosphorus in the digestive juice; according to the invention, through researching the change rule of the P form in the high-temperature pyrohydrolysis process and the influence on P release in the combined treatment process of the pyrohydrolysis and the anaerobic digestion, the optimal process condition for recovering phosphorus from the phosphorus-containing sludge by adopting the pyrohydrolysis and the anaerobic digestion is obtained.

Description

Method for recovering phosphorus from phosphorus-containing sludge

Technical Field

The invention belongs to the technical field of sludge treatment, and particularly relates to a method for recovering phosphorus from phosphorus-containing sludge.

Background

In China, municipal sewage treatment plants mostly adopt biological treatment processes, a large amount of excess sludge is produced every day, the annual sludge yield in China is more than 4000 million tons at present, but the sludge treatment problem is not well solved all the time. In addition, in the urban sewage treatment process, sewage is discharged after reaching the standard through a series of treatments, and a large amount of pollutants originally contained in the sewage are enriched, concentrated and transferred into sludge, so that the resource crisis faced by human beings can be solved to the greatest extent by recycling and resource utilization of the sludge.

The recovery of phosphorus from excess sludge has been agreed at home and abroad and sludge is considered the second large phosphorus reservoir. For example, precipitation-enhanced biological phosphorus removal techniques utilizing inorganic phosphorus fertilizers (e.g., struvite) are common phosphorus recovery processes used in sewage treatment plants. The average value of the total phosphorus of the dry sludge in China is 2.2 percent, and the maximum value can reach 3.7 percent, which is equivalent to 22 ten thousand tons of phosphorus. Nowadays, the problem of phosphorus resources is increasingly prominent, the reserves of natural phosphorite are less and less, the demand of human activities for phosphorite is larger and larger, and the recovery of phosphorus from sludge by utilizing different treatment technologies and strategies to reduce the consumption of phosphorus resources is an important research field.

Anaerobic digestion can degrade organic matters in the sludge, kill pathogenic microorganisms, realize stabilization, reduction and harmlessness of the sludge, and become an important means for treating excess sludge. The phosphorus-rich sludge releases a large amount of free phosphorus to the supernatant of the digestion solution in the anaerobic digestion process, and then various physical and chemical methods are adopted to recover and obtain safe and harmless precipitation products, so that the phosphorus-rich sludge enters industrial production to realize efficient and safe reutilization of phosphorus. The phosphorus release of the excess sludge by the anaerobic digestion method has the advantages of obvious phosphorus release effect, stable operation, low cost and the like, and is an effective way for realizing industrial production. However, the colloidal structure of the sludge and the cell walls of the cells are difficult to hydrolyze in the anaerobic digestion operation process, so that the problems of long digestion time, low efficiency and low phosphorus recovery rate exist when the anaerobic digestion method is adopted to recover the phosphorus in the excess sludge at present.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a method for recovering phosphorus from phosphorus-containing sludge, so that the recovery rate of phosphorus in the phosphorus-containing sludge is improved, and the recovery time is shortened, thereby improving the recovery efficiency of phosphorus.

In order to achieve the purpose, the invention provides the following technical scheme:

a method for recovering phosphorus from phosphorus-containing sludge comprises the following steps:

mixing phosphorus-containing sludge with water, hydrolyzing to obtain a mixed hydrolysate, adding anaerobic granular sludge, performing anaerobic digestion, and recovering phosphorus in the digestive juice.

Further, the method also comprises the steps of drying the phosphorus-containing sludge at 70 ℃ to constant weight, grinding and sieving by a 60-mesh sieve before mixing the phosphorus-containing sludge with water.

Further, the mass ratio of the phosphorus-containing sludge to the water is 1: 10.

Further, the hydrolysis temperature is 140-200 ℃, the hydrolysis time is 10-60min, and the hydrolysis is carried out under a closed condition.

Further, the hydrolysis temperature is 170 ℃ and the hydrolysis time is 30 min.

Further, the volume ratio of the anaerobic granular sludge to the mixed hydrolysate is 1: 1.

