Methods for Phosphorus Recovery from Sludge Through Anaerobic Fermentation of Desorption Liquid Using Nano-Phosphorus Removal Materials

Abstract

This invention provides a method for promoting phosphorus recovery from sludge through anaerobic fermentation using desorption liquid from nano-phosphorus removal materials. The method includes the following steps: weighing an appropriate amount of nano-phosphorus removal adsorbent and adding it to phosphorus-containing wastewater until adsorption is saturated; filtering out the nano-phosphorus removal adsorbent and washing its surface with water; continuing to add the adsorbent to a desorption solution to obtain desorption liquid; adding the desorption liquid and concentrated sludge in a certain proportion to a container and introducing nitrogen gas for anaerobic fermentation; after anaerobic fermentation, collecting the anaerobic fermentation supernatant, adjusting the pH to neutral, adding FeSO4·7H2O at a certain Fe / P molar ratio, and stirring to form a precipitate; rinsing the precipitate and freeze-drying to obtain lapis lazuli. This invention directly reuses the desorption liquid from nano-phosphorus removal materials in anaerobic fermentation of sludge. It not only utilizes the acidity generated during anaerobic fermentation to neutralize the alkalinity of the desorption liquid but also promotes sludge dissolution and acid production, releasing phosphorus from the sludge and increasing phosphorus recovery.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling and post-processing technology, and in particular relates to a method for promoting anaerobic fermentation of sludge to recover phosphorus using nano-phosphorus removal material desorption liquid. Background Technology

[0002] Phosphorus (P) is a non-renewable resource essential for human survival. However, rapid industrialization and agricultural expansion have led to over-exploitation of phosphate mines, putting immense pressure on this finite resource. Wastewater treatment plants (WWTPs) are a critical node in the global phosphorus cycle, serving the dual functions of environmental regulation and resource recovery. Globally, WWTPs remove approximately 1.3 million tons of phosphorus annually. If effectively recovered, this amount could meet 15–20% of current global phosphorus demand, thus alleviating the pressure of phosphate reserve depletion. At the same time, phosphorus overload remains a significant threat to aquatic ecosystems: phosphorus concentrations exceeding 0.02 mg-P / L increase the risk of eutrophication, triggering harmful algal blooms and biodiversity loss. Therefore, developing technologies that combine deep phosphorus removal with efficient recovery capabilities is crucial.

[0003] Nanomaterials, due to their high specific surface area and strong adsorption properties, have shown great potential in the field of phosphorus removal from wastewater. Iron-based, zirconium-based, and lanthanide nanocomposites have all demonstrated strong phosphorus adsorption capabilities in various studies. For example, patent application CN120189923A discloses a lanthanum-loaded nanostructured composite phosphorus removal material (La@N series). Using La@N series phosphorus removal materials with a crosslinking degree of 4%–15%, the phosphorus adsorption capacity can reach 200–320 mg / g.

[0004] However, regardless of the type of nano-phosphorus removal material, phosphorus adsorption and regeneration are required for recycling. After treatment with common desorbents (such as NaCl, NaOH, Na2CO3 solutions, etc.), a large amount of high-concentration phosphorus desorption liquid (containing alkali and salt) is generated. The desorption liquid is often discharged after direct neutralization (adjusting the pH value) or after reprecipitation. However, this post-treatment process can easily cause secondary loss of phosphorus resources. In particular, the desorption liquid containing salt / alkali also indirectly increases the overall wastewater treatment cost during the treatment process, limiting the large-scale and sustainable application of nano-phosphorus removal materials.