Further, the temperature of anaerobic digestion is 37 ℃, and the anaerobic digestion time is 1-20 days.

Further, the anaerobic digestion time is 3 d.

Further, the specific method for recovering the phosphorus in the digestion solution comprises the following steps: and (3) taking the supernatant of the digestive juice, adjusting the pH value, adding a magnesium source, standing after the reaction is finished, and separating to obtain a phosphorus-containing precipitate.

Further, the pH is adjusted to 9.5; the magnesium source is MgCl₂·6H₂O。

Compared with the prior art, the invention has the following beneficial effects:

(1) the method comprises the following steps of firstly, carrying out high-temperature pyrohydrolysis pretreatment on the phosphorus-containing sludge, heating to ensure that partial cell bodies in the sludge are heated and expanded to be broken, breaking cell walls (membranes) of microorganisms, and releasing organic matters such as intracellular protein, colloid and the like to promote the dissolution and hydrolysis of the organic matters; compared with the traditional ultrasonic and ozone oxidation methods, the high-temperature pyrohydrolysis method has stronger wall breaking capacity on sludge organic matter extracellular polymers, and is beneficial to subsequent biochemical treatment of sludge.

(2) According to the invention, through researching the change rule of the P form in the high-temperature pyrohydrolysis process and the influence on P release in the combined treatment process of the pyrohydrolysis and the anaerobic digestion, the optimal process condition for recovering phosphorus from the phosphorus-containing sludge by adopting the pyrohydrolysis and the anaerobic digestion is obtained.

(3) The invention discloses a mechanism of the influence of high-temperature pyrohydrolysis on the phosphorus form and the phosphorus form in the subsequent anaerobic digestion process through the research on the phosphorus form by the high-temperature pyrohydrolysis and the phosphorus form in the subsequent anaerobic digestion process, and provides a theoretical basis for a phosphorus recovery method in phosphorus-containing sludge.

(4) The method has the characteristics of small equipment loss, simple and convenient operation, high recovery efficiency, cost saving and the like.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is a flow chart of the present invention;

FIG. 2 is a graph of TP content in solid phase hydrolysate as a function of hydrolysis time;

FIG. 3 is a graph showing the distribution of the amount of P extracted from a solid phase hydrolyzate at different hydrolysis temperatures, wherein H is shown in FIG. 3(a)₂O-P, FIG. 3(b) is NaHCO₃-P, FIG. 3(c) is NaOH-P, FIG. 3(d) is HCl-P;

FIG. 4 is a chart of the XANES spectrum of the P edge of the solid phase hydrolysate of the standard and solid phase pyrohydrolysis at 170 ℃; wherein FIG. 4(a) is a XANES spectrum of P side of the standard, and FIG. 4(b) is a XANES spectrum of P side of the solid phase hydrolysate obtained by solid phase thermal hydrolysis at 170 ℃;

FIG. 5 is a chart of the XANES spectrum of the P edge of the solid phase hydrolysate obtained by solid phase pyrohydrolysis; wherein FIG. 5(a) is a K-edge XANES spectrum of P of the solid phase hydrolysate obtained by solid phase pyrohydrolysis for 30min at different temperatures, and FIG. 5(b) is a K-edge XANES spectrum of P of the solid phase hydrolysate obtained by solid phase pyrohydrolysis for 60min at different temperatures;

FIG. 6 is a graph of TP change in the solid phase of anaerobic digestion;

FIG. 7 is a graph showing the solid phase digestion products from solid phase anaerobic digestion³¹A P NMR spectrum;

FIG. 8 is a spectrum of XANES at edge P of the solid phase digest obtained by solid phase anaerobic digestion, wherein FIG. 8(a) is a spectrum of XANES at edge P of the solid phase digest obtained by solid phase anaerobic digestion after thermal hydrolysis, and FIG. 8(b) is a spectrum of XANES at edge P of the solid phase digest obtained by SS anaerobic digestion;

FIG. 9 is a graph showing the distribution of various forms of phosphorus in the solid phase of anaerobic digestion.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The description and examples are intended to be illustrative only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.