[0005] Therefore, it is necessary to provide a desorption liquid post-treatment method that can be used in conjunction with existing nano-phosphorus removal materials to reduce the treatment cost of desorption liquid while avoiding secondary loss of phosphorus resources; and to support the sustainable application of nano-phosphorus removal materials. Summary of the Invention

[0006] This invention addresses the problems of high treatment costs and secondary phosphorus loss in the post-treatment of desorption liquid from existing nano-phosphorus removal materials, which limit the large-scale and sustainable application of nano-phosphorus removal materials. It provides a method for promoting anaerobic fermentation of sludge to recover phosphorus from desorption liquid of nano-phosphorus removal materials. This method avoids phosphorus loss and waste of neutralizing agents caused by direct neutralization treatment of desorption liquid, and reduces wastewater treatment costs.

[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0008] A method for promoting phosphorus recovery from sludge through anaerobic fermentation using nano-phosphorus removal material desorption liquid, characterized by comprising the following steps:

[0009] S1. Weigh an appropriate amount of nano-phosphorus adsorbent and add it to phosphorus-containing wastewater to remove phosphorus through adsorption until the adsorption is saturated.

[0010] S2. Filter out the nano phosphorus removal adsorbent from step S1 and wash the surface of the adsorbent with water.

[0011] S3. Continue to add the adsorbent to the desorption solution to desorb phosphorus and obtain the desorbed solution;

[0012] S4. Add the desorption liquid obtained in step S3 and the concentrated sludge into a container in a certain proportion, introduce nitrogen gas, and carry out anaerobic fermentation.

[0013] S5. After anaerobic fermentation is completed, collect the anaerobic fermentation supernatant; adjust the pH of the anaerobic fermentation supernatant to neutral, add FeSO4·7H2O at a certain Fe / P molar ratio, and stir to form a precipitate;

[0014] S6. Rinse the precipitate and then freeze-dry to obtain lapis lazuli.

[0015] Furthermore, in step S3, the desorption solution is at least one of NaOH solution, NaCl solution, and Na2CO3 solution.

[0016] Furthermore, the desorption solution has a mass concentration of 5%.

[0017] Preferably, the concentration of the concentrated sludge in step S4 is above 30 g / L.

[0018] Preferably, the volume ratio of desorption liquid to sludge in step S4 is 1:2.

[0019] Preferably, the anaerobic fermentation time in step S4 is not less than 20 days.

[0020] Preferably, the anaerobic fermentation temperature is 35°C, and the mixture is shaken during the anaerobic fermentation process.

[0021] Preferably, the oscillation speed is 180 r / min.

[0022] Preferably, the Fe / P molar ratio in step S5 is 1.5.

[0023] Preferably, the freeze-drying time in step S6 is not less than 24 hours.

[0024] The advantages of this invention are: the desorption liquid from the nano-phosphorus removal material can be directly reused in anaerobic fermentation of sludge. This not only neutralizes the pH of the desorption liquid during the anaerobic fermentation process but also promotes sludge dissolution and acid production, releasing phosphorus from the sludge and increasing phosphorus recovery. This provides a new approach for the post-treatment of desorption liquid after phosphorus removal from wastewater, avoiding phosphorus loss and waste of neutralizing agents caused by direct neutralization of the desorption liquid, and reducing wastewater treatment costs.

[0025] The method of using nano-phosphorus removal material desorption liquid to promote anaerobic fermentation and phosphorus recovery from sludge in this invention has good adaptability to municipal sludge. The desorption liquid after phosphorus removal from wastewater using nano-phosphorus removal material not only promotes sludge hydrolysis and increases the acid production of anaerobic fermentation, but also recovers high-value products such as volatile fatty acids (VFAs); it enhances resource and energy recovery, improves the phosphorus release and conversion efficiency of sludge, and ultimately increases the phosphorus release efficiency by 1.21-2.93 times.

[0026] This invention combines water pollution control and sludge reduction treatment, and develops an integrated technology that synergistically achieves "sludge reduction - phosphorus energy recovery - resource regeneration", solving the problems of high post-treatment costs, resource loss and environmental risks in the wastewater treatment industry. Attached Figure Description

[0027] Figure 1 XRD patterns of the recovered products of embodiments and Comparative Example 2 of the present invention;

[0028] Figure 2 SEM images of the recovered products of embodiments and Comparative Example 2 of the present invention;

[0029] Figure 3 These are physical images of the recovered product samples from embodiments and Comparative Example 2 of the present invention;

[0030] Figure 4 This is a diagram showing the pH changes during the anaerobic fermentation process of the embodiments and Comparative Example 2 of the present invention;

[0031] Figure 5 This is a graph showing the changes in phosphorus concentration during the anaerobic fermentation process of the embodiments and Comparative Example 2 of the present invention.