The phosphorus-containing sludge used in the following examples is excess sludge from a rural and rural sewage treatment plant in Beijing, which uses a modified Bardenphos process as the primary sewage treatment method. And drying the phosphorus-containing sludge in a 70 ℃ ventilation drying oven to constant weight to obtain dry sludge (SS), wherein the content of phosphorus in the SS is higher, and the total content of phosphorus (TP) is 96.18 +/-2.87 mg/g. The extraction contents and distribution of the various elemental components in SS are shown in table 1, which indicates that SS has a high phosphorus recovery value.

TABLE 1

Element(s)	H₂O(％)	NaHCO₃(％)	NaOH(％)	HCl(％)
					P	2.59±0.01	3.50±0.11	27.93±3.85	44.94±1.53
Ca	17.62±3.47	11.96±0.32	5.67±0.56	78.09±4.18
					Fe	0±0	0.76±0.01	0±0	79.53±19.71
Al	0±0	0±0	21.07±3.28	36.16±1.88
					Mg	13.30±1.23	8.38±0.28	0±0	60.16±0.76
Mn	1.82±0.104	0.63±0.18	0±0	89.53±17.46

In the following examples and comparative examples 1 to 2, the anaerobic granular sludge was prepared as follows:

adding nutrient substances into water according to the mass ratio of COD to N to P of 200 to 5 to 1 to obtain simulated wastewater, wherein N is derived from ammonium sulfate and phosphorus is derived from potassium dihydrogen phosphate; sodium bicarbonate is used to maintain the alkalinity of the inlet water to 2000mg/L (CaCO)₃Metering), the pH of inlet water is 7.2-8.2, the SS and activated carbon particles are uniformly mixed according to the mass ratio of 21: 1, the mixture is added into a UASB simulation reactor, the flow rate of simulation wastewater is controlled to be 0.25L/h, the hydraulic retention time is 11.39h, and the anaerobic granular sludge is obtained after 60 days of operation.

Examples

The method for recovering phosphorus from the phosphorus-containing sludge comprises the following steps:

(1) drying the phosphorus-containing sludge in a 70 ℃ ventilation drying oven to constant weight, grinding, and sieving with a 60-mesh sieve to realize homogenization of the sludge to obtain dry sludge;

(2) adding deionized water into the dry sludge obtained in the step (1) according to the mass ratio of 1: 10, uniformly mixing, placing in a liner of a reaction kettle made of PPL material, and carrying out high-temperature pyrohydrolysis under a closed condition according to the following setting requirements: setting the hydrolysis temperature at 140-200 ℃, the interval temperature at 15 ℃, the hydrolysis time at 10-60min, and obtaining the mixed hydrolysate;

and after the reaction kettle is cooled to room temperature, taking out the mixed hydrolysate, and centrifuging for 20min at 5000 r/min. Separating supernatant and sludge, drying the sludge at 70 ℃ to constant weight, grinding, and sieving with a 60-mesh sieve to obtain a solid-phase hydrolysate sample;

determination of the total amount of elements in the solid phase hydrolysate: taking 150mg of each sample obtained in the step (3), calcining at 600 ℃ for 2h, adding 20ml of 1mol/L HCl into obtained residues, shaking at room temperature for 16h, centrifuging, taking supernate, passing through a 0.45-micron filter membrane, and measuring Total Phosphorus (TP) in the filtrate by using an inductively coupled plasma emission spectrometer (ICP-OES), wherein the change of TP content in solid-phase hydrolysate at different temperatures along with hydrolysis time is shown in figure 2;

and (3) determining the forms of elements in the solid-phase hydrolysate: determining the content of different types of phosphorus in each sample by using a modified Hedley continuous extraction method, determining the content of P in each extracting solution by using ICP-OES, and determining the fixing effect of the metal element on P by combining XANES analysis as shown in figure 3, and as shown in figures 4 and 5, wherein figure 4(a) is a K-edge XANES spectrum of P of a standard substance, and figure 4(b) is a K-edge XANES spectrum of P of a solid-phase hydrolysate obtained by solid-phase thermal hydrolysis at 170 ℃; FIG. 5(a) is a chart showing XANES spectrum of P side of solid phase hydrolysate obtained by solid phase pyrohydrolysis for 30min at different temperatures, and FIG. 5(b) is a chart showing XANES spectrum of P side of solid phase hydrolysate obtained by solid phase pyrohydrolysis for 60min at different temperatures; linear Combination Fitting (LCF) of the K-edge XANES spectra for P was performed to further reveal P variation under different THP conditions, as shown in table 2;

the sludge is subjected to high-temperature pyrohydrolysis (THP) for 30min and then fixed in H in the solid-phase hydrolysate₂O-P and NaHCO₃The relative abundance of-P is higher. Also, THP is optimal at 160 to 180 ℃, where the THP duration has less effect on its hydrolysis products. Therefore, from the viewpoint of bioavailability P, the temperature of 170 ℃ is 30min, which is a better processing condition for THP.

TABLE 2

Note that n.d. indicates no detection

(3) Anaerobic digestion of phosphorus-containing sludge: based on the angle of bioavailability, selecting mixed hydrolysate (marked as THP) hydrolyzed at 170 ℃ for 30min in the step (2) and mixed liquid (marked as SS) of dry sludge and deionized water which are not hydrolyzed as a substrate to perform anaerobic digestion test, placing the substrate into an anaerobic digestion reactor, adding anaerobic granular sludge with the same volume, reacting at constant temperature of 37 ℃ under anaerobic condition, setting 6 groups of experiments according to reaction time of 0d, 1d, 3d, 5d, 10d and 20d, centrifuging the mixed liquid obtained by reaction for 20min at 5000r/min to obtain supernatant and sludge, and centrifuging the supernatant for 20minAfter filtration through a 0.45 μm filter, the solubility TP was determined by ICP-OES as shown in FIG. 6; drying the sludge at 70 deg.C to constant weight, grinding to obtain solid phase digestion product, wherein³¹The P NMR spectrum is shown in fig. 7, and the immobilization of the metal element on P is explored in combination with XANES analysis, as shown in fig. 8, wherein fig. 8(a) is a K-edge XANES spectrum of P of the solid phase digest obtained by solid phase anaerobic digestion after thermal hydrolysis, and fig. 8(b) is a K-edge XANES spectrum of P of the solid phase digest obtained by SS anaerobic digestion; linear Combination Fitting (LCF) of the K-edge XANES spectra for P was performed to further reveal P changes under different THP conditions, as shown in table 3, and the determination of each form P in the solid phase digest by the method of determination of the total amount of elements in the solid phase hydrolysate is shown in fig. 9.

TABLE 3

Note that n.d. indicates no detection

As can be seen from FIG. 5, thermal hydrolysis promotes the release of phosphorus in the anaerobic sludge digestion process (AD), especially in the initial stages (0-3 d) of anaerobic digestion, where 3d is the optimal time to recover phosphorus from the digestive juice. Under the condition of extremely low content of organic phosphorus, THP reduces the relative abundance of bioavailable P in solid-phase digested sludge, and simultaneously, the content of more stable HCl-P is increased, and other extraction states P are more stable. As can be seen from FIG. 6, the chemical shifts of solid anaerobic digested sludge of SS were-7.4136 ppm, -7.5326ppm, -7.5446ppm for 0d, 3d and 10d, respectively, and those of anaerobic digested sludge of THP were-8.2211 ppm, -7.9336ppm and-8.2687 ppm. The chemical shift of the solid phase anaerobic digestion sludge of THP is shifted in the negative direction, so that the THP is supposed to have certain influence on the binding distribution condition of P and metal in the solid phase. As can be seen from FIG. 4, FIG. 5 and Table 2, the spectral characteristics of SS and solid phase hydrolysate were less similar to the spectra of hydroxyapatite (Hydroxylacetate) and octacalcium phosphate (OcataCa), which showed small fluctuations between 2147-2150eV, indicating that these samples contained a certain amount of Fe-P. Meanwhile, the P form between solid-phase hydrolysis products has obvious difference, Fe-P changes along with the temperature and the reaction time of THP, and the relative abundance of Ca-P changes slightly. As can be seen from FIG. 7 and Table 3, there are distinct pre-edge and post-edge white line peaks in all samples, indicating the presence of Fe-P and Ca-P. THP has almost no influence on the form distribution of Ca in the AD solid phase, and Fe and Ca have strong solid action on P. The distribution of Al-P, Fe-P, Ca-P is stable in the process of anaerobic digestion, but Ca-P is interconverted, the transformation of Hydroxylacetate to OcataCa is promoted under the action of THP, and the transformation amount reaches the maximum when the digestion time is 3 d.