[0032] Figure 6 This is a graph showing the changes in the cumulative amount of VFAs during the anaerobic fermentation process of the embodiments and Comparative Example 2 of the present invention;

[0033] Figure 7The image shows the XRD pattern of the recovered product of Comparative Example 1 of the present invention.

[0034] Figure 8 This is a SEM image of the recovered product of Comparative Example 1 of the present invention.

[0035] In the figure, R0, R1, R2, R3, and R4 represent the recovered products obtained from Comparative Example 2, Example 1, Example 2, Example 3, and Example 4, respectively. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This invention is achieved through the following steps:

[0038] S1. Weigh an appropriate amount of nano-phosphorus adsorbent and add it to phosphorus-containing wastewater to remove phosphorus through adsorption until the adsorption is saturated.

[0039] S2. Filter out the nano phosphorus removal adsorbent from step S1 and wash the surface of the adsorbent with water.

[0040] S3. Continue to add the adsorbent to the desorption solution to desorb phosphorus and obtain the desorbed solution;

[0041] S4. Add the desorption liquid obtained in step S3 and the concentrated sludge into a container in a certain proportion, introduce nitrogen gas, and carry out anaerobic fermentation.

[0042] S5. After anaerobic fermentation is completed, collect the anaerobic fermentation supernatant; adjust the pH of the anaerobic fermentation supernatant to neutral, add FeSO4·7H2O at a certain Fe / P molar ratio, and stir to form a precipitate;

[0043] S6. Rinse the precipitate and then freeze-dry to obtain lapis lazuli (Fe3(PO4)2·8H2O).

[0044] In step S3, the desorption solution is at least one of NaOH solution, NaCl solution, and Na2CO3 solution; the mass concentration of the desorption solution is preferably 5%; to facilitate monitoring of changes in phosphorus concentration, the phosphorus content of the supernatant of the desorption solution is tested once in step S3.

[0045] Preferably, in step S4, the concentration of concentrated sludge is above 30 g / L; the volume ratio of desorption liquid to sludge is 1:2; the anaerobic fermentation time is not less than 20 days; and the changes in phosphorus concentration and volatile fatty acids (VFAs) of the supernatant are detected every 2 days and at the end of fermentation.

[0046] Preferably, the Fe / P molar ratio in step S5 is 1.5; the phosphorus concentration of the supernatant needs to be measured.

[0047] In step S6, after freeze-drying for 24 hours, the blue iron crystals can be subjected to XRD and SEM detection.

[0048] The sludge in step S3 refers to activated sludge (WAS). WAS is a major byproduct of wastewater treatment, containing a large amount of organic matter, essential nutrients (N, P), and heavy metals.

[0049] Anaerobic fermentation (AF) technology can reduce and stabilize sludge volume while recovering volatile fatty acids (VFAs), thus becoming a mainstream sludge treatment process. However, the surface of sludge (WAS) is often coated with extracellular polymeric substances (EPS), which hinders hydrolysis efficiency. Therefore, traditional AF fermentation typically suffers from low phosphorus release efficiency, poor acid production performance, and excessively long reaction cycles. To address these issues, methods such as thermal hydrolysis pretreatment (THP) are commonly employed. However, the significant energy and chemical consumption associated with these methods substantially increases costs, hindering practical application.

[0050] The invention is characterized by linking the originally completely independent wastewater treatment and sludge reduction processes together. It makes full use of the salt and alkali in the desorption liquid of the nano-phosphorus removal material in wastewater treatment to promote the dissolution and acid production of sludge, release phosphorus from the sludge, and increase the recovery of phosphorus. It also utilizes the anaerobic fermentation process of sludge to partially neutralize the desorption liquid, reducing the cost of neutralizing agents.

[0051] The following examples and comparative examples further illustrate the desorption solution treatment process and technical effects of nano-phosphorus removal materials.

[0052] The embodiments use La@N2 disclosed in patent application CN120189923A as the nano-phosphorus removal material.

[0053] Example 1

[0054] The La@N2 phosphorus removal and desorption solution treatment process includes the following steps:

[0055] S1. Prepare 500 mL of phosphorus solution with a concentration of 50 mg / L and a pH of 7, add 0.5 g of La@N2, and shake at room temperature for 24 h until adsorption saturation.

[0056] S2. Filter out the adsorbed La@N2 and wash the surface with deionized water;

[0057] S3. Add the cleaned La@N2 adsorbent to 50 mL of 5% NaCl solution and shake at room temperature for 4 h to obtain the desorption solution;

[0058] S4. Mix the desorption liquid from step S3 with 100 mL of concentrated sludge (TSS = 36398 mg / L, VSS = 15082 mg / L, pH = 6.67) and add it to the reactor. Purge with nitrogen for 5 min to remove air. Seal the reactor and shake it at 35 °C at a speed of 180 r / min for anaerobic fermentation for 20 days.

[0059] S5. After fermentation, filter out the supernatant and adjust the pH to 7.0 with 1M NaOH and / or 0.1M HCl; then add FeSO4·7H2O with a Fe / P molar ratio of 1.5, stir for 30 minutes to form a precipitate, and take the supernatant to measure the phosphorus concentration.

[0060] S6. Rinse the precipitate formed in step S5 with oxygen-free deionized water, and then freeze-dry for 24 hours; take the dried crystals for XRD and SEM detection.

[0061] After 20 days of anaerobic fermentation, the pH of the supernatant in this example increased from 6.34 to 7.67; the initial phosphorus concentration of the desorption broth was 134.7 mg / L, and the phosphorus concentration of the supernatant after anaerobic fermentation was 149.52 mg / L, which was 1.21 times that of Comparative Example 2 and 1.11 times that of the initial phosphorus concentration; the cumulative yield of VFAs was 1637.44 mg COD / L, which was 3.74 times that of Comparative Example 2; XRD and SEM analysis of the samples yielded the following results: Figure 1 , 2 As shown, the recycled product is blue-green in color.

[0062] Example 2

[0063] The treatment process for the La@N2 phosphorus removal and desorption solution is basically the same as in Example 1, except that the desorption solution in step S3 is 50 mL of 5% NaOH.

[0064] After 20 days of anaerobic fermentation, the pH of the supernatant in this example decreased from 13.50 to 13.32; the initial phosphorus concentration of the desorption broth was 233.75 mg / L, and the phosphorus concentration of the supernatant after anaerobic fermentation was 362.32 mg / L, which was 2.93 times that of Comparative Example 2 and 1.55 times that of the initial phosphorus concentration; the cumulative yield of VFAs was 236.18 mg COD / L, which was 0.54 times that of Comparative Example 2. XRD and SEM analyses were performed on the samples, and the results are as follows... Figure 1 , 2 As shown. The recovered product is brownish-red, as... Figure 3 As shown.

[0065] Example 3

[0066] The treatment process for the La@N2 phosphorus removal and desorption solution is basically the same as in Example 1, except that the desorption solution in step S3 is 50 mL of 5% Na2CO3 + 5% NaCl.

[0067] After 20 days of anaerobic fermentation, the pH of the supernatant in this example decreased from 10.50 to 9.72; the initial phosphorus concentration of the desorption liquid was 99.79 mg / L, and the phosphorus concentration of the supernatant after anaerobic fermentation was 312.36 mg / L, which was 2.53 times that of Comparative Example 2 and 3.13 times that of the initial phosphorus concentration; the cumulative yield of VFAs was 5055.54 mg COD / L, which was 11.54 times that of Comparative Example 2. XRD and SEM analyses were performed on the samples, and the results are as follows... Figure 1 , 2 As shown. The recycled product is grayish-green, as... Figure 3 As shown.