(4) Adding 3 mol. L to the supernatant obtained by centrifugation in the step (3)^-1NaOH and HCl to adjust the pH to 9.5, with MgCl₂·6H₂O as magnesium source, stirring and reacting at room temperature (20 + -5 deg.C) with a constant temperature magnetic stirrer (Asahi 85-2A) at a rotation speed of 200r min^-1And standing and precipitating after the reaction is finished, separating and recovering the phosphorus-containing precipitate, and calculating to obtain the phosphorus recovery rate of 65%.

Comparative example 1

(1) adding deionized water into the phosphorus-containing sludge according to the mass ratio of 1: 10, uniformly mixing, placing the mixture into an inner container of a reaction kettle made of a PPL material, and hydrolyzing for 30min under a closed condition at the hydrolysis temperature of 170 ℃ to obtain mixed hydrolysate;

(2) after the mixed hydrolysate obtained in the step (1) is cooled to room temperature, placing the mixed hydrolysate in an anaerobic digestion reactor, adding anaerobic granular sludge with the same volume, reacting at the constant temperature of 37 ℃ for 3d under an anaerobic condition, and centrifuging the mixed solution obtained by the reaction for 20min at 5000r/min to obtain supernatant and sludge;

(3) adding 3 mol. L to the supernatant obtained by centrifugation in the step (2)^-1NaOH and HCl to adjust the pH to 9.5, with MgCl₂·6H₂O as magnesium source, stirring and reacting at room temperature (20 + -5 deg.C) with a constant temperature magnetic stirrer (Asahi 85-2A) at a rotation speed of 200r min^-1And standing and precipitating after reacting for a certain time, precipitating and recovering phosphorus in the solution, and calculating to obtain the phosphorus recovery rate of 53%.

Comparative example 2

(2) adding deionized water into the dry sludge obtained in the step (1) according to the mass ratio of 1: 10, uniformly mixing, placing the mixture into an inner container of a reaction kettle made of a PPL material, setting the hydrolysis temperature to be 170 ℃ under a closed condition, and hydrolyzing for 30min to obtain mixed hydrolysate;

(3) after the mixed hydrolysate obtained in the step (2) is cooled to room temperature, placing the mixed hydrolysate in an anaerobic digestion reactor, adding anaerobic granular sludge with the same volume, reacting at the constant temperature of 45 ℃ for 3d under an anaerobic condition, and centrifuging the mixed solution obtained by the reaction for 20min at 5000r/min to obtain supernatant and sludge;

(4) adding 3 mol. L to the supernatant obtained by centrifugation in the step (3)^-1NaOH and HCl to adjust the pH to 9.5, with MgCl₂·6H₂O as magnesium source, stirring and reacting at room temperature (20 + -5 deg.C) with a constant temperature magnetic stirrer (Asahi 85-2A) at a rotation speed of 200r min^-1And standing and precipitating after reacting for a certain time, precipitating and recovering phosphorus in the solution, and calculating to obtain the phosphorus recovery rate of 60%.