[0068] Example 4

[0069] The treatment process for the La@N2 phosphorus removal and desorption solution is basically the same as in Example 1, except that the desorption solution in step S3 is 25 mL of 5% NaCl solution + 25 mL of 5% Na2CO3 solution.

[0070] After 20 days of anaerobic fermentation, the pH of the supernatant in this example decreased from 10.29 to 9.54; the initial phosphorus concentration of the desorption liquid was 104.08 mg / L, and the phosphorus concentration of the supernatant after anaerobic fermentation was 317.45 mg / L, which was 2.57 times that of Comparative Example 2 and 3.05 times that of the initial phosphorus concentration; the cumulative yield of VFAs was 5414.15 mg COD / L, which was 12.36 times that of Comparative Example 2. XRD and SEM analyses were performed on the samples, and the results are as follows... Figure 1 , 2 As shown. The recycled product is grayish-brown, as... Figure 3 As shown.

[0071] Comparative Example 1

[0072] The La@N2 phosphorus removal and desorption solution treatment process includes the following steps:

[0073] S1. Prepare 500 mL of phosphorus solution with a concentration of 50 mg / L and a pH of 7, add 0.5 g of La@N2, and shake at room temperature for 24 h until adsorption saturation.

[0074] S2. Filter out the adsorbed La@N2 and wash the surface with deionized water;

[0075] S3. Add the cleaned La@N2 adsorbent to 50 mL of 5% Na2CO3 solution and shake at room temperature for 4 h to obtain the desorption solution;

[0076] S4. Adjust the pH of the desorption solution to 7.0 with 1M NaOH and / or 0.1M HCl; then add FeSO4·7H2O with a Fe / P molar ratio of 1.5, stir for 30 min to form a precipitate;

[0077] S5. Rinse the precipitate formed in step S5 with oxygen-free deionized water, and then freeze-dry for 24 hours; take the dried crystals for XRD and SEM detection.

[0078] In step S3, the pH of the supernatant was 10.5, and the phosphorus concentration was 99.86 mg / L. The recovered product was blue-green. XRD and SEM analyses of the sample yielded the following results: Figure 7 , 8 As shown.

[0079] Comparative Example 2

[0080] No desorption solution is used.

[0081] S1. Take 50 mL of anoxic water and 100 mL of concentrated sludge (TSS = 36398 mg / L, VSS = 15082 mg / L, pH = 6.67) and add them to the reactor. Purge with nitrogen for 5 minutes to remove air. Seal the reactor and shake it at 35°C at a speed of 180 r / min to carry out anaerobic fermentation. Test the initial phosphorus concentration of the supernatant at the start of fermentation.

[0082] S2. After fermentation, filter and collect the supernatant. Adjust the pH to 7.0 with 1M NaOH and 0.1M HCl. Under anaerobic conditions, add FeSO4·7H2O to make the Fe / P molar ratio 1.5, stir for 30 min, and take the supernatant to measure the P concentration.

[0083] S3. Rinse the precipitate with deionized water and freeze-dry for 24 hours, then perform crystal XRD and SEM analysis.

[0084] After 20 days of anaerobic fermentation, the pH of the supernatant increased from 6.75 to 8.01; the initial phosphorus concentration in the supernatant at the start of fermentation was 80.26 mg / L, and the phosphorus concentration after fermentation was 123.61 mg / L, which was 1.54 times the initial phosphorus concentration; the cumulative yield of VFAs was 438.14 mg COD / L. XRD and SEM analyses were performed on the samples, and the results are as follows... Figure 1 , 2 As shown. The recycled product is grayish-green, as... Figure 3 As shown.

[0085] As can be seen from the above examples and comparative examples, the final recovered product is lapis lazuli. However, the crystal form of lapis lazuli is greatly affected by the type of desorption solution, and the composition of the desorption solution has a significant impact on phosphorus release and VFA accumulation in the concentrated sludge. Figure 5 ,6 As shown, overall, the desorption liquor promotes acid production and phosphorus release from the concentrated sludge, enabling sludge reduction and resource recovery. Simultaneously, the acid produced by the sludge neutralizes the desorption liquor, reducing the cost of neutralization treatment; increasing the final phosphorus recovery rate; and enhancing the overall resource and energy recovery rate.

[0086] It should be noted that the desorption solution used in Example 2 had an excessively high concentration of NaOH and was too alkaline. Although this promoted the dissolution and hydrolysis of sludge and released a large amount of organic substrate, the excessive alkalinity also caused a large number of acid-producing microorganisms to die, which was not conducive to the formation of VFAs. Therefore, when using the treatment method of the present invention for the desorption solution of nano-phosphorus removal materials, it is best to avoid excessive alkalinity of the desorption solution.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for promoting anaerobic fermentation and phosphorus recovery from sludge using a nano-phosphorus removal material desorption solution, characterized in that, Includes the following steps: S1. Weigh an appropriate amount of nano-phosphorus adsorbent and add it to phosphorus-containing wastewater to remove phosphorus through adsorption until the adsorption is saturated. S2. Filter out the nano phosphorus removal adsorbent from step S1 and wash the surface of the adsorbent with water. S3. Continue to add the adsorbent to the desorption solution to desorb phosphorus and obtain the desorption solution; the desorption solution is a mixture of 5% Na2CO3 + 5% NaCl solution or 5% Na2CO3 solution in equal volume ratio with 5% NaCl solution. S4. Add the desorption liquid obtained in step S3 and the concentrated sludge into a container in a certain proportion, introduce nitrogen gas, and carry out anaerobic fermentation. S5. After anaerobic fermentation is completed, collect the anaerobic fermentation supernatant; adjust the pH of the anaerobic fermentation supernatant to neutral, add FeSO4·7H2O at a certain Fe / P molar ratio, and stir to form a precipitate; S6. Rinse the precipitate and then freeze-dry to obtain lapis lazuli.

2. The method for promoting anaerobic fermentation and phosphorus recovery from sludge using the desorption liquid of the nano-phosphorus removal material according to claim 1, characterized in that, The concentration of the concentrated sludge in step S4 is above 30 g / L.

3. The method for promoting anaerobic fermentation and phosphorus recovery from sludge using the desorption liquid of the nano-phosphorus removal material according to claim 1 or 2, characterized in that, In step S4, the volume ratio of desorption liquid to sludge is 1:

2.

4. The method for promoting anaerobic fermentation and phosphorus recovery from sludge using the desorption liquid of the nano-phosphorus removal material according to claim 1 or 2, characterized in that, The anaerobic fermentation time in step S4 shall not be less than 20 days.

5. The method for promoting anaerobic fermentation and phosphorus recovery from sludge using the desorption liquid of the nano-phosphorus removal material according to claim 1 or 2, characterized in that, The anaerobic fermentation temperature is 35℃, and the mixture is shaken during the anaerobic fermentation process.

6. The method for promoting anaerobic fermentation and phosphorus recovery from sludge using the desorption liquid of the nano-phosphorus removal material according to claim 5, characterized in that, The oscillation speed is 180 r / min.

7. The method for promoting anaerobic fermentation and phosphorus recovery from sludge using the desorption liquid of the nano-phosphorus removal material according to claim 1, characterized in that, In step S5, the Fe / P molar ratio is 1.

5.

8. The method for promoting anaerobic fermentation and phosphorus recovery from sludge using the desorption liquid of the nano-phosphorus removal material according to claim 1, characterized in that, In step S6, the freeze-drying time shall be no less than 24 hours.

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