Comparative example 3

(3) after the mixed hydrolysate obtained in the step (2) is cooled to room temperature, placing the mixed hydrolysate in an anaerobic digestion reactor, adding anaerobic granular sludge with the same volume, reacting at the constant temperature of 37 ℃ for 3d under an anaerobic condition, and centrifuging the mixed solution obtained by the reaction for 20min at 5000r/min to obtain supernatant and sludge; the preparation method of the anaerobic granular sludge comprises the following steps:

adding nutrient substances into water according to the mass ratio of COD to N to P of 200 to 5 to 1 to obtain simulated wastewater, wherein N is derived from ammonium sulfate and phosphorus is derived from potassium dihydrogen phosphate; maintaining the pH value of inlet water to be 8.5-9.0 by using sodium bicarbonate, uniformly mixing the dry sludge obtained by the method in the step (1) and activated carbon particles in a mass ratio of 21: 1, adding the mixture into a UASB (upflow anaerobic sludge blanket) simulation reactor, controlling the flow rate of simulated wastewater to be 0.25L/h and the hydraulic retention time to be 11.39h, and operating for 60 days to obtain anaerobic granular sludge;

(4) adding 3 mol. L to the supernatant obtained by centrifugation in the step (3)^-1NaOH and HCl to adjust the pH to 9.5, with MgCl₂·6H₂O as magnesium source, stirring and reacting at room temperature (20 + -5 deg.C) with a constant temperature magnetic stirrer (Asahi 85-2A) at a rotation speed of 200r min^-1And standing and precipitating after reacting for a certain time, precipitating and recovering phosphorus in the solution, and calculating to obtain the phosphorus recovery rate of 51%.

Comparative example 4

adding nutrient substances into water according to the mass ratio of COD to N to P of 190 to 5 to 1 to obtain simulated wastewater, wherein N is derived from ammonium sulfate and phosphorus is derived from potassium dihydrogen phosphate; maintaining the pH value of inlet water to be 7.2-8.2 by using sodium bicarbonate, uniformly mixing the dry sludge obtained by the method in the step (1) and activated carbon particles according to the mass ratio of 21: 1, adding the mixture into a UASB (upflow anaerobic sludge blanket) simulation reactor, controlling the flow rate of simulated wastewater to be 0.25L/h and the hydraulic retention time to be 11.39h, and operating for 60 days to obtain anaerobic granular sludge;

(4) adding 3 mol. L to the supernatant obtained by centrifugation in the step (3)^-1NaOH and HCl to adjust the pH to 9.5, with MgCl₂·6H₂O as magnesium source, stirring and reacting at room temperature (20 + -5 deg.C) with a constant temperature magnetic stirrer (Asahi 85-2A) at a rotation speed of 200r min^-1And standing and precipitating after reacting for a certain time, precipitating and recovering phosphorus in the solution, and calculating to obtain the phosphorus recovery rate of 55%.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be able to cover the technical solutions and the inventive concepts of the present invention within the technical scope of the present invention.

Claims

1. A method for recovering phosphorus from phosphorus-containing sludge is characterized by comprising the following steps:

mixing the phosphorus-containing sludge with water, hydrolyzing to obtain a mixed hydrolysate, then adding anaerobic granular sludge for anaerobic digestion, and recovering phosphorus in the digestive juice.

2. The method of claim 1, further comprising the steps of drying the phosphorus-containing sludge to constant weight at 70 ℃, grinding, and sieving with a 60 mesh sieve before mixing the phosphorus-containing sludge with water.

3. The method of claim 1, wherein the mass ratio of phosphorus-containing sludge to water is 1: 10.

4. The method as claimed in claim 1, wherein the hydrolysis temperature is 140-200 ℃, the hydrolysis time is 10-60min, and the hydrolysis is performed under a closed condition.

5. The method as claimed in claim 1, wherein the volume ratio of the anaerobic granular sludge to the mixed hydrolysate is 1: 1.

6. The method of claim 1, wherein the anaerobic digestion is at a temperature of 37 ℃ for a period of 1-20 days.

7. The method according to claim 1, wherein the specific method for recovering phosphorus in the digestion solution is as follows: and (3) taking the supernatant of the digestive juice, adjusting the pH value, adding a magnesium source, standing after the reaction is finished, and separating to obtain a phosphorus-containing precipitate.

8. The method of claim 7, wherein the adjusting the pH to 9.5; the magnesium source is MgCl₂·6H₂O